Rolling mill bearing refers to the rolling industry, that is, non-ferrous metal, ferrous metal, and non-metallic products calendering. It is used for bearing of calendering roll system and roller. Usually, four-row cylindrical roller bearings are used to bear radial load, thrust roller or thrust ball bearings, and radial angular contact ball or radial roller bearings are used to bear axial load. Now, oil-air lubrication or oil mist lubrication and grease are mostly used for lubrication and cooling.
Classification of rolling mill bearings
(1) Spherical roller bearing
At that time, two sets of self-aligning roller bearings were installed on the same roll neck in parallel. The rolling speed can reach 600 rpm. However, with the increase of speed, its disadvantages become more and more prominent: short bearing life, large consumption, low precision of finished products, serious wear of roll neck, large axial movement of the roll, etc.
(2) Four-row cylindrical roller bearing + thrust bearing
The cylindrical roller bearing has the advantages of large load capacity, high limit speed, high precision, separable and interchangeable inner and outer rings, easy processing, low production cost, and convenient installation and disassembly. The thrust bearing bears axial force, and the specific structural type can be selected according to the characteristics of the rolling mill.
Under heavy load and low speed, it is equipped with a thrust roller bearing to bear thrust load with small axial clearance. When the rolling speed is high, with angular contact ball bearing, not only the limit speed is high, but also the axial clearance can be strictly controlled. The roller can get a close axial guide and can bear a general axial load. This type of bearing not only has the advantages of long service life and high reliability but also has the advantages of high precision and easy control. Therefore, it is widely used in a wire rod mill, plate mill, foil mill, double backup roll mill, cold rolling mill, and hot rolling mill.
(3) Four row tapered roller bearing
The tapered roller bearing can bear both radial force and axial force without thrust bearing, so the main engine is more compact. The inner diameter of the tapered roller bearing is a loose fit with the roller neck, which is very convenient for installation and disassembly. However, sometimes sliding creep may be caused by a loose fit. Therefore, the inner diameter is often machined with a spiral oil groove. This configuration is still widely used, such as work roll of four high hot rolling mill and cold rolling mill, blooming machine, and steel beam rolling mill.
Four-row cylindrical roller bearing and four-row tapered roller bearing are almost all used in roll neck, roller, and rolling press of rolling mill. Compared with other roller bearings, these bearings have lower friction. As these bearings are usually installed on the roll neck with an interference fit, they are particularly suitable for high-speed rolling mill applications. The low cross-section of these bearings allows the use of a relatively large journal diameter compared to the roll diameter. Because it can be loaded with many rollers, its radial load capacity is very high.
Factors affecting the service life of rolling mill bearings
Rolling mill bearing is an important part of the rolling mills. In the process of rolling mill operation, the bearing supports the roll, bears the rolling force, and keeps the correct position of the roll. Whether the quality of rolling mill bearing is reliable or not and the length of service life directly affects the reliability of rolling mill operation. There are many factors that affect the service life of rolling mill bearings. A series of internal and external factors, such as bearing material, structural design, manufacturing accuracy, installation and sealing, lubrication, and cooling, will affect the service life of rolling mill bearings.
The bad working conditions are the main reason for the early failure of rolling mill bearings. Generally speaking, the service conditions of bearings mainly include the load and its distribution, lubrication, sealing, speed transmission, working temperature, heat dissipation conditions, etc. when the bearing quality and service parts are the same, the service life will be greatly different if the working conditions are different.
1. Effect of carbide on bearing's service life
The microstructure of high carbon bearing steel will change into undissolved carbide, acicular martensite, and retained austenite after over quenching and low temperature tempering treatment. The content and distribution of undissolved carbide, the size of acicular martensite, and retained austenite affect the apparent properties of bearing. The lower the content of undissolved carbide in bearing steel is, the higher the hardness of bearing steel is The less the content, the higher the carbon concentration and hardness of the martensite matrix.
A small amount of undissolved carbide in quenched bearing steel is helpful to improve the wear resistance of bearing and obtain fine grain cryptocrystalline martensite, so as to improve the toughness and fatigue strength of bearing; the particle size of carbide has a great influence on the bearing life, and the service life of bearing steel with carbide particle less than 0.6um will be significantly improved The size of the carbide particles is much lower than that of the general bearing steel, and the distribution of the carbide particles is more uniform, and it will not appear as a strip distribution; the network carbide distribution will affect the relationship between the matrix grains, which will reduce the anti-fatigue limit of the bearing. When the stress between the rolling body and raceway exceeds the fatigue limit, cracks will gradually appear, thus shortening the shaft Bearing life.
