1 girthgear

pinion

3 segment

b facewidth

da

tipdiameter

dmax

max.drumdiameter

Picture 1. Terms and definitions of an open gear

Girthgearsaremanufacturedfromsegments.A girth gear is divided into 816 segments,whicharejoinedbybolts.Thesegmentlengthtypicallyvariesbetween0.81.6m.Shortseg-ments enable the use of small versatile andaccuratemachines. Due to this, optimal and

precisetoothreliefscanbeproduced.Castingofshortsegments iseasy,securinghighandeven material strength properties. Segmentsareinterchangeable,whichreducessparepartcosts.Short segments also enable easy andcost-efficienttransportation.

Agirthgearcanbesingleordoublepiniondriv-en.Apinionismanufacturedasasinglepartwithanintegratedshaft.Thepinioncanalsobeseparate and mounted on a separate shaft,supportedbybearings,orontheoutputshaftofthemaingearunit.

The rotationspeedofadrumnormally variesbetween0.50rpmcorrespondingtothepe-ripheralvelocityfrom0.3to10m/softhegirthgear.ThenominalpowerofastandardKumeragirthgearisupto8MWpermesh,i.e.,16MWwhendoublepiniondriven.

INTRODUCTION

3

GEAR TECHNOLOGY

Themanufacturingmethodofgirthgearsena-bles wide possibilities for geometrymodifica-tions.Typically,thetoothgeometryisaccordingtoTable1.

Pinionflanksaremodifiedbytip,rootandendreliefs.Themodificationscompensatethede-flectionofthedrivesystem,thushighcontactpressureonthetoothedgescanbeavoided.

Table 1. Typical geometry of a girth gear

Min. Max. Standard

Module 0 40 7

Pressureangle,[] 4

Helixangle,[] 0 45 0

Numberofteeth:

Girthgear 100 300

Pinion 18 30

Facewidth,[mm] 100 500

Referencediameter[mm] 000 nolimitation

Quality ISO AGMA

GirthGear 810 97

Pinion 7 10

Thetoothloadcarryingcapacitycanbecalcu-latedaccordingtothefollowingstandards:

ANSI/AGMA 6004-F88 Gear Power RatingforCylindricalGrindingMills,Kilns,CoolersandDryers

ISO 6336 Calculation of load capacity ofspurandhelicalgears

DIN3990Calculationofloadcapacityofcy-lindricalgears

4

GEAR TECHNOLOGY

Table 2. Minimum service factors according to AGMA 6004 (* < 1.5 rpm)

Application Durability, CSF

Strength, KSF

Coolers 1.00* 1.5*

Dryers 1.00* 1.5*

Kilns 1.00* 1.75*

GrindingMills:

Ball 1.5 .5

Autogenous 1.5 .4

Rod 1.5 .5

Agirthgearcanbeassembledtoadrumwithaflangedconnectionorwithspringelements.

Picture 2. The FE-method is utilized for deformation and stress calculation of a whole girth gear including the strength calculation of the fixing structure

5

MATERIALS

A commonmaterial for girth gears has beenspheroidal graphite cast ironEN1563GJS800-. Nowadays, austempered ductile iron,ADI,EN1564GJS1000-5ismoreandmoreused.Itsprincipalattributeisitshighstrength-to-weightratio.

In the past, pinions were often made fromthrough-hardenedsteel.Atpresent,thestand-

ardmaterial forKumerapinions is case-hard-ened17CrNiMo7-6.Teetharegroundafterheattreatment.Thepinionshaveasubstantiallyim-provedload-carryingcapacity,betterqualityofteeth,andgoodsurfacequalityoftoothflanks,resultinginbetteroperationalreliability.Pinionsarealsolesswidewiththesamenominalout-put torque, which improves the load distribu-tionacrossthefacewidth.

