WD Rolling Mill Bearings | Four-row Tapered Roller Bearings

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Rolling Mill Bearings

WD Rolling Mill Bearing: Four-row tapered roller bearings

WD four-row tapered roller bearings(fig) 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 .

WD 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 seatings under the prevailing load conditions causing wear to the seatings 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, bearings have a helical groove in the bore and/or lubrication grooves in the side faces of the inner rings . These grooves enable lubricant to be supplied to the contact surfaces of the inner ring and seating. Additionally, the grease-filled grooves can absorb the wear particles.

WD four-row tapered roller bearings are produced with dimensional accuracy corresponding to

-	Normal tolerances for metric bearings
-	Normal tolerances for inch bearings.

The running accuracy of all bearings is to tolerance class P5 specifications

The Normal and tolerances class P5 for the metric bearings conform to ISO 492-2002. The values of the Normal tolerances for inch bearings follow tolerance class 4 according to ANSI/ABMA Standard 19.2-1994. The ISO Standard 578:1987, which also covered this tolerance class for inch bearings was withdrawn in 1997.

Internal clearance：

WD four-row tapered roller bearings are delivered as ready-to-mount bearing units with an axial internal clearance adapted to the actual application. The bearing components must be arranged in the prescribed order and may not be interchanged with components of another bearing.

WD four-row tapered roller bearings having a clearance other than that of the basic design are identified by the designation suffix C followed by a three or four-figure number which is the mean value of the axial internal clearance expressed in µm .

Working Temperature ：

WD four-row tapered roller bearings are subjected to a unique heat treatment process that enables the bearings to be operated up to +150 ℃ without any inadmissible dimensional changes occurring.


Cages：
Four-row tapered roller bearings are fitted with either ：
Four pressed steel window-type cages
Four steel pin-type cages

Minimum load ：

In order to provide satisfactory operation, WD four-row tapered roller bearings, like all ball and roller bearings, must always be subjected to a given minimum load. Otherwise the inertia forces of the rollers and cages, and the friction in the lubricant, can have a detrimental influence on the rolling conditions in the bearing arrangement and may cause damaging sliding movements to occur between the rollers and raceways.

The requisite minimum load to be applied can be obtained from: Frm = 0,02 C

where：

Frm = minimum radial load, kN

C = basic dynamic load rating (se product tables), kN

The weight of the components supported by the bearing, together with external forces, usually exceeds the requisite minimum load. If this is not the case, the four-row tapered roller bearing must be subjected to an additional radial load.

Equivalent dynamic bearing load ：

P = Fr + Y1Fa	Fa/Fr ≤ e
P = 0.67Fr + Y2Fa	Fa/Fr > e

The values for the calculation factors e, Y1 and Y2 can be found in the product tables.

Equivalent static bearing load ：

P0 = Fr + Y0Fa

Values for the calculation factor Y0 can be found in the product tables.

Design of bearing arrangements ：

Roll neck requirements

In most rolling mill applications WD four-row tapered roller bearings are mounted with a loose fit on the roll neck. The roll neck journal and the axial abutment for the inner rings must have a certain minimum hardness. The recommended hardness is

45 Shore (≈ 34 HRC) for the roll neck surface

60 Shore (≈ 45 HRC) for the axial abutements for the inner rings

Axial location of inner rings on the roll neck

The inner rings must not be axially clamped. There must remain a total clearance between the bearing rings and their abutments of 0,2 to 1,3 mm .

Mounting instructions ：

When mounting WD four-row tapered roller bearings, the components must be assembled in the correct order. To facilitate this, they are marked with letters . All the components of one bearing are also marked with the same serial number so that mixing is avoided if several bearings are being mounted at the same time.

As in the majority of applications the direction of load is constant with respect to the outer ring only approximately one quarter of the outer ring raceway will be under load. For this reason the side faces of the outer rings are divided into four zones marked I to IV. The markings for zone I are also joined by a line across the outside diameter of the rings . When the bearings are first installed it is customary for zone I to lie in the direction of the load. Depending on the operating conditions, the outer rings should be turned through 90° after a given period of service when the rolls are changed so that a new zone comes under load.

Detailed mounting and maintenance instructions will be supplied on request.