Bearing Failure Analysis

Proper lubrication is vital to bearing life. If a visual inspection shows any change in the colour of the grease, or if it smells burnt, it indicates a potential lubrication failure which will lead to a failure of the bearing. If a Lithium-based grease has been used, the surface may become brittle and can shine like a varnish: tapping it with a sharp instrument may shatter it. If the bearing is running in an oil bath and insufficient fluid is reaching the races, they may be dry to the touch and possibly ‘blued’. Any of these signs warrant detailed examination immediately.

If one side of a bearing is not properly aligned in relation to the other, the path of the balls or rollers will run from one side of the race to the other, and it will do this around one half of the circumference on the non-rotating surface. The rotating ring will also most likely have a wide roller path, which can often result in frictional forces producing a temperature high enough to either disrupt the efficiency or destroy the lubricant.

Contamination is one of the most common causes of bearing failure and the cause is generally straightforward: the presence of foreign objects inside the bearing. In most cases, contamination will leave visible surface marks such as pitting, scoring or scratches. However, users should not assume that there is no contamination based purely on a visual inspection, especially if the operating environment is one where fine mists of fluids or superfine dust particles may be present. We can advise on initial bearing selection to protect from contaminants in the first place, and we can provide testing as required to ensure long service life. Failure prevention is far cheaper than replacement.

Irrespective of whether it is caused by adjacent component failure or simply the build-up of static, electric arc erosion occurs when a current passes through a bearing and is broken at the contact point between the races and rolling elements. In turn, this can result in high temperatures at localised parts of the bearing which can result in surface pitting on the contacting faces. We can advise on how to avoid this occurring in your project.

Unsurprisingly, there are many ways in which a bearing cage can sustain damage, but amongst the most common causes are excessive wear, lack of lubrication, excessive vibration and overspeeding. If you have experienced cage damage previously then talk to us, we can usually isolate the cause and recommend the most efficient remedy.

Brinelling is damage to the bearing raceway. It is most commonly caused by incorrect installation or incorrect replacement of a bearing, sometimes when a thrust force has been applied either deliberately or inadvertently. Generally, brinelling can be recognised by tiny indentations on the shoulder of the race which correspond to the location of the balls. Users should beware that one direct cause of brinelling can be hammer blows to the bearing, or a shock load exerted on a static shaft. We can advise on ways to identify potential causes of brinelling on your project and help you manage them out of the equation.

In a static bearing, damage to bearing rings which is caused by vibration is what causes damage known as false brinelling. It can be caused by the machine in which the bearing is installed, and sometimes it can also be caused during the transportation of the equipment itself. Users should watch out for indentations on the axial and circumferential parts of the raceways. It may appear very similar to brinelling, but false brinelling is readily characterised by the degradation of the material as a result of a combination of both mechanical and chemical action.

This type of failure evidenced by a flaking of the raceway.  In short, fatigue failure is a result of a weakening in the grain of the bearing steel. It usually starts invisibly to the eye beneath the surface and then migrates to the raceway. This may be normal near to the end of the life of a bearing but it can occur quite readily at any point in its life as a result of excessive loads being applied. We can assist at the design stage to help you be sure to specify bearings that are truly up to the projected static and dynamic loads expected, and thus help prevent fatigue failure from ever occurring.

By examining the wear path pattern in a bearing that has been removed from service, it is possible to obtain an idea of the conditions under which the bearing has been operated. By recognising the difference between normal and abnormal wear on the pathway we can ascertain whether or not the bearing has been used properly