Hardening and tempering c1912英文原版机械工程MACHINERY教程教材教案VIP

Hardening and tempering c1912英文原版机械工程MACHINERY教程教材教案 TJ7IRLFv.4625CENTSB3Dlfl77flHARDENING ANDTEMPERINGFOURTHREVISED EDITIONMACHINERYS REFERENCEBOOK NO.46PUBLISHED BYMACHINERY,NEW YORKMACHINERYS REFERENCESERIESEACH NUMBERISONEUNITIN APLETELIBRARY OFMACHINEDESIGN ANDSHOP PRACTICEREVISED ANDREPUBLJSHEDFROM MACHINERYNUMBER46HARDENING ANDTEMPERINGFOURTHREVISED EDITIONCONTENTSModernSteel HardeningPlants-3Hardening Steel,byE.R.MARKHAM-10Pack-Hardening Gages,byE.R.MARKHAM-15Forging,Hardening andAnnealing High-Speed Steel,by W.J.TODD-19LocalHardeningandTempering,by WILLIAMA.PAINTER-22Electric HardeningFurnaces-32Miscellaneous HardeningMethodsand Suggestions-35Copyright,1912,The IndustrialPress,Publishers ofMACHINERY,49-55Lafayette Street,New YorkCityCHAPTER IMODERNSTEEL HARDENINGPLANTSFrom timeimmemorial wheniron inits mostcrude formwas intro-ducedintothe manufacturing and mercialfield,it has beenawell-known and aeptedfact thatheat withitsvarying degreesofintensityhas adirect actionon boththe physicaland chemicalprop-ertiesof the metal when theironis submittedtoitsaction;and,as adirectresult,the entirestructure of the ironis altered,and byalteringor changingthe methodsof applicationof the heat treatment,any desiredstructure of themetal,either steelof castiron,may beobtained.Inspite of the factthat thetruth of the aboveexpositionwas generallyacknowledged,verylittle,if any,use wasmade ofit;but asscience developed,petition grewkeener andkeener,and thegeneralcryinthe manufacturing worldbecamereducedcost andgreateroutput.To balancetheeffect of increased powerand conse-quentlylarger machines,the workingstrengthofthecuttingtool,together with the workingstress of the machinemembers,had to begreatly increased,and,during thepast decade,theheattreatment hasdonemore thanitssharein the workof aomplishingthedesiredresults.There arebut fewproperly plannedand equippedhardening plants.In the present chapter,however,two examplesof first-class hardeningroomswill bedescribed,the onebeing thatof the WorcesterPoly-technic Institute,Worcester,Mass.,and theother the hardening plantinstalled by Wheelock,Lovejoy&Co.,in their New Yorkstore.The WorcesterPolytechnic InstitutePlant*The WorcesterPolytechnic plantconsists of a roomof spacioussizein thedesign ofwhich thefort of the operatorwas wellprovidedfor.The temperatureand ventilationof the room iscontrolled bothbyafan andlarge windowswhich admitsubdued naturallight butexcludethedirectsunlight,whichissoundesirableinthis kindofwork.These windowsare providedwith shuttersso that the naturallightmay be excluded;artificial illuminationis obtained by means of incan-descent electricbulbs.The roomappears to a visitor,atfirst,some-whatlike adungeon,as thewalls andceilingare paintedadeadblack,which colorprevents anyreflection of the variouscolored rayswhen the operatorisexperimenting oncolor work.After thisfirstimpressionhasleft thevisitor andhe hasbee austomedto thelight,the nextthing thatcatches hiseyeis therow ofvarious shapedfurnacesplaced symmetricallyon the right sideof theroom.Forconvenience andsimplicity,we willdesignate thesefurnaces(from righttoleft in Fig.1)by theletters A,B,C andD.Furnace A(constructed*MACHINERY,April,1909.347553No.40-HARDEXINGAND TEMPERINGby the AmericanGas Furnace Co.)is builton theprincipleof themuffle furnace,isof the boxtype,andwill readilyheat ablockofsteel8x4x14inches.Atemperature of from2000to2100degrees F.may bereadily obtained by meansofthis heater,whichis usedtoheatsuch workas requiresan evenheat and which wouldbe destroyedbyoxidation and