【O-ring】Material analysis of the sealing ring

       What are the materials of the sealing ring, and what are their advantages and disadvantages?

       The melting point of PTFE is 327℃, the density is 2.18-2.3g/cm3, and the Shore hardness is D50-65. It has excellent chemical stability and self-lubrication. It is the most widely used and most abundant variety of fluorine-containing plastics. Excellent comprehensive properties, such as: high and low temperature resistance, corrosion resistance, aging resistance, non-adhesion, high insulation, high lubrication, non-toxic. However, PTFE has poor creep resistance, poor wear resistance, and large expansion coefficient of products, so it is usually necessary to improve these shortcomings by filling and modification. Commonly used fillers are copper powder, carbon fiber, glass fiber, graphite, molybdenum disulfide, polyphenylene ester, polyether ether ketone, etc. One or more substances can be filled according to different working conditions and uses.

       PTFE has "cold flow" properties. That is, the plastic deformation (creep) of material products under long-term continuous load, which brings certain limitations to its application. For example, when PTFE is used as a gasket, the bolts are tightened so tightly that a certain compressive stress is exceeded, which will cause the gasket to "cold flow" (creep) and be crushed. These shortcomings can be overcome by adding appropriate fillers and improving the structure of parts.

      PTFE has outstanding non-stick properties, which limit its industrial application. It is an excellent release material, which in turn makes it extremely difficult to bond to other surfaces.

      The linear expansion coefficient of PTFE is 10 to 20 times that of steel, which is larger than that of most plastics, and its linear expansion coefficient changes very irregularly with the change of temperature. In the application of PTFE, if insufficient attention is paid to this aspect, it is easy to cause losses.

      The modified polytetrafluoroethylene seals filled with carbon fibers have great improvements in compression resistance, wear resistance, creep resistance and tensile strength, and at the same time increase the hardness of the products, which are suitable for rotary seals. It is used in the production of spring energy storage pan plug seals, automobile gearbox oil rings, etc. Carbon fiber may be oxidized and decomposed in strong acid environment, so it is not recommended for use in strong acid conditions.

       The PTFE hydraulic seal modified by filling glass fiber has great improvement in compression resistance, wear resistance, creep resistance and tensile strength, and at the same time improves the hardness of the product, which is suitable for rotary sealing. It is usually used to make gaskets, spring energy storage plug seals, automobile gearbox oil rings, etc. Glass fibers may decompose in alkaline environments and are therefore not recommended for use in alkaline or water-containing applications.