Silicon Nitride Cam Roller

The silicon nitride ceramic cam roller system is made up of three components: a silicon nitride cam roller, a steel cam lobe, and a steel pin. Increased cylinder operating pressures and fuel injection pressures have been required as a consequence of the requirement for more efficient diesel engines and more strict emissions regulations. These situations increase the contact stresses in critical components, which can result in wear, galling, microwelding, and eventually component failure. To address these issues, different material choices are needed. Silicon nitride has unique tribological and physical characteristics (low mass coupled with high strength and resistance to contact fatigue) that enable it to be used in applications involving high contact stresses.

Features of Si3N4 Cam Rollers

◆ The steel pin is much harder than the metal system's equivalent bronze pin, making it more resistant to wear caused by unclean lubricant and other debris.

◆ Silicon nitride is a good tribological couple with steel. At both flooded and starved lubrication conditions, silicon nitride and steel show low and consistent friction.

3. The wear on the ID of silicon nitride rollers is about a factor of three to ten less than that of comparable metal rollers.

◆ The silicon nitride ceramic roller rotates easily due to the minimal wear and friction of the pin to ceramic silicon nitride roller contact, as well as the light weight of silicon nitride (60 percent lighter than metal) and resulting low rotational moment of inertia. This significantly lowers or eliminates skidding and sliding on the cam lobe, thus removing one of the primary sources of contact fatigue and wear in a metal cam roller system.

◆ Silicon nitride has a higher resilience to contact fatigue than bearing steels (see below figure). As a result, silicon nitride rollers can withstand greater contact pressures without pitting or spalling. This removes another potential point of failure in metal systems.

◆ Adhesive wear should be negligible or absent with silicon nitride-steel contacts, removing another cause of wear and contact fatigue in the metal cam roller system. Due to the change in contact with different materials, studies indicate that when a highly polished ceramic roller is employed, the wear of the metal cam is decreased despite an increase in contact stress.

◆ The crown profile of a cam roller made of silicon nitride should be sufficiently broad to keep the line contact away from the ceramic roller's edges. Contact stresses will usually be greater in a silicon nitride system than in steel for the same steel-to-steel profile, although an optimized ceramic profile may mitigate this.

Material Data Sheet

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