Development of a Shrink Fitter for Ceramics Bearings

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All ceramic ball bearings of Si_3N_4, type 6204, were used to examine an effects of a shrink fitter, a new machine element, on the bearing life. The shaft and the housing were made of a high Cr steel, SUJ2. The material of the cage of the ceramic bearing was stainless steel, SUS304. Two kinds of oils were used as lubricants. A rotational speed of a test machine was 7,000 rpm.The interferences between the ceramic bearing and a metal shaft, and between the ceramic and a metal housing, will increase and decrease at elevated temperature, since their coefficient of thermal expansions are different from each other. The interstice between the ceramic bearing and the metal housing can be thought to cause a large bending moment of the outer race of the bearing and lead to a failure of the outer race. If the shrink fitter of aluminum alloy, A2017, is placed at the interface between the bearing and the housing, such interstice will never appear even at the elevated temperature, because of the sufficient thermal expansion of the shrink fitter. Therefore the bending moment of the outer race, which shorten the bearing life will never exist.We confirmed the effect of the shrink fitter on the bearing life experimentally. The life of the ceramic bearing with the shrink fitter was longer than that without the shrink fitter.