1. General information on lubrication

Everyday experience offers many examples of friction, adhesion and wear between solid bodies: a considerable force must be exerted to slide a heavy piece of furniture across the floor, thus overcoming the friction of the furniture's feet on the floor; unmolding a pie or cake after baking can prove problematic due to the adhesion between the dough and the mold if the latter has not been properly buttered beforehand; it's the wear and tear of pencil lead (and the adhesion of graphite to paper) that makes it possible to write on a sheet of paper. Metal shaping poses similar problems:

• in wire drawing, excessive wire-die friction causes wire breakage;

• in hot forging between deep dies, the formed part can remain bonded to one of the dies.

Practitioners routinely observe a marked...