Abstract:Based on the characteristics and working conditions of work roll bearings of rolling mills, this paper analyzes the relevant requirements and precautions in the process of assembly, inspection, use and adjustment of bearings in view of the phenomenon that bearings are easily damaged.

Key words:Rolling mill; Bearings; Inspect; adjust

1 Introduction 

Rolling mill In the rolling production process, roll bearings are used to support the roll, maintain the correct position of the roll in the frame and rotation accuracy, reduce the friction and wear between the roll and the support. Therefore, roll bearings should have a small coefficient of friction, sufficient strength and stiffness, long service life and easy to check and adjust. At present, the rolling speed is getting faster and faster, the tolerance requirements are getting smaller and smaller, and the quality requirements are getting higher and higher, and strengthening the online maintenance, inspection and adjustment of bearings has become an important work to reduce the bearing loss and reduce the production cost.

2 Work roll bearing condition of four high mill

The single-stand universal reversible four-high mill is a second-hand equipment imported from Spain and was produced by the American Masta Company in the 1940s. The working environment of the four-high rolling mill is harsh, the temperature is high, the dust and the cooling water in the rolling process are easy to enter the bearing box. This will not only make the grease emulsification failure, but also cause friction and damage to the working surface of the bearing. From May to June 2012, four work roller bearing burning accidents occurred in the plate company, resulting in direct economic losses of more than 1 million yuan, of which each set of bearings is more than 300,000 yuan, the processing cycle is 18 months, but also to book in advance, to bring great passive production. The inspection and analysis of these four accidents are not caused by the quality of bearings, but because of the improper assembly, inspection and adjustment of bearings. It can be seen that the correct maintenance method and reasonable adjustment assembly are the key to extending the service life of bearings.

3 Mill work roll bearing structure

The work roller bearing of the mill of the plate company is a four-row tapered roller bearing produced by the TIMKEN Company of the United States, and its model is EE749259DW-749335-749335CD. The bearing specifications are: inner diameter 660.01mm, outer diameter 855.014mm, total width 320mm, radial rated load of 1,314KN, axial rated load of 226.8KN, rated speed of 500r/Min. Its specific structure is shown in Figure 1, which is composed of two double inner rings, one double outer ring, two single outer rings, two outer adjusting gaskets, one inner adjusting gasket, as well as a rolling body and a cage. The bearing has the advantages of high rotation accuracy, small friction coefficient, separable inner and outer rings, and the conical rolling element can be removed from the cage, which provides convenient conditions for the inspection and adjustment of the bearing, so as to improve the assembly quality and use accuracy.

4 Bearing inspection and adjustment

(1) Inspection during operation. According to the requirements of the process regulations, the bearing is regularly listened to, looked at and measured. Use a special instrument, one end of the end cover of the bearing and the radial housing of the bearing seat, the other end of the ear to listen to the bearing in the process of operation, whether there is a crash and mechanical friction sound; Depending on the installation position, lubrication; Measure the vibration offset, and finally determine whether the bearing is in a normal state during operation, and take corresponding measures if an anomaly is found.

(2) Inspection at rest. Check the fastening of related spare parts to ensure that they are in correct positions. The greater the momentum of the rolling roller shaft, the greater the axial force generated, and the more serious the impact on the bearing. Because of this, often check the fastening of the components, can reduce the damage of the drive shaft to the bearing, extend the bearing life.

(3) Disintegration inspection. Roll bearings must be taken out of the bearing box regularly for inspection, and the inspection cycle can be divided into three months, six months, or even one year according to the actual monthly output. In the process of bearing inspection, it is necessary to make timely, detailed and accurate records. The inspection work can be roughly divided into the following steps:

①Record the bearing position. Record the loading position of the bearing seat, the loading time and the used outer ring bearing area (there are four marks on the bearing outer ring, this mark allows the inspector to record the used bearing area of the outer ring).

②Remove the bearing. Remove the end cover of the bearing seat and lift out the bearing step by step using special tools.

③Clean the bearings. The bearing can be cleaned with kerosene or special cleaning agent, and the purpose of cleaning is to check the wear and use of the bearing.

