It has been a long time since I shared with you some knowledge about air tightness testing. Today I will tell you about several testing methods for air tightness testing.
First of all, we need to know that the principle of air tightness detection is that the product cavity is filled with gas of a certain pressure (safe and pollution-free). After reaching the set pressure value, the gas supply is cut off. After the gas pressure is stabilized for a period of time, the pressure sensor detects the attenuation of the pressure. If the attenuation exceeds the judgment threshold, the product is judged to be leaking.
However, there are various products to be tested, and of course there is more than one method for air tightness testing.So how do we choose in daily testing?
There is a little secret:
Waterproof or not, choose leaky points;
Test the breathable film and choose real water.
What are the principles and processes of these testing methods?Let the editor introduce it to you in detail~
Direct pressure principle
Here’s how it works
After pressing the instrument start button, the in-machine test action is divided into the following four steps
1. Positive pressure charging: the compressed air provided by the air compressor becomes a predetermined test pressure (such as 1 0Kpa) through the pressure regulating valve,The opened solenoid valve 6 and the opened solenoid valve 3 are filled into the sealed cavity between the test mold and the test product.After the inflation setting time is reached, the solenoid valve 6 and the solenoid valve 3 are always closed.
2. Pressure stabilization: When the solenoid valve 3 is closed, the compressed air filled into the mold fluctuates to a certain extent. At this time, a voltage stabilization time needs to be set to allow the compressed air to reach a stable state. During the voltage stabilization stage, the solenoid valves 6, 4, and 3 always remain closed. The pressure sensor continuously monitors the pressure during the stabilization process and records the pressure when the stabilization is completed
P1.
3. Test: When the pressure stabilization time is reached, enter the product leakage test stage. During the set test time, the solenoid valves 6, 4, and 3 always remain closed. The pressure sensor continuously detects and calculates the pressure change deviation △P, and displays it as the leakage value.The larger the △P value, the greater the leakage of the product.
4. Judgment:
(1)Large leakage test: When the test pressure P1 of the product is less than the set lower limit of inflation pressure, it means that the air pressure cannot be filled, the product leaks greatly, and the instrument determines that the tested product is NG;
(2) Microleakage test: When the leakage value △P of the product is greater than the set leakage upper limit, it means that the product has microleakage and exceeds the leakage acceptance standard. If the instrument determines that the product is NG;
(3) Only when the test pressure of the product P1> sets the lower limit of air inlet and the leakage value is less than the set upper limit of leakage, the instrument will determine that the product is OK.
5. Exhaust: When the test is completed, the compressed air in the mold must be evacuated, so an exhaust time must be set. During the exhaust time, solenoid valve 4 opens. The pressure sensor continuously monitors the pressure during the exhaust process.
From the above, it can be seen that to judge whether a product is qualified, firstly, it is necessary to see whether the pressure is still the set pressure value after stabilization. If not, it means that the compressed air filled leaked through the product being tested; secondly, it is necessary to see whether the leakage amount is within the specified leakage value range during the test.During the entire test, the control panel automatically opens or closes each solenoid valve, and the display screen displays the test results or receives instructions input by the operator (the instrument has both direct and indirect test functions, solenoid valve 2 is never used during the test of semi-finished products).class="dpu8C _2kCxD " style="max-width: 100%; overflow-x: visible; font-size: 18px; line-height: 30px; color: rgb(34, 34, 34); margin-top: 24px; font-family: arial; text-wrap: wrap; background-color: rgb(255, 255, 255);">
Differential pressure detection
The principle is as shown in the figure below
1. Inflation: close solenoid valve 4, open solenoid valves 6 and 3, and inflate the test mold and standard port. After the inflation time T3, close solenoid valves 6 and 3. If the inflation exceeds the set upper and lower limits, the test will stop and an alarm will be issued for air pressure over limit NG;
2. Pressure stabilization: During the voltage stabilization stage, solenoid valves 6, 4, and 3 are always closed. The differential pressure sensor detects the pressure changes from the standard port and the test port. If a large pressure difference is detected, it means there is a large leakage in the product, and the instrument stops working and alarms.
3. Test (slight leakage):When the voltage stabilization time is reached, the product leakage test phase is entered. During the set test time, the differential pressure sensor pressure PC1 is recorded before the start of the test time (after voltage stabilization). The pressure after the test is PC2, then △P is PC1-PC2, and △P is the test leakage value.The larger the △P value, the greater the product leakage.
