Indirect test air tightness detection device and detection method

Abstract

The invention provides an air tightness detection device and detection method for indirect testing, and relates to the technical field of air tightness testing. Comprising a gas source pipeline, a first gas channel and a second gas channel, the first gas channel and the second gas channel are communicated with the gas source pipeline, the first gas channel is suitable for being communicated with a standard container, the second gas channel is suitable for being connected with a test workpiece, and a throttle pipe is arranged between the standard container and the test workpiece. The two ends of the throttle pipe are connected with differential pressure sensors. And a throttling hole of which the overflowing sectional area is smaller than that of the first gas channel and that of the second gas channel is formed in the throttling pipe, so that a differential pressure test value at the two ends of the throttling pipe is amplified when the test workpiece leaks gas. According to the scheme, the accuracy of air tightness detection is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of air tightness testing, and in particular to an air tightness detection device and a detection method for indirect testing. Background Art

[0002] The existing air tightness test methods are to inflate the inside of the product and then measure the gas state inside the product or convert the volume of gas discharged from the inside of the product into the leakage rate of the product. These methods have more or less problems such as low efficiency, low automation, low accuracy (depending on the accuracy of the equipment or electrical components used), and high cost.

[0003] The indirect air tightness test device indirectly detects the pressure difference in the pipeline through a high-precision differential pressure sensor, which is converted into the throttle flow rate and finally converted into the leakage rate of the workpiece. However, the leakage rate of the product cannot be calculated by only reading the value of the differential pressure sensor, and the accuracy is low. Summary of the invention

[0004] The invention discloses an indirect test air tightness detection device, aiming to improve the above-mentioned problem.

[0005] The present invention adopts the following scheme:

[0006] An indirect test air tightness detection device comprises: a gas source pipeline, a first gas channel and a second gas channel connected to the gas source pipeline, wherein the first gas channel is suitable for connecting to a standard container, the second gas channel is suitable for connecting to a test workpiece, and a throttling tube is arranged between the standard container and the test workpiece, and differential pressure sensors are connected to both ends of the throttling tube; a throttling hole with a flow cross-sectional area smaller than that of the first gas channel and the second gas channel is provided in the throttling tube, so as to amplify the differential pressure test value at both ends of the throttling tube when the test workpiece leaks.

[0007] Furthermore, the flow cross-sectional area of ​​the throttle hole is 0.008 mm2 to 0.03 mm 2 .

[0008] Furthermore, a first air intake valve is provided on the first gas channel, and a second air intake valve is provided on the second gas channel, so as to control the opening and closing of the first gas channel and the second gas channel respectively.

[0009] Furthermore, the first gas channel and the second gas channel are connected to an exhaust channel for exhausting gas, and an exhaust valve is provided on the exhaust channel.

[0010] Furthermore, the gas source pipeline is provided with an electronic proportional regulating valve and a switch main valve for adjusting and controlling the test gas pressure, and a pressure sensor is provided on the gas source pipeline.

[0011] Furthermore, the leakage amount of the workpiece to be tested is obtained by the following leakage rate formula:

[0012]

[0013] Where Q is the leakage, P is 1 V is the absolute pressure of the gas in the standard end container after pressure stabilization. 1 is the volume of the standard end container, P atm is standard atmospheric pressure, P 2 V is the absolute pressure of the gas in the workpiece after stabilization. 2 is the volume of the workpiece to be measured, R is the gas constant, Δp is the steady-state differential pressure after pressure stabilization measured by the differential pressure sensor, A is the cross-sectional area of ​​the throttling tube, T 0 is the ambient temperature.

