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Method of revising the rated life of motor bearings

by:JNSN     2021-12-18
The formula (2) expresses the basic rating life (L10) with a reliability of 90%. Depending on the application, a high reliability life with a reliability higher than 90% is sometimes required. In addition, the use of special materials can sometimes extend the life of motor bearings, and even the difference in use conditions such as lubrication can also affect the life of the bearings. Considering the above factors, the life after the basic rating life is modified is called the modified rating life, which can be calculated by equation (8). L nau003da1a2a3 (8) L 10: basic rating life, 106 revolutions (reliability is 90%) a1: reliability coefficient.. Refer to (1) item a2: bearing material coefficient. Refer to item (2) here, L na : Revise the rating life, the reliability is 100-n% (that is, the failure rate is n%) after considering the bearing characteristics and use conditions and other factors. a 3: Bearing service condition factor. Refer to item (3) [Remarks] When selecting bearing size with reliability higher than 90%, special attention should be paid to the strength of shaft and housing. (1) Reliability coefficient a 1 When calculating the modified rated life with a reliability coefficient of not less than 90% (that is, the failure rate is not more than 10%), select the coefficient according to Table 6. Table 6: Reliability factor a 1 Reliability,% Lna a190 L10a 195 L5a 0.6296 L4a 0.5397 L3a 0.4498 L2a 0.3399 L1a 0.21 When the lubricant kinematic viscosity decreases during operation, the ball bearing is less than 13mm2/s{13cSt}Roller bearing is less than 20mm2/s {20cSt} When the rotation speed is particularly low, dmn: The product of the rolling element pitch circle diameter and the rotation speed is less than 10000mm rpm. When impurities are mixed in the lubricant, the relative tilt of the inner ring and the outer ring is large. Note] When the bearing is used at high temperature, the hardness decreases, The basic dynamic load rating must be corrected (refer to Table 4) (2) Material coefficient a2 Depending on the bearing material (steel type, quality), manufacturing process and design, bearing characteristics related to life may change, then use the coefficient a2 is corrected. When high-quality vacuum degassed steel is used or there are very few inclusions in the steel, a2>1. For conventional bearing materials, a2u003d1. (3) Use condition factor a3 When bearings are used under conditions that directly affect their life (especially lubrication conditions), use factor a3 for correction. When the lubrication conditions are normal, a3u003d1, and when the lubrication conditions are particularly good, a3>1 can be used. But under the following conditions, take a3<1.
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