《机电专业英语》期末考试试卷（试卷编号 A ）
（闭卷100 分钟）
.Translations of Phrases and Expressions(2΄×15=30΄)
1.heat treatment﹍﹍﹍﹍﹍﹍﹍﹍
2.room temperature﹍﹍﹍﹍﹍﹍﹍﹍
3.raw material﹍﹍﹍﹍﹍﹍﹍﹍
4.worm gear﹍﹍﹍﹍﹍﹍﹍﹍
5.flame cutter﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
… be concerned﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
﹍﹍﹍﹍﹍﹍﹍﹍
15.carbon dioxide﹍﹍﹍﹍﹍﹍﹍﹍
二．C alculations(5΄+10=15΄)
1.How much current will flow through a 24Ω electric heater when voltage of 240V is applied?
2.A transformer supplies a load with 30A at 120V .If the primary voltage is 2400V,find:
(a)the secondary voltamperes;
(b)the primary voltamperes;
And (c)the primary current.
三．Reading Comprehensions(30΄)
Iron and Steel
The earth contains a large number of metals which are useful to man.One of the most important of these is iron.Modern industry needs considerable quantities of this metal,either in
the form of iron or in the form of steel.A certain number of non-ferrous metals,including aluminum and zinc,are also important,but even today the majority of our engineering products are of iron or steel.Moreover,iron possesses magnetic properties,which have made the development of electrical power possible.
The iron ore which we find in the earth is not pure.It contains some impurities which we must remove by smelting.The process of smelting consists of heating the ore in a blast furnace with coke and limestone,and reducing it to metal.Blasts of hot air enter the furnace from the bottom and provide the oxygen which is necessary for the reduction of the ore.The ore becomes molten,and its oxides combine with carbon from the coke.The non-metallic constituents of the ore combine with the limestone to form a liquid slag.This floats on top of the molten iron,and passess out of the furnace through a tap.The metal which remains is pigiron.
We can melt this down again in another furnace—a cupola—with more coke and limestone,and tap it out into a ladle or directly into mould.This is cast-iron.Cast-iron does not have the strength of steel.It is brittle and may fracture under tension.But it possesses certain properties which make it very useful in the manufacture of machinery.In the molten state it is very fluid,and
therefore it is easy to cast it into complicated shapes.Also it is easy to machine it.Cast–iron contains small proportions of other substances.These non-metallic constituents of cast-iron include carbon,silicon and sulphur,and the presence of these substances affects the behaviour of the metal.Iron which contains a small quantity of carbon,for example wrought-iron,behaves differently from iron which contains a lot of carbon.
The carbon in cast-iron is present partly as free graphite and partly as a chemical combination of iron and carbon which we call cemmentite.This is a very hard substance,and it makes the iron hard too.However ,iron can only hold about 1.5% of cementite.Any carbon content above that percentage is present in the form of free graphite.Steel contains no free graphite,and its carbon content ranges from almost nothing to 1.5%.We make wire and tubing from mild steel with a very low carbon content,and drills and cutting tools from high carbon steel.
Questions
1.(3΄×3=9΄)True and false statements
(1)( )Heat treatment is a process of heating metals to
alter their mechanical properties.
(2)( )A steel part must be heated to the critical
temperature in order to be completely austenitized.