Friction

Although plastics may not be as hard as metal products, there are those that have excellent resistance to wear and abrasion. Plasdc hardware products such as cams, gears, slides, rollers, and pinions frequentiy provide outstanding wear resistance and quiet operadon. Smooth plasdc surfaces result in reduced friction, as they do in pipes and valves.

The fricdonal properties of TPs, specifically the reinforced and filled types, vary in a way that is unique from metals. In contrast to metals, even the highly reinforced plastics have low modulus values and thus do not behave according to the classic laws of friction. Metal-to-thermoplastic friction is characterized by adhesion and deformation resulting in frictional forces that are not proportional to load, because friction decreases as load increases, but are proportional to speed, The wear rate is generally defined as the volumetric loss of material over a given unit of time. Several mechanisms operate simultaneously to remove material from the wear interface. However, the primary mechanism is adhesive wear, which is characterized by having fine particles of plastic removed from the surface.

Presence of this powder is a good indication that rubbing surfaces are wearing properly. Conversely, the presence of melted plastic or large gouges or grooves at the interface normally indicates that the materials are abrading, not wearing, or the pressure velocity (PV) limits of the materials may be exceeded.

The ease and economy of manufacturing gears, cams, bearings, slides, ratchets, and so on with injection-moldable TPs have led to a widespread displacement of metals in these types of applications. In addition to their inherent processing advantages, the products made from these materials are able to dampen shock and vibration, reduce product weight, run with less power, provide corrosion protection, run quietly, and operate with little or no maintenance, while still giving the design engineer tremendous freedom.

These characteristics can be further enhanced and their applications widened by fillers, additives, and reinforcements. Compounding properly will yield an almost limitiess combination of an increased load-carrying capacity, a reduced coefficient of friction, improved wear resistance, higher mechanical strengths, improved thermal properties, greater fatigue endurance and creep resistance, excellent dimensional stability and reproducibility, and the like.

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