2. Effect of bainite on bearing's life
The characteristics of bainite structure can improve the proportional limit, bending strength, yield strength, and area reduction of carbon chromium bearing steel, improve the toughness of bearing steel, enhance the bearing capacity of impact force, fracture force, and friction force, and also contribute to the good maintenance of bearing size.
3. Influence of load conditions on bearing's life
The bearings used in rolling mills mainly include the following types: multi cylindrical roller bearing, four-row tapered bearing, and double row spherical roller bearing. Without considering the quality of the bearing itself, the service life of the bearing under working conditions is mainly determined by the load on the bearing.
Due to the increased rolling force of the rolling mill, the only multi-row bearing can be used in roll neck. The design concept of multi-row bearing is to rely on multi-row rolling elements to uniformly carry the load, and then enhance the bearing capacity. However, in the actual process of rolling mill, the bearing capacity of the multi-row rolling element can not be completely uniform, and even a large deviation will occur. The main factors causing the deviation include At the same time, the bearing load distribution is also affected by rolling force, axial force, and bending force.
This will inevitably lead to the deformation of the load of each rolling element under the condition that the equivalent load of the bearing as a whole is unchanged, and eventually lead to partial load. Once the eccentric load is formed, it will continue to increase with continuous use, until the amount of load borne by a certain rolling element exceeds the ultimate bearing capacity of the rolling element, resulting in local overload fracture.
The eccentric load is a serious impact on bearing life. In addition to the above analysis will lead to unbalanced load distribution of each row of rollers, it will also lead to a single row roller tilt, resulting in stress to local concentration, resulting in a rolling element sliding phenomenon. Once the rolling conditions are changed, the contact slip between the bearing roller and the inner and outer rings will occur, resulting in bearing heating and damage.
4. Influence of lubrication quality on bearing's life
The bearing can not be used reliably for a long time without the guarantee of lubrication quality. During normal operation, rolling mill bearing will suffer from various kinds of friction. The load area of the outer ring raceway is the most serious part to bear internal friction. There must be a radial oil gap in the bearing operation process, and the roller rolling will only be in the load area, so the non-load area will be in the semi rolling and semi sliding state, When the roller enters the load area from the non-load area, the speed of the roller will increase suddenly. In the process of the sudden increase of the speed, the roller and the raceway will rub violently, and at the same time, they will bear and come from the impact load in the rolling process.
In this case, if the lubrication of the bearing is poor, the roughness of the part surface will continue to increase, which will lead to the gradual increase of wear and pressure on the roller unit surface. At the same time, the sliding friction occurs between the rolling element and raceway, between the rolling element and the cage, between the cage and the inner and outer rings during the operation of the bearing It will increase with the increase of load. The existence of sliding friction will cause the relative creeping of bearing components. In order to reduce the wear caused by the relative creeping of bearing components, it is necessary to maintain good lubrication between bearing components. The lubricating oil film can well isolate the contact surface between various parts and avoid the direct friction contact between metals. At the same time, good lubrication can also play a good role in heat dissipation, which can reduce the friction heat in operation.
5. Influence of sealing quality on bearing's life
Because of the bad running environment of rolling mill bearing, the probability of bearing contamination will increase. Therefore, it is necessary to keep the bearing seal well to avoid contamination of grease. Usually, the bearings used in rolling equipment are mainly polluted by cooling water and scale.
After the grease is polluted by water, the anti-fatigue degree of bearing material will be reduced, thus resulting in cracks. If the grease is polluted by iron oxide scale, the situation will be even worse. The iron oxide scale will damage the internal lubrication conditions of the bearing, and the bearing surface will have friction wear.
After the bearing is polluted by cooling water and iron oxide scale, the ring will deteriorate in the process of use. With the increase of pollutants, the ring will crack and the bearing will be damaged. Therefore, the ideal bearing seal can effectively improve the service life of the bearing and reduce the probability of sudden bearing damage affecting the production.
Please check the Product Guide to select suitable bearings for your machinery.
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