6. General characteristics of counter materials

The quality of the counter-material or rotor is related to that of the lining, and the assembly must have a high coefficient of friction and above all stability, which requires a sufficiently fine structure. The rotor must withstand the mechanical stresses of braking torque transmission, have low elongation, low wear (above all, it must only wear by maintaining a suitable surface finish, without roughness or cracking), and not deform under the effect of heating (limited expansion, good conductivity, high mass capacity).

• The effect of erosion: the metal of the rotor must above all resist erosion resulting, like seizure, from the phenomenon of welding. If a silica grain of a few tenths of a millimetre is lodged in a lining firm enough to support it, on contact with the cast-iron rotor, the grain is covered with light metal particles, and the...