A SIMPLIFIED WAY OF ESTIMATING A DYNAMIC LOAD RATING FOR THRUST ROLLER BEARINGS

The method of calculating the bearing capacity of rolling bearings is described in the ISO 281 standard. The calculation procedure for roller thrust bearings presented there, depending on the value of the nominal bearing angle, requires the selection of one of two formulas. Then, using the table, one reads the value of the factor depending on the geometry of the bearing components. To facilitate and speed up calculations (and perhaps also increase their accuracy), this article proposes a formula that is adapted to numerical applications, replaces linear interpolation with a proper non-linear function and allows calculations to be made for a specific value of the nominal bearing angle, but not within the range of 15°. The difference between the values calculated according to the proposed formula and the value calculated according to ISO 281 is, on average, around 3%.

Study on the Life Distribution and Reliability of Roller Based Linear Bearing

A study on the life distribution and reliability for roller guides with cage is carried out with a total number of 90 test samples in two lots (Ns = 38 and 52), and fatigue life distribution functions, such as two and three parameters Weibull distribution, and log-normal distribution are used for analyzing the test data. The basic dynamic load rating formula standardized by ISO in 2004 is also compared with the life test data in relation to the effect of crowning on both ends of the carriage raceway. Weibull slope, compatibility of distribution functions and λbm factor are also examined.

Rolling Fatigue Life and Reliability of Ball Screws

The experimental formula based on Lundberg-Palmgren theory has been used for the calculation of basic dynamic load rating of ball screws because its contact state resembles that of angular contact ball bearings. However, the compatibility between the theoretical and the actual rating life of ball screws has not been yet confirmed by life tests and probability theory. The inherent properties of ball screws are also not considered in this formula. In this paper, the authors deal with the development of ball screw life test machine and fatigue life test for ball screws with a total number of 31 test samples. Type and occurrence location of the initial failure of each sample are investigated. The fatigue life test data are analyzed with two and three parameters Weibull distribution functions. The basic dynamic load rating of the ball screws are also estimated from the life test data. The results are summarized as follows: (1) Initial failures are generated at the surface of the balls and the nut raceway as a spalling. (2) The life distribution of the test data fairy well fits three parameters Weibull distribution function. (3) Basic dynamic load rating, which is estimated by the life test, is approximately in agreement with that of manufacturer’s catalog.