Methods of Correcting the Rating Life of Motor Bearings

Equation (2) represents 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 prolong the life of motor bearings, and even different operating conditions such as lubrication can affect bearing life. The life after the basic rating life is corrected taking into account the above factors is called the corrected rating life, which can be calculated by formula (8). L nau003da1a2a3 (8) L 10: Basic rating life, 106 revolutions (90% reliability) a1: Reliability factor.. Refer to item (1) a2: Bearing material factor. Refer to item (2) Here, L na : Corrected rating life, turning into a life with a reliability of 100-n% (that is, a failure rate of n%) after taking into account factors such as bearing characteristics and operating conditions. a 3: Bearing service condition factor. Refer to item (3) [Remarks] When selecting a bearing size with a reliability higher than 90%, special attention should be paid to the strength of the shaft and housing. (1) Reliability coefficient a1 When calculating the revised rated life with a reliability coefficient of not less than 90% (that is, the failure rate not greater than 10%), select the coefficient according to Table 6. Table 6: Reliability factor a1 Reliability, % Lna a190 L10a 195 L5a 0.6296 L4a 0.5397 L3a 0.4498 L2a 0.3399 L1a 0.21 When the kinematic viscosity of the lubricant decreases during operation, the ball bearing is less than 13mm2/s {13cSt} The roller bearing is less than 20mm2/s {20cSt} When the rotation speed is particularly low, dmn: The product of the pitch circle diameter of the rolling element and the rotation speed is less than 10000mm r/min. When impurities are mixed in the lubricant, the relative inclination 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, the bearing characteristics related to the life may change, and the coefficient is used in this case. a2 is corrected. When using high-quality vacuum degassed steel or steel with very few inclusions, a2>1. For conventional bearing materials, a2u003d1. (3) Use condition coefficient a3 When the bearing is used under conditions that directly affect the life (especially lubrication conditions), use the coefficient a3 to correct it. When the lubricating conditions are normal, a3u003d1 can be taken, and when the lubricating conditions are particularly good, a3>1 can be taken. But under the following conditions, take 1.