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Reasons for bad bearing press fitting curve and solutions

wallpapers Tech 2021-01-19
At present, the assembly of the bearings, rear gears and journals mostly adopts cold press assembly technology, and the press assembly equipment is a recording system controlled by a hydraulic machine and a computer. After axle grinding, rear gear turning and phosphating, the bearings are configured according to the base axle system together with the bearing. The displacement-pressure compound curve truly reflects the quality of the press fit. Under normal circumstances, the pass rate of one-time press-fitting of bearings can reach more than 96.3%. The reasons for a small number of poor bearings in one-time press-fitting are concentrated on the press-fitting curve, and there are often curve peaks or lags, and steep tons.
 
Mechanism analysis of bearing assembly
 
The bearing is assembled as an interference cold press. The inner diameter of the seal seat, the inner diameter of the bearing inner ring and the journal interference are between 0.05 and 0.102mm, and the inner diameter of the rear stop and the anti-neck interference is between 0.018 and 0.085mm. During the assembling process, the top 1 of the bearing press is extended to accurately position the wheelset, and the clamping device fixes the wheelset. Subsequently, the press-fitting oil cylinder pushes the bearing placed on the bearing bracket. When the press-fitting force overcomes the positive pressure on the press-fitting mating surface (in the press-fitting process, the journal, backstop and bearing components will produce elastic and plastic deformation, and the mating surface When the friction force generated by the positive pressure is formed, the bearing and the rear block and the axle journal are relatively moved, so as to realize the assembly of the bearing, and finally print the displacement-pressure reflecting the pressure change with the position and the pressure holding time. 
 
Measures and effects
 
When machining parts, ensure the roughness of the bearing seal seat and the intermediate ring and eliminate the sharp edges of the lead-in part. After grinding the axle, the lead-in part of the journal should be polished by arc transition sand cloth or oil stone to ensure this Smooth transition at the place.
 
The axle journal and the anti-neck are processed by two machine tools. Affected by the difference in the accuracy of the grinding machine and the second clamping of the workpiece, it is easy to cause a certain deviation in the coaxiality of the axle journal and the anti-neck relative to the reference shaft. Because the parts of the axle journal are already tight at this time, the work is still proceeding with the axle journal as the benchmark. The rear gear will first overcome the sharp edges at the introduction part (the curve rises and then falls) and then press in the axle with interference coefficient Anti-neck (curve rises again), affected by the deviation of anti-neck grinding, the curve will then continue to rise or fall first and then rise or drop slightly, and finally, enter the holding pressure t. However, the anti-neck of the axle journal is ground by a machining center, and its dimensional accuracy and positioning accuracy are quite accurate. In addition, in the rear gear processing, it is necessary to strictly control the processing quality and eliminate sharp edges, so as to facilitate the inverted alignment of the rear gear on the axle neck.
 
The selection of rear gear and axle anti-neck must be carried out in strict accordance with the specified interference amount. At the same time, adjust the flow of hydraulic oil at both ends and the working time to eliminate the phenomenon of the no-climbing process.

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