_------ FOCUS _ The Submerged Induction of Gears

D.W. Ingham and G. Panish

This article is based o.n experience and refinement of papers prelliDusly presented gear design and manufacturing in Heal Treatment ~fMetals. procedures, to accommodate 1998.,1 arId 1998.2, pub- the induction hardening lishedb,.; The Woy; on Heal process now en ure lilia'l gears Treatment Cemre, Aston so treated are of guaranteed University, Asto" Triangle, quality, The process's purpose Birmingliam B4 7ET, UK. is to produce a continuous Tnis ,article was also pre- hardened layer, wllicll extends sented a.' the 1999 Fall alongthe tootIJ.lenglb and from Technical Meeting of ,the the [Ooth.' tip .. down, its flank, America'i GetU MtlnuJilctur- around tile fillet and root area Fig!. 1-Typicallwd'enjJg pattern. us Association. and up tile opposite flank to Ole Prifltedwith permission nexl tooth's tip (Fig, I). and to of the copyrigld Iwlder; tI,e ensure the depth of the ha:!dL American Gear Manufac- ened zone is sufficient, so the turers Association, 1500 subsurface high tooth stresses King Street. Suite 201, are cOlltainedin theh.igh Alexamlria, Virginia 22314. strength regions. Copies of the paper are In the submerged, toolh-by- available from the tooth process, the inductor Assoc.iation~ Statements pre- (Fig. 2), which has essentially sented in this paper are ,those the same shape as the space of the Authors ,and may not' between two adjacent gear l'epllesent' .tl,·e position or teeth. is energized and tra- opinio" ,0/ tire Ameri:ctm versed along the tooth space, Gear Mallufactz4rers Associa- heating and austen.itiz.ill1g the tiOIl. neighboring tooth surfaces, includingthe root-fillets, as it Introduction goes. The heating operation The tooth-by-tooth, sub- OCCUfi below the quenehant's merged induction hardening surface so, a soon as the IFig. 2:-:The induclor. process for gear tooth surface inductor has moved on, tt is hardenmg has been successful- replaced, by the surrounding ly performed al David Brown queachant; thus, healing and for more than 30 years, That are localized. pro- experienc~acked up by in- gressive •.and of short duration. depth research and develop- The heated and quenched ment-has given David Brown zone is so localized that distor- engineers a much greater tion and growth problems, understanding of. and conti- which tend to plague carburize dence in, the results obtainable case hardening, are essentially from the process. Also, field avoided. High . urface hardness

28 MA.RCH/APRIL 2001 •. GEAR TECHNOLOGV • www.gflllr/flChflology.com • .".ww.paws.transmlssion.com • 11HEAT TREATING FOCUS 11 _

and surface compressive resid- energy by the 14:] workhead i ual stresses, imparted by me in the gear han- .i I process. ,dramaticaUy improve dling machine. : the contact and bending fatigue The water-cooling tank sup- I".' strengths, plies three recireulatory line : This article deal...swith many a) to the inductor. which is ! ~ aspects of the proees itsellf. capable of some heating via its ! ! describes problem areas, con- own resistance and by radia- siders applications and discuss- lion &om tlte workpiece during I ' es the product's properties and processing; I I quality. b) to the qllencnant's heat The Induction Hardening exchanger; and , Process c) to the generator and the I r------~I At David Brown, the fre- workheaduansformer, 0.89 mm

quency used for gear induction The control console man- (lear hardening is 9.,6 kHz. and the ages the induction hardening Tooth range of tooth sizes processed. process by control of the indue- is 8 to 38 module. Figure 3is a tor traverse speed, inductor schematic drawing of the facil- energizing and de-energizing, 1.65mm ity, which is adjacent to a gen- quenchant flow, cooling water erator, water-cooling tank, oil- supplies, etc.. circulation tank and oontrol Over many years, David console. Brown performed research The gear handling machine projects onlhe proce s, be ides Fig. 5-Typical indllctoM.D-worlIlJlace COllp'ling.. rigidly supports the gear, accu- pr-oduction hardening. Con-

