第二部分 二级强化班翻译练习
1. An ordinary nut loosens when the forces of vibration overcome those of friction. In a nut and lock washer combination, the lock washer supplies an independent locking feature preventing the nut from loosening. The lock washer is useful only when the bolt might loosen because of a relative change between the length of the bolt and the parts assembled by it. This change in the length of the bolt can be caused by a number of factors-creep in the bolt, loss of resilience, difference in thermal expansion between the bolt and the bolted members, or wear. In the above static cases, the expanding lock washer holds the nut under axial load and keeps the assembly tight. When relative changes are caused by vibration forces, the lock washer is not nearly as effective.
当振动力大于摩擦力时，普通螺帽就会松动。但螺帽与锁紧垫圈配合使用时，锁紧垫圈的自锁紧特性就可以防止螺帽松开。只有当螺栓长度与其所装配零件间距离出现变化，导致螺栓松动时，锁紧垫圈才起作用。螺栓长度变化可能有多种原因——螺栓内部蠕动、无回弹力、螺栓与栓接件之间不同的热膨胀量，或者出现磨损。当上述情况出现在静态条件下时，锁紧垫圈轴向胀开顶紧螺帽，保持组件紧固。但如果相对变化是由振动引起的，这时锁紧垫圈几乎就不起作用。
2. Riveting is the commonest method of assembling aircraft. A medium bomber requires
160,000 rivets and a heavy bomber requires 400,000 rivets. Some of the forms of rivets are solid rivets with chamfered shanks, tubular or hollow rivets, semitubular rivets, swaged rivets, split rivets, and blind rivets. Solid rivets are used where great strength is required. Tubular rivets are used in the fastening of leather braces. Split rivets are used frequently in the making of suitcases. The materials used in making rivets are aluminum alloys, Monel metal, brass, and steel. Aluminum rivets make possible the maximum saving in weight, and are also quite resistant to corrosion.
铆接是最常用的装配飞机的方法。一架中型轰炸机需要16万个铆钉，而一架重型轰炸机需要40万个铆钉。铆钉形状可以是斜柄实心铆钉、管形或空心铆钉、半管形铆钉、挤压铆钉、开口铆钉、埋头铆钉等。实心铆钉用在高强度的场合。管形铆钉用于紧固各种皮带。开口铆钉常用于制造箱包。用于制造铆钉的材料有铝合金、蒙乃尔合金、铜和钢。铝铆钉可以最大程度地减轻重量而且相当抗腐蚀。
3．Helical gears have certain advantages；for example，when connecting parallel shafts they have a higher load-carrying capacity than spur gears with the same tooth numbers and cut with the same cutter．Because of the overlapping action of the teeth，they are smoother in action and can operate at higher pitch-line velocities than spur gears. The pitch-line velocity is the velocity of the pitch circle. Since the teeth are inclined to the axis of rotation，helical gears create an axial thrust. If used singly，this thrust must be absorbed in the shaft bearings．The thrust problem can be overcome by cutting two sets of opposed helical teeth on the same blank.
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斜齿轮具有某些优点。例如：连接两平行轴时，斜齿轮比齿数相同、使用相同刀具切削的直齿轮有更大的承载能力。由于轮齿的重迭作用，斜齿轮运行更平稳，节线速度比直齿轮更快。节线速度就是节圆的速度。由于轮齿向旋转轴倾斜，所以斜齿轮会产生轴向推力。如果单独使用，推力就必须由轴承来承受。推力问题可以通过在同一坯件上切削两组相反的斜齿来克服。
4. Timing belts Timing belts have evenly spaced teeth on their bottom side which mesh with grooves cut on the periphery of the pulleys to produce a positive，no-slip，constant-speed drive, similar to chain drives．They are often used to replace chains or gears，reducing noise and avoiding the lubrication bath or oiling system requirement. They have also found widespread application in miniature timing applications．Timing belts， known also as synchronous or cogged belts，require the least tension of all belt drives and are among the most efficient．They can transmit up to 150 KW at speed up to 800 mps．There is no lower limit on speed．Disadvantages are high first cost，grooving the pulleys，less overload and jam protection，no clutch action，and backlash.
同步齿形皮带在其内表面有均匀分布的齿，齿与在滑轮圆周上所开齿槽相啮合产生刚性、无滑动、恒速的驱动，与链式传动类似。它们常用于替代链条或齿轮，可以减小噪音又不需要润滑槽或润滑系统。同时也广泛应用于微型定时操作中。同步齿形皮带也叫做同步或楔形齿皮带，在所有带式传动中需要张力最少而效率最高。它们可以以800米／秒速度传送动力最高达150千瓦，且无低速限制。缺点是初始成本高；必须给带轮开槽；没有过载及卡滞保护；没有离合器作用和齿间隙。
5. Alloy Steels：Plain carbon steels are made up primarily of iron and carbon, while alloy
steels include these same elements with many other elemental additions．The purpose of alloying steel is either to enhance the material’s physical properties or its ultimate manufacturability．The physical property enhancements include improved toughness-tensile strength, hardenability，(the relative ease with which a higher hardness level can be attained) , ductility and wear resistance．The use of alloying elements can alter the final grain size of a heat-treated steel，which often results in a lower machinability rating of the final product．The primary types of alloyed steel are：nickel，chromium， manganese， vanadium，molybdenum, chrome-nickel, chrome-vanadium, chrome-molybdenum, and nickel-molybdenum.
