Test method for equivalent leak rate of vacuum leak of composite vacuum pressure molding process

Abstract

The application belongs to the technical field of testing and specifically relates to a test method for equivalent leak hole vacuum leakage rate in a composite material vacuum pressure forming process average . The application calculates a large pressure difference vacuum average leakage rate Q through a test on a large vacuum pressure change range, instead of a vacuum leakage rate value Q at any vacuum pressure in the vacuum pressure range, and the maximum relative error is less than 1%, solving the distortion problem of the vacuum leakage rate value at a certain vacuum pressure caused by the response nonlinearity of a vacuum pressure gauge, and not requiring a large vacuum container volume, so that an ordinary vacuum pressure gauge can meet the test requirements and is convenient and practical.

Description

Technical Field

[0001] This invention belongs to the field of testing technology, specifically relating to a method for testing the equivalent leakage rate of vacuum holes in a composite material vacuum pressure forming process. Background Technology

[0002] Vacuum pressure molding of composite materials involves laying pre-impregnated composite layers on a rigid mold, sealing the composite layers with a vacuum membrane and self-adhesive strips, and then heating and pressurizing the composite layers under vacuum conditions to complete the molding process. However, air leakage is common at the sealing points of the self-adhesive strips, leading to air bubbles and defects in the composite product, affecting its performance. Ultrasonic leak testing is a simple and effective method. To locate leaks and test the vacuum leak rate using ultrasonic leak testing technology, equivalent-sized leak holes need to be pre-embedded in the self-adhesive strips. The vacuum leak rate of different pore sizes is then tested according to standard methods to establish a quantitative relationship between pore size and vacuum leak rate. Based on this, the acoustic signal characteristics of leaks with different pore sizes are further studied to establish a quantitative relationship between pore size, vacuum leak rate, and acoustic signal (sound intensity or sound pressure).

[0003] Vacuum leak rate testing is conducted according to the "Static Pressure Boost Method for Vacuum Leak Rate Testing" in GB / T 32218-2015. The vacuum leak rate is calculated by testing the change in vacuum pressure within a certain volume of space over a certain time interval. The basic principle is: evacuate the system to the highest vacuum level, then close the evacuation valve and pump, test the change in vacuum pressure over time, and calculate the leak rate using the following formula:

[0004]

[0005] Q: Vacuum leakage rate, in Pa·m 3 / s

[0006] V: Volume of the vacuum container, in meters (m³) 3 ;

[0007] t1: Start time, in seconds;

[0008] t2: The time at which the event ends, in seconds;

[0009] T1: Initial temperature;

[0010] T2: The temperature at the end;

[0011] P1: Initial pressure, in Pa;

[0012] P2: End pressure, unit Pa.

[0013] Since the temperature remains constant at the start and end of the test, the leak rate calculation formula simplifies to:

[0014]

[0015] Currently, the vacuum leak rate tests reported in the literature mainly focus on high-vacuum systems, where the vacuum leak rate is very low, generally less than 10. -2 Pa.m 3 / s. The literature "Zhong Boyang, Wang Wei, Li Fangfang, et al. Effects of different gases and pressures on the leakage rate of vacuum leaks [J]. Journal of Vacuum Science and Technology, 2017, 37(4)" uses a leakage rate of 2.3×10 -6 Pa.m 3 The influence of different inlet pressures and gases on the vacuum leakage rate was studied using a leak with a pressure of / s. The literature "Liu Cixian, Zhang Dixing, Feng Yan, et al. Study on leakage rate of metal flattened positive pressure leak under different pressures [J]. Vacuum and Cryogenics, 2011, 17(4)" investigated the variation law of leakage rate of metal flattened positive pressure leak with inlet and outlet pressures, where the leakage rate of the leak under different pressures was 10 - 6 Pa.m 3 The above studies, due to the very small leakage rate of the leak and the very slow pressure change inside the container, have sufficient time to measure the minute pressure changes inside the container, thus accurately measuring the leakage rate value at a certain pressure.

[0016] The vacuum pressure forming process for composite materials does not require a high vacuum level; a relative vacuum of -96 kPa is generally sufficient to meet the process requirements. Minor leaks in the system are permissible, typically with a leak rate of less than 10%. -3 Pa.m 3 A flow rate on the order of / s is sufficient. However, improper operation during the setup of the vacuum pressure forming device can easily lead to significant leakage, with an equivalent pore diameter between 0.3mm and 0.8mm and a vacuum leakage rate between 1 Pa·m. 3 / s~8Pa.m 3 / s does not meet the requirements of the vacuum pressure forming process for composite materials, and must be able to detect and eliminate it.

