Rothe Erde® wire-race bearings.The proven bearing concept.

A ThyssenKruppTechnologies

companyRothe Erde

TK

2 Global success with quality slewing bearings and rings.

Our production programme includes ball and rollerbearing slewing rings, wire-race bearings, turn-tables, and seamless-rolled steel and non-fer-rous metal rings.

Rothe Erde has gained a strong globalmarket position with its slewing bearingprogramme. Rothe Erde slewing bear-ings are produced in Germany as wellas by our subsidiaries in GreatBritain, Italy, Spain, the UnitedStates, Japan, Brazil and China.Furthermore, we have establishedsales organizations and agenciesto represent us in all major in-dustrial markets. The Rothe Erdering programme also occupiesa top-ranking position in theinternational marketplace.

Our domestic and interna-tional production facilities areunited in their serious com-mitment to quality. In all ouractivities – from applicationsconsulting and design engi-neering to production and com-prehensive customer service –we are working to DIN EN ISO9001:2000.

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Rothe Erde wire-race bearings are the product of dedicated researchand development. The typical features of our wire-race bearings

are the high-strength races for the rolling elements. A wire-racebearing system allows structural and material combinations

as well as cross sections which are out of reach of any con-ventional antifriction bearing.

Dimensions, cross sections and the ring material of thebearings can be optimally matched to all applicationrequirements. Depending on their purpose, RotheErde wire-race bearings can be ball bearings, rollerbearings or a combination design of wire-racebearing and surface-hardened bearing. RotheErde wire-race bearings extend the range ofapplications for open-centre slewing bearings.They offer decisive advantages over conven-tional surface-hardened slewing bearingdesigns like high running accuracy, low anduniform torque resistance even when dis-torted, resistance to corrosion, low weightdue to the surrounding aluminium alloybearing rings and low maintenance.

Our bearing programme ranges from dia-meters as small as 80mm to diameters of upto 14m. Over 120,000 manufactured bearingsbear witness to the success of this special

antifriction bearing technology.

4 Rothe Erde wire-race bearings.A successful bearing concept.

The surrounding bearing ringsare not directly exposed to roll-ing friction, they do not have tobe made from steel but can con-sist of non-ferrous metals, castiron or synthetic materials. Inparticular, Rothe Erde wire-racebearings with light alloy bearingrings have gained special impor-tance. The same load carryingcapacity as that of comparablesteel bearings is achieved byusing an aluminium alloy of highmechanical strength as ring ma-terial. Compared to steel bear-ings of identical cross sections,aluminium wire-race bearingsweigh approx. 60 % less.

Tests at renowned institutes oftechnology as well as our ownR&D work have demonstratedthat the high mechanical strengthof this wrought aluminium alloymeans that the gearing can alsobe cut directly into one or morebearing rings.

A light alloy wire-race bearingcan be made corrosion-proofand maintenance-free by usingappropriate materials for therolling elements and races. Thecorrosion behaviour of aluminiumbearing rings can be significantlyimproved by a surface treatment.

5Weight comparison.Steel versus aluminium.

61.2 %Weight saved

Apart from the weight savings already mentionedRothe Erde light alloy wire-race bearings areparticularly advantageous in applications wherethe bearing is required to withstand shock loadsand travelling vibrations. Due to aluminium’ssmaller modulus of elasticity in comparison withsteel and the additional elastic deformation betweenthe races and race beds in the bearing rings, shockloads are absorbed much more smoothly, so thatbrinelling in the races and striation can be prevented.

The high elasticity of the wrought aluminium alloycharacterized by a low modulus of elasticity causesthe elongation differential to be fully absorbed bythe wire-race bearing.

Weight comparison betweenlight alloy and steel bearingsequal in size with the sameload-carrying capacity and anexternal diameter of 2200 mm.

641 kgWeight of the steel bearing

249 kgWeight of the aluminium wire-racebearing with identical cross section

Design types.Various approaches to the solution.

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Roller bearing slewing rings

Cross-rollerwire-racebearing

Three-wire-race rollerbearing

Fig. 3

Fig. 1

Double-rowinclined axiswire-race roller bearing

Fig. 4

Fig. 7

Fig. 5

Fig. 6

Fig. 2

Three-rowwire-raceroller bearing

• Transmission of axial, radial and tilting moments

• Almost constant frictional torque even if deformed and in a slanted position

• High stiffness

Bearing inclination

Fric

tiona

l tor

que

Centric axial loadapprox. 170 kN

Out

-of-

flat a

ssem

bly

face

/3 x

0.5

mm

Flat

ass

embl

y fa

ce

Frictional torque Mr as a function of the bearing inclination and distortion

Three-wire-race roller bearing

Out

-of-

flat a

ssem

bly

face

/3 x

1.0

mm

Mr Mr MrNm Nm Nm

25°20°15°10°5°0°

1000

800

600

400

200

0

1000

800

600

400

200

0

1000

800

600

400

200

025°20°15°10°5°0° 25°20°15°10°5°0°

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Ball bearing slewing rings

Single-row four-point wire-race ball bearing • Transmission of axial, radial,

and tilting moments

Double-row four-point wire-race ball bearing• Bilaterally acting to transmit

high axial loads• Self-retaining, i.e. the zero-play

condition is always warranted,even under a different thermalexpansion of the inner and outer bearing rings.

