With the popularity of cold rolling strip Market in the past few years, a large number of six high cold rolling mills have been put on line in China. With the passage of time, equipment damage, AGC transformation and equipment speed-up, the work roll and intermediate roll positioning bearings of most cold rolling mills began to burn for a short time, resulting in extremely abnormal production.

Taking 156134 double row angular contact ball bearing on the site of X customer as an example, this paper analyzes the problems as follows:

Bearing structure diagram

Bearing damage on site

1. The early phenomenon is the upper intermediate roll, and the cage on the side of roll body drops copper powder or is worn and cracked. Check that the opposite cage is normal.

2.In the later stage, it is a short time online burning and locking fault. As a result, the roller and bearing box can only be disassembled by force and seriously damaged.

3.For the bearing not burnt before disassembly, the outer ring was found to be worn abnormally, all of which were local falling off or opposite spalling, and the damaged position was the outer ring near the roller body side.

4. The fitting room and bearing end face are worn abnormally, with scratch and sinking.

Installation structure and stress distribution

At present, there are many structural configurations of cold rolling mills in China, as shown in the figure above. The four row cylindrical roller bearing with positioning bearing and the double row angular contact ball bearing with X customer's site are shown in the figure above. When the roll system is running, the main bearing bears all the radial load, and the positioning bearing bears the pure axial load. According to the above bearing damage phenomenon and location, it can be clearly judged that: when the bearing is running The axial force is transferred from the drive side of the rolling mill to the operation side, that is, the axial force is transferred from the No.5 compression sleeve to the inner ring of the bearing, and then to the rolling element close to the distance ring, and then to the outer ring close to the distance ring by the rolling body. The final stress point is the connection of No. 6 calipers.

Summary analysis

1. From the third point of the damage phenomenon, it can be clearly judged that the outer ring of the bearing has received a large abnormal axial force. Due to the pure axial load borne by the bearing in the roller system, the normal axial force should be 360 ° uniform stress on the outer ring raceway, while the damage of the physical object has local and opposite spalling damage, which indicates that the axial load is inclined, and then according to the stress analysis of the installation structure, It can be seen that the main factor leading to the deflection of axial load is the 6-caliper joint. The deflection of the stress point at the connection of the caliper results in the axial load deflection of the bearing, resulting in the irregular operation of the rolling element, which produces large clamping force and frequent impact force on the cage, and then leads to the wear and fracture of the cage.

2. The third point of the damage phenomenon can be clearly seen that the damaged bearing has abnormal wear on the end face, mainly including the extension end face of the outer ring gland and the end face of the fixed distance ring connecting the inner ring. Therefore, it can be judged that there is serious relative sliding friction between the bearing and the mating contact parts during the operation, and the axial direction of the outer ring of the bearing is not The bearing is compressed and has a clearance of 0.5-1.0 mm, so the bearing has a large axial movement during operation. Due to the lower hardness of the accessories compared with the bearing, it is easy to be worn and sunk due to irregular wear. When the bearing is subjected to axial force in another direction, the end face is close to the contact surface of the opposite mating part (at this time, the end face has been irregularly worn), resulting in the relative inclination of the inner and outer rings of the bearing. It will also lead to the irregular operation of the rolling element, which will produce larger clamping force and frequent impact force on the cage, and then lead to the wear and fracture of the cage.

3.The axial load overload of bearing can be judged from the damage degree and time. Since the current roll system configuration selected at the initial stage of the rolling mill is in normal operation, it can indirectly prove that the roll system configuration is in line with the actual working conditions, but with the long time of equipment damage and the lack of follow-up equipment maintenance, and AGC upgrading equipment speed up, especially 1. Outer ring distance ring 2. Inner ring distance ring 3. Bearing 4. Outer gland 5. Compression sleeve 6. Caliper joint 7. Bearing liner 8. Wear and deformation of non consumable parts such as transmission shaft will cause additional axial force of roller system and overload of bearing.

Further analysis of the larger axial force sources, there are generally the following factors caused or triggered:

4.the wear of the mill mill liner plate and the asymmetrical abnormal wear cause the cross difference of the roller system, and also cause the abnormal axial load and the bearing damage.

5.the deformation of bearing pedestal, especially the bearing seat that has been burnt, fits the end face (boss or shoulder) with the bearing end face. The parallelism of the bore diameter of the bearing seat is too poor, which leads to the phenomenon of bias load when the bearing is subjected to axial load again, that is, the ability of bearing anti axial load is greatly reduced, which causes the bearing axial load overload and causes burning loss.

6.the transmission shaft, although connected to the working roll, will cause periodic vibration of the transmission shaft, lead to the instability of the intermediate roll (there is offset), intensify the wear of the lining plate, and lead to uneven wear on the working roll surface, and also cause abnormal axial load.

Summarize the law

Through market research, the damage of angular contact ball bearing of work roll or intermediate roll of cold rolling mill basically follows the following five rules:

1.The damaged bearing is positioning bearing, i.e. the bearing housing lug is connected with the frame or the cross moving device of equipment caliper. Its main function is to limit the axial displacement of the roller under the working condition and bear the axial force in two directions during the rolling process.

2.The damaged position is fixed, that is, the damaged position will not be transferred, and most of them are fixed at one place, such as the upper or lower transmission side of the intermediate roll or the upper or lower transmission side of the work roll.

3.The damaged bearing surface is fixed, that is, the damaged position is single row damage near the main bearing side or the gland side.

4. At the initial stage of damage, copper powder is dropped from the cage, or some rolling elements are partially peeled off, that is, cage pocket deformation. Under this condition, the bearing can be found out in time when the bearing is off the machine, and the bearing can be replaced; the later phenomenon is that the cage is directly cracked or burned on the line, and the bearing can no longer be found offline under this condition.

5. The damage time is short, ranging from hours to days.

6. The main factors are axial load bias load or axial load overload.

Improvement measures

According to the market research and customer feedback of bearing damage form, DMD company combined with its cloud steel rolling platform, aimed at the burning problem of cold rolling mill positioning bearing, reflected the targeted customized service, and optimized the bearing based on the original bearing, especially the axial load of bearing, load distribution, contact angle, bearing material, cage material, etc Optimization and upgrading ensures the on-line operation life and stability of the bearing, which is more suitable for the field conditions of customers.