Leak detection equipment; Leak detection method

Abstract

To provide a leak inspection method and a leak inspection device that can correctly determine the quality of a body to be inspected concerning leakage regardless of a difference in pressure condition during leakage amount measurement.SOLUTION: A leak inspection method includes: introducing gas with pressure to a body to be inspected having a hollow part and subsequently measuring a leakage amount (detected leakage amount) while sealing the body to be inspected, and measuring the internal pressure (first inspected pressure) of the body to be inspected during the measurement; acquiring a reference inspected pressure and the maximum allowable value of leakage (reference leakage amount) when leakage is measured with the internal pressure of the body to be inspected as the reference inspected pressure; converting at least one of the detected leakage amount and the reference leakage amount so that the detected leakage amount and the reference leakage amount become a value when the reference inspected pressure and the first inspected pressure are the same pressure, considering that the volume of a sealed closed space of the body to be inspected including the hollow part changes depending on the internal pressure of the closed space; and comparing the detected leakage amount and the reference leakage amount after the conversion to correctly determine the presence or absence of leakage from the body to be inspected regardless of a difference in pressure condition during the leakage amount measurement.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a leak inspection apparatus and a leak inspection method for inspecting leaks in an inspection object (such as a container or a pipeline) having a hollow portion.

Background Art

[0002] Conventionally, when inspecting leaks in an inspection object such as a container or a pipeline having a hollow portion, after introducing a gas such as air into the inspection object at a predetermined inspection pressure (for example, 400 kPa to 500 kPa), it is sealed, and then the leak amount is measured from the subsequent pressure change. Whether the inspection is passed or failed is determined by comparing the measured leak amount with a predetermined threshold value (reference leak amount) (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the leak amount of a gas is expressed in units such as [Pa·m 3 / s]. 1 Pa·m 3 / s means that the leak amount is 1 m 3 in 1 second under the pressure condition of 1 Pa at the leakage destination. This is because, according to Boyle's law, a gas is represented by the product of volume and pressure. The leak amount may also be expressed in units such as [mL / min], but this is an abbreviation assuming that the pressure condition at the leakage destination is atmospheric pressure, and it is accurately expressed in units such as [atm·mL / min].

[0005]

[0006] Thus, when discussing leakage rates, it is necessary to consider the pressure conditions at the source of the leak, or the pressure difference between the source and destination of the leak. For example, even when measuring the leakage rate of the same object under inspection, the measured leakage rate will vary depending on the pressure conditions at the destination (usually atmospheric pressure) and the pressure conditions at the source of the leak (inspection pressure: the internal pressure of the object under inspection at the time of leakage measurement).

[0007] However, in conventional leak testing, even though the permissible range of the test pressure was set to, for example, 400kPa to 500kPa, the reference leak amount used to compare the measured leak amount with the pass / fail judgment was a predetermined fixed value, which sometimes led to misjudgments.

[0008] Figure 19 shows an example of the relationship between the inspection pressure, the leakage rate, and the pass / fail judgment based on the standard leakage rate. The permissible range for the inspection pressure is 400kPa to 500kPa, and the standard leakage rate is a fixed value of 11.2mL / min regardless of the inspection pressure. If the measured leakage rate exceeds the standard leakage rate, it is judged as a defective product (with leakage), and if the measured leakage rate is less than or equal to the standard leakage rate, it is judged as a passable product.

[0009] Graph A shows the relationship between inspection pressure and leakage rate for test object a, which is the sample with the maximum allowable leakage rate. At an inspection pressure of 450 kPa, the leakage rate of test object a is 11.2 mL / min. Graph B shows the relationship between inspection pressure and leakage rate for test object b (an example of a defective product) which has a higher leakage rate than test object a, and Graph C shows the relationship between inspection pressure and leakage rate for test object c (an example of a good product) which has a lower leakage rate than test object a.

[0010] For example, if the leakage rate of a defective product, item b, is measured at an inspection pressure of 450 kPa, the measured leakage rate will be higher than the standard leakage rate of 11.2 mL / min, and therefore item b will be judged as defective. However, if the leakage rate of item b is measured at, for example, an inspection pressure of 410 kPa, the measured leakage rate will be lower than the standard leakage rate of 11.2 mL / min, and therefore item b will be incorrectly judged as good. The shaded area E1 in the figure is the region where a defective product is incorrectly judged as good (acceptable) due to the low inspection pressure during measurement.

[0011] Furthermore, when the leakage rate of a good product (tested object c) is measured at an inspection pressure of 450 kPa, the measured leakage rate is less than the standard leakage rate of 11.2 mL / min, so tested object c is judged to be a good product. However, if the leakage rate of tested object c is measured at, for example, an inspection pressure of 480 kPa, the measured leakage rate will be more than the standard leakage rate of 11.2 mL / min, so tested object c will be incorrectly judged as a defective product. The shaded area E2 in the figure is the area where a good product is incorrectly judged as a defective product (failed) due to the high inspection pressure during measurement.

[0012] Thus, even though testing is possible as long as the test pressure is within the acceptable range (for example, 400kPa to 500kPa), if the reference leak amount used to compare the measured value for pass / fail determination is a predetermined fixed value, there is a risk of misjudgment.

[0013] Furthermore, the inventors of this application have found that it is difficult to accurately maintain a constant inspection pressure (for example, exactly 450 kPa) when measuring the leakage amount for the following reasons.

[0014] (Reason 1) It is difficult to accurately pressurize and introduce gas to the predetermined pressure indicated by the leak testing device (for example, 450 kPa). Therefore, testing was considered possible if the pressure inside the object being tested was within an acceptable range such as 400 kPa to 500 kPa.

[0015] (Reason 2) When a gas is pressurized and sealed inside the object under test, and then a predetermined time (setup period) is waited before measuring the leakage rate, even if the length of the setup period is uniform, the pressure drop during the setup period will vary depending on the magnitude of the leak (for example, when the leakage rate is small, the pressure drop during the setup period will be smaller compared to when the leakage rate is large). Therefore, even if the target test pressure can be accurately reached when sealing after pressurization, the pressure conditions at the time of measurement after the setup period will differ depending on the leakage rate.

[0016] (Reason 3) The original pressure conditions for leakage will differ depending on the length of the settling period. In other words, even if the amount of leakage is the same, the original pressure conditions for leakage at the start of measurement (for example, the pressure conditions inside the body being tested) will differ depending on the length of the settling period. That is, the longer the settling period, the more pressure drop will occur due to leakage during that time, and the pressure conditions will differ between a case with a long settling period and a large pressure drop and a case with a short settling period and a small pressure drop.

[0017] (Reason 4) When a gas is pressurized and introduced into the object under test and sealed, and then the leakage amount is measured after a settling period has elapsed, if the leakage is large, the gas containing the heat itself is released directly to the outside of the object under test, rather than heat escaping through the walls, and the pressure inside the object under test decreases (the temperature drops and the pressure drops as it enters a state close to adiabatic expansion). As a result, the initial pressure conditions for leakage (the pressure inside the object under test after a uniform settling period has elapsed) will differ. In other words, the pressure convergence time (time constant) due to temperature changes will differ depending on the size of the leakage, and since the time it takes for the temperature to drop will also differ, the time it takes for the initial pressure for leakage to drop will also differ.

[0018] In leakage measurement, the pressure drop (differential pressure ΔP [Pa]) after pressurizing and sealing the workpiece with gas is measured, but the measurement is not given in [mL / min] or [Pa·m]. 3 To compare the measured differential pressure with a standard leak rate set in units of [mL / min] or [Pa·m], the differential pressure of the measured value should be expressed in [mL / min] or [Pa·m]. 3 It is necessary to convert the leakage rate to a unit of [ / s].

[0019] The formula for converting the differential pressure ΔP [Pa], measured as the leakage rate, into the leakage rate Q [mL / min] is Q [mL / min] = ΔP [Pa] × Vw [mL] × 60 / (T [s] × Patm [Pa]) … Equation A T [s]: Measurement time of ΔP, Vw: Volume of the leakage source That is, to convert the differential pressure ΔP [Pa] into the leakage rate Q [mL / min], the volume Vw [mL] of the leakage source is required. Also, the leakage rate Q [mL / min] changes in proportion to the volume Vw [mL] of the leakage source.

[0020] Similarly, the formula for converting the differential pressure ΔP [Pa] into the leakage rate Q‘ L [Pa·m 3 / s] is Q‘ L [Pa·m 3 / s] = ΔP [Pa] × V W [mL] / (T [s] × 1000000) Equation B That is, the leakage rate Q‘ L [Pa·m 3 / s] changes in proportion to the volume Vw [mL] of the leakage source. Therefore, in order to determine the pass / fail of the leakage inspection based on the leakage rate [mL / min] (or [Pa·m 3 / s]), it is necessary to consider the volume of the leakage source. Also, when the leakage source is a flexible body, the volume of the leakage source changes depending on the pressure during inspection.

[0021] For example, generally, a plastic bottle becomes soft and slightly dents when held by hand. When air pressure is applied to a flexible body such as this plastic bottle, in the case of an extremely low pressure, even a soft plastic bottle will not deform and the internal pressure will preferentially increase. However, when the pressure rises slightly, the plastic bottle will deform and expand as if it slightly caves in when held by hand (in which case the pressure becomes difficult to rise). When the pressure is further increased, the deformation of the plastic bottle stops in a state where it is fully stretched and enlarged (the volume change decreases), and only the pressure preferentially increases, and eventually the plastic bottle will burst.

[0022] When measuring the leakage of a flexible body like this, rather than a rigid body, the measurement is performed using a virtual equivalent volume (virtual volume, virtual internal volume, equivalent volume, or equivalent internal volume). However, since the virtual equivalent volume changes depending on the pressure during measurement, this must be taken into account when expressing the differential pressure ΔP [Pa] of the measured value in [mL / min] or [Pa·m]. 3 It is necessary to convert the leakage rate to a unit of [ / s]. Moreover, even though the appearance is almost unchanged, it is often necessary to use several times the value for virtual equivalent volume, etc.

[0023] Furthermore, the inventors of this invention have discovered that, when the object under inspection (workpiece / master) is a rigid body, the notion that the volume of the leak source is constant regardless of the pressure during leak measurement must be disregarded.

[0024] In other words, the closed space that is sealed when gas is pressurized and introduced during leak rate measurement contains not only the hollow part of the object under inspection, but also piping within the inspection device, piping connecting the inspection device and the object under inspection, and even fixtures connecting the object under inspection to the piping, and in the case of through-type objects under inspection, fixtures that seal the other ends. If there are flexible parts in this area (for example, piping made of nylon tubes, polyurethane tubes, etc., or rubber valve seats for on-off valves, etc.), the volume of the sealed closed space will change in accordance with the pressure. Therefore, even if the object under inspection is a rigid body, it is necessary to take into account the influence of these flexible parts. The following is an example of experimental results that led the inventor of this application to discover this point.

[0025] Figure 20 shows the results of an experiment in which a stainless steel pipe (rigid body), the object under test, was connected to a leak testing device via a 0.9m nylon tube at one end, and the other end was blocked with a jig to measure the leakage rate. From 400[kPa] to 460[kPa], the experimental values ​​closely match the leakage rate of the straight pipe model using Hagen-Poiseuille's law, but a slight discrepancy is noticeable between 460[kPa] and 500[kPa].

[0026] The cause of the discrepancy is presumed to be as follows: • Estimated cause (1): The rubber valve seats of the piping and on / off valves inside the inspection device had a slightly different volume between 460[kPa] and 500[kPa] compared to 400[kPa]. • Estimated cause (2): The volume of the 0.9m nylon tube differed slightly between 460[kPa] and 500[kPa] compared to 400[kPa].

[0027] Figure 21 shows the results of an experiment in which a stainless steel pipe (rigid body), the object under test, was connected to a leak testing device via a 5.0m polyurethane tube at one end, and the other end was sealed with a jig to measure the leakage rate. From 400[kPa] to 410[kPa], the experimental values ​​closely match the leakage rate of the straight pipe model using Hagen-Poiseuille's law, but a slight discrepancy is noticeable between 410[kPa] and 500[kPa].

[0028] Since the rubber valve seats of the piping and on / off valves inside the inspection device are the same as in Figure 20, the reason why Figure 20 and Figure 21 differ significantly is thought to be the following estimated reason (3). • Estimated cause (3): The 5.0m polyurethane tube, which is softer than the 0.9m nylon tube, exhibits a greater volume change.

[0029] Figure 22 shows the results of an experiment in which a copper pipe (rigid body), the object under test, was connected to a leak testing device via a 2.0m polyurethane tube at one end. The object under test then branched into six sections, and the other ends of the six branched sections were blocked with a jig to measure the leakage amount. Compared to Figures 20 and 21, there is a significant difference between the leakage amount of the straight pipe model using Hagen-Poiseuille's law and the experimental value. The reason for this is presumed to be as follows.

[0030] • Estimated cause (4): Despite using the same polyurethane tube as in Figure 21, but shortening its length (5.0m → 2.0m) and connecting it to the leak testing device, a significant difference occurred. This is thought to be due to the jigs used for occlusion (seven jigs in total, including both the other end and one end).

[0031] Thus, even if the object being inspected is rigid, flexible materials (for example, nylon tubes, polyurethane tubes) are used in other parts (piping, valves, etc.), so it is necessary to take into account the effects of volume changes in these flexible parts.

[0032] Conventional measuring instruments have aimed to improve accuracy and obtain precise measurement values. However, the present invention aims to solve the above problem and provides a leak inspection method and leak inspection apparatus that can correctly determine the quality of an object under inspection regarding leaks, regardless of differences in pressure conditions during leak measurement. [Means for solving the problem]

[0033] The essence of the present invention for achieving this objective lies in the inventions described in the following sections.

[0034] [1] A leak inspection method for inspecting whether or not there is leakage in an object to be inspected that has a hollow portion, A leak rate measurement step involves introducing a pressurized gas into the object to be inspected, sealing it, and then measuring the detected leak rate, which is the amount of leakage per unit time from the object to be inspected. A test pressure measurement step in which a first test pressure indicating a representative value of the internal pressure of the object under test during the period in which the above measurement was performed is determined based on the internal pressure measured once or multiple times at predetermined timings after the introduction of pressurization, A reference value acquisition step involves obtaining a reference inspection pressure and a reference leakage amount that indicates the maximum allowable value of the leakage amount per unit time from the object under inspection when the measurement is performed using the representative value as the reference inspection pressure, A conversion step in which at least one of the detected leak amount and the reference leak amount is converted using a function having a variable into which the pressure value before conversion is substituted and a variable into which the pressure value after conversion is substituted, such that the detected leak amount and the reference leak amount are the values ​​when the reference inspection pressure and the first inspection pressure are the same pressure. It has, In the aforementioned conversion step, The amount of leakage detected is converted to the value obtained when the first inspection pressure is the same as the standard inspection pressure, or The aforementioned standard leakage amount is converted to the value obtained when the standard inspection pressure is the same as the first inspection pressure, or The detected leakage amount is converted to the value obtained when the first inspection pressure is the same as the third pressure, and the reference leakage amount is converted to the value obtained when the reference inspection pressure is the same as the third pressure. has A leak testing method characterized by the following:

[0035] In the above invention and the invention described in [8] below, at least one of the detected leak amount and the reference leak amount is converted so that the detected leak amount and the reference leak amount obtained by measurement are the same values ​​as when the reference inspection pressure and the inspection pressure at the time of measurement are the same pressure. This conversion allows the values ​​to be standardized to the same pressure conditions even if the leak amount of the object under inspection is measured at a pressure different from the reference inspection pressure. "Same pressure" may be the reference inspection pressure, the first inspection pressure, or a separate third pressure. When the pressure is standardized to the reference inspection pressure, the detected leak amount is converted; when the pressure is standardized to the first inspection pressure, the reference leak amount is converted; and when the pressure is standardized to the third pressure, both the detected leak amount and the reference leak amount should be converted.

