PTFE-based materials as a group are a well known standard for seal materials, which are applied in various hydraulic equipment [1-2]. PTFE is superior with respect to chemical and thermal resistance as well as low friction. Thus, PTFE is chemically compatible with almost all media and can operate in a wide temperature range [3]. The weaknesses of virgin PTFE are the wear and deformational properties. However, these properties can be improved dramatically by incorporating suitable fillers, which makes it possible to develop PTFE-based sealing materials with overall excellent properties.

　　Glass and bronze are widely applied as fillers for PTFE under well-lubricated conditions. PTFE/Glass fiber materials have high seal efficiency but moderate extrusion strength, and require a hard counter surface in order to avoid hardware damage due to the abrasiveness of glass fibers.

　　PTFE/Bronze materials combine high extrusion resistance,high wear resistance and high seal efficiency, but in critical applications scratches can in principle be created in two different ways:

　　1) bronze is a relatively soft material but in demanding applications, a high contact temperature may lead to tribo-oxidation generating hard abrasive particles (sulphides and oxides) .

　　2) bronze particles may offer a good substrate for hard particles to attach to thereby increasing their grinding action.

　　Carbon/graphite particles and carbon fibers are widely applied fillers for PTFE under poorly lubricated conditions. Carbon/graphite is mild against the counter surface, and depending on the specific filler type, a good extrusion resistance can be achieved. However, Carbon/graphite tends to suffer from a low wear resistance. PTFE/Carbon fiber materials typically have a good wear resistance but a lower extrusion resistance relative to PTFE/Bronze. PTFE/Carbon fibers maintain a porous surface in service, giving good lubrication of the contact area but also somewhat reduced seal efficiency.

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