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The Submerged Induction Hardening of Gears

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The Submerged Induction Hardening of Gears _------------ HEAT TREATING FOCUS _ The Submerged Induction Hardening 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 quenching 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 transformer 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-tempering 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 steel ~ 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, +<WO - study showed that for an experience has shown that on 817M40 (4340) steel in the occasions, the exit pattern +300.- quenched and ternperedcondi- could be improved by cancel- 1: ..200 tion, three seconds were ing the dwelJ and running ~ SAJ: UWsteel required to achieve carbon through 011 full power. or by I..l00ot-_tL_e_m_pe~~_-at~2OO"C_:_- -!--~""'f--=-- ......,""""""""--,!-~ solution, and that a degree of running through and de-ener- 2 3 , 8 9 IDistance from coarsening with a slight reduc- gizing during the exit. Those surface.mm tion of hardness took place are minor adjustments aimed after nine seconds.
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