rately rotating, aligning and sequently. relationships be- 8..5,moo indexing it duril'lgprocessing. tween hardening parameters 900 35kWpower 800 150mm/min The water-cooled inductor is and hardened depth/pattern traverse speed secured to a workhead trans- have been establi hed., eliminat- I u 700... 'e!'600 former that is mounted OD a ing the need 1.0 establish pa- carriage in the gear handling rameters on separate test pieces. ~500.. ~4()()1 machine (Fig. 4). The work- The process is controlled by Io! head transfonner can be set to several signi ...ficant parameters •. 300 I traverse a distance of more these being: 200 I 100 than. one meter on linear bear- 1) .The Inductor Workpiece *, Leading edge 01inductor raac lies measurement position Gap. ing tracks. The inductor's actu- The space between the 4 6 8 10 12 Ti14 16 18 20 22 24 26 2830 32: IITle', seconlls __ al travel length is controlled by inductor and the gear tooth is Fig. hAn example ol the temperature d'istributionl within 61geertooli1l during ,In preset Limit switches. The critical. The surface-to-volume iinduclor pass. Tb depth and localionoh.l1e Ilimperaluruen-sor is indicated ,against machine is meant for the ratio differences around the leach temperatllra Icurve. process's submerged version, tooth profile demand different 700,...... ------,'60 with the inductor at the bottom ,ellergy requirements. Conse- center position. Consequently, quently, the shaping of the "- ...... , ...... _- much of the handling equip- inductor (Fig. 5) i important to 6DO ment is in an open tank filled optimize the coupling, The !

with quenchanr during process- inductor is designed for rigidi- II u a:: :I: ing and drained for loading and ty to ensure accurate geometri- .,,; !:l setting up.. cal positioning. I [ ! • 45 1:'" The generator, which pro- Research has shown the ' I :I:

vides lip 'to 75 kW, cenvertsjhe heating effect is controilled by I 400 -41 jI 18 the inductor's design, The i main power supply of 380 V, ~3G , 33 5'0 Hz. to a medium. frequency David Brown design includes ("I (9.6 kHz)1 supply at a nominal two copper sides connected by voltage of 500 V. That is trans- a copper bridge along the root i Distance from surface, mm formed [0 a supply of 50-V Taennocouples in the body of ! Il1g.7-TJpical b&rdeningplttern. www.pow ..rtrensmtsstoo.eom ,. www·ge .. rtecnnology.com • GEAR TECHNOLOGY' MARCH/APRIL 2001 291 _------HEATT,REATING,FO,CUS------I a tooth being hardened have be in the approximate range of I shown a typical temperature 125 mm per minute to 350

+400 I ! profile (Fig. 6). On the mid- mm per minute.

+300 I,' flank position, two tempera- 4) Quenching and cooling

I ture peaks are experienced, jets. Surrounding the mounted +2001 I coinciding w.ith passage of the inductor are: a) the fore and I +100 mductor's copper sides .. In the an qnenchant curtain jets, root position, a single peak is which help stabilize the vapor found, associated with the cop- phase that occupies the cou- per bridge. pling space and hasten and

Surl~ hatd~ 750HV David Brown's practice control the quenching, and b) involves the exclusive use of the si:de sprays-also curtain ~. numerically controlled rna- jets-which play on the tooth 8.2·moduie chine shaping of inductor top edge and adjacent flank to 3%CrIMQ 6teel blanks. The use of accurate control the heating pattern on tempered a1200'C shaping means it is only neces- the tooth's top and the sary for the operator to ensure amount of back- on that the inductor is aligned, the adjacent tooth addendum. ~II------central. to the tooth. space, and The settings for those jets,

+300 that the root gap is correct. and the quantities of quench- When that is done, the induc- ant flowing through them, are tor-to-workpiece gap at other important

+'00 I positions around the inductor 5) Power switching; When will be correct. a tooth space is to be hardened, 5 6 7 a a Distance ITom ilUrfllC!!. mm 2) The Power. As power is the inductor is automatically

! increased, the depth of heating advanced into the tooth space 1 is increased for a tooth size. II to a distance equal to about hal1 j naturally follows that the larger the inductor's length. Ar that I ~ ! the tooth size, the larger the point. the inductor is energized, 630HV ! . SAE .4J.40 ~ power requirements. and-after a hort dwell at the tempered at' BO"C i 3) Inductor Traverse entry-the inductor's traverse I Speed. Traverse speed deter- along the tooth pace com- mines the depth of heating by mences. Similarly, at the allowing more time for heat tooth's exitend, the inductor ..700 ' diffusion. Sufficient time stops, dwells and Is de-ener- , should be available to allow gized. That generally en ures +600 - Surface hardl1ess 650HV transformation to au stern teo a satisfactory hardening pat- Research by a dilatometry tern at the tooth ends. But, +

is homogeneous w.ith re peet range and hence some addi- -500 to carbon. and the carbides' tional tempering. particle size is small. which 2) MicmstTuctures. An favors easy so.luI1011during the induction-hardened, low-tem- -400 - short induction heating period, perature tempered material's i.e, 3-.10 seconds. The as- I hardened layer usually consists of fine tempered . ! hardened and tempered fl",. trength need not exceed and the tructure has II. much ! ' 0.45-0.50% staal 2 ClMrVTI 8.boul 1.000 N/mm • relined allsteniticgrain-sire-I 90 minute soak per,iod

