Bearing is a vulnerable part. Although it is processed with high-performance steel with very small tolerance, its service life is always limited.
Related reading: 14 Types of Bearings
In fact, the load imposed on the bearing will eventually lead to material fatigue failure, thus limiting its service life.
However, in many cases, the bearing cannot reach its designed rated life, which will affect its service life under many other external factors, leading to premature failure of the bearing.
The main causes of bearing failure are:
1. Oxidation corrosion
When the bearing is polluted by water, old oil, hydraulic fluid or corrosive additives, it is very easy to be oxidized by the acidic substances in the pollutants, resulting in oxidative corrosion, resulting in a large number of rust or pits, as shown in the figure below.
To effectively avoid this situation, the bearing shall be cleaned and old lubricating oil shall be removed before installation, and water shall not contact the bearing.
2. Fretting corrosion
When micro displacement occurs between the bearing ring and the rolling element, it will lead to fretting corrosion of the bearing and oxidation layer on the outer surface of the bearing, as shown in the figure below.
In order to effectively avoid this situation, before installing the bearing, the bearing accuracy should be checked.
The bearing ring and shaft should generally have an interference fit. If the accuracy is not enough to prevent interference, fretting will occur. Interference fit will make installation difficult.
Anti fretting paste and induction heater should be used to install the bearing on the shaft.
3. Microseismic friction and abrasion
Under static state of bearing, vibration or oscillation will shear oil film, and corrosion caused by friction between rolling element and raceway is shown in the figure below.
To avoid this situation, the bearing must be placed horizontally when it is stored to avoid storing the bearing near the vibration source, such as compressor or vibration device.
4. Surface peeling
When the bearing is not lubricated enough or the oil film is broken, small, very fine and hard particles will wear the bearing, causing the bearing surface to peel off, as shown in the following figure.
In order to prevent this situation, the bearing should choose the appropriate lubricant (quantity and viscosity) and automatic lubrication system. During and after the installation of the bearing, avoid the intrusion of solid particles and liquids, and check the bearing temperature level.
5. Surface depth peeling
When the bearing is subject to solid pollution, or corrosive liquid enters the bearing, and the shell or shaft is dislocated or deformed, the bearing surface defects (indentation, impact, corrosion, excessive stress, etc.) will cause deep peeling, as shown in the following figure.
To prevent this from happening, during the installation of the bearing, avoid introducing pollutants, and control the geometry and quality of the valve seat to avoid stress caused by bearing misalignment.
6. Deep peeling inside
When the bearing bears cyclic stress, the bearing will have deep groove peeling, which is usually oval, as shown in the following figure.
To prevent such damage, ensure bearing compatibility, use a monitoring system on the equipment to detect vibration and noise associated with the onset of fatigue induced spalling, and follow a predictive maintenance schedule for bearing replacement.
7. Electric erosion
When the bearing is electrified, it will cause electric corrosion, resulting in pits or grooves, as shown in the following figure.
To avoid such damage, it should be ensured that the current does not pass through the bearings, and for generator and motor applications, ceramic insulated bearings should be selected.
8. Plastic deformation
When the bearing is installed incorrectly or severely short circuited and overloaded, plastic deformation will occur and pits will be generated on the raceway, as shown in the following figure.
To prevent this, the bearings should be installed using the correct installation method and tools, while ensuring that the rolling elements do not transmit static overloads.
When the bearing bears impact, overload, bending force, fatigue or excessive thermal stress, the bearing will break suddenly, as shown in the following figure.
To avoid this kind of damage, check the condition of the bearing seat before installation, use the correct installation method and tools to install the bearing, do not hit the bearing directly with a hammer, and replace the noisy bearing quickly during use.
10. Wear under the action of particles
When solid particles wear in the boundary lubrication of the bearing, this will happen, and the rolling shell and raceway will produce matt surfaces, stripes or pits, as shown in the following figure.
To avoid this, the bearing shall be fully lubricated with clean lubricants, and appropriate sealing devices, such as dust cover or seals, shall be selected.
11. Friction and wear
When the bearing temperature rises and causes significant sliding, the mutually welded metal components will rub and wear, as shown in the following figure.
In order to prevent this, appropriate lubricants should be used according to the quantity and quality, and appropriate bearings should be used according to the load and speed.
12. Stripping caused by axial overload
When the axial load of the bearing is too large, one side of the bearing raceway will peel off, as shown in the figure below.
To avoid this, the bearing should be selected correctly, and check whether the floating bearing can move freely.
Related reading: 9 Factors to Be Considered In Bearing Selection
Wrap it up
In view of this, in general, we recommend:
1. When the bearing is stored, the bearing shall be placed flat in an air-conditioned room with constant temperature as far as possible;
2. Although the bearing is very hard, it is better to avoid repeated stacking of cartons with heavy bearings to avoid crushing the bearing;
3. The installation and maintenance of bearings shall be checked and comply with relevant standards;
4. Refer to the plan and assembly drawing when installing, and use professional installation tools for installation;
5. The bearing shall be kept clean and shall be operated under clean conditions as far as possible;
6. Before commissioning, the bearing shall be lubricated with proper amount of grease;
7. Ensure the effectiveness of the sealing device.