1、06FTM05Development of a Gear Rating Standard -A Case Study of AGMA 6014-A06by: F.C. Uherek, Rexnord Geared ProductsTECHNICAL PAPERAmerican Gear Manufacturers AssociationDevelopment of a Gear Rating Standard - A CaseStudy of AGMA 6014-A06Frank C. Uherek, Rexnord Geared ProductsThe statements and opin
2、ions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractThe AGMA Mill Gearing committee recently released AGMA 6014 rating gears for grinding mill and kilnservice.Inthedevelopmentofthisstandard,t
3、hecommittee tooka differentapproach todetermining theendresult of the standard writing process. Through review of previous standards, the reluctance of the usercommunity to support the street version of 6004, performance history for these long life (over 20 years)applications, and extreme size of th
4、is type of gearing, the committee achieved consensus on a new ratingmethodderivedfrom2101ratingpractice.Afactorcomparisonbetween6014and2101ispresentedaswellas their interaction to explain the goal of the committee to develop a document that reflects actual fieldexperience of operating sets in servic
5、e.Copyright 2006American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314October, 2006ISBN: 1-55589-887-41Development of a Gear Rating Standard A Case Study of AGMA 6014-A06Frank C Uherek, Rexnord Geared ProductsIntroductionThe AGMA Mill Gearing committee rec
6、ently re-leased AGMA 6014 rating gears for grinding milland kiln service. In the development of this stan-dard,thecommitteetookadifferentapproachtode-termining the end result of thestandard writingpro-cess. Through review of previous standards, thereluctance of the user community to support thestree
7、t versionof theinplacestandard AGMA 6004,performance history for these long life (over 20years) applications, andextremesizeof this typeofgearing, the committee achieved consensus on anew rating method derived from the AGMA 2001rating practice. A factor by factor comparison be-tween 6014 and 2001 is
8、 presented as well as theirinteraction to explain the goal of the committee todevelopadocumentthatreflectsactualfieldexperi-ence of operating sets in service.Explanation of gearing for grinding millsand kilnsGrinding mill and kiln service are an unusual instal-lation for gearing when compared to tra
9、ditional en-closed gear drive installations. But this applicationhasbeenutilizedforovereightyyears.Thegrindingprocess, more accurately termed a tumbling pro-cess, uses horizontalrotatingcylinders thatcontaingrinding media and the material to be broken. Thematerial moves up the wall of the drum until
10、 gravityovercomescentrifugalforcesanditdropstothebot-tomofthedrumtocollidewiththeremainingmateri-al. This breaks up the particles and reduces theirsize. Kilns rotate at far slower speeds to enableevenfiringoftheircontents.Powerrangesfrom100to20000HP(75to15000kW)ineithersingleordualmotor configuratio
11、ns.The pinion is mounted on pillow blocks driven by alow speed motor or a motor and enclosed reducer.Formillapplications,thegearismountedonthemillusing a flange bolted connection. See figure 1 forone type of installation. For a kiln, various types ofspringplatesareused.Boththecenterdistanceandalignm
12、entareadjustableeither byshimmingthepil-low blocks or moving the mill. Lubricant is typicallyeither high viscosity oil (1260 cSt 100 C)sprayedonthegearin15minuteintervalsoralowerviscosityoilorgreaseproductsprayedonthepinionevery few minutes. Alternately, lubrication can beapplied by continuous spray
13、 or dip immersionmethods.Figure 1. Grinding Mill InstallationGearsizescanrangeupto46feet(14meters)indi-ameterwithfacewidths approaching50inches(1.2meters). Typical tooth sizes range from 20 to 40module (1.25 DP to 0.64 DP). Single stage reduc-tion gears range from 8:1 toas muchas 20:1. Gearmaterials
14、 aretypically throughhardened cast steel,fabricated rolled steel or spheroidal graphic iron.Pinions are carburized, induction hardened, orthroughhardenedsteels. For smallinstallations, ei-ther a one or two piece design is used with the splitjoints located in the root of a tooth. Four piece de-signs
15、arealsomadewhenweightor pouringcapac-ity becomes an issue.How to Develop a Gear StandardThedailylifeofagearengineerinvolvesmanyactiv-ities. A large amount of time is spent designinggears sets for specific applications and comparingthese designs to standard practice. The engineerneeds tobalancereliab
16、ility, manufacturing,installa-tion, and cost against “good design practice”. Oneindicator of gooddesignpracticeisanindustrygearrating standard. This is a consensus drivendocument that strives to use a best practice com-mensurate with material capacity, installation skill,lubrication,quality,andanaly
17、sistoindicatehowwella specific design meets the industry and end userexpectations.2To develop a gear rating standard, a collection of text and formulas one needs to begin the process with thekey formula:Purpose =ni= 1People DiscussionMj= 1ExamplesText = 2Ballot = DocumentThecreationofastandarddoesno