Therefore, gear cutting and I;. though that i. not usually ! other machining operation apparent. Process parameters i -100-- a 100 !500 [0 are not difficuh to perfonn, .1' are selected avoid develop- I . .. ! Tempering Temperauira. ·C .R uUing Properties menl orf coarse marten ·1.tIC: 1) .l:iardlltss. Fi.gure 1! rnicrostructures. which can j Fig:. 11J.--!Eftecto~UII:plring 0l11111rtaC81 residual com .rressivllIrnS.1II shows a typicalltardness di 1Ii- i negalive1:y influence the hard- I bution, Induction hardened ur- I ened layer's toughness, :

faces, for which the carbon ' - All induction hardened 1 700 content is nominally 0..40% C, i layer's microstructure does not i ! u 1Ia1ly have hardne S value I always appear marten itic, but ; ! 600 of more than 55 HRC. and lip sometimes tends to resemble i co· to 60 HRC. a hardened. i the original quenched and ! ;: -.... ! ::c Tempering al 200-250°C tempered structure, though! I .,.:i' 500 reduce hardne liightly 10 c: much finer. Still. induction !;,., 'E -. about 54-57 HRC. Two fea- hardening's hardness values. ::c.' tures hould be noted: an added are typical of the marlensitic i ! ~I plateau of hardne (broken condition. ! .Ii lie), and a trough :in the curve 3) .Resi4ual Stresses.! 300 just. below l!he case-core june- Healing of a steel. surface by I tion, The first feature. which is indllction currents will be i 2DO - o 2 3 4. 5 occasionally observed. may accompanied by thermal I Distancelrom surface, mm relate to the extent of carbon expansion and a superimposed i Fig. 11-Eflecllol tempering Ionthe hardness profile ,0. an !inductiDn hlrd,nedl gear solutionand the degree of ear- contraction when the material t ·Iooth Uanl!(SAEI140steel). www.pow9rlrIlI!Sminiofl,com ,. www.gBSrlllchnoiogy.com • GEAR TECHN:OL'OGY , MARCH/APRIL 2001 .31

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CIRCLE 175 _------BEATTREATIIN:G FOCUS _

~passes through the austenite for carburized case depths. I transformation temperature The magnitude of the sur- I range. As a result, yielding may face residual stresses devel- ; occur somewhere in the heated oped during induction harden- ! layer, probably close 10 the ing is thought to be related to ~eventual caselcore junction, the depth of hardening (Fig. i and will contribute to. the resid- 9). though tne stresses are i ual stress distribution. But, the modified by tempering. as : stresses" development will be Figure 10 illustrates. Temper- i mainly due to the martensitic ing's effect on the hardness of i transformation. an AISI 4140 induction hard- i Martensite formation in the ened gear tooth surface is ! induction heated and quenched shown iiii Figure ] I, noting f layer involves a volume thai. the most used tempering

I ! increase above that of the temperature range for induc- ~ underlying core material, plac- tion hardened gears is