[0017] According to GB / T 32218-2015, during the testing of large leaks and leakage rates in the vacuum pressure molding process of composite materials, due to the large leaks and leakage rates, the vacuum level decreases rapidly within a limited volume. Limited by the response speed of the vacuum gauge, it is difficult to accurately measure small changes in vacuum pressure, leading to abnormal vacuum leakage rate values ​​calculated at a certain vacuum level. We have used a 10000mL nominal volume (calibrated volume 13749.4mL) vacuum flask as a vacuum container to test vacuum leaks with pore sizes ranging from 0.3mm to 0.8mm. We found that when calculating the vacuum leakage rate with a pressure difference less than 1kPa, the calculated vacuum leakage rate value often showed a sudden increase or decrease as the vacuum level decreased, as shown in Table 1.

[0018] Table 1. Detection results of vacuum pressure and leakage rate changes for leak (hole diameter 0.429 mm) labeled 22G.

[0019]

[0020] This result is clearly unreasonable and incorrect.

[0021] In existing technologies, the aforementioned defects are often eliminated by improving the accuracy of the vacuum gauge or increasing the volume of the vacuum container. However, the GJM-120 metrological-grade digital pressure gauge used in the above experiment has an accuracy of 0.02%, which is high enough and is a high-precision vacuum gauge that can be configured in a typical laboratory. In addition, the vacuum container used in the above experiment is a filtration flask with a nominal volume of 10000mL (calibrated volume of 13749.4mL), which is already large enough. Further increasing the volume would be inconvenient to use and would not completely avoid the unreasonableness of the test results shown in Table 1. Summary of the Invention

[0022] To address the problems in existing technologies, this application provides a method for testing the vacuum leakage rate of equivalent leaks in a composite material vacuum pressure forming process. The inventors studied the variation of vacuum leakage rate with vacuum pressure for leaks with apertures ranging from 0.3 mm to 0.8 mm. They found that as the vacuum level decreases, i.e., the relative vacuum pressure increases from approximately -99 kPa to 0 kPa, the vacuum leakage rate gradually decreases. However, within the vacuum pressure range of -99 kPa to -70 kPa, the change in vacuum leakage rate is very slow and essentially constant. Above -70 kPa, the rate of decrease in vacuum leakage rate accelerates significantly (e.g., ...). Figure 1 (As shown in the figure). The figure below shows the change in vacuum leakage rate with vacuum pressure for leaks of different orifice diameters.

[0023] This invention addresses the testing of equivalent leakage rate in the vacuum pressure forming process of composite materials, proposing a method to calculate the average value Q of the large-difference vacuum leakage rate by testing a wide range of vacuum pressure variations. average , which replaces the vacuum leakage rate value Q at any vacuum pressure within the vacuum pressure range.

[0024] The method for testing the equivalent leakage rate of composite material vacuum pressure molding proposed in this invention includes the following steps:

[0025] (1) Construct a test system for the equivalent leakage rate of composite material vacuum pressure forming, including:

[0026] 1) A pre-formed composite layer is laid on the flat glass, and the vacuum membrane is sealed to the flat glass with vacuum sealing strips to form a composite material vacuum bag pressing device. The device has an air extraction interface.

[0027] 2) Insert the equivalent leak hole into the vacuum sealing strip and press firmly to ensure that the outer wall of the equivalent leak hole is fully bonded and sealed with the vacuum sealing adhesive to prevent air leakage;

[0028] 3) Connect the vacuum bag press device, vacuum container, vacuum valve, and vacuum pump using a vacuum extraction pipe;

[0029] (2) Seal the equivalent leak, turn on the vacuum valve and vacuum pump, evacuate the system until the vacuum level reaches -99kPa or higher, and then turn off the vacuum valve and vacuum pump.

[0030] (3) Check the system's sealing performance; the blank leakage rate should not exceed 10%. -3 Pa.m 3 If the air leak is on the order of / s, then the leaks in the system should be checked and eliminated.

[0031] (4) Reopen the vacuum valve and vacuum pump to evacuate the system until the vacuum level reaches -99kPa or higher, then close the vacuum valve and vacuum pump.

[0032] (5) Record the vacuum pressure P1 and time t1, immediately open the equivalent leak hole, the pressure gradually rises, and after a certain time interval, record the pressure P2 and time t2. Calculate the average leakage rate Q according to formula (3). average Q represents the leakage rate value under any vacuum pressure within the range of P1 to P2.

[0033]

[0034] in:

[0035] Q average Average vacuum leakage rate, in Pa·m 3 / s;

[0036] V: Volume of the vacuum container, in meters (m³) 3 ;

[0037] t1: The start time of the test, in seconds;

[0038] t2: The time when the test ends, in seconds;

[0039] P1: Relative vacuum pressure at the start of the test, in Pa;

[0040] P2: Relative vacuum pressure at the end of the test, in Pa.

