Four sets of fcd96136420 / P5 bearings for the backup roll of roughing mill in a copper cold rolling plant were damaged abnormally recently. The service life of the bearings on the mill was 6 months according to the record of operation, and all of them failed to meet the quality assurance (12 months on-line operation). Abnormal damage has seriously affected daily production.

The daily rolling speed of the rolling mill is 130m / min, the high speed can reach 300m / min, the rolling force is 300t, the lubrication is oil mist lubrication, the new bearing inner ring is reserved for grinding before leaving the factory, the bearing inner raceway is hot installed on the roller, it needs to be grinded to ensure the necessary accuracy, the bearing works on the machine for 90 days, and the machine maintenance, and the load area is converted to the shaft in the required service life The outer diameter of the bearing inner sleeve can be polished one to three times according to the grinding steps marked in the grinding drawing. In accordance with the above data and operating conditions, it is extremely abnormal to damage three sets of bearings continuously for six months.

Through the on-site communication with equipment engineers, assembly technicians and roll grinding team leader, we can understand the actual situation: the fcd96136420 / P5 bearing used on site is purchased together with the equipment, and the mapping pictures of the bearing are as follows;

 FIG. 1                       FIG. 2

The first figure is to measure the dimension tolerance of the new inner sleeve diameter of the bearing. The field measurement dimension is: φ 528.2mm. Four inner sleeve raceway diameters are measured on site, and the sizes are all φ 528.2mm (the inner raceway diameter has allowance for grinding). This shows that the outer diameter processing dimensions of the bearing inner sleeve are consistent and the processing technology of the bearing factory is very stable. Figure 2 shows the outer bearing assembly, and the outer ring surface roughness reaches ra0.8um. The roller surface is treated with superfinishing. The edge stress relief slope is processed on both sides of the roller. The number of rolling elements is 4-32. The retainer is a two-body comb structure. The outer component has no defects from the overall structure analysis, which is not the main cause of bearing damage.

The on-site inspection showed that there was sufficient lubricating oil in the bearing cavity, and there was no oil shortage. The assembly team leader also confirmed that there was no oil shortage. Check the inner ring surface of the removed roller diameter. After a long time of reciprocating rolling, the surface condition is still good, as shown in the figure below;

FIG. 3

 After the above analysis and detection. The diameter of the inner ring raceway of the roller was detected with an outside micrometer on site, and the measured size was φ 528-0.45 (the inner diameter of the outer component roller compound circle was φ 528 + 0.15). It can be confirmed that the actual radial clearance of the bearing after installation is 0.60mm. Through the communication with the field technicians, the bearing is a new bearing for the first time.

From the above communication, it can be concluded that the bearing damage has nothing to do with the bearing design, production and processing quality. The main reason is that too much grinding of inner ring raceway diameter results in too large radial clearance and too small bearing bearing load and unloading angle, which leads to bearing premature overload fatigue damage. Through the communication with the grinding roller operators, they do not know what size section of the inner ring raceway diameter needs to be grinded to. They only use their own daily grinding feeling to repair and process.

After the above exchanges, the suggestions are as follows;

1) The working radial clearance of fcdp96136420 / P5 bearing is taken from C3 group, and the clearance value is 0.33mm-0.39mm.

2) The inner ring supply size is φ 528.2mm, and the roll diameter interference is φ 528 (+ 0.172 to + 0.132). The diameter of inner ring raceway shall be ground to φ 528 (- 0.18-0.24).