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EuOp0-news 发布时间: 2020-07-15 07:17:27

“北京赛车pk10总图”Itistoberegrettedthattherehavenotbeenbooksespeciallypreparedtoinstructmechanicalstudentsintherelationsbetweenheat,force,motion,andpracticalmechanism.Thesubjectis,ofcourse,treatedatgreatlengthinmodernscientificworks,butisnotconnectedwiththeoperationsofmachineryinawaytobeeasilyunderstoodbybeginners.Atreatiseonthesubject,called"TheCorrelationandConservationofForces,"publishedbyD.Appleton&Co.ofNewYork,isperhapsasgoodabookonthesubjectascanatthistimebereferredto.TheworkcontainspaperscontributedbyProfessorsCarpenter,Grove,Helmholtz,Faraday,andothers,andhastheadvantageofarrangementinshortsections,thatcompassthesubjectwithoutmakingittedious.

(1.)Whatshoulddeterminethesocialrankofindustrialcallings?—(2.)Whyhavethephysicalsciencesandmechanicartsachievedsohonourableaposition?—(3.)Howmaythegeneralobjectoftheengineeringartsbedescribed?—(4.)Whatisthedifferencebetweenscienceandartasthetermsaregenerallyemployedinconnectionwithpracticalindustry?

Thereciprocatingcuttingmovementbeingbutfourinchesorless,acrankisobviouslythebestmeanstoproducethismotion,andasthemovementistransversetotherack,whichmaybelongandunwieldy,itisequallyobviousthatthecuttingmotionshouldbeperformedbythetoolsinsteadoftherack.

Fittingprocesses,beingthefinalonesinconstructingmachinery,aremorenearlyinconnectionwithitsuseandapplication;theyconsistintheorganisationorbringingtogethertheresultsofotherprocessescarriedoninthedraughtingroom,patternshop,foundry,andsmithshop.Iwillnotconsumespacetoexplaintheconverseofthissystemofinventing,norattempttodescribehowachanceschemerwouldproceedtohuntaftermechanicalexpedientstoaccomplishthevalvemovementintheexamplegiven.

Thedifferencebetweenhandandmachineoperations,andthelabour-savingeffectofmachines,willbefartherspokenofinanotherplace;thesubjectisalludedtohere,onlytoenablethereadertomorefullydistinguishbetweenmachineryoftransmissionandmachineryofapplication.Machineryofapplication,directedtowhathasbeentermedcompressionprocesses,suchassteamhammers,drops,presses,rollingmills,andsoon,actuponmaterialthatisnaturallysoftandductile,orwhenitissoftenedbyheat,asinthecaseofforging.

Itisnowproposedtoreviewthestandardtoolsofafittingshop,noticingthegeneralprinciplesoftheirconstructionandespeciallyoftheiroperation;notbydrawingsnordescriptionstoshowwhatalatheoraplaningmachineis,norhowsomeparticularengineerhasconstructedsuchtools,butupontheplanexplainedintheintroduction,presumingthereadertobefamiliarwiththenamesandpurposesofstandardmachinetools.Ifhehasnotlearnedthismuch,anddoesnotunderstandthenamesandgeneralobjectsoftheseveraloperationscarried[121]oninafittingshop,heshouldproceedtoacquainthimselfthusfarbeforetroublinghimselfwithbooksofanykind.

(1.)Whatisgainedbyarrangingamachinetoperformseveraldifferentoperations?—(2.)Whatmaybelostbysuchcombination?—(3.)Whatisthemainexpenseattendingtheoperationofmachinetools?—(4.)Whatkindofimprovementinmachinetoolsproducesthemostprofitableresult?—(5.)Whataretheprincipalcauseswhichhaveledtomachinecombinations.

Machinerysubjectedtodestructivewear,andtobeoperatedatadistancefrommachineshops—locomotiveenginesforexample—ifnotconstructedwithstandarddimensions,may,bythedetentionduetorepairing,causealossandinconvenienceequaltotheirvalue;ifashaftwheelbearing,orevenafittedscrewboltisbroken,timemustbeallowedtomakethepartsnew;andinordertofitthem,thewholemachine,orsuchofitsdetailsashaveconnectionwiththebrokenparts,mustbetakentoashopinordertofitbytrial.

Assuming,forexample,thatamachinewillcostasmuchasthewagesofanattendantforoneyear,whichisnotfarfromanaverageestimateforironworkingmachinetools,andthatinterest,wear,andrepairsamounttotenpercent.onthissum,thentheattendancewouldcosttentimesasmuchasthemachine;inotherwords,thewagespaidtoaworkmantoattendamachineis,onanaverage,tentimesasmuchastheotherexpensesattendingitsoperation,powerexcepted.Thisassumed,itfollowsthatinmachinetoolsanyimprovementdirectedtolaboursavingisworthtentimesasmuchasanequalimprovementdirectedtotheeconomyoffirstcost.

