Silicon nitride cam rollers are used in the valve train of heavy-duty diesel engines, as part of either a rocker arm assembly or a roller lifter assembly because metal rollers fail by galling and contact fatigue. The stress level of the cam rollers and valve train components has increased dramatically over recent years because of increases in the fuel injection pressure and cylinder operating pressures required to meet emission standards.




Ceradyne has developed high-volume machining techniques that allow precise formation of crowned profiles on the outer diameters of cam rollers that result in minimum contact stress distributions on the ceramic and the mating metallic component, further increasing reliability of the system.





Silicon nitride was selected as the material choice for a number of reasons: its contact fatigue resistance was superior to bearing steels; the coefficient of friction was significantly lower than a corresponding steel on steel system; and the weight was 40% that of steel which reduced the rotating moment of inertial of the rollers. The result was the elimination of significant warranty problems associated with the valve train, an increase in the cam life and the ability of engines to meet new emissions regulations.