Damage to rolling bearings caused by overheating: severe discoloration of bearing components*). The raceway/rolling body has serious plastic deformation. The temperature changes drastically. The bearing has stuck several times, see Fig. 77. The hardness is lower than 58HRC. Reason: usually no longer detect failed bearings due to overheating. Possible reasons: The working clearance of the bearing is too small, especially the insufficient lubrication of the bearing at high speed. The radial preload caused by the external heat source is excessive. The operation is blocked due to the fracture of the cage. Remedial measures: Increase the bearing clearance if there is external Heat source, to ensure slow heating and cooling, that is to make the entire set of bearings evenly heated, avoid accumulation of lubricants, improve lubrication 47. Evaluate the running characteristics and damage of the removed bearings. Rolling bearing contact mode 77: The rollers on the raceway of the overheated cylindrical roller bearing have left deep adhesive impressions. *) Description of discoloration: When the bearing shows a tempered color, it is related to overheating. The brown and blue appearance is related to the temperature and the length of overheating time. This phenomenon is very similar to the phenomenon of coloring due to high lubricating oil temperature (see section 3.3.1.1). Therefore, it is not possible to judge whether the operating temperature is too high from the discoloration alone. From the discoloration area, it can be judged whether the discoloration is caused by tempering or grease: the latter usually only appears in the load-bearing area of u200bu200brolling elements and rings, while the former usually covers a large area on the bearing surface. However, the only way to determine whether there is high temperature operation is hardness testing. Bearing scratches: For separable cylindrical roller bearings or tapered roller bearings, there are missing materials on the rolling elements and raceways that are parallel to the axis and equally spaced from the rolling elements. Sometimes there are several sets of marks in the circumferential direction. Usually there is this trace only in the circumferential direction of about B/d instead of the entire circumferential direction, see Figure 76. Reason: When installing a single ferrule and a ferrule with rolling elements, they are misaligned and rubbed against each other. It is especially dangerous when moving components with large masses (when the thick shaft equipped with the bearing inner ring and rolling element assembly is pushed into the outer ring already installed in the bearing housing). Remedy: Use suitable installation tools to avoid misalignment. If possible, rotate slowly when installing the components.