Incastingandforgingoperationsthematerialistreatedwhileinaheatedandexpandedcondition;thenatureoftheseoperationsissuchthataccuratedimensionscannotbeattained,sothatbothforgingsandcastingsrequiretobemadeenoughlargerthantheirfinisheddimensionstoallowforshrinkageandirregularities.Finishingasaprocessconsistsincuttingawaythissurplusmaterial,andgivingaccuratedimensionstothepartsofmachinerywhenthematerialisatitsnaturaltemperature.Finishingoperationsbeingperformedassaiduponmaterialatitsnormaltemperaturepermitshandling,gaugingandfittingtogetherofthepartsofmachinery,andasnearlyallotherprocessesinvolveheating,finishingmaybecalledthecoldprocessesofmetalwork.Theoperationsofafittingshopconsistalmostentirelyofcutting,andgrindingorabrading;apropositionthatmayseemnovel,yettheseoperationscomprehendnearlyallthatisperformedinwhatiscalledfitting.

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网友评论

  • 雨花郡主u94kS

    Tosumup—Wehavethefollowingpropositionsinregardtomovingandhandlingmaterial:

     Designing,orgeneratingtheplansofmachinery,maybeconsideredtheleadingelementinengineeringmanufacturesormachineconstruction,thatonetowhichallothersaresubordinate,[75]bothinorderandimportance,andisthatbranchtowhichengineeringknowledgeisespeciallydirected.Designingshouldconsist,first,inassumingcertainresults,and,secondly,inconceivingofmechanicalagentstoproducetheseresults.Itcomprehendsthegeometryofmovements,thedispositionandarrangementofmaterial,theenduranceofwearingsurfaces,adjustments,symmetry;inshort,alltheconditionsofmachineoperationandmachineconstruction.Thissubjectwillbeagaintreatedofatmorelengthinanothersection.

  • 雪灵芝z7V2c

    Anapprenticemaylearnthatpowerisnotincreasedordiminishedbybeingtransmittedthroughatrainofwheelswhichchangebothspeedandforce,andhemaybelievethepropositionwithouthavinga"conviction"ofitstruth.Hemustfirstlearntoregardpowerasaconstantandindestructibleelement—somethingthatmaybeweighed,measured,andtransmitted,butnotcreatedordestroyedbymechanism;thenthenatureofthemechanismmaybeunderstood,butnotbefore.

  • 如萱紫儿tbB0h

    Abeginner,unlessheexercisesgreatcareinthepencil-workofadrawing,willhavethedisappointmenttofindthepapersoonbecomingdirtyfromplumbago,andthepencil-linescrossingeachothereverywhere,soastogivethewholeaslovenlyappearance.Hewillalso,unlessheunderstandsthenatureoftheoperationsinwhichheisengaged,makethemistakeofregardingthepencil-workasanunimportantpart,instead[82]ofconstituting,asitdoes,themaindrawing,andtherebyneglectthataccuracywhichalonecanmakeeitheragood-lookingoravaluableone.

  • 但法国0p7Jg

     Shrinkage,orthecontractionofcastingsincooling,isprovidedforbyaddingfromone-tenthtoone-eighthofaninchtoeachfootinthedimensionsofpatterns.Thisisasimplematter,andisaccomplishedbyemployingashrinkruleinlayingdownpattern-drawings[97]fromthefigureddimensionsofthefinishedwork;suchrulesareaboutone-hundredthpartlongerthanthestandardscale.

  • 大笨蛋W5vsH

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  • 扒皮成TYaLG

    (1.)Whatisprincipalamongthedetailsofsteammachinery?—(2.)Whathasbeenthemostimportantimprovementrecentlymadeinsteammachinery?—(3.)Whathasbeentheresultofexpansiveenginesgenerallystated?—(4.)Whyhaswaterprovedthemostsuccessfulamongvariousexpansivesubstancesemployedtodeveloppower?—(5.)Whydoesacondensingenginedevelopmorepowerthananon-condensingone?—(6.)Howfarbackfromitsdevelopmentintopowercanheatbetracedasanelementinnature?—(7.)Hasthepropertyofcombustionacommonsourceinallsubstances?

     

  • 草莓果LQrR9

     

  • 绿卡纸lnKUc

    CHAPTERIII.ENGINEERINGASACALLING.

     Thefittingorfinishingdepartmentofengineeringestablishmentsisgenerallyregardedasthemainone.

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