All bearings have temperature limits. Usually the material weakens above a certain temperature and the bearing can no longer handle any meaningful load or speed. Provided a suitable lubricant is used, chrome steel bearings can handle temperatures up to 150°C while 440 grade stainless steel bearings can be used at temperatures of up to 300°C. Above these temperatures, a change of material is required.
We stock full ceramic bearings with no ball retainer, also known as full complement bearings, for temperatures above 300°C. Customers also use them for high temperatures below this limit where a lubricant may pose a problem, 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 in excess of 800°C. It is not possible to provide a suitable grease or oil that will perform at these temperatures but, fortunately, our full ceramic bearings will operate without a lubricant. This is also an advantage in high temperature vacuum applications. Both types of full ceramic bearing retain good strength up to their upper temperature limit.
ZrO2, or zirconia, has a similar rate of thermal expansion to steel so care should be taken with the internal clearance of the bearing to make sure there is sufficient play remaning at the maximum operating temperature. This is less of an issue with silicon nitride due to its very low thermal rate of expansion although calculations should still be done to ensure the bearing will have sufficient residual play. This low rate of expansion should be taken into account when considering shaft and housing fits with Si3N4 bearings at high temperatures. These fits can change greatly if the shaft or housing is made of a material with a greater coefficient of expansion such as 316 stainless steel.
Our full ceramic bearings can be supplied with ball retainers and also seals made from PEEK or PTFE but these limit the maximum temperature to approximately 250°C.