There are three things in life that you should never break: promises, trust and someone’s heart. Pretty much everything else will break eventually, including steel bearings. Here, Chris Johnson, managing director of bearing specialist SMB Bearings, explains how to avoid shortening their lifespan.
It’s easy to believe that something made of steel will last forever. After all, we all grew up on tales of Superman, the indestructible Man of Steel. However, no matter how well you care for bearings in your plant equipment, or even your car or bike, they will eventually wear and need to be replaced. This is because they have what’s known as a fatigue life. 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.
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 but you can take a step towards extending bearing life by selecting a bearing made from high quality steel that will have fewer non-metallic inclusions.
While spalling is inevitable, there are mistakes in installation and errors in maintenance that can greatly speed up this process and bring your bearing’s life to a premature end.
Abrasion and 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, through the gap between a metal shield and the bearing inner ring or via a damaged contact seal. If the seal is damaged during installation or routine maintenance, the bearing remains vulnerable to debris from any nearby processes. Contamination reduces the bearing’s efficiency and increases the levels of noise and vibration so it is important to maintain clean work areas and use clean lubricants.
When contamination is in the form of water entering the bearing, corrosion will occur if the bearings are made from standard steel. Contact type bearing seals may help to prevent water ingress 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. For example, poor mounting practices or dropping a bearing during installation often results in true brinelling where dents appear in the raceway and cause excessive vibration during rotation. This can be avoided by simply applying pressure only to the part to be press fitted at installation.
Loads and over-heating
Putting too much load on your bearings will compress the raceway and cause premature and severe spalling. This will also put great stress on other parts of the machinery and eventually cause the bearing to fail. Therefore, it’s important to make sure you have a bearing that is suited to the application and is capable of handling larger loads.
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 can 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.
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 solution.
If you take care of your bearings and avoid the common mistakes discussed above, you should be able to trust in a long, happy life with your bearings, totally free from heartbreak.