[0036] [2] Volume change acquisition step to acquire the volume change due to the internal pressure of the sealed closed space including the hollow portion of the object under inspection. It further possesses The leak inspection method according to [1], characterized in that

[0037] In the above invention and the invention described in [9] below, the calculation to convert the measured differential pressure [Pa] into a leakage rate in units of [mL / min] requires the volume of the leak source. Furthermore, in the case of a soft body, the volume of the leak source changes depending on the internal pressure of the leak source. Therefore, the volume change due to the internal pressure of the sealed closed space, including the hollow portion of the object under inspection, is obtained.

[0038] [3] In the conversion step, the volume of the sealed closed space including the hollow portion of the object under inspection changes depending on the internal pressure of the closed space, and the conversion is performed accordingly. The leak inspection method according to [1] or [2], characterized in that

[0039] In the above invention and the invention described in

[10] below, the conversion becomes more accurate by taking into account that the volume of the sealed closed space including the hollow portion of the object under inspection changes depending on the internal pressure of the closed space.

[0040] [4] The method further comprises a determination step of comparing the converted detected leakage amount with the reference leakage amount to determine whether or not there is leakage in the object under inspection. A leak inspection method according to any one of [1] to [3], characterized in that [1] to [3].

[0041] [5] In the leakage amount measurement step, after pressurizing a gas to the same pressure into a leak-free reference body having a hollow portion and the object under test, the amount of leakage from the object under test is obtained based on the pressure difference between the internal pressure of the object under test and the internal pressure of the reference body, measured while each of the reference body and the object under test is sealed as an independent closed space. A leak inspection method according to any one of [1] to [4], characterized in that [1] to [4].

[0042] In the above invention and the invention described in

[12] below, the differential pressure between the internal pressure of the object under inspection and the internal pressure of the reference object, both pressurized to the same pressure, is measured, making it possible to perform highly accurate measurements under high pressure.

[0043] [6] If there is a discrepancy between the measurement of the first inspection pressure and the measurement of the detected leakage amount, the system further includes an inspection pressure correction step of correcting the measured first inspection pressure to the value at the time of measurement of the detected leakage amount. A leak inspection method according to any one of [1] to [5], characterized in that

[0044] In the above invention and the invention described in

[13] below, it is preferable that the time of measurement of the inspection pressure be midway between the start and end of the measurement period for the amount of detected leakage. However, if, for example, the time of measurement of the inspection pressure is set to the start of the measurement period for the amount of detected leakage, or if the leakage is measured after a settling period has elapsed for the pressure drop to stabilize to some extent after sealing, the time may be settling during the settling period before the start of measurement of the amount of detected leakage, or further, if a pressure gauge for measuring the internal pressure of the object under inspection is not provided after sealing, the time may be settling after pressurization is complete but before sealing. In such cases where there is a discrepancy between the time of measurement of the inspection pressure and the time of measurement of the amount of detected leakage, the first inspection pressure measured at the discrepancy timing is corrected to match the value at the time of measurement of the amount of detected leakage.

[0045] [7] In the inspection pressure correction step, the correction is performed taking into account the amount of leakage detected. The leak inspection method according to [6], characterized in that

[0046] In the above invention and the invention described in

[14] below, a difference in pressure drop after sealing occurs depending on the amount of leakage. Therefore, the first inspection pressure, measured at a time staggered from the time of leakage measurement, is corrected taking the amount of leakage into account (the correction amount is increased or decreased according to the amount of leakage).

[0047] [8] A leak inspection device for inspecting whether or not there is leakage in an object to be inspected that has a hollow portion, A leak rate measuring unit measures the amount of leakage, which is the amount of leakage from the object to be inspected, after pressurizing the object to be inspected and then sealing it. An inspection pressure measuring unit that measures a first inspection pressure indicating the internal pressure of the object under inspection when the above measurement is performed, A reference value acquisition unit that acquires a reference inspection pressure and a reference leakage amount that indicates the maximum allowable value of the leakage amount from the object under inspection when the measurement is performed with the internal pressure of the object under inspection as the reference inspection pressure, A conversion unit that converts at least one of the detected leak amount and the reference leak amount so that the detected leak amount and the reference leak amount are the values ​​when the reference inspection pressure and the first inspection pressure are the same pressure, to have death, The conversion unit is, The amount of leakage detected is converted to the value obtained when the first inspection pressure is the same as the standard inspection pressure, or The aforementioned standard leakage amount is converted to the value obtained when the standard inspection pressure is the same as the first inspection pressure, or The detected leakage amount is converted to the value obtained when the first inspection pressure is the same as the third pressure, and the reference leakage amount is converted to the value obtained when the reference inspection pressure is the same as the third pressure. A leak detection device characterized by the following features.

[0048] [9] The object under inspection further comprises a volume change acquisition unit that acquires the volume change due to the internal pressure of the sealed closed space, including the hollow portion of the object under inspection. The leak inspection device according to [8], characterized in that

[0049]

[10] The conversion unit takes into account that the volume of the sealed closed space, including the hollow portion of the object under inspection, changes depending on the internal pressure of the closed space, and performs the conversion. A leak inspection device according to [8] or [9], characterized in that

[0050]

[11] The system further comprises a determination unit that compares the converted detected leak amount with the reference leak amount to determine whether or not there is a leak in the object being inspected. A leak inspection device according to any one of [8] to

[10] , characterized in that

[0051]

[12] The leakage amount measuring unit pressurizes gas to the same pressure into a reference body having a hollow portion and the object under test, and then, with the reference body and the object under test sealed as independent closed spaces, it obtains the leakage amount from the object under test based on the pressure difference between the internal pressure of the object under test and the internal pressure of the reference body. A leak inspection device according to any one of [8] to

[11] , characterized in that

[0052]

[13] If there is a discrepancy between the measurement of the first inspection pressure and the measurement of the detected leakage amount, the inspection pressure measuring unit corrects the measured first inspection pressure to match the value at the time of measurement of the detected leakage amount. A leak inspection device according to any one of [8] to

[12] , characterized in that

[0053]

[14] The inspection pressure measuring unit performs the correction taking into account the detected leakage amount. The leak inspection device according to

[13] , characterized in that [Effects of the Invention]

[0054] According to the leak inspection method and leak inspection apparatus of the present invention, the quality of the inspected object regarding leaks can be correctly determined regardless of differences in pressure conditions during leakage measurement. [Brief explanation of the drawing]

[0055] [Figure 1] This figure shows the schematic configuration and inspection flow of the leak inspection device according to the present invention. [Figure 2] This is a flowchart showing the flow of the inspection process performed by the leak detection device. [Figure 3] This figure shows a graph illustrating the relationship between pressure and leakage rate (without considering volume change due to pressure change (δ1=1, δ2=0 in Equation 4) and with considering volume change (δ1=0.8, δ2=2.207)). [Figure 4] This figure shows a graph that approximates the theoretical values ​​of leakage amounts for different test pressures passing through a single reference point using a linear function. [Figure 5] This figure shows the graph of a linear function passing through two leakage measurement points. [Figure 6] This figure shows a linear function whose slope is represented by the graph in Figure 5 and whose height is represented by the reference point in Figure 4. [Figure 7] This figure shows the leak inspection device from Figure 1 with the addition of a variable valve and flow meter for determining the virtual equivalent volume. [Figure 8] This figure shows graphs illustrating the relationship between pressure and leakage rate (one with pressure correction applied only to ΔP, and another with pressure correction applied to Vw[mL] as well). [Figure 9] This figure shows that the relationship between pressure and leakage rate differs under various conditions of the measurement system. [Figure 10]This figure shows the results of converting the leakage amounts of each test object b (defective product) and test object c (good product) at different test pressures to the values ​​obtained when the leakage amount is measured at the standard test pressure (450 kPa). [Figure 11] This figure schematically shows the change in the internal pressure of the workpiece when a leak test is performed according to the flowchart in Figure 2. [Figure 12] This figure shows the detected leakage amount, the converted leakage amount without temperature compensation, and the converted leakage amount with temperature compensation for workpieces W1 and W2 in Figure 11. [Figure 13] This diagram shows the change in internal pressure of workpiece W1, which has a lot of leakage, when the inspection pressure is high, and the change in internal pressure of workpiece W2, which has little leakage, when the inspection pressure is low. [Figure 14] This figure shows the detected leakage amount, the converted leakage amount without temperature compensation, and the converted leakage amount with temperature compensation for workpiece W1, which leaked a lot when measured at a low inspection pressure, and workpiece W2, which leaked little when measured at a higher inspection pressure. [Figure 15] This figure shows the control performance of the electro-pneumatic regulator and the results of the leak test when inspecting a large number of workpieces with a set pressure of 500 kPa ± 40 kPa. [Figure 16] This figure shows the relationship between the converted leak amount and the inspection pressure, with the measurement of the inspection pressure being considered the start of the leak amount measurement. [Figure 17] This figure shows the changes in internal pressure of the workpiece and master during leak testing (without exaggeration). [Figure 18] This figure illustrates the conversion with and without temperature compensation for workpieces with low leakage, relatively low leakage, high leakage, and relatively low leakage. [Figure 19] This figure shows an example of the relationship between inspection pressure, leakage amount, and pass / fail determination based on the standard leakage amount in conventional leak testing. [Figure 20] This figure shows the results of an experiment in which one end of a stainless steel pipe (rigid body), which was the object under test, was connected to a leak testing device via a 0.9m nylon tube, and the other end was sealed with a jig to measure the amount of leakage. [Figure 21]This figure shows the results of an experiment in which one end of a stainless steel pipe (rigid body), which was the object under test, was connected to a leak testing device via a 5.0m polyurethane tube, and the other end was sealed with a jig to measure the amount of leakage. [Figure 22] This figure shows the results of an experiment in which one end of a copper pipe (rigid body), which was the object under test, was connected to a leak testing device via a 2.0m polyurethane tube. The object under test then branched into six branches, and the other ends of the six branching points were sealed with a jig to measure the amount of leakage. [Figure 23] This figure shows the theoretical relationship between pressure and leakage rate on a logarithmic graph. [Modes for carrying out the invention]

[0056] Embodiments of the present invention will be described below with reference to the drawings.

[0057] Figure 1 shows the schematic configuration and inspection flow of the leak inspection device 10 according to the present invention. Hereafter, all pressures will be gauge pressures. The leak inspection device 10 is a device for inspecting leaks in objects to be inspected that have a hollow section (for example, piping in heat exchangers, containers such as hot water storage tanks). The object to be inspected that has a hollow section is called the workpiece. A container etc. made of the same shape and material as the workpiece, which has been confirmed to be leak-free, is called the master. The workpiece and the master are different containers etc. that have the same mechanical and thermodynamic parameters.

[0058] Furthermore, if the workpiece and master are different containers with the same mechanical and thermodynamic parameters, a large workpiece will require a large master, resulting in a large space being needed for the inspection device. Therefore, it may be possible to use a smaller master and a conversion factor to achieve the same result as if the master were the same size as the workpiece.

[0059] The leak inspection device 10 is equipped with a pressure source connection port 11, a workpiece connection port 12, and a master connection port 13. The leak inspection device 10 has a first pipe 21 as an internal conduit, one end of which is connected to the pressure source connection port 11. The first pipe 21 branches into two in the middle, becoming a second pipe 22 and a third pipe 23. The other end of the second pipe 22 is connected to the workpiece connection port 12, and the other end of the third pipe 23 is connected to the master connection port 13.

[0060] A first on-off valve 31 is inserted into the first pipe 21. The second pipe 22 is equipped with a second on-off valve 32, a first pressure gauge 41, and a third on-off valve 33 in the order from the branching point with the first pipe 21 toward the workpiece connection port 12. The third pipe 23 is equipped with a fourth on-off valve 34, a second pressure gauge 42, and a fifth on-off valve 35 in the order from the branching point with the first pipe 21 toward the master connection port 13.

[0061] A differential pressure gauge 43 is connected between the second pipe 22 between the second shut-off valve 32 and the third shut-off valve 33, and between the third pipe 23 between the fourth shut-off valve 34 and the fifth shut-off valve 35. In addition, an exhaust pipe 24 branches off from the third pipe 23 at a predetermined point between the first shut-off valve 31 and the fourth shut-off valve 34, and an exhaust valve 38 is provided in the middle of the exhaust pipe 24. The end of the exhaust pipe 24 is an exhaust port and is open to the atmosphere.

[0062] The leak inspection device 10 has an inspection processing unit 50 that controls the inspection flow, performs measurements, and makes leak determinations based on the measurement results. The inspection processing unit 50 is a circuit whose main components are a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. The CPU executes processing according to a program stored in the ROM, thereby controlling, measuring, and determining the inspection operation of the leak inspection device 10.

[0063] The inspection processing unit 50 is equipped with the following functions: a leak rate measurement unit 51, an inspection pressure measurement unit 52, a reference value acquisition unit 53, a conversion unit 54, a determination unit 55, and a volume change acquisition unit 56. The leak rate measurement unit 51 measures the detected leak rate, which is the amount of leakage from the object under inspection after pressurizing and introducing gas into the object under inspection and then sealing it. Here, the leak rate measurement unit 51 uses a differential pressure gauge 43 to detect the difference between the internal pressure of the workpiece and the internal pressure of the master at the start of the measurement period and the difference between the internal pressure of the workpiece and the internal pressure of the master at the end of the measurement period, as the differential pressure corresponding to the leak rate.

[0064] The inspection pressure measuring unit 52 performs the function of measuring a first inspection pressure, which indicates the internal pressure of the object under inspection when the leakage amount measuring unit 51 has measured the leakage amount.

[0065] The reference value acquisition unit 53 performs the function of acquiring the reference inspection pressure and the reference leakage amount, which is the maximum allowable value of the leakage amount from the object under inspection when the internal pressure of the object under inspection is used as the reference inspection pressure for leakage measurement. For example, it receives input of the reference inspection pressure and the reference leakage amount from an administrator or the like and stores them.

[0066] The conversion unit 54 performs the function of converting at least one of the detected leak amount and the reference leak amount so that the detected leak amount and the reference leak amount are the values ​​that would occur if the reference inspection pressure and the first inspection pressure were the same pressure. "The same pressure" may be the reference inspection pressure, the first inspection pressure, or a separate third pressure. If the pressure is standardized to the reference inspection pressure, the detected leak amount is converted to the value under the reference inspection pressure; if the pressure is standardized to the first inspection pressure, the reference leak amount is converted to the value under the first inspection pressure; and if the pressure is standardized to a separate third pressure, both the detected leak amount and the reference leak amount should be converted to the values ​​under the third pressure.

[0067] Here, the conversion described above is performed taking into account that the volume of the sealed closed space, including the hollow portion of the object under inspection, changes depending on the internal pressure of the closed space. When converting the differential pressure ΔP [Pa] detected as the leakage amount to the leakage amount Q [mL / min], the volume Vw of the sealed closed space, including the hollow portion of the object under inspection, is relevant, as shown in equation A. Since the volume Vw of the closed space, including the soft material, changes depending on the pressure inside the closed space, the conversion unit 54 takes this into account when performing the conversion described above. The leak inspection device 10 also supports cases where the conversion is performed without taking into account that the volume of the sealed closed space, including the hollow portion of the object under inspection, changes depending on the internal pressure of the closed space. Note that this volume includes the diaphragm of the differential pressure gauge that measures the differential pressure inside the leak inspection device, the piping from the inspection device to the object under inspection, and the jig that seals the object under inspection, and is not limited to the volume of the object under inspection alone.

