This article introduces the characteristics and common failure phenomena of cold rolling roll bearings, focusing on the causes of their failures.
Keywords: cold rolling roll bearings; damage causes; fatigue damage
Roller bearings are very important in the composition of cold rolling mills. They can withstand large loads, work in poor environments, and have good performance. However, because of this, coupled with easy water intrusion and difficulty in disassembly and assembly, the bearings are easily damaged, which has an impact on cold-rolled products. Therefore, it is extremely necessary to analyze the cause of damage.
Characteristics and fault phenomena of cold rolling roll bearings
Compared with ordinary bearings, cold-rolled roller bearings can carry heavier loads, usually 2 to 5 times that of ordinary standards. During the work process, their running speeds can vary widely. Normally, cold rolling roll bearings need to work in a relatively harsh environment. Therefore, impurities such as iron oxide chips can easily enter and cause damage.
During operation, cold-rolled rolling bearings will have certain failures, mainly as follows: first, during the process of disassembly and cleaning, fatigue damage will often be seen on the inner and outer ring raceways, and the color will change. , the hardness is reduced, accompanied by cracks, serious damage to the rolling elements, etc.; secondly, during operation, the temperature of the bearing part increases and obvious noises can be heard, and in severe cases, smoke and stuck may occur.
Analysis of the causes of damage to cold rolling roll bearings
Fatigue damage of inner and outer ring raceways
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 degree of surface wear will increase, and in severe cases, fatigue damage will occur. On this basis, the fine materials on the surface will continue to fall off, and over time they will accumulate between the rolling elements and raceways. The stress will increase and become highly concentrated, leading to cracks. As the cracks continue to expand, the surface will fall off and become pitted. Appear, cycle back and forth, and eventually cause serious damage.
The reasons for poor bearing lubrication mainly include the following aspects: First, the labyrinth seal components composed of the water retaining ring and the bearing seat are worn, resulting in large pores between them. This may be due to assembly problems and failure to accurately perform the bearing seat. Positioning to cause friction with the labyrinth seal of the water retaining ring: Or the bearing is affected and damaged during rolling, and the internal water retaining ring and bearing seat are displaced, causing friction at the labyrinth seal. In addition, it may also be in the axial direction. The upper inner ring is not tight, so the water retaining ring cannot be fixed in its original position. Secondly, due to the failure of the sealing rubber due to long-term use and the reduction of the elastic modulus of the spring, a good sealing effect cannot be achieved. In this case, the rolling emulsion will leak and flow into the bearing seat, and the lubricating oil will be diluted and lose its original content. There is a certain lubrication effect, which often occurs in the lower roller bearing.
The inner and outer rings become discolored and hardened due to fever
This phenomenon is quite serious. Due to the large temperature rise of the bearing, the fitting gap between the inner ring and the roller shaft becomes larger, causing relative sliding. At the same time, relative sliding occurs between the outer ring and the bearing seat. Under the above effects, the bearing temperature further rises. High, in the case of reciprocating cycles, the inner and outer rings will heat up and become discolored, and the hardness will decrease. In addition, the axial tightening capacity is reduced. For example, if the shaft end bolts of the bearing inner ring are loosened or the bolts are damaged due to excessive axial force, the inner ring will run away.
The most serious fault
The temperature of the bearing area increases and obvious noises can be heard. In severe cases, smoke and jamming may occur. This type of problem is the most serious among bearings.
The material used in the inner and outer rings of the bearing is relatively thin, has high hardness, low softness, is wear-resistant and pressure-resistant, but has very poor bending and shear resistance. Its use must be matched with the roller shaft and bearing seat to increase the overall performance. Among them The concentrated force must be shared by the roller shaft and the bearing seat. Once the inner ring and the roller shaft and the outer ring and the bearing seat are not well matched, it is extremely easy to cause the inner and outer rings to bear strong force alone and cause rupture. Therefore, it is necessary to make strict regulations on the size and shape of the shaft and bearing seat, and ensure that they meet the requirements. Typically, problems tend to occur in rollers and bearing seats that have been used for a long time.
During operation, the cold-rolled strip runs at a high speed, which may lead to deviation, strip breakage or exceeding the maximum load. If the overload protection capability is weak, the bearing may be seriously damaged under the strong impact force and the running speed may be reduced. The inner ring and outer ring are thus caused, and in severe cases, problems such as rupture and jamming ensue. The roller shaft and bearing seat are seriously damaged, their specifications and shapes are changed, and the surface is worn, and then grooves or serious problems occur. Deformation.
During the process of assembling the shaft, if the problem is not carefully detected, it will be difficult to find the problem, or if you know that there is a problem but do not take the necessary measures to improve it, then install it. At this time, due to the strong impact force generated during rolling, the bearing will be damaged. The possibility of rupture of the inner and outer rings will increase, and other components such as rolling elements and brackets will be damaged.
Damage to the above bearings or poor lubrication effects will cause the bearing temperature to rise significantly, and accurate judgments can be made through human touch.
Excessive radial force
Back-up roller bearings can withstand large rolling forces, but due to material shape and other reasons, instantaneous high pressure can easily occur under a certain pressure. In this case, the rolling force will increase significantly, and the bearing force will exceed the maximum If this type of operation is carried out for a long time, its lifespan will be adversely affected. In addition, if the material is wedge-shaped, the force on one side will also exceed the standard. If the force on one side is too large, the rolling elements will break, the support frame will be damaged, and the bearing life will be reduced.
Roll bending force and tension are the radial forces that the work roll shaft is often subjected to. Due to the shape of the raw material, additional roll bending force must be added during the rolling process. When the roll bending force is applied to the bearing seat, the working shaft will bend so as to roll out a strip with good shape. However, the roll bending force will also cause the bearing to receive uneven force. The force is mainly concentrated on the inner and outer rolling elements. At this time, the load capacity of the bearing is seriously reduced, and the inner and outer raceways are worn.
Excessive axial force
In addition to the rolling force, the work roll shaft will also be affected by axial force, which will have an impact on the work roll shaft, and this force is often ignored. Theoretically, the axial force is 1% to 2% of the rolling force. However, in fact, the force can reach or even far exceed 5% of the rolling force, so the roll will move and the axial force will be used. The fixing bolts break, causing the work to be interrupted. In severe cases, the bearings are directly burned. There are many reasons for the increase in axial force, such as the intersection of rolling axes, rolling asymmetry, unstable operation of the transmission system, etc., but the main reason is the intersection between the rolls, especially the axis of the transmission roll.
Conclusion
Compared with ordinary bearings, cold rolled roller bearings have better performance. However, it will be damaged to varying degrees during use. Therefore, the cause of the damage should be carefully analyzed, and the best solution should be found during exploration to ensure the quality of cold-rolled products.
