Air tightness detection device for indirect test
By using a throttling tube and a differential pressure sensor in the airtightness testing device, an indirect testing model was established, which solved the problems of low efficiency and low accuracy in existing airtightness testing and achieved high-precision airtightness testing, especially accurate leakage rate measurement under micro-leakage conditions.
Patent Information
- Application Number
- CN202423135742.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-19
- Publication Date
- 2026-02-27
- Estimated Expiration
- 2034-12-19
AI Technical Summary
Existing airtightness testing methods are inefficient, have low automation, low accuracy, and high cost. Directly reading differential pressure sensors cannot accurately calculate the product's leakage rate.
An indirect airtightness testing device is used. By connecting a standard container to the throttling tube of the test workpiece, the leakage rate is indirectly detected by a differential pressure sensor. A model is established from the differential pressure of the external throttling tube to the flow rate of the throttling tube to the leakage rate of the test workpiece. Combined with the leakage rate test pressure supplementary model under different test pressures, the test accuracy is improved.
It achieves high-precision airtightness testing, suitable for large-volume workpieces, especially for accurate leakage rate measurement under micro-leakage conditions, improving testing efficiency and accuracy.
Smart Images
Figure CN223955086U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to airtightness test technical field, specifically, relate to a kind of airtightness detection device of indirect test. BACKGROUND
[0002] The existing airtightness test method is to inflate the product, then measure the product internal gas state or discharge the volume of gas from the product to convert the leakage rate of the product. These methods have problems of low efficiency, low automation, low precision (depending on the precision of the used equipment or electrical components), high cost, etc.
[0003] The airtightness indirect test device indirectly detects the pressure difference on the pipeline through a high-precision differential pressure sensor, and converts it into a throttle hole flow rate and finally into the leakage rate of the workpiece. However, only reading the value of the differential pressure sensor cannot calculate the leakage rate of the product, and the accuracy is low. UTILITY MODEL CONTENT
[0004] The utility model discloses an airtightness detection device for indirect test, aiming at improving the above-mentioned problems.
[0005] The utility model adopts the following scheme:
[0006] An airtightness detection device for indirect test comprises a gas source pipeline, a first gas channel and a second gas channel connected in communication with the gas source pipeline, wherein the first gas channel is adapted to communicate with a standard container, the second gas channel is adapted to connect a test workpiece, and a throttle pipe is arranged between the standard container and the test workpiece, and differential pressure sensors are connected to both ends of the throttle pipe; the flow area of the throttle pipe is smaller than that of the first gas channel and the second gas channel.
[0007] Further, the flow area of the throttle pipe is 0.008-0.03 square millimeters.
[0008] Further, a first air inlet valve is arranged on the first gas channel, and a second air inlet valve is arranged on the second gas channel to control the on-off of the first gas channel and the second gas channel, respectively.
[0009] Further, the first gas channel and the second gas channel are connected to an exhaust channel for exhaust, and an exhaust valve is arranged on the exhaust channel.
[0010] Further, an electronic proportional regulating valve and an on-off valve are arranged on the gas source pipeline to adjust and control the test gas pressure, and a pressure sensor is arranged on the gas source pipeline.
[0011] Advantages:
[0012] The scheme indirectly tests the leakage rate of the test workpiece by establishing a connecting throttle pipe of an external container and the test workpiece, indirectly testing the differential pressure of the connecting throttle pipe, establishing a gas tightness test model of the differential pressure of the connecting throttle pipe, the throttle pipe flow and the leakage rate of the test workpiece, first proposing a leakage rate test pressure supplement model under different test pressures, establishing a perfect gas tightness indirect test method, and amplifying the differential pressure test value of the two ends of the throttle pipe under the micro leakage condition by adjusting the effective cross-sectional area of the throttle pipe, and improving the gas tightness test precision. BRIEF DESCRIPTION OF DRAWINGS
[0013] Fig. 1 is a structure schematic view of the gas tightness detection device for indirect test of the embodiment of the utility model;
[0014] Fig. 2 is a throttle pipe state diagram of the gas tightness detection device for indirect test of the embodiment of the utility model;
[0015] Fig. 3 is a relationship diagram in the embodiment of the utility model;
[0016] Icon: electronic proportional regulating valve 1, on-off total valve 2, pressure sensor 3, first air inlet valve 4, second air inlet valve 5, exhaust valve 6, differential pressure sensor 7, first gas passage 8, second gas passage 9, throttle pipe 10, gas source pipeline 11, test workpiece 12, standard container 13, exhaust passage 14. DETAILED DESCRIPTION
[0017] Embodiment 1
[0018] In combination Figs. 1 to 3 , the embodiment provides a gas tightness detection device for indirect test, which comprises: a gas source pipeline 11, a first gas passage 8 and a second gas passage 9 connected and communicated with the gas source pipeline 11, wherein the first gas passage 8 is adapted to be communicated with a standard container 13, the second gas passage 9 is adapted to be connected with a test workpiece 12, and a throttle pipe 10 is arranged between the standard container 13 and the test workpiece 12, and differential pressure sensors 7 are connected to two ends of the throttle pipe 10; the flow area of the throttle pipe 10 is smaller than that of the first gas passage 8 and the second gas passage 9, so as to amplify the differential pressure test value of the two ends of the throttle pipe 10 when the test workpiece 12 leaks.
