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PTFE, that is Polytetrafluoroethylene, commonly known by its trade name Teflon or the Chinese nickname "Plastic King" . It is a high-performance engineering plastic comprehended for its extreme chemical inertness and extensive operating temperature range.
PTFE is called the "Plastic King" because it is virtually independent by almost any involved strong acid, strong base, or strong oxidizing agent. Even aqua regia (a powerful acid mixture that can dissolve gold) has no alternative against it. Therefore, it is an irreplaceable sealing material when dealing with highly corrosive media (for instance, concentrated sulfuric acid, hydrochloric acid, nitric acid, etc.).
Extremely Low Friction Coefficient
PTFE has one of the lowest coefficients of friction among all solid materials. Its surface is very smooth, like the ice. This results in very low operating torque when used as a sealing surface in valves (especially frequently operated ball valves and butterfly valves), and it prevents sticking to the valve disc or ball.
Although its chemical resistance is excellent, being a plastic, PTFE has two main key drawbacks:
1.Lack of Elasticity: Unlike rubber (X5, X6), it cannot be compressed and squished to fill the gaps. Therefore, pure PTFE seals often require additional structures like springs to guarantee a tight seal.
2.Cold Flow: Under the long-term and continuous high pressure, PTFE can be occurred slow plastic shaping deformation (flowing resemble a very thick liquid), potentially resulting in sealing failure.
Simply put, X5 and X6 are specific formulations of rubber, while PTFE is a plastic. Their primary differences lie in material composition, temperature resistance, suitable media, hardness and elasticity.