[0014] The present invention also provides a method for indirectly testing air tightness, using the air tightness detection device for indirect testing, comprising the following steps:

[0015] S1, inflation, adjust the electronic proportional regulating valve to the set inflation pressure, open the switch main valve, the first air inlet valve, and the second air inlet valve, and inflate the system to a stable set pressure before deflation;

[0016] S2, pressure stabilization: close the electronic proportional control valve and the switch main valve, and keep the first air inlet valve and the second air inlet valve open, so that the pressure in the pipeline and the container tends to be stable;

[0017] S3. Airtightness test: Keep the electronic proportional control valve and the switch main valve closed, keep the first air inlet valve and the second air inlet valve open, read the average value of the differential pressure sensor during the airtightness test phase. When the differential pressure value is close to zero, it means that the test product has good airtightness. The larger the differential pressure value, the greater the leakage rate of the test workpiece.

[0018] Furthermore, it also includes: S4, exhaust: after the test phase is completed, exhaust begins, the first air inlet valve, the second air inlet valve and the exhaust valve are opened, and the gas in the standard containers and the workpiece to be tested in the two end stations is exhausted to restore the pressure to the ambient atmospheric pressure.

[0019] Beneficial effects:

[0020] This scheme establishes a connecting throttling tube based on an external container and a test workpiece, and indirectly tests the leakage rate of the test workpiece by indirectly testing the differential pressure of the external throttling tube. An airtightness test model of external throttling tube differential pressure → throttling tube flow → test workpiece leakage rate is established. For the first time, a leakage rate test pressure supplement model under different test pressures is proposed, and a complete indirect airtightness test method is established. By adjusting the effective cross-sectional area of ​​the throttling tube, the differential pressure test value at both ends of the throttling tube in the case of micro-leakage is amplified to improve the airtightness test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of an indirect test airtightness detection device according to an embodiment of the present invention;

[0022] Figure 2 It is a state diagram of a throttle tube of an indirect test air tightness detection device according to an embodiment of the present invention;

[0023] Figure 3 In the embodiment of the present invention Relationship diagram;

[0024] Icons: electronic proportional control valve 1, switch main valve 2, pressure sensor 3, first air intake valve 4, second air intake valve 5, exhaust valve 6, differential pressure sensor 7, first gas channel 8, second gas channel 9, throttle tube 10, gas source pipeline 11, test workpiece 12, standard container 13, exhaust channel 14. DETAILED DESCRIPTION

[0025] Example 1

[0026] Combination Figures 1 to 3 The present embodiment provides an indirect test air tightness detection device, comprising: a gas source pipeline 11, a first gas channel 8 and a second gas channel 9 connected to the gas source pipeline 11, wherein the first gas channel 8 is suitable for connecting to a standard container 13, the second gas channel 9 is suitable for connecting to a test workpiece 12, and a throttling tube 10 is arranged between the standard container 13 and the test workpiece 12, and differential pressure sensors 7 are connected to both ends of the throttling tube 10; a throttling hole with a flow cross-sectional area smaller than that of the first gas channel 8 and the second gas channel 9 is provided in the throttling tube 10, so as to amplify the differential pressure test value at both ends of the throttling tube 10 when the test workpiece 12 leaks.

[0027] In this embodiment, a first air intake valve 4 is provided on the first gas channel 8, and a second air intake valve 5 is provided on the second gas channel 9 to control the on and off of the first gas channel 8 and the second gas channel 9, respectively. Furthermore, the first gas channel 8 and the second gas channel 9 are connected to the exhaust channel 14 for exhaust, and the exhaust channel 14 is provided with an exhaust valve 6 for exhausting after the test is completed. In addition, an electronic proportional control valve 1 and a switch main valve 2 are provided on the gas source pipeline 11 to adjust and control the test gas pressure, and a pressure sensor 3 is provided on the gas source pipeline 11 to facilitate the control of the gas pressure of the adjustment system.

[0028] In this embodiment, the standard container 13 is a container with good airtightness or a good workpiece, and the test workpiece 12 can be a bathroom product, such as a shower head, a faucet, etc., including but not limited to these.

