Four-row tapered roller bearings
Four-row tapered roller bearings (fig 1) are used successfully worldwide for rolling mill bearing arrangements where rolling speeds are slow to moderate. Because of their design they are able to take up those axial loads which occur in such applications in addition to radial loads and generally no separate thrust bearings are required in such arrangements. This means that the roll necks can be relatively short and the chocks at both sides of the roll can have the same design (fig 2).
Four-row tapered roller bearings, because of their design, must be installed as complete bearings in the chocks. To enable quick roll changes to be made they must therefore have a loose fit on the roll necks. Loose fits have the disadvantage that the inner rings wander on their seats under the prevailing load conditions causing wear to the seats which normally have a lower hardness than the rings. To alleviate the effects of a loose fit to some extent, i.e. to reduce wear, SKF bearings have a helical groove in the bore and/or lubrication grooves in the side faces of the inner rings (fig 3). These grooves enable lubricant to be supplied to the contact surfaces of the inner ring and seat. Additionally, the grease-filled grooves can absorb the wear particles.
SKF produces an extensive range of four-row tapered roller bearings which covers not only the conventional designs with intermediate rings between the outer and/or inner rings (fig 4), but also a new design with modified rings which integrate the intermediate rings (fig 5). The particular advantages of these four-row tapered roller bearings without intermediate rings which have been developed by SKF include
- simpler mounting because of fewer components
- improved load distribution over the four rows of rollers, leading to less wear and longer service life
- simpler axial location on the roll necks because of reduced inner ring width tolerances
- dimensional equivalence to conventional four-row tapered roller bearings with intermediate
To enable these advantages to be exploited in all applications, those bearings of conventional design with intermediate rings produced by SKF are gradually being converted to the new design.