How to define the position of the shaft, including the radial and axial positions, is the first consideration. Generally, the shaft adopts a double support structure, and the radial position of the shaft is defined by two supports, and each support should have a radial or angular contact bearing for radial positioning. The axial position can be axially displaced by two supports in each direction, and the axial displacement of the two directions can be limited by one support. Under normal circumstances, different axial positioning modes can obtain different running precisions. Therefore, when designing the support structure, the specific scheme of axial positioning should be selected according to the accuracy of the operation of the shaft and the working conditions.
In the case of simultaneous radial and axial loads, the bearings are often mounted in pairs in angular contact bearings and tapered roller bearings. Angular contact bearings are mounted in pairs in three arrangements. The outer faces of the two bearing outer rings are mounted opposite each other in a back-to-back installation. The two supporting force acting points fall outside the supporting span. Because of the large span of the support, the axial rigidity of the shaft cantilever is good, and the inner and outer rings are disengaged when the shaft is heated and extended, so that the shaft does not get stuck, so it is widely used. However, if a preloaded installation is used, the amount of preload will be reduced when the shaft is heated. The narrow faces of the two bearing outer rings are mounted opposite each other in a face-to-face manner.
The force application points of the two supports fall within the support span. The arrangement is simple in structure, convenient in assembly and disassembly, and debugging, and is also widely used. It is mainly used in occasions where the short axis and the temperature rise are not high, but it is necessary to leave a spare play. The axial clearance should not be too large, too much to reduce the running accuracy of the shaft. When the axial load is large and multiple bearings are required to be received at the same time, the series connection of the outer ring width and the narrow side of the bearing is often used. The bearing point of each bearing falls on the same side of the bearing, so it is called the same direction. When using this arrangement, care should be taken to ensure that each bearing can bear the load as evenly as possible, both structurally and manufacturingly.
When the machine is in operation, the temperature of the main shaft or the drive shaft is higher than the temperature of the adjacent parts, so the shaft will heat up. In order to keep the rotation of the shaft flexible, in the design of the support structure, while meeting the requirements of axial positioning accuracy, the requirements of the shaft to be freely stretched by heat are also considered. The way of axial positioning and axial expansion is corresponding.
The bearing clearance is adjusted to control the running accuracy of the shaft. The axial position adjustment of the shaft is to meet the special requirements of some meshing transmissions. For example, in a worm drive, the worm axis must fall within the mid-plane of the worm gear to ensure proper engagement, thus requiring the worm shaft to adjust its position axially. In bevel gear transmission, the apex of the conical cone of the two bevel gears must coincide, thus requiring both bevel gear shafts to be axially adjusted.
