材料的选择

第三讲材料的选择Lesson3:SelectingMaterials1木材的类型Typesofwood硬木（阔叶木）和软木（针叶木）Hardwoodsandsoftwoods树木通常被划分为两个种类：硬木和软木Treesareoftendividedintotwoclasses:hardwoodsandsoftwoods有些软木比硬木的硬度更大，所以其名字会被误解（反过来也一样）Thesenamescanbemisleadingbecausesomesoftwoodsareharderthansomehardwoods(thereverseisalsotrue)3木材的类型Typesofwood硬木和软木Hardwoodsandsoftwoods硬木树种通常都有较宽的树叶（部分例外），在秋季或冬季会落叶。Hardwoodtreesusuallyhavebroadleavesthat,withsomeexceptions,areshedinautumnorwinterintemperateclimates软木树种通常都有针状或鳞片状的树叶，一般情况下都是常绿的并且有年轮。Softwoodtreesusuallyhaveneedleorscale-likeleavesthat,inmostcases,remaingreenandareretainedyear-round4木材的类型Typesofwood硬木和软木Hardwoodsandsoftwoods硬木在建筑中通常用于地板和内装工程（楼梯，壁橱，踢脚线，门窗线条等）Hardwoodsareusedinconstructionmostlyforflooringandinteriorwoodwork(e.g.stairs,cabinetry,baseboards,trimaroundwindowsanddoors,etc.)软木一般被用于结构框架，封板，混凝土支模，脚手架和其他建筑构件Softwoodsareusedforframing,sheathing,concreteforms,scaffoldingandmanyotherbuildingcomponents耐久性好的软木（比如西部红柏，花旗松）可用于屋面瓦，墙面外挂板，窗框和外门等外部构件Somemoredurablespeciesofsoftwoodareusedforexteriorcomponentssuchasroofandwallshingles,windowframesandexteriordoors5软木材的制造Manufacturingsoftwoodlumber制造过程始于伐树Manufacturingprocessbeginswithharvestingtrees树木被砍下后，树枝先被去除，切割成一定长度方便卡车运送Treesarecutdown,strippedofbranchesandcuttolengthfortransportbytruck这样形成的原木再被运往锯木厂Resultinglogsarethenshippedtoasawmill砍伐之后的区域将种上树苗使森林再生Harvestedareasarereplantedwithtreeseedlingstoregeneratetheforest6软木材的制造Manufacturingsoftwoodlumber原木在锯木厂进行加工Thelogsareprocessedbythesawmill树皮在加工的过程中被去除Barkisremovedfromthelogs去掉树皮的木材将被锯成的初步的木板Debarkedlogsaresawntointoroughplanks这些厚木板之后会被切边，重新切割成特定尺寸和长度Theseplanksarethenedged,resawntospecificdimensionsandcuttostandardlengths7软木材的制造Manufacturingsoftwoodlumber之后把生材由垫块隔开堆放进行风干或者窑干Thisgreenlumberisthenstackedwithspacersandeitherair-driedorkiln-dried大多数软木是在窑内烘干而不是风干Mostsoftwoodlumberiskiln-driedratherthanairdried尽管花费更大，但窑干更快速，过程更方便控制Althoughmorecostly,kilndryinglumberisaquickerandeasiertocontrolprocess8软木材的制造Manufacturingsoftwoodlumber需将生材干燥的重要原因：Thereareseveralimportantreasonstodrygreenlumber:1.减少收缩变形Reducesproblemswithshrinkage2.减少变色、腐坏及虫害Reducessusceptibilitytostaining,decayandinsectdamage3.使得木材可以被防腐处理Enableswoodtobetreatedwithpreservatives9软木材的制造Manufacturingsoftwoodlumber需将生材干燥的重要原因：Thereareseveralimportantreasonstodrygreenlumber:4.改善木材握钉及施胶能力Improvesstrengthandtheholdofnails,screwsandglue5.保证油漆和其他表面材料的更好的粘结力Allowspaintsandotherfinishestoadherebetter6.