Polytetrafluoroethylene (Teflon or PTFE),commonly known as the “plastic king”, is a polymer compound made of tetrafluoroethylene by polymerization, with excellent chemical stability, corrosion resistance, sealing, high lubrication non-viscosity, electrical insulation and good anti-aging endurance.

  PTFE is easy to cold flow and creep under pressure and high temperature, so it is generally used for low pressure, medium temperature, strong corrosion and do not allow pollution of the medium, such as strong acid, alkali, halogen, medicine and so on. The safe operating temperature is 150℃ and the pressure is below 1MPa. Filled PTFE strength will increase, but the use temperature can not exceed 200℃, otherwise the corrosion resistance will decrease. The maximum use pressure of PTFE packing is generally not more than 2MPa.

  Due to the increase in temperature, the material will creep, resulting in a significant decrease in seal pressure. Even if the temperature is suitable, with the extension of time, the compression stress of the sealing surface will decrease, resulting in “stress relaxation phenomenon”. This phenomenon will occur in all kinds of gaskets, but the stress relaxation of PTFE pad is more serious, and should be vigilant.

  The friction coefficient of PTFE is small (compression stress is greater than 4MPa, the friction coefficient is 0.035~0.04), and the gasket is easy to slip outward when pre-tightening, so it is best to use the concave and convex flange surface. If the flat flange is used, the outer diameter of the gasket can be contacted with the bolt to prevent the gasket from sliding outside.

  Because the glass lining equipment is sintered after spraying a layer of enamel on the metal surface, the glaze layer is very brittle, coupled with uneven spraying and glaze layer flow, the surface flatness of the flange is poor. The metal composite gasket is easy to damage the glaze layer, so it is recommended to use the core material made of asbestos board and rubber PTFE packing. The packing is easy to fit with the flange surface and resistant to corrosion, and the use effect is good.

  There are many factories in the temperature, pressure is not high in the strong corrosive medium, the use of asbestos rubber plate wrapped PTFE raw material belt, for often disassembled manholes, pipes. Because the production and use are very convenient, quite popular.