I I ing the har~ened surface i? a 200-250°C. ! state of residual compression, 4) .Bellding fatigue. lt is I which is balanced by residual crucial thaI the entire surface of ~tension imhe core, just beneath £he toolh roosfi llet region is Fig. 12-EHecl ,oithe amount of flank hardening on the,lbending,lll fatigue stIlmgtb 01 case (Fig. 8). The change gear le,th. S1eel 10.55%C. core :strength 880, Nlmml. IIh.e hardened. A mis ed area in that I from compression to tension region, either along the filJet or i occurs at a depth where the at the tooth end, will lower the i hardness is about 40 HRC. But, bending fatigue trength orne 1200' la)Contour j unlike the and '"' 1000 I 25%, compared with the tooth's E hardened 1 hardening process, which strength before induction hard- ~800 transforms the core before the zi i ening (Ref. 3). Baumganl (Ref. i600 j carburized layer, an inducrion 4)confmned the 25% loss (Fig. I heated surface layer will lose 12). With adequate rootrfillet heat during quenching to the ...... ,,- l hardening. the fatigue strength - ...... ------I quenchant and by conduction will be 60% (0 70% of that of a r into the workpiece's cooler carburized gear (Ref. 3) when ! body. The outcome is a resid- the surface hardness and the 200 i ual stress distribution where case depth are within reason- ! the compressive stresses in the able limits, i.e. 590 Hv to 650 ! hard case may have a high Hv, and minimum fillet case i value at some distance from the depth/modnie ratio is 0.25 to ! surface but stiU within the 0.30. ! case's harder part. Even so, the Fatigue tests employing a IIlIFllm'k i amount of surface com pres- beam type test piece, with lhardened [ sian is determined by the machined notches to simulate t hardened layer's depth .. The a 29 module gear tooth with a ! core tensile residua] stresses, stre S concentration factor of i which peak just below the 1.4, produced fatigue limit I hardened layer, need to be values of 510 Nlmm2 for a ~ carefully considered by gear 0.55% C plain carbon steel; ! designers, notingthat a deeper 527 Nlmm2 for a 0.50% C i case will push the "offending" chromium-vanadium steel; i residual tensile peak. deeper. to and 564 N/mm2 to 630 N/mm2 1 where the applied bend:ing for steels 4140 and 4340. The : stresses are of a low order: trend. was that the fatigue limit i That feature results in the ro e with core strength (772 fig ..U...... lh bending fatigue strength of indulrtor-h~rdened 8I!lm!31.lIIodll:le,gear_teeth 1 specification of a higher case Nlmm2 to 1.020 N/mm2), (vanous. steels): (a) centaur hardened; (b)flank bardened. Broken hnes denole scatter i d ~- h th .~. -rl d 1.. I d band lor D.IN3990. - , teptn: an wou oe emp aye which perhaps reflected each 34 MA.RCHIAPRIL 200t • GEAR TECHNOLOGY· www.lIeer,·echn0/olly.com • www.pow8r.rransmiss!on.com _____ HEATT1R~ATING FOCUS __ ._

steel's resistance to significant. ! dation nol to exceed 55 HRC

yielding- - under load. Po1 aror Ii urface hardness forlhe we of test ' (Ref. 3) on. 8 .mm module I tooth bending strength. is !in gears, produced the re uns line with current practice. not- hOWD in Figure 13 for full I ing that their contact. fatigue tooth pace induction hard- plots, shown in Figure IS, rep- ened and nank: induction hard- resent surface hardnesses of 52 ened teeth. HRCand 6] HRC. When the S) Conlllci JaJjgue~ A sur- surface hardness was 6] HRC. Toollnk Engineering face's contact fatigue strength the contact fatigue trength was ,offers hydraulicarbors made of a light Is related to its 'tensile strength I comparable to thai. of a ease metal alloy that and the urface material's hard- ! hardened gear of the same sur- weigh up to ness. Contact fatigue tests ! face hardness. Unfortunately, 70% less than using discs and having no. I! willi such urface hardne s, a comparable, Feather light steel arbor. nnentional sliding uggested ] orne tooth bending failures hydraui'ic that induction hardened sur- 1 occurred with the induction arbors can be faces had pining fatigue: hardened gears. In other tests manufactured with runout as low as (Ref. 5) 011 gears of about 6] trengths of about 80% of that I',:, 2 microns. The ,clamping of carburized and hardened KRC, the induction hardened sleeves are replaceable. ThIs urfaces (Fig. 14). Winter and i gear had a life (to tbe onset of tooting is suitable for measuring. testing, balancing. gear grinding Weiss confirmed !!hat eoserva- ! pitting) Ibat was 1..7 timesihat and other applications. tion (Ref. 3). With actual gear j of a case hardened gear. Again. r_ ~ II ... """-,_ TooUnk Engineering tests, they concluded that I some induction hardened gears 2870 Wilderness Place -_..- ...... -.g. induction hardened gears had l experienced tooth breakage. --""'KlInI!!--~.a..-_._..... Bould!lr. Co. 80301 ... 303,938.8570 '---..a._"'''''''- fA!( 303.938.8572 85 % of 'the contact fatigue 1 which may confirm Willter and Of.....• t~ • I.ll.• C.D. 0i'I~ strenlh of their case hardened I Weiss' recommendation. But. ••~.,..."....1!iI1IIIng. counterpart . Their recommen- i during contact fatigue tests, CIRCLE 17B 1~r------9 SPlliRA.L BEVEL GEARS fliransmiissions)