the decarbonizingaction of theair.Reamers,man-drels,taps anddrills in their finishedstate aregood examplesofthis typeofwork.Furnace B,known as thebarium chlorideheater,is circu-lar inform andlined withfire-brick,and the chloride solutionis heatedin a cruciblebuiltoffire-resisting material.This furnaceisofsuf-ficient sizeto aommodateall ordinarytools,andis employedto heatsuchgrades of steel asrequire arather hightemperature,as high-speedHARDENING PLANTS5steels,andwhich,at the same time,must bewell protectedin heating.This form of heattreatment iswell adapted to thosetypes andformsof toolswhich tendtoheat unevenly,thus producingan unbalanceddistributionof the shrinkagestrains with the aompanyingcracks.FurnaceCis of the samegeneral designas furnaceB,with theexcep-tion that this heaterismade useofinconnection with the leadbath.As the lead meltsat aparatively lowtemperature,this furnaceIsused whena lowertemperature thanthat obtainedwith the chloridesolutionisdesired,forexample,whenheatingcarbonalloysteel.Furnace Disdevotedto anentirely differentoperation,namely,oiltempering.Either linseedor machineoil is used inthis heater,whichis brought into actionwhen thedesired rangeof temperatureisbe-tween thelimitsof300and630degrees F.Thefuel usedinall ofthesefurnacesis the ordinarycitygas,due toitsconvenience andreadyaessibility,but oilfuel couldbe employedifso desiredby theoperator.As will be seenfrom theengraving,all the furnaces areprovidedwithhoods of convenient formconnected with an exhaustline,so that all poisonousfumes and gases from thelead,cyanide,bariumchloride,etc.,may beeliminated from the atmosphereoftheroom.Atvarious andconvenient positionsabout the plant are to be found rec-tangular tanksofconvenientsize,containing waterand brineof vary-ing densities.All theother baths,as forexample,the variousgradesof oiland othercooling baths,are keptin coveredcylindrical galvanizedirontanksIn order to properlycare for and treat the air-hardeningsteels,an airjetis providedwith apressure of about2pounds.The onefeaturewhich removesthisplantfrom theclassoftheordinary manufacturingestablishment andplacesit in the ranksofthoseofscientific researchandinvestigation,isits pletesetofmeasuringinstruments,including theBriston andLe Chatelierpyrom-eters and thermometers coveringa rangeof temperaturebetween thelimitsofand2960degrees F.On one ofthewalls oftheroomis tobefound theBristol pyrometer,whichis ofthe thermo-electric type,and consistsofapermanent magmoving coiltype ofgalvanometer.Thescaleis graduatedtoreaddirectindegrees.Leads fromtheinstrumentextend over the entireroom,so thatitis a matterof afewsecondsonlyto connectwiththe thermo-couple andobtain anydesiredtemperature.If anyquestion asto theauracy ofthe instru-ment,or theaction ofgravity onitsoscillating partsis advanced,aLe Chatelierpyrometer,operating on the sameprinciple buthaving averticalsupport,may bebroughtinto action and thefirst readingsverified.As indicatedby theabove description,all gradesof steelfrom the15-point carbonsteel to the high-speed,alloy,air-and water-hardeningsteel may be convenientlyand efficientlyhandled andtreated.Wheelock,Lovejoy&Co.s HardeningPlant*The illustrations,Figs.2and3,show twoviews ofa hardeningplantinstalledbyWheelock,Lovejoy&Co.,(selling agentsforFirth Sterling*MACHINERY,November,1908.6No.46HARDENING ANDTEMPERINGSteel Co.,McKeesport,Pa.)in thebasement oftheirNewYork storeat23Cliff St.The equipmentis interestingin thatitrepresents thelatestdevelopmentofgasfurnacehardening andtemperingbaths.Fig.2shows ageneral viewoftheplantlooking towardthestreet,while Fig.3is aview taken