Steel is the primary mating surface used in wet brakes and clutches and can be used as the primary heat sink or the means to dissipate the energy into the ambient surroundings. In a “dry” application, the steel mating plate is the reaction surface which, in conjunction with the friction material, delivers a co-efficient of friction of up to 0.90.
In a “wet” or oil-immersed application, oil molecules are trapped between the steel mating plate and the friction material. The surface roughness of the steel mating plate and the texture of the friction material combine on shear of the oil to deliver a co-efficient of friction of up to 0.15. Surface roughness is therefore critical to the application and has to be compatible with the opposing friction material.
Steel quality and hardness are application dependent but equally important. Usually a material such as CS 70 would be typical with a minimum hardness of Roc C 25. Further processes such as induction hardening and blackodising are used as required.