[0068] The determination unit 55 performs the function of determining whether or not there is leakage in the object being inspected by comparing the converted detected leakage amount with the standard leakage amount.

[0069] The volume change acquisition unit 56 acquires the volume change due to the internal pressure of the sealed closed space, including the hollow portion of the object under inspection. For example, it receives settings for the leakage rate [mL / min] at multiple pressure points within the allowable range of the inspection pressure. For example, it receives setting inputs for at least two points from 12.96 [mL / min at 500kPa], 9.69 [mL / min at 402kPa], and 11.03 [mL / min at 450kPa]. Based on these, it performs calculations of coefficients for conversion that take into account the effect of volume change due to internal pressure.

[0070] A workpiece 61 is connected to the workpiece connection port 12 of the leak inspection device 10. In this example, the workpiece 61 is a through-type container with an inlet and an outlet (for example, a heat exchanger for a water heater). The inlet of the workpiece 61 is connected to the workpiece connection port 12, and the outlet is connected to the sixth on-off valve 36. When the sixth on-off valve 36 is opened, the outlet of the workpiece 61 is exposed to the atmosphere.

[0071] A master 62 is connected to the master connection port 13. In this example, the master 62 is a through-type container, similar to the workpiece 61, having an inlet and an outlet. The inlet of the master 62 is connected to the master connection port 13, and the outlet is connected to the seventh on-off valve 37. When the seventh on-off valve 37 is opened, the outlet of the master 62 is exposed to the atmosphere.

[0072] Workpiece 61 undergoes the following process from manufacturing to the end of inspection. Master 62 is maintained connected to master connection port 13. The leak inspection device 10 inspects new workpieces 61 one after another. After being manufactured through the brazing process (P1), workpieces 61 are piled up on a cage trolley and left for about 10 minutes to settle to ambient temperature + 10°C (P2). Then, they are placed on an isothermal fan unit 6 that blows air and cooled by exposure to air for several minutes (P3). After that, they are attached to the leak inspection device 10 and inspected (P4). Once the inspection is complete, they are removed from the leak inspection device 10 and sent to the next process (P5).

[0073] A pressurized gas supply source 3 is connected to the pressurized gas source connection port 11 of the leak inspection device 10 via an electro-pneumatic regulator 2. A pressure gauge 5 is also connected to the piping between the electro-pneumatic regulator 2 and the pressurized gas source connection port 11. The pressurized gas supply source 3 is installed outdoors, for example, and along the piping leading to the electro-pneumatic regulator 2, it also supplies pressurized gas to various machines that use pressurized gas as power (e.g., air tools).

[0074] For example, the pressurized gas supply source 3 consists of an air compressor (compressor, commonly called a "baby compressor" in the case of a small one) that produces pressurized gas, a tank that temporarily stores the pressurized air from the compressor (a buffer air tank that minimizes pressure fluctuations), and a pressure sensor installed in the tank.

[0075] When pressurized gas is used, the amount of pressurized air stored in the tank decreases. When the pressure detected by the pressure sensor reaches a preset lower limit, the pressurized gas supply source 3 activates the compressor and sends pressurized air to the tank (baby controller). When the pressure detected by the pressure sensor reaches a preset upper limit, the compressor stops. As a result, the pressure of the pressurized gas supplied from the tank of supply source 3 fluctuates within a predetermined range. In addition, if the amount of pressurized gas used exceeds the compressor's capacity, the pressurized gas from supply source 3 may be supplied at a level below the preset lower limit. Aftercoolers, dryers, etc., may be added as needed.

[0076] The electro-pneumatic regulator 2 performs the function of controlling the downstream side to reach a set pressure (in reality, it is not possible to pressurize beyond the pressure supplied from the supply source 3, so the administrator monitors the supply pressure and sets a predetermined range below the supply pressure to control it to reach the set pressure). In detail, the set value of the electro-pneumatic regulator 2 is sent from the inspection processing unit 50 of the leak inspection device 10. This set value is, for example, a set range such as 500kPa ± 40kPa, which the user inputs to the leak inspection device 10, and the electro-pneumatic regulator 2 continues to control the downstream pressure to reach the set value (for example, 500kPa) by reacting to and correcting in real time to changes in the source pressure based on this 500kPa setting.

[0077] While the leak inspection device 10 is pressurizing and introducing gas into the workpiece 61, the electro-pneumatic regulator 2 continues the aforementioned control, and the inspection processing unit 50 of the leak inspection device 10 closes the first on-off valve 31 when a predetermined time (for example, 10 seconds) has elapsed since the start of pressurizing and introducing gas into the workpiece 61. Then, if the pressure of the first pressure gauge 41 at the time up (when the first on-off valve 31 is closed) is within a predetermined allowable range (for example, 500kPa ± 40kPa), it is determined that pressurization has been performed normally and the process proceeds to the leak amount inspection step; otherwise, it is determined that there is a pressurization error. For example, if the allowable range is 500kPa ± 40kPa, the process proceeds to the leak amount inspection step at the same pressure whether the pressure at the time up is 480kPa or 530kPa.

[0078] Furthermore, the pressure at the time-up may deviate from the set value (for example, 500 kPa) for the following reasons. Specifically, if another machine powered by pressurized gas, which is branched off from the piping from the supply source 3 to the electro-pneumatic regulator 2, uses an unexpectedly large amount of pressurized gas just before the end of the period during which the leak inspection device 10 is introducing pressurized gas to the object under inspection, the electro-pneumatic regulator 2 may not be able to control the rapid drop in pressure of the pressurized gas supplied from the supply source 3 in time, resulting in the pressure at the time-up falling below the set value. For example, a pressure that was controlled at 500 kPa may drop to 470 kPa just before the first on-off valve 31 is closed.

[0079] Figure 2 is a flowchart showing the flow of the inspection process performed by the leak inspection device 10. The leak inspection device 10 receives input settings for a reference inspection pressure (Ptest) and a reference leak amount (Qref) which indicates the maximum allowable value of the leak amount from the workpiece (object under inspection) when the internal pressure of the workpiece is set to the reference inspection pressure (Step S100: Reference value recognition process). Here, the reference leak amount (Qref) is set as a value in units of [mL / min].

[0080] The standard test pressure (Ptest [kPa]) and standard leak rate (Qref [mL / min]) are paired, and how to set them should be made known to the administrator, for example, by including this information in the instruction manual for the leak testing device 10.

[0081] For example, if the pressure range to be set for the electro-pneumatic regulator 2 is 500kPa + 40kPa to 500kPa - 30kPa, then it is sufficient to define whether the reference test pressure should be 500kPa (the ± reference value) or the median value of 505kPa. The leak testing device 10 can then recognize the reference test pressure (Ptest) from the set pressure range based on that definition. Alternatively, the set value of the reference test pressure (Ptest) can be directly input to the leak testing device 10.

[0082] Next, information is obtained showing the relationship between the internal pressure and volume change of the sealed closed space, including the inside of the workpiece, formed in the leak inspection process described later (step S101, volume change acquisition process). Here, pairs of the internal pressure of the sealed closed space, including the inside of a predetermined workpiece with leakage, and the amount of leakage at that internal pressure (unit: [mL / min]) are obtained for multiple internal pressures (preferably multiple internal pressures within the allowable range of the inspection pressure).

[0083] For example, the system accepts inputs such as a pair of leak rates of 9.69 [mL / min] at 402kPa and 402kPa, a pair of leak rates of 11.03 [mL / min] at 450kPa and 450kPa, and a pair of leak rates of 12.96 [mL / min] at 500kPa and 500kPa. At least two internal pressure values ​​need to be input. Based on these values, the system calculates coefficients and other factors for conversion, taking into account the effect of volume changes due to internal pressure.

[0084] The leak inspection device 10 opens all on-off valves 32-38 except for the first on-off valve 31, and in this state, the worker connects the workpiece 61 and master 62 to the leak inspection device 10 in an open-air state as shown in Figure 1 (step S102).

[0085] The leak inspection device 10 then closes the exhaust valve 38, and in this state, controls the first on / off valve 31 to open for a predetermined time (20-30 seconds) and then close it to scavenge (pre-purge) the inside of the workpiece 61 and master 62 (step S103). The scavenging flow rate is, for example, about 50-100 liters in atmospheric pressure equivalent.

[0086] Subsequently, the sixth valve 36 and the seventh valve 37 are closed, and then the second valve 32 and the fourth valve 34 are closed to separate the workpiece 61 and the master 62 from an open state to the atmosphere into independent, sealed spaces (step S104).

[0087] Subsequently, a temperature compensation measurement process is performed in which the differential pressure between the closed space on the workpiece 61 side and the closed space on the master 62 side is measured using a differential pressure gauge 43 while the workpiece is left unattended for a predetermined period of time (step S105). The change in differential pressure measured in the temperature compensation measurement process (the difference between the differential pressure at the start of the temperature compensation measurement process (the differential pressure between the closed space on the workpiece 61 side and the closed space on the master 62 side) and the differential pressure at the end (the differential pressure between the closed space on the workpiece 61 side and the closed space on the master 62 side)) is defined as ΔPt1, and the measurement time in the temperature compensation measurement process is defined as Ta.

[0088] Next, a leak inspection process is performed. In the leak inspection process, first, pressurized gas is introduced from the pressurized gas supply source 3 to the workpiece 61 and master 62 to a predetermined inspection pressure (for example, within a set range such as 500kPa ± 40kPa) (step S106: pressurization step). Specifically, the second on-off valve 32 and the fourth on-off valve 34 are opened to connect the workpiece 61 and master 62, then the first on-off valve 31 is opened to pressurize the gas from the supply source 3 to the workpiece 61 and master 62, and once the pressurization is complete, the first on-off valve 31 is closed.

[0089] Here, as mentioned above, the gas is pressurized and introduced while the pressure is controlled by the electro-pneumatic regulator 2 (for example, controlled to reach a set value of 500 kPa). After a predetermined time has elapsed from the start of pressurization (for example, 10 seconds), the first on-off valve 31 is controlled to close regardless of the pressure situation at that time (for example, even if it is outside the set range of 500 kPa ± 40 kPa).

[0090] If the pressure Pt (pressure indicated by the first pressure gauge 41) at the time of sealing after pressurization is complete (when the first on-off valve 31 is closed) is outside the set range (for example, 500kPa ± 40kPa), an inspection error is recorded at that point. If it is within the set range, the second on-off valve 32 and the fourth on-off valve 34 are further closed to create pressurized, independent closed spaces for the workpiece 61 and the master 62 (step S106).

[0091] After that, a settling period is waited for the temperature change (pressure change) to stabilize to some extent, and during the subsequent measurement period, the change in differential pressure between the closed space on the workpiece 61 side and the closed space on the master 62 side is measured with the differential pressure gauge 43 (Step S107: Measurement Step). The amount of change in differential pressure measured in the leak inspection process (the difference between the differential pressure at the start of measurement in the leak inspection process and the differential pressure at the end of measurement in the leak inspection process) is denoted as ΔPr, and the length of the measurement period (time) in the measurement step of the leak inspection process is denoted as Tr.

[0092] Furthermore, the inspection processing unit 50 measures the internal pressure of the workpiece 61 when the differential pressure ΔPr is measured using the first pressure gauge 41 and records this as the inspection pressure (step S108). For example, the internal pressure at the midpoint between the start and end of the measurement period, or the internal pressure at the start of the measurement period, is measured using the first pressure gauge 41 and recorded as the inspection pressure. The internal pressure of the workpiece 61 at the time of measurement (inspection pressure) is denoted as Ptw.

[0093] Furthermore, if the leak is large, even after the temperature change (pressure change caused by the temperature change) has stabilized, it will take even longer for the pressure change caused by the leak to stabilize (the internal pressure decreases due to the leak, and this decrease reduces the leak itself), resulting in a difference between the time it takes for the temperature change to stabilize and the time it takes for the pressure change to stabilize. Also, if the leak is large, the temperature tends to stabilize faster than the pressure change because, rather than heat escaping through the wall, the air containing the heat itself is directly released outside the workpiece, and the pressure inside the workpiece decreases (the temperature drops due to a state close to adiabatic expansion). Therefore, the pressure drop during the settling period will differ depending on the size of the leak, that is, the time it takes for the pressure drop to stabilize (the time constant related to the pressure drop) will differ depending on the size of the leak.

[0094] Next, the workpiece 61 and master 62 are depressurized and released to the atmosphere (step S109: depressurization step). Specifically, the second on-off valve 32 and the fourth on-off valve 34 are opened to connect the workpiece 61 and master 62, and then the exhaust valve 38 is opened to depressurize and release to the atmosphere. At this time, the sixth on-off valve 36 and the seventh on-off valve 37 may also be opened. After that, the worker replaces the workpiece 61 and proceeds with preparing for the inspection of the next workpiece.

[0095] Next, the inspection processing unit 50 derives a temperature compensation value PH1 corresponding to the inspection pressure during measurement from the differential pressure ΔPt1 obtained in the temperature compensation measurement process (the difference between the differential pressure at the start and the differential pressure at the end of the temperature compensation measurement process) using the following formula (step S110). PH1[Pa]=ΔPt1[Pa]×(Tr[s] / Ta[s])×((Ptw[Pa]+Patm[Pa]) / Patm[Pa]) …Formula 1 Here, Ta is the measurement time [s] in the temperature compensation measurement process, Tr is the measurement period for the leakage amount [s], Ptw is the internal pressure of the workpiece during leakage amount measurement [Pa], and Patm is atmospheric pressure (101325 [Pa]).

[0096] Furthermore, PH1 [Pa] is converted to a temperature compensation value H1 [mL / min] based on the leakage rate in units of [mL / min] using the following formula. H1[mL / min] = PH1[Pa]×Vw[mL]×60 / (Tr[s]×Patm[Pa]) …Equation 2 The Vw used in this formula is the virtual equivalent volume (Vw at Ptw) of the sealed closed space containing the workpiece at the internal pressure Ptw when the leakage amount was measured in step S107. For reference, if the entire closed space is considered a rigid body, Vw can be determined by various well-known methods. For example, fill the workpiece with water and weigh it. The volume of the pipe between the measuring instrument and the workpiece can be determined by measuring the diameter with calipers and the length with a measuring tape to find the cylindrical volume inside the pipe. These are then added together. Alternatively, connect a known volume (e.g., 1000 ml) in parallel with the workpiece and calculate the volume inversely from the pressure (pressure gauge 41) before and after opening and closing the valve. If the pressure after opening and closing the valve is half the pressure before opening and closing the valve, then by inverse calculation based on Boyle's Law, the volume of the closed space on the workpiece side will be 1000 ml.

[0097] Next, the inspection processing unit 15 converts the differential pressure ΔPr, which represents the leakage amount measured in step S107, into a leakage amount Qr [mL / min] in units of [mL / min] using the following formula. Qr[mL / min] = ΔPr[Pa]×Vw[mL]×60 / (Tr×Patm[Pa]) …Equation 3 The Vw used in this formula is also the virtual equivalent volume (Vw at Ptw) of the sealed closed space containing the workpiece at the internal pressure Ptw when the leakage amount was measured in step S107. Then, the detected leakage amount (Qr [mL / min]) is corrected with the temperature compensation value H1 (step S111), and this is further converted to the value when the internal pressure of the workpiece at the time of measurement (inspection pressure) is the reference inspection pressure to obtain the converted leakage amount Qs (step S112: conversion step).

