Abstract: Combining with the process characteristics of single-stand six-high reversing rolling mill, the paper points out the shortcomings in the design of work roll bearing seat, analyzes the reasons that affect the improvement of rolling mill production efficiency due to improper maintenance and use of bearing seat, and puts forward a solution to the design deficiencies, which is verified and implemented in actual production, and achieves the expected results.

1, the main role of bearing seat accessories

The locking ring is the main attachment of the bearing seat. When the bearing seat is installed on the roll neck, the axial positioning of the roll is realized by hinged clasp. The clasp is of separate construction, and the two halves of the clasp are welded together with a pin and connecting plate. The inner side of the clamp ring is milled with a flat keyway, and the bearing inner ring spacer (pressure shoulder ring) is connected with the roll by a flat key, and rotates with the roll. The function of the operating arm of the working roll operating side bearing seat is that the front end of the operating arm is equipped with a roll changing hook head, which is convenient for quick roll changing. The side of the operating arm is equipped with oil-gas lubricating oil nozzle, and the lubricating oil path is processed inside to realize oil-gas lubrication of the bearing. The operating arm is provided with an axial limit block and a locking groove to position it axially with the frame. The upper and lower sliders on the bearing seat support lug not only move on the roll changing trolley track, but also enter the bending roll block of the frame to transfer rolling force.

2. Operation condition before improvement

In the actual production, there have been many cases of clasp falling off in the rolling process, resulting in tandem movement of bearing seat, difficult extraction of roll change, and even thrust bearing burning accidents. When the working roll operating side bearing box is in use, the phenomenon of the connecting screws between the operating arm and the box are often loosened, broken, and the hook head is sunk, as well as the oil and gas lubricating oil nozzle is stuck. Because the hook head of the roll changing vehicle cannot hook the hook head of the front end of the operating arm, the roll cannot be pulled out of the frame, which affects the production downtime of 270min every month. Serious wear of the upper and lower skateboards will also cause difficulties in roller change. When the rolling mill is calibrated, if the wear of the sliding plate on the operating side and the driving side is inconsistent, the size of the sliding plate is too out of tolerance, the deviation of the roll gap will increase. The rolling process will also affect the precision of plate shape control, make the rolling force tilt.

3. Cause of the problem

1) After physical inspection of the falling clasp, the conclusion is that most of the reasons for the falling clasp are caused by the opening welding of the pin shaft and the welding position of the two halves of the clasp. In addition, due to the welding is not firm, and improper operation in the process of assembly caused more damage to the clasp. In 2013 alone, more than 50 sets were damaged, which increased the cost of production and maintenance and also brought difficulties to the smooth production.

2) As for the operating arm, the structure of the bearing seat and the extraction hook of the roll changing trolley are analyzed, and the following conclusions are drawn:

The reason why the screws connecting the operation arm and the box are broken

The reason is that when the work roller is locked in the frame, the length of the locking cylinder on both sides of the frame window is different, resulting in the operation arm (door frame) skewed to one side, and the difference between the two sides is 5 ~ 10mm. The operation arm is connected to the box at the root, and is fastened by 2 M12×35 screws. The length of the operating arm is 710mm. When it is skewed, it will be broken due to insufficient strength of the screws.

Reasons why the screws connecting the operation arm and the box are loose

Because of vibration in the rolling process, fastening screws did not take anti-loose treatment caused by.

The reason for the front end hook of the operating arm to sink

Manipulator width manufacturing tolerance is 100-0.1-0.3; The width of the bearing box groove is 100+0+0.2, and the larger tolerance is Max=0.5; Minor tolerance Min=0.1. In actual measurement, even if two M12×35 screws of the operating arm are fastened, the operating arm can swing up and down. If the gap reaches 0.4 ~ 0.5mm, the hook head will drop 6 ~ 8mm under the influence of its own weight. In addition, the operation arm hook head wear is serious also affect the smooth roll.

