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Causes and remedies for deep scratches and drag marks on contact surfaces of rolling bearings

by:JNSN     2022-03-13
In addition to localized fractures, cracks and other pits on the raceway or rolling element surface, there is often extensive surface damage resulting from wear caused by rolling bearing sliding. In addition to service conditions, the degree of damage is inherently affected by the viscosity and cleanliness of the lubricant. Wear phenomena due to poor lubrication: The contact surfaces are dull and rough, see Figures 28 and 66. The abrasive substance darkens the color of the lubricant; when a brass cage is used, the color of the lubricant turns yellow. Grease also hardens. In many cases, however, moisture reduces the consistency of the lubricant and makes it thinner. Wear results in reduced preload or increased bearing clearance. If foreign particles are the cause of wear, there will be severe scratches on the surface of the rolling elements, see Figure 67. Under unfavorable conditions, the raceways of FAG rolling bearings experience uneven wear in their circumferential direction. The raceway surface is striped, see Figures 68 and 69. This wear leads to fatigue failure, please refer to chapter Fatigue caused by wear. Reason (1): Contamination of lubricant film (fine hard particles such as dust, or water) that cannot be carried Rolling contact mode 66: Worn, rough raceways 67: Wear marks are first detected on the rolling element surface Remedy: Use a lubricant with a higher load-carrying capacity, e.g. with a higher viscosity lubricant or shorten the lubricant with EP additives 433.3.4.2 Scratching on the outer diameter of the rolling elements: Circumferential dents in the contact area of u200bu200bthe rolling elements. There are parallel circumferential traces on the rollers, see Figures 70 and 71, and balls often show a ball of yarn, see Figure 72. Not to be confused with edge traces (see section The edge of the track formed by the edge running is smooth due to plastic deformation, while the scratch has sharp edges. Hard particles are often embedded in the cage pockets, causing galling, see Figure 73. Reason (2): Contaminated lubricant; hard particles are embedded in the cage pockets and act like abrasive particles on the grinding wheel Remedy: Ensure clean installation conditions Improve sealing and filtering lubricants 44 Evaluation of removed bearings Running characteristics and damage Rolling contact mode 72: Scratches on the ball surface like wool balls 73: External particles embedded in the beam of cylindrical roller bearings Cage Slip marks Phenomenon: Rolling elements slip, especially large and heavy rollers, Such as full complement bearings. Slip roughens raceways or rolling elements. Material often builds up with drag marks. Usually not evenly distributed on the surface but in the form of dots, see Figures 74 and 75. Minor pitting is often found, see section Fatigue due to poor lubrication. Reason (3): When the load is too low and the lubrication is poor, the rolling elements slip on the raceway. Sometimes also because the load-bearing area is too small, the rollers decelerate rapidly in the cage pockets in the non-load-bearing area, and then accelerate sharply when entering the load-bearing area. Speed u200bu200bchanges rapidly. Remedial measures: Use a bearing with low load capacity. Bearing preload, such as using a spring to reduce bearing clearance, also ensure sufficient load to improve lubrication scratching phenomenon: For separable cylindrical roller bearings or tapered roller bearings, The rolling elements and raceways are missing material parallel to the axis and equidistant from the rolling elements. Sometimes there are several sets of marks in the circumferential direction. This trace is usually found only in the circumferential direction of about B/d rather than the entire circumference, see Figure 76. Reason (4): When installing a single ferrule and a ferrule with rolling elements, it is not aligned and rubs against each other. It is especially dangerous when moving components of large mass (when the thick shaft 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 Avoid misalignment If possible, install components with a slow turn.
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