18、toccurinavacu-um.Onemusthaveaclearpurposeinmindastotheoutcome of the process during development. Inmany cases, standards committees look at thecur-rent edition document and update it to account fortheworkofothertechnicalcommittees,newdiscov-eries inmaterial andlubrication, better manufactur-ing and
19、tolerance control, and results of the ISO“methodA”ratingpractice,i.e.fullscaletesting,andfield experience.AGMA has worked extensively to eliminate the dif-ferences in North American, European, and Asianratingpractices throughits work with ISO TechnicalCommittee 60. A gear should rate the same whenus
20、ing the same materials, processing, and accep-tance criteria - regardless of the location ofmanufacturer.Standardshavebeenupdatedworld-wide to support this convergence.The key issue is to know the outcome of the stan-dardswritingprocessbeforeonestarts.If thegroupis not clear what needs to be accompl
21、ished, theycan never be sure when they are finished.Given a clear purpose, the next stepis people. Thegroup of standard writers needs to be a diverse lot.Gearmanufacturers,metallurgists,lubricantsuppli-ers, and end users all need a seat at the table. Ev-eryone has a different view of the problem and
22、 thenature of the solution. Many AGMA publicationshave in its scope the following text:This standard is intended for use by the experi-enced gear designer, capable of selecting rea-sonable values for the factors. It is not intendedfor use by the engineering public at large.Thechallengeis todefinean“
23、experiencedgearde-signer”- andtocreatethemwheretheydonotexist.Committee members should be made up of peoplewithknowledgeinthesubjectathandaswellasper-sons who are knowledgeable in gearing but not inthe specific application under discussion. This al-lows for cross pollination of ideas from other area
24、sof thestandardwritingcommunity as wellas ensur-ing that theconcepts inthe standardare clearly ex-plained without the use of specific applicationjargon.It is also critical to include new gear designers whohavenotdevelopedastandardbefore.Tomaximizetheunderstandingofasubject,itisbesttobeontheground fl
25、oor of the area under discussion. Partici-patinginthesemeetings gives moreinsight intothedecisionmakingprocessandthebackgroundofthestandard. This provides significant understandingand a competitive advantage in the marketplace.Also key is the inclusion of the end users of theequipment since they enj
26、oy the benefits, or suffertheeffects of usingthegear designunder realwordconditions. They canprovideinsightonloadingpat-terns,dutycycle,installationissues,andproductlifecycle expectations.Thirdpartiessuchasconsultantscanexplainhowtouse the standard to their customers who developspecifications for ge
27、ar procurement. Bearing andlubricant suppliers bring the knowledge of theirproducts to the specific application at hand. Inturn,theyreceiveinsightintohowtheirproductsareusedin this application.When this knowledgeable group of people is col-lected, they need to move to the root of the matterand deter
28、mine how to convey their combined wis-dom andexperienceto the“experienced gear engi-neer” who is reading the standard for the first time.Thesediscussions areinvaluabletoproduceacon-sistent document that covers the interest of allstakeholders in theprocess. Topics can rangefromthe impact of tooth ali
29、gnment deviations on a 30inch (760 mm) long gear tooth, to deciding the rea-sonable life expectancy for a 200 ton gear set.During the authoring process, formulas will bechangedbasedonthediscussionsheldabove.Thereality check is to make sure that each change intext and numeric values supports the purp
30、ose thatwasdeterminedatthebeginningoftheprocess.Toooften, participants come to the process with a limit-ed view of gear design, such as carburized hard-enedandgroundAGMA quality A5gearingforgeardrives used in high speed applications. Standard3practicesandexpectationsfor manufacturingaccu-racythatare
31、achievablewithgearingthatis15inch-es(380mm)indiameterbecomesomewhatdifficultwhen the gear diameter is 450 inches (11430 mm).If the experiencebase oneworks from is higher ac-curacy gearing (for example quality range A7) andwrites the standard using calculations that assumethat level of accuracy for t
32、ooth elements, the stan-dardwillnotreflectrealitywhenusedwithgearofanA11 quality basis.The final gear rating is the effect of a collection ofvarious factors that are interrelated. If the perfor-mancedataandexperienceindicates that thestan-dard is 10% too low, and each factor is moved ac-cordingly, t
33、he result may become a 46% increase(1.104) after adjusting four factors. To prevent this,an early step in the process is to develop a suite ofexample problems that cover the size range of theproductsratedbythedocument,their varyingaccu-racy and manufacturing methods, and from differ-entmaterialsandi
34、nstallations.Usefulexamplesaretaken from real world experiences with successfuland unsuccessful installations. Then the interac-tions of the various factors can be tested on thisgroupof examples todiscover any unintendedcon-sequences of formula manipulation.Alltheseelements,people,discussions, andex
