“疫”后花开 迈向诗和远方来王家大院 体验晋商文化

PHwj1-news 发布时间: 2020-07-13 04:28:19

“飞艇不连挂五码”Thisproblemofwhethertomovethematerialortomovethetoolsinplaning,isanoldone;bothopinionandpracticevarytosomeextent,yetpracticeisfastsettlingdownintoconstantrules.

Third.—Thesoundnessofsuchpartsasaretobeplaned,bored,andturnedinfinishing;thisisalsoamatterthatisdeterminedmainlybyhowthepatternsarearranged,bywhichisthetopandwhichthebottomordragside,themannerofdrawing,andprovisionsforavoidingdirtandslag.[164]

Mechanicalengineering,likeeveryotherbusinesspursuit,isdirectedtotheaccumulationofwealth;andastheattainmentofanypurposeismoresurelyachievedbykeepingthatpurposecontinuallyinview,therewillbenoharm,andperhapsconsiderablegainderivedbyanapprenticeconsideringatthebeginningthemainobjecttowhichhiseffortswillbedirectedafterlearninghisprofessionortrade.Sofarasanabstractprincipleofmotives,thesubjectisofcourseunfittoconsiderinconnectionwithengineeringoperations,orshopmanipulation;butbusinessobjectshaveapracticalapplicationtobefollowedthroughoutthewholesystemofindustrialpursuits,andareaspropertobeconsideredinconnectionwithmachine-manufacturingasmechanicalprinciples,orthefunctionsandoperationofmachines.

Withrunningdies,blanksmaybeclampedwhenamachineisinmotion,andastheblankdoesnotrevolve,itmay,whenlong,besupportedinanytemporarymanner.Thediescanbeopenedandclosedbythedrivingpoweralso,andnostoppingofamachineisnecessary;sothatseveraladvantagesofconsiderableimportancemaybegainedbymountingthediesinarunninghead,aplanwhichhasbeengenerallyadoptedinlateyearsbymachinetoolmakersbothinEnglandandAmerica.

1.Thatthedropandvalve,whiletheymustactrelatively,cannotmoveinthesametime,orindirectunison.

Irregularityofcoolingmaybetheresultofunequalconductingpowerindifferentpartsofamouldorcores,oritmaybe[98]fromthevaryingdimensionsofthecastings,whichcontainheatastheirthickness,andgiveitoffinthesameratio.Asarule,thedragorbottomsideofacastingcoolsfirst,especiallyifamouldrestsontheground,andthereisnotmuchsandbetweenthecastingsandtheearth;thisisacommoncauseofunequalcooling,especiallyinlargeflatpieces.Airbeingabadconductorofheat,andthesandusuallythinonthecopeortopside,theresultisthatthetopofmouldsremainquitehot,whileatthebottomtheearth,beingagoodconductor,carriesofftheheatandcoolsthatsidefirst,sothattheiron'sets'firstonthebottom,afterwardscoolingandcontractingonthetop,sothatcastingsarewarpedandleftwithinherentstrains.

Asecondpointtobenoticedinhammersofthisclassisthenatureoftheconnectionwiththedrivingpower.Inallcasestherewillbefoundanequivalentfortheelastichelveofthetrip-hammer—eitheraircylinders,deflectingsprings,orotheryieldingattachments,—interposedbetweenthecrankandthehammer-head,alsoaslippingfrictionalbeltorfrictionalclutchesfordriving,asinthecaseoftrip-hammers.

Presumingthereadertorememberwhatwassaidofsteamhammersinanotherplace,andtobefamiliarwiththeusesandgeneralconstructionofsuchhammers,letitbesupposedsteam-hammers,withtheordinaryautomaticvalveaction,thosethatgiveanelasticorsteam-cushionedblow,arewellknown.Supposefurtherthatbyanalysingtheblowsgivenbyhammersofthiskind,itisdemonstratedthatdeadblows,suchasaregivenwhenahammercomestoafullstopinstriking,aremoreeffectualincertainkindsofwork,andthatsteam-hammerswouldbeimprovedbyoperatingonthisdead-strokeprinciple.

AproofofthislastpropositionisfoundinthefactthatathoroughlathemanwillperformnearlyasmuchworkanddoitaswellonanoldEnglishlathewithplainscrewfeed,ascanbeperformedonthemorecomplicatedlathesofmodernconstruction;butaseconomyofskillissometimesanequalorgreaterobjectthanasavingofmanuallabour,estimatesoftoolcapacityshouldbemadeaccordingly.Themainpointsofalathe,suchasmaymostreadilyaffectitsperformance,arefirst—truthinthebearingsoftherunningspindlewhichcommunicatesaduplicateofitsshapetopiecesthatareturned,—second,coincidencebetweenthelineofthespindleandthemovementofthecarriage,—third,acrossfeedofthetoolatatruerightangletothespindleandcarriagemovement,—fourth,durabilityofwearingsurfaces,especiallythespindlebearingsandslidingways.Tothesemaybeaddedmanyotherpoints,suchasthetruthoffeedingscrews,rigidityofframes,andsoon,butsuchrequirementsareobvious.

OneoftheearliestcaresofanapprenticeshouldbetodivesthismindofwhatIwillcalltheromanceofmechanicalengineering,almostinseparablefromsuchviewsasareoftenacquiredintechnologicalschools.Hemustrememberthatitisnotascienceheisstudying,andthatmathematicsdealonlywithonebranchofwhatistobelearned.Specialknowledge,orwhatdoesnotcomewithinthescopeofgeneralprinciples,mustbegainedinamostpracticalway,attheexpenseofhardwork,bruisedfingers,andadisregardofmuchthattheworldcallsgentility.

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    CHAPTERXII.BELTSFORTRANSMITTINGPOWER.

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    Althoughasystembutrecentlydeveloped,theemploymentofhydraulicmachineryfortransmittingandapplyingpowerhasreachedanextendedapplicationtoavarietyofpurposes,andgivespromiseofastillmoreextensiveuseinfuture.Consideredasameansoftransmittingregularlyaconstantamount[54]ofpower,waterapparatusismoreexpensiveandinferiorinmanyrespectstobeltsorshafts,anditsusemustbetracedtosomespecialprincipleinvolvedwhichadaptshydraulicapparatustotheperformanceofcertainduties.Thisprinciplewillbefoundtoconsistinstoringuppowerinsuchamannerthatitmaybeusedwithgreatforceatintervals;andsecondly,inthefacilitiesaffordedformultiplyingforcebysuchsimplemechanismaspumps.Anengineoften-horse-power,connectedwithmachinerybyhydraulicapparatus,mayprovideforaforceequaltoonehundredhorse-powerforone-tenthpartofthetime,thepowerbeingstoredupbyaccumulatorsintheinterval;orinotherwords,themotivepoweractingcontinuouslycanbeaccumulatedandappliedatintervalsasitmayberequiredforraisingweights,operatingpunches,compressiveforging,orotherworkofanintermittentcharacter.Hydraulicmachineryemployedforsuchpurposesismoresimpleandinexpensivethangearingandshafts,especiallyintheapplicationofagreatforceactingforaconsiderabledistance,andwhereacylinderandpistonrepresentadegreeofstrengthwhichcouldnotbeattainedwithtwicetheamountofdetail,ifgearing,screws,levers,orotherdeviceswereemployedinstead.

     Thetwopropositionsmaybeconsistentwitheachotherorevenidentical,buttherestillremainsanapparentdifference.

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     Separatingmachines,suchasboltsandscreens,whichmaybecalledaclass,requirenoexplanation.Theemploymentofmagneticmachinestoseparateironandbrassfilingsorshopwaste,maybenotedasarecentimprovementofsomeimportance.

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