[0098] Furthermore, the conversion is performed assuming that the volume of the sealed closed space including the hollow portion of the object under inspection (the closed space between the closed second on-off valve 32 and the closed sixth on-off valve 36 (including the hollow portion of the workpiece 61)) changes depending on the internal pressure of the closed space. In order to perform the conversion that takes this volume change into account, the following formula uses δ1: contribution rate and δ2: offset value.

[0099] An example of a conversion formula is shown below. This is the conversion formula used with Hagen-Poiseuil's straight pipe model, to which δ1 is the contribution rate and δ2 is the offset value. Qs= δ1×(Qr-H1)×((Ptest×1000+Patm) 2 -Patm 2 ) / ((Ptw×1000+Patm) 2 -Patm 2 )-Δ QOS +δ2...Equation 4 Qs [mL / min]: Equivalent leakage rate, Qr [mL / min]: Detected leakage rate, H1 [mL / min]: Temperature compensation value, Δ QOS [mL / min] : Judgment value offset value, Ptest[kPa]: Reference inspection pressure, Patm: 101325[Pa], Ptw[kPa]: Workpiece internal pressure during leakage measurement, If temperature compensation is not performed, H1 should be set to zero "0". The offset value is, for example, to accommodate slight fluctuations depending on the season, and is not required. However, as will be shown later, the offset value may be used to handle the conversion of leak information of the inspected object, the amount of leak, or the standard amount of leak entered by the administrator.

[0100] δ1 is a coefficient that changes the slope of the graph. δ2 is used to correct for the deviation of the converted leak amount at the reference inspection pressure from the reference leak amount due to the change in slope by δ1 (so that the converted leak amount at the reference inspection pressure matches the reference leak amount).

[0101] Furthermore, if δ1=1 and δ2=0, the formula becomes the one that assumes the volume of the sealed closed space, including the hollow portion of the object under inspection, does not change depending on the internal pressure of the closed space (i.e., the entire closed space is considered a rigid body, corresponding to Hagen-Poiseuille's straight-tube model).

[0102] The internal pressure of a workpiece during leakage measurement fluctuates due to reasons such as (Reason 1) to (Reason 4) as described in the section on problems the invention aims to solve. Furthermore, if even a part of the wall surface of a sealed closed space, including the hollow portion of the object under inspection, contains a soft material (for example, a pipe made of nylon tubing, polyurethane tubing, etc., or a rubber valve seat for an on-off valve), the volume of the closed space (leak source) changes due to its internal pressure. The formula A, which converts the differential pressure ΔP [Pa] to the leakage rate Q [mL / min], includes the volume of the leak source.

[0103] Therefore, comparing the reference leak rate (Qref [mL / min]), which is the maximum allowable leak rate when measured at the standard inspection pressure, with the detected leak rate (Qr [mL / min] or Qr corrected by the temperature compensation value H1) measured under a pressure different from the standard inspection pressure, does not allow for a correct determination of the quality of the workpiece in terms of leaks. For this reason, in step S112, a conversion is performed using the aforementioned Equation 4 so that the detected leak rate and the reference leak rate are values ​​under the same pressure conditions, including the volume change of the leak source due to the internal pressure of the leak source.

[0104] The inspection processing unit 50 determines whether the converted leakage amount Qs [mL / min] is greater than the reference leakage amount Qref [mL / min] (step S113). If the converted leakage amount Qs [mL / min] is greater than the reference leakage amount Qref [mL / min] (step S113; Yes), it determines that there is a leak (step S114) and terminates this process. If the converted leakage amount Qs [mL / min] is less than or equal to the reference leakage amount Qref [mL / min] (step S113; No), it determines that there is no leak (step S115) and terminates this process.

[0105] Note that even if the leakage rate is expressed in units of [mL / min], it may be expressed in [Pa·m]. 3 The unit may be in units of [ / s]. The differential pressure ΔP [Pa] is given by the leakage rate Q [Pa·m] using the above formula B. 3 This is converted to / s].

[0106] Alternatively, the reference leakage rate Qref [mL / min] at the standard test pressure may be converted to the leakage rate at the test pressure during measurement using the following conversion formula, and compared with the measured leakage rate (Qr, or (Qr-H1) if temperature compensation is applied). Converted standard leakage amount = δ1×(Qref)×((Ptw×1000+Patm) 2 -Patm 2 ) / ((Ptest×1000+Patm) 2 -Patm 2 )-Δ QOS +δ2

[0107] When comparing based on leakage rate, the unit of reference leakage rate is [mL / min] or [Pa·m]. 3 [ / s] is often used, and the period (time) that forms the basis of the reference leakage rate can be [min] or [s], but for comparison purposes, it is sufficient that the period that forms the basis of the converted leakage rate and the reference leakage rate are the same. For example, both the time for the converted leakage rate and the time for the reference leakage rate can be standardized to the same time, such as [h] or [24h], instead of [min] or [s], for comparison.

[0108] Next, we will show an example of how to determine δ1 and δ2 in Equation 4. The leakage rate is expressed by the following equation 5. Leakage amount = (πd 4 / 128Lμ) × ((P1 2 -P2 2 ) / 2P2)...Formula 5 Assuming a standard leak rate of 11.03 [mL / min at 450kPa], we determine any combination of d and L that satisfies Equation 5 when the leak rate is 11.03 [mL / min at 450kPa]. Here, we define d as L: 1 [mm].

[0109] Specifically, the values ​​in Equation 5 are as follows: Leakage rate: 11.03 [mL / min] = 1.83833 × 10 -7 [m 3 / s], π:3.141592, μ (viscosity of air at 20°C, air (Pa·s)): 0.0000181 [Pa·s] P1:450[kPa G]=551325[Pa[ANR]], P2: 0[kPaG]=101325[Pa[ANR]], And, If we set L to 1 [mm] = 1 / 1000 [m], then d is 0.017448819 [mm] = 0.017448819 / 1000 [m]. There is a correlation between L and d; changing one changes the other, and there are infinitely many combinations of these. However, the leakage amount calculated using Equation 5 is always the same, so either L or d can be set to any value.

[0110] In Equation 5, where d and L are the values ​​above, the leakage rate at a given pressure P1 can be determined by changing P1. A hole showing a leakage rate of 11.03 [mL / min at 450kPa] will show the leakage rate shown in Graph 91 of Figure 3 when the pressure changes. This corresponds to the case where volume change due to pressure is not considered.

[0111] For a soft object (a sealed closed space including the hollow portion of the object being inspected in the leak inspection device 10) with a standard leak rate of 11.03 [mL / min at 450kPa], suppose the leak rates measured at different pressures were, for example, 12.96 [mL / min at 500kPa] and 9.69 [mL / min at 402kPa].

[0112] Substituting the above three values ​​into Equation 4, ΔQs= δ1 × (12.96) × (((450) + 101.325) 2 -101.325 2 ) / ((500+101.325) 2 -101.325 2 )+ δ2 =δ¹×(9.69)×(((450)+101.325) 2 -101.325 2 ) / ((402+101.325) 2 -101.325 2)+ δ2 =δ¹×(11.03)×(((450)+101.325) 2 -101.325 2 ) / ((450+101.325) 2 -101.325 2 )+ δ2 Solving at least two of the above equations yields, for example, δ1 = 0.8 and δ2 = 2.207.

[0113] That is, if δ1 = 0.8 and δ2 = 2.207, then the above three equations become as follows. 10.87419943 [mL / min at 450kPa] = 0.8 × (12.96) × (((450) + 101.325) 2 -101.325 2 ) / ((500+101.325) 2 -101.325 2 )+ 2.207 Equation 4a 11.57348215 [mL / min at 450kPa] = 0.8 × (9.69) × (((450) + 101.325) 2 -101.325 2 ) / ((402+101.325) 2 -101.325 2 )+ 2.207 …Equation 4b 11.031 [mL / min at 450kPa] = 0.8 × (11.03) × (((450) + 101.325) 2 -101.325 2 ) / ((450+101.325) 2 -101.325 2 )+ 2.207 …Equation 4c The line passing through point 12.96 [mL / min at 500kPa] (graph in equation 4a) passes through the point 10.87419943 [mL / min at 450kPa], while the line passing through point 9.69 [mL / min at 402kPa] (graph in equation 4b) passes through the point 11.57348215 [mL / min at 450kPa], showing a slight discrepancy.

[0114] The equation of the line passing through 11.031 [mL / min at 450kPa], that is, the following equation corresponding to equation 4c, ΔQs=0.8×(11.03)×(((450)+101.325) 2 -101.325 2 ) / ((Ptw+101.325) 2 -101.325 2 )+ 2.207 Figure 3 shows graph 92 obtained by varying Ptw, for example, from 380 to 520 [kPa]. In this case, curves are obtained that pass near 12.96 [mL / min at 500kPa], 9.69 [mL / min at 402kPa], and 11.03 [mL / min at 450kPa].

[0115] For example, the leakage amount under the inspection pressure (Qr-H1) obtained in step S111 of Figure 2 may be compared with the leakage amount obtained by converting the reference leakage amount to the leakage amount under the inspection pressure according to Graph 92 (the converted reference leakage amount) to determine whether there is a leak or not.

[0116] Another example of a conversion formula is shown below. This formula has been appropriately set so that the conversion result approximates the measured value.

[0117] Q[mL / min]=δ2+δ1×(Ptw-δ3)×δ2×((101.325+Ptw) 2 -101.325 2 ) / ((101.325+δ3) 2 -101.325 2 )...Equation 6 Correction factor δ1: 0.00238242345067852 When δ2 is 402 [kPa], 9.69 [mL / min] leaks, so "9.69" [mL / min]. δ3: When it leaks at 9.69 [mL / min], the pressure is 402 [kPa], therefore, "402" [kPa]. For example, since the value is 12.96 [mL / min at 500kPa], if we calculate the correction factor δ1 to satisfy this condition, we obtain the correction factor δ1: 0.00238242345067852.

[0118] Furthermore, for example, since the value is 11.03 [mL / min at 450kPa], if we determine the correction factor δ1 to satisfy this condition, we obtain the correction factor δ1: 0.00238438860741623. Equation 6 is, for example, an equation based on 9.69 [mL / min at 402kPa], so the correction factor δ1 may also be determined using an equation based on 12.96 [mL / min at 500kPa], which is measured on a leaky soft material that is used as the standard by the leak inspection manager, or a predetermined standard value of 11.03 [mL / min at 450kPa].

[0119] δ1, δ2, and δ3 can be determined from at least two values ​​chosen from measured values ​​or predetermined reference values. Using Equation 6, curves with values ​​approximately equivalent to 12.96 [mL / min at 500kPa], 9.69 [mL / min at 402kPa], and 11.03 [mL / min at 450kPa] can be obtained. These curves may be used as the reference leakage rate (reference value) [mL / min] under each pressure and compared with the measured leakage rate [mL / min]. Figure 3 shows Graph 93, which corresponds to Equation 6 for the correction coefficient δ1 that results in 11.03 [mL / min at 450kPa]. This is a fairly close approximation to the measured value.

[0120] The conversion formula may be created using a program that automatically generates an approximation curve passing through several sample points. For example, the program may automatically generate equations for approximation curves passing through 9.69 [mL / min at 402kPa], 11.03 [mL / min at 450kPa], and 12.96 [mL / min at 500kPa], and this can then be applied to the conversion formula.

[0121] Next, we will show an example of correcting the measured leakage rate Qr (paired with the pressure at the time of measurement) so that it is the value under the pressure (reference test pressure) paired with a predetermined reference value, and then comparing it with the predetermined reference value. The example below shows the differential pressure ΔPs [Pa] converted to [mL / min] and graphed, and shows an example where the function representing the leakage rate is f(x) + b, with f(x) being the part related to pressure (x) and b being the part unrelated to pressure (x). b is the intersection (shift) with the y-axis when x = 0.

[0122] 1. Input multiple sets of leakage rate Qr and measured pressure values ​​into a program that automatically creates an approximation curve, have it calculate the approximation curve, and display the equation of that approximation curve. With two sets of input, only a linear (first-order function) can be calculated, but with three or more sets of input, a polynomial (double-order function) can be calculated. 2. Suppose the equation of the displayed approximation curve is y = f(x) + b, for example, f(x) = 0.001x. 3. If the predetermined reference value is, for example, 45 [mL / min at 450kPa], then the formula for converting the leakage rate Qr before conversion (the corresponding test pressure at the time of measurement is Pr) to the value under the pressure (at 450kPa) paired with the predetermined reference value is: Converted leakage rate Qs [mL / min at 450kPa] = Leakage rate Qr [mL / min] before conversion - (f(Pr[Pa]) + b) + (f(reference pressure 450000[Pa]) + b) This is the result.

[0123] If the leakage rate Qr before conversion is, for example, 50.0 [mL / min at 500kPa], then when this is converted to a value at 450kPa, the converted leakage rate Qs [mL / min at 450kPa] = original leakage rate 50 [mL / min at 500kPa] - (f(Pr: 500000 [Pa]) + b) + (f(reference pressure: 450000 [Pa]) + b). The conversion example above uses a linear function f(x) = 0.001x, but the same method can be used for biquadratic functions as well. The obtained Qs [mL / min at 450kPa] may be compared to a predetermined reference value (45 [mL / min at 450kPa]).

[0124] Next, we will explain a method for determining the effect of the virtual equivalent volume Vw from a minimum of two points (a pair of leakage rate and test pressure considered as one point) and correcting the leakage rate by reflecting that effect. This method eliminates the need to use the flow meter 73 shown in Figure 7 later, or the inspected object (reference leakage rate sample) that exhibits the same leakage rate as a predetermined reference value. For example, it can be used when the maximum leakage rate is specified in the drawings from the client, or when the maximum leakage rate is set from a theoretical value.

[0125] First, assuming a predetermined value for the virtual equivalent volume Vw, and a set reference value of 10 [mL / min] at 500 [kPa], we substitute this into Equation 5 to find the combination of hole diameter d and pipe length L that passes through 10 [mL / min] at 500 [kPa], and then determine the theoretical leakage amount when the inspection pressure changes, as shown in Graph 95 of Figure 8, which will be described later. For the sake of simplicity, although the graph is originally as shown in Figure 23, it is shown here as a linear function in Figure 4.

[0126] Next, measure the leakage rate of the leak sample at two or more points. This leak sample does not need to be a reference leak sample that shows the same leakage rate as a predetermined reference value. If the two measured points are, for example, 6.4 [mL / min] at 400 [kPa] and 9.6 [mL / min] at 600 [kPa], then in the case of a linear function, it will take the shape shown in Figure 5. The graph in Figure 5 passes through 8.0 [mL / min] at 500 [kPa], but does not pass through 10 [mL / min] at 500 [kPa] as in Figure 4, and the slope is also different. There are three reasons for this, as follows.

[0127] First point: The hole diameter (actually a pair of hole diameter d and hole length L) in the leak sample is different from the hole diameter (actually a pair of hole diameter and hole length) that is assumed to have been present in the workpiece (reference leak sample) that shows a predetermined reference leak amount (leak amount at inspection pressure). Second point: The hypothetical equivalent volume Vw at 500 [kPa], which was assumed as a predetermined value, differs from the actual value. Third point: The virtual equivalent volume Vw [mL] differs depending on the test pressure.

[0128] Firstly, when the hole length is fixed, the larger the hole diameter, the greater the leakage, and the graph in Figure 4 shifts vertically (in the leakage direction), while the slope remains unchanged. Therefore, it can be corrected with δ² in Equation 4. Figure 23 shows the relationship between inspection pressure and leakage on a logarithmic graph for multiple samples with the same hole length but different hole diameters. It can be seen that the graph shifts vertically when the hole diameter changes. The same is true for the graph in Figure 4, which is simplified to a linear function.

