Combined Cylindrical Roller / Tapered Roller Bearings

Combined cylindrical roller/tapered roller bearings, also referred to as “Kombi” bearings, have been developed by SKF. They comprise two single row cylindrical roller bearings and one double row tapered roller bearing, and support radial loads and axial loads separately. The outer cylindrical roller bearings have high load carrying capacity and are only subjected to radial loads. The cylindrical rollers are guided between two integral flanges on the inner ring, whilst the low flange on the inboard side of the outer ring serves to hold the bearing together until it is mounted. The tapered roller bearing with steep contact angle positioned between the two cylindrical roller bearings has two rows of rollers in a face-to-face arrangement and takes the axial load.

Kombi Bearing

These “Kombi” bearings are employed as work roll bearings on four-high stands of both hot and cold rolling mills and of cold sheet rolling mills. Increased demands with respect to the quality and accuracy of the rolled product as well as further developments in the production process for sheet steel involving the introduction of contra-bending and axial displacement of the rolls have meant that work roll bearing loads have been considerably increased. This means that the four-row tapered roller bearings normally used as work roll bearings can often not meet the requisite life demands because of the much heavier radial and axial loads applied.

Kombi Bearing – cold sheet rolling mills

Design Because of the need for frequent roll changes, the “Kombi” bearings are mounted with a loose fit on the roll necks. To alleviate the inevitable wear, the cylindrical roller bearings have a helical groove in the inner ring bore and radially extended grooves in the side faces of both inner and outer rings. The inner ring of the tapered roller bearings has a clearance fit on the roll neck.

Kombi Bearings – Design

An intermediate ring with annular groove and lubrication holes is positioned between the two outer rings of the tapered roller bearing. The designation suffix HA1 signifies that the inner and outer rings are case hardened.

Kombi Bearings

Dimensions The dimensions of the combined cylindrical roller/tapered roller bearings have the same dimensions as the four-row tapered roller bearings traditionally used as work roll bearings.

Tolerances SKF “Kombi” bearings are generally produced with dimensional accuracy to tolerance class P6 specifications. The running accuracy corresponds to tolerance class P5 specifications. Classes P6 and P5 conform to ISO 492:1994, classes 6 and 5, respectively.

Internal clearance The internal clearance has been chosen to suit the application, i.e. the radial internal clearance of the cylindrical roller bearings of the smaller bearings (d = 400 mm) lies within the C2 range and that of the larger bearings within the Normal radial internal clearance range. The axial internal clearance of the tapered roller bearings is between 40 and 80 �m for the smaller sizes and between 350 and 400 �m for the larger.

Cages The cylindrical roller bearings are fitted with a machined brass cage

Cylindrical Roller Bearings with a Machined Brass Cage

or a window-type cage of steel.

Cylindrical Roller Bearings with a Window-Type Cage of Steel

The tapered roller bearing has two steel window-type cages.

Tapered Roller Bearing with Two Steel Window-Type Cages

Speeds In operation, relative movements occur between the inner rings of the “Kombi” bearings and there will be an increase in friction between the side faces of the rings at high speeds. If the bearings are to be used at speeds in excess of 12 m/s, it is recommended that the SKF application engineering service be consulted.

Load carrying capacity and life The basic dynamic and static load ratings are given in the product table for each row of rollers. If assistance is required in calculating bearing life, please contact the SKF application engineering service.

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