The fundamental equation is simple, but using the “Co- Efficient of Friction” (CoF) correctly is less obvious.

In scientific terms a materials CoF is the ratio between the mass (load) of a part and the force required to slide it over another surface.

In the case of thermoplastics, the mating surface is normally steel. One thing that is often ignored in assessing a CoF value is the conditions under which the material will be operating. Numerous factors influence the CoF; therefore, there is no one value of CoF for a material.

It is true that there are typical values. These unqualified values can be useful where they are used to compare materials. But for a true value of CoF to be established for a material, the conditions under which the material will be working needs to be specified – otherwise the number has little true value. Major problems can arise when the CoF values, without any qualification, are used for engineering calculations.