The Calculation and Selection of Bearings of Increased Reliability

The drive of a machine-tool includes a reducer, whose shafts are mounted on rolling bearings. Each shaft is supported by at least two bearings. There can be four or more bearings in the reducer. Even if one of them fails, the performance of the reduction gear unit is compromised. Bearings form a system, the reliability of which determines the reliability of the drive of the machine. Until recently, reliability of bearings in the reducer was determined by the standard 90 % reliability, regardless of the reliability of the other bearings. Today, the requirements to this characteristic are considerably more demanding. The number of failures of new equipment during the first year of operation should not exceed 1 % (99 % reliability), and during the fifth year should be no more than 10% (90% reliability). To meet these requirements, the reliability of each part of the machine must be above 99 % and 90 % respectively. In this paper, the reliability of the bearings is determined using the three-parameter Weibull distribution. A systematic approach to the calculation of bearings is proposed. In accordance with the reliability of the system, the reliability of individual bearings is calculated. Then, the life of each bearing is determined depending on the load and the bearing’s reliability. The service life of the bearing system is calculated as a derivative of the life of bearings in the system. As a result, the selection of bearings of increased reliability is ensured.

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