Vacuum sealing technology

    In vacuum sealing, air leakage is mainly due to the leakage between the metal surface and the gasket, in addition to the material itself and welding (which can be handled by leak detection). Due to insufficient sealing and compression, the flange surface roughness is not appropriate, Thermal deformation, mechanical deformation and vibration of the pipeline will cause air leakage between the gasket and the flange surface. In addition, after flange connection, due to bolt deformation, elongation and plastic deformation of the gasket after long-term use, the resilience (also called restoring force) declines, the sealing material is aging, cracks, deterioration and other factors will also cause air leakage.

    In the vacuum seal, the O-ring seal has good sealing performance. It is a compressive seal and also has the ability to self-seal, so it is a very versatile sealing material. Metal sealing structures are often used in ultra-high vacuum technology, such as soft metal (gold, silver, lead) systems, or oxygen-free copper gaskets for CF flanges, etc. In addition, the application of PTFE O-rings solves the problem of rubber The medium that cannot be used in the circle (such as strong acid, strong alkali, organic solvent and corrosive gas, etc.). At the same time, it can also be used in high temperature and high vacuum.

    In the field of low vacuum, the problems caused by vacuum are not prominent, and rubber and PTFE materials can meet the requirements of use.

    In the medium vacuum field, the permeability of the sealing material should be considered. Generally, rubber pads with good compactness and low air permeability are used. When the medium is corrosive, use Teflon gasket. Impurities and ingredients in polymer materials such as rubber and polytetrafluoroethylene volatilize in vacuum, mainly caused by molecular diffusion after pressure drops, and this diffusion is related to temperature sealing. The higher the temperature, the greater the diffusion speed.

    Satellites and spacecraft operate in high-vacuum space and are strongly radiated by cosmic rays. It is better to use Teflon gaskets. Because the amount of gas released by PTFE material under high vacuum is very small, the spectrum analysis proves that the gas released by PTFE under vacuum is water vapor, carbon dioxide, oxygen and nitrogen, etc. These gases are all from the atmosphere at room temperature. The medium adsorbed is released in high vacuum. Therefore, in order to maintain high vacuum, the PTFE mat must be pretreated before use.

    When rubber materials are used as seals, in addition to considering air permeability, there is also the problem of diffusion of adsorbed molecules. In order to eliminate the adsorbed gas of the material in the atmosphere, the gasket and the vacuum container are generally heated to 250-450°C for baking. Among several rubber pad materials, only fluororubber pad materials can be used for this baking treatment. During the baking process, water cooling treatment should be considered for the gasket part. If you want to avoid the trouble of such treatment, it is best to use metal gasket materials or other structural sealing materials as the gasket.

(huiputech)