Rolling bearings may be damaged during operation due to various reasons, such as improper assembly, poor lubrication, invasion of moisture and foreign objects, corrosion, and overload, which can all lead to premature bearing damage. Even under normal installation, lubrication, and maintenance, after a period of operation, the bearings may experience fatigue peeling and wear, making them unable to function properly. In short, the causes of failures in rolling bearings are very complex. The main forms and causes of faults in rolling bearings are as follows.
1. Fatigue peeling
The inner and outer raceways and rolling surfaces of rolling bearings both bear loads and roll relatively. Due to the action of alternating loads, cracks first form at a certain depth below the surface, and then expand to the contact surface, causing peeling pits to occur on the surface and develop into large areas of peeling. This phenomenon is fatigue peeling. Fatigue peeling can cause increased impact loads, vibrations, and noise during operation. In general, fatigue peeling is often the main cause of failure in rolling bearings. Generally, the bearing life refers to the fatigue life of the bearing, and the bearing life test is the fatigue test. The test procedure stipulates that the fatigue peeling pit with an area of 0.5mm2 on the raceway or rolling element is considered as the end of the bearing life. The fatigue life of rolling bearings is highly dispersed, and within the same batch of bearings, their high and low life can differ by tens or even hundreds of times. This highlights the importance of fault monitoring for rolling bearings from another perspective.
2. Wear and tear
Due to the invasion of dust and foreign objects, the relative movement of the raceway and rolling element can cause surface wear, and poor lubrication can also exacerbate wear. The result of wear is an increase in bearing clearance, surface roughness, and a decrease in bearing operating accuracy, which also reduces the machine's motion accuracy and increases vibration and noise. For mechanical bearings, it is often the amount of wear that limits their lifespan.
In addition, there is also a type of micro vibration wear. When the bearing does not rotate, due to the effect of vibration, there is slight and repeated relative sliding between the rolling element and the contact surface of the raceway, resulting in wear, forming vibration like wear marks on the raceway surface.
3. Plastic deformation
When the shaft is subjected to excessive impact or static loads, additional loads caused by thermal deformation, or foreign objects with high hardness invade, dents or scratches will form on the surface of the raceway. This will cause severe vibration and noise in the bearing during operation. And once there is an indentation, the impact load caused by the indentation will further cause peeling of the nearby surface.
4. Rust
Rust is one of the more serious problems in rolling bearings, and high-precision bearings may lose accuracy due to surface rust and cannot continue to work. Direct invasion of moisture, acid, or alkaline substances can cause bearing corrosion. When the bearing stops working, the temperature of the bearing drops to the dew point, and water in the air condenses into droplets that attach to the surface of the bearing, which can also cause corrosion. In addition, when there is current passing through the inside of the bearing, the current may pass through the contact points on the raceway and rolling element, causing a thin oil film to cause electrical sparks and generate electrical corrosion, forming a washboard like unevenness on the surface.
5. Fracture
Excessive load may cause bearing parts to break. Improper grinding, heat treatment, and assembly can all cause residual stress, and excessive thermal stress during operation can also cause bearing parts to fracture. In addition, improper assembly methods and processes may also cause blocks to fall off at the edges of the bearing ring and the chamfers of the rollers.
6. Gluing
When working under poor lubrication and high-speed heavy loads, due to frictional heating, bearing parts can reach high temperatures in a very short period of time, resulting in surface burns and adhesion. The so-called bonding refers to the phenomenon where metal on the surface of one component adheres to the surface of another component.
7. Damaged cage
Improper assembly or use may cause deformation of the cage, increase friction between it and the rolling element, and even make some rolling elements stuck and unable to roll. It may also cause friction between the cage and the inner and outer rings.