1. The influence of carbides on bearing life

After high-carbon bearing steel is quenched and tempered at low temperature, the tissue will become insoluble carbides, needle-like martensitic and residual austenitic. The content of insoluble carbides and the morphological distribution of carbides, the size of needle-like martensitic and the residual austenitic affect the apparent properties of the bearing. The lower the content of insoluble carbides in the bearing steel, the higher the hardness of the bearing steel. The reason is that the less the content of insoluble carbides, the carbon concentration of the martensitic matrix will increase and the hardness will be higher.

The small amount of insoluble carbides present in the quenched bearing steel helps to improve the wear resistance of the bearing and also helps to obtain fine grain cryptocrystalline martensitic, thereby improving the toughness and fatigue strength of the bearing; the particle size of the carbide has a great impact on the bearing life. Bearing steel carbide particles are less than 0.6um, and its service life will be significantly improved. For high-quality bearing steels, the size of the carbide particles is much lower than that of ordinary bearing steels, and the distribution of carbide particles is also more uniform, and it will not appear in a ribbon distribution; the distribution of reticulated carbides will have an impact on the connection between the matrix grains. The service life will be significantly improved. The size of the carbide particles of high-quality bearing steels is much lower than that of ordinary bearing steels, and the distribution of carbide particles is also more uniform, and it will not appear in a ribbon distribution; The distribution of reticulated carbides will have an impact on the connection between the matrix grains , Which will reduce the fatigue resistance limit of the bearing. When the stress between the rolling element and the raceway exceeds the fatigue limit, cracks will gradually occur, thereby shortening the bearing life.

2. The influence of Bainite on bearing life

The characteristics of Bainite tissue will improve the proportional limit, bending strength, yield strength and cross-section shrinkage of carbon-chromium bearing steel, improve the toughness of bearing steel, and enhance the bearing's ability to withstand impact, fracture, and friction. At the same time, it also contributes to the good retention of bearing size.

3. The influence of load conditions on bearing life

There are mainly the following types of bearings used in rolling mills, multi-cylindrical roller bearings, four-row tapered bearings, and double-row spherical roller bearings. Regardless of the quality of the bearing itself, the bearing life used under working conditions is mainly determined by the load on the bearing.

Due to the increasing rolling force of rolling mills, only multi-row bearings can be used in rolling necks. The concept of multi-row bearing design is to rely on multi-row rolling elements to carry evenly and thereby enhance the bearing carrying capacity. However, in the actual process of rolling mills, the bearing of multi-row rolling elements cannot be completely uniform and even large deviations will occur. The main factors that cause deviations include deviations from the design and manufacture of the bearing itself, the installation accuracy of the bearing seat and the wear of the rolling mill components. At the same time, the bearing distribution is also affected by rolling force, axial force and bending roller force.

This will inevitably cause the load borne by each column of rolling elements to deform under the condition that the overall equivalent load of the bearing remains unchanged, which will eventually lead to partial load. Once the partial load is formed, it will continue to intensify with continued use until the amount of load borne by a certain column of rolling elements exceeds the limit carrying capacity of the rolling element, resulting in local overload and rupture.

Partial load is a situation that seriously affects the life of the bearing. In addition to the unbalanced load distribution of each row of rollers analyzed above, it will also cause the single row of rollers to tilt, causing the stress to be concentrated locally, resulting in the sliding phenomenon of the rolling element. Once the rolling conditions are changed, the contact between the bearing rolling element and the inner and outer rings will slip, causing the bearing to heat up and then damage.

4. The influence of lubrication quality on bearing life

The long-term reliable use of bearings is inseparable from the guarantee of lubrication quality. Rolling mill bearings are subject to friction in many ways during normal operation. Among them, the load area of the outer ring raceway is the part that bears the most serious internal friction. During the operation of the bearing, there will definitely be a radial oil gap, and the rolling of the roller will only be in the load area. In this way, the non-load area will be in a semi-rolling and semi-sliding state. During the process of entering the load area from the non-load area, the speed of the roller will suddenly increase. In the process of sudden increase in speed, the roller and the raceway will rub violently, and at the same time it will withstand and come from the impact of the steel rolling process. load.

In this case, if the bearing is poorly lubricated, the roughness of the surface of the parts will continue to increase, which will lead to a gradual increase in wear, and the pressure on the unit surface of the roller will also continue to increase. At the same time, during the bearing operation, there is sliding friction between the operating rolling element and the raceway, the operating rolling element and the cage, the cage and the inner and outer rings, and this sliding friction will increase with the increase of the load, the presence of sliding friction will cause the occurrence of relative crawling between the bearing components, in order to reduce the wear caused by the relative crawling of the bearing components, it is necessary to maintain good lubrication between the bearing components, and the lubricating oil film can be well isolated. The contact surface between the various components avoids direct frictional contact between metal and metal. At the same time, good lubrication will also play a good role in heat dissipation, which can reduce the transmission of frictional heat in operation.