A Study of Methods to Eliminate the bright Zone on Bearing Ball Tracks for Main Shafts of Machine Tools

The "Bright Zone" caused by contact fatigue wear and offen revealed on bearing ball tracks of the main shafts of precision machine tools after short running (from over ten minutes to two hours) is studied experimentally by means of a simulation tester on which the original tracks and rollers are compared with tracks or rollers coated with TiN, MoS2 and Ag by PVD and tracks treated by vacuum heat treatment after grinding. The topography of wear surfaces is observed by TEM. The experimental results are analysed theoretically and discussed deeply.The following conclusions have been made by authors: a. TiN coating can prevent tracks from forming during running proc-ess, because TiN has a high hardness and an excellent wear resistance. The main drawback of this method is that the wear of uncoated rollers matched with coated tracks increases severely, thus it results in worsening of bearing accuracy and reduction of service life. Therefore, a further research should be necessary before the application of this method to industrial production. b. MoS2 coating on tracks or rollers has excellent effects of antifriction and wear resistance. "Bright Zone" is not found on MoS: coated tracks or rollers even after running under the load which is higher than that in the normal work conditions of machine tools. c. Vacuum heat treatment can remove degenerate layers caused by grinding and increase hardness and wear resistance of track surfaces.The deformation after treatment is smaller than that after quenching under conditions of co mmonprotective atmosphere. This method is able to keep machining allowances and correct dimensions, therefore it is an effective method to eliminate the "Bright Zone" on bearing ball tracks for main shafts of machine tools.