teflon It is easy to be internally cooled and stress relaxed under bearing capacity and high temperature weather, so it is generally used for low pressure, normal pressure, strong corrosion and chemical substances that cannot pollute the environment, such as strong acid, strong alkali, halogen bulb, drugs, etc. The operating temperature of safety factor is 150 ℃, and the pressure is below 1MPa. Although the tensile strength of filled PTFE is higher, the application temperature is not more than 200 ℃, and the professional ability of corrosion resistance is reduced. PTFE gasket The operating pressure generally does not exceed 2MPa.
Due to the rise of temperature, the raw materials cause stress relaxation, resulting in a significant reduction of sealing pressure. Even if the temperature does not rise, with the increase of time, the thermal stress of the convex surface fastening will decrease, leading to "stress relaxation". This situation can be caused in all kinds of gaskets, but the stress relaxation of PTFE gaskets is relatively serious, so attention should be paid.
The friction coefficient of polytetrafluoroethylene is relatively small (the fastening thermal stress exceeds 4MPa, and the friction resistance is 0.035~0.04). The gasket is easy to move outward when torque is applied, and the concave convex flange surface should be selected. When selecting the flange in the plane design drawing, the gasket aperture can be contacted with the foundation screw, and the foundation screw can be used to prevent the gasket from sliding outward. As the glass lining equipment is forged after spraying a layer of glaze on the metal material surface, the glaze layer is too brittle. In addition, the uneven spraying and the fluidity of the glaze layer make the flatness of the flange surface poor. Metal composite gasket is easy to damage the glaze layer, so it is recommended to use asbestos rubber plate plus polytetrafluoroethylene gasket of silicone rubber. This kind of packing pad is easy to comply with the flange surface and is corrosion resistant.
Many factories use asbestos rubber sheets wrapped with polytetrafluoroethylene (PTFE) raw tape in the strong corrosive chemicals with low temperature and pressure, which is used for the frequently disassembled access holes and pipelines. It is very popular because of its convenient production and use.