[0019] In the embodiment, the first gas passage 8 is provided with a first gas inlet valve 4, and the second gas passage 9 is provided with a second gas inlet valve 5 for controlling the opening and closing of the first gas passage 8 and the second gas passage 9 respectively. Further, the first gas passage 8 and the second gas passage 9 are connected to an exhaust passage 14 for exhausting gas, and the exhaust passage 14 is provided with an exhaust valve 6 for exhausting gas after the test is completed. In addition, an electronic proportional regulating valve 1 and an on-off master valve 2 are arranged on the gas source pipeline 11 for adjusting and controlling the test gas pressure, and a pressure sensor 3 is arranged on the gas source pipeline 11 for controlling the gas pressure of the adjusting system.
[0020] In the embodiment, the standard container 13 is a container with good airtightness or a good product workpiece, and the test workpiece 12 can be a bathroom product such as a shower head, a faucet, etc., but is not limited thereto.
[0021] It should be noted that in the embodiment, the exhaust port of the test workpiece 12 needs to be sealed during the test, so that the gas is pressurized in the system. The flow area of the throttle pipe is 0.008 mm2~0.03 mm2, and the first gas passage 8 and the second gas passage 9 can adopt a conventional gas pipe, for example, a gas guide pipe with a pipe diameter of 5 mm~15 mm. The flow area of the throttle pipe is much smaller than the flow area of the first gas passage 8 and the second gas passage 9, so that when the test product end leaks, part of the gas at the standard container 13 end will be supplemented to the test product end through the throttle pipe 10. When the flow area of the throttle pipe 10 is small, the gas will be accelerated during the flow process, thereby increasing the test differential pressure value between the two ends of the throttle pipe 10, and amplifying the differential pressure between the standard container 13 end and the test product end caused by the tiny gas leakage, so as to facilitate measurement.
[0022] In an embodiment, airtightness indirect test leakage rate model is disclosed, a leakage rate test pressure supplement model under different test pressures is proposed, and a perfect airtightness indirect test method is established. Specifically, the leakage amount of the workpiece to be tested is obtained by the following leakage rate formula:
[0023] ;
[0024] Wherein, is the leakage amount, is the absolute pressure of the gas in the standard end container after pressure stabilization, is the volume of the standard end container, is the standard atmospheric pressure, is the absolute pressure of the gas in the workpiece to be tested after pressure stabilization, is the volume of the workpiece to be tested, is the gas constant, is the steady-state differential pressure measured by the differential pressure sensor 7 after pressure stabilization, The cross-sectional area of the throttling tube 10 is... The ambient temperature.
[0025] The derivation process of the above leakage rate formula is as follows:
[0026] Based on the law of conservation of mass and Boyle's ideal gas law, for the standard container 13 and the workpiece under test at a constant thermodynamic temperature (room temperature)... Under the following conditions:
[0027] (1)
[0028] (2)
[0029] In formula (1): (Pa) represents the absolute pressure of the gas inside the standard end container after stabilization and leakage, respectively. (ml) represents the volume of the standard end container. (Pa) represents standard atmospheric pressure. (ml / min) represents the gas volumetric flow rate of the throttling tube 10 connecting the standard end container and the workpiece to be tested. (min) represents the test time. In equation (2): (Pa) represents the absolute pressure of the gas inside the workpiece under test after stabilization and after leakage, respectively. (ml) represents the volume of the workpiece to be tested. (ml / min) represents the leakage rate at the inlet of the leakage hole in the workpiece under test at the test pressure.
[0030] From formulas (1) and (2), we can obtain:
[0031] (3)
[0032] (4)
[0033] In formula (3)(4): These represent the pressure drop of the standard end container and the workpiece under test during the leakage test, respectively. , .
[0034] When the standard end container and the workpiece under test are filled with gas to reach the same pressure during the inflation and pressure stabilization phases, the product... A leak causes a drop in pressure inside the product, at which point... There is a pressure difference between the two products. To balance the pressure of the two products, some gas will flow from... Inflow In the middle, make Therefore, we can conclude that:
[0035] (5)
[0036] According to the continuity equation The volume flow rate of the gas through the orifice 10 can be obtained :
[0037] (6)
[0038] In equation (6) : (ml / min) is the compressed air flow rate through the orifice 10, is the flow velocity of the fluid at the outlet of the orifice 10 (m / s), is the cross-sectional area of the orifice 10 (mm2).
