东方雨虹:上下联动筑抗疫堡垒 创新思路安全复工

00RJU-news 发布时间: 2020-07-07 04:12:09

“【UPoGQ】38乐和彩”CHAPTERXXII.PATTERN-MAKINGANDCASTING.Shopsystemmayalsobeclassedasabranchofengineeringwork;itrelatestotheclassificationofmachinesandtheirpartsbysymbolsandnumbers,torecordsofweight,theexpenseofcast,forged,andfinishedparts,andapportionsthecostoffinishedmachineryamongthedifferentdepartments.Shopsystemalsoincludesthemaintenanceofstandarddimensions,theclassificationandcostoflabour,withothermattersthatpartakebothofamechanicalandacommercialnature.

Afinisher'senginelatheconsistsessentiallyofastronginflexibleshearorframe,arunningspindlewithfromeighttosixteenchangesofmotion,aslidinghead,ortailstock,andaslidingcarriagetoholdandmovethetools.

(1.)Whatcausestoolstobendorbreakinhardening?—(2.)Whatmeanscanbeemployedtopreventinjurytotoolsinhardening?—(3.)Cantheshadesoftemperbeproducedonapieceofsteelwithouthardening?—(4.)Whatformsalimitofhardnessforcuttingtools?—(5.)Whataretheobjectsofsteel-layingtoolsinsteadofmakingthemofsolidsteel?

This,again,reachesthepropositionthatpowerisheat,andheatispower,thetwobeingconvertible,and,accordingtomodernscience,indestructible;sothatpower,whenused,mustgiveoffitsmechanicalequivalentofheat,orheat,whenutilised,developitsequivalentinpower.Ifthewholeamountofheatrepresentedinthefuelusedbyasteam-enginecouldbeapplied,theeffectwouldbe,asbeforestated,fromtentofifteentimesasgreatasitisinactualpractice,fromwhichitmustbeinferredthatasteam-engineisaveryimperfectmachineforutilisingheat.Thisgreatlossarisesfromvariouscauses,amongwhichisthattheheatcannotbedirectlynorfullycommunicatedtothewater.Tostoreupandretainthewaterafteritisexpandedintosteam,astrongvessel,calledaboiler,isrequired,andalltheheatthatisimpartedtothewaterhastopassthroughtheplatesofthisboiler,whichstandasawallbetweentheheatanditswork.

Oneoftheproblemsconnectedwiththehandlingofmaterialistodeterminewherehand-powershouldstopandmotive-powerbegin—whatconditionswilljustifytheerectionofcranes,hoists,ortramways,andwhatconditionswillnot.Frequentmistakesaremadeintheapplicationofpowerwhenitisnotrequired,especiallyforhandlingmaterial;thetoocommontendencyofthepresentdaybeingtoapplypowertoeverypurposewhereitispossible,withoutestimatingtheactualsavingthat,maybeeffected.Acommonimpressionisthatmotivepower,whereverappliedtosupplanthandlabourinhandlingmaterial,producesagain;butinmanycasesthe[66]fallacyofthiswillbeapparent,whenalltheconditionsaretakenintoaccount.

Thesubjectisanintricateone,andhasbeensomuchaffectedbytheinfluenceofmachineimprovement,andacorrespondingdecreaseinwhatmaybecalledspecialknowledge,thatrulesandpropositionswhichwouldfiftyyearsagoapplytotheconditionsofapprenticeship,willatthepresentdaybewrongandunjust.Viewedinacommercialsense,asanexchangeofconsiderationsorvalues,apprenticeshipcanberegardedlikeotherengagements;yet,whatanapprenticegivesaswellaswhathereceivesarealiketooconditionalandindefinitetobeestimatedbyordinarystandards.Anapprenticeexchangesunskilledorinferiorlabourfortechnicalknowledge,orfortheprivilegeandmeansofacquiringsuchknowledge.Themasterispresumedtoimpartakindofspecialknowledge,collectedbyhimatgreatexpenseandpains,inreturnforthegainderivedfromtheunskilledlabourofthelearner.Thisspecialknowledgegivenbythemastermaybeimpartedinalongerorshortertime;itmaybethorough[20]andvaluable,ornotthorough,andalmostuseless.Theprivilegesofashopmaybesuchastooffsetalargeamountofvaluablelabouronthepartoftheapprentice,ortheseprivilegesmaybeofsuchacharacterastobeofbutlittlevalue,andteachinferiorplansofperformingwork.

