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Paper machine bearing failure analysis case

by:JNSN     2022-03-12
Design data at home and abroad show that the ordinary clearance group (!') is only suitable for general use conditions, that is, the load under ordinary load (radial load '#$%!u0026', and the inner ring speed is the limit speed of the bearing. (#) or less. Therefore, our company selects imported bearings with clearance group of !*, precision + class or , class, which can not only bear large radial load, but also self-align. It will not be affected by radial Too much clearance will cause noise and vibration. After analysis, for equipment with large load and high speed, if the interference between the bearing and the shaft is insufficient (that is, the preload does not meet the requirements), the inner ring will rotate due to the load bearing the load. The creep (-u0026../) sliding phenomenon in the circumferential direction will occur between the inner ring and the shaft, which will gradually increase the wear degree of the mating surface, and the shaft and the outer casing will be damaged. At the same time, the worn powder penetrates into the bearing, causing heat and heat. Vibration. In addition, the influence of the temperature difference of the bearing, shaft and housing on the fit interference cannot be ignored. The reduction of the inner ring interference due to the temperature difference! 12 can be calculated as follows: !12'#$##% (!210%#1* (22) In the formula: !2 is the temperature difference between the inside of the bearing and the outer casing, 31 is the nominal inner diameter of the bearing, 22 is between the inner ring of the bearing and the outer casing, due to the difference in temperature difference and expansion coefficient, the interference will sometimes increase On the other hand, since the bearing is installed on the shaft and the housing due to the interference allowance, the ring will expand or contract and cause stress and damage. Referring to the technical standard provided by '45, the interference should be controlled within 6 of the shaft diameter. 7 %#### or less. In addition, the frictional heat generated by the rotation of the bearing is dissipated through the shaft and the casing. The heat dissipation condition of the casing is better than that of the shaft, so the temperature of the outer ring of the bearing is about (8% lower than that of the inner ring and rolling elements) #3. Moreover, since the hollow shaft of the dryer passes steam, heat is transferred from the shaft to the bearing, and under high-speed operation, the temperature difference between the inner and outer rings of the bearing is larger. The radial clearance will be reduced due to the thermal expansion difference of the ring. Its value can be calculated as follows: ' 3'# ! 3 ! 4. In the formula: ' 3 is the reduction in radial clearance caused by the temperature difference between the inner and outer rings, the linear expansion coefficient of 22# bearing steel ('%9$ (0%#1:)! 3 inner and outer ring temperature difference, 3! 4+ outer ring raceway diameter, NSK ball bearing! 4+'% 7 ((;4<1), roller bearing! 4+'% 7 ; (*4<1), subtract '3' from the actual clearance after installation! 5 is the effective clearance!. Take the 113644 bearing as an example, the oil heating method is adopted, and the temperature reaches %9#3 at room temperature In between, according to different temperature sections, measure the change of bearing inner and outer ring size and radial clearance, and compare with the change of bearing seat inner diameter in different temperature sections, it is found that the size change of bearing inner and outer ring basically conforms to the high carbon The thermal expansion law of chromium bearing steel, and the bearing of ordinary clearance group is not suitable for drying cylinder and press roll. Due to the high ambient temperature of the drying cylinder (steam temperature is as high as 9##3 or more), the press roll has a large load (working The line pressure is as high as 99# u003d 72), considering that the heat and pressure of the equipment body will cause axial expansion and swimming, so use the !* series clearance group bearings instead, the operation side guarantees the most Small working clearance%>#$2, the minimum working clearance on the transmission side is 9## $2. In order to avoid the uneven change of impact force and affect the bearing installation quality, a hydraulic pump is used to install the bearing. In addition, the drying cylinder bearing seat and the bearing outer ring are changed from the original transition fit to the clearance fit, and the relative clearance control range; # 8:# $2. Various types of press roll drive side bearing seat and bearing outer ring are changed from the original transition fit to the interference fit, and the interference amount is controlled at 9# 8;# $2. The operation side bearing seat and the bearing outer ring are changed from the original transition fit to the clearance fit, and the relative clearance control range; # 8:#$2. $ Common irregular operations in bearing assembly For the installation of cylindrical bore roller bearings, many operators use the illegal method of red sleeve (fire heating), which is very wrong. Fire roasting is not only difficult to control the temperature, but more importantly, it is easy to change the material of the bearing, causing internal injuries, and the inner ring of the bearing is locally heated, causing stress concentration, easy deformation or even bursting, shortening the service life of the bearing. It is recommended to use oil heating method or electric heating method to ensure that the bearing is heated evenly to eliminate the above disadvantages. For SKF roller bearings with tapered holes, hydraulic tightening should be used to make the inner ring of the bearing evenly stressed, and the tightening force can be easily controlled to avoid various injuries caused by hammering. Conclusion: After practical exploration and continuous improvement, the wide paper machine of Qingdao Ruijing Electromechanical Equipment Co., Ltd. has been put into normal operation smoothly. The other 9 paper machines of width; 2 were renovated to increase the pressing area of u200bu200blarge-diameter rolls, the diameter of large-diameter rolls was % %*##22, the total weight of a single piece was about 9# @, and the maximum design line pressure was 9(# u003d '72, Swedish 45AB9*9:;5 is adopted for the bearings at both ends, and the matching dimensions are adjusted according to the actual situation. No accidents affecting production due to bearing damage have occurred so far. 9##9 Shanghai Electric Group Paper Machinery Co., Ltd. and the company jointly developed a large paper machine with a width ($( 2, working speed: ## 272CD, the whole machine installation and the bearing coordination and installation values u200bu200bof each component are all provided by the company, and now the machine has been put into normal production.
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