Table 3. Material properties

Material Hardness Tensile strength[N/mm2]

Allowable contact stress

[N/mm2]

Allowable bending stress

[N/mm2]

Youngs modulus

[kN/mm2]

Girth gear

EN1563GJS800- 8030HB 800 700 48 185

EN1564GJS1000-5(ADI) 300360HB 1000 100 30 159

Pinion

EN1008417CrNiMo7-6 586HRC 100 1500 500 06

6

MATERIALS, ADI

The standardization of the ADI material hasproceededinrecentyears,whichfacilitatesitsuse. The standards ASTM A897/A897M-06,EN1564:1997,and ISO17804:005outlinethe ADI grades varying inmechanical proper-ties. The information sheet AGMA 939-A07AustemperedDuctileIronforGearscoverstheareasofdesigning,purchasingspecifyingandverifyingtheADImaterial, inparticular forap-plications in gears and power train compo-nents.

ADI is producedby heat treating ductile iron,usingtheaustemperingprocess.Austemperingis a specialized, isothermal heat treatment.When compared to conventional ductile iron,ADIcanhaveovertwicethestrengthforagivenlevelofductility.ADIcanhaveafatiguestrength

comparabletothatofcastandforgedsteels.ADIsstrengthcanbegreatlyenhancedbysub-sequentgrinding,filletrollingorshotpeening.

TheausferritematrixinADIundergoesastraintransformation hardening when exposed to ahigh normal force. This same strain transfor-mation hardening is what gives ADI a betterwearresistancethanthebulkhardnesswouldindicate. Other attributes of ADI material in-clude good noise dampening, fracture tough-ness,lowtemperatureproperties,andreason-ablestiffness.ADIhasa0% lowerYoungsModulusthansteel.Ingears,thisresultsinalarger contact area for a given input load. Insome cases, this has been shown to reducecontactstressandnoise.

Table 4. Properties of different ADI-grades

ADI 750 900 1050 1200 1400 1600

Herzianresistance Modest Moderate Fair Good Good Verygood

Bendingresistance Verygood Good Good Fair Modest Poor

Machinability Verygood Good Poor

Shotpeening Good Good

Loadcapacity Moderate High Veryhigh

Exceedsductileiron

Competeswith

through-hardening

Exceedsthrough-hardening

Competeswith

nitridedsteel

Exceedsflame

hardening

Competeswithcasehardening

7

LUBRICATION

Themostcommontypeofoperationallubrica-tion is automatic interval spray lubrication,wheretheappliedlubricationvolumeiscontrol-ledbythesprayaswellaspausetimes.

Ifadrumisrotatedbyagirthgearbeforethelubricationsystemistakenintooperation,prim-inglubricationisrecommended.Apriminglubri-cantpreventsdamageduringinitialoperation.Thepriminglubricantisappliedoncetoalltoothflanksbyabrushorspatula.

Basedonexperience, it canbestated thatagirth gears rolling strength and scuffing load

capacityareimprovedbyreducingflankrough-nessandincreasingtheeffectivecontactratio.Duringtherunning-inperiod,limitedwearisin-tentionallyproducedatthetoothflanks,whichimprovesthetoothsurfaceroughnessandfur-therincreasestheloadcontactarea.

During the running-in, increased lubricantthroughputisnecessarytoflushouttheinitialmetalwear generated through the removalofthe surface peaks and high spots during thefirststagesoftheprocess.Anaveragerunning-intimeis300hours.

Table 5. Lubricant consumption for running-in and operational lubrication

ApplicationConsumption (g/cm/op. hour.)

Running-in Operational

Rotarydrumdrives(coolers) 4 1.01.5

Singlepinionkilndrives 5 1.5.0

Singlepinionmillorkilndrives 6 .0.5

Singlepinionmilldrivesanddoublepinionkilndrivesoflargedimensions

7 .53.0

Doublepinionmilldrives 8 3.03.5

8

SELECTION

SelectionDeterminetheminimumdiameterofthegirthgear(table9)ddrum