Generally speaking, the standard stipulates that the operating temperature of rolling bearings of general small and medium-sized motors shall not be higher than 95℃. How high a temperature can high-temperature bearings actually withstand at most? This is mainly determined by conditions such as the heat resistance temperature limits of bearing steel, cages, sealing materials, and lubricants.

The heat treatment dimensional stability temperature of bearing steel.

For common bearing steels, there is a heat treatment stability temperature. Below this temperature, the bearing maintains dimensional stability, and the hardness of the bearing steel material also meets the usage requirements. Generally, the heat treatment stability temperature of bearings is 150°C. The heat treatment stability temperatures of high - temperature bearings of various manufacturers may vary.

FAG: For bearings with an outer diameter less than 240mm, it is 150°C; for bearings with an outer diameter greater than or equal to 240mm, it is 200°C; for other bearings, it is marked with a suffix.

SKF: For deep - groove ball bearings, it is 120°C; for cylindrical roller bearings, it is 150°C; for spherical roller bearings, it is 200°C.

Temperature range of bearing cages

Generally, steel or brass cages can withstand a relatively wide temperature range. The heat - resistant temperature of steel cages can reach 300℃, and that of brass cages can reach 250℃. However, for nylon cages, they can generally withstand a temperature range of - 40℃ to 120℃.

Temperature range of seals

For sealed bearings with metal dust covers, there is no special need to consider the temperature range. For seals made of rubber materials, it needs to be considered. The operating temperature range of nitrile butadiene rubber (NBR) is - 40℃ to 120℃. It can work stably below 100℃ and work briefly at 120℃. For fluororubber (FKM), it can work stably in the range of - 30℃ to 200℃ and work briefly at 230℃.

Temperature range allowed for bearing grease

Temperature is one of the most important factors affecting lubrication life. As the temperature rises, the viscosity of the base oil of the grease decreases. Based on the grease life calculated at 70℃, for every 15℃ increase in the operating temperature, the life will be halved. The allowable operating temperature of the bearing used in the motor should be the intersection (the narrowest range) of the allowable temperature ranges of all components of the bearing. Only within this range can the safe operation of the bearing be ensured. Therefore, whether the bearing can operate in a high - temperature environment mainly depends on the selection of the lubricant, followed by the bearing seal material (only for sealed bearings) and the cage, and finally the bearing steel. In practical applications, the generally measured temperature is the temperature near the outer ring of the bearing. The maximum difference between different measurement methods and positions can be 15℃. Generally, the bearing housing has better heat dissipation conditions than the shaft, so the temperature of the inner ring and rolling elements is 5 - 10℃ higher than that of the outer ring. Therefore, when the test position is outside the bearing chamber, if the measured temperature is 95℃, the temperature at the hottest point of the inner ring may reach 120℃. This has reached the stable heat - resistant temperatures of the nylon cage, the bearing steel of the SKF deep - groove ball bearing, and the grease.