[0041] ΔP: Pressure difference relative to vacuum level;

[0042] The equivalent perforation diameter of the present invention is 0.3mm to 0.8mm, and it is made of rigid material. The two ends are located inside and outside the vacuum pressure forming device, respectively.

[0043] Preferably, P1 is the highest vacuum level at the start of the test, and P2 is the relative vacuum pressure measured after a certain period of time after the equivalent leak is opened, which is -90kPa to -70kPa; the absolute value of P1 is greater than the absolute value of P2.

[0044] More preferably, P1 is the highest vacuum level at the start of the test, -99 kPa.

[0045] More preferably, the relative vacuum pressure difference ΔP is between 10 kPa and 30 kPa.

[0046] Preferably, the volume of the vacuum container is between 10,000 mL and 30,000 mL.

[0047] This invention calculates the average leakage rate Q of a large-pressure-difference vacuum by testing a wide range of vacuum pressure variations. average It replaces the vacuum leakage rate value Q at any vacuum pressure within the vacuum pressure range, with a maximum relative error of less than 1%. It solves the problem of distortion of the vacuum leakage rate value at a certain vacuum pressure caused by the nonlinear response of the vacuum pressure gauge. Moreover, it does not require a large vacuum container volume, and ordinary vacuum pressure gauges can meet the testing requirements, making it convenient and practical. Attached Figure Description

[0048] Figure 1 The vacuum leakage rate of different orifice diameters varies with vacuum pressure.

[0049] Figure 2 This is a schematic diagram of the present invention;

[0050] in:

[0051] Figure 1 In the diagram, a) aperture is 0.3 mm; b) aperture is 0.6 mm; c) aperture is 0.8 mm.

[0052] Figure 2 In the diagram, 1—flat glass, 2—vacuum membrane, 3—sealing strip, 4—composite material, 5—equivalent leak, 6—vacuum container, 7—evacuation pipe, 8—vacuum pressure gauge, 9—evacuation valve, 10—vacuum pump, 11—vacuum bag pressure device. Detailed Implementation

[0053] The following detailed embodiments further illustrate the above-described content of the present invention, but should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Unless otherwise specified, the following embodiments are all implemented using conventional prior art.

[0054] Example 1

[0055] like Figure 2As shown:

[0056] A pre-formed composite layer 4 is laid on the flat glass 1, and the vacuum membrane 2 is sealed to the flat glass 1 with vacuum sealing strip 3 to form a composite material vacuum bag pressure device 11. The device has an air extraction interface.

[0057] An equivalent leak hole 5 with a diameter of 0.3 mm is inserted into the vacuum sealing strip 3. Press firmly to ensure that the outer wall of the equivalent leak hole 5 is fully bonded and sealed with the vacuum sealing strip 3 to prevent air leakage.

[0058] The vacuum bag pressing device, vacuum container 6, vacuum valve 9, and vacuum pump 10 are connected by a vacuum extraction pipe 7. The vacuum container has a volume of 10000mL and is equipped with a GJM-120 vacuum pressure gauge 8.

[0059] The equivalent leak 5 was sealed, vacuum valve 9 was opened, and the system was evacuated to -99 kPa. Vacuum valve 9 was then closed, and the change in vacuum pressure over time was observed and recorded. The blank leak rate of the system was calculated according to formula (3), and the result was 0.002 Pa. 3 / s, the system's sealing meets the test requirements, ready for testing.

[0060] Reopen vacuum valve 9 and vacuum pump 10 to evacuate the system until the vacuum level reaches above -99 kPa, then close vacuum valve 9 and vacuum pump 10.

[0061] Record the vacuum pressure P1 and time t1, immediately open the equivalent leak hole 5, and automatically record the change of vacuum pressure over time using the testing software. When the vacuum pressure P2 reaches -70 kPa, record the time t2, and calculate the average leak rate Q according to formula (3). average Simultaneously, calculate the leakage rate Q under various vacuum pressures, and calculate Q... average The error between Q and Q. See Table 2.

[0062] Table 2 Leakage Rate Values ​​in Example 1

[0063]

[0064] Example 2

[0065] Following the method in Example 1, the average leakage rate Q was tested when the vacuum pressure reached -80 kPa. average The error between the value and the leakage rate Q under various vacuum pressures was calculated. See Table 3.

[0066] Table 3 Leakage rate values ​​in Example 2

[0067]

[0068]

[0069] Example 3

[0070] Following the method in Example 1, the average leakage rate Q was tested when the vacuum pressure reached -90 kPa. average The error between the value and the leakage rate Q under various vacuum pressures was calculated. See Table 4.

