机械专业英语董建国第6章讲解

1、Unit 6 TEXT READING MATERIAL Unit 6 Unit 6 TEXT Machine 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, g

2、ears, 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 inst

3、ances, 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 sha

4、ft drives other gears that may rotate faster or slower, depending upon the number of teeth on the basic wheels. Unit 6 Fig. 6-1 Nut and bolt Fig. 6-2 Spring Unit 6 Fig. 6-3 Shaft and bearing Unit 6 Fig.6-4 Clutch Unit 6 Other fundamental machine elements have evolved from wheel and lever. A wheel mu

5、st have a shaft 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. Pro

6、per application 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 an

7、d mechanical 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

8、 standardized. Unit 6 LEARN TO SPEAK Mr. 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 ar

9、e they? Mr. Xie:They 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 6 Mr. Liu:What can the spur gears be used for? Mr. Xie:Spur gears are used to transmit power and rotary motion between parallel shafts.

10、 Mr. Liu:How do you distinguish 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 wh

11、ere noise control is not a problem. Unit 6 Mr. 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 6 NEW WORDS AND EXPRESSIONS combi

12、nation kBmbI5neIF(E)n n. 组合，组合物 component 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 6 associate E5sEJFIEt v. 联合，结合 key ki: n. 键 subassembly sQbE5semblI

13、n. 组合件，部件 coupling 5kQplIN n. 联轴节，联轴器 clutch klQtF n. 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 6 rivet 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 e

14、stablish I5stAblIF vt. 确定，建立 dimension dI5menF(E)n n. 尺寸 Unit 6 v. 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 6 refer 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

15、 driving element 主动元件 driven element 被动元件 Unit 6 NOTES 1Thus, if a machine is completely 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。

16、Unit 6 2The 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 drives other gears that may rotate faster or slower, depending upon the number of teeth on the basic

17、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。 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

18、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 6 EXERCISES 1Discuss the following questions in English: (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 thos

19、e that are false. (1) Gears are used as building blocks for the construction of most devices, 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 el

20、ements have developed. ( ) (4) A coupling is a machine element which joins two shafts. ( ) (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

21、machinery. (2) In sentence 9, the“it” refers to ( ). (a) the brake. (b) the shaft. (c) the clutch. 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, bearin

22、gs, clutches, couplings, etc. Unit 6 5Rephrasing (1) The most common machine element is the gear, 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 simple

23、st construction. (4) Manufacturing engineers have centered their efforts on the development of standardized elements. (5) These parts are produced in large quantities with a high degree of perfection at reduced cost. Unit 6 READING MATERIAL Gears The transmission of rotary motion from one shaft to a

24、nother occurs in nearly every machine one can imagine. Gears constitute one of the best of the 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 d

25、rive. The speed ratio between the shafts carrying a pair of gears depends upon the number of teeth 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

26、 developed for different purposes. If the shafts are parallel, any of three types may be used: 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 intersectin

27、g 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 6 Fig. 6-5 Spur gear and pinion Fig. 6-6 Bevel gears Unit