大运河沿线非物质文化遗产亟待保护传承

rJBm3-news 发布时间: 2020-07-10 08:46:25

“幸运5分彩现场开奖直播【7ce】”Itwillbewellforanapprenticetobeginatonce,assoonashecommencesashopcourse,tonotethemannerofhandlingmaterial,watchingtheoperationofcranes,hoists,trucks,tackle,rollers;inshort,everythingthathastodowithmovingandhandling.Themachineryandappliancesinordinaryusearesimpleenoughinamechanicalsense,buttheprinciplesofhandlingmaterialarebynomeansasplainoreasytounderstand.Thediversityofpracticeseeninvariousplansofhandlingandliftingweightsfullyatteststhelastproposition,anditisquestionablewhetherthereisanyotherbranchofmechanicalengineeringthatistreatedlessinascientificwaythanmachineryofthisclass.Idonotalludetothemechanismofcranesandotherdevices,whichareusuallywellproportionedandgenerallywellarranged,buttotheadaptationofsuchmachinerywithreferencetospecialorlocalconditions.Therearecertaininherentdifficultiesthathavetobeencounteredintheconstructionandoperationofmachinery,forliftingandhandling,thatarepeculiartoitasaclass;amongthesedifficultiesisthetransmissionofpowertomovablemechanism,theintermittentandirregularapplicationofpower,severestrains,alsotheliabilitytoaccidentsandbreakagefromsuchmachinerybeingcontrolledbythejudgmentofattendants.Inplaningandturning,thetoolsrequirenoexactform;theycanberoughlymade,excepttheedge,andeventhis,inmostcases,isshapedbytheeye.Suchtoolsaremaintainedatatriflingexpense,andthedestructionofanedgeisamatterofnoconsequence.Theform,temper,andstrengthcanbecontinuallyadaptedtothevaryingconditionsoftheworkandthehardnessofmaterial.Thelineofdivisionbetweenplaningandmillingisfixedbytwocircumstances—thehardnessanduniformityofthematerialtobecut,andtheimportanceofduplication.Brass,cleaniron,softsteel,oranyhomogeneousmetalnothardenoughtocauserisktothetools,canbemilledatlessexpensethanplaned,providedthereisenoughworkofauniformcharactertojustifytheexpenseofmillingtools.Cuttingtheteethofwheelsisanexamplewheremillingisprofitable,butnottotheextentgenerallysupposed.Inthemanufactureofsmallarms,sewingmachines,clocks,andespeciallywatches,wherethereisaconstantandexactduplicationofparts,millingisindispensable.Suchmanufacturesareinsomecasesfoundedonmillingoperations,aswillbepointedoutinanotherchapter.

Byexaminingintothefacts,anapprenticewillfindthatalltrulysuccessfulestablishmentshavebeenfoundedandbuiltuponthemechanicalabilitiesofsomepersonorpersonswhoseskillformedabaseuponwhichthebusinesswasreared,andthattrueskillistheelementwhichmustintheendleadtopermanentsuccess.Thematerialandthelabourwhichmakeupthefirstcostofmachinesare,takinganaverageofvariousclasses,nearlyequallydivided;labourbeinginexcessforthefinerclassofmachinery,andthematerialinexcessforthecoarserkindsofwork.Thematerialispresumedtobepurchasedatthesameratesbythoseofinferiorskillasbythosethatarewellskilled,sothatthedifferenceinthefirst,ormanufacturingcostofmachinery,isdeterminedmainlybyskill.

CHAPTERXXIII.FORGING.

2.Thepowerofasteam-engineisderivedbyexpandingwaterinaconfiningvessel,andemployingtheforceexertedbypressurethusobtained.

Forotherkindsofworktherearedrawingsfurnished,andtheplansaredictatedbytheengineeringdepartmentofmachinery-buildingestablishments,butpattern-makersmaketheirownplansforconstructingtheirwork,andhaveeventoreproducethedrawingsofthefitting-shoptoworkfrom.Nearlyeverythingpertainingtopatternsislefttobedecidedbythepattern-maker,who,fromthesamedrawings,andthroughtheexerciseofhisjudgmentalone,maymakepatternsthataredurableandexpensive,ortemporaryandcheap,astheprobableextentoftheirusemaydetermine.

Thisobjectisattainedinplaningmachinesbythefrictionofthebelts,whichnotonlycushionstheplatenlikeaspring,butinbeingshiftedopposesagraduallyincreasingresistanceuntilthemomentumisovercomeandthemotionreversed.Bymultiplyingthemovementoftheplatenwithleversorothermechanism,andbyreasonofthemovementthatisattainedbymomentumafterthedrivingpowerceasestoact,itisfoundpracticabletohaveaplaten'shiftitsownbelts,'aresultthatwouldneverhavebeenreachedbytheoreticaldeductions,andwasnodoubtdiscoveredbyexperiment,liketheautomaticmovementofenginevalvesissaidtohavebeen.

