All bearings have temperature limits. Typically, the material weakens above a certain temperature and the bearing can no longer withstand any meaningful load or speed. Chromium steel bearings can withstand temperatures up to 150°C, while grade 440 stainless steel bearings can be used at temperatures up to 300°C if a suitable lubricant is used. Above these temperatures, ceramic materials are required.Ceramic bearings are ideal for high temperature environments such as furnace applications Full ceramic bearings.
We stock full ceramic bearings, also known as full complement bearings, suitable for temperatures above 300°C. Customers can also use them at high temperatures below this limit, in which case problems may arise with the lubricant, for example, due to contamination. Our full complement ZrO2 full ceramic bearings can be used at temperatures up to 400°C, while our full complement Si3N4 bearings have been successfully used at temperatures in excess of 800°C. It is impossible to provide grease or oil suitable for these temperatures, but luckily our full ceramic bearings can operate without lubricant. This is also an advantage in high temperature vacuum applications. Both types of full ceramic bearings maintain good strength up to their upper temperature limits.
ZrO2 or zirconia has a similar thermal expansion rate to steel, so attention should be paid to the internal clearance of the bearing to ensure adequate clearance at the highest operating temperature. This is less of an issue with silicon nitride due to its very low thermal expansion, but calculations should still be made to ensure that the bearing has sufficient residual clearance. This low expansion should be taken into account when considering shafts and housings for use with Si3N4 bearings at elevated temperatures. These fits can change significantly if the shaft or housing is made of a material with a higher coefficient of expansion, such as 316 stainless steel.
Our all-ceramic bearings can be equipped with ball cages and seals made of PEEK or PTFE, but they limit the maximum temperature to about 250°C. It may be preferable to use looser radial clearance at high temperatures, especially when the inner ring temperature may be higher than the outer ring temperature, as this will reduce the radial clearance of the bearing. Our high temperature ceramic bearings come standard with a looser C3 radial clearance.
