Causes and meanings of rolling trajectories of failed bearings
Regardless of whether the rolling bearing fails or not, marks will appear on the contact surface between the ring and the rolling element for each type of bearing that has been worked. These marks are produced when the surface structure produced during processing becomes rough or smooth during operation. Small pits produced by the circulation of very small external particles are also one of the characteristics. From these traces, conclusions can be drawn about the quality of lubrication, the cleanliness of the lubricant, the direction of the load, and the distribution of the load in the bearing. Normal track: If the lubricating oil film can sufficiently separate the rolling elements from the raceway, the rolling elements rotating under load will leave a bright track on the raceway. However, each form of trajectory is largely related to the brightness of the surface, but it should be possible to identify almost all machining marks, especially with a magnifying glass and a microscope (compared to the non-contact area at the edge of the raceway!). Individual pits caused by small foreign particles are inevitable. When the lubrication is quite good, those traces can only indicate the location of the load zone in the bearing, see Figure 23. When the temperature is above about 80 °C, the raceways or rolling elements usually change color. It is caused by a chemical reaction between steel and lubricant or additives in the lubricant, and usually has no adverse effect on the operating life of the bearing. On the contrary: these surface characteristics usually show the anti-wear properties of additives. Usually these colors are brown or blue. However, these colors do not determine the operating temperature that causes the discoloration. Although the operating conditions are very similar, different colors are sometimes observed on the bearing rolling elements. The discoloration caused by this lubricating oil should never be confused with the tempering color caused by excessive temperature, which can be found in failed bearings, but rarely occurs, see section 3.3.5. Sometimes this kind of trace can be found in the equatorial zone of the steel ball. When the angular contact ball bearing always rotates around the same axis of rotation, such a trajectory can be found. Any such traces can not lead to a significant reduction in life related conclusions, as shown in Figure 24. 1923: Normal trajectory, the surface structure is still visible, only small dents caused by external particles 24: Steel ball with an equatorial circumferential line 25: Direction Core bearings bear radial loads, such as deep groove ball bearings. Under the action of a point load, in a bearing seat with sufficient rigidity, without radial preload, the track on the stationary ring is shorter than half of the circumferential direction of the raceway. Under the action of the circumferential load, the trajectory is distributed in the circumferential direction of the raceway. a: Outer ring point load, inner ring circumferential load b: Inner ring point load, outer ring circumferential load trajectory form is related to the external load direction and rotation state (point load or circumferential load, axial load, combined load), see figure 25 to 27. A theoretical-practical comparison can reveal important information about unexpected load conditions, such as disturbed floating bearing functions. Under the action of pure radial load, the circumferential trajectory produced on the stationary ring is mainly related to the size of the load, the size of the bearing clearance, and the rigidity of the mating parts. The larger the load, the smaller the clearance, the smaller the stiffness of the bearing seat, and the larger the trajectory of the load-bearing area. 26: Axial load of radial bearings, such as deep groove ball bearings. On the inner and outer rings, the trajectory is distributed eccentrically in the circumferential direction of the entire raceway. 27: Deep groove ball bearings are subjected to combined axial and radial loads. On the inner ring (circumferential load), there is a continuous wide track in the circumferential direction of the entire raceway. On the outer ring (point load), the trajectory of the radial load zone is wider than the trajectory of the rest of the circumference.