Short shaft under ordinary working temperature (span L<400mm), the pivot point is often fixed in a one-way way at both ends, and each bearing is subjected to axial force in one direction respectively. In order to allow the shaft to work with a small amount of thermal expansion, bearing installation should be left with 0.25mm-0.4mm of axial clearance (clearance is very small, structure drawings do not need to be drawn), the amount of clearance is commonly used shims or adjusting screws to adjust. When the shaft is longer or the working temperature is higher, the thermal expansion and contraction of the shaft is larger, and it is appropriate to use the pivot structure with one end fixed in both directions and one end moving. The fixed end is supported by a single bearing or a bearing group in both directions, while the free end ensures that the shaft is free to move when it expands and contracts. In order to avoid loosening, the inner ring of the traveling bearing should be fixed axially with the shaft (often using elastic retaining ring). When using cylindrical roller bearing as a traveling pivot, the outer ring of the bearing should be fixed axially with the machine base, and rely on the movement between the roller and the ring to ensure the free expansion and contraction of the shaft. The shaft that requires left and right bi-directional travel can use the shaft system structure with two ends of travel. For the high speed active shaft of herringbone gear transmission, in order to automatically compensate for the error of the helix angle on both sides of the wheel teeth, so that the teeth are evenly stressed, the structure of the shaft system that allows a small amount of axial play left and right is used, so both ends are selected cylindrical roller bearings. The low-speed gear shaft system that engages with it must be fixed at both ends so that both shafts can be axially positioned. The bearings are generally positioned on the shaft with a shoulder or sleeve, and the positioning end face is kept in good perpendicularity with the axis. To ensure reliable positioning, the radius r1 of the shoulder must be smaller than the radius r. The height of the shoulder is usually no more than 3/4 of the height of the inner ring, too high to facilitate bearing disassembly. The axial fixing of the inner ring of the bearing should be based on the size of the axial load by using shaft end retaining ring, round nut, shaft elastic retaining ring and other structures. The outer ring is fixed by the end face of the housing hole, elastic retaining ring for hole, pressure plate, end cap and other forms. When the number of loaded rolling body changes, it will produce the excitation when a radial load is loaded on a certain bearing, it carries the load of the rolling body number in operation will have some changes, which caused the load direction of the shift. The resulting vibration is inevitable, however, the bearing vibration and noise seem to be reduced nowadays, why is this? It is because the bearings are now designed with preload to reduce, loaded on all rolling elements, thus reducing vibration and noise. Although the use of preloading, but, also can not completely lift the vibration, noise trouble. So, how to further reduce the noise? 1、 Stop the excitation vibration between the excitation part and the resonance part. 2、 Change the stiffness to change the critical frequency. 3、 Remove the critical excitation vibration.

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