Backing Bearings

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Precision and endurancefor cluster rolling millsSKF backing bearings

Improved running accuracy

Extended service lifeReduced life-cycle costs



SKF backing bearings designedfor long service life

Cluster mills provide a high degree of reduction ratio at high rollingspeeds and specific rolling pressure. Moreover, the final product has tocomply with highest requirements relative to flatness and surfacefinish.

A pre-requisite is extremely high running accuracy of rolls and back-ing bearings († fig. 1), which transmit the roll forces into the housing.

Fig. 1

Backing bearings are based on a cylindrical roller bearing. They can have up

to three rows of rollers and are available with or without cages or seals Backing bearings mounted in a cluster mill

Backing bearings: featuresSKF backing bearings for cluster or Sendzimir mills are cylindrical roller

bearings with a thick outer ring to support the intermediate rolls andsubsequently the work rolls.

These bearings, which can have up to three rows of rollers, areavailable in several designs appropriate to the mill design (or configu-ration). Within the standard SKF assortment, backing bearings areavailable with or without seals; they are also available with or withoutcages.

Backing bearings for cluster rolling mills



SKF backing bearings are characterized by a number of standardfeatures.

The outside diameter of the outer ring has a logarithmic profileto substantially reduce edge loading during operation.The optimized internal geometry reduces friction and heatgenerated by the bearing.A high purity bearing steel improves wear characteristics.A unique heat treatment process balances heat stabilizationand wear-resistance.

Backing bearings: advantages

SKF backing bearings in the standard assortment shown on pages 6 and 7 can provide a number of benefits. These include

optimized running accuracyclose section height tolerancesincreased load carrying capacityimproved wear-resistanceextended service life.

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Fig.

Dynamic measurement of an assembled backing bearing

Advantage: optimized running accuracy

SKF’s advanced manufacturing processes enable tighter runningaccuracy tolerances. Higher running accuracy means better, more evensupport of the intermediate and work rolls during operation to providea more consistent, high quality rolled product.

Advantage: close section height

Using computer controlled measuring, sorting and assembly proced-ures, the section height tolerance can be kept within narrow limits.To do this, all inner and outer rings are measured individually andmatched with rollers of the appropriate size. The assembled bearingsare then dynamically checked († fig. ) and sorted according to their

actual running accuracy. This process controls the maximum deviationof the section height of all SKF backing bearings to within 5 μm, evenduring operation.



Advantage: increased load carrying capacity

To obtain optimum load distribution and the lowest stress levels withina bearing, SKF uses a quasi-logarithmic profile both in the roller/race-way contact surfaces as well as on the outside surface of the outer ring(† fig. ).

The logarithmic profile of the roller/raceway contact surfaces maxi-mizes the contact area, enabling the bearing to accommodate heavy

static and dynamic loads. The effective load carrying capacity of thebacking bearing is also enhanced by the logarithmic profile of the out-side support surface.

Advantage: improved wear-resistance

All SKF backing bearings are produced from ultra-clean bearing steeland the steel is subjected to a unique bainitic heat treatment process.This process provides a surface hardness in excess of 58 HRC whilemaintaining good ductility of the rings.

The improved surface structure enables the lubricant film to be builtup reliably. This also contributes to a reduction in wear.

Advantage: improved resistance against cracking

Backing bearings are typically not susceptible to cold welding to theintermediate rolls, and there is little risk of heat cracks occurring in theside faces of the bearing where they make contact with the thrustwashers. Compressive stresses at the raceway surface resulting fromthe bainitic heat treatment († fig. 4) make the rings tougher andand more resistant to cracking. Increased ductility also means that thebearing is better able to withstand the over-rolling of contaminants.

Advantage: extended service life

Improved wear resistance resulting from the ultra clean steel and opti-mized heat treatment process used to make SKF backing bearings cansignificantly extend their service life. The logarithmic profile of the out-er ring also improves service life as it maintains a favourable distribu-tion of load and stresses within the bearing.

Should wear tracks appear on the backing bearings, the SKF

Remanufacturing Services († page 8) can help. Remanufacturing canreturn the bearings to a like-new condition, to fully exploit the life of the bearing.

The application

Backing bearings have been specially developed for use on the backingbearing shafts of cluster (Sendzimir) mills. Several bearings arearranged on a stationary support shaft. The thick-walled outer ringsare in direct contact with the intermediate rolls and finally support thework rolls.

The rolling forces are transmitted to the housing via the backing

bearings, support shafts and saddles.Uniform load distribution of the roll force on each backing bearing

depends on its dimensional accuracy.SKF backing bearings are excellent at providing such support.

Fig.

Logarithmic contact profile and stress distribution

Fig. 4

Internal stress condition after bainitic heat

treatment

tensioncompression

5mm

1mm 15

10

20

Backing bearings for cluster mills

4



The product range

Backing bearings for cluster mills are manufactured in varioussizes and designs for support shaft diameters ranging from 70 to 180mm; the outside diameters range from 160 to 406 mm.

The product tables on the following pages show the standardassortment. For other sizes, check SKF for availability.

Bearing data – general

Dimensions

Backing bearings are tailored products and have dimensions that arenot standardized either internationally or nationally. The standardassortment of SKF backing bearings shown on pages 6 and 7 coversthe most common sizes used in cluster mills.

Tolerances

The inner rings are produced with a running accuracy that is better

than P4. The running accuracy of the outer rings is better than SP(Special Precision). For cluster mills the section height of all backingbearings on one support shaft must be as close as possible. Therefore,the bearings are graded into section height groups († table 1) andare marked accordingly.