The reason why the hook head cannot be hooked by the operation arm hook head is that the upper and lower swinging distance of the hook head mechanical device is about 15mm. It is connected with the operation arm hook head as a crescent, and the contact area is small. When the front-end hook head of the operating arm is sunk, the trolley hook head and the hook head on the operating arm only contact about 5mm in the vertical direction, which directly leads to the box can not be pulled out when the roll is changed.

Due to the sinking of the operating arm, the oil and gas lubricating oil feed nozzle on the frame can not be correctly inserted into the oil and gas lubricating oil nozzle, or the one-way valve core is stuck, or the valve core positioning copper ring is damaged, resulting in the oil and gas lubricating oil transmission is not smooth, and the bearing is burned and melted due to the lack of oil in serious cases.

3) In the process of bearing seat maintenance, whether it is the upper bearing seat or the lower bearing seat, the lower slide wear is very serious, and the wear of the upper slide is relatively small. The reasons are as follows:

First, the lower slide directly contacts the track of the roller changing trolley, and it can enter the frame after three sections of track joint. If the track joint appears high and low level difference, the skateboard will scratch, loose and damage the skateboard when it passes through here.

Second, serious track wear, roughness, or track surface is not clean, will aggravate the wear of the skateboard.

Third, the vibration in the rolling process makes the fastening screw loose on the skateboard, the screw cap on the skateboard friction with the track, the track scratch when changing the roll.

4. Improvement measures

1) The two sides of the two halves of the clasp rings were simultaneously milling plane keyways. The processing length of the pin shaft was 1 ~ 2mm larger than the width of the clasp ring, and the pin shaft beyond the section of the clasp ring was riveted or trimmed into a mushroom head shape with hand tools. The damaged clasp was re-drilled and repaired by welding process. However, when assembling the clasp, we intentionally placed the big end face of the pin shaft on the inside to make it contact with the end face of the bearing spacer (interpressure ring), as shown in Figure 3.

2) We replaced the 2 M12×35 screws on the operating arm and box body with 2 M16×35 screws, and used spring washers to prevent loose. The diameter and depth of the countersunk hole of the manipulator are also processed accordingly, and the rolling is carried out by machine test. In view of the upper and lower swing of the operating arm and the sinking phenomenon of the hook head, the measures taken are as follows: Add copper gaskets under the fastening part of the operating arm and the box, and install gaskets of different thicknesses according to the size of the gap. Tilt the operating arm upward at a small Angle to ensure that the bearing box is in good condition before loading, and the operating arm cannot swing up or down. But after the end of rolling roll change, or often appear hook head down, box out of the phenomenon. And the installation of the gasket is easy to fall off, there is no fundamental solution to the problem. To this end, we also designed the operation arm and the box reinforcement device drawings, reinforcement device parts after processing will be installed on the box, the specific installation steps are; First, find the level of the operating arm and the box and install the reinforcement device. Secondly, the plug gauge is used to detect the coordination gap between the operating arm and the box, and different thickness gaskets are installed. Tighten 2 M16×35 screws later. See Figure 2 for the improved operation arm.

5. The effect of improved bearing seat

1) After the improvement of the clasp, its advantages are reflected in: it can be assembled smoothly without selecting the positive and negative sides of the clasp in the assembly process. Avoid in the rolling process due to opening welding caused by the phenomenon of clasp off. It is helpful to repair the damaged clasp quickly and reduce the production cost.

2) After more than a year of use, there is no operation arm screw break phenomenon. After the operation arm is reinforced, the connection between the operation arm and the box body is checked to achieve the expected purpose of the design. After the machine rolling test of the improved bearing box, the loading roll and the pumping roll are smoothly normal, and the oil-gas lubricating oil nozzle is connected normally.

3) After improving the maintenance and management level of upper and lower sliding plates of bearing seat, the deviation of rolling force is significantly reduced.

6. Conclusion

In order to make the mill with advanced technology and high precision fully play its function, it is necessary to increase the intensity of mill maintenance and improve the level of maintenance. Only by studying and analyzing the causes of restricting the production efficiency of rolling mill, and taking corresponding measures to improve them, can we continuously meet the demand of producing high precision products.

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