The full name of tetrafluoroethylene is polytetrafluoroethylene or PTFE, Teflon, etc., hereinafter referred to as tetrafluoroethylene.
In 1969, foreign countries expanded tetrafluoroethylene into a low-density material with high toughness and porosity, called expanded polytetrafluoroethylene, and was used in sealing. Expanded PTFE not only retains the original unique properties of tetrafluoride, that is, good chemical stability, low friction coefficient, aging resistance, etc., but also expands the temperature application range. Improved mechanical strength, and has some new characteristics (porosity, air permeability, hydrophobicity and extremely high toughness, etc.).
Currently, expanded graphite and asbestos are widely used as sealing materials in the industry, but they all have some problems. Due to the low strength and lack of application theory of expanded graphite, its application effect and scope are limited to a certain extent. Asbestos products not only gradually precipitate out the crystal water as the temperature increases, and the fiber strength will decrease accordingly, but the capillary fibers in asbestos are very harmful to the human body after being inhaled into the respiratory system. Some industrially developed countries have already begun to restrict the use of asbestos products, and proposed plans to find asbestos substitutes. Expanded PTFE tape is an ideal new sealing material. The main performance of the expanded PTFE tape is: the density is 0.2~0.3g/cm-3; the thermal conductivity is 0.17kcal/m*h, (at 0℃): the temperature range is -268~315℃; the pressure range is over 211kgf/cm2 (consult the manufacturer when the pressure is higher than this); natural temperature is 504±38℃; friction coefficient is 0.2; matrix tensile strength is 527kgf/cm2; elastic modulus is 3515kg/cm2. (At 73°C): Chemical compatibility is inert except for fluorine and alkaline metals.
According to the information, there are currently three new products for expanded PTFE sealing products, namely flange sealing tape (for gaskets), stem packing and GFO fiber pump packing.
The PTFE flange sealing tape is a white opaque solid ribbon with high toughness and softness. A sticky tape is attached to this ribbon, so it is called a sealing tape. It has flexibility, compressibility, and high tensile strength, that is, it does not pollute the medium or be corroded by the medium, and has excellent chemical stability. It will not deteriorate after long-term use in a wide temperature range.
The valve stem packing is made of expanded PTFE film. It also has the excellent performance of PTFE flange tape, and has a small friction coefficient. The applicable temperature is -268~288℃. It is convenient to fill and is suitable for worn valve stems. A good seal can also be achieved.