Inmachinerytherulingformiscylindrical;instructuresotherthanmachinery,thosewhichdonotinvolvemotion,therulingformisrectangular.

(1.)Underwhatconditionsishydraulicapparatusasuitablemeansfortransmittingpower?—(2.)Towhatclassofoperationsishydraulicapparatusmostlyapplied?—(3.)Whyisnotwaterassuitableamediumasairorsteamintransmittingpowerforgeneralpurposes?

Fifth.Thecostofspecialadaptation,andtheusualinconvenienceoffittingcombinationmachineswhentheirpartsoperateindependently,oftenequalsandsometimesexceedswhatissavedinframingandfloorspace.

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  • 雨花郡主kQYcX

    Itisnotproposedatthistimetotreatoftheconstructionofmachineryfortransmittingpower,buttoexamineintotheconditionsthatshoulddeterminewhichoftheseveralplansoftransmittingisbestincertaincases—whetherbelts,gearing,orshaftsshouldbeemployed,andtonotetheprinciplesuponwhichtheyoperate.Existingexamplesdonotfurnishdataastotheadvantagesofthedifferentplansfortransmittingpower,becauseagivendutymaybesuccessfullyperformedbybelts,gearing,orshafts—evenbywater,air,orsteam—andthecomparativeadvantagesofdifferentmeansoftransmissionisnotalwaysaneasymattertodetermine.

     Thetitleofadrawingisafeaturethathasmuchtodowithitsappearance,andtheimpressionconveyedtothemindofanobserver.Whileitcanaddnothingtotherealvalueofadrawing,itissoeasytomakeplainletters,thattheapprenticeisurgedtolearnthisassoonashebeginstodraw;nottomakefancyletters,norindeedanykindexceptplainblockletters,whichcanberapidlylaidoutandfinished,andconsequentlyemployedtoagreaterextent.Bydrawingsixparallellines,makingfivespaces,andthencrossingthemwithequidistantlines,thepointsandanglesinblocklettersaredetermined;afteralittlepractice,itbecomestheworkofbutafewminutestoputdownatitleorothermatteronadrawingsothatitcanbeseenandreadataglanceinsearchingforsheetsordetails.

  • 雪灵芝8hGAQ

  • 如萱紫儿ecmFL

  • 但法国Uz1Lw

    Theseremarksuponhammersarenotintroducedhereasamatterofcuriosity,norwithanyintentionoffollowingmechanicalprinciplesbeyondwheretheywillexplainactualmanipulation,butasameansofdirectingattentiontopercussiveactingmachinesgenerally,withwhichforgingprocesses,asbeforeexplained,haveanintimateconnection.

     

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    CHAPTERVI.ONTHENATUREANDOBJECTSOFMACHINERY.

     Startingagainfromthecuttingpoint,andgoingtheotherwayfromthetooltotheframe,thereis,first,aclampedandstayedjointbetweenthematerialandplaten,next,arunningjointbetweentheplatenandframe;thisisall;onejointthatisfirmbeyondanychanceofmovement,andamovingjointthatisnotheldbyadjustablegibs,butbygravity;aforcewhichactsequallyatalltimes,andisthemostreliablemeansofmaintainingasteadycontactbetweenmovingparts.

  • 草莓果G9n3J

    CHAPTERII.MECHANICALENGINEERING.

     Inmetalworking,owingtoamoreperfectdivisionoflabour,andamoreintelligentmanipulationthaninwood-working,thereislesscombinationinmachines—infact,acombinationmachineformetalworkisrarelyseenatthisday,andneverundercircumstanceswhereitoccasionsactualloss.Theadvantageofcombination,assaid,canonlybeintheframingandfloorspaceoccupiedbythemachines,buttheseconsiderations,tobeestimatedbyaproperstandard,arequiteinsignificantwhencomparedwithotheritemsinthecostofmachineoperating,suchastheattendance,interestontheinvestedcostofthemachine,depreciationofvaluebywear,repairing,andsoon.

  • 绿卡纸J1PqM

     Theintricacyofthesubjectrendersitadifficultonetodealwithexceptbytheaidofdiagrams,andassuchmechanismmaybeinspectedinalmostanymachinefittingshop,attentioniscalledtothesubjectasoneofthebestthatcanbechosenfordemonstrationbydiagrams.Problemsofthesevariablespeedmovementsarenotonlyofgreatinterest,buthaveapracticalimportancenotfoundinmanybetterknownproblemswhichtakeuptimeuselesslyandhavenoapplicationinapracticalway.

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