Design of bearing arrangements
Single row tapered roller bearings must either be used with a second bearing (fig. 1) or as a matched pair (fig. 2, fig. 3). The bearings must be adjusted against each other until the requisite clearance or preload is obtained (→ Bearing preload). To maximize bearing performance and operational reliability, the appropriate clearance or preload must be selected and then applied during the mounting process. When the operating clearance in a bearing arrangement is too large, the load carrying capacity of both bearings cannot be fully utilized. Excessive preload increases friction, which increases the amount of frictional heat and reduces bearing service life.
Fits for inch bearings
In contrast to metric bearings, which are machined to a minus tolerance, inch bearings are machined to a plus tolerance (table 1). Therefore, the deviations for shaft and housing diameters for metric bearings are not applicable. Suitable fits for inch bearings can be obtained from the recommended fits for metric bearings. Table 2 and table 3 provide the shaft and housing fits for inch tapered roller bearings that are valid for Normal tolerance bearings in typical applications.
Fits for matched bearings
The axial internal clearance of matched bearings arranged face-to-face or back-to-back (table 4) provides an appropriate operating clearance when the bearings are mounted on shafts machined to:
- d ≤ 140 mm → m5Ⓔ
- 140 mm < d ≤ 200 mm → n6Ⓔ
- d > 200 mm → p6Ⓔ
These shaft seat tolerance classes are recommended for normal to heavy rotating loads on the inner ring. If tighter fits are selected, be sure that the bearings are not “clamped” and that they are able to rotate freely. For additional information about shaft tolerances, contact the SKF application engineering service.
For stationary outer ring loads, the recommended housing bore tolerance class is J6Ⓔ or H7Ⓔ.
When adjusting tapered roller bearings against each other, the bearings must be rotated so that the rollers assume their correct position, i.e. the large end face of the rollers must be in contact with the guide flange.