The sintering process of polytetrafluoroethylene is composed of three stages: heating, heat preservation and cooling. Extrusion Molding is that polytetrafluoroethylene resin is added into the material cavity of the extruder to pressurize, and then it is extruded into the mouth mold to form dense pipes, bars and other products, and then it is sintered and cooled to make products with certain specifications. The characteristics of extrusion molding are continuous molding, which is the continuous molding process. Isobaric forming, also known as hydraulic forming, is used to manufacture sleeve, storage tank, hemispherical shell, large circular plate, tower column, circular tube of PTFE with large volume, large blank and square billet for cutting large sheet metal, etc., and also to manufacture three-way elbow, guide tube and other products with complex shape of the whole PTFE lined composite structure.
Polytetrafluoroethylene has soft mechanical properties and very low surface energy.
1. High temperature resistance: long-term use temperature 200 ~ 260 ℃;
2. Low temperature resistance: soft at - 100 ℃;
3. Corrosion resistance: resistant to aqua regia and all organic solvents;
4. Weather resistance: aging life in plastics;
5. High lubrication: small and medium friction coefficient of plastic (0.04);
6. Non adhesion: it has a small surface tension of solid materials and does not adhere to any substance;
7. Non toxic: with physiological inertia; excellent electrical performance, it is an ideal C-class insulation material. A thick layer of newspaper can block 1500V high voltage; it is smoother than ice.
The isobaric molding of PTFE has the characteristics of simple equipment, fast production, simple mold structure, easy operation, uniform compression of products, good quality and resin saving. Molding is a common method of PTFE. Some products with simple shape, such as plate, bar, sleeve, film blank and base plate, can be molded. The molding method basically consists of four steps: mixing, pre molding, sintering and cooling. That is to say, at room temperature, polytetrafluoroethylene is shaped into dense preforms, which are heated above the melting point, so that it changes from crystalline phase to amorphous phase, forming dense, continuous and transparent elastomers, and in the process of changing into crystalline phase through cooling.
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