[0039] Since the differential pressure across the orifice 10 is small, the gas flow velocity is slow, and it can be treated as an isothermal process. Therefore, the isothermal Bernoulli equation (ignoring gravity and friction) at the two ends of the orifice 10 is as shown in Fig. 2
[0040] According to the gas state equation , the Bernoulli equation at the cross sections on both sides of the orifice 10 can be obtained:
[0041] (7)
[0042] In equation (7) : is the gas constant, for dry air , are the stagnation velocity and the outlet-side fluid velocity, respectively (m / s), are the stabilized stagnation pressure (i.e., the absolute pressure of the gas in the standard container) and the absolute pressure at the outlet side of the orifice 10, respectively, is the stabilized steady-state differential pressure measured by the differential pressure sensor 7, is the ambient temperature.
[0043] For simplicity of calculation, it is assumed that the cross section of the orifice 10 (at the inlet) connected to the standard container 13 is in a stagnation state, and the stagnation velocity can be obtained:
[0044] (8)
[0045] Taking the average velocity , equation (6) can be used to obtain the average compressed air flow rate through the orifice 10 :
[0046] (9)
[0047] Deduction of the final leakage rate model for indirect air tightness test under different pressures
[0048] Assuming that the gas flows steadily at the leakage, the upstream pressure of the leakage is the test pressure and the downstream pressure is the atmospheric pressure in the leakage test, because the flow characteristics of the gas at the leakage change with the pressure, the pressure compensation condition and the correction coefficient of the leakage rate model need to be considered according to the classification of different test pressures.
[0049] 1) When , i.e. the test pressure is lower than 1.893 times the atmospheric pressure, because the leakage rate is small and the flow rate is slow, the friction can be ignored, and the whole process can be regarded as an isothermal process. According to the Boyle gas state equation, the conversion formula of the compressed air flow and the air flow under the standard atmospheric pressure is Substituting equation (5) into equation (6) can obtain the leakage amount under the standard atmospheric pressure and room temperature:
[0050] ; (10)
[0051] 2) When , i.e. the test pressure is greater than or equal to 1.893 times the atmospheric pressure, the gas flow rate reaches the speed of sound at the outlet, at this time the gas cannot exchange energy with the outside world, and the whole leakage process is regarded as an isentropic adiabatic process. According to fluid mechanics, the gas flows through the narrow leakage at the speed of sound, which is easy to form "blockage" flow. When the inlet pressure of the leakage is constant, the environmental pressure (back pressure) is equal to the critical pressure (0.5283 ) at this time, the mass flow rate at the outlet reaches the maximum, and the mass flow rate at the outlet will not increase with the increase of the differential pressure, and the "blockage" phenomenon appears. It is shown that the measured differential pressure or flow rate is smaller than the actual one.
[0052] In view of this situation, different leakage holes are regarded as different valves or flow nozzles in the leakage test process, and the judgment condition formula of the blockage flow is introduced to judge the whole process:
[0053] ; (11)
[0054] In equation (11): is the ratio of the working differential pressure to the absolute pressure at the inlet, and here ; is the specific heat ratio coefficient, , is the specific heat ratio, and the specific heat ratio of air is ; is the critical differential pressure ratio.
[0055] At this time, the energy equation of the one-dimensional constant isentropic gas flow is introduced:
[0056] ; (12)
[0057] In equation (12) is the isentropic exponent, for air , is the critical pressure of the gas when it reaches the speed of sound.
[0058] When the gas reaches the speed of sound at the exit, the pressure at the exit section should be It can be derived that the critical differential pressure ratio should be By calculation, when equation (11) holds, i.e. the leak is in the "choked" state. At the same time, this phenomenon raises a key issue: the selection of the appropriate calculation method. Although the expansion coefficient method is favored today for its high accuracy and ease of calculation, due to the difference in flow capacity of different leaks, the expansion coefficient method may not be applicable here. In contrast, the compression coefficient method provides a more appropriate solution in this case, as it can calculate the flow rate at other pressures through the flow rate at the critical state, given the differential pressure.
[0059] According to the compression coefficient, the volumetric flow rate (i.e. the leak rate) formula should be:
[0060] ; (13)
[0061] In equation (13): is the flow coefficient, is the pressure difference between the upstream and downstream, is the specific gravity of the fluid, where , and are the gas densities at the working pressure and at the standard state, respectively.
