Abstract: The causes of rolling mill bearing failure are analyzed. The results show that 40% ~ 50% of bearing failure is due to improper installation, adjustment, use and maintenance. From the use point of view, the measures to improve the service life of bearing are put forward, such as: improve the coaxiality between bearing seat holes, and appropriately increase the tolerance of bearing seat holes; Improve the lubrication mode; Reasonable selection and installation of bearings; Adopt bearing transposition working method, etc. Practice has proved that the effect is good.

70% of the failures of our country's normal mill scale bearing are fault failure [1], namely the abnormal failure, and the majority of them are breaking failure. The reasons leading to bearing failure can be roughly attributed to two aspects: one is internal factors, such as design, manufacturing process and raw material quality. The other is external factors, such as the installation and adjustment, maintenance and repair of bearings in use. In order to improve the service life of the bearing, it is necessary to analyze the failure of the bearing from the above two aspects, find out the real cause of the failure of the bearing, and take specific measures to improve the life of the rolling mill bearing.

Based on the situation of mill bearing used in our factory for many years, the failure of mill bearing used is analyzed statistically. The results show that 40% ~ 50% of bearing failures are caused by improper installation, adjustment, use and maintenance. Therefore, it is very important to study and improve it.

1. Improve the coaxiality between bearing seat holes, and increase the tolerance of bearing seat holes

Due to the low manufacturing accuracy of the rolling mill, long service life and low adjustment accuracy of the frame, after the completion of the rolling mill assembly, there is a large coaxiality difference between the bearing holes, which makes the bearing at both ends of the rolling mill frame bearing uneven stress, local stress concentration, when poor lubrication is easy to produce high friction heat, resulting in local pitting, spalling, thermal adhesion and locking of the bearing. Therefore, according to the actual situation of rolling mill, the improvement measures are taken: first, when installing and adjusting the stand, the bearing seat is corrected by the level, the coaxiality of the two bearing seat holes is improved, and the tilt and cross of the center line are reduced. The other is to properly enlarge the tolerance of rolling mill shaft bearing seat hole, such as: roughing mill bearing seat hole by

Bearing seat hole for medium mill

2. Improve the lubrication mode

Grease lubrication is now used. Because the structure of vertical rolling mill determines that when the roll rotates, the grease injected from the middle of the upper bearing seat and the outside of the bearing seat (towards the roll head) can not enter the inner part of the rolling mill bearing well, and is easy to lose, resulting in the working surface of the bearing in a state of oil depletion, leading to the early failure of the bearing. Therefore, the oil circuit of the bearing seat is improved, and the oil filling port is added on the inner side of the shaft bearing seat (towards the roll body) to improve the grease filling effect, so that the bearing is well lubricated and the service life of the bearing is prolonged. In addition, the bearings of our short stress line rolling mill are also lubricated by grease and assembled without grease. That is, the newly opened bearing is installed without grease first. After assembly, grease is injected into the bearing through the oil circuit on the bearing seat. In this way, the bubbles in the grease will be saved in the bearing due to the advance injection of grease, and the vacuum gap generated in the assembly process of the bearing will be reduced.

3 Rolling mill bearing installation

Because the fixed end of the short stress line mill is also the precision adjustment end of the mill, the previous assembly adjustment is not paid attention to, resulting in poor axial adjustment, resulting in premature bearing failure. Through exploration and summary, the method of bearing installation and roller body accurate adjustment is improved, as shown in Figure 1.

(1) Four rows of cylindrical roller bearings shall load their outer ring components into the bearing seat according to the transition fit.

(2) Install the inner bearing end cover, and fasten the bearing end cover to the inner side of the bearing seat with a bolt after the stop is pushed to the position.

(3) Push the four rows of cylindrical roller bearings against the inner bearing end cover stop, so that the stop against the outer ring of the four rows of round column roller shaft bearing, and the clearance is zero.

(4) Install the outer bearing end cover, the stop top the other side of the outer ring of the four rows of round column roller bearing, the gap is zero, and fasten the shaft bearing end cover on the outside of the bearing seat with a bolt.

(5) Screw the axial adjustment sleeve into the outer end cover of the shaft bearing, turn it to the end cover of the bearing and then return a pitch (4mm).

(6) Make the adjusting and setting ring of the cochlear rod close to the outer side shaft cap, and fix the adjusting and setting ring of the worm on the bearing cap with an M16 screw.

