机械专业英语董建国第6章

1、Unit 6TEXT READING MATERIAL Unit 6Unit 6TEXTMachine Elements However simple, any machine is a combination of individual components generally referred to as machine elements or parts. Thus, if a machine is completely dismantled, a collection of simple parts remains such as nuts, bolts, springs, gears

2、, cams and shaftsthe building blocks of all machinery. A machine element is, therefore, a single unit designed to perform a specific function and capable of combining with other elements. Sometimes certain elements are associated in pairs, such as nuts and bolts or keys and shafts. In other instance

3、s, a group of elements is combined to form a subassembly, such as bearings, couplings, and clutches. Unit 6 The most common example of a machine element is a gear, which, fundamentally, is a combination of the wheel and the lever to form a toothed wheel. The rotation of this gear on a hub or shaft d

4、rives other gears that may rotate faster or slower, depending upon the number of teeth on the basic wheels.Unit 6Fig. 6-1 Nut and bolt Fig. 6-2 SpringUnit 6Fig. 6-3 Shaft and bearingUnit 6Fig.6-4 ClutchUnit 6 Other fundamental machine elements have evolved from wheel and lever. A wheel must have a s

5、haft on which it may rotate. The wheel is fastened to the shafts with couplings. The shaft must rest in bearings, may be turned by a pulley with a belt or a chain connecting it to a pulley on a second shaft. The supporting structure may be assembled with bolts or rivets or by welding. Proper applica

6、tion of these machine elements depends upon knowledge of the force on the structure and the strength of the materials employed.Unit 6 Many machine elements are thoroughly standardized. Testing and practical experience have established the most suitable dimensions for common structural and mechanical

7、 parts. Through standardization, uniformity of practice and resulting economics are obtained. Not all machine parts in use are standardized, however. In the automotive industry only fasteners, bearings, bushings, chains, and belts are standardized. Crankshafts and connecting rods are not standardize

8、d.Unit 6LEARN TO SPEAKMr. Liu:Good afternoon, Mr. Xie.Mr. Xie:Good afternoon, Mr. Liu.Mr. Liu:May I ask you a few questions?Mr. Xie:Yes, of course. What are the problems?Mr. Liu:How many kinds of gears are there in common use?Mr. Xie:There are four kinds of gears. Mr. Liu:What are they?Mr. Xie:They

9、are spur gears, helical gears, worm gears, and bevel gears.Mr. Liu:Are gears important in nearly all of machinery?Mr. Xie:Yes, they are. Unit 6Mr. Liu:What can the spur gears be used for?Mr. Xie:Spur gears are used to transmit power and rotary motion between parallel shafts.Mr. Liu:How do you distin

10、guish the driving element, and the driven element?Mr. Xie:The smaller of two gears in mesh is called driving element, and the other is called driven element.Mr. Liu:Where are the spur gears used for?Mr. Xie:They are used for low speed applications and those situations where noise control is not a pr

11、oblem.Unit 6Mr. Liu:And where are the helical gears used for?Mr. Xie:They are used for high speed, large power transmission, or where noise abatement is important.Mr. Liu:Thank you for telling me about these.Mr. Xie:Not at all.Unit 6NEW WORDS AND EXPRESSIONScombination kBmbI5neIF(E)n n. 组合，组合物compon

12、ent kEm5pEJnEnt n. 元件，组件dismantle dIs5mAnt(E)l vt. 分解(机器)，拆开nut nQt n. 螺母，螺帽v. 上(拧，装)螺母spring sprIN n. 弹簧v. 弹回cam kAm n. 凸轮，偏心轮machinery mE5Fi:nErI n. 机器，机械perform pE5fC:m v. 执行，完成Unit 6associate E5sEJFIEt v. 联合，结合key ki: n. 键subassembly sQbE5semblI n. 组合件，部件coupling 5kQplIN n. 联轴节，联轴器clutch klQtF n

13、. 离合器fundamentally fQndE5mentElI adv. (从)根本上hub hQb n. 轮毂evolve I5vRlv v. 进化，演变assemble E5semb(E)l v. 安装，装配n. 组件Unit 6rivet 5rIvIt n. 铆钉 v. 铆接，铆weld weld v.&n. 焊接，熔焊adj. 焊接的thoroughly 5WQrElI adv. 完全地，彻底地standardize 5stAndEdaIz vt. 标准化establish I5stAblIF vt. 确定，建立dimension dI5menF(E)n n. 尺寸 Unit 6v.