4. Determination: When the △P from the standard port to the test port is greater than the set leakage upper limit, it means that the product has slight leakage, and the instrument determines that the test product is NG. If the leakage value is less than the set leakage upper limit, the instrument will determine that the product is OK
5. Exhaust: After the test is completed, the compressed air in the mold must be evacuated, so an exhaust time must be set. During the exhaust time, solenoid valve 3,4. Open all 4. Bleed the pressure.wrap; background-color: rgb(255, 255, 255);">
Traffic detection
The flow principle is as shown in the figure below
This structure is in the pre-inflation mode. During the air intake time, the solenoid valve 1 is first opened to pre-inflate the product to be tested. Then during the test time, the solenoid valve 2 is opened and the solenoid valve 1 is closed during the test time. At this time, the pressure from the flow sensor passes through the test. After the test is completed, the flow sensor records the flow rate.
Leakage detection
The principle of the leakage detector is shown in the figure below
1. Look at the bubbles
1Place the product.Open the cylinder cover, place the product on the tray and secure it,
2.Pressurize the water.Open the manual valve and push the adjusted pressure into the upper part of the cylinder, which is the green part in the picture!If the product leaks, the air pressure will enter the product at this time.34, 34); margin-top: 24px; font-family: arial; text-wrap: wrap; background-color: rgb(255, 255, 255);">
3 Soak in water. After pressurization, control the cylinder to let the product sink into the water along with the tray.
4 Pressure release. After the product is immersed in water, open the manual valve and remove the pressure in the upper space so that the pressure is normal pressure. If the product leaks, the pressure inside the product will be higher than the normal pressure! At this time, you can check whether the product is leaking by observing whether there are bubbles.
2. Real water test
1 Place the product: Open the cylinder cover, place the product on the tray and secure it
3 Add predetermined pressure to the water and stabilize the pressure to the set time. At this time, the product is underwater, and there are things such as
500Kpa pressure can simulate the water testing situation of the product at a depth of 50 meters underwater;
4.Weigh the pressure relief well.Open the manual valve and remove the pressure above the water.Take out the product and dry it with a rag! Then put it on a high-precision balance scale to determine whether there is any leakage.34, 34); margin-top: 24px; font-family: arial; text-wrap: wrap; background-color: rgb(255, 255, 255);">
Real water detection
Real water detection schematic
1 Exhaust: open the negative pressure drainage device and open the solenoid valve Y4, exhaust, determine whether there are scratches on the breathable film guide, whether it is attached properly, whether the silica gel is well sealed, if the exhaust pressure exceeds the upper and lower exhaust limits,The instrument will automatically stop and report NG;
2.Add water: Close the solenoid valve negative pressure drainage device and solenoid valve Y4, open the pressure regulating valve and solenoid valve Y3 to prepressurize the water storage tank, and push the water to the surface of the breathable membrane to be measured. If the pressure exceeds the upper and lower limit of adding water, the instrument will automatically stop and report NG;
3. Pressurization: The instrument continues to send signals to the pressure regulating valve to increase the pressure to the set test pressure. If the pressure exceeds the upper and lower limits of the inlet air, the instrument automatically stops and reports NG;
4. Voltage stabilization: Close the pressure regulating valve and solenoid valve Y3 to enter the voltage stabilization stage;
5. Test: The instrument starts from the moment when the voltage stabilization ends, and records the water pressure value P1, and the water pressure value P2 after the test time;
6. Judgment: The leakage mixture value (△P = P1 - P2) exceeds the upper and lower leakage limits, the instrument automatically stops and reports NG. If steps 2 to 6 are within the range, the instrument outputs the OK signal and proceeds to the last step.
7.Drainage: Open the negative pressure drainage device and solenoid valves Y4, Y5, and Y2 to drain away all the water in the mold and the test port, and empty the gas tank.The test is completed.
Okay, today’s air sealing knowledge is shared here. Here is an after-class exercise: If I want to test a waterproof breathable membrane, what kind of testing method should I use? (The answer is in the formula)
Choose the right instrument and you won’t be tired of testing! More than 2,000 customers have witnessed the development of Hirays, and more than fifty engineers are on call at any time. 7-day fast delivery is a commitment to you and a requirement for ourselves. Choosing Hirays means choosingStable and High Quality.