The position of the maximum wall thickness of the rings is markedon one side of the inner and outer rings with an arrow. Two moremarkings can be found on the outer ring side face: to the left of thearrow the serial number of the bearing is marked and to the right of the arrow the section height group is marked († fig. 5).

Table 1

Section Section heightheight group tolerance

measureddynamically

– μm

A or 4 0 to –5

B or –5 to –10

C or 0 –10 to –15

Material

SKF backing bearings belonging to the standard assortment are pro-duced from extremely clean bearing steel and are bainite hardened.

Load carrying ability

The basic load ratings quoted in the tables take into consideration fac-

tors arising from the support of the outer rings by the intermediaterolls.

However, for reasons of strength and deformation of the outer ring,the value of the maximum permissible radial force Fr should not beexceeded.

The permissible static load acting on a backing bearing should notexceed the value of F0r or C0, whichever is smaller.

Lubrication

Depending on the design and application, backing bearings can belubricated with

greaseoilan oil/air mixturethe lubricant used for rolling.

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Backing bearing markings

11 B

Fig. 5

5



70 160 44,98 90 90 82,8 108,8 1 5 2¥4 10,5 1568 B 1160 44,98 90 90 82,8 108,8 1 5 2¥4 12 1568 BC 2165 47,5 120 118 90 110 1,5 5 1 14,5 BCZ-0510 3

165 47,5 120 118 90 110 1,5 5 1¥1 14,6 BCZ-050 AA 3

90 220 64,98 120 120 130 149 1,1 5 2¥6 30 1677 AB 4

220 64,98 120 120 130 149 1,1 5 2¥6 26,5 1677 AC 5220,02 65 96 94 120 150 2,3 6 6 20,5 BCZ-0508 6220,02 65 120 119 119 177 2 6 6 26 BCZ-0507 7220,02 65 122 119 117,5 177 2 6 6 26,74 BCZ-051 9

100 225 62,48 120 120 120,3 156,3 1,1 5 2¥6 28 15018 A 1

225 62,48 120 120 120,3 156,3 1,1 5 2¥6 24,5 15018 C 2225 62,5 120 118 130 183 2,3 - - 26,1 BCB 6495 A/HB1 8

225 62,5 120 120 131 145 2 - - 27,7 BCZ-051 8225 62,47 80 80 120,3 156,3 1,1 5 6 20,6 BCZ-0514 10

225 62,48 120 118 128,5 182,2 0,5 5 1 27 BCZ-0509 9

110 260 74,98 98 98 134 190 1 6 6 31 BCB 564 10

260 74,98 110 109 145 220 1 6 6 33,5 BCZ-0504 11 10 300 84,97 172,64 172,64 159,4 218,4 2,7 8 2¥6 72,5 148 B 2

300 84,97 172,64 172,64 159,4 218,4 2,7 8 2¥6 72,5 148 BC 2300 84,97 160 159,5 159,4 218,4 2,7 6,5 2¥6 66,6 1908 A/HA 2300,02 84,99 132 129 204 3 8 6 49 BCZ-0517 A 11

180 406,42 113,16 171,04 171,04 217,3 293,4 1,1 8 2¥6 120 1688 AB 12

406,42 113,16 217 217 217,3 293,4 1,1 8 2¥6 165 1500 AB 12406,42 113,16 224 224 217,3 293,4 1,1 8 2¥6 170 15515 AB 12

1) No. of lubrication holes

Backing bearings for cluster cold rolling millsd 70 – 180 mm

Dimensions Mass Designation Design

d D H B C d1, F D1, E rmin K N1)

mm – kg – –

C

B

K

H

d ED

r

F

d1 D1

d1 D1

F E

d D11

1

2

3

4

5

6





® SKF is a registered trademark of the SKF Group.

© SKF Group 2007The contents of this publication are the copyright of the publisher and may not bereproduced (even extracts) unless permission is granted. Every care has been takento ensure the accuracy of the information contained in this publication but no liabilitycan be accepted for any loss or damage whether direct, indirect or consequentialarising out of the use of the information contained herein.

Publication 658 EN · June 2007

This publication supersedes publication 5090.

Printed in Sweden on environmentally friendly paper.

The SKF Remanufacturing Services

Precision backing bearings represent a considerable investment. Whenthey can no longer fully meet the demands placed on them, it is gener-ally the case that remanufacturing can return these bearings to like-new condition. Remanufacturing offers a number of advantages– economically and environmentally.

From an environmental standpoint, remanufacturing saves rawmaterials, energy and machining costs. From an economic standpoint,you don’t have to pay for many of the raw materials, energy and

machining costs associated with a new bearing.

SKF Remanufacturing Services:proven procedures and OEM quality

SKF has established well-proven procedures for the remanufacturingof backing bearings. The service includes the usual regrinding of theouter ring but when required can include much more.

After the bearing has been thoroughly cleaned and inspected, allworn or damaged components are reworked or replaced to bring thebearing back to specification.

The procedures include the following steps:

receive the backing bearings, preferably as a complete set;dismantle and clean the bearings;perform wear and damage analysis;regrind the outer ring outside surfaceand refresh the logarithmic profile;rework or, if appropriate, replace components;assemble, inspect and reclassify section height groups;deliver bearings with an evaluation and test report.

A remanufacturing service at SKF takes some three to six weeks.

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Backing Bearings