Analysis and research on damage causes of cold rolling roll bearing
Abstract: In this paper, the characteristics and common failure phenomena of cold rolling roll bearings are introduced, and the reasons for their failure are emphatically studied.
Key words: cold roll bearing; Cause of damage; Fatigue damage
Introduction: Roll bearing is more important in the formation of cold rolling mill, it can withstand large loads, can work in poor environment, and has good performance. However, because of this, coupled with easy water, disassembly and other difficulties, the bearing is easy to damage, affecting the cold rolled products. Therefore, it is necessary to analyze the cause of its damage.
First, the characteristics of cold rolling roll bearings and fault phenomena
Compared with ordinary bearings, cold-rolled roll bearings can carry heavier loads, usually up to 2 to 5 times the ordinary standard, and their operating speed can vary widely during the working process [1]. Under normal circumstances, cold rolling roller bearings need to work in a relatively harsh environment, so impurities such as iron oxide chips are easy to enter and cause damage.
In the process of operation, cold rolling rolling bearings will have certain failures, mainly as follows: first, in the process of disassembly and cleaning, it is often seen that there is fatigue damage at the inner and outer ring raceways, and it will change color, hardness is reduced, and accompanied by cracks, serious damage to the rolling body; Second, during the operation, the temperature of the bearing part rises and an obvious sound can be heard, and in serious cases, smoke and other phenomena will occur.
Analysis on the damage causes of cold rolling roll bearing
(1) inner and outer ring raceway fatigue damage
In the case of long-term use, the inner and outer rings of the bearing will wear, if the lubrication effect is not good, the surface wear degree will increase, and fatigue damage will occur in serious cases. On this basis, the fine material on the surface will continue to fall off, and over time it will accumulate between the rolling element and the raceway, and the stress will increase and be highly concentrated, resulting in cracks. With the continuous expansion of cracks, the surface will fall off, the pockmarked surface will appear, and the reciprocating cycle will eventually cause serious damage.
The reasons for the poor lubrication effect of bearings mainly include the following aspects: First, the labyrinth seal component composed of the water baffle ring and the bearing seat is worn, and large pores are generated between them, which may be caused by assembly problems, and the bearing seat is not accurately positioned, causing friction between it and the labyrinth seal of the water baffle ring: Or the bearing is affected and damaged during rolling, the internal water retaining ring and the bearing seat are displaced, and friction occurs at the fan seal. In addition, the inner ring may not be tightened in the axial direction, and the water retaining ring cannot be fixed in the original position. Second, due to the long-term use of sealing rubber failure, the spring's elastic modulus reduction can not achieve a good sealing effect, in this case, the rolling emulsion will leak into the bearing seat, the lubricating oil is diluted, lose the original lubrication effect, this situation often appears in the lower roller bearing.
(2) The inner and outer ring fever discoloration, hardness reduction
This phenomenon is more serious, due to the larger temperature rise of the bearing, the gap between the inner ring and the roller becomes larger, resulting in relative sliding, while the outer ring and the bearing seat also occur relative sliding, the bearing temperature is further increased under the above action, under the reciprocating cycle, the inner and outer ring fever discoloration, hardness reduction. In addition, the axial fastening ability is reduced, such as the shaft end bolt of the bearing inner ring is loose or the axial force is too large to cause the bolt damage, etc., will occur.
(3) The most serious failure
The temperature of the bearing part rises and the obvious sound can be heard, and in serious cases there will be smoke and dead phenomenon, such problems are the most serious in the bearing.
The inner and outer ring of the bearing is made of thin material, high hardness and low softness, wear resistance and pressure resistance but poor bending and shear resistance, which must be used with the roller and bearing seat to increase the overall performance, in which the concentrated force must be shared by the rolling shaft and bearing seat. Once the inner ring and the roller and the outer ring and the bearing seat are not well matched, it is extremely easy to cause the inner and outer ring to bear a strong force alone and break. Therefore, it is necessary to strictly regulate the size and shape of the axle and bearing seat, and be sure to ensure that it meets the requirements. Usually, the problem tends to occur in the roller and bearing seat after a long time of use.
During operation, the speed of cold rolling belt is fast, which may lead to deviation, broken belt or exceeding the maximum load. If the overload protection ability is weak, the bearing may be seriously damaged under the strong impact force, resulting in the running of the inner ring and the running of the outer ring. In serious cases, problems such as rupture and jamming will follow, and the rolling shaft and bearing seat will be seriously damaged. Its size and shape change, the surface is worn, and then grooves or severe deformation occur.
In the process of assembling the assembly shaft, if it is not carefully tested, the problem is difficult to find, or it is clear that there is a problem but does not take the necessary measures to improve the installation and application, at this time, due to the strong impact force generated during rolling, the possibility of breaking the inner and outer rings of the bearing will increase, and the rest of the components such as the rolling element and the protection bracket will be damaged.
The above bearing damage or poor lubrication effect will lead to a significant increase in bearing temperature, and accurate judgment can be made by human touch.
(4) Excessive radial force
Back-up roll bearings can withstand a large rolling force, but due to the shape of the material and other reasons, under a certain pressure, easy to occur instant high pressure, in this case, the rolling force will be greatly increased, bearing force beyond the maximum range, long-term operation of this kind, its life will be adversely affected. In addition, if the material is wedge-shaped, its unilateral force will also exceed the standard, the unilateral force is too large, the rolling element is broken, the support frame is damaged, and the bearing life is reduced.
Roll bending force and tension are the radial forces that work rolls are often subjected to. Due to the shape of the raw material, extra bending force must be increased during rolling. When a roll bending force is applied to the bearing seat, the working shaft is bent in order to roll a strip with good shape. However, the roll bending force will also cause the bearing to be subjected to uneven force, the force is mainly concentrated on the internal and external rolling element, at this time the bearing load capacity is seriously reduced, and the internal and external raceway is thus worn.
(5) Excessive axial force
In addition to the rolling force, the axial force on the work roll will also be affected, which will affect the work roll, and this force is often ignored. In theory, the size of the axial force is 1% to 2% of the rolling force, but in practice, the force can reach or even far exceed 5% of the rolling force, so the roll will shift, the axial bolt used for fixing will break, resulting in work interruption, and the bearing will be directly burned in serious cases [2]. There are many reasons for the increase of axial force, such as crossing of rolling axes, asymmetric rolling, unstable operation of the transmission system, etc., but the main reason is that there is a cross between rolls, especially the axis of the transmission rolls.
Iii. Conclusion
Compared with ordinary bearings, the performance of cold-rolled roll bearings is better. However, it will be damaged to different degrees in the process of use, so we should carefully analyze the reasons for its damage, and find the best solution in the exploration to ensure the quality of cold rolled products.
[References]
[1] Li Xiangyang, Ma Jia, Cui Junli. Analysis of Damage Causes of vertical grinding Bearing [J]. Cement, 2019,000 (009): 42-44.
[2] Sun Yujie. Discussion on the Management of Cold Rolling Roll in Service Process [J]. Metal World, 2019,203 (03):14-17
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