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_------.-."HEATTREATliNG FOCUS ------using narrow faced gears using quenching oil as the ll1Cll results inlootlt breakage frac- coolant, tures initialed attbe early con- The tooth-by-tootltinduc- 1600 tact damage on the tooth Hanks. Lion hardening process :in other Pitflills organLzations had an early his- Induction hardellinglias tory of tooth cracking prob- problems, ln the wrung beat lems (Ref. 1), usualliy via the treater's hands, the results can use of steel having too high a FVA oil 3: 1.:Pitting be di astrou . But, a number of carbon content and/or too low 1000 D Craterin!! problems hav,ebeen recog- a hardenability togeth· r with I[J Pittil!g ,and cr,g1ering nized and eliminated d'uring Ih use of higher quench rates .. 101 10' David Brown's years of experi- 3) .Melting and Over- Number 01 load cycles ence. That recognition provid- healing; IT the local tempera- ed insight and a clearer under- ture become too high due to, lib} CklS :deel,. fi,1 HlIC standitng of the process. fior example, too, close a cou- J) Baek: .tempe.ri'l~g. The ple,lhe.re will bea risk of sur- hardening ofa si.ngl'e tooth face overheating or melting. means the tooth surface attains Overlleating produces 3. coarse a temperature in excess of martensitic miceostrucnire in 720°C. The quencham re- the as-quenched surface, A 'FYI!. oH3.4: moves much of the heat, bur melted area produces a surface 6.Crate ring some heat conducts through layer with a dendritic structare 101 the looth. That heat can-par- and a sublaycr of 'overheated Number ,of load cycles t.icul.ar.ly with small pitch material (Fig. 1.7). Such OCCUl'- fi'g'. ls-tDMaCf 'migus' resistlnce 0'iDiluctlOD-I'I.nl8IId !I'" lJetllnm ,agal,nd camurizod teeth('~ lal42CrM04 steall52 HRC: (bliCk, 45 steelJ(il HRC. Performa.nce of teelh:-resull in "back-temper- rences are to be avoided, case hardenedleeth shown shaded. ing" of the adjacent, previously although localized occurrences hardened tooth. at tooth end run out... can be Jet t~t "Back tempering" is con- dressed to remove I:heeffects. trolled by side cooling jets, 4): Unhardened areas. In7u,C, lor ,- IndlC,t"O,,1 - !I~ which are positioned to Flgure 18 bows examples of Gear Gsal 100111 tooth lmpinge omhe adjacent (oo!h's induction hardened gears top edge and direct flow down where small areas are left its flank (Fig. 16)..A considera- unhardened. (bl CaRect lion is !hal. tile adjacent tooth. In (a), an inductor did not "sees" the conducted heat a lit- dwell at either end of a gear tle later than the heated tooth tooth, causing a small area, a surface, and therefore the ide "thumbnail," to receive insuffi-