④Bearing inspection. After cleaning, perform a visual inspection, rotate the cage or rolling body, and check the outer diameter and raceway of each rolling body as well as the inner ring of the bearing. If the inner ring raceway surface is spalling, the loose part can be worn off, and the edge of the spalling area can be flattened; If the inner raceway spalling damage area exceeds 1/4 of its width, it will no longer be repaired. A comprehensive inspection of the bearing outer ring, the status of the outer ring can reflect the problems existing in the roll and bearing. If the outer ring is rusted, it indicates that the seal is damaged or does not play the role of sealing, and cooling water enters; If there is serious abrasion, it indicates that there is debris such as particles or oxide skin in the grease.

⑤Bearing clearance measurement and adjustment. After checking the bearing wear, put the bearing on the platform. The lower bearing ring should be supported on a foundation fixture with a stop hole, and a certain gap should be reserved to enable the bearing to rotate freely. When stacking bearings, it must be in accordance with the order of disassembly, can be A end up or A end down, but be sure to ensure that it is A, B, C, D, E or E, D, C, B, A order, remember that the parts are not interchangeable. In order to facilitate better detection of bearing clearance and stability, it is necessary to load a weight approximately equal to the weight of the bearing on the outer ring. After loading, appropriate light lubricating oil should be added on the roller to protect the bearing, so that the bearing can get a good positioning of the components during a long time of rotation. After the positioning is completed, the gap values of B, C and D are measured by the plug gauge in the four directions of 90° on the bearing, and the tightness of the plug gauge should be kept appropriate during the measurement. Taking the bearing with the original clearance of 0.3mm as an example, the calculation method of the clearance is as follows: It is known that the original clearance is 0.3mm, and the clearance to be trimmed is 0.6mm. After re-grinding, it is necessary to ensure that the clearance value is 1.5 times of the original clearance value, that is, 0.45mm. If the clearance to be measured is 30mm, the required clearance value is 0.45mm, and the thickness of the gasket is 30.45mm(30+0.45=30.45mm). The three adjustment pads B, C and D are calculated by the above method.

⑥Check and repair the bearing seat. First of all, it is necessary to clean and check the lubricating oil road in the hole of the bearing seat, and then test whether the size and cylindricity of the bearing box meet the assembly requirements, the cylindricity of the box should not exceed 0.05mm, and the maximum clearance between the hole and the bearing outer ring of the box is 0.08~0.3mm.

⑦Cleaning inspection of seals. Seals have a very important role in bearings, such as wear and damage to seals must be replaced with new parts.

⑧Reinstall the bearings. A layer of lubricating oil should be evenly applied in the bearing seat hole first, and then back loaded according to the sequence of bearing placement (pay attention to changing the bearing bearing area). The bearing outer ring is a stationary part, and the bearing area accounts for about 1/4 of the diameter of the outer ring when the machine is working, and the bearing area of the upper roll is above the bearing seat, and the bearing area of the lower roll is below the bearing seat, so after each inspection, according to the recorded position of the last bearing area, turn 1/4 circle, so that a new position is used as the bearing area. When the bearing outer ring is spalling in a large area, it can still be used on the machine by repairing and selecting the appropriate bearing area, which will improve the service life and use accuracy of the bearing. When the bearing is installed, the thickness of the adjustment pad is measured by the method of lead pressing at the four corners of the bearing seat. The thickness of the measured four corners of the lead sheet is added to obtain the average value, and the thickness of the gasket is 1.5 times the average value, which is done in order to provide a safety factor to ensure that the bearing will not be too tight when working after adjustment; Ensure the safe use of bearings.

5 Use effect

Through the use and observation of nearly half a year, the roll bearing is used normally without any accident. This not only ensures the service cycle of the bearing, but also effectively avoids the adjustment of the bearing clearance in use, reduces the abnormal consumption caused by the adjustment of the bearing, saves manpower and material resources, and ensures the smooth production.

6 Conclusion

There are many factors that affect the service life of bearings, such as the choice of tolerance fit, the choice of clearance, the choice of bearing seal, the choice of lubricant, etc. At the same time, it also has a great relationship with the fluctuation of rolling force. Its wear forms are also diverse, but as long as you understand the damage causes of roll bearings, take good inspection and repair for the use of roll maintenance and adjustment, the damage of roll bearings can be effectively prevented, and the consumption of roll bearings can be reduced to the maximum extent, thereby improving the service life of roll bearings, improving the utilization rate of roll bearings, and achieving the goal of reducing bearing consumption.