American colonies.After the i the French under well."he says. To convert degrecs Fahrenhcit to degrees Celsius,subtract 32.and then multiply the result by five-ninths.To convert from Celsius to Fahrenheit. multiply by nine-fifths,and then add 32. Words and Expressions respoctive ris'pektiv] ad.各白的 centierude ['sentireid] ,百分度的 随兰的 a.气象上的 benchmark[btm]n.基准 日
Part II Components,Mechanisms and Machinery
Unit 1 ■ Shafting they can n erform their basic functi of rot ade from metal bars of various lengths and machincd to dimension the surface.isusd in a great variety of shapes and applications Because shafts carry loads and transmit power,they are btto the stresses and strains of operating machine parts.Standardized procedures have been evolved for determining the material characteristics and size requirements for safe and economical construction and operation. Types Solid sharting The pormal form of shafting is a solid bar.Solid shafting i ohtainable commercially in roundd har stock un to 15 cm in diameter:it is produced by hot-rolling and cold-drawing or by machine-finishing with diameters in increments of 6 mm or less.For larger sizes.special rolling procedures are rquired,and for extremly large shafts,billets are forged to the proper shape.Particularly in solid shafting.the shaft is stepped toallow greate strength in the middl portion with minimum on the ends at th To minimize weights solid shafting is bored out or drilkd.r hollow
Uni证1 haft betw ss.The center of large shafts made from ingots are often bored out to remove imperfections and also to allow visual inspection for forging cracks Functions Shafts used in special ways are given specific names,although fundamentallya applications involve transmission of tore. Axke The primary shafting conection between a wheel and a housing is an ax It may simply be the extension of a round member from each side of the rear of a wagon,and on the end of each the hub of a wagon wheel rotatess Similarly.railroad car axkes are large.round bars of steel spanning between th car whecls,supporting the car frame with bearings on the axle ousid e th igs,【hey abo transmit to red.A spindle from the round tarering stick on a spinning wheel on which the thread is twistcd. Head A short stub shaft mounted as part of a motor or engine or extending directly therefrom is a head shaft.An example is the power take off shaft on a tractor. coary shaft that is dri n by a main shaft and fro is supplic t.Often th in shaft to anothe used as an auxiliary shaft between two other shafts.is termed a jackshaft
to rooess eimment machines.Belts ooerate on pulkys to transmit the tomue from onc linc to another and from the shafting to the machincs.Clutches and oouplings conto the transfer of power from the shafting. The delivery of power to the machines in a shop has gencrally been converted from line shafting to individual electric motor drives for each machine.Thus,in a moder processing plant,line shafting is obolete. Words and Expressions shafting'ad与] 几传动轴轴系 sendker [Sand] a山.心形销 o-rollin taper L'teipal machine-finishine ning whed spindle ['spindl] ,《机器中的)轴， ingot[] hub hub] obdlete [aleli:t】d.拉度的，装国的 span [speen] Notes Shafting.made from round metal bars of various lengths and machined to