Due to the inaccurate measurement of the shaft diameter and the bearing housing hole or the roughness of the mating surface does not meet the standard requirements, an excessive interference fit is caused, so that the nsk bearing race is greatly squeezed, resulting in a decrease in the radial clearance of the bearing itself. It makes the bearing difficult to rotate, generates heat, and the wear is intensified or stuck. In severe cases, the inner and outer races of the bearing will be cracked during installation. The non-rotating seat often adopts a gap or a small interference, so that the rotation of the seat may cause a slight creep, and the contact surface of the race with the rolling element is continuously replaced, and the raceway of the race is evenly worn. At the same time, it is also possible to eliminate the axial jam of the rolling elements in the bearing due to the thermal elongation of the shaft. However, if the gap is too large, the non-rotating seat will rotate together with the rolling elements, causing severe wear of the shaft (or the bearing housing hole) and the inner race (or the outer race), and the friction causes the bearing to heat and vibrate.
B. Improper assembly method
When the interference of the nsk bearing and the shaft diameter or the bearing housing hole is small, the press-in method is often used for assembly. The easiest way is to use a copper rod and a hand hammer to symmetrically tap the bearing with an interference fit in a certain order to make the bearing smoothly pressed in. In addition, it is also possible to use a sleeve made of soft metal to be hammered in or pressed by a press. If improperly operated, the seat will be deformed and cracked, or the hammer will be hit on the non-interference fit seat, which will cause the raceway and the rolling element to be indented or the bearing to be indirectly damaged.
C. Improper temperature control during assembly
When the nsk bearing is assembled, if it has a large interference with the shaft diameter, it is usually assembled by hot charging. The bearing is placed in the oil drum filled with organic oil. The outside of the oil drum is heated by hot water or flame. The temperature of the oil required for the process is controlled at 80 ° C ~ 90 ° C, generally not more than 100 ° C, and the maximum is not more than 120 ° C. After the bearing is heated, it is quickly taken out and placed on the journal. If the temperature is not properly controlled, the heating temperature will be too high, which will cause the bearing to temper and the hardness will decrease. The bearing will be prone to wear, peeling and even cracking during operation.
D. Improper gap adjustment 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 bearings with adjustable clearance, because of the proportional relationship between the axial clearance and the radial clearance, the installation is to adjust the axial clearance to obtain the required radial clearance, and they are generally Used in pairs (ie at both ends or at one end of the shaft), therefore, it is only necessary to adjust the axial clearance of one bearing. Generally, the gasket is used to adjust the axial clearance, and some can also be adjusted by screws or thrust rings.
For nsk bearings whose gaps are not adjustable, the radial clearance is determined according to the standard at the time of manufacture and cannot be adjusted. After such bearings are mounted on the shaft diameter or in the bearing housing bore, the actual radial clearance is called Assemble the radial clearance, and make the radial clearance of the assembly just enough to cause the necessary working radial clearance during operation to ensure the 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.
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