[0029] It should be noted that in this embodiment, during the test, the exhaust port of the test workpiece 12 needs to be sealed so that the gas can maintain pressure in the system. The cross-sectional area of ​​the throttle hole is 0.008 mm2 to 0.03 mm 2 The first gas channel 8 and the second gas channel 9 can adopt conventional gas pipes, such as gas guide pipes with a diameter of 5mm to 30mm. The flow cross-sectional area of ​​the throttling hole is much smaller than the flow cross-sectional area of ​​the first gas channel 8 and the second gas channel 9. Therefore, when a leak occurs at the test product end, part of the gas at the standard container 13 end will be supplemented into the test product end through the throttling tube 10. When the flow cross-sectional area of ​​the throttling tube 10 is small, the gas will be accelerated during the flow process, thereby increasing the test differential pressure value at both ends of the throttling tube 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.

[0030] In one embodiment, a leak rate model for indirect air tightness testing is disclosed, a leak rate test pressure supplement model under different test pressures is proposed, and a complete indirect air tightness testing method is established. Specifically, the leakage amount of the workpiece to be tested is obtained by the following leak rate formula:

[0031]

[0032] Where Q is the leakage, P is 1 V is the absolute pressure of the gas in the standard end container after pressure stabilization. 1 is the volume of the standard end container, P atm is standard atmospheric pressure, P 2 V is the absolute pressure of the gas in the workpiece after stabilization. 2 is the volume of the workpiece to be measured, R is the gas constant, Δp is the steady-state differential pressure after pressure stabilization measured by the differential pressure sensor 7, A is the cross-sectional area of ​​the throttling tube 10, T 0 is the ambient temperature.

[0033] The derivation process of the above leakage rate formula is as follows:

[0034] According to the conservation of mass and Boyle's ideal gas state equation, for the standard container 13 and the workpiece to be tested at a constant thermodynamic temperature (room temperature) T 0 =300K condition:

[0035] P 1 V 1 =P 1 'V 1 +P 2 q z Δt ; (1)

[0036] P 2 V 2 =P2 'V 2 +P 2 Q t Δt-P atm q z Δt ; (2)

[0037] In formula (1): P 1 , P 1 '(Pa) are the absolute pressure of the gas in the standard end container after pressure stabilization and leakage, V 1 (ml) is the volume of the standard end container, P atm (Pa) is standard atmospheric pressure, q z (ml / min) is the gas volume flow rate of the throttling tube 10 connecting the standard end container and the workpiece to be tested, and Δt (min) is the test time. In formula (2): P 2 , P 2 '(Pa) are the absolute pressure of the gas in the workpiece to be tested after pressure stabilization and leakage, V 2 (ml) is the volume of the workpiece to be tested, Q t (ml / min) is the leakage rate at the entrance of the leakage hole of the workpiece to be tested under the test pressure.

[0038] From formulas (1) and (2), we can get:

[0039] ΔP 1 V 1 =P 2 q z Δt; (3)

[0040] ΔP 2 V 2 =P 2 Q t Δt-P 2 q z Δt; (4)

[0041] In formula (3) and (4): ΔP 1 , ΔP 2 are the pressure drops of the standard end container and the workpiece to be tested during the leak test, where ΔP 1 =P 1 -P 1 ', ΔP 2 =P 2 -P 2 '.

[0042] When the standard end container and the workpiece to be tested are filled with gas to reach the same pressure during the filling and pressure stabilization stages, the product V 2 Leakage causes the pressure inside the product to drop. At this time, V 1 ,V 2There is a pressure difference between the two products. In order to balance the pressure of the two products, some gas will flow from V 1 Flow into V 2 In the 1 =ΔP 2 , from which we can get:

[0043]

[0044] According to the continuity equation q = vA, the gas volume flow rate q through the throttling tube 10 can be obtained: z :

[0045] q z =v×A×10 2 ×60 ; (6)

[0046] In formula (6): q z (ml / min) is the compressed air flow rate through the throttling tube 10, v is the flow velocity of the fluid at the outlet of the throttling tube 10 (m / s), and A is the cross-sectional area of ​​the throttling tube 10 (cm2).