I jets need to be longer than the cient heating to effect harden- inductor. ing. To correct that fault, atten- A sm311 amount of soften- tion must be given to how far ing by back tempering is the inductor is introduced into almost inevitable and hoeld the tooth space before energiz- be accepted inlhe gear design. ing and how long It dwells there It is inherent in the process that in '!he energized state before 311the teeth exceptme 1 tone tarting its heating traverse. will experience the "back-tern- Such a defect may invite per" effect and that one tooth faligue cracking during service. (the fIrst) will have two flanks In (b), a poorly shaped or which experience the effect. damaged inductor led. to a. nar- 2) Root and Flank row band of uahardened sur- Crac/ci"g. Tooth root and/or face at the tooth fi.lIet. Within flank cracking has never really Ilhe hardened mface~, tile been II problem with the ub- residual stresses are compees- Fig. 17-O"verfleating andllm.BH[ng: (II overlleating (x450); (bl melting (xl0IU; leI over· heatingl with ,IItrace' ot melting (x540l. Slssl; BUM4D. merged, toolh-by-tooth process sive ..But i.n unhardened .areas, 36 MARCH/APRil 2001 • GEAR TECHNOLOGY' www.gslJr/9chnolol1y.com • www.pow9·rlrll·/l.smisslon.com • HIEAT TREAnNG, IFOCUS ••• _i til ~ such as those hown.fhere willi : degrees, and good to know SURREll be tensile residual stresses of a ! where the potential problem .'- areas might be. Tooth profile ~.= '...= ::t=:s~!·al~I movements due W induction u ~ill bave a. vel)' poor bending hardening are ilJu trated in Q,J, fatigue strength. Figure 20, where the shape ~ In (c), iasutficiemaneation change is less than 0.012 mm. to process parameters led to the Gear rims might also have a hardened layer being !:hin, or slight tendency to take on a ...... missing. near the '1ooth's end ..,It disbola shape, when the gear '$...4 is nermal forthe end hardened diameter al. me ends of the -< pattern to differ a little from teeth. is greater than the mid- ClJ that furthera'long the tooth; face width. The extent of the ~ there tends to be a smal shape change is affected by rim f-I amoun; of case thinning near thickne s and tooth face width; th,e exit end at a poiru midway the thinner the rim and the up Ute tooth face" as the top greater the face width, the The Lime is always right for row in Figure 18 shows. In greater the risk of that form of SUHRE.", spiral bevel gears. extreme circumstances, the distortion, Therefore. the thinner area may break: out to designer must take mat into Suhner \I:rnufoounng. Inc the surface. account at an early tage of 1'0 '1101 I~}t. Rome. GA3OIb2·1~}t l~lOI'" '0f).23'·1!1);~ • f\.~·(J6...!.~~i One very important factor design. Given that tendency, it IlIMII,uluIMiI!>:IUJlII . in relation to tooth end harden- is not advisable to induction S Ion expert, harden gear rims "shrunk" onto ----- ing problems is having the COf- SUHRER rect tooth end shape. chamfers a center, Welded fabrication and beveled edge . gear construction, on the other CIRCLE 16-3 5) ,uneven harde,ning pat- hand, is suitable. terns. Uneven han:l'elling pat- The ends of small- and terns are mainly due to IX>Or intermediate-sized teeth. which positioning of the inductor in are required to be induction the tooth space or to a lack of hardened, should be generous- ly radiused, On the other hand, inductor rigidity. Poor inductor Mode'l 'GSZO"4T alignment also causes uneven 1Mgt pinion teeth, for whi.ch a G'ear Sllaper hardening. deep case is specified and $86,395 . 6) Distortion alldgrowth. which are not planned to be ,20'"IDiamet'er Shape and volume changes are flank ground, should be 4" (or W') Face Widt,h no!:" as a rule, viewed as being tapered about 0.1 mm over the ignificant to induction harden- end '120m of flank, at both ing. Still, it is good to keep in 'ends of each flank, a· wel.l as mind that they do OCCIlf, having a 3 mm radius at the though generally to small edges. That is done to counter

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CIRCLE 1'56 .www.pOW!ilrtr.!!nsmluIOIl.com ... WW.QaBrlftchnology.com • GEAR TECHNOLOGV • MARCH/APRIL 200" 37 _------_1 HEATTREATINGFOCUS1 _

Table l-AGMA gear ratmqs lor vanous heat-treated conditions the minor growth that can wheel with a carburized and Gear tooth size AGMA rating (kWf occur at the flank ends due to hardenedpinion, or a through Through Through ; I c rbon induction hardening, thereby hardened wheel with an indue- hardened hardened Nitrided Indudion Module OP ':ass- 10 UTS of to UTS of 4140 hardened hardeMd causing hard meshing poinls in tion hardened pinion. 772Nlmm2 1158N1mm2 critical areas. Helical gear After an induction harden- 2 12.7' 1.52.9 3.3 3,6 (,2 2.5 10 J 5.66,6 7,,2 8,3 teeth need to be more gener- ing process is chosen, the engi- 3 8.5 5 9.4 11.1: 12.1 14 ously rounded at the acute " 6.35 11.6 21.8 26 28,3 32.9 neer should design the gear

