Common faults of needle roller bearings and their cause analysis ) The outer race is peeled off and cracked; (6) The bearing raceway and rolling elements are indented. 2. Analysis of the cause of the failure (1) The inspection before assembly is not careful, the bearing should be cleaned before assembly and carefully check the inner and outer races, rolling elements and cage of the bearing for rust, burrs, bumps and cracks; check the bearing Whether the clearance is appropriate, whether the rotation is brisk and free, and whether there is a sudden blocking phenomenon; at the same time, check the shaft diameter and the size, roundness and cylindricity of the bearing seat hole and whether there are burrs or uneven unevenness on the surface. For the split bearing seat, a gap of 0.1mm ~ 0.25mm should be reserved between the joint surface of the bearing cap and the bearing base and the outer surface of the outer race to prevent 'clamping' at the 'tile openings' on both sides of the outer seat. The reduced clearance caused by the 'help' phenomenon, the wear is accelerated, and the bearing is damaged prematurely. (2) Improper assembly. Improper assembly will lead to the above-mentioned various failure forms of the bearing, as well as the following situations: A. Improper coordination The matching between the inner hole of the bearing and the shaft adopts the basic hole system, and the matching between the outer circle of the bearing and the bearing seat hole adopts the basic shaft system. Generally, the shaft and bearing inner race of centrifugal pumps, centrifuges, reducers, motors and centrifugal compressors that work under normal load conditions are matched with j5, js5, js6, k5, k6, and m6, and the bearing seat hole is matched with the bearing. The outer race is matched with j6 and j7. Rotating races (the inner races of most bearings are rotating races, the outer races are not rotating races, and the opposite is true for a small number of bearings), usually an interference fit is used to prevent the races from falling on the shaft diameter under load. Rolling and sliding occurs on the mating surfaces with the housing bore. However, sometimes due to the inaccurate measurement of the shaft diameter and the bearing seat hole or the roughness of the mating surface does not meet the standard requirements, resulting in excessive interference fit, the bearing seat ring is greatly squeezed, resulting in the radial clearance of the bearing itself. Reduce, make the bearing difficult to rotate, generate heat, aggravate wear or get stuck, and in severe cases will cause the inner and outer races of the bearing to crack during installation. Non-rotating races often use a fit with little clearance or interference, so that non-rotating races may cause tiny creeping, so that the contact surfaces between races and rolling elements are constantly replaced, and raceways of races are evenly worn. At the same time, it can also eliminate the axial jamming of the rolling elements in the bearing due to thermal elongation of the shaft. However, if the clearance fit is too large, the non-rotating race will rotate with the rolling elements, causing serious wear on the shaft (or bearing seat hole) and the inner race (or outer race), and friction will cause the bearing to heat and vibrate. B. Improper assembly method When the interference between the bearing and the shaft diameter or the bearing seat hole is small, the press-in method is often used for assembly. The simplest method is to use a copper rod and a hand hammer to symmetrically tap the bearing seat ring with an interference fit in a certain order, so that the bearing can be pressed in smoothly. In addition, soft metal sleeves can also be used to drive in with a hand hammer or a press. If the operation is improper, the race will be deformed and cracked, or if the hand hammer hits the race with non-interference fit, the raceway and rolling elements will be indented or the bearing will be damaged indirectly. C. Improper temperature control during assembly When the needle roller bearing is assembled, if the interference with the shaft diameter is large, it is generally assembled by the shrinkage method. The bearing is put into the oil drum containing the oil, and the outside of the oil drum is heated with hot water or flame. The process requires the heated oil temperature to be controlled at 80°C to 90°C, generally not exceeding 100°C, and most Z will not exceed 120°C . After the bearing is heated, quickly take out the sleeve and put it on the journal. If the heating temperature is too high due to improper temperature control, the bearing will be tempered and the hardness will be reduced, and the bearing will be easily worn, peeled off, and even cracked during operation. D. Improper adjustment of clearance during assembly The clearance of needle roller bearings is divided into radial clearance and axial clearance. Its function is to ensure the normal operation and lubrication of the rolling elements and to compensate for thermal elongation. For bearings with adjustable clearance, because there is a 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 It is used in pairs (that is, installed on both ends or one end of the shaft), so it is only necessary to adjust the axial clearance of one bearing. Generally, shims are used to adjust the axial clearance, and some can also be adjusted with screws or thrust rings.
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