[0129] The second point concerns the virtual equivalent volume Vw. As is clear from Equation 3, the larger Vw is, the greater the leakage. The graph in Figure 4 shifts in the vertical direction (leakage), but the slope remains unchanged. Therefore, it can be corrected by δ² in Equation 4.

[0130] If the virtual equivalent volume Vw [mL] differs for each test pressure, the slope of the graph in Figure 4 changes. For example, if the volume at 450 kPa is used as the reference, the leakage rate changes according to the increase or decrease in pressure around 450 kPa, so the slope of the graph changes around 450 kPa, and the intercept changes accordingly. Therefore, it can be corrected using δ1 and δ2 in Equation 4.

[0131] Therefore, by determining δ1, which has the same slope as the graph in Figure 5, and δ2, which has the same height (passing through the reference value of 10 [mL / min] at 500 [kPa]), we can obtain Figure 6, which allows us to estimate the leakage amount at the reference inspection pressure, even when the leakage amount is measured at an inspection pressure different from the predetermined reference inspection pressure (leakage amount at inspection pressure).

[0132] For determining whether a workpiece passes or fails in terms of leaks, there are two methods: Method A, which involves converting the measured leak amount to a value under a paired inspection pressure with the reference leak amount and comparing it to the reference leak amount; and Method B, which involves converting the reference leak amount to a value under a paired inspection pressure with the measured leak amount and comparing it to the measured leak amount. Figure 6 can be used as a conversion reference value for comparison in Method B. Furthermore, if δ1, δ2 and Equation 4 are given, the leak amount (Qr-H1) can be converted to the leak amount (converted leak amount Qs) under a predetermined reference leak amount (leak amount at inspection pressure) and a paired pressure (reference inspection pressure), so it can be compared with a fixed reference value using Method A.

[0133] Below are two specific examples of a method for determining the effect of the virtual equivalent volume Vw from at least two points and correcting the leakage rate for pressure.

[0134] (Specific example 1) This section describes an alternative to Hagen-Poiseuille's equation (graph) for pressure correction of leakage based on a minimum of two points. For simplicity, a linear function approximation will be used. An example will be shown in which the measured leakage amount Qr (paired with the pressure at the time of measurement) is corrected to match the value under a predetermined reference pressure (reference test pressure), and then compared with the predetermined reference value.

[0135] The example below graphs the differential pressure ΔPs [Pa] converted to [mL / min], and the leakage rate f(x) is given by y = 0.08 × (x) × 10 -3 An example is shown where -0 is used. δ1 (slope) in Equation 4 corresponds to 0.08, and δ2, which is the intersection (shift) with the y-axis when x=0, corresponds to 0.

[0136] 1. Have the supervisor measure the measured leakage rate Qr (paired with the pressure at the time of measurement). The workpiece used at this time should show the same leakage rate as a predetermined reference value (paired with the reference inspection pressure) (the leakage rate when the pressure at the time of measurement and the reference inspection pressure are the same value). However, if the reference value is determined by a theoretical value, it will not show the same leakage rate, so an example of that case is provided.

[0137] First, a program that automatically creates an approximation curve using the leakage rate Qr (paired with the pressure at the time of measurement) is used to generate the approximation curve, and the equation of that approximation curve is then displayed. 2. The equation of the displayed approximation curve is y = 0.08 × (x) × 10 -3 Let's assume it was -0. 3. The predetermined standard value is 45 [mL / min at 450kPa]. Substituting ×=450 into the above equation, we obtain 36 [mL / min at 450kPa], which is a difference of 9 [mL / min at 450kPa] from 45 [mL / min at 450kPa]. This difference is because the workpiece measured by the supervisor did not show the same leakage rate as the predetermined standard value (difference in the diameter of the leak hole). If we were to use a workpiece that showed the same leakage rate as the standard value and have the supervisor take the measurement, the equation of the approximate curve would be f(x), which is y = 0.08 × (x) × 10 -3 The result is +9 (if the diameter of the hole in Equation 5 is changed, the slightly curved shape described later remains the same, and the part corresponding to the slope in the linear function exemplified here becomes approximately the same, and the difference in hole diameter only shifts almost entirely in the vertical direction, so the amount of vertical shift is 9).

[0138] If the leakage rate Qr before conversion was, for example, 50.0 [mL / min at 500kPa], then converting this to the value at 450kPa would give 49 [mL / min at 450kPa] = 0.08 × (500) × 10 -3 A value of +9 is obtained. This obtained value of 49 [mL / min at 450kPa] may be compared with a predetermined reference value (45 [mL / min at 450kPa]).

[0139] Incidentally, if the predetermined reference value is 45 [mL / min at 450kPa], the theoretical value using Hagen-Poiseuille's law (corresponding to graph 91 in Figure 3 showing the case where δ1=1) can be expressed, for example, as a linear function f(x): y=0.1×(x), then y=0.08×(x)×10 -3 +9 corresponds to graph 92 in Figure 3, and δ1 in equation 4 is the coefficient obtained from the measured value divided by the coefficient of the theoretical value, so δ1 = 0.8 and δ2 = 9.

[0140] (Specific example 2) Using Hagen-Poiseuille's formula, the leakage rate can be pressure-corrected (converted to a value under a pressure paired with a predetermined reference value, for example) with only one measurement taken in advance by the administrator. However, there are three problems that necessitate two or more prior measurements.

[0141] Point 1: If the volume of the sealed closed space, including the hollow portion of the object under inspection (workpiece), does not change with pressure, the leakage rate can be pressure-corrected using Hagen-Poiseuille's equation without prior measurement (converting the leakage rate to a value under a pressure that is paired with, for example, a predetermined reference value). However, in most cases, the volume of the closed space changes with pressure, resulting in a slope different from that of Hagen-Poiseuille's equation (because the virtual equivalent volume Vw changes with pressure, it is necessary to newly determine a variable such as δ1 in equation 4).

[0142] Point 2: The leaking specimen (workpiece: a predetermined leak limit sample) used by the administrator for measurement may not necessarily show the same value as the predetermined standard value (leakage amount and pressure pair).

[0143] Point 3: To find the linear function f(x)+b that represents the leakage rate, at least two measurements are required. Similarly, two measurements are also required for equation 6, which applies Hagen-Poiseuille's equation, which curves slightly in an arc.

[0144] As described above, if at least two setting inputs are received, the slope (e.g., δ1 in Equation 4) can be determined, and equations and graphs for pressure correction of the leakage amount can be created. However, regarding the problem that a predetermined leakage limit sample does not necessarily show the same value as a predetermined reference value (a pair of leakage amount and pressure at the time of measurement) (see Part 2 above), for example, the leakage amount can be determined by inputting the predetermined reference value pressure into the equation created with at least two setting inputs, and the difference from the predetermined reference value leakage amount can be handled using an offset (e.g., δ2 in Equation 4).

[0145] Next, we will explain how to determine the volume Vw (virtual equivalent volume) of a sealed closed space including the hollow portion of the object under inspection (assuming the entire closed space is flexible) at different pressures, and how to apply this volume Vw to equation A to convert the differential pressure [Pa] to the leakage rate [mL / min].

[0146] Figure 7 shows the leak inspection device 10 of Figure 1 with the addition of variable valves 71 and 72 and a flow meter 73 to determine the virtual equivalent volume. The piping material, length, etc., are the same on both the master and work side, and the virtual equivalent volume determined from this is the same when both variable valves 71 and 72 are closed.

[0147] The virtual equivalent volume is determined in the following steps 1 to 8. Note that the dotted line on the master side represents the three-way branch pipe (where the first pipe 21 branches into the second pipe 22 and the third pipe 23), the piping from the branch pipe to the variable valve 72 (the third pipe 23), and the volume from the inlet of the variable valve 72 to the closed portion inside the variable valve 72 (virtual equivalent volume).

[0148] <Step 1> Close both variable valve 71 and variable valve 72, and confirm that the leakage volume is 0 [mL].

[0149] <Step 2> A provisional value for the volume (virtual equivalent volume) is entered into the leak detection device 10. For example, 526.8 [mL] is entered as a provisional value.

[0150] <Step 3> Pressurize the workpiece side (for example, 450 kPa), and while observing the flow meter 73, operate the variable valve 71 to fix the valve opening so that it is close to a predetermined reference value (leakage rate, for example, 10 mL / min at 450 kPa).

[0151] <Step 4> On the workpiece side, the opening of the variable valve 71 fixed in step 3 is maintained, and on the master side, the variable valve 72 is closed. Both the leakage amount A at the provisionally input volume of 526.8 [mL] and the leakage amount B measured by the flow meter 73 are measured. Leakage amount A is obtained by converting the differential pressure value measured by the differential pressure gauge 43 to [mL / min] using formula A by applying the provisionally input volume of 526.8 [mL].

[0152] For example, if the average of three readings is 8.929865517 [mL / min] for the leak testing device and 9.326666667 [mL / min] for the flow meter 73, then the virtual equivalent volume at 450 [kPa] can be calculated as: (Hypothetical input virtual equivalent volume) × (Leakage rate of flow meter 73 / Leakage rate of leak testing device). 550.20851 [mL] (= 526.8 [mL] × 9.326666667 [mL / min] / 8.929865517 [mL / min]) is obtained.

[0153] <Step 5> As mentioned above, equation 5 (leakage amount = (πd) 4 / 128Lμ) × ((P1 2 -P2 2 Using equation 5) (2P2), we determine the relationship between holes that exhibit a leakage rate of 9.326666667 [mL / min] at 450 [kPa]. Here, the hole length L is set to 1 [mm], and the hole diameter d is determined.

[0154] Leakage rate: 9.326666667 [mL / min] = 1.55454 × 10 -7 [m 3 / s], π:3.141592 μ (viscosity of air at 20°C, air (Pa·s)): 0.0000181 [Pa·s] P1:450[kPa G] =551325[Pa[ANR]] P2: 0[kPa G] =101325[Pa[ANR] ], L: 1 [mm] = 1 / 1000 Therefore, the diameter of the hole, d, is 16.7706417982308 [μ] = 16.7706417982308 / 1000000 [m].

[0155] If either the length of the hole or the diameter of the hole is temporarily fixed, the other can be determined, and for any combination, if the pressure [kPa] applied to the hole is determined, the leakage rate [mL / min] can be determined. Therefore, if we use the above values ​​for d and L in Equation 5 and create a graph showing the relationship between pressure P2 and leakage rate, we get Graph 95 in Figure 8.

[0156] Graph 95 in Figure 8 is as described above. In equation A (Q[mL / min] = ΔP[Pa]×Vw[mL]×60 / (Tdet×Patm[Pa]) …Equation A), only ΔP[Pa] is pressure-corrected, while Vw[mL] remains a fixed value, unchanged from the value under the test pressure (450[kPa]).

[0157] <Step 6> Similar to step 4, the flow meter 73 is used to measure how much the leakage rate changes at the upper limit (400 kPa) and lower limit (500 kPa) of the test pressure range. Graph 96 in Figure 8 plots the values ​​measured by the flow meter 73, and these values ​​are equivalent to the pressure-corrected values ​​of both ΔP [Pa] and Vw [mL] in equation A.

[0158] <Step 7> The difference between graphs 95 and 96 in Figure 8 is the difference that arises depending on whether or not Vw[mL] in equation A is pressure-corrected. For example, the virtual equivalent volume at 450[kPa] was 550.20851[mL], but as can be seen from the comparison of graphs 95 and 96, the virtual equivalent volume at 400[kPa] must be slightly higher than that at 450[kPa] to match the measurement value at flowmeter 83, and the virtual equivalent volume at 500[kPa] must be slightly lower than that at 450[kPa] to match the measurement value at flowmeter 83.

[0159] Specifically, the virtual equivalent volume is 558.3393406 [mL] at 400 [kPa] = 550.20851 [mL] × 1.014777726 times (k = 1.014777726, as explained later) 550.20851 [mL] at 450 [kPa] = 550.20851 [mL] × 1 (k=1 as described later) 543.2902174[mL] at 500[kPa] == 550.20851[mL] × 0.987426053 times (k = 0.987426053 as described later) This is the result.

[0160] <Step 8> The virtual equivalent volume is expressed as k × Vw [mL], where k is a coefficient value for each test pressure. Therefore, an approximate formula showing the relationship between test pressure and k is created from the virtual equivalent volumes of the three points mentioned above. For example, a linear function, a quadratic function, etc. (e.g., =(( 4 × 10 -7 ) × (Inspection pressure) 2 By setting ()) - (0.0007 × inspection pressure) + 1.214), we can determine k at the actual inspection pressure and then calculate the virtual equivalent volume at the actual inspection pressure.

[0161] Furthermore, instead of using the test pressures performed in Step 4 (with an upper limit of 400 kPa and a lower limit of 500 kPa), measuring how much the leakage rate changes at two different pressures, such as 450 kPa in Step 3 and another point (for example, 500 kPa), allows for the determination (estimation) of the virtual equivalent volume with measurements at least at two points.

[0162] As shown in Figure 9, the graphs illustrating the values ​​of K at different pressures show that they vary depending on the various conditions of the measurement system. Therefore, it is necessary to use a leak detection device that corresponds to the one actually used for leak testing. Figure 9 shows the results obtained from preliminary tests related to the experiments in Figures 20 to 22.

[0163] The conversion method for determining the leakage rate [mL / min] from the differential pressure ΔPr [Pa] measured in the leak inspection process in step S106 of Figure 2 is as follows.

[0164] The temperature compensation value used is PH1 = ΔPt1(Tr / Ta) × ((Ptw + Patm) / Patm). First, using Hagen-Poiseuille's straight-tube model, the measured differential pressure ΔPr [Pa] is converted to the differential pressure under the standard test pressure (converted differential pressure ΔPs [Pa]) with temperature compensation using the following formula 7.

[0165] ΔPs=(ΔPr-PH1)×((Ptest×1000+Patm) 2 -Patm 2 ) / ((Ptw×1000+Patm) 2 -Patm 2 )-ΔPOS...Equation 7 ΔPs[Pa]: Converted differential pressure value, ΔPr[Pa]: Detected differential pressure value, PH1[Pa]: Temperature compensation value, ΔPOS[Pa]: Judgment value offset value, Ptest[kPa]: Reference inspection pressure, Patm: 101325[Pa], Ptw[Workpiece internal pressure during leakage measurement[kPa]] Next, ΔPs is converted to the leakage rate ΔQs [mL / min]. The coefficient value k mentioned earlier is used for this conversion.

[0166] Qs[mL / min] = ΔPs[Pa]×kVw[mL]×60 / (Tdet×Patm[Pa]) …Equation 8 k is the value at Ptw [workpiece internal pressure [kPa] during leakage measurement]. For example, k at Ptw is determined using the approximate formula showing the relationship between the inspection pressure and k obtained in step 8. Vw is the virtual equivalent volume at Ptest [kPa]: reference inspection pressure.

[0167] As previously mentioned, the dotted line indicated on the variable valve 72 in Figure 7 represents the volume (virtual equivalent volume) from the inlet of the variable valve 72 to the closed portion inside the variable valve 72, including the three-way branch pipe, the piping from the branch pipe to the variable valve 72. The piping between the master connection port 13 and the master 62 is made slightly longer (for example, 20 cm longer) and directly connected (directly connected without the three-way branch pipe, the piping from the branch pipe to the variable valve 72, and the variable valve 72). The piping is then gradually shortened until the measurement value is the same as before the direct connection, for example, 9.326666667 [mL / min] near 10 [mL / min] at 450 [kPa].

