Bearings with a cylindrical bore
With non-separable bearings, the ring that is to have the tighter fit should generally be mounted first. The seat surface should be lightly oiled with thin oil before mounting.
If the fit is not too tight, small bearings may be driven into position by applying light hammer blows to a sleeve placed against the bearing ring face. The blows should be evenly distributed around the ring to prevent the bearing from tilting or skewing. The use of a mounting dolly instead of a sleeve enables the mounting force to be applied centrally (fig 1).
If a non-separable bearing is to be pressed onto the shaft and into the housing bore at the same time, the mounting force has to be applied equally to both rings and the abutment surfaces of the mounting tool must lie in the same plane. In this case a bearing fitting tool should be used, where an impact ring abuts the side faces of the inner and outer rings and the sleeve enables the mounting forces to be applied centrally (fig 2).
With self-aligning bearings, the use of an intermediate mounting ring prevents the outer ring from tilting and swivelling when the bearing with shaft is introduced into the housing bore (fig 3). It should be remembered that the balls of some sizes of self-aligning ball bearings protrude from the side faces of the bearing, so that the intermediate mounting ring should be recessed in order not to damage the balls. Large numbers of bearings are generally mounted using mechanical or hydraulic presses.
With separable bearings, the inner ring can be mounted independently of the outer ring, which simplifies mounting, particularly where both rings are to have an interference fit. When installing the shaft, with the inner ring already in position, into the housing containing the outer ring, make sure that they are correctly aligned to avoid scoring the raceways and rolling elements. When mounting cylindrical and needle roller bearings with an inner ring without flanges or a flange at one side, SKF recommends using a mounting sleeve (fig 4). The outside diameter of the sleeve should be equal to the raceway diameter F of the inner ring and should be machined to a d10 tolerance. Drawn cup needle roller bearings are best mounted using a mandrel, see mounting instructions in section Drawn cup needle roller bearings.
It is generally not possible to mount larger bearings in the cold state, as the force required to mount a bearing increases very considerably with increasing bearing size. The bearings, the inner rings or the housings (e.g. hubs) are therefore heated prior to mounting.
The requisite difference in temperature between the bearing ring and shaft or housing depends on the degree of interference and the diameter of the bearing seat. Bearings should not be heated to more than 125 °C as otherwise dimensional changes caused by alterations in the structure of the bearing material may occur. Bearings fitted with shields or seals should not be heated above 80 °C because of their grease fill or seal material.
When heating bearings, local overheating must be avoided. To heat bearings evenly, SKF electric induction heaters (fig 5) are recommended. If hotplates are used, the bearing must be turned over a number of times. Hotplates should not be used for heating sealed bearings.
The internal clearance of single row angular contact ball bearings and tapered roller bearings is only established, in contrast to other radial bearings with cylindrical bore, when one bearing is adjusted against a second bearing. Usually these bearings are arranged in pairs either back-to-back or face-to-face, and one bearing ring is axially displaced until a given clearance or preload is attained. The choice of clearance or preload depends on the demands placed on the performance of the bearing arrangement and on the operating conditions. Additional information about bearing preloads can be found in the section Bearing preload so that the recommendations in the following refer only to the adjustment of internal clearance in bearing arrangements with angular contact ball bearings and tapered roller bearings.
The appropriate value for the clearance to be obtained when mounting is determined by the conditions when the bearing is under load and at the operating temperature. Depending on the size and arrangement of the bearings, the materials from which the shaft and housing are made and the distance between the two bearings, the initial clearance obtained on mounting may be smaller or larger in actual operation. If, for example, differential thermal expansion of inner and outer rings will cause a reduction in clearance during operation, the initial clearance must be sufficiently large so that distortion of the bearings and the detrimental consequences of this are avoided.
Since there is a definite relationship between the radial and axial internal clearance of angular contact ball bearings and tapered roller bearings, it is sufficient to specify one value, generally the axial internal clearance. This specified value is then obtained, from a condition of zero clearance, by loosening or tightening a nut on the shaft or a threaded ring in the housing bore, or by inserting calibrated washers or shims between one of the bearing rings and its abutment. The actual methods used to adjust the clearance and measure the set clearance are determined by whether a few or many bearings are to be mounted.
One method is to check the set axial clearance, for example, of a hub bearing arrangement, using a dial gauge attached to the hub (fig 6). It is important when adjusting tapered roller bearings and measuring the clearance that the shaft, or housing, is turned through several revolutions in both directions to be sure that there is proper contact of the roller ends with the guide flange on the inner ring. If the contact is not correct, the measured result will be inaccurate and the desired adjustment will not be achieved.
Detailed instructions for a selected bearing can be found at skf.com/mount.