使木材处理及运输更方便Makesiteasiertohandleandtransport10软木材的制造Manufacturingsoftwoodlumber干燥之后，木材被送过刨床，校直，磨平，统一尺寸Afterdrying,thelumberisputthoughaplanermillwhereitisstraightened,smoothedanduniformlysized11软木材的制造Manufacturingsoftwoodlumber木材制造的最后一个过程是将木材分等级Finalstepinthemanufacturingprocessisgradingandsortingthelumber12软木材尺寸Softwoodlumbersizes木材相关称呼：Lumberterminology:13边面Edge端面End宽度WidthorDepth厚度Thickness正面SideorFace软木材尺寸Softwoodlumbersizes木材的厚度和宽度：Thicknessandwidthoflumberisexpressedintwoways:1.名义尺寸-在进行干燥和最终处理之前的生材尺寸Nominalsize–Referstotheapproximatesize(ininches)ofgreenlumberbeforeitisdriedandreceivesfinalprocessinginaplanermill2.实际尺寸-进行干燥和刨光处理之后的实际尺寸Dressedsize–Referstoactualsizeoflumberafteritisdriedandsurfacedinaplanermill14软木材尺寸Softwoodlumbersizes结构规格材常用的尺寸（厚度和宽度）:Commonsizes(thicknessandwidth)offraminglumber:15实际尺寸公制（英制）ActualDressedSizemetric(imperial)名义尺寸（英制）NominalSize(imperial)38x89mm(1½x3½in.)2x438x140mm(1½x5½in.)2x638x184mm(1½x7¼in.)2x838x235mm(1½x9¼in.)2x1038x286mm(1½x11¼in.)2x12软木材尺寸Softwoodlumbersizes结构用规格材的长度Commonlengthsofframinglumber:2.4米至7.2米，其中以600毫米递增的每一个长度2.4to7.2min600mmincrements中国内地能买到的最长材料为6.1米LongestmaterialavailableinChinais6.1m常见长度：Usuallengths:168英尺8ft.10英尺10ft.12英尺12ft.14英尺14ft.16英尺16ft.18英尺18ft.20英尺20ft.2.44m3.05m3.66m4.27m4.88m5.49m6.10m含水率与变形Moisturecontentandshrinkage木材的含水率极为影响其表观及耐久性Moisturecontentoflumberisanimportantfactorinitsperformanceanddurability含水率是指木材内所含水分的质量占其烘干质量的百分比Moisturecontentistheweightofwatercontainedinwoodexpressedasapercentageoftheweightofoven-drywood木材的含水率会随着周围的空气稳定下来，但会随着环境的变化而变化Moisturecontentofwoodwilleventuallyequilibriumwiththesurroundingairandthenrespondtochangingconditions17含水率与变形Moisturecontentandshrinkage木材会干缩和湿胀Woodshrinkswhenitdriesandswellswhenitiswet生材干燥时会有明显的收缩Significantshrinkageoccursasgreenwooddries木材各方向变形不一致-顺纹方向变形很小-横纹方向变形很大Wooddoesnotshrinkorexpandequallyinalldirections-verylittleshrinkage/expansionalongthegrain(lengthwise)-significantshrinkage/expansioncanoccuracrossthegrain木材干燥过程中可能会有翘曲出现Warpingmayalsooccuraswooddries18翘曲类型Typesofwarps翘弯Bow扭弯Crook扭曲Twist瓦弯Cup收缩现象Shrinkageeffects含水率与变形Moisturecontentandshrinkage推荐的含水率：Recommendedmoisturecontentlevels:结构中的规格材在封板之前最高含水率不超过19%Dimensionlumberforframingshouldhaveamaximummoisturecontentlevelof19%beforeitisenclosed一般此时，木材平均含水率在15%，绝大部分收缩已经没有了Atthislevel,theaveragewoodmoisturecontentwillbelower(about15%)andmostshrinkagehasalreadyoccurred可用仪器测试木材的含水率Awoodmoisturemetercanbeusedtomeasurethemoisturecontentofdimensionallumber19探针型木材含水率测试仪Pin-typewoodmoisture软木材分级Softwoodlumbergrading结构用材必须是经过分等级的Lumberusedforframingmustbegraded方便