(7) Push the thrust bearing into the axial adjusting sleeve, so that the outer ring of the shaft bearing is close to the axial adjusting sleeve.

(8) Screw the adjusting nut into the adjusting flange, fix the two assembled parts on the bearing end cover with bolts through the worm adjusting positioning ring.

(9) Rotate the adjusting nut so that the stop of the adjusting screw is against the outer ring on the other side of the thrust bearing and is locked.

(10) Connect the adjusting nut to the axial adjusting sleeve with a bolt.

(11) Load the bearing press sleeve from the inside of the bearing seat so that the boss is against the shaft ring in the middle of the thrust bearing.

(12) Install the roller equipped with the bearing inner ring and retaining ring into the bearing seat, so that the bearing inner ring supports the bearing press sleeve. (13) Load the end cover so that the stop of the end cover is against the shaft ring in the middle of the thrust bearing, and connect the end cover with the bearing press sleeve with a fixed bolt.

(14) Insert the rod pin into the positioning hole of the end cover and the roll head, tighten the positioning bolt, and connect the roll head and the end cover together. After such installation and adjustment, the mill axial installation and adjustment precision has been greatly increased, so that the failure rate of shaft bearing is reduced, the quality of rolling material is improved.

4. Reasonable selection of bearings

The thrust shaft bearing of our middle rolling mill is originally designed and selected as double row angular contact ball bearing (4936X3D). Due to the long-term use and wear of rolling mill parts, the pendulum between bearing seat and stress column is out of tolerance, so that the double row angular contact ball shaft cannot be in normal operation Its carrying capacity is reduced a lot, which often causes the rolling mill to stop and seriously affects the normal production. Therefore, two-way double row tapered roller bearing (829232X3) with more reasonable structure is selected to replace double row angular contact ball bearing (4936X3D), achieving good results [2].

5 Use transposition method

When the mill is working, the whole set of shafts bear a large radial rolling force. At the same time, the inner ring rotates with the rolling roll, but the outer ring does not rotate [3]. For the outer ring, in the rolling process, the outer ring raceway always at a fixed point under continuous rolling force, will make the outer raceway fatigue stripping prematurely, resulting in shaft bearing failure. For this reason, we use the bearing transposition and achieve good results.

Measures are as follows:

(1) Establish bearing use files, and record the bearing up and down time, cleaning and transposition and installation based on the axle seat number of each frame.

(2) Mark reference point C on each shaft bearing seat, mark 1, 2, 3 and 4 on the positions 90° apart from the end faces of each set of bearing outer rings.

(3) When assembling the new bearing outer ring and roller assembly on the bearing seat, align the point marked 1 with the reference point C of the bearing seat and make a record. According to the use experience, the bearing outer ring and roller assembly shall be removed from the bearing seat at 1/2 of its service life (integer multiple of the roll replacement cycle) (the outer ring shall be removed by hydraulic equipment to reduce the damage of the outer ring).

(4) Rotate the outer ring so that point 2 is aligned with point C, assemble and operate according to (3).

(5) Proceed in turn according to the above method until the four points on the outer ring are completed. The whole replacement process is a cycle.

(6) After the cycle, the bearing is thoroughly cleaned and checked. If no abnormality is found in all parts of the bearing, it indicates that the bearing still has the use value and can be re-installed and used. Align the midpoint between points 1 and 3 on the outer ring with point C for installation and record. At 1/4 of its service life, remove the bearing outer ring and roller assembly from the bearing seat.

(7) Rotate to the middle point between points 2 and 4 in the outer ring to align with point C, assemble and record. Press (6) to operate.

(8) Push according to the method described above until the 4 middle points are finished. The whole replacement process is called the second cycle. Repeat the above operating procedures until the bearing is damaged. You can have a third or fourth cycle.

The field test of the bearing transposition working method has obtained good results. Taking the bearing of the fourth rolling mill in the bar as an example, the tested life of the bearing is 450h and the changing cycle of the rolling mill is 72h before the changing process is used. After using bearing transposition working method, the cumulative service life of bearings is 1440h, which greatly exceeds the previous experience life.

By improving the using method of rolling mill bearing, the service life of rolling mill bearing is significantly increased, the downtime of rolling mill failure is reduced, the production efficiency is improved and the production cost is reduced.以上翻译结果来自有道神经网络翻译（YNMT）· 通用领域