Four causes and preventive measures of bearing faults in vertical grinding roller

Date: 2019-07-03 Views:

Roller grinding is the key grinding component in vertical grinding, and roller bearing is the core of roller grinding. Once the roller bearing fails, it will have a direct impact on the running performance of the vertical mill. Therefore, it is very important to check and repair the roller bearing fault in time to ensure the normal operation of the production line.

Analysis of Operation and damage of 01 Roller

1.1 Operation and status of grinding rollers


There are two cement vertical mills in a cement plant, both of which are four-roll vertical mills. in the process of actual operation, bearing damage occurs many times, the maintenance period is long and the loss is serious. There have been attempts to increase the output of the mill and minimize the damage of the roller bearing, but after many attempts, the vibration of the mill is too large.

Therefore, only two rollers can be used for operation. After the equipment is put into operation in October,2016, because of the lack of rich experience, the damage of the roller bearing is not fully realized and the damage of the roller bearing is not fully realized, and the two rollers are operated for a long time, and the two rollers are reserved for standby.

1.2 damage to grinding rollers


In August 2017, due to the fracture of the bolt at the end of the roller, the roller pulled out nearly 305 mm from the whole part.

After removal, during the treatment and inspection of the bearing, it is found that there are obvious regular indentation marks on the inner ring raceway of the bearing, and then when the roller is replaced from the seal, it is found that all the bearings have such a situation. There are two plates of bearings in the roller.

During the inspection after opening the bearing, it is found that the cylindrical roller also has indentation on the inner ring rolling surface of the bearing, and all have certain regularity, and most of them have a ball corresponding to each indentation. And indentation and wear on the ball and raceway surface of double-row conical bearings.

Analysis on the characteristic of the bearing failure of the roller shaft of the 02 mill


During the use of the cement grinding roll, there is a sound "processus" of the rhythm, and as the grinding roller is continuously pressurized, the sound will increase, and the vibration of the mill will increase significantly; however, if it is no-load auxiliary power-on, there is no such sound.

It is found that the roller has high flexibility and no lag. At the same time, the rocker arm bearing has been checked separately, but this kind of situation has not been found.

Cause Analysis of 03 bearing damage


First, because two rollers are used to run diagonally for a long time, two rollers are used as backup, so two spare rollers are suspended in the mill for a long time (mainly with two cylinders as support).

In the process of supporting, the role of the cylinder is mainly flexible, so under the vibration of the mill, it can float limited, but with a long time of vibration, there will be impact indentation on the bearing.

Secondly, for materials, moisture and so on, cement vertical grinding has very high requirements. No matter any influence, the vibration of the mill will occur in the process of operation, while for the grinding roller and other equipment, the vibration for a long time will have a negative impact on it.

Third, on the support and positioning, all the bolts of the four M42 are used to fix the roller bearing and the roller skin. The bolt has the strength of Grade 8.8. In the process of being used at the beginning, it is often broken, which causes the roller to come off and so on. The strength of the modified bolt was then 10.9, and the condition of such a failure did not occur again.

fourthly, the service life of the bearing can also be influenced by the bearing oil seal damage and the like, If the wind pressure is not enough, the oil seal can be sucked into the cement particles, the lip of the oil seal is damaged, and the entry of sundries and the like is caused, and the use of the bearing is affected.

4. Discussion on targeted preventive measures


First, in view of the fact that the four-roller present at the present stage is not fully operational, a strict weekly roll-in-use system is developed. In this way the damage to the bearing can be reduced to a minimum.

Second, check the bearing pressure plate bolt of the roller every month to avoid the occurrence of fracture. At the same time, check the impurities in the lubricating oil inside the bearing and understand the use of the bearing in time.

And thirdly, the air volume and the wind pressure of the closed fan are controlled, a pressure transmitter is arranged on the air pipe, and the purpose of carrying out the numerical control and transmission of the air volume wind pressure value is realized. At the same time, the use of the oil seal needs to be checked regularly.

And fourthly, the vibration of the grinding machine is reduced, the situation of material particle size and water is effectively controlled, and the operation parameters of the grinding machine are optimized.

05. Repair measures for bearing


If two plates of Timken bearings are replaced, the total cost will be about 200000, and the maintenance cost will be nearly 100000 yuan. The most important thing is to return to the factory for maintenance. Finally, referring to the relevant data, after measuring the main parameters such as the outer ring of the bearing, the following scheme to repair the bearing is worked out.

5.1 Repair measures for tapered roller bearing


In the process of repairing tapered roller bearings, only the indentation on the outer ring raceway surface is treated by grinding. Because the outer ring of the bearing has almost 0.2mm indentation, the hardness of the raceway surface is 9.6. the requirements for the use of this bearing can be fully met, and the outer ring 0.23mm is ground down and the indentation is removed.

After calculation, grind off the spacer ring in the middle of the bearing by 2.8mm. The grinding measurement requires a higher assembly to ensure that the assembly shaft can be less than 0.04 mm in the clearance. Test the operation of the bearing to ensure that it can meet the standard range and then complete the assembly.

5.2 repair measures for cylindrical roller bearings


Because the bearing inner assembly is not too much damaged, only the inner ring roller surface has indentations. During the measurement of the clearance, it is found that the range is about 0.35mm. At the same time, the indentation is ground off about 0.20mm after the completion of the measurement, and ensure that the repaired clearance is controlled within the range of 0.60mm, which is basically consistent with the use requirements.

In the implementation of the above-mentioned repair scheme, the outer ring of the two sets of tapered roller bearings is removed, and after the measurement and comparison, the selection of the damaged outer ring is not a very serious outer ring to be replaced. And then the return factory performs the repair treatment on the cone and the cylindrical roller bearing. After a week of working procedures, the technical requirements are in agreement with each other.

During the assembly of bearings and rollers, the axial clearance of bearings is 0.01mm after actual measurement. According to the concept of zero clearance, we also control the clearance in a small range in the process of calculation. In addition, in the actual operation process, the roller environment has reached about 100 ℃, so the small clearance will not lead to the holding of the bearing, on the contrary, it is very helpful for the operation of the bearing.

After the actual operation in the field, all the indexes of the roller meet the requirements, and the sudden noise has been eliminated, which cost more than 20,000 yuan this time, which saves a lot of maintenance cost.

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