In the manufacture of engines,Air tightness detectorPlaying a vital role in ensuring product quality, Chery Automobile Engine Division adoptsHai RuisiOnline airtight leak testing technology has accumulated valuable experience in the setting of leak testing parameters and the use of leak testing equipment through many years of testing applications.To manage early vehicles“Air leakage, water leakage, oil leakage” The problem of three leaks, especially the stubborn problem of three leaks in its engine, during the engine manufacturing process, manufacturers used to use“Leak detection by immersion in water”Carry out leak detection on the engine's cylinder block, cylinder head, exhaust pipe and intake pipe to find unqualified workpieces.This method cannot accurately obtain the leakage amount of the workpiece being tested, and the liquid generates tension inside the leak hole, which increases the flow resistance. This method often misses detection, and there are also problems such as the need for drying and the inability to realize automation.With the advent of air tightness leak detection equipment and the maturity of technology, problems in this area have been greatly improved.

With the improvement of casting quality, processing quality and assembly quality, as well as the application of online air-tight leak detection technology since the 1980s, the three-leakage problem of the engine has finally been completely controlled, and the engine quality has been reliably guaranteed.The online air-tight leak test using Shenzhen Hiraysi's leak detectors on cylinder block, cylinder head and other production lines can effectively avoid problems being discovered only after leak tests are performed after the assembly is assembled, thereby reducing unnecessary losses.It can effectively reduce quality problems and safety hazards caused by leakage due to lack of sealing.

In the engine block and cylinder head production line, according to the requirements for seal leakage, we at Hirays have developed professional accessory leakage testing and final airtight leak testing equipment. Some leak testing procedures are also equipped with water testing equipment as needed, which is mainly used to check and determine the leakage points of workpieces that fail the gas test. Of course, not all leakage points can be found through water testing.Here we mainly introduce the application of our company's online airtight leak testing technology in the cylinder block and cylinder head production lines.

Air tightness test principle

Air is compressible and has a low and negligible viscosity, which means that air passes through the leak 100 to 400 times faster than liquid.Air has essentially no surface tension, which makes it easier than liquid to pass through small leaks.However, a leak that allows air to pass through is not necessarily a leak for liquids.This is why it is necessary to define a maximum allowable air leakage volume when conducting leak tests using air as the medium.What people usually say about detecting leaks is to ensure the sealing and waterproofness of the product. As long as the air leaks out within the allowed range, it is okay.Because air leakage may lead to water leakage.Oil leak.In this case, the sealing, waterproofing and leakage effects we want can be achieved.

Physics research has concluded“Ideal gas”The regularity of state changes“The equation of state of an ideal gas”, that is:

PV/T=R

In the formula, P is the gas pressure, V is the volume of the gas, T is the temperature of the gas, and R is the gas universal constant, that is, a constant that is universally applicable to all gases (note: air is infinitely close to an ideal gas).

This equation shows that when the temperature is constant, after a certain period of time (generally greater than 20s), the volume of its inner cavity does not change, and if the pressure in the cavity drops by a certain value ΔP, the workpiece can be determined“There is a leak”.This is the basic principle of using gas to test the sealing performance of workpieces.The electronic air leak tester that uses this principle for leak testing has become the fastest, most effective and most practical automatic leak testing instrument to date.

Of course, whether a workpiece leaks or not is a relative concept. Each workpiece has a certain amount of air leakage.“No leakage”Doesn't exist.When we say that the workpiece has no liquid leakage, we can define an air leakage rate accordingly.We test most parts with air as the medium to ensure no liquid leakage, so we cannot define that these workpieces do not leak air or other gases.

Main parameters of air tightness test

To test the volume of the workpiece, the leak detector manufacturer needs to reasonably determine the following parameters based on the user's production line production rhythm requirements and the actual working conditions of the workpiece:

1. Test pressure

The test pressure is generally equivalent to the actual pressure of various media during engine operation.

2. Test the beat

The leakage test of the workpiece generally includes four stages, namely inflation, pressure stabilization, testing and exhaust.The time setting of each stage must first ensure that there is no leakage in the clamp, and secondly, set a long enough inflation time for testing. If the inflation time is not enough, the required detection pressure may not be reached.