from thestreet end.The furnacein therear,with ahood similar to theone in the foregroundof Fig.2,is forheatinga chloride of barium bath,this beingvery suessfullyusedfor hardeningBlue Chipsteel,and the following descriptionrelatesto thepractice.The toolsto be hardened arefirst pre-heated,using thesmall Americangasfurnace shownnext to thechlorideof bariumfurnace.The pre-heating savestime in the barium bath,andis absolutelynecessary toavoidchecking orcracking thetools,as will be concededwhenitisFig.2.Hardening Plant,Wheelock,Lovejoy&Co.,looking1toward Streetknown that the temperature ofthe barium bath iskept atbetween2100and2200degrees F.After the tools arepre-heated,they areimmersedin the bariumbath,being suspendedby an iron wire,or,in thecaseof smallparts,in sheetnickel baskets.The reasonforusing sheetnickelfor the baskets isthat chlorideof bariumhas a slight dissolvingeffect on ironand theexposure ofa largearea ofsheet ironin thebath wouldeventually destroythebaskets.Nickelis notaffected toaperceptible extent,nor isthe thiniron wireused tosuspend ordinarytools.The temperature ofthe bariumbathis regulatedby aBristol thermo-electric pyrometer.This instrument,shown attheleft inFig.4,issimilar to a Westonammeter orvoltmeter,and the fire endis a thermselectric couple.The heat ofthe bath effectsthethermo-electric coupleandgenerates acurrent thatdeflects theindicatorof the indicatinginstrument tocorrespond withthe temperature.For convenienceinHARDENING PLANTS7operation,theindicatinginstrumentis providedwith adouble hand,one hand,A,being controlledby the temperature ofthebath,while theother,B,isamarker setby the operator toindicate thetemperaturewhich hedesires tocarry.This markerismade with a diskat theendthat coversa holein theindicating handwhen thetwo coincide,as theydo v;henthetemperature hasreached thepredeterminedpoint*Thus,an operatorwhose eyesare dazzledby theheat ofthe bathdoesnot haveto painfullystudy thegraduations tosee whetherthe pointerhasreached thecorrectposition,but byglancingat theinstrumenthe canreadily determinewhen theindicatoris directlybeneath themarkerreferred to.The immersionof apiecepre-heated to a dullred immediatelycausesthe indicatorto drop,thetemperatureofthe bath fallingperhaps30,Fig.3.View ofHardeningPlantshown inPig.2,takenfromStreet End40or even50degrees.The fallin temperatureis duetoabsorption ofheat by the piece,being thesame as the refrigeratingeffect ofa lumpofice thrownintoapot ofboiling water,and severalminutes may berequired toraise thetemperatureofa largepiece to the temperaturethatisrequired.For hardeningBlue Chipsteel,a temperatureof2120to2140degrees F.has beenfound mostsuitable.After thistem-peratureis attained,the partisallowed tosoak for a fewmoments,then islifted outand dippedinto thecooling bathshown attheright,Fig.2,and leftinFig.3,which consistsof cotton-seed oilagitated bypressedairadmittedat the bottom.The cotton-seedoiliscon-tained in a largeiron barrelsurrounded bywaterin awoodentub.The parthardenedis allowedto remainin the bath untilit is quitecold.In practice,theoperatorhardens abatch andthen removesthepieces bymeansofa wirebasket hangingimmersed in theoil.It isremendedthatmilling cutters,end mills,slitting saws,etc.,made ofNo.46HARDENING ANDTEMPERINGBlue Chipsteel,beused,ingeneral,without drawingthetemper.Theywill have the requisitehardness andtoughness tostandupto themajorityofwork.However,anoilbathheated bygasandregu-latedbya thermometerisprovidedfortemperingsuchtoolsasrequireit.Chlorideof bariumisa whitetransparentsalt(BaCl2OH,)whichmelts at a temperatureofabout1700degrees,the waterof