Single-row axial four-point wire-race ball bearing• Transmission of axial

and a certain amount of radial loads

Fig. 8

Fig. 10

Fig. 9

Axial wire-race roller bearing

Radial wire-race roller bearing

Single-row inclined axiswire-race roller bearing

All bearings can on principle also be designed with external, internaland special gearing or with a separate gear ring.

Single-row roller bearing slewing rings

• Transmission of a purely radialor axial load component or simultaneous transmission of both load components

• High stiffness in load direction

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Four-point wire-raceball bearingWith integrated 4-wayslip ring and retainingring with spring suspen-sion system. Particularlydesigned for the trans-mission of electric currentand limitation of the fric-tional torque in case of amajor deformation of thecompanion structure.Furthermore equippedwith earthing plugs tocompensate the potentialbetween the bearing rings.

Four-row wire-race roller bearingParticularly designed totransmit loads due tothe different expansionbehaviour of the outerand inner companionstructure or to preventradial clearance in thiscontext.

Hybrid-type four-pointwire-race ball bearingThe raceways of theinner ring are surface-hardened, the racewaysof the outer ring have awire filling. Particularlydesigned to enable thenecessary cast designto act at the same timeas outer ring.

Hybrid-type three-rowwire-race roller bearingThe raceways of theouter ring are surface-hardened, the racewaysof the inner rings have awire filling. Particularlydesigned to compensateraceway tilts due to theexpansion of the innercompanion structure.

Three-wire racebearingWith integrated ringmotor. Particularly de-signed to integrate thedrive into the bearing.

Segmented wire-raceball bearingParticularly designed forlimited available space.

Fig. 16

Fig. 14

Fig. 15

Fig. 11

Fig. 12

Fig. 13

Special designs.

9Bearing components.The possibilities.

Bearing rings• Aluminium

Surface: corrosion-proof• Steel normalized or hardened and tempered

Surface: corrosion-proof• Stainless steel, selection as required

(e.g. acid-resistant steels)• Special steels, selection as required

(e.g. magnetoresistive steels)• Bronze

(e.g. seawater-resistant bronze)

Rolling elements• Bearing steel, also

corrosion-resistant

Wire races• Hardened or naturally

hardened steels

Gear rings• The material can be selected as for the

bearing rings.• The gearing cut into the ring can be hardened.

Material combinations• Material combinations in one bearing are also

possible (e.g. rings of aluminium and gear ring of hardened and tempered steel).

Raceway: wires with rollers

10 Design and dimensioning.Mobilizing engineering solutions.

Fr

Fr

Fa

M

M

Fa

Fa

b

a

M

Bearing stress

RequirementStructures with slewing bearings normally requiredesign types which are able to transmit all occurringloads with one bearing. These are normally axial,radial and tilting moments.

These bearings must furthermore be suited towithstand the complete spectrum of operatingconditions, as for example• High and low temperatures including

temperature fluctuations• Overpressures and negative pressures • Deformations of the companion structure• Weight limits• Limitation of the frictional torque• Low maintenance• Corrosion resistance• Magnetoresistive behaviour• Open center to run through supply lines or

as access opening

Design and dimensioningThe bearings are individually designed and dimen-sioned for every application, this means that thebuyer is not required to customize to specifiedgeometries of catalogue bearings and character-istics but the bearing can be designed accordingto the customer’s structure and the specification.

A newly developed Rothe Erde computer pro-gramme is available to dimension the bearing.This is based on the finite element method (FEM)and can also consider companion structures andtheir behaviour under load when requested bythe customer.

Bearing unloaded Bearing under load (exaggerate illustration)

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Result: The Rothe Erde wire-race bearingRothe Erde wire-race bearings fulfill the describedrequirements. Due to the fact that the rolling ele-ments do not roll on the bearing rings but on thewires which are in the bearing rings, the materialselection and material combination of the compo-nents are nearly unlimited.

Decades of experience in design and productionand not at least the 120,000 bearings serving inpractice confirm that this bearing concept is right.

We are ready to develop a tailor-made solution fornew applications at any time.

In addition, wire-race bearings offer the possibilityof a more economical repair since it is often suffi-cient to replace individual components such aswire races, rolling elements, spacers and seals inorder to reuse a repaired bearing.