35、am-ples need to be integrated into a complete docu-ment. The creation of text is a challenging processfor engineers. Since precision is crucial, the typicalengineering sentence becomes a series of con-nected clauses supported by a number of commasand the occasional semicolon. Yet the users of thesta
36、ndardarepeoplewhodidnotattendthemeetingor whose native language is not English. Thereforeclarityandconsistencyofwordingisvital.Oneofthebesttrainingexperiencesforanewdesignengineertobecomeexperiencedintheartofgeardesignistobecome the editor of the standard. In this role, theeditor is responsible not
37、only for consistent wordusage, e.g. gear manufacturer, gear supplier, gearprovider, gear designer; but also for translating thevarious thoughts of the committee members into acoherent document. Because of this, the editor be-comes extremely familiar with the concepts in thedocument. They also develo
38、p the ability to “word-smith” phrases to achieve agreement among allparties.When the process is complete, two ballots are re-quired. One is by the committee members andserves as a final check to make sure that thethoughtsandconceptshavebeenclearlycommuni-cated. The second is a general ballot of the
39、AGMAmembership that can flush out any comments fromindividualswhocannotparticipateonthecommitteebut have an opinion on the matter at hand.The Ancient and Current PastAGMA 321DesignPracticeforHelicalandHerring-bone Gears for Cylindrical Grinding Mills, Kilns andDryers was first approved for use in Oc
40、tober 1943.Various iterations occurred with the last major re-writein1968whenthestandardwasupdatedtousethe formulations of AGMA 211 Surface Durability(Pitting) of HelicalandHerringboneGear TeethandAGMA 221 Rating the Strength of Helical and Her-ringbone Gear Teeth. The last editorial correctionswere
41、 issued in March 1970.Thebaseratingpracticeusesconceptsthatpredateour current AGMA 2001 thinking. The ratingformulas for gearing in this standard are:Pac=npd2Cv126000FCmIsacCp2C2HPat=npdKv126000FCmsatJPdWherePac= Allowable transmitted power for pitting(HP)np=pinion speed (rpm)d = operating pitch dia
42、meter (in)Cv= dynamic factor pittingF = face width (in)Cm= load distribution factorI=Ifactorsac= allowable contact stress number (lbs/in2)Cp= elastic coefficient (lbs/in2)0.5CH= hardness ratio factorPat= Allowable transmitted power for bend-ing (HP)sat= allowable bending stress number (lbs/in2)J=Jfa
43、ctorPd= transverse diametral pitch (in- 1)The major influence factors were assigned specificvalues based on the size and experience of the in-dustry with this type of gearing. Two dynamic fac-tors wereused, butbothwereafunctionof thepitch4linevelocityoftheset.Loaddistributionfactorwasafunction of fa
44、ce width only, covering the range of 2inches to 40 inches (50 to 1016 mm) with modifica-tionfactorstoadjustitsvaluewhenteethwerehard-enedaftercompletion.Theallowablecontactstresswas reducedby thestandard;however nometallur-gical properties other than hardness were dis-cussed. Thehardness ratiofactor
45、 was expandedtocover a ratio range of 1:1 to 20:1. The allowablebending stress was also reduced by the standardbut it also remained only a function of hardness.Service factors ranged from 1.0 for kiln and dryerservice up to 1.5 to 1.65 for grinding mill service.Brief reviews of the formulas disclose
46、 that a largenumber of gear rating factors are not present. Sizefactor, surface condition factor, overload factor,temperaturefactor,reliabilityfactorandstresscycle(Life) factor wereset tounity. Theinfluence of toothattribute accuracy, i.e. lead, pitch and profile, wasnot present andtheimpact of toot
47、h modifications toimprove load sharing was ignored.Despite these omissions, gears designed to thisstandard experienced 20 years of service life. Bothend users and original equipment manufacturersappreciatedtheconservatismbuiltintothestandardtoaccountforinstallationchallengesandlubricationissuesforth
48、esecriticalserviceapplications.Signifi-cant numbers of original equipment manufacturerscurrently specify AGMA 321.05 for new and up-graded installations. The reasons why will becomeapparent shortly.The Recent PastArevolutionsweptthegearratingcommunityinDe-cember 1982 when the AGMA Helical Gear Ratin
49、gcommittee issued AGMA 218.01 Rating the PittingResistanceandBendingStrengthof Spur andHeli-cal Gear Teeth. This document was a major over-haul of AGMA 211 and AGMA 221 with updates tolife factor, dynamic factor, and load distribution fac-tor. Recognizingthis change, theMill Gearingcom-mittee began a review of the 1970 issue of AGMA321andissuedtheir first draft of anewratingmeth-od, AGMA 6004, in March 1984. In May 1988AGMA 6004 was approved for publication and su-perseded AGMA 321.The base rating formulas for gearing when using aservice factor in this standard are:Pac=
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