crystalliza-tion beingdriven offat amuch lowerheat.The saltvolatilizes at anextremely hightemperature,the lossatthetemperature requiredforheating high-speed steel being negligible.The wastebecause ofvolatili-zationis,say,two poundsfrom amass of barium weighing75poundswhen heldata temperaturebetween2000and2300degreesforfivehours.This propertyofthechlorideofbariumbath of standinghightemperatures withoutrapid volatilizationis joinedwith othersequallyimportant.The pieceheated isprotected from the atmosphereduringFIRE ENDOFPYROMETERGASAIRMachinery,N.Y.Fig.4.Vertical Cross-section ofChloride of Barium Furnacetheheating periodby the bath,of course,but theprotective influenceextendsstillfurther.A thincoatingof bariumclingsto the piecewhenit islifted outfor immersionin thecooling bath,thus preventingoxidation.The effectofthebarium on the steelseems to be limitedtoaslightmottling thatquickly disappearsunder theaction ofclean-ingandbuffing wheels.The coatingofbarium remainingwhen dippedpreventsthe coatingof burnedoilso troublesometo remove,so thatonthe wholethe processprobably producesthe cleanestwork of anybath known.Wheelock,Lovejoy&Co.have improvedthefurnaceandcrucibleused for thechlorideofbariumbath.The monformoffurnaceand cruciblein useemploys aparatively shallowcrucible,whichnecessitates makinga jointbetween the top ofthe crucibleand thefire-brick cover.This givestrouble byloosening andpermitting theHARDENINGPLANTS9hot gasestoescape around the edgeof thecrucible.The improvedconstructionillustrated inFig.4utilizes adeeper crucible,thetopofwhich esflush withthe fire-brick coverand simplifiesthe construc-tion.The deepcruciblealso givesa greatervolumeof chlorideofbarium,consequently therefrigeratingeffectofthepre-heatedsteelparts,when immersedin thebath,is notso great.This illustrationalsoshows the fire end,C,ofthepyrometer immersedin thebath.Ithas beenfound advisable to employcrucibles madefor steelmelting,theordinarygraphite crucibleused forbrass meltinggiving troublebyflaking off into thebarium.The equipmentoftheplantincludesanair pressorandex-hauster,the formerbeing requiredfor theair blastin thefurnacesand foragitating theoil bath,while theexhauster connectedwith thesmokepipes andhood,drawsoff thehot airandgases,thus keepingthe working conditionsfairly fortable,even in the hottestweather.Anefficient ventilatingsystemis aprime requirement,inasmuch asthefumes ofthebariumare somewhatobnoxious andbesides wouldhave a seriousrusting effectonthe steel stockif permittedto pervadethebasement whereit isstored.The UseofBariumChloride forHeating-Steel forHardening-In anarticle in the April,1911,number ofMACHINERYit waspointedout thatbarium chloride baths forhardening high-speed steelhave cer-tain disadvantageswhich preventtheir usageinmanycases.Toolsheated forhardening in a cruciblecontaining barium chloride have asoft scaleor filmof softmetal,perhaps about0.003to0.006inch deepalloverthe surface ofthetool.Thus whenheating high-speedstee,!toa temperatureoffrom2100to2400degrees F.,which isthe proper heatfor high-speed steel,the resultsare notsatisfactoryif thetools cannotbe ground after hardening,so astoremove thesoft scaleor filmofmetal.Tests madeto ascertain the exactinfluence ofbariumchloridebathsindicate thatwhenever thissaltis usedas a heating bath,ifc shouldnot be permittedto reacha temperatureof more than2050degrees F.It hasbeen conclusivelyproved thathigh-speedsteel toolsheatedinbarium chloridedo not stand ashigh cuttingspeed asdo toolshardenedby heatingin an ovenfurnace.It seemsthat,particularlyat highheats,some ofthe tungstenand carbonis removedfrom