AGMA 12FTM13-2012 Gear Material Selection and Construction for Large Gears.pdf
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1、12FTM13AGMA Technical PaperGear Material Selectionand Construction forLarge GearsBy F.C. Uherek RexnordIndustriesGear Material Selection and Construction for Large GearsFrank C. Uherek, Rexnord IndustriesThe statements and opinions contained herein are those of the author and should not be construed
2、 as anofficial action or opinion of the American Gear Manufacturers Association.AbstractFor gears larger than 3 m (10 feet) in diameter, construction of gear blanks tend to be divided into cast steel,ductileiron,andforgedrimweldedwebstructuresforuseincylindricalgrindingmillsandkilns. Thispaperwillre
3、viewtheapplication,variousoptionsformaterialselection,andtheimpactofselectionontoothgeometry. Agroup of sample gears are developed to compare each of the materials and methods of blank construction.Each sample is discussed in light of structural stress, deflection, expected life, handling weight, ma
4、terialorigin, fabrication method, inspection requirements during construction, and impact of selection on fieldperformance. Basedontheabove,aroadmapisdevelopedlistingcriticalconsiderationsandoptimaluseofeach material and method of construction in this application.Copyright 2012American Gear Manufact
5、urers Association1001 N. Fairfax Street, Suite 500Alexandria, Virginia 22314October 2012ISBN: 978-1-61481-044-53 12FTM13Gear Material Selection and Construction for Large GearsFrank C. Uherek Rexnord IndustriesIntroductionThe purpose of any gear mesh is to transmit rotary motion and torque from one
6、location to another at aconsistent rate. Various rating practices from AGMA, ISO, and others go into great detail about the toothproportions, accuracy requirements, materialselection,andcuttingmethods toproduceatooththatsatisfiesthe requirements of the application. However, standards do not provide
7、all information necessary to makesurethetorqueatthegeartoothisactuallymovedtothepieceofdrivenequipment,i.e.,gearblankdesign. Inmostencloseddriveapplications,adiskofthesamefacewithaboreandkeywayissufficient. However,whenin the realm of large gears, defined as 3 m (10 feet) in diameter and above, a so
8、lid blank fulfils the designengineers maxim of makingthepart difficult tomanufactureandimpossibletoinstall. Blankdesignneedstobe driven by the application and the range of materials available to ensure sufficient stress capacity is avail-ableattheteeth,aswellastheabilitytoconnectwiththedrivenequipme
9、nt. Thispapercoverstheseissuesina specific area of use: gearing for cylindrical grinding mills and kilns.BackgroundGrindingmillandkilnserviceareunusualinstallationsforgearingwhencomparedtotraditionalenclosedgeardriveinstallations, but theseapplications havebeenutilizedfor over eighty fiveyears. The
10、grindingprocess,moreaccurately termedatumblingprocess, uses horizontalrotatingcylinders that contain thematerial tobebroken potentially augmented by grinding media. The material moves up the wall of the drum until gravityovercomes centrifugal forces, and it drops to the bottom of the drum to collide
11、 with the remaining material.This breaks up the particles and reduces their size. Kilns rotate at far slower speeds to enableeven firingoftheircontents. Powerrequiredforthisprocessrangesfrom75to18000kW(100to24000HP),ineithersingleor dual motor configurations.In this type of application, the pinion i
12、s mountedon pillowblocks drivenby alow speedmotor or a motor andenclosed gear drive. For mill applications, the gear is mounted on the mill using a flange bolted connection(seeFigure 1for onetypeof flangeinstallation). For akiln, various types of spring plates are used. Boththecenter distanceandalig
13、nment areadjustableeither by shimmingthepillowblocks ormovingthemill. Lubric-antistypicallyeitherhighviscosityoil(1260cSt100C)sprayedonthegearin15minuteintervalsoralowerviscosityoilorgreaseproductsprayedonthepinioneveryfewminutes. Alternately,lubricationcanbeappliedby continuous spray or dip immersi
14、on methods.Figure 1. Grinding mill installation4 12FTM13Gear sizes can range up to 14 meters (46 feet) in diameter with face widths approaching 1.2 meters (50inches). Typical toothsizes rangefrom 20to 40module (1.25DP to0.64 DP). Singlestage reductiongearsrangefrom8:1toasmuchas20:1. Gearmaterialsare
15、typicallythroughhardenedcaststeel,fabricatedrolledsteel, or spheroidal graphitic iron. Pinions are carburized, induction hardened, or through hardened steels.Forsmallinstallations,eitheraoneortwopiecedesignisusedwiththesplitjointslocatedintherootofatooth.Four and six piece designs are also utilized
16、when weight or pouring capacity becomes an issue.Structure requirementsBased on the application, these gears need to have large bores to accommodate the mill or kiln shell. Thisenables useof reductionratios not normally thought of as reasonable(i.e.,8:1to20:1) inasinglestage. Thegears are bolted to
17、the mill through a flange connection or mounted on tangential spring plates to allow forthermal growth. See Figure 2.Thenextstepistoconnecttheboreofthegeartotheteeth. ThisisdonebyeitherusingaBox,alsoknownasaDelta or Y shape, or tee shape structure. See Figure 3.A typical ring gear has a series of wi
18、ndows cut into the material for handling and weight considerations, asshown in Figure 4.Over time design rules have been developed to address the material shape distribution of the variouselements of the ring gear structure. Rexnord has over 5000 gears in service with design lives exceeding 25yearst
19、hatconfirmstheserulesandcalculationsarereflectfieldrequirements. Thepurposeofthestructureistoprovidestability at thetoothlocation toensure theassumptions madeat therating phaseof gear develop-ment are supported by the actual blank design. Annex C of ANSI/AGMA 6014-A06 discusses the followingconsider
20、ations for blank designS reduction of strength rating by moving the location of bending fatigue failure into the gear rim from thetooth root (KBmfactor);S effect of rim deflection on the load distribution factor, Km;S influence of the mating element on load distribution factor, Km;S definition of dy
21、namic alignment techniques to achieve correct mesh patterns.Figure 2. Flange mounting and spring mounting options5 12FTM13Figure 3. Box/Y/delta and tee shape cross sectionFigure 4. Side view of ring gearRimthicknessisasignificantparameterinthedesign. Thereisaminimumvalueofthethicknessspecifiedbyther
22、atingstandards toensureanybendingstrengthfailureofteethwouldtravelthroughthebaseof thetoothand not through the rim of the blank. Based on field experience, AGMA 6014 suggests designs having abackup ratio mB1.0mB=tRht(1)wheremBis back-up ratio;tRis gear rim thickness below the tooth root, in;htis gea
23、r tooth whole depth, in.This avoids the need to derate the gear to move the failure mode to a more conventional area. Otherstandards,suchasANSI/AGMA 2001-D04,feelavalueof1.2ismoreappropriate. Apoint ofdebateiswhat6 12FTM13isconsideredtheinsiderimofagear. Conservativethinkingwouldrequirethatanymissin
24、gmaterialbelowthetooth root is the start of the inside rim diameter. Many designs feature a groove in the side of the gear formounting of a dust shield. This groove is located to generate a backup ratio of0.65 to 0.80. The loss ofsupport,typically13mm(0.5inch),isnotconsideredsignificantwhenworkingwi
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