[0047] Since the pressure difference between the two ends of the throttle tube 10 is small and the gas flow rate is slow, it is treated as an isothermal process. Therefore, the isothermal Bernoulli equation (ignoring gravity and friction) exists at both ends of the throttle tube 10. The state is as follows: Figure 2 Shown

[0048] According to the gas state equation The Bernoulli equation on the cross sections at both ends of the throttling tube 10 can be obtained:

[0049]

[0050] In formula (7): R is the gas constant, for dry air R = 278.1N×m×(kg×k) -1 , v 0 、v 1 (m / s) are the stagnation velocity and the outlet fluid velocity, P 1 , P 1 -Δp are the stagnation pressure after stabilization (i.e., the absolute pressure of the gas in the standard end container) and the absolute pressure at the outlet of the throttling tube 10, Δp is the steady-state differential pressure after stabilization measured by the differential pressure sensor 7, T 0 is the ambient temperature.

[0051] To simplify the calculation, it is assumed that the section of the throttling tube 10 (at the inlet) connected to the standard container 13 is in a stagnant state, and the stagnation velocity v 0 =0, we can get:

[0052]

[0053] Take the average speed Substituting into equation (6) we can obtain the average compressed air flow rate q passing through the throttle tube 10: z :

[0054]

[0055] Derivation of the final leakage rate model for indirect airtightness test under different pressures:

[0056] Assuming that the gas flows steadily in the leak, in the leak test, the upstream pressure of the leak is the test pressure and the downstream pressure is the atmospheric pressure. Because the flow characteristics of the gas at the leak change with the pressure, it is necessary to consider the pressure compensation conditions and correction factors of the leakage rate model according to different test pressure classifications.

[0057] 1) When P 2 <1.893P atm , that is, when the test pressure is lower than 1.893 times the atmospheric pressure, the friction can be ignored due to the small leakage rate and slow flow rate, and the whole process can be regarded as an isothermal process. According to Boyle's gas state equation, the conversion formula of compressed air flow rate and air flow rate under standard atmospheric pressure is Substituting into formula (5) we can get the leakage under standard atmospheric pressure and room temperature:

[0058]

[0059] 2) When P 2 ≥1.893P atm , that is, when the test pressure is greater than or equal to 1.893 atmospheres, the gas flow rate reaches the speed of sound at the outlet. At this time, the gas has no time to exchange energy with the outside world, and the entire leakage process is regarded as an isentropic adiabatic process. According to fluid mechanics, the gas flows through a narrow leak at the speed of sound, which is easy to form a "blocked" flow. When the inlet pressure of the leak is constant, the ambient pressure (back pressure) is equal to the critical pressure (0.5283P 2 ), the mass flow rate at the outlet reaches the maximum, and the mass flow rate at the outlet does not increase with the increase of differential pressure, resulting in a "blockage" phenomenon. This is manifested as the measured differential pressure or flow rate being smaller than the actual one.

[0060] In view of this situation, different leak holes are treated as different valves or flow nozzles during the leak test, and the judgment condition formula of the blocking flow is used to judge the whole process:

[0061] X≥F γ X T ; (11)

[0062] In formula (11): X is the ratio of the working differential pressure to the absolute pressure at the inlet, where X = (P 2 -P atm ) / P2 ; F Υ is the specific heat ratio coefficient, F Υ =Y / 1.4,Y is the specific heat ratio, the specific heat ratio of air is 1.4;X T is the critical differential pressure ratio.

[0063] At this time, the energy equation of a one-dimensional constant isentropic airflow is introduced:

[0064]

[0065] In formula (12), k is the isentropic index. For air, k = 1.4, p * is the critical pressure at which the gas reaches the speed of sound.

