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Analysis of the running track of the failed bearing

by:JNSN     2021-12-28
Trajectory phenomenon when a failed rolling bearing is radially overloaded: Figure 33 shows the circumferential trajectory on the two rings when radially overloaded, which can cause thermal damage under extreme conditions, see chapter 3.3.5. Reasons: The shaft/bearing seat interference is too large, the temperature difference between the inner and outer rings is too large, the bearing clearance is too small, there is an elliptical deformation track phenomenon: there are several separate track areas on the circumference of the stationary ring raceway, see Figure 34. Reason: The bearing seat or shaft is elliptical, such as circumferential deformation caused by machining or tapping a threaded hole near the bearing mating surface. The bearing seat has different stiffness in the circumferential direction and has a large interference with the outer ring. Measure the thin-walled bearings and store them vertically 23 to evaluate the running characteristics and damage of the removed bearings. Rolling contact mode 33: Deep groove ball bearing with radial over-preload. There are trajectories in the entire circumferential direction, and even ferrules that bear a point load. 34: Oval deformation of deep groove ball bearings. There are two opposite radial load zones formed on the elliptical deformed outer ring (point load) track. The abnormal trajectory determines whether the trajectory is normal or not to a large extent depends on the bearing application. For example, when the bearing is mainly subjected to radial load, there is a normal trajectory, but when the same trajectory appears in the bearing condition with axial preload, it is abnormal, which indicates incorrect bearing installation. Therefore, it is necessary to understand the bearing conditions in order to correctly evaluate the trajectory. Of course, some basic failure phenomena can usually be evaluated by trajectory. Trajectory phenomenon when lubrication is insufficient: The visible trajectory and the surface topography observed through a microscope may be related to the quality of lubrication. Under the condition of medium load and no completely separated lubricant film, dark and rough trajectories can be formed. The thinner the lubricant film, the greater the impact on the surface. For this, you can refer to an example where the surfaces are not completely separated, see Figure 28. When the load in the contact area is high, the track is bright and pressure-polished, which forms a clear contrast with the unloaded area of u200bu200bthe track, see Figure 29. Reason: Insufficient amount of lubricant in the bearing. Under the working temperature and speed, the lubricant viscosity is insufficient (see the 'Rolling Bearings' catalog, revised rating life calculation) Remedy: Improve the lubricant supply so that the viscosity of the lubricant adapts to the working conditions Use lubricants that contain effective additives Use surface-coated bearing parts When there is contamination in the bearing or lubricant, we must first distinguish the difference between solid and liquid contaminants. Phenomenon caused by solid pollutants: When external particles circulate on the raceway, they will cause pits. When observing the trajectory under a microscope, soft particles, hardened steel particles and hard gravel particles can be distinguished by the form of pits, as shown in Figures 30, 31, and 32. Extremely large and hard foreign particles have a great influence on the life of the bearing. More specific content can be found in the description of fatigue failure, please refer to the fatigue caused by the cyclic movement of external particles in chapter A large number of small and hard foreign particles can cause the contact surface to become rough, as shown in Figure 28, and accelerate abrasive wear. Evaluate the running characteristics and damage of the removed bearing. Rolling contact mode 30: pits caused by soft particles 31: pits formed by hardened steel particles 32: pits formed by hard gravel phenomena caused by liquid contamination : Water is one of the main liquid pollutants. A small amount of water can be sucked into the lubricant. It will reduce the lubrication effect and leave traces as shown in Figure 29. When there is a lot of moisture in the bearing, there will be a dim track. The pressure polishing track of fatigue damage is also caused by corrosion or overload. Please refer to chapter Causes of fatigue caused by poor lubrication: Inappropriate sealing. The installation environment is not clean. Condensate) Lubricating oil is not clean and remedial measures: To improve the sealing installation environment, clean, and clean the mating parts, if necessary, clean the entire oil system before the coating work (before the first rotation of the bearing). Trajectory phenomenon: Only the fixed-end bearing in the fixed-floating bearing configuration will have such a trajectory, as shown in Figure 35b. This trajectory is generated under the action of axial force (Figure 26). In most cases, you will find that the floating bearing also has a small axial load (preferably no). Reason: The floating function of the floating end bearing is impaired (wrong fit, radial thermal expansion, overturning, fretting corrosion) Unexpected large axial thermal expansion Remedy: Check the fit and the geometric tolerance of the mating parts, change the installation and Operating conditions Use bearings with internal axial displacement function: cylindrical roller bearings N, NU, NJ24, evaluate the operating characteristics and damage of the removed bearing. Rolling contact mode 35: Fixed-floating configuration of two deep groove ball bearings. a: The deep groove ball bearing at the working end is used as a positioning bearing, and the deep groove ball bearing at the driving end is used as a floating bearing. b: Bearing track under normal operation. The trajectory of the positioning bearing shows the characteristics of the bearing bearing the combined load, and the trajectory of the floating bearing shows that it bears pure radial load or mainly bears radial load. c: Bearing trajectory under harmful axial preload (the outer ring of the floating bearing cannot move). The trajectory of each bearing shows the characteristics of the combined load. The symmetrical trajectory of the two bearings indicates a harmful axial preload.
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