Inspection of Bearings

Bearing Cleaning

When bearings are inspected, first record the appearance of the bearings and check the amount and condition of the residual lubricant. After the lubricant has been sampled, the bearings should be cleaned. In general, light oil or kerosene may be used as a cleaning solution.

Dismounted bearings should first be given a preliminary cleaning followed by a finishing rinse. Each bath should have a metal net to submerge the bearings in oil without touching the sides or bottom of the tank. If the bearings are rotated with foreign matter in them during preliminary cleaning, the raceways may be damaged. Lubricant and other deposits should be removed in the oil bath during an initial rough cleaning with a soft brush or similar.

After the bearing is relatively clean, give it a finishing rinse. The finishing rinse should be performed carefully by rotating the bearing while keeping it immersed in rinsing oil. Always keep the rinsing oil clean. 

Inspection and Evaluation of Bearings

After being thoroughly cleaned, examine the condition of bearing raceways and external surfaces, the amount of cage wear, the increase in internal clearance, and degradation of tolerances. Carefully check these points and examine for possible damage or other abnormalities to determine if the bearing can be reused.

For small, non-separable ball bearings, hold the bearing horizontally in one hand, and then rotate the outer ring to confirm that it turns smoothly. Separable bearings such as tapered roller bearings may be checked by individually examining their rolling elements and the outer ring raceway.

Large bearings cannot be rotated manually; however, the rolling elements, raceway surfaces, cages, and contact surface of the ribs should be carefully examined visually.

The more important a bearing is, the more carefully it should be inspected. The determination to reuse a bearing should be made only after considering the degree of bearing wear, the function of the machine, the importance of the bearing in the machine, operating conditions, and the time until the next inspection.

However, if any of the following are true, reuse is not possible and replacement is necessary:

     (a) Cracks exist in the inner or outer rings, rolling elements, or cage.
     (b) Flaking is present on the raceway or rolling elements.
     (c) There is significant smearing of the raceway surfaces, ribs, or rolling elements.
     (d) The cage is significantly worn or rivets are loose.
     (e) Rust or scoring is present on the raceway surfaces or rolling elements.
     (f) Significant impact or brinell traces exist on the raceway surfaces or rolling elements.
     (g) There is significant evidence of creep on the bore or periphery of the outer ring.
     (h) Discoloration by heat is evident.
     (i) Significant damage to the seals or shields of grease-sealed bearings has occurred.