[0066] When the gas reaches the speed of sound at the outlet, the pressure at the outlet section should be 0.5283 of the inlet pressure, so the critical differential pressure ratio should be X T =0.4717. By calculation, it is found that when P 2 ≥1.893P atm When (11) is established, the leak hole is in a "blocked" state. At the same time, this phenomenon leads to a key issue: choosing an appropriate calculation method. Although the expansion coefficient method is now popular because of its high accuracy and convenience of calculation, it may not be applicable here due to the differences in the flow capacity of different leak holes. In contrast, the compression coefficient method is based on the known differential pressure condition. The flow rate at other pressures can be calculated from the flow rate at the critical state. Obviously, in this case, the compressibility coefficient method provides a more appropriate solution.

[0067] According to the compression coefficient, the volume flow rate (i.e. leakage) formula should be:

[0068]

[0069] In formula (13): C V is the flow coefficient, ΔP is the upstream and downstream pressure difference, S G is the specific gravity of the fluid, where ρ and ρ std are the gas densities at working pressure and standard conditions, respectively.

[0070] According to formula (13), for the same leak hole, when the test pressure is constant, C v ×(S G ) -(1 / 2) is a constant, i.e. a function The slope of is constant, and the volume flow rate Q can be plotted against Graph of the relationship in blocking and non-blocking cases. Figure 3 Shows hypothesis C v ×(SG ) -(1 / 2) = 1, flow diagram of obstruction and non-obstruction under relative pressure of 45 psi (similar to 60 psi), Q 1 is the flow curve when it is not blocked, Q 2 is the flow curve when blocked. It can be seen that as the differential pressure increases, the volume flow increases. When the differential pressure exceeds a certain value and blocks, the volume flow does not increase with the increase of the differential pressure to reach the maximum value. If there is no blockage, Q and It is still a linear relationship.

[0071] At this time, the flow rate and differential pressure at the critical point (blocking point) can be used to calculate the flow value that should be achieved at a certain pressure when there is no blockage. Assume that X = X T The flow rate of the leakage hole is Q * It can be measured experimentally that at the test pressure P 2 ,ΔP=P 2 -P atm In the case of , the unblocked flow is Q. Figure 3 It can be seen that X1 and X2 are proportional, from which it can be concluded that Q and Q * Relationship (correction factor):

[0072]

[0073] In formula (14), Q * With Q in formula (5) t are equal, and then the final leakage rate formula can be obtained through equations (5)(9)(10)(14):

[0074]

[0075] It can be seen from formula (15) that when the flow cross-sectional area of ​​the throttling tube 10, the test pressure, the pressure loss at both ends of the throttling seam (the steady-state value tested by the differential pressure sensor 7), and the volume ratio of the workpiece to be tested and the standard end container are known, the leakage rate of the workpiece to be tested under different pressures can be calculated.

[0076] Example 2

[0077] The present invention also provides a method for indirectly testing air tightness, using the air tightness detection device for indirect testing, comprising the following steps:

[0078] S1, inflation, adjust the electronic proportional regulating valve 1 to the set inflation pressure, open the switch main valve 2, the first air inlet valve 4, and the second air inlet valve 5, and inflate the system to a stable set pressure before deflation;

[0079] S2, pressure stabilization: close the electronic proportional control valve 1 and the switch main valve 2, and keep the first air inlet valve 4 and the second air inlet valve 5 open, so that the pressure in the pipeline and the container tends to be stable;

[0080] S3, airtightness test: keep the electronic proportional control valve 1 and the switch main valve 2 closed, keep the first air intake valve 4 and the second air intake valve 5 open, read the average value of the differential pressure sensor 7 during the airtightness test phase, when the differential pressure value is close to zero, it means that the test product has good airtightness, and the larger the differential pressure value, the greater the leakage rate of the test workpiece 12.