6 4.23 I' 38.7 7.2.9 84.5 94.9 111 angle's edge, the amount accordingly. 8 3.18 88;6, 167 19_ 218 256 12 2.12 282 530 615, 691 815 depending on tooth size. 1) Double helical gears 20 1.27 I "163 2192 2558 28'15 3390 Applications should have a gap between the JO 0.65 3521' 6636 772'l 8680 10258 Induction hardening joins Results based on 25 pinion teeth running against 75 wheel teeth; helicaf two helixes into which the with face' width 0.4 x centres. an array of heat treatment inductor can pass when it has processes available to the completed a tooth traverse, Table 2-ApprolHiate heal treatment r~ designer. A process compari- Gear tooth size AGMA rating (kW) Modern bobbed gears will Ind!!Ction Induction Carbon SOil of the AGMA 218 gear rat- have that anyway. and gears Module OP' Nitrided hardened hardened case- ings for a range of gear tooth need at 50kHz' etlOkHz hardened that to be finished by gear 2: 12.7 sizes is shown in Table L It tooth flank grinding win have a. 2;5 10 • • can be seen that carburized and substantial gap. 3 8.5 • • 635 • • case hardened gears provide 2) Uthere is a shoulder 6" 4.23 .' • • •.' • • the best ratings for both tooth adjacent to the end of the gear 8 3.18 12 2.12 • • • '.• durability (contact fatigue) and portion. there should be a radi- 20 1.27 • 0.65 • '. tooth bending fatigue gear al gap between the ends of the 30' • '.• properties. But, for the larger teeth. and the houlder. tooth sizes, induction harden- 3) A generous root fillet Run-outof ing provides a significant radius should be included and , hardened layer advantage over or narrow tip widths should be Region through hardening. avoided. of Hardened Is,yer The different heat treatment Typical David Brown appli- conducted heat processes tend to suit a range cations for induction hardened of tooth sizes. Table 2 provides gears are: 'Tensile an overview of the data. Tooth- .•Mill pinions on girth gear ,surface by-tooth induction hardening stress driven rotating roms where the is suited to relatively large pinion mates with. a cast steel teeth-or 10kHz frequency wheel (Fig. 21). from 8 module to 3D module. • Heavy-duty crane travel Induction hardening, Compressive drive gearing where the needed surface' stress because it requires a high level contact accuracy bybeavily of technical and manual skill, is loaded carburizedl gearing can- Fig.19-Residual stress althe edge 101a hardened Ilyer"I~) suited to larger gears, whicll.- not be achieved! in a continuous- by their size and weight-are Iy flexing gear case (Fig. 22). Profile before Profile after expensive tocarburize. • Sugar mill drive gears hardeningl hardening, I ! Induction hardening might where price competitiveness is I I be beneficial when distortion combined w:ith heavy torque i and growth. due to carburizing transmission (Fig. 23), I and hardening is large enough • applications in to require excessive amounts of both rolling mill main drives ! corrective flank grinding. with (Fig. 24), and in shear applica- ! a corresponding 'thinning of the tions (Fig. 25) where each i case and the risk of grinding tooth frequently feels heavy steps at the tooth. fillet, shock loads. as well as Induction hardening can be coiler/uncoiler boxes. best used by ensuring a good • Cement mill drives where 'combination with the mating high torques are continuously IFig.2O-I)istortillnl in 'Iooth fOl1lllc81lSedilby Ihl1dening (greilly ,uIggal'lledl. gear, i.e, an induction hardened a.pplied for long periods (Fig. 26). 38 MARCH/APRIL 2001 • GEAR TECHNOLOGY' www,gesrlechnology,com '. www.oowertrensmleston.com Austempered Ductile (ADO outperfonns steel as demonstrated in these road test results on bypoid gem): Switching from steel Austempered to dB Hypoid Gears: ADI vs. Steel Ductile Iron (ADI) will also add these 70~----~~~--~------~ benefits: • Casl to nearer net shape and reduced machining cost -ligater weight method because of the gears' • Lower a erall cost overall size or because oftooth ize considerations. Also. it can AppliedProcess,Inc. 1000 2000 3000 is the world leader in R.PM. (road lest) compete with. other processes austernpering. Call for which strength require- today or visit our ments .are too, severe for website to learn how through hardened gears bUI fall Austemperingcan male your parts quieter, _t--,-_~ hart of the strengths from car- ~'-'-'Tel. (734) 464·2030 burizing am! hardening .. www.appliedprocess.com For gears hardened by the process, the surface strength properties (bending and 0011- tact fatigue) are much higher 2,0 liig, 22-:Helvy-duty ,cnlO8,1r8vel drivB (typically 40%) than the high- geLring'. est practicable through hard- R:EISHAUER Applications for induction ened gear but marginally less C:NC MACHINES hardened gears include a vari- than carburized, case hardened AIRE READY ety of applications where the gears (typically another 20% TO WORK economic balance requires a higher). Also, through hard- FORY,OUI high strength. 