The working temperature of the lubricating part is an important basis for selecting grease. The typical component that uses grease is a rolling bearing. As far as the relationship between bearing temperature and grease life is concerned, every 10-15 ° C increase in bearing temperature reduces the grease life by about 1/2. Generally, the temperature of the outer ring of the bearing is about 15 ° C lower than the temperature of the inner ring. The temperature of the bearings working at low and medium speeds (3000-5000r / min) is similar to the temperature of the internal medium.
For machine bearings used indoors, such as machine tools, intermittently started motors, hand tools, instruments and precision machinery, the general operating temperature range is 10-50 ° C. For transportation machinery, construction machinery, agricultural machinery and other outdoor working mechanical bearings, the general working temperature changes with changes in atmospheric temperature. Atmospheric temperature changes in most areas of China from -40-40 ° C. Increasing load, accelerating speed, increasing ambient temperature, overfilling grease, and long-term continuous operation all cause the rolling bearing temperature to rise. For example, 240 bearings working at a neck load of 1470N (150kgf) and a speed of 8000r / min can reach a temperature of 40-70 ° C. For wheel bearings of trucks traveling along the avenue, the temperature can reach 40-80 ° C. Large generator bearings can reach temperatures of 89-90 ° C, and rolling bearings such as aircraft landing gear and high-temperature motors can reach 150-200 ° C or higher.
Considering the temperature resistance of grease, not only the dropping point of the grease, but also the type of base oil, oxidation resistance, evaporation performance and so on. The maximum temperature of 40-50 ° C should be mineral oil calcium-based grease or lithium-based grease; the maximum temperature of 100-120 ° C should be mineral oil lithium-based grease or mineral oil composite soap-based grease; the maximum temperature of 150 ° C should be mineral oil or synthetic hydrocarbon Lithium-based, aluminum-based or barium-based greases for oils; maximum lithium-based, polyurea, bentonite or amide greases should be selected for ester oils, synthetic hydrocarbons, and alkyl silicone oils at a maximum temperature of 180-200 ° C; maximum temperatures of 250 ° C should be selected Phenyl silicone oil, perfluoropolyether urea-based grease or fluorine-containing grease; the highest temperature of 300 ℃ should be selected from high phenyl silicone oil boron nitride grease or silicone grease.
The above is the case of high temperature, and the working temperature of the lubricating part is lower in some cases. Generally, the temperature is below -30 ° C. Synthetic oil grease must be used, especially some miniature bearings for instruments, and the starting torque is small. Special attention should be paid when selecting grease. The minimum temperature limit for synthetic oil grease is -80 ° C.