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• High corrosion resistance to acids and alkalis but may degrade after prolonged exposure to hot water or steam. Studies have also been carried out on low temperature degradation of zirconia in the presence of moisture or water. There is evidence of some surface weakening but the effect on bearing performance is inconclusive and not thought to seriously affect zirconia nitride bearings at low temperatures or room temperature.
• Wide temperature range from -190°C to 400°C without cage
• Non magnetic and electrically insulating
• Lower speed and load than steel bearings
• Not suitable for low noise applications
• Higher flexural strength and lower elastic modulus than other ceramics so better for small shock loads and interference fits
• Expansion similar to chrome steel and same as 440 stainless so no problem to use with steel shaft at high temperature
• Very good corrosion resistance to water, salt water, acids and alkalis
• Very wide temperature range from -210°C to 800°C without cage
• Lower speed and load than precision steel bearings but Si3N4 balls are used in high speed hybrid bearings
• Much lighter than steel or Zirconia
• Very low thermal expansion so consider shaft/housing fits for high temperature applications
• Not recommended for shock loads or interference fits
• Best corrosion resistance of the ceramics
• Best high temperature performance up to 1600°C without cage
• Non magnetic
• Electrically conductive
• Most brittle so cannot tolerate shock loads
• Not supplied from stock
Full ceramic bearings are much more expensive than steel bearings so are normally used in environments that are too hostile for steel bearings. They have good to excellent corrosion resistance depending on the material and the chemicals encountered and are normally supplied without lubrication. They are non-magnetic and, apart from silicon carbide, are electrically insulating. Full ceramic bearings may have PTFE or PEEK retainers or be supplied as full complement type i.e. without a retainer. They can be used in very high temperatures if supplied as full complement.
As ceramics are more brittle than steel, full ceramic bearings, particularly silicon nitride and silicon carbide, are not recommended where heavy shock loads are likely due to the risk of cracking. Full ceramic bearings will accept approximately 10% to 20% of the load of a steel bearing due to the greater brittleness. The limiting speed of a full ceramic bearing is only about 25% of the speed of the same steel bearing due to the inferior roundness of the rings and greater risk of sudden failure due to the lower flexural strength compared to steel.
Using silicon nitride or silicon carbide bearings with steel shafts or housings in high temperature applications can cause fitting problems due to the large difference in expansion coefficient. Bearing damage can occur if allowance is not made for the the greater expansion of a steel shaft in a ceramic inner ring at high temperature. There is less of a problem with Zirconia as the coefficient of expansion is much more similar to steel. For more information see the section on Shaft/Housing Fit.
Silicon nitride is the most popular for the balls in hybrid bearings as it has only 40% of the density of bearing steel but is much harder giving greater wear resistance. Hybrid bearings are also capable of higher speeds due to the lower centrifugal force generated by the ceramic balls. However, due to the lower elasticity of the balls, the contact area between the balls and the raceway is smaller which causes a higher contact pressure. This can cause the raceways to wear faster. The speed increase for hybrid bearings is approximately 30-40% with adequate lubrication. Hybrid bearings can also operate better with limited lubrication but running speed should be reduced. They are also less subject to ball skidding under high acceleration with a low load.