Theoretically, the longer the test time, the more helpful it is to obtain accurate test accuracy, but this is not suitable for the actual needs of the production line. The beat of the leak test machine should match the overall beat of the production line while ensuring test accuracy.Additionally, using reduced-volume padding in the fixture can help speed up testing.When the test pressure of the workpiece is high, the test volume of the workpiece is large, the leakage rate of the workpiece is small, and there is pressure deformation in the sealing part of the workpiece and fixture, the test time needs to be extended to ensure the test accuracy of the leakage rate of the workpiece.

3. Leak rate

The leakage rate standards of various engine parts and assemblies should meet the requirements of the actual working conditions when the engine is running, and are closely related to the material and structure of the workpiece and the technical status of the leak detector. All parameters of Shenzhen Hiraysi's leak detector meet the requirements. If the leakage rate is too high, it will cause quality problems such as oil leakage, water leakage and air leakage in the engine. If the leakage rate is too low, it will increase the bill of materials and increase the manufacturing cost of the engine.

We can use the leak detector to back-detect the leak rate of the sample to calculate the critical point of leakage as the leak detection standard.Expressed as parameters commonly used for leak rate testing of engine parts and assemblies.

In addition, in order to ensure test accuracy, the air tightness test has certain requirements on the material selection and structural design of the test sealing element, sealing design, workpiece positioning tightening device and sealing fixture. For example: the sealing element should have no elastic creep, oil resistance and pressure resistance; sealing design helps to reduce unnecessaryUncertain factors in the sealing test; the sealing fixture must provide appropriate pressure to seal the workpiece under test. The clamping force should be about 3 times the test pressure. At the sametime, the strength of the fixture support frame must be sufficient to support this pressure, and each sealing cylinder should have a reliable guide to ensure the accurate sealing position. The fixture has no leakage on site.

Issues that should be paid attention to during air tightness testing

1. Quality of compressed air

The compressed air must be clean and dry. If water or oil is mixed into the leak tester, it will cause the precision pressure sensor to malfunction.In order to completely prevent the mixing of water and oil, it is required to install an oil mist separator and an air dryer as a pre-filter.Especially in the negative pressure operation mode, impurities are absolutely not allowed to enter the inside of the leak tester.

The stability of compressed air will also affect the test accuracy. Compressed air with a large flow rate, adjusted and higher than the test pressure (at least 105Pa higher than the test pressure) should be supplied to the pressure regulating valve, which can improve the stability of the test.

2. Cleanliness of workpiece

For workpieces that need to be tested for leakage, they should be cleaned and dried first to avoid foreign matter affecting the test accuracy or causing wear of the sealing components.When a gas test is performed on a leak hole that has experienced liquid leakage, the leakage volume will become smaller or disappear, making it difficult to measure the actual leakage volume. Therefore, in the comparative test of the leakage volume, a gas leakage test must be performed first.

3. Workpiece and ambient temperature

According to Bo-Ma's law (PV=nRT), when the volume remains unchanged, temperature changes will cause pressure changes, which ultimately affects the test accuracy.In order to ensure the testing accuracy of the leakage rate, the temperatures of the workpiece and the environment should be consistent.In the cylinder block and cylinder head production line, workpieces generally need to be heated and cleaned before being tested for leaks. To ensure that the temperatures of the workpieces and the environment are consistent, a cooling device needs to be installed at the outlet of the cleaning machine.To ensure test accuracy, a temperature compensation device can also be applied.The leak detection instrument of Shenzhen Hiraysi has a built-in temperature compensation system, which can effectively reduce leak detection errors due to various factors.

4. Requirements for testing trachea and accessories

Rigid nylon tubes with low pressure expansion and jacketed embedded joints must be used to reduce countermeasures.In order to prevent movement during a short test, the piping should be fixed as much as possible.Copper pipes and steel pipes cannot be used for piping, because these materials are easily affected by the ambient temperature and cause test errors; quick-plug connectors cannot be used because the deformation of the internal O-ring will affect the test accuracy.

5. Inspection and maintenance of leak test machine

In order to ensure the accuracy of the sealing test, in addition to the above, it is also important to perform regular inspections and maintenance of the leak test machine and ensure that the leak detector machine is in good technical condition.

In the manufacturing of engines, air tightness testing plays a vital role in ensuring product quality and is an important indicator for controlling engine quality. Therefore, the air tightness leak detector of Shenzhen Hirays Automation Technology Co., Ltd. can be used to do this“100% tested, 100% qualified”。