Let your bearings grow old gracefully
10 May 2021
No matter how well you care for bearings, they will eventually wear and need to be replaced. This is because they have what’s known as a fatigue life. Chris Johnson explains how to avoid shortening their lifespan
WITHOUT ANY adverse conditions, the time it takes for a bearing to reach its fatigue life can take years. However, predicting when this will happen is very difficult. Contrastingly, it’s easy to identify a bearing that is approaching the end of its life, as cracks begin to appear in the steel raceway and the balls and the surfaces will begin to flake. This creates a build up of debris in the bearing, which leads to friction and there is usually an increase in noise and vibration when the bearing is in use.
This process is known as spalling. It occurs because non-metallic inclusions in the steel begin to crack under repeated pressure and these cracks grow and work their way to the surface. There’s nothing that can be done to avoid this.
However, the first step to extending bearing life is to make sure you select a manufacturer that can be relied on to use high quality steel that will have fewer non-metallic inclusions.
Abrasion & corrosion
Allowing contamination of bearing lubrication is one of the fastest ways to kill a bearing. There are several ways abrasive dirt can enter a bearing. If the seal is damaged or tampered with during installation or routine maintenance, dust will be able to enter the bearing. If the seal is not replaced, it remains vulnerable to debris from any nearby processes. It is also possible to introduce abrasives by selecting a sub-standard bearing lubricant.
However small the particles of grit may be, the motion of the bearing grinds the foreign material across the surface of the steel raceway and balls, changing the geometry of the bearing. This will reduce the bearing’s efficiency and increase the levels of noise and vibration, which will have a detrimental impact on surrounding components, so it is important to maintain clean work areas and use clean lubricants.
When contamination is in the form of water entering the bearing, or precipitating water accumulating in the bearing when the machine is cooling, you will certainly get corrosion if the bearings are made from standard steel. The areas where rolling elements are in contact with the raceway are most vulnerable because the pressure of the balls during idle periods may force lubricant away from the area of contact.
Contact type bearing seals may prevent corrosion and a lubricant with a corrosion inhibitor will also help. However, in some cases you may need to invest in bearings made from corrosion resistant materials.
Bearings are delicate components, so something as simple as applying too much pressure during installation can cause you serious problems down the line. For example, poor mounting practices or dropping a bearing during installation often results in true brinelling.
This is where dents appear in the raceway which cause excessive vibration during rotation. This can be avoided by simply applying pressure only to the part to be press fitted at installation.
Another easily avoided phenomenon is electrical fluting. Electrical fluting presents as a regular pattern over the bearing. This results from an electrical current passing through the bearing, which is often caused by static electricity from conveyer belts and current from unsatisfactory welding setups.
If you ensure that welds are grounded and that there is a grounding strap on nearby conveyors you can easily avoid this problem.
Loads & over-heating
When you combine heat with heavy loads you get a whole new pool of problems. Any process that involves high temperatures creates the risk that bearings will overheat. When a bearing exceeds its maximum temperature, the load capacity of the steel rapidly reduces, and the bearing is easily deformed, often resulting in complete, catastrophic failure.
In addition, heat will cause bearing lubrication to evaporate and deplete. If your bearings are operating at more than the rated temperature of the lubricant, life is drastically decreased so it makes sense to specify a lubricant that will cope with more than the expected maximum temperature.
Whatever the application, if you want to keep your bearings rolling right on up to their predicted fatigue life you need to take care of them. If bearings keep failing, it is probably because the size, shape, type, material or lubrication is not suitable for your application. In these instances, you should approach a bearing specialist, like SMB Bearings, that can advise you on the most suitable and cost-effective replacement.
Chris Johnson is managing director of SMB Bearings