12 Application examplesfor wire-race bearings.

SOFIA – stratosphere observatory for infrared astronomyFor this project, Rothe Erde delivered an aluminumthree-row wire-race roller bearing with a boltedsteel gear ring for the rough adjustment of thetelescope. The telescope is in the rear of a con-verted Boeing 747.

During the flight, a sort of “sliding roof” opens toenable the telescope to make astronomic obser-vations in the infrared range.

SOFIA is a joint German/American project(DLR/NASA) to explore the universe. The infraredtelescope was produced by order of DeutschesZentrum für Luft- und Raumfahrt (DLR) e.V. withfunds from the German Federal Ministry forEducation and Research (Bundesministerium fürBildung und Forschung, BMBF).

Computer image of SOFIA

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Gemini – Optical telescopesRothe Erde delivered two three-row wire-race rollerbearings for the two Gemini telescopes. The bear-ing rings are made of aluminium. The bearingsenable the adjustment of the M2 mirror.

In addition, a surface-hardened three-row precisionbearing was supplied to adjust the M3 mirror.Astronomic faculties use these telescopes for theirextensive research.

One of these telescopes is located in Hawaii, theother in Chile.

Gemini telescope

Gemini barrel

Articulated busesRothe Erde supplies hybrid-type four-point bearingsfor the articulation of buses, consisting of a wire-race bearing part and a surface-hardened part.

The majority of the articulated buses are referredto as pushers, i.e. the engine and entire drive unitare located in the rear section, in the trailer.

This concept puts a lot of specific requirementson the articulation, such as buckling stability, forinstance, which is achieved by means of a compli-cated electronically-controlled damping system.

Mechanism of articulated buses

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Electric light bulb productionRothe Erde wire-race bearings are used in indexing tables for theproduction of electric light bulbs. The production of electric lightbulbs causes strong vibrations on the machine. Rothe Erde slewingbearings absorb them without any problem. When the bearingsare repaired, the raceway systems can furthermore be readjustedto the original delivery condition.

Mounting situation – production of electric light bulbs

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Trolley bus, Berne

The integrated managementsystem of Rothe Erde consists of the following elements:• Quality assurance system

after DIN EN ISO 9001:2000,• Environmental control

after DIN/ISO 14001 and• Industrial safety

after OHSAS 18001.

16 MaQUS.The integrated management systemof Rothe Erde.

Rothe Erde is conscious of its responsibilities towards its staff, itsbusiness partners and the general public.

It is the declared aim to cultivate and strengthen customer relations,to manufacture products of the highest quality and to minimizeharmful consequences to the environment, the general public andto property. Preserving resources and continuously improving proce-dures are important elements in company policy.

Rothe Erde products are designed and manufactured in accordancewith the internal definitions of the company and customer require-ments, taking as a basis approved and assured calculation methods,design guidelines and manufacturing methods.

Management-Handbuch Rothe Erde®

Produktbereich Großwälzlager.

„Qualität, Umweltschutz, Arbeitssicherheit“

Management handbook Rothe Erde®

Product range Slewing Ring Bearings.

„Quality, environmental control, industrial safety“

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Quality assurance, environmental protection and safety are RotheErde’s economic success factors.

The basis of the management system is the documentation of allprocesses and sequences as defined by the procedural rules andworking instructions with consideration for the requirements of laws,regulations, guidelines, specifications and agreements.

Effective quality assurance, environmental control, industrial andmechanical safety can only be achieved with motivated personnel.A regular exchange of experience hand-in-hand with training andfurther education enhances the awareness of personnel at all levelsand improves both expertise and the responsibility for actions.

18 Research and development.

Using the most modern technol-ogies, the Rothe Erde Researchand Development Centre sub-jects all new bearing designs torelentless and assiduous testing.It investigates further develop-ments and prepares ground-breaking, practical solutions.Findings, experience and newideas are thus transferred intoproducts for the market as awhole and for specific customers.

Frictional torque measurement at sub-zero temperature in the climatic test chamber

Research and development isone of the central fields of ourproduct development. In cooper-ation with the technical depart-ments, the bearings and theircomponents are developed andtested here under most differentconditions. Amongst otherthings, this includes tests athigh or sub-zero temperaturesranging from - 60 °C to 250 °C,frictional torque measurementsand stiffness measurements.Investigations ordered by thecustomer are also possible.

Climatic test chamber

Frictional torque measurement at room temperature

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Frictional torque measurement with original companion structureof the Gemini telescope.

Tightness test (“splash water test”) of a wire-race bearing with inte-grated slip rings for electric current transmission (see page 8, fig. 14)

Frictional torque measurement in a slanted position

Rothe Erde GmbHTremoniastrasse 5-11D-44137 DortmundPhone: +49 (2 31) 186 -0Fax: +49 (2 31) 186 -25 00E-mail: sondertechnik@thyssenkrupp.comInternet: www.rotheerde.com

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