What is the Method of Leak Detection for Aerospace Vacuum Products?
- introduction
The development process of aerospace products involves a large number of components or parts with sealing performance requirements, even the whole product, such as the sealing cabin of manned spacecraft, satellite propellant fuel tank, hydrogen nickel battery for primary power supply on board, antenna for satellite communication, frequency standard light source for time recording and other on board instruments. The sealing performance of aerospace products is directly related to the launch success rate and on orbit service life of spacecraft. Leakage detection runs through the whole process of aerospace product design, manufacturing, key process point control, component performance, whole satellite exit, launch and operation, and is an important means to ensure the sealing performance of aerospace products.
There are many kinds of leak detection methods used in the aerospace field, which can be divided into two types: coarse detection and fine detection in terms of detection accuracy. The coarse detection is mainly used for the detection of large leaks, which is suitable for the qualitative analysis of sealing performance in the process of product development. The fine inspection is mainly used for the measurement and positioning of small leakage holes, and is suitable for the quantitative detection of product sealing performance. The fine inspection method is mainly introduced. From the measurement principle, the fine inspection can be divided into helium mass spectrometer leak detection, pressure change leak detection and original quality inspection leak detection. In the selection of detection methods, we need to consider comprehensively from the requirements of sealing performance index, volume size and structure complexity, detection safety, detection cost and other aspects. Some experts think that helium mass spectrometer leak detection method should be preferred in the leak detection of aerospace products.
- Analysis of helium mass spectrometer leak detection method
Helium mass spectrometer leak detection method is to measure the helium leakage of the tested parts by using the helium partial pressure measurement principle of helium mass spectrometer leak detector. When there is a leak on the sealing surface of the tested part, the helium gas and other components of the leak gas will leak out from the leak. After the leak gas enters the helium mass spectrometer leak detector, only the partial pressure signal value of helium in the gas will be given due to the selective identification ability of the helium mass spectrometer leak detector. On the basis of obtaining the helium signal value, the leak to helium leakage can be obtained by the method of standard leak comparison.
- Pressure change leak detection method
The leak detection method of pressure change is to measure the total leak rate of the tested product by using the pressure change of the sealed container inside the tested product.
In general, according to the state of pressure increase or decrease, the pressure change method can be divided into static pressure rise method and static pressure drop method. If the pressure before the measurement interval is less than the pressure after the measurement interval, it is called static pressure rise method, otherwise it is called static pressure drop method.
- Leak detection method of primary working medium
The original working medium leak detection is a method to measure the leak rate of the inspected part by using the working medium filled in the inspected part as the leak gas. When the original work is used for leakage inspection, the inner part of the inspected part has been filled with leakage gas before inspection, and no additional pressure charging equipment is required. If there is a leak in the tested part, the leakage gas inside the tested part will leak into the surrounding environment of the tested part through the leak. The leak gas can be introduced into the measuring sensor by means of atmospheric sampling or vacuum collection to realize the leak detection of the tested part. The sensor often used is the mass spectrometer.
In the field of aerospace products, the leak detection method of primary working medium is mainly used in the detection of satellite propellant in launch site, common bottom dangerous gas in rocket, NiMH battery and gas leakage outside the space station. However, with the development of aerospace industry, we have reason to believe that the leak detection method of primary working medium The application of this method will be more and more extensive.
- Development trend of aerospace product leakage technology
With the continuous development of space technology, especially the development of China’s manned space, the long-term work requirements of space station, lunar exploration project and deep space exploration and other space projects, it is inevitable to put forward new requirements for spacecraft sealing and leak detection technology. In the future, leakage detection technology should focus on the following aspects:
(1) Research on leak detection technology of different sealing structures. The space station is a spacecraft for long-term work. In order to ensure the long-term safe operation of the space station in orbit and the safety of astronauts, it is necessary to detect the leakage of the sealed cabin of the space station. The sealing structures of the space station that need leakage detection include: the detection of leakage inside the cabin, the detection of double static sealing structure of the space station and the detection of leakage rate outside the cabin.
(2) Leak rate detection of sealed vessel with minimum leak rate. In lunar exploration and deep space exploration, in order to ensure the authenticity of the composition analysis of the “soil” on the surface of the planet, it is necessary to encapsulate the detection sample with a minimum leakage rate, which is required to reach 10-13pa · m3 / s. In order to meet the requirements of minimum leakage rate detection, it is necessary to study the high sensitivity detection device and detection method to evaluate the sealed container.
(3) Research on leak detection technology of spacecraft sealing device in space environment. Through the ground test and seal evaluation, the leakage detection and leakage rate measurement of the sealed container with liquid medium in the space operation process are determined to ensure the long life index requirements of the spacecraft in orbit operation.
(4) New materials, structures and structures used in spacecraft seal design
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