However, it is found that the elastoplastic deformation ability and stability of PTFE under temperature change are still not very ideal, and there is a large cold flow trend; At the same time, since the operating pressure of pneumatic ball valve varies widely, the lip seal seat made of polytetrafluoroethylene as the sealing material is still prone to leakage under low pressure conditions or in long-term use. The way to solve this problem is to use a combined seal seat composed of an elastic expansion ring and a PTFE lip seal seat. It can rely on the good elastic-plastic deformation ability of the metal elastic expansion ring, enhance its overall elastic-plastic deformation ability and compensation ability, and improve the sealing ability of the pneumatic ball valve.

Compared with other welding methods, TIG welding has the following characteristics:
(1) Argon is insoluble in metal and does not react with metal. The tetrafluoro compensator can effectively isolate the air around the welding area. During TIG welding, the arc can also automatically clean the oxide film on the surface of the workpiece. Therefore, it is possible to weld nonferrous metals, stainless steels and various alloys that are easy to be oxidized, nitrided and chemically vivid and are not easy to be welded by other welding methods.
(2) Good welding process performance. The arc can be extinguished stably even under very small welding current; No spatter, no slag, beautiful weld formation; The heat source and welding wire can be controlled separately, so the heat input is easy to adjust, especially suitable for welding thin plates and ultra-thin plates; It can stop welding at various positions and is easy to complete mechanized and automatic welding.
(3) The ability of tungsten electrode to carry current is poor. Excessive current will cause tungsten electrode condensation and evaporation, and its particles may enter the molten pool to form tungsten inclusions. Therefore, TIG welding uses low current, shallow weld penetration, low deposition speed and low consumption rate.
(4) As inert gas is more expensive and costs more than other welding methods, it is mainly used for welding products with higher requirements.
(5) The request for workpiece liquidation is high. As inert gas maintenance is used, there is no metallurgical deoxidation or dehydrogenation. In order to prevent defects such as pores and cracks, oil stains and rust on the workpiece must be removed strictly before welding.
(6) The intensity of ultraviolet ray generated by argon arc welding is 5~30 times that of shielded metal arc welding. Under ultraviolet radiation, oxygen molecules and atoms in the air collide with each other to generate ozone, which is harmful to welders. In addition, the use of radioactive tungsten electrodes in argon tungsten arc welding will also be harmful to welders. At present, the cerium tungsten electrode that has been applied is less harmful to welders.
(7) The ability to resist wind is poor, especially the ability to resist lateral wind.