[0062] According to equation (13), for the same leak, when the test pressure is constant, is a constant, i.e. the slope of the function , the relationship between the volumetric flow rate and in the choked and unchoked cases can be plotted. Fig. 3 The plots of the flow rate in the choked and unchoked cases at a relative pressure of 45 psi (similar at 60 psi) are shown, assuming = 1. In the plots, is the flow rate curve in the unchoked case, is the flow rate curve in the choked case, it can be seen that as the differential pressure increases, the volumetric flow rate also increases; when the differential pressure exceeds a certain value, causing choking, the volumetric flow rate does not increase with the increase in differential pressure to a maximum value; if it is not choked, and It is still a linear relationship.
[0063] At this time, the flow rate and differential pressure of the critical point (blockage point) can be used to obtain the flow rate value of a certain pressure when not blocked. Assuming The flow rate of the leakage hole is The unblocked flow rate can be measured by experiment under the condition of test pressure , , . It can be seen from Fig. 3 that and are proportional, and thus the relationship (correction coefficient) between and can be obtained:
[0064] ; (14)
[0065] In formula (14) is equal to in formula (5), and thus the final leakage rate formula can be obtained through formulas (5), (9), (10), and (14):
[0066] ; (15)
[0067] As can be seen from formula (15), under the condition that the flow area of the throttle pipe 10, the test pressure, the pressure loss (the steady-state value tested by the differential pressure sensor 7) of the throttle gap, and the volume ratio of the workpiece to be tested to the standard end container are known, the leakage rate of the workpiece to be tested under different pressures can be calculated.
[0068] Example 2
[0069] The utility model also provides a kind of detection method of indirectly testing air tightness, using the air tightness detection device of indirect testing, comprising the following steps:
[0070] S1, inflation, electronic proportional regulating valve 1 is adjusted to set inflation pressure, open switch total valve 2, first inlet valve 4, second inlet valve 5, to the set pressure of stable system before deflation is filled;
[0071] S2, stable voltage: electronic proportional regulating valve 1 and switch total valve 2 are closed, first inlet valve 4 and second inlet valve 5 remain open, so that the pressure in pipeline, container tends to be stable;
[0072] S3, air tightness test: keep electronic proportional regulating valve 1 and switch total valve 2 closed, first inlet valve 4 and second inlet valve 5 remain open, read the average value of differential pressure sensor 7 in air tightness test stage, when differential pressure value is close to zero, it indicates that the air tightness of test product is good, and the greater the differential pressure value, the greater the leakage rate of test workpiece 12.
[0073] S4, exhaust: after the test phase is completed, exhaust is started, the first intake valve 4, the second intake valve 5 and the exhaust valve 6 are opened, the gas in the standard container 13 in the two-end station and the workpiece to be tested is exhausted to restore the pressure to the ambient atmospheric pressure.
[0074] The present scheme can be used for high-precision micro-leakage air tightness testing by reducing the cross-sectional area of the throttle pipe; the indirect testing method is irrelevant to the volume of the workpiece 12 and is suitable for air tightness testing of large volume.
[0075] It should be understood that the above are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above embodiments, and any technical solution falling within the scope of the present application is within the protection scope of the present application.
[0076] The above introduction of the drawings used in the embodiments only shows some embodiments of the present application and should not be considered as a limitation on the scope, and for those skilled in the art, other related drawings can be obtained without creative labor.
Claims
1. An indirect test air tightness detection device, characterized in that, The utility model relates to a test gas pressure control system, which comprises: a gas source pipeline, a first gas passage and a second gas passage connected to the gas source pipeline, wherein the first gas passage is adapted to be connected to a standard container, the second gas passage is adapted to be connected to a test workpiece, a throttle pipe is arranged between the standard container and the test workpiece, and differential pressure sensors are connected to both ends of the throttle pipe; the flow area of the throttle pipe is smaller than that of the first gas passage and the second gas passage.
2. The indirect-tested hermeticity inspection apparatus according to claim 1, wherein, The flow area of the throttle pipe is 0.008-0.03 square millimeters.
3. The indirect-tested hermeticity inspection apparatus of claim 1, wherein, A first air inlet valve is arranged on the first gas passage, and a second air inlet valve is arranged on the second gas passage to control the opening and closing of the first gas passage and the second gas passage, respectively.
4. The indirect-tested hermeticity inspection apparatus of claim 3, wherein, The first gas passage and the second gas passage are connected to an exhaust passage for exhaust, and an exhaust valve is arranged on the exhaust passage.
5. The indirect-tested hermeticity inspection apparatus of claim 4, wherein, An electronic proportional regulating valve and an on-off master valve are arranged on the gas source pipeline to adjust and control the test gas pressure, and a pressure sensor is arranged on the gas source pipeline.