Finishingasaprocessisasecondaryandnotalwaysanessentialone;manypartsofmachineryarereadyforusewhenforgedorcastanddonotrequirefitting;yetafinishingshopmustinmanyrespectsbeconsideredtheleadingdepartmentofanengineeringestablishment.Plans,drawingsandestimatesarealwaysbasedonfinishedwork,andwhenthepartshaveaccuratedimensions;hencedesigns,drawingsandestimatesmaybesaidtopassthroughthefittingshopandfollowbacktothefoundryandsmithshop,sothatfinishing,althoughthelastprocessintheorderofthework,isthefirstoneafterthedrawingsineveryothersense;eventhedimensionsinpattern-makingwhichseemsfarthestremovedfromfinishing,arebaseduponfittingdimensions,andtoagreatextentmustbemodified[119]bytheconditionsoffinishing.

Theseare,however,nottheonlyreasonswhichhaveledtoarunningplatenforplaningmachines,althoughtheyarethemostimportant.

Adifficultywhicharisesinhardeningtoolsisbecauseofthecontractionofthesteelwhichtakesplaceinproportiontothechangeoftemperature;andasthetimeofcoolingisinproportiontothethicknessorsizeofapiece,itfollows,ofcourse,thatthereisagreatstrainandatendencytobreakthethinnerpartsbeforethethickerpartshavetimetocool;thisstrainmaytakeplaceeitherfromcoolingonesidefirst,ormorerapidlythananother.

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网友评论

  • 雨花郡主AYepw

     Inmakingnotes,asmuchaspossibleofwhatiswrittenshouldbecondensedintobriefformul?,aformofexpressionwhichisfastbecomingthewrittenlanguageofmachineshops.Readingformul?isinagreatdegreeamatterofhabit,likestudyingmechanicaldrawings;thatwhichatthebeginningisamazeofcomplexity,afteratimebecomesintelligibleandclearataglance.

  • 雪灵芝DO7xo

  • 如萱紫儿hOrJH

  • 但法国f0tgy

    Reactionwheelsareemployedtoalimitedextentonly,andwillsoon,nodoubt,beextinctasaclassofwater-wheels.Inspeakingofreactionwheels,IwillselectwhatiscalledBarker'smillforanexample,becauseofthefamiliaritywithwhichitisknown,althoughitsconstructionisgreatlyatvariancewithmodernreactionwheels.

     

  • 大笨蛋Z2T17

    v

  • 扒皮成QT3M1

    (1.)Namefivemachinesastypesofthoseemployedinthegeneralprocessesofconvertingmaterial.—(2.)Namesomemachines,theobjectofwhichistoaugmentforce—Onetoattainspeed—Onedirectedtotheguidanceoftools.—(3.)Whatisthedifferencebetweenthehotandcoldtreatmentofironastoprocesses—Astodimensions?—(4.)

     

  • 草莓果L3HXM

    Thesearebutafewofmanyinfluenceswhichtendtoirregularcooling,andaredescribedwithaviewofgivingacluefromwhichothercausesmaybetracedout.Thewantofuniformityinsectionswhichtendstoirregularcoolingcanoftenbeavoidedwithoutmuchlossbyadispositionofthemetalwithreferencetocoolingstrains.This,sofarastheextrametalrequiredtogiveuniformitytoortobalancethedifferentsidesofacasting,isawastewhichengineersaresometimeslothtoconsentto,andoftenneglectindesignsformouldedparts;yet,asbeforesaid,thedifficultyofirregularcoolingcaninagreatdegreebecounteractedbyaproperdistributionofthemetal,withoutwasting,ifthematterisproperlyunderstood.Nooneispreparedtomakedesignsforcastingswhohasnotstudiedthesubjectofcoolingstrainsasthoroughlyaspossible,frompracticalexamplesaswellasbytheoreticaldeductions.

     

  • 绿卡纸BuH6t

     Thesefourtypescomprehendthemotive-poweringeneraluseatthepresentday.Inconsideringdifferentenginesformotive-powerinawaytobestcomprehendtheirnature,thefirstviewtobetakenisthattheyarealldirectedtothesameend,andalldealwiththesamepower;andinthiswayavoid,ifpossible,theimpressionoftherebeingdifferentkindsofpower,asthetermswater-power,steam-power,andsoon,seemtoimply.Wespeakofsteam-power,water-power,orwind-power;butpoweristhesamefromwhateversourcederived,andthesedistinctionsmerelyindicatedifferentnaturalsourcesfromwhichpowerisderived,orthedifferentmeansemployedtoutiliseandapplyit.

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