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Brinelling and False Brinelling

Vibration Experts

False Brinelling on a shaft

What is the difference between Brinelling and False Brinelling? What causes Brinelling and False Brinelling? Keep reading and find out!

Brinelling

Brinelling is named after the Brinell scale of hardness.  In the Brinell hardness test, a small ball is pressed into the surface of a material using a specific amount of force. The size of the indentation that occurs in the material is a measure of its hardness. Brinelling is an indentation in the surface of a material. It is a permanent plastic deformation that occurs when the yield strength of the material has been exceeded.

Figure 1 Linear Motion Tips – Brinelling

Brinelling can occur in rolling element bearings when large static loads cause the balls or rollers to create indentations on the race. These are usually spaced the same distance apart as the balls or rollers. It can also be caused by a single impact or a repeated impacting. The main point is that the forces of the balls pressing against the race exceeds the yield strength of the material. The result in a permanent dimple or dent. These excessive forces may occur during transportation, in storage or during the bearing installation process. Special care must be taken when pressing or clamping bearings to avoid causing damage.

False Brinelling

False Brinelling in a stationary bearing creates a similar pattern of marks on the race separated by the distance between the balls or rollers. This wear pattern is called “fretting.” False Brinelling occurs when vibration pushes the oil out of the contact surface between the balls or rollers and the race. The loads in this case are not enough to cause permanent damage or indentations in the race. However, the polishing of the race surface causes it to look like Brinelling. This is why it is called “false brinelling.” Because the races are polished by surface-to-surface contact in the absence of oil, but are not actually damaged, the wear pattern should disappear after a short break in period.

Figure 2 Timken – False Brinelling
Figure 3 Timken – False Brinelling on a Shaft

                                                                     

False Brinelling in a stationary bearing often occurs during transportation. Bearings can be subjected to vibration from trains or forklifts passing by or other sources of vibration when they are in storage. Standby machines can be damaged if they are not isolated from the vibration coming from other machines running nearby.

It’s also possible for false brinelling or fretting to occur in rotating bearings if the rotational speed causes the balls or rollers to make contact with only specific parts of the races over and over again. This causes a similar wear pattern. In this case however, the distance between the wear marks will not match the distance between the balls or rollers.

Take Care of Your Bearings!

The Proactive approach to bearing care includes being careful about how bearings are shipped, stored and installed. Brinelling and False Brinelling can be avoided by using correct packaging, rotating stationary shafts and storing bearings in cabinets that are mounted on vibration isolators and that have damping material on the shelves.     

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