(4) Improper adjustment of bearing clearance during assembly
The gap of the rolling bearing is divided into a radial gap and an axial gap, and its function is to ensure the normal operation and lubrication of the rolling elements and to compensate for the thermal elongation.
For a bearing with adjustable clearance, because of the proportional relationship between the axial clearance and the radial clearance, the installation is to obtain the required radial clearance as long as the axial clearance is adjusted, and they are generally For the use (that is, at the two ends or one end of the shaft), therefore, it is only necessary to adjust the axial clearance of one bearing.
However, for the reducer, attention should be paid to the tooth surface engagement when adjusting the bearing clearance. Generally, the axial gap is adjusted by a gasket (pressing wire method), and some can also be adjusted by screws or thrust rings.
If the gap adjustment is too large or the end cap of the reducer is loose during operation, the bearing clearance will be too large, which will not only cause the vibration of the bearing itself, the noise is large, the cage is easy to be damaged, etc., but also the gear surface meshing is not caused to cause the reducer to hit. Tooth accident. For example, DY's No. 2 kiln reducer, SS company No. 1 kiln coal mill reducer's teething accident is mainly caused by excessive bearing axial clearance and tooth surface misalignment.
For rolling bearings whose clearance is not adjustable, the radial clearance is determined according to the standard at the time of manufacture and cannot be adjusted. After such bearings are installed in the shaft diameter or in the bearing housing bore, the actual radial clearance is called assembly. Radial clearance, the assembly should be such that the radial clearance of the assembly can just cause the necessary working radial clearance during operation to ensure flexible rotation of the bearing.
When such a bearing is in operation, the shaft is relatively displaced due to the temperature rise when the temperature rises, so that the radial clearance of the bearing is reduced, and even the rolling elements are caught between the inner and outer races. This can be avoided by leaving an axial gap between one of the double-bearing rolling bearings (the other bearing is fixed on the shaft and in the housing) and the side cover.
A typical example is PY's No. 2 grate cooler No. 9 fan. The 8-disc bearing was replaced within one month. Finally, it was suspected that the bearing quality was not good and it was changed to an imported bearing, which still did not help.
The real reason is that when the maintenance personnel replace the bearing, the gasket added between the upper and lower bearing housings is lost, so that after the upper cover is pressed, the outer ring deformation of the bearing is flattened, the radial clearance becomes small or almost zero, and the bearing runs once. When heat is generated and the expansion is blocked, it will burn out due to rapid high temperature. In the worst case, the bearing will be burned after running for an hour or two.
After checking the lead wire of the fan bearing, it was found that the over-winning amount of each part of the mating surface of the bearing seat was very different. The most parts were added with 0.23mm gasket. The minimum part had almost no added gasket, and only the sealing glue was used to compensate. . After the bearing clearance is suitable, the operating temperature is about 40 °C, and everything is normal.
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