广西壮族自治区人民代表大会常务委员会任命名单

Pdtff-news 发布时间: 2020-07-15 11:32:20

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2.Plansofadaptationandarrangementofthecomponentpartsofthemachinery,ororganisationasitmaybecalled.Tofollowthismatterfurther.Itwillbefoundinsuchmachinesasaredirectedmainlytoaugmentingforceorincreasingtheamountofpowerthatmaybeappliedinanyoperation,suchassawingwoodorstone,theeffectproducedwhencomparedtohandlabourisnearlyasthedifferenceintheamountofpowerapplied;andthesavingthatsuchmachineseffectisgenerallyinthesameproportion.Amachinethatcanexpendtenhorse-powerinperformingacertainkindofwork,willsavetentimesasmuchasamachinedirectedtothesamepurposeexpendingbutonehorse-power;thisofcourseappliestomachinesfortheperformanceofthecoarserkindsofwork,andemployedtosupplantmerephysicaleffort.Inothermachinesofapplication,suchasaredirectedmainlytoguidance,orspeedofaction,suchassewingmachines,dove-tailingmachines,gear-cuttingmachines,andsoon,thereisnorelationwhateverbetweentheincreased[59]effectthatmaybeproducedandtheamountofpowerexpended.

Mechanicalengineeringhasbytheforceofcircumstancesbeendividedupintobranchesrelatingtoengineeringtools,railwaymachinery,marineengines,andsoon;eitherbranchofwhichconstitutesaprofessionwithinitself.Mostthoroughstudywillberequiredtomastergeneralprinciples,andthenafurtherefforttoacquireproficiencyinsomespecialbranch,withoutwhichthereisbutlittlechanceofsuccessatthepresentday.

CHAPTERXXXVIII.GAUGINGIMPLEMENTS.Inregardtoshadedelevations,itmaybesaidthatphotographyhassupersededthemforthepurposeofillustratingcompletedmachines,andbutfewestablishmentscaretoincurtheexpenseofink-shadedelevations.Shadedelevationscannotbemadewithvariousdegreesofcare,andinalongerorshortertime;thereisbutonestandardforthem,andthatisthatsuchdrawingsshouldbemadewithgreatcareandskill.Imperfectshadedelevations,althoughtheymaysurpriseandpleasetheunskilled,areexecrableintheeyesofadraughtsmanoranengineer;andasthemakingofshadedelevationscanbeofbutlittleassistancetoanapprenticedraughtsman,itisbettertosavethetimethatmustbespentinordertomakesuchdrawings,andapplythesamestudyandtimetoothermattersofgreaterimportance.

(1.)Howmaythearrangementofanestablishmentaffectitsearnings?—(2.)Whyisthearrangementofengineeringestablishmentsgenerallyirregular?—(3.)Whyshouldanerectingshopbeabaseofarrangementinengineeringestablishments?—(4.)Whataretheprincipalmaterialsconsumedinengineeringworks?—(5.)Whyisnotspecialexperienceasafeguideinformingplansofshoparrangement?

Theextremenicetywithwhichgaugingimplementsarefittedseemsatfirstthoughttobeunnecessary,butitmustberememberedthatacylindricaljointinordinarymachinefittinginvolvesaprecisionalmostbeyondthesenseoffeeling,andthatanysensiblevariationinturninggaugesisenoughtospoilafit.

Withoutanywishtodiscouragetheambitionofanapprenticetoinvent,whichalwaysinspireshimtolaudableexertion,itisneverthelessbesttocautionhimagainstinnovations.Theestimateformedofourabilitiesisveryapttobeinverselyasourexperience,andoldengineersarenotnearlysoconfidentintheirdeductionsandplansasbeginnersare.

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    Atruemovementofcarriagesisdependentupontheamountorwearingpoweroftheirbearingsurface,howthissurfaceisdisposedinreferencetothestraintoberesisted,andtheconditionsunderwhichtheslidingsurfacesmove;thatis,howkeptincontact.Thecuttingstrainwhichistobemainlyconsidered,fallsusuallyatanangleofthirtytofortydegreesdownwardtowardthefront,fromthecentreofthelathe.Toresistsuchstrainaflattopshearpresentsnosurfaceatrightanglestothestrain;thebearingsarealloblique,andnotonlythis,butallhorizontalstrainfallsononesideoftheshearonly;forthisreason,flattopshearshavetobemademuchheavierthanwouldberequiredifthesumoftheircrosssectioncouldbeemployedtoresisttransversestrain.Thisdifficultycan,however,bemainlyobviatedbynumerouscrossgirts,whichwillbefoundinmostlatheframeshavingflattops.

     Thearrangementofpatternswithreferencetohavingcertainpartsofcastingssolidandcleanisanimportantmatter,yetonethatiscomparativelyeasytounderstand.Supposingtheironinamouldtobeinameltedstate,andtocontain,asitalwaysmust,loosesandand'scruff,'andthattheweightofthedirtistomeltedironastheweightofcorkistowater,itiseasytoseewherethisdirtwouldlodge,andwhereitwouldbefoundinthecastings.Thetopofamouldorcope,asitiscalled,containsthedirt,whilethebottomordragsideisgenerallycleanandsound:theruleistoarrangepatternssothatthesurfacestobefinishedwillcomeonthebottomordragside.

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    Keepinginviewwhathasbeensaidaboutanelasticconnectionfortransmittingmotionandpowertohammers,andcushioningthevibratoryorreciprocatingparts,itwillbeseenthatsteamasadrivingmediumforhammersfillsthefollowingconditions:

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    Platensasarulerunbackattwicetheforwardorcuttingmovement,andasthemotionisuniformthroughouteachstroke,itrequirestobestoppedattheextremesbymeetingsomeelasticoryieldingresistancewhich,touseasteamphrase,"cushions"orabsorbsthemomentum,andstartstheplatenbackforthereturnstroke.

     Apattern-makernosoonerseesacastingthanheimaginesthekindofpatternemployedinmouldingit;amoulderwillimaginetheplanofmouldingandcastingapiece;whileanengineerwillcriticisethearrangement,proportions,adaptation,andgeneraldesign,andifskilled,asheoughttobe,willalsodetectataglanceanyuselessexpenseinpatternsormoulding.

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     Asmolecularadhesionkeepstheparticlesofmattertogethersoastoformsolids,sotheforceofgravitykeepsobjectsintheirplace;andtoattainaproperconceptionofforces,especiallyinhandlingandmovingmaterial,itisnecessarytofamiliarisethemindwiththisthought.

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