[0081] S4, exhaust: after the test phase is completed, exhaust begins, opening the first air inlet valve 4, the second air inlet valve 5 and the exhaust valve 6, exhausting the gas in the standard container 13 at both ends and the workpiece to be tested to restore the pressure to the ambient atmospheric pressure.

[0082] This solution can be used for high-precision micro-leakage air tightness testing by reducing the cross-sectional area of ​​the throttle hole; the indirect testing method is independent of the volume of the test workpiece 12 and is suitable for large-volume air tightness testing.

[0083] It should be understood that the above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention.

[0084] The above description of the drawings used in the implementation manner only illustrates certain embodiments of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

Claims

1. An indirect test airtightness detection device, characterized in that: include: A gas source pipeline, a first gas channel and a second gas channel connected to the gas source pipeline, wherein the first gas channel is suitable for connecting to a standard container, the second gas channel is suitable for connecting to a test workpiece, and a throttling tube is arranged between the standard container and the test workpiece, and differential pressure sensors are connected to both ends of the throttling tube; the throttling tube has a throttling hole with a flow cross-sectional area smaller than that of the first gas channel and the second gas channel, so as to amplify the differential pressure test value at both ends of the throttling tube when the test workpiece leaks.

2. The airtightness detection device for indirect testing according to claim 1, characterized in that: The flow cross-sectional area of ​​the throttling hole is 0.008mm2~0.03mm2.

3. The airtightness detection device for indirect testing according to claim 1, characterized in that: The first gas channel is provided with a first intake valve, and the second gas channel is provided with a second intake valve, so as to control the opening and closing of the first gas channel and the second gas channel respectively.

4. The airtightness detection device for indirect testing according to claim 3 is characterized in that: The first gas channel and the second gas channel are connected to an exhaust channel for exhausting gas, and an exhaust valve is disposed on the exhaust channel.

5. The airtightness detection device for indirect testing according to claim 4, characterized in that: The gas source pipeline is provided with an electronic proportional regulating valve and a switch main valve for regulating and controlling the test gas pressure, and a pressure sensor is provided on the gas source pipeline.

6. The airtightness detection device for indirect testing according to claim 5, characterized in that: The leakage rate of the workpiece to be tested is obtained by the following leakage rate formula: Among them, Q is the leakage, P1 is the absolute pressure of the gas in the standard end container after pressure stabilization, V1 is the volume of the standard end container, P atm is the standard atmospheric pressure, P2 is the absolute pressure of the gas in the workpiece to be measured after pressure stabilization, V2 is the volume of the workpiece to be measured, R is the gas constant, Δp is the steady-state differential pressure after pressure stabilization measured by the differential pressure sensor, A is the cross-sectional area of ​​the throttling tube, and T0 is the ambient temperature.

7. A method for indirectly testing air tightness, characterized in that: The airtightness detection device for indirect testing according to claim 5 or 6 is characterized in that it comprises the following steps: S1, inflation, adjust the electronic proportional regulating valve to the set inflation pressure, open the switch main valve, the first air inlet valve, and the second air inlet valve, and inflate the system to a stable set pressure before deflation; S2, pressure stabilization: close the electronic proportional control valve and the switch main valve, and keep the first air inlet valve and the second air inlet valve open, so that the pressure in the pipeline and the container tends to be stable; S3. Airtightness test: Keep the electronic proportional control valve and the switch main valve closed, keep the first air inlet valve and the second air inlet valve open, read the average value of the differential pressure sensor during the airtightness test phase. When the differential pressure value is close to zero, it means that the test product has good airtightness. The larger the differential pressure value, the greater the leakage rate of the test workpiece.

8. The indirect airtightness testing method according to claim 7, characterized in that: Also includes: S4, exhaust: After the test phase is completed, exhaust begins. Open the first air inlet valve, the second air inlet valve and the exhaust valve to exhaust the gas in the standard containers and the workpiece to be tested at both ends to restore the pressure to the ambient atmospheric pressure.

Images