thetools intothebath,thus changingthe structureofthesurface ofthe toblbeingheated.When anamountof,say,0.010inchis groundofffrom thecuttingedges of tools,the influenceoftheheating inbarium chlorideisless noticeableinfact,sometimes notnoticeableatallbut whenthetools cannotbe groundafterhardening,barium chlorideis not aheatingmedium whichcan beremended underany circumstances.Itis understood,of course,that,for heatingtools thatcan begroundafter hardening,andalsofor heatingcarbonsteeltools,thebarium,chloridebathpossesses certain advantages.CHAPTER IIHARDENING-STEEL*Every shophas oneor moremen whoare consideredauthorities onhardening.In manycasesthemanisreally anexpert,iscareful,and usesgood judgmentin heatingthe steeland inquenching inthebath;and if the pieceis ofsufficient size,he issure to take thestrainsout byreheating directlyafter takingfrom thebath.In somecase?,however,the suessof oneoperationis measuredby thefailureofothers.Thusif the steel passesthrough thefiery ordealwith enoughofit leftintact todo the work it is considereda suessfuloperation;if not,the faultmust bein thesteel.A manufacturingconcern oncechangedthe brandoftool steel theywere usingthree timesin lessthanayear,because theman doingthe hardeningreported adverselyoneachmake,after attemptingto hardenit.The brandsfurnished werefromthree ofthe leadingmakers oftool steel.After receivingrepeatedplaints inregard to themans inabilityto hardenthe steelsuess-fully,oneofthe makersadvised themanufacturer toletsome expertinhardening trythe steel.Some millingmachine cutterswere madefromeach brandofthe rejectedsteeland sentto thesteelmakers.Theyall cameback hardenough,withoutcracks,provingthatthetrouble wasnot inthe steel.An expensivesteelis notnecessarily asatisfactory investment,andacheapbrand may be veryexpensive.It isnecessary tounderstandjust whatis neededinasteel fora givenpurpose.Some makershavedifferentgrades ofsteel fordifferent purposesonefortaps andsimilartools,another formilling machinecutters,etc.while othersput outasteel thatis very satisfactory formost purposes.Each has a goodargumentin favorof hisparticular methodof manufacture.In someshopsitisthought advisable to use a gradeofsteeladaptedtoeachindividualclassoftool;whileinothershops,wheredetailisnotfollowed asclosely,this wouldcause noend ofconfusion.That partofthe subjectmust beleftto thejudgment oftheindividual shop.But thetreatment ofthe steelinthefire andthebath,in orderto besuessful,must bealong certainlines.The suessfulhardeneris hewhofinds outwhat particularqualityis neededinthe piece heis tohardenwhether extremehardness,toughness,elasticity,ora-bination oftwo of these qualities.Then hemust knowthe methodtouse in ordertoproduce thedesired result.The shapeof thepiece,thenature ofthesteel,the usetobemade ofthe article,must allbe takenintoconsideration.He mustalso begoverned somewhatbythekindof firehe isto use.*MACHINERY,February,1902.HARDENING STEEL11Heatingthe SteelSomebrands ofsteelwillnotstand,without injury,the rangeofheat that otherswill;some requiremore heatthan othersin ordertoharden atall.When hardening,no steelshould heheated hotterthanis necessarytoproduce the desiredresult.With somebrandsthatgiveoff theirsurface carbonvery readilyitisnot advisableto heattheminanopenfire,exposed tothe actionofthe blastand outsideair,as theproducts ofbustion extractthe carbonto such an extentthatthesurfacewill besoft evenwhentheinterior isextremely hard.While thismight notmaterially affecta toolthatis tobeground,itwouldspoil atap,a formedcutter,or similararticle,whose outsidesurfacecould notbe removed.In hardeninganything of