[0071] Table 4 Leakage rate values ​​in Example 3

[0072]

[0073] Example 4

[0074] Example 4 differs from Example 1 in the following two aspects: (1) the equivalent leak hole 5 has a diameter of 0.6 mm; (2) the vacuum container 6 has a volume of 20,000 mL, and the rest are identical. The average leak rate Q was tested when the vacuum pressure reached -70 kPa. average The error between the leakage rate value Q and the value under various vacuum pressures was calculated. See Table 5.

[0075] Table 5 Leakage rate values ​​in Example 4

[0076]

[0077]

[0078] Example 5

[0079] Example 5 differs from Example 1 in the following two aspects: (1) the equivalent leak hole 5 has a diameter of 0.8 mm; (2) the vacuum container 6 has a volume of 30,000 mL, and the rest are identical. The average leak rate Q was tested when the vacuum pressure reached -70 kPa. average The error between the leakage rate value Q and the leakage rate value Q under various vacuum pressures was calculated. See Table 6.

[0080] Table 6 Leakage rate values ​​in Example 5

[0081]

[0082]

[0083] The above embodiments and their data further confirm that the average leakage rate (Q) of a large-pressure-difference vacuum can be calculated by testing a large range of vacuum pressure variations using the method of the present invention. average This method replaces the vacuum leakage rate (Q) at any vacuum pressure within the specified vacuum pressure range. Its maximum relative error is less than 1%, which solves the problem of distortion of the vacuum leakage rate at a certain vacuum pressure caused by the nonlinear response of the vacuum pressure gauge. Furthermore, it does not require a large vacuum container volume, and ordinary vacuum pressure gauges can meet the testing requirements, making it convenient and practical.

Claims

1. A method for testing the equivalent leakage rate of vacuum perforation in a composite material vacuum pressure forming process, characterized in that, The steps include: (1) Construct a test system for the equivalent leakage rate of composite material vacuum pressure forming, including: 1) A pre-formed composite layer is laid on the flat glass, and the vacuum membrane is sealed to the flat glass with vacuum sealing strips to form a composite material vacuum bag pressing device. The device has an air extraction interface. 2) Insert the equivalent leak hole into the vacuum sealing strip and press firmly to ensure that the outer wall of the equivalent leak hole is fully bonded and sealed with the vacuum sealing adhesive to prevent air leakage; 3) Connect the vacuum bag press device, vacuum container, vacuum valve, and vacuum pump using a vacuum extraction pipe; (2) Seal the equivalent leak, turn on the vacuum valve and vacuum pump, evacuate the system until the vacuum level reaches above -99kPa, and then turn off the vacuum valve and vacuum pump. (3) Check the system's airtightness. The blank leakage rate should not exceed 10-3 Pa·m3 / s. Otherwise, check and eliminate any leaks in the system. (4) Reopen the vacuum valve and vacuum pump to evacuate the system until the vacuum level reaches -99kPa or higher, then close the vacuum valve and vacuum pump. (5) Record the vacuum pressure P1 and time t1, immediately open the equivalent leak hole, the pressure gradually rises, and after a certain time interval, record the pressure P2 and time t2. Calculate the average leakage rate Q according to formula (3). average Q represents the leakage rate value under any vacuum pressure within the range of P1 to P2; in: Q average Average vacuum leakage rate, in Pa·m 3 / s; V: Volume of the vacuum container, in meters (m³) 3 ; t1: The start time of the test, in seconds; t2: The time when the test ends, in seconds; P1: Relative vacuum pressure at the start of the test, in Pa; P2: Relative vacuum pressure at the end of the test, in Pa; ΔP: Pressure difference relative to vacuum.

2. The method for testing the equivalent leakage rate of a composite material vacuum pressure forming process according to claim 1, characterized in that, The equivalent leakage hole has a diameter of 0.3mm to 0.8mm and is made of a rigid material. The two ends are located inside and outside the vacuum pressure forming device, respectively.

3. The method for testing the equivalent leakage rate of a composite material vacuum pressure forming process according to claim 1, characterized in that, P1 is the highest vacuum level at the start of the test, and P2 is the relative vacuum pressure measured after a certain period of time after the equivalent leak is opened, ranging from -90 kPa to -70 kPa; the absolute value of P1 is greater than the absolute value of P2.

4. The method for testing the equivalent leakage rate of a composite material vacuum pressure forming process according to claim 3, characterized in that, P1 represents the highest vacuum level at the start of the test, which is -99 kPa.

5. A method for testing the equivalent leakage rate of a composite material vacuum pressure forming process according to claim 3 or 4, characterized in that, The relative vacuum pressure difference ΔP is between 10 kPa and 30 kPa.

6. The method for testing the equivalent leakage rate of a composite material vacuum pressure forming process according to claim 1, characterized in that, The volume of the vacuum container is between 10,000 mL and 30,000 mL.

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