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Analysis case of paper machine bearing failure

by:JNSN     2021-12-24
Design data at home and abroad shows that the ordinary clearance group (!') is only suitable for general use conditions, that is, to bear ordinary load (radial load '#$%!u0026' below the load, and the inner ring speed is the limit speed of the bearing (#) or less. Therefore, our company selects imported bearings with a clearance set of !*, accuracy + or ,. This type of bearing can not only withstand large radial loads, but also can automatically adjust the center. The clearance is too large to cause noise and vibration. After analysis, for equipment with heavy load and high speed, if the interference between the bearing and the shaft is insufficient (that is, the pre-tightening force does not meet the requirements), the inner ring will rotate due to the load. There will be a creep (-u0026../) sliding phenomenon in the circumferential direction between the inner ring and the shaft, which will gradually increase the wear of the mating surface and damage the shaft and the shell. At the same time, the worn powder invades the inside of the bearing, causing heat and Vibration. In addition, the influence of the temperature difference of the bearing, shaft and housing on the fit interference cannot be ignored. The reduction of the inner ring interference due to the temperature difference! 12 can be calculated by the following formula:! 12'#$##% (!2·10%#1* (22) In the formula: !2———The temperature difference between the inner and outer shell of the bearing, 31——The nominal inner diameter of the bearing, 22 Between the bearing inner ring and the outer shell, due to the difference in temperature and expansion coefficient , The amount of interference will sometimes increase. On the other hand, due to the amount of interference left, the bearing is installed on the shaft and the housing, the ring will expand or contract to produce stress and damage. Refer to the technical standards provided in '45, interference The amount should be controlled below 6 7 %#### of the shaft diameter. In addition, the friction heat generated by the rotation of the bearing is dissipated through the shaft and the housing. The heat dissipation condition of the housing is better than that of the shaft, so the outer ring of the bearing has a higher temperature than the inner ring, The temperature of the rolling elements is low (8%#3. Moreover, due to the steam passing through the hollow shaft of the dryer, 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 greater. The radial clearance will be caused by The thermal expansion difference of the ferrule decreases. Its value can be calculated as follows: '3'#! 3! 4. In the formula:' 3—The radial clearance reduction caused by the temperature difference between the inner and outer rings, 22 #———Bearing steel wire expansion coefficient ('%9$(0%#1:)! 3———Temperature difference between inner and outer ring, 3! 4+———Outer ring raceway diameter, ball bearing! 4+ '% 7 ((;4<1), roller bearing! 4+'% 7 ;(*4<1), subtract '3 from the actual clearance after installation! 5, which is the effective clearance!. To 113644 bearing as an example, using oil boiling heating method, between normal temperature and %9#3, according to different temperature ranges, measure the change of the bearing inner and outer ring size and radial clearance, which is different from the inner diameter of the bearing seat Comparing the changes in the temperature section, it is found that the dimensional changes of the inner and outer rings of the bearing basically conform to the thermal expansion law of high-carbon chromium bearing steel, while the bearings of the ordinary clearance group are not suitable for drying cylinders and press rolls. Due to the relatively high ambient temperature in the drying cylinder section High (steam temperature as high as 9##3 or above), heavy load on the press roll (working line pressure as high as 99# u003d u003d'72), considering that the equipment body will be heated and compressed when it is rotating, it will cause axial expansion and swimming, so it is used instead !* series of clearance group bearings, the minimum working clearance on the operating side is guaranteed %>#$2, and the minimum working clearance on the transmission side is 9## $2. In order to avoid the uneven impact force change and affect the bearing installation quality, a hydraulic pump is used to install the bearing. In addition, the drying cylinder bearing seat and the outer ring of the bearing are changed from the original transition fit to the clearance fit, and the relative clearance control range; # 8: # $2. The transmission side bearing seat and bearing outer ring of various types of press rolls are changed from the original transition fit to the interference fit, and the interference is controlled at 9# 8 ;# $2. The operating side bearing seat and the outer ring of the bearing 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 roller bearings with cylindrical bores, many operators use the red sleeve (fire roasting and heating) illegal method, 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, which causes stress concentration, easy deformation or even bursting, and shortens the service life of the bearing. It is recommended to use oil boiling heating method or electric heating method to ensure that the bearing is evenly heated to eliminate the above-mentioned disadvantages. For roller bearings with tapered bores, hydraulic tightening assembly should be used to make the inner ring of the bearing evenly stressed, and the tightening force is easy to control to avoid various injuries caused by hammering. Conclusion: After practical exploration and continuous improvement, the paper machine of Qingdao Ruijing Electromechanical Equipment Co., Ltd. has been smoothly put into normal operation. The other 9 paper machines for width reduction; 2 were modified separately, and the large-diameter roll pressing area was added. The large-diameter roll diameter is% %*##22, and the total weight of a single piece is about 9# @, and the maximum design line pressure is 9(# u003d'72, the bearings at both ends are made of Swedish 45AB9*9:;5, and the matching dimensions of all parts are adjusted according to the actual situation. There has been no accident that affects production due to bearing damage. 9##9 Shanghai Electric Group Paper Machinery Co., Ltd. and the company jointly developed a large paper machine with cutting width ($( 2, working speed: ## 272CD, the installation of the whole machine and the bearing coordination and installation values u200bu200bof each component are all provided by the company. Now the machine has Put into normal production.
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