1'hr~ughllard- ened gears at the high strength ened wheel and consequently levels must use low tempering an even higher duty pillion, or temperatures, which can result when the ratings demand a car- in retention of internaJ stresses burized pinion, but not a car- residual from the quenching burized wheel. process. The intemal tensile The whole [age of indu - stress can, combined with trial gear drives can benefit applied service load, be detri- The Crown Power Train with ills remarkable experience In gears from properties produced by mental to gear life. production has developed a CNC gear inspection machine for; the process. Consequently. with suitable • quick, easy and aHordable service • Check cylindrical: gears in lead, pitch and involute profile Conclusions gear de ign modifications. the • Module between O.5mm and 16.00mm (1.'610 50DP), The submerged!. tooth-by- submerged induction harden- • Outside diameter betwoon 10.00mm and 420.00mm(.4" to 1'6.5") tooth.induction surface harden- ing process serves as an alter- PRICE: $ 120,OOO.OO·FOBCrown Included Ihroo days of training ing proces for medium and native to either through harden- large gear manufacture has ing or carburizing. Request Information: been used successfully by Contact fatigue strength Call: +39 '030 7156530 David Brown for more than relates to surface hardness. Fax: +39' 030' 1'059035 http://www.crown.!t WI three decades. comes into it Therefore, given adequate case CfOWll@,crownJt own for gears that cannot be thickness. one might expect an surface hardened by other induction hardened gear to be CIRCLE 122 ww, ....ao .... rtrensmteston.com "...... g .. art.""noIOlly·"om • GEAR TECHNOLOGY· MARCHIAp·RIL 2·D01 39 fairly comparable to at carbu- Geoffrey Panish rized gear of the same design is a gear consultant wUh 42 years and surface hardness. Hear of work experience in metallurgy, 27 of them ill gear metallurgy. He testing seems to. support. that, was head of metallurgical research and ilis common for a carbur- and development at lkTvid Brown Gear Industries Ltd., where he ized pinion to be run with all worked for 15yelll'S, specializing in induction hardened wheel. gear heal treatment processes and Induction hardening had material properties. Also. he was problems in the past; in many chief metallurgist and deputy quali- induction hardening plants, the ty manager at British Jeffrey 'Fig,23-Sugar mill drives. Diamond Dresser UK. where he problems still abound. But, worked for J 2 years, specializing in learning from experience and gear heal treatment processing and understanding the process. quality. quality control techniques Call be established that minimize IDavid W. Ingham the likelihood of process relat- is a manager at David Brown ed service problems. Special Products Ltd. with respon- sibility jor providing gears, gear- The process is gear tooth boxes and service in the United friendly. Finally, a more Kingdom and South America. A detailed technical appraisal. of metallurgist, he joined David Brown in 1970. starting ill metal- the process was published in lurgical research and development. Refs. 6 and 7. In the 1970s and 1980s. he worked 011 projects that included develop- References ml:mts in submerged induction Fig. 2~Sleel mill applications, I. Bojnican, V. "Problems of hardening. He is a member of the Hardeni ng Gear Wheel Institute of Materials and a char- Indentations." Int. Symp. for tered engineer. Metallurgy and Heat Treatment, Warsaw, 1967. 2. Shepelyakovskii, K. Z. and I. N. Shklyarov. "Strength and Endurance of Heavily Loaded Machine Pans Heat Treated by Various Methods." Metat; I Teml. Obra. Metallov, No. 7, July 19"68,(2). 3. Winter, H. and T. Weiss. "The Load Carrying Capacity of Induction and Flame Hardened Gears." PaT! I. Flank Strength, Antriehstechmk 27. No. 10, 1988, (57). Pan 2, Root Strength, Amriebstechnn: 27, No. 12. 198B,(45). 4. Baumgartl, E. "Influence of the Various Methoos .of Surface Heat Treatment on the Behaviour in Service of Hardened Gear Teeth." Inl. Symp. for Metallu.rgy and Heal Treatment, Warsaw, 1967. 5. Townsend, ,0., A. l'UI'7Jl and M. Yell Us Wbt You Dink ••• Chaplin, "The Surface Fatigue Life of Contour Induction Hardened ArSI If you found this IIrticle of 1552 Gears," AGMA Technical interest and/or useful, please Paper 95FTM5. circle 311. 6. Parrish. G., n.w. Ingham and Chaney. "The Submerged Induction If you did not care for this Hardening of Gears Pari 1," Heat Treatment ajMeta/s, 1998.1, pgs. 1·8. article, circle 312. 7. Parrish. G., D.W. Ingham and Chaney. "The Submerged Induction If you would like to respond to this or any other article in Hardening of Gears Pan 2." Heat this editionof G68r TBChnoIDgy, Treatment of Metal.f, 1998.2, pgs. pleasefax your to 43-50. response die attention of Randy Stott, man- 8. Jacobsen, M. "Designers' Control agingeditor, at 847-43HI618or of the Manufacturing Process," Part send e-mail messegn to 3 of Gear Design Series. Automotive [email protected]. Fig',.26a Fig,26b Design Engineering. 1.969.

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