Insert bearings are not intended to accommodate axial displacement of the shaft relative to the housing. The distance between bearing positions should therefore be short to avoid excessive induced axial loads as a result of thermal expansion of the shaft.
Design for small axial displacementTo accommodate small axial displacement, the bearings should be supported by resilient sheet metal support surfaces or walls (fig. 1).
Design for larger axial displacementIn applications where there are low speeds and light loads, an insert bearing with grub screws can be used to accommodate axial displacement. The shaft at the non-locating bearing position should be provided with one or two grooves, 120° apart, to engage a modified grub screw:
- Hexagon socket grub (set) screws with a dog point, in accordance with ISO 4028, but with a fine thread according to the product table. The grub screw should be secured by a nut and a spring or star lock washer (fig. 2).
The screws and groove(s) accommodate changes in shaft length and prevent the shaft from turning independently of the bearing. The sliding surfaces between the shaft and inner ring and those in the shaft grooves should be coated with a lubricant paste.
Recommended fits for insert bearings are listed in table 1. Fig. 3 illustrates the relative position of the upper and lower limits of the most commonly used ISO shaft tolerance classes for insert bearings, except for those with a standard inner ring. The values for these tolerance classes are listed in table 2.