14、 标尺寸uniformity jU:nI5fR:mEtI n. 均匀性，一致性obtain Eb5teIn v. 获得automotive C:tE5mEJtIv adj. 自动的，汽车的distinguish dIs5tINwIF v. 区别abatement E5beItmEnt n. 消除Unit 6refer to 指的是，称为combine with 与相结合in other instances 在其它情况下spur gear 直齿轮driving element 主动元件driven element 被动元件Unit 6NOTES 1Thus, if a machine is co

15、mpletely dismantled, a collection of simple parts remains such as nuts, bolts, springs, gears, cams and shaftsthe building blocks of all machinery. 因此，如果把机床完全拆开，就可以得到像螺母、螺栓、弹簧、齿轮、凸轮及轴等简单零件这是所有机器的标准元件。 if引导条件状语从句，表示如果。 Unit 6 2The most common example of a machine element is a gear, which, fundamental

16、ly, is a combination of the wheel and the lever to form a toothed wheel. The rotation of this gear on a hub or shaft drives other gears that may rotate faster or slower, depending upon the number of teeth on the basic wheels. 机械零件中最常见的是齿轮，它实际上是由轮子和杆组成的带有齿的轮子。装在轴套轮毂或轴上的旋转齿轮驱动其它齿轮做加速或减速转动，这取决于基准齿轮的齿数。

17、 Unit 6 “which”引导非限制性定语从句，修饰“gear”，不定式“to form a toothed wheel”作状语，表示结果。 分词“depending upon”作状语。 3Not all machine parts in use are standardized, however.然而，并不是所有已经使用的零件都是标准的。 “Not all”是不完全否定，其含义是“并非所有”。句中“hower”的位置可以比较灵活，可以放在句首，也可以放在句子中间，还可以放在句子后面。Unit 6EXERCISES 1Discuss the following questions in E

18、nglish: (1) What is machine element? (2) What do the bolts do? (3) Where are the springs used? (4) Which elements are associated in pairs?Unit 6 3Place a “T” after sentences that are true and an “F” after those that are false. (1) Gears are used as building blocks for the construction of most device

19、s, apparatus, and machinery. ( ) (2) A pair of gears with different numbers of teeth will rotate at different speeds. ( ) (3) The most common machine element is the gear from which other fundamental machine elements have developed. ( ) (4) A coupling is a machine element which joins two shafts. ( )

20、(5) All machine parts have been developed in to standardized designs. ( )Unit 6 4Contextual reference. (1) In sentence two,“the building blocks”refers to ( ). (a) machine elements. (b) devices, apparatus and machinery. (2) In sentence 9, the“it” refers to ( ). (a) the brake. (b) the shaft. (c) the c

21、lutch.Unit 6 (3) In sentence 11, the“it” refers to ( ). (a) the pulley. (b) the shaft. (c) the belt. (4) In sentence 13,“these machine elements” refers to( ). (a) bolts and rivets. (b) wheels, shafts, bearings, clutches, couplings, etc. Unit 6 5Rephrasing (1) The most common machine element is the g

22、ear, which combines features of the wheel and the lever. (2) The hardness of a gear determines its ability to resist wear. (3) In the design, calculations must make the forces fit the materials in the simplest construction. (4) Manufacturing engineers have centered their efforts on the development o

23、f standardized elements. (5) These parts are produced in large quantities with a high degree of perfection at reduced cost. Unit 6READING MATERIALGears The transmission of rotary motion from one shaft to another occurs in nearly every machine one can imagine. Gears constitute one of the best of the

24、various means available for transmitting this motion. Unit 6 A gear is virtual a wheel with very accurately shaped teeth. These teeth mesh with the teeth of another gear, thus providing a positive-motion drive. The speed ratio between the shafts carrying a pair of gears depends upon the number of te

25、eth in the gears. For example, if a 20-tooth gear drives a gear of 50 teeth, the smaller gear will have to turn 2 1/2 times to cause the larger one to make 1 turn. Unit 6 Various types of gearing have been developed for different purposes. If the shafts are parallel, any of three types may be used:

26、spur, helical, or herringbone. Spur gears are the simplest and least expensive type. They are generally used on drives requiring moderate speeds. Bevel gears serve to transmit power between two intersecting shafts. With a worm-gear drive, it is possible to obtain large speed reduction at a right-angle drive. Rack-and-pinion drives are used where it is desirable to transform the rotary motion of one part into linear motion for the other part, or vice versa(as shown in Fig.6-8).Unit 6Fig. 6-5 Spur gear and pinion Fig