[0168] For example, if the same measurement value is obtained at a point 10 cm longer, a pipe length (e.g., 10 cm) equivalent to the virtual equivalent volume at 450 [kPa] in the dotted line section can be obtained. In actual leak measurements in factories, etc., the component for measuring the virtual equivalent volume in the dotted line section is unnecessary because the virtual equivalent volume has already been determined, and by using a pipe that is, for example, 10 cm longer, costs can be reduced.

[0169] Incidentally, the only difference between Figure 20 and Figure 21 is that a 5.0m polyurethane tube, which is softer than the nylon tube, was used for the 0.9m nylon tube. Although the tube is thought to expand depending on the degree of pressurization (the degree of difference in pressurized pressure, such as when it is 400[kPa] or 500[kPa]), the tube is thought to be made almost uniformly, so it is impossible to identify localized deformation.

[0170] Furthermore, if the virtual equivalent volume Vw becomes, for example, 300% of the actual volume (in the case of k=3.0 in Figure 9), deformation can be detected as a difference of 0.1 mm or more using a displacement sensor. However, considering that the actual volume appears almost unchanged, deformations of the magnitude of ±0.1 cannot be detected by a displacement sensor. Conventionally, it was thought that there would be no volume change if the object being inspected was a rigid body.

[0171] This invention was made possible because we discovered that even if the object being inspected is a rigid body, if there is a flexible body in part of the inspection system (for example, a pipe made of nylon tube, polyurethane tube, etc., or a rubber valve seat for an on-off valve), the volume within the sealed closed space changes in response to the pressure.

[0172] Next, we will elaborate on how the virtual equivalent volume can be determined (estimated) by measurements at at least two points.

[0173] In a case like that shown in Figure 20, the test pressure range of 400-460 kPa is defined as δ1 = "1", H1 = "0", Δ QOSUsing Equation 4, where δ² is set to "0", the Hagen-Poiseuille straight-pipe model, which can be calculated using only one arbitrary point, shows excellent agreement with the actual leak. Assuming that the allowable range of the inspection pressure is 3σ (standard deviation 99.7%), and that two points corresponding to 2σ (standard deviation 95.4%) are measured by the manager, these two points are located almost exactly on the Hagen-Poiseuille straight-pipe model. From this result, it can be seen that no misjudgments occur in the judgment based on predetermined reference values ​​across the entire range of the inspection pressure.

[0174] In other words, using measurements at any two points with a leaking workpiece, under the conditions shown in Figure 20, it can be seen that the volume Vw of the sealed closed space including the hollow part of the object under inspection can be treated as a rigid body that does not change with pressure throughout the entire range of the inspection pressure (this can also be rephrased as saying that the virtual equivalent volume does not change even when the pressure is changed).

[0175] By increasing the number of measurement points, for example, deformation of a nylon tube begins around 460-470 kPa (see not only Figure 20 but also inflection point A in Figure 9), and the accuracy of the judgment can be improved by calculating the leak for a portion of the inspection pressure range by treating the entire closed space as a flexible body, and calculating the leak for the remaining section (for example, 400[kPa]-460[kPa]) by treating the entire closed space as a rigid body (by finding the inflection point where it changes from a rigid to a flexible body). However, with measurements at only two appropriate points, the leak conversion error becomes large, for example, when measuring close to 500 kPa.

[0176] In a case like that shown in Figure 21, the leakage rate of the straight pipe model using Hagen-Poiseuille's law closely matches the experimental value up to the test pressure range of 400 [kPa] to 410 [kPa], but a slight discrepancy is noticeable between 410 [kPa] and 500 [kPa]. For example, it is thought that deformation of materials such as polyurethane begins around 410 to 420 kPa. If we have the manager measure two points corresponding to 2σ (standard deviation 95.4%), we can see that misjudgments will occur unless the volume Vw of the closed space is assumed to be a flexible material whose volume changes with pressure across the entire test pressure range (for example, it is possible to determine the virtual equivalent volume by finding k from the two points, but since k is only the average between the two points, the conversion error will be large).

[0177] Furthermore, by increasing the number of measurement points, it is possible to determine the value of K for each pressure range, which is used in Equation 4 to calculate δ1 and the virtual equivalent volume (k × Vw [mL]). By treating a portion of the inspection pressure range (e.g., 400 [kPa] to 410 [kPa]) as a rigid body for the entire closed space, and the remaining portion (e.g., 410 [kPa] to 500 [kPa]) as a flexible body for the entire closed space, the accuracy of the leak detection can be improved. However, with measurements at only two appropriate points, only the average value of K between those two points can be determined, so the leak conversion error becomes large, for example, when measuring close to 400 kPa.

[0178] In a case like that shown in Figure 22, the leakage rate of the straight-pipe model using Hagen-Poiseuille's law does not match the experimental value across the entire range of the test pressure. Therefore, it is thought that deformation of the fixture, etc., begins at a fairly low pressure (e.g., 200 kPa). Also, it is thought that additional deformation, such as that of polyurethane, begins around 410-420 kPa. Therefore, by increasing the number of measurement points, it is possible to find the inflection point where the virtual equivalent volume changes along the way, thereby improving the accuracy of the leak determination. However, with measurements at only two points, only the average K value between the two points can be obtained, so the leakage conversion error will be large depending on whether or not the inflection point is included in that interval.

[0179] As described above, it is assumed that the administrator will be asked to take measurements at least at two points on the leaking workpiece and input them into the leak inspection device 10. However, it is also possible to automate multi-point measurements across the entire inspection pressure range, or even outside the inspection pressure range, and collect the data necessary for automatic conversion (pairs of the internal pressure of the closed space and the amount of leakage at that internal pressure).

[0180] Figure 10 shows the results of converting the leakage rates of the inspected object b (defective product) and inspected object c (good product) shown in Figure 19 at each inspection pressure using Equation 4 described above, so that they correspond to the values ​​obtained when the leakage rate is measured at the standard inspection pressure (450 kPa). In this example, the standard inspection pressure paired with the standard leakage rate of 11.2 mL / min is set to 450 kPa.

[0181] Graph B2 in Figure 10 is a graph obtained by applying the conversion according to the present invention (a conversion that takes into account that the volume of a sealed closed space changes due to the pressure inside the closed space) to the slightly curved graph B relating to the object under inspection b in Figure 19. Graph C2 in Figure 10 is a graph obtained by applying the conversion according to the present invention (a conversion that takes into account that the volume of a sealed closed space changes due to the pressure inside the closed space) to the slightly curved graph C relating to the object under inspection c in Figure 19. Both graphs B2 and C2 are shown only within the permissible range of the inspection pressure.

[0182] As shown in graphs B2 and C2, the converted leakage rates of test object b and test object c are approximately constant regardless of the test pressure. Therefore, regardless of the pressure at which the measurement is performed (within the allowable range of the test pressure, 400kPa to 500kPa in this example), the quality of the leak in the test object (workpiece) can be correctly determined by comparing the converted leakage rate with the fixed reference leakage rate of 11.2 mL / min.

[0183] In the case of a defective product, for example, if the detected leakage amount measured at an inspection pressure of 410 kPa, which is lower than the standard inspection pressure of 450 kPa (the value at 410 kPa in Graph B), is compared with the standard leakage amount of 11.2 mL / min, it will be incorrectly judged as a good product because the detected leakage amount is less than the standard leakage amount. However, when comparing the leakage amount obtained by performing the conversion according to the present invention (converted leakage amount) with the standard leakage amount, the converted leakage amount (the value at 410 kPa in Graph B2) will be greater than the standard leakage amount, and it will be correctly judged as a defective product.

[0184] In the case of a good product, for example, if the amount of leakage detected measured at an inspection pressure of 490 kPa, which is higher than the standard inspection pressure of 450 kPa (the value at 490 kPa in Graph C), is compared with the standard leakage rate of 11.2 mL / min, the detected leakage rate is greater than the standard leakage rate, leading to a misjudgment that the product is defective. However, when comparing the converted leakage rate obtained by performing the conversion according to the present invention (the value at 490 kPa in Graph C2) with the standard leakage rate, the converted leakage rate is less than the standard leakage rate, and the product is correctly judged to be a good product.

[0185] Figure 11 is a schematic graph showing the changes in internal pressure, etc., of workpiece 61 and master 62 when a leak test is performed according to the flowchart in Figure 2. The internal pressure of workpiece 61 is shown as measured by the first pressure gauge 41, and the differential pressure between workpiece 61 and master 62 is shown as measured by the differential pressure gauge 43. The internal pressure of master 62 should be shown as measured by the second pressure gauge 42, but it is drawn above graph 82, which shows a smaller leak amount than graph 81, as a curve that is almost the same as graph 82 (not shown).

[0186] Theoretically, the "measurement value of differential pressure gauge 43" = "measurement value of first pressure gauge 41" - "measurement value of second pressure gauge 42", so differential pressure gauge 43 is unnecessary. However, because it is necessary to measure the differential pressure with high precision, a separate dedicated differential pressure gauge 43 is provided.

[0187] Figure 11 shows a magnified portion of the graph (changes in internal workpiece pressure during the leak measurement period). The pressure changes are exaggerated. Without magnification, the graph will look like Figure 17.

[0188] As shown in Figure 11, when the workpiece and master are sealed from an open-air state to separate closed spaces in step S104 of Figure 2 (time t0), the internal pressure of the workpiece initially rises due to the heat contained within the workpiece, and then gradually decreases due to heat dissipation. In the temperature compensation measurement process of step S104, the pressure drop during the period Ta shown in Figure 11 is measured as ΔPt1.

[0189] Since the workpiece 61 may be inspected after a predetermined time following manufacturing (for example, after welding is completed), the pressure drop is easily measured. On the other hand, the master is often at the same temperature as the ambient temperature, so the pressure change during this period is not measured. Therefore, the same value as the pressure drop measured by the first pressure gauge 41 is also measured as ΔPt1 by the differential pressure gauge 43.

[0190] Subsequently, during the pressurization step of the leak inspection process in step S106 (period t3-t4 in Figure 11), the internal pressure of the workpiece rises to Pt as gas is pressurized and introduced into the workpiece. After sealing the first on-off valve 31, the internal pressure of the workpiece gradually decreases due to temperature drop and leakage. After sealing, the decrease in internal pressure gradually stabilizes during the settling period (period t4-t5 in Figure 11). The amount of leakage is measured during the measurement period (Tdet; t5-t6) after the settling period. The amount of leakage is measured as the difference between the differential pressure ΔP1 (measured with differential pressure gauge 43) between the internal pressure of the workpiece and the internal pressure of the master at the start of the measurement period (t5) and the differential pressure ΔP2 (measured with differential pressure gauge 43) between the internal pressure of the workpiece and the internal pressure of the master at the end of the measurement period (t6), which is measured as the detected differential pressure ΔPr (ΔPr = (ΔP2 - ΔP1)).

[0191] Normally, a predetermined period is provided from the time the gas is pressurized and introduced into the workpiece until the first on-off valve 31 is sealed. Also, since there is no leakage in the master, the internal pressure of the workpiece gradually decreases solely due to the temperature drop.

[0192] Graph 81 in Figure 11 relates to a defective workpiece W1 with significant leakage (for example, corresponding to the inspected object b in Figure 10), and graph 82 relates to a good workpiece W2 with minimal leakage (for example, corresponding to the inspected object c in Figure 10). Up to time t4, the internal pressure measured by the first pressure gauge 41 of workpieces W1 and W2 shows the same change. The pressure Pt at the completion of pressurization is the same for both the defective workpiece W1 with significant leakage and the good workpiece W2 with minimal leakage, but the pressure drop during the settling period is greater for workpiece W1 with significant leakage than for workpiece W2 with minimal leakage. Therefore, at the start of the measurement period (t5), the internal pressure of workpiece W1 with significant leakage is lower.

[0193] As a result, the differential pressure between the leak-free master 62 and the workpiece W1 (measured by the differential pressure gauge 43) is greater for the workpiece W1 with more leakage than for the workpiece W2 with less leakage. However, since the figure is magnified, the differential pressure measured by the differential pressure gauge 43 (e.g., ΔPt1) and the pressure drop during the settling period measured by the first pressure gauge 41 are extremely small. If this is not magnified, the display will look like Figure 17. In the conversion method according to the present invention, a larger magnification is applied as the internal pressure (inspection pressure) of the workpiece during measurement decreases. This is because, for example, Ptest in Equation 4 is the same for workpieces W1 and W2, while Ptw is less for workpiece W1 and less for workpiece W2. As a result, the less leakage there is and the larger Ptw is, the smaller the conversion magnification applied to ΔPr[Pa] (detected differential pressure value) according to Equation 4 becomes. Therefore, the magnification applied to workpiece W1, which has a larger leakage rate, is larger than the magnification applied to workpiece W2, which has a smaller leakage rate.

[0194] In the example in Figure 11, the pressure difference (ΔP2-ΔP1) between the pressure drop from Pt at t5 ΔP1 and the pressure drop from Pt at t6 ΔP2, as measured by the first pressure gauge 41, is such that workpiece W1 with more leakage > workpiece W2 with less leakage. The difference with the master 62 is measured using the differential pressure gauge 43, and the differential pressure of the master 62 subtracted from ΔP1 and ΔP2 (ΔPm = ΔP2-ΔP1 of master 62) is the same. If we let ΔPr1 be the detected differential pressure of workpiece W1 with more leakage and ΔPr2 be the detected differential pressure of workpiece W2 with less leakage, then these two also have the relationship ΔPr1 > ΔPr2.

[0195] The detected differential pressure ΔPr1 is converted to a leak rate in units of [mL / min] to obtain the detected leak rate Qr1 [mL / min], and the detected differential pressure ΔPr2 is converted to a leak rate in units of [mL / min] to obtain the detected leak rate Qr2 [mL / min].

[0196] Figure 12 shows the detected leak rate [mL / min], the converted leak rate [mL / min] without temperature compensation, and the converted leak rate with temperature compensation for workpieces W1 and W2 in Figure 11. In this example, workpiece W1, which has a large leak, has a low internal pressure measured by the first pressure gauge 41, but the differential pressure with the master 62 measured by the differential pressure gauge 43 (detected differential pressure ΔPr1) is large, and Ptw is small, so a large multiplier is applied to the conversion according to the present invention. As a result, for example, the differential pressure ΔP before conversion to the leak rate Qr1 [mL / min] shows a large value. Workpiece W2, which has a small leak, has a high internal pressure measured by the first pressure gauge 41, but the differential pressure with the master 62 measured by the differential pressure gauge 43 (detected differential pressure ΔPr2) is small, and Ptw is large, so a small multiplier is applied to the conversion according to the present invention. As a result, for example, the differential pressure ΔP before conversion to the leak rate Qr2 [mL / min] shows a small value.

[0197] In the case of no temperature compensation, the converted leakage amount is obtained by multiplying the detected leakage amount Qr1 by a high factor for workpiece W1, which has a lot of leakage, and by multiplying the detected leakage amount Qr2 by a low factor for workpiece W2, which has little leakage. In the case of no temperature compensation, workpiece W2, which has little leakage, is marked as failed even though it should have passed. This phenomenon indicates that the workpiece was inspected while still hot, for example, after welding, without being sufficiently cooled to the same temperature as the master, and therefore failed the inspection. If sufficient cooling had been performed, the converted value without temperature compensation would be the same as the converted value with temperature compensation, and workpiece W2, which has little leakage, would pass.

