Friction, Wear, and Hardness Properties

Friction is the resistance against change in the relative positions of two bodies touching one another. If the area of contact is a plane, the relative motion will be a sliding one and the resistance will be called sliding or kinetic friction. If the material in the area of contact is loaded beyond its strength, abrasion or wear will take place. Both phenomena are affected by numerous factors such as the load, relative velocity, temperature, and type material. 

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

The frictional 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. 

The ease and economy of manufacturing gears, cams, bearings, slides, ratchets, and so on with injection-moldable TPs have 

These characteristics can be further enhanced and their applications widened by fillers, additives, and reinforcements. Compounding properly will yield an almost limitless combination of an increased loadcarrying 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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