1. Different bearing types

Any relative movement between two surfaces is slowed down by a resisting force which has the effect of :

• cause wear and tear;

• consume energy;

• generate heat that can lead to welding between surfaces.

The guiding of one part by another is subject to the difficulties described above. In fact, the problem of rotational guidance is a very old one, dating back to the history of the wheel.

The solution consisted of :

a ) firstly, to reduce friction between the two surfaces by using lubricants and guiding materials adapted to the problem, known as antifriction materials. Initially, these lubricants were oils or greases and corresponded to a so-called unctuous regime; more recently, solid lubricants...