[0198] The converted leakage amount with temperature compensation is the converted leakage amount without temperature compensation, further reduced by the temperature compensation value H1 corrected by each respective factor. For workpiece W1 with high leakage, this corresponds to the intersection of graph B, which shows the inspected object b in Figure 10, and the air pressure of 450 kPa, i.e., the intersection with graph B2. This is shown as point b in Figure 18, which shows the case with temperature compensation. For workpiece W2 with low leakage, this corresponds to the intersection of graph C, which shows the inspected object c in Figure 10, and the air pressure of 450 kPa, i.e., the intersection with graph C2. This is shown as point c in Figure 18.

[0199] Workpiece W1, which has a large leak, is inherently a defective product, and therefore also fails when comparing its converted leak amount with the standard value (standard leak amount). Workpiece W2, which has a small leak, is inherently a good product, and therefore also fails when comparing its converted leak amount with the standard value (see the temperature-compensated converted value in Figure 12).

[0200] Figure 13 adds graph 83, which shows the change in internal pressure of workpiece W1' with relatively high leakage (showing, for example, an intermediate leakage amount between workpiece W1 and the reference value) when the pressure at the completion of pressurization is lower within the allowable range than the pressure Pt in Figure 11 (for example, when the air pressure is slightly over 420 kPa in Figures 10 and 18), and graph 84, which shows the change in internal pressure of workpiece W2' with relatively low leakage (showing, for example, an intermediate leakage amount between workpiece W2 and the reference value) when the pressure at the completion of pressurization is higher within the allowable range than the pressure Pt (for example, when the air pressure is slightly under 480 kPa in Figures 10 and 18).

[0201] As shown in Graph 83, the pressure drop after sealing (from t4 onwards) of workpiece W1', which has a relatively high leakage rate and was measured at an inspection pressure lower than pressure Pt, is gradual and similar to the pressure drop after sealing of workpiece W2', which has a relatively low leakage rate and was measured at the inspection pressure of pressure Pt (measurement point at Pt: 450kPa, point c in Figure 18) (point c' in Figure 18 shows the same pressure drop as point c). Furthermore, in the example in Figure 13, the detected differential pressure ΔPr3 of workpiece W1', which has a relatively high leakage rate and was measured at an inspection pressure lower than pressure Pt, is the same as the detected differential pressure ΔPr2 of workpiece W2', which has a relatively low leakage rate and was measured at the inspection pressure of pressure Pt (points c and c' in Figure 18 show the same leakage rate).

[0202] On the other hand, the pressure drop after sealing (from t4 onwards) of workpiece W2' with relatively little leakage, measured at an inspection pressure higher than pressure Pt, is similar to point b in Graph 81 (point b in Figure 18), which is close to the pressure drop after sealing of workpiece W1 with a lot of leakage, measured at the inspection pressure of pressure Pt (point b in Figure 18). This can be seen by comparing Graph 84 and Graph 81. Furthermore, in the example in Figure 13, the detected leakage amount ΔPr4 of workpiece W2' with relatively little leakage, measured at an inspection pressure higher than pressure Pt, is the same as the detected differential pressure ΔPr1 of workpiece W1 with a lot of leakage, measured at the inspection pressure of pressure Pt (points b and b' in Figure 18 show the same leakage amount).

[0203] Therefore, if the values ​​are compared to the reference values ​​without performing the conversion according to the present invention, workpiece W1' with a relatively high leakage rate measured at an inspection pressure lower than pressure Pt will be misidentified as a good product, and workpiece W2' with a relatively low leakage rate measured at an inspection pressure higher than pressure Pt will be misidentified as a defective product.

[0204] Figure 14 shows the detected leak amount, the converted leak amount without temperature compensation, and the converted leak amount with temperature compensation for workpiece W1', which had a relatively high leak rate, measured at an inspection pressure lower than pressure Pt in Figure 13, and workpiece W2', which had a relatively low leak rate, measured at an inspection pressure higher than pressure Pt. The detected differential pressure ΔPr3 for workpiece W1', which had a relatively high leak rate, measured at an inspection pressure lower than pressure Pt, is converted to a leak rate in units of [mL / min] to obtain the detected leak amount Qr3 [mL / min]. The detected differential pressure ΔPr4 for workpiece W2', which had a relatively low leak rate, measured at an inspection pressure higher than pressure Pt, is converted to a leak rate in units of [mL / min] to obtain the detected leak amount Qr4 [mL / min].

[0205] Here, for workpieces W1' with relatively high leakage measured at an inspection pressure lower than pressure Pt, the detected leakage amount Qr3 and temperature compensation value H1 are converted to ultra-high magnification, while for workpieces W2' with relatively low leakage measured at an inspection pressure higher than pressure Pt, the detected leakage amount Qr4 and temperature compensation value H1 are converted to ultra-low magnification.

[0206] In the case without temperature compensation, for the work piece W1' with a relatively large amount of leakage measured at an inspection pressure lower than the pressure Pt, the converted leakage amount is a value obtained by multiplying the detected leakage amount Qr3 by an extremely high magnification factor. For the work piece W2' with a relatively small amount of leakage measured at an inspection pressure higher than the pressure Pt, the converted leakage amount is a value obtained by multiplying the detected leakage amount Qr4 by an extremely low magnification factor. Without temperature compensation, for the work piece W2' with a relatively small amount of leakage, it is judged as non-conforming although it should be conforming originally. This phenomenon indicates a state where the work piece is inspected in a hot state without sufficient cooling until it reaches the same temperature as the master after, for example, welding, resulting in non-conformance. If sufficient cooling is performed, the converted value without temperature compensation will be the same as the converted value with temperature compensation, and the work piece W2' with a relatively small amount of leakage will be judged as conforming.

[0207] The converted leakage amount in the case with temperature compensation is a value obtained by further subtracting the temperature compensation value H1 corrected by each magnification factor from the converted leakage amount in the case without temperature compensation. That is, the converted leakage amount in the case with temperature compensation for the work piece W1' with a relatively large amount of leakage measured at an inspection pressure lower than the pressure Pt is a value obtained by subtracting the extremely high magnification of the temperature compensation value H1 from the value obtained by multiplying the detected leakage amount ΔQr3 by an extremely high magnification factor (when converted to Pt: 450 kPa, it is the c” point in Fig. 18). The converted leakage amount in the case with temperature compensation for the work piece W2' with a relatively small amount of leakage measured at an inspection pressure higher than the pressure Pt is a value obtained by subtracting the extremely low magnification of the temperature compensation value H1 from the value obtained by multiplying the detected leakage amount ΔQr4 by an extremely low magnification factor (when converted to Pt: 450 kPa, it is the b” point in Fig. 18).

[0208] Even when the leakage amount (detected leakage amount) of the work piece W1' with a relatively large amount of leakage is measured to be small because the leakage amount is measured at a low inspection pressure, by performing the conversion according to the present invention, The converted leakage amount of the relatively work piece W1' with a large amount of leakage > the reference value and the work piece W1' is judged as a defective product.

[0209] Furthermore, even if the leakage amount (detected leakage amount) of workpiece W2', which has relatively little leakage, is measured as high due to the high inspection pressure used for leakage measurement, the conversion according to the present invention can be performed. Equivalent leakage amount of workpiece W2' with relatively little leakage < Reference value Therefore, workpiece W2' is judged to be a good product.

[0210] Next, we will explain the pressure fluctuations caused by workpiece leakage and the time fluctuations (the time it takes for the pressure drop to stabilize) caused by workpiece leakage. Regardless of the size of the leak, the settling period (time) until the temperature change (pressure change caused by the temperature change) stabilizes does not differ much. However, if there is a large amount of leakage, the internal pressure of the workpiece caused by that leakage drops significantly, and the length of time it takes for this drop to stabilize depends on the size of the leak. Therefore, it is preferable to wait until the pressure drop (pressure change caused by the leak) stabilizes before measuring the amount of leakage (differential pressure ΔPr). However, doing so requires a long inspection time and reduces inspection efficiency (it is not possible to efficiently inspect a large number of workpieces).

[0211] The leak inspection device 10 according to the present invention focuses on the fact that the measured leakage amount changes depending on the internal pressure (inspection pressure) of the workpiece at the time of measurement, and converts the measured leakage amount to the value that would be obtained if measured under a standard inspection pressure. That is, whether the detected differential pressure ΔPr is measured when the leakage is small and the pressure change is stable, or when the detected differential pressure ΔPr is measured when the leakage is large and the pressure change is unstable, these are converted to the converted leakage amount ΔQs [mL / min] that would be obtained if measured under a standard inspection pressure (taking into account that the volume changes depending on the inspection pressure) and the leakage amount is determined, so that the leakage amount can be measured before the pressure change caused by the leakage stabilizes, without having to wait for the pressure change caused by the leakage to stabilize.

[0212] In more detail, when the leakage rate is large, the pressure drop during the settling period is larger compared to when the leakage rate is small, so the internal pressure of the workpiece (inspection pressure) at the time of measurement becomes lower, and the leakage rate is measured as smaller. However, in the leak inspection device 10 according to the present invention, regardless of the pressure conditions within the allowable range at which the leakage rate (differential pressure) is measured, the measured leakage rate (differential pressure) is converted to the leakage rate when measured at the standard inspection pressure (when converting to a leakage rate ΔQs [mL / min], the volume change due to pressure is also taken into account in the conversion), so that the leakage rate can be determined by a constant judgment criterion regardless of the inspection pressure at the time of measurement.

[0213] Next, if the leakage rate is large, the internal pressure of the workpiece during measurement (inspection pressure) will be low, and the leakage rate will be measured as small. One might think that setting a lower standard leakage rate (maximum allowable leakage rate) would achieve the same effect as the present invention, but this is not the case. Here, we will explain in detail the differences using the example of a portable pot being the object under inspection. For example, consider the case where three types of pots with identical external shapes but differing only in length—350cc, 600cc, and 1000cc—are subjected to a water immersion test, and the case where the leakage rate is measured by introducing pressurized gas, as in the leak inspection device 10.

[0214] As is well known, the submersion test is a testing method in which air pressure is applied to the object under test and it is submerged in water, and the leakage of air bubbles from the holes is visually confirmed. The amount of air bubbles generated is roughly proportional to the air pressure minus the surface tension. Even if there is a hole (and leakage is detected by a helium detector or air leak tester), as long as the air pressure is not strong enough to overcome the surface tension, which is proportional to the circumference of the hole, no air bubbles will leak out, and the test will pass. Furthermore, because of the disadvantage of surface tension, the test can be conducted using the limit air pressure that will not damage the pot, in order to confirm that there are no holes.

[0215] In other words, in the submersion test of a pot, which applies the limit air pressure that will not damage the pot, the same standard is used for pots of any size. That is, the volume of the pot is not taken into consideration. Surface tension can be calculated from the Young-Laplace equation, and since a bubble with radius R in water is approximately equal to the radius of the hole, the standard for the submersion test of a pot can be rephrased as follows: if the radius of the hole is below a specified value, it passes; if it is above a specified value, it fails, regardless of the size of the pot.

[0216] However, in the case of an air leak tester, which measures the amount of leakage after pressurizing and introducing gas into the object under test and then sealing it, even if the same air pressure is applied to 350cc, 600cc, and 1000cc sizes, if the holes are of the same diameter, the pressure drop will be greater for the 350cc size and smaller for the 1000cc size. This is similar to the phenomenon where, when the amount of leakage is large, the internal pressure of the workpiece during measurement (inspection pressure) becomes low, and the amount of leakage is measured as smaller. Therefore, when detecting leakage with an air leak tester, the amount of leakage will be less for the 350cc size and higher for the 1000cc size. In other words, if you switch from a pot, which could be subjected to a submersion test using the same inspection standard where the volume of the pot is ignored or the same, to a regular air leak tester, it becomes impossible to perform the inspection using the same inspection standard, and in mixed inspections, the standard will have to be changed for each inspection, making the inspection complicated.

[0217] In contrast, the leak inspection device 10 and leak inspection method according to the present invention employ a method in which a gas is pressurized and introduced into the object to be inspected, then sealed and the amount of leakage is measured. However, the measured amount of leakage is converted to a value that would be obtained if measured at a predetermined standard inspection pressure, based on the internal pressure of the workpiece (pot in this example) at the time of measurement. Therefore, mixed inspections can be performed without changing the standard for each inspection.

[0218] Furthermore, while it might seem that the solution to the problems this invention aims to solve could be achieved by simply narrowing the permissible range of the inspection pressure, we will explain why this is not the case.

[0219] Figure 15 shows the control results for 4271 inspections (250 enlarged views) conducted with the electro-pneumatic regulator 2 set to a value of 500kPa ± 40kPa. Although the electro-pneumatic regulator 2 was set to 500kPa during the factory's break time, the inspection pressure was less than 500kPa because compressed air from a pressurized gas supply source was used by other equipment during the inspection. In the figure, filled circles indicate cases where a workpiece that was acceptable passed the inspection, or a workpiece that was unacceptable failed the inspection, while white circles indicate cases where a workpiece that was acceptable failed the inspection, or an unacceptable workpiece passed the inspection.

[0220] This figure shows that misjudgments are not necessarily limited to cases where the inspection pressure deviates significantly from the set value. In other words, for workpieces where the leakage amount when inspected at the standard inspection pressure is close to the standard leakage amount, a misjudgment can occur even if the inspection pressure is only slightly different from the standard inspection pressure. This can be seen in Figure 19, where even if the allowable range of the inspection pressure is narrowed, for example from 440kPa to 460kPa, it still includes regions E1 where defective products are misjudged as passing and regions E2 where good products are misjudged as failing. Furthermore, as shown in Figure 15, there is a large variation in pressure after pressurization, so if the allowable range of the inspection pressure is narrowed, many cases occur where the pressure at the completion of pressurization does not fall within the allowable range, resulting in errors and making it impossible to perform inspections smoothly. Thus, narrowing the allowable range of the inspection pressure does not solve the problem of the present invention.

[0221] To explain why the control results shown in Figure 15 occurred, products are manufactured daily in the factory, and updates to the production line (including the installation of inspection lines using the leak inspection device 10) are carried out during times when the production line is shut down, such as during lunch breaks, after work hours, on weekends, and during the New Year holidays, so as not to disrupt daily production. In other words, the leak inspection device 10 is set up under extremely stable conditions during times when other machines powered by pressurized gas, which are branched off and connected from the piping from the supply source 3 to the electro-pneumatic regulator 2, are not in operation, and therefore the situation shown in Figure 15 has not been noticed by managers until now.

[0222] Although embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to those shown in the embodiments, and any changes or additions that do not depart from the spirit of the present invention are also included in the present invention.

[0223] In this embodiment, Hagen-Poiseuille's straight-pipe model was used to calculate the conversion of the detected leak amount (detected differential pressure) to the converted leak amount (converted differential pressure). However, the orifice flow rate formula specified in JIS 8762-2 may also be used, or a linear function showing the relationship between inspection pressure and leak amount, obtained from the leak amounts at different inspection pressures between at least two points of a predetermined leak limit sample, may be used. Furthermore, a sub-function using leak amounts at three or more different pressures may also be used. Moreover, multiple such functions may be combined (combined with weights).

[0224] Furthermore, when pairing the change in differential pressure measured in the leak inspection process (the difference between the differential pressure at the start of measurement in the leak inspection process and the differential pressure at the end of measurement in the leak inspection process), ΔPr[Pa] (or ΔQr[mL / min]), with the internal pressure value of the workpiece at the time of measurement (inspection pressure), it is preferable that the timing of the inspection pressure measurement be the median time between the start of measurement in the leak inspection process and the end of measurement in the leak inspection process. However, it is also permissible to measure the inspection pressure at other timings. For example, the start of measurement may be used as the timing for measuring the inspection pressure.

