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It’s been a long time since I shared some knowledge about air tightness testing with you. Today I’m going to tell you about several testing methods for air tightness testing.

First of all, we need to know that the principle of air tightness testing 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 air pressure stabilizes 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 there is certainly more than one method for air tightness testing.So how do we choose in daily testing?

There is a little formula:

Completely sealed, choose airtight (direct pressure& differential pressure);

Allow leakage, select flow rate;

Waterproof or not, choose the leak point;

Test the breathable membrane and choose real water.

What are the principles and processes of these testing methods?Let me introduce it to you in detail~

Direct pressure principle

The working principle is as follows

After pressing the instrument start button, the in-machine test operation is divided into the following four steps:

1. Positive pressure charging: The compressed air provided by the air compressor changes to the predetermined test pressure (such as 10Kpa) through the pressure regulating valve, and is filled into the sealed cavity between the test mold and the test product through the opened solenoid valve 6 and the opened solenoid valve 3.After the inflation set time is reached, the solenoid valve 6 and the solenoid valve 3 are closed.During the inflation phase, solenoid valve 4 and solenoid valve 2 always remain 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 phase, solenoid valves 6, 4, and 3 always remain closed.Pressure sensor - continuously monitors the pressure during the stabilization process and records the pressure when the stabilization is completed

P1。

3. Test: When the voltage stabilization time is reached, the product leakage test phase is entered. During the set test time, solenoid valves 6, 4, and 3 always remain closed.The pressure sensor continuously detects and calculates the change in pressure △P, and displays it as the leakage value. The larger the △P value, the greater the product leakage.

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 inflated, the product has a large leakage, 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 product’s test pressure P1> The instrument will determine that the product is OK only when the set air intake lower limit is set and the leakage value is less than the set leakage upper limit.

5. Exhaust: When the test is completed, the compressed air in the mold must be exhausted, so an exhaust time must be set. During the exhaust time, solenoid valve 4 opens.Pressure sensor - constantly monitors the pressure during the exhaust process.

From the above, it can be seen that to judge whether a product is qualified, firstly, it depends on whether the pressure is still the set pressure value after stabilization. If not, it means that the charged compressed air leaked through the product being tested; secondly, it depends on whether the leakage amount during the test is within the specified leakage value range.During the entire test process, the control panel automatically presses the buttons to open or close 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 testing functions. When testing semi-finished products, solenoid valve 2 is never used).

Differential pressure detection

The principle is shown in the figure below

1. Inflate: 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 be stopped and the air pressure over limit NG will be alarmed;

2. Voltage stabilization: During the voltage stabilization phase, solenoid valves 6, 4, and 3 always remain closed.The differential pressure sensor detects 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 will stop working and alarm.

3. Test (micro-leakage): When the voltage stabilization time is reached, enter the product leakage test stage. During the set test time, record the differential pressure sensor pressure PC1 before the test time starts (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. Judgment: 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 exhausted, so an exhaust time must be set. During the exhaust time, solenoid valves 3 and 4 are both opened.Bleed the pressure.

Traffic detection

The flow principle is shown in the figure below

This structure is in pre-inflation mode. During the air intake time, the solenoid valve 1 is first opened to pre-inflate the product to be tested, and then during the testbetween, open the solenoid valve 2 during the test time and close the solenoid valve 1. At this time, the pressure from the flow sensor passes through. After the test is completed, the flow sensor records the flow rate.

Note: The instrument will stop immediately only when the test pressure and flow rate exceed the sensor star range, otherwise the instrument will continue to work until the end of the test.

Leak detection

The principle of leak detection machine is shown in the figure below

1. Look at the bubbles

1 Place the product.Open the cylinder cover, place the product on the pallet and secure it,

2. Pressurize the water.Open the manual valve and rush the adjusted pressure into the upper half of the cylinder, which is the green part in the picture!If the product leaks, air pressure will enter the product.

3 Soak in water.After the pressurization is completed, the cylinder is controlled to allow the product to sink into the water along with the tray.

4 Pressure relief.After the product is immersed in water, open the manual valve to 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 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 pallet and secure it

2 Soak in water.Control the cylinder to let the product sink into the water along with the tray I

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 like

A pressure of 500Kpa can simulate the water testing situation of the product at a depth of 50 meters underwater;

4. Weigh the relief well.Open the manual valve and relieve the pressure above the water.Take the product out and dry it with a rag!Then put it on a high-precision balance scale to bear weight.Determine whether there is a leak.

Real water detection

Real water detection schematic diagram

1 Pumping: Open the negative pressure drainage device and open the solenoid valve Y4, pump air, and determine whether there are scratches on the breathable membrane guide, whether it is properly attached, and whether the silicone seal is good. If the pumping pressure exceeds the upper and lower pumping 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 for 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 air intake at this time, 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 ends;

6. Judgment: If the leakage mixture value (△P = P1 - P2) exceeds the upper and lower limits of leakage, the instrument will automatically stop and report NG. If steps 2 to 6 are within the range, the instrument will output an OK signal and proceed 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 water in the test port, empty the gas tank, and 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 and breathable membrane, what kind of testing method should I use?(The answer is in the formula)

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