[0225] When the timing of measuring the inspection pressure is set to the start of measuring the differential pressure ΔPr, the graph showing the relationship between the converted leak amount and the inspection pressure shows a slight downward slope, as shown in Figure 16. Ideally, the converted leak amount should be a constant value regardless of the inspection pressure, but as long as the error between the actual correct converted leak amount and the measured value falls within a predetermined range within the allowable range of the inspection pressure, there is no problem with the inspection accuracy.

[0226] If the timing for measuring the test pressure is set to the start of the differential pressure ΔPr measurement period, the test pressure can be obtained at the same timing regardless of the length of the differential pressure ΔPr measurement period (without changing the timing of the test pressure measurement according to the length of the measurement period), thus achieving sufficient effectiveness with a simple method.

[0227] This indicates that the timing of the inspection pressure measurement can be set at a predetermined time interval from the median time between the start and end of the leak inspection process. For example, it can be before the start of measurement or after the end of measurement in the leak inspection process. The goal is to obtain the inspection pressure that should be paired with the measured leak amount (detected differential pressure or detected leak amount).

[0228] Furthermore, if there is a discrepancy between the measurement of the inspection pressure and the measurement of the detected leakage amount (detection differential pressure), the measured inspection pressure may be corrected to match the value at the time of the detection leakage amount measurement. Moreover, it is preferable to perform this correction while taking the detection leakage amount into account. That is, it is preferable to change the amount of correction of the detection pressure according to the magnitude of the detection leakage amount. As shown in Figure 11, the pressure drop after sealing depends on the magnitude of the leak, and the pressure drop is greater when there is a lot of leak than when there is little leak. Therefore, if the amount of pressure drop between the measurement of the inspection pressure and the measurement of the detection leakage amount (for example, the median time between the start and end of measurement in the leak inspection process) is changed according to the detection leakage amount measured in the leak inspection process, and the above correction is performed, a more accurate correction can be achieved.

[0229] Furthermore, when not performing a mixed inspection in which a plurality of workpieces with different sizes are inspected one after another, the measurement timing of the inspection pressure paired with the detected leakage amount (detected differential pressure) may be after the completion of the pressurized introduction of gas into the workpiece and before sealing (before closing the first on-off valve 31). For example, when the leak inspection device is configured not to include the first pressure gauge 41 and the second pressure gauge 42 with respect to the leak inspection device 10 shown in FIG. 1, the pressure gauge 5 is used (for example, a counterpart of the pressure gauge 5 is provided in the first pipe 21 and used), and the inspection pressure is acquired at the above timing (before sealing after the completion of the pressurized introduction). Then, as described above, the acquired inspection pressure may be corrected so as to be the value at the time of measuring the detected leakage amount. It is better to take into account the detected leakage amount in this correction.

[0230] Also, when there is a deviation between the measurement timing of the inspection pressure and the measurement timing of the detected leakage amount, instead of correcting the measured inspection pressure so as to be the value at the time of measuring the detected leakage amount, the reference leakage amount used for the leakage determination may be corrected. That is, taking into account the leakage amount from the workpiece during the time from the measurement timing of the inspection pressure (for example, after the completion of the pressurized introduction of gas and before closing the first on-off valve 31) to the measurement timing of the detected leakage amount (for example, the median time between the start and end of the measurement in the leakage inspection process), the reference leakage amount (maximum allowable leakage amount) may be set to a value less than the original value (for example, manually input and set to be less).

[0231] Furthermore, using a sample of the workpiece indicating the maximum allowable leakage amount, the pressure drop from closing the first on-off valve 31 to the measurement time of the leakage amount (the median time of the measurement period of the leakage inspection process) is measured, and based on the measurement result, the inspection processing unit 50 may automatically determine how much less the reference leakage amount (maximum allowable leakage amount) should be set. Note that this method is not limited to the case where the measurement timing of the detection pressure is after the completion of the pressurized introduction of gas and before closing the first on-off valve 31. It can also be used as a correction when, for example, before or after a predetermined time from the median time of the measurement period of the leakage inspection process after closing the first on-off valve 31. In that case, it can be corrected for each measurement without using a sample indicating the maximum allowable leakage amount.

[0232] Furthermore, in this invention, it is sufficient to convert at least one of the detected leak amount and the reference leak amount so that both are values ​​obtained when measured under the same pressure conditions. The detected leak amount may be converted to be the value obtained when the leak amount is measured at the reference inspection pressure, or the reference leak amount may be converted to be the value obtained when measured at the detection pressure, or both the detected leak amount and the reference leak amount may be converted to be the values ​​obtained when measured at a third pressure that is neither the inspection pressure nor the reference inspection pressure. In any case, the various variations described above can be taken.

[0233] In this embodiment, an example was shown in which the leak inspection device 10 measures the differential pressure between the workpiece 61 and the master 62, but a configuration that directly measures the pressure of the workpiece 61 is also acceptable.

[0234] Furthermore, when measuring the differential pressure between the workpiece 61 and the master 62 as a leak inspection device 10, instead of measuring the differential pressure between the workpiece 61, which is the object to be tested for leakage (the object under inspection), and the master 62, which does not have leakage, a dual-workpiece method is also acceptable, in which the object under inspection is connected to both (in this case, it is the workpiece 62, not the master 62, and the differential pressure with workpiece 61 is measured). Such a dual-workpiece method is used when the number of leaking items under inspection is extremely small (for example, less than 5%). Conventionally, the pressure used in the calculation to convert the detected leakage amount (detected differential pressure) of workpiece 61 to the converted leakage amount (converted differential pressure) was, for example, the pressure of the first pressure gauge 41. However, when measuring with the dual-workpiece method, there may be cases where there is no leakage in workpiece 61 but there is leakage in workpiece 62. In such cases, the leakage amount measured by the differential pressure gauge 43 will be displayed as a negative value, but it is preferable to use the pressure of the second pressure gauge 42, for example, when calculating the pressure to convert the detected leakage amount (detected differential pressure) of workpiece 62 to the converted leakage amount (converted differential pressure).

[0235] In other words, the leak inspection device 10 cannot determine whether it is performing a conventional inspection using a leak-free master or an inspection using both workpiece methods described above. Therefore, if the leakage amount measured by the differential pressure gauge 43 is positive (indicating a leak in the workpiece 61), it is preferable to use the pressure of the first pressure gauge 41, for example, as the pressure used in the calculation. If the leakage amount is negative (indicating a leak in the master 62 or workpiece 62), it is preferable to use the pressure of the second pressure gauge 42, for example, as the pressure used in the calculation. Even if there is a leak in the master 62 or workpiece 62, the values ​​of the pressure of the first pressure gauge 41 and the second pressure gauge 42 may be assumed to be approximately the same, and the calculation may be performed using the value of the first pressure gauge 41. Furthermore, if it is possible to input that both workpieces are involved, instead of displaying a negative value, it is also acceptable to display that there is a leak in the master 62 or workpiece 62, and to display the leakage amount as a positive value instead of a negative value.

[0236] The present invention is not limited to leak testing devices, but also includes leak testing methods. The leak testing method is performed on an external computer or the like. For example, the leak testing device may be configured without a testing processing unit 15, and the functions equivalent to those of the testing processing unit 15 (including the function of performing the leak testing method according to the present invention) may be handled by an external computer or the like.

[0237] Conventional measuring instruments have aimed to improve accuracy and obtain precise measurements, but as shown in Figure 19, they had the problem of misjudgments occurring when judging based on predetermined reference values ​​(there was a problem that improving the accuracy of the leakage amount reduced the accuracy of the judgment). In contrast, the present invention aims to make the most accurate pass / fail judgment possible by having the user of the inspection device provide sample values ​​of the leaking workpiece (at least two sample values ​​paired with leakage amount and pressure), and correcting predetermined reference values ​​or the inspection values ​​of the newly inspected workpiece based on these sample values.

[0238] In other words, since the leaking sample and the workpiece being newly inspected are different, the pressure-converted leak rate of the newly inspected workpiece (for example, the leak rate converted to a value under a predetermined reference pressure paired with a specific pressure) must naturally undergo correction (conversion) based on estimation. Therefore, compared to conventional methods (for example, methods that extend the same method as the leak rate measured at the same pressure as a predetermined reference pressure paired with a specific pressure), it is not possible to obtain an accurate value, and it remains an incomplete estimate (for example, as shown in Graph 93 in Figure 3, it is not always possible to obtain a perfect match).

[0239] However, in contrast to the problem of misjudgments occurring with conventional measuring instruments based on predetermined reference values, the present invention can at least reduce the rate of misjudgments. Manufacturers of measuring instruments have traditionally focused on accurately determining the leakage amount, considering pass / fail judgment merely an auxiliary function. However, workers who use these instruments in factories and other settings are not in the business of checking the leakage amount; their job is to distinguish between good and defective products, and they only look at the pass / fail judgment screen. The present invention aims to improve the accuracy of the pass / fail judgment function that users desire, rather than the measurement accuracy that manufacturers of measuring instruments tend to focus on.

[0240] Furthermore, it also has the following advantages. For example, conventionally, using inexpensive polyurethane tubing would result in unexplained leakage errors, forcing the use of nylon tubing. However, with the present invention, even when using inexpensive polyurethane tubing over long distances (e.g., 20m), correction and conversion are performed, which not only avoids misjudgment but also improves measurement accuracy, among other advantages. [Explanation of Symbols]

[0241] 2… Electro-pneumatic regulator 3…Source of pressurized gas 5…Pressure gauge 6…Isothermal fan unit 10… Leak detection device 11…Pressure source connection port 12…Workpiece connection port 13…Master connection port 15…Inspection Processing Section 21...First piping 22...Second piping 23...Third piping 24... Exhaust pipe 31…First shut-off valve 32... Second shut-off valve 33...Third shut-off valve 34…Fourth shut-off valve 35…5th valve 36…6th valve 37…7th valve 38... Exhaust valve 41…First pressure gauge 42... Second pressure gauge 43... Differential pressure gauge 50…Inspection Processing Unit 51... Leakage measurement unit 52...Inspection pressure measurement section 53...Reference value acquisition section 54…Conversion section 55…Judgment section 56...Volume change acquisition unit 61...Work 62... Master 71, 72... Variable valve 73…Flow meter

Claims

1. A leak test method for inspecting whether an object to be inspected, which has a hollow section, has leaks. A leak amount measurement step involves introducing a pressurized gas into the object to be inspected, sealing it, and then measuring the detected leak amount, which is the amount of leakage per unit time from the object to be inspected. A test pressure measurement step in which a first test pressure indicating a representative value of the internal pressure of the object under test during the period in which the above measurement was performed is determined based on the internal pressure measured once or multiple times at predetermined timings after the introduction of pressurization, A reference value acquisition step involves obtaining a reference inspection pressure and a reference leakage amount that indicates the maximum allowable leakage amount per unit time from the object under inspection when the measurement is performed using the representative value as the reference inspection pressure, The system includes a conversion step in which at least one of the detected leak amount and the reference leak amount is converted using a function having a variable into which the pressure value before conversion is substituted and a variable into which the pressure value after conversion is substituted, such that the detected leak amount and the reference leak amount are the values ​​when the reference inspection pressure and the first inspection pressure are the same pressure. In the aforementioned conversion step, The amount of leakage detected is converted to the value obtained when the first inspection pressure is the same as the standard inspection pressure, or Convert the aforementioned standard leakage amount to the value obtained when the standard inspection pressure is the same as the first inspection pressure, or The detected leakage amount is converted to the value obtained when the first inspection pressure is the same as the third pressure, and the reference leakage amount is converted to the value obtained when the reference inspection pressure is the same as the third pressure. A leak testing method characterized by the following:

2. Volume change acquisition step: Acquires the volume change due to the internal pressure of the sealed closed space, including the hollow portion of the object under inspection. It further possesses The leak inspection method according to feature 1.

3. In the conversion step, the conversion is performed taking into account that the volume of the sealed closed space, including the hollow portion of the object under inspection, changes depending on the internal pressure of the closed space. The leak inspection method according to claim 1 or 2, characterized by the features described above.

4. The method further includes a determination step of comparing the converted detected leak amount with the reference leak amount to determine whether or not there is a leak in the object being inspected. A leak inspection method according to any one of claims 1 to 3.

5. In the leakage measurement step, after pressurizing a gas to the same pressure into a leak-free reference body having a hollow section and the object under test, the leakage amount from the object under test is obtained based on the pressure difference between the internal pressure of the object under test and the internal pressure of the reference body, measured while each of the reference body and the object under test are sealed as independent closed spaces. A leak inspection method according to any one of claims 1 to 4.

6. The system further includes an inspection pressure correction step, which corrects the measured first inspection pressure to match the value at the time of measurement of the detected leakage amount if there is a discrepancy between the measurement of the first inspection pressure and the measurement of the detected leakage amount. A leak inspection method according to any one of claims 1 to 5, characterized by the above.

7. In the inspection pressure correction step, the correction is performed taking into account the amount of leakage detected. The leak inspection method according to feature 6.

8. A leak inspection device for checking for leaks in an object to be inspected that has a hollow section, A leak rate measuring unit measures the amount of leak per unit time from the object under inspection, which is the amount of leak from the object under inspection, after pressurizing and introducing gas into the object under inspection and then sealing it. An inspection pressure measuring unit determines a first inspection pressure, which represents a representative value of the internal pressure of the object under inspection during the period in which the above measurements were taken, based on the internal pressure measured once or multiple times at predetermined timings after the introduction of pressurization. A reference value acquisition unit that acquires a reference inspection pressure and a reference leakage amount that indicates the maximum allowable value of the leakage amount per unit time from the object under inspection when the measurement is performed with the representative value as the reference inspection pressure, A conversion unit that converts at least one of the detected leak amount and the reference leak amount using a function having a variable to which the pressure value before conversion is substituted and a variable to which the pressure value after conversion is substituted, such that the detected leak amount and the reference leak amount are the values ​​when the reference inspection pressure and the first inspection pressure are the same pressure. It has, The conversion unit is, The amount of leakage detected is converted to the value obtained when the first inspection pressure is the same as the standard inspection pressure, or Convert the aforementioned standard leakage amount to the value obtained when the standard inspection pressure is the same as the first inspection pressure, or The detected leakage amount is converted to the value obtained when the first inspection pressure is the same as the third pressure, and the reference leakage amount is converted to the value obtained when the reference inspection pressure is the same as the third pressure. A leak detection device characterized by the following features.

9. The system further includes a volume change acquisition unit that acquires the volume change due to the internal pressure of the sealed closed space, including the hollow portion of the object under inspection. The leak inspection device according to feature 8.

10. The conversion unit takes into account that the volume of the sealed closed space, including the hollow portion of the object under inspection, changes depending on the internal pressure of the closed space, and performs the conversion. The leak inspection device according to claim 8 or 9.

11. The system further includes a determination unit that compares the converted detected leak amount with the reference leak amount to determine whether or not there is a leak in the object being inspected. A leak inspection device according to any one of claims 8 to 10, characterized by the above.

12. The leakage rate measuring unit, after pressurizing a gas to the same pressure into a leak-free reference body having a hollow section and the object under test, and then measuring the difference in pressure between the internal pressure of the object under test and the internal pressure of the reference body while each of the reference body and the object under test are sealed as independent closed spaces, obtains the leakage rate from the object under test. A leak inspection device according to any one of claims 8 to 11, characterized by the above.

13. The inspection pressure measuring unit corrects the measured first inspection pressure to match the value at the time of measurement of the detected leakage amount if there is a discrepancy between the measurement of the first inspection pressure and the measurement of the detected leakage amount. A leak inspection device according to any one of claims 8 to 12, characterized by the above.

14. The inspection pressure measuring unit performs the correction taking into account the detected leakage amount. The leak inspection device according to feature 13.

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