6. Rolled steel，which includes bar，rod，and structural steels，is produced by rolling the steel
into shape．Hot-rolled steels are formed into shape while the metal is red-hot．The metal passes through a series of rollers，each a 1ittle closer to the next one．As the steel passes through the last rollers，hot water is sprayed over it，forming a bluish scale．This steel is fairly uniform in quality and is used for many different kinds of parts．Hot-rolled bars of the best quality are used to produce cold-finished steels. Cold-finished steels are used when great accuracy，better surface finish，and certain mechanical properties are needed．
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7. Roll forming is a continuous process for forming metal from sheet，strip，or coiled stock
into shapes of essentially uniform cross section．The material is fed between successive pairs of rolls， which progressively shape it until the desired cross section is produced．During the process，only bending takes place；the material thickness is not changed except for a slight thinning at bend radius .
Forging is one of the oldest metalworking processes known to man．As early as 2000 B C．，forging was used to produce weapons，implements，and jewelry．The process was performed by hand using simple hammers．
Casting is the introduction of molten metal into a cavity or mold where，upon solidification，it becomes an object whose shape is determined by mold configuration．
8. Two broad categories of metal-casting processes exist：ingot casting (which includes continuous casting) and casting to shape. Ingot castings are produced by pouring molten metal into a permanent or reusable mold．Following solidification these ingots (or bars，slabs，or billets，as the case may be) are then further processed mechanically into many new shapes. Casting to shape involves pouring molten metal into molds in which the cavity provides the final useful shape，followed only by machining or welding for the specific application.
9. The three main types of arc welding processes used today are shielded meta1-arc welding，
gas tungsten-arc welding，and gas metal-arc welding．Shielded metal-arc welders perform their skill by first striking an arc at the starting point of a weld and maintaining this electric arc to fuse the metal joints．The molten metal from the tip of the electrode is then deposited in the joint，together with the molten metal of the edges，and solidifies to form a sound and uniform connection. The arc welding operator is expected to select the proper electrodes for the job or be able to follow instructions as stated in the job specifications，to read welding symbols，and to weld any type of joint using the technique required.
10. Tempering Tempering is a process of reducing the degree of hardness and strength and
increasing the toughness．It removes the brittleness from a hardened piece．It is a process that follows the hardening procedure and makes the metal as hard and tough as possible . Tempering is done by reheating the metal to low or moderate temperature，followed by quenching or by cooling in air . As the metal is heated for tempering , it changes in colour．These colours are called temper colours．You can watch these colours to know when the correct heat is reached．A more accurate method，of course，is to watch the pyrometer．Many parts and projects are completely tempered．Others are tempered in one section，and the rest remains in the hardened state．
11. Hardening is a process of heating and cooling steel to increase its hardness and tensile
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strength，to reduce its ductility，and to obtain a fine grain structure．The procedure includes heating the metal above its critical point or temperature，followed by rapid cooling．As steel is heated，a physical and chemical change takes place between the iron and carbon．The critical point，or critical temperature，is the point at which the steel has the most desirable characteristics．When steel reaches this temperature—somewhere between 1,400 and 1,600°F —the change is ideal to make for a hard, strong material if it is cooled quickly．If the metal cools slowly, it changes back to its original state．By plunging the hot metal into water，oil，or brine (quenching)，the desirable characteristics are retained．The metal is very hard and strong and less ductile than before．
12. Accuracy of sensors, transducers, and associated signal-conditioning devices is important in control system applications for two main reasons. The measurement system in a feedback control system is situated in the feedback path of the control system. Even though measurements are used to compensate for the poor performance in the open-loop system, any errors in measurements themselves will enter directly into the system and cannot be corrected if they are unknown. Furthermore, it can be shown that sensitivity of a control system to parameter changes in the measurement system is direct. This sensitivity cannot be reduced by increasing the loop gain, unlike in the case of sensitivity to the open-loop components.
13. An expert system is an intelligent computer program that uses knowledge and inference procedures to solve problems that are difficult enough to require significant human expertise for their solution. The knowledge of an expert system consists of facts and heuristics. The facts constitute a body of information that is widely shared, publicly available, and generally agreed upon by experts in a field. The ―heuristics‖ are mostly private, little discussed rules of good judgment （rules of plausible reasoning, rules of good guessing) that characterize expert-level decision making in the field. The performance level of an expert system is primarily a function of the size and quality of the knowledge base that it possesses.
14. An expert system differs from more conventional computer programs in several important
respects. In expert system there is a clear separation of general knowledge about the problem (the rules forming a knowledge base) from information about the current problem (the input data) and the methods for applying the general knowledge to the problem (the rule interpreter). In a conventional computer system program, knowledge pertinent to the problem and methods for utilizing this knowledge are all intermixed so that it is difficult to change the program. In an expert system the program itself is only an interpreter (or general reasoning mechanism) and the system can be changed by simply adding or subtracting rules in the knowledge base.
15. Internet technology can be used to distribute and share information inside the organization
as well as to connect to the outside. Many organizations are starting to build internal networks
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called intranets based on Internet technology. An intranet is an internal organizational network that is modeled on the Web. It uses the existing company network infrastructure, Internet communication standards, and the software developed for the World Wide Web. By applying Internet technology to their own business applications, companies can communicate and distribute information across the enterprise while keeping unauthorized users out.
16. Viruses have become a particular risk with the advent of internet technology, which makes
it much easier to pass and spread viruses. Such technologies as Java and Active X pose important new problems. An Active X applet could automatically install itself in the background on a system and load a new file. Antivirus researchers fear a hostile applet could introduce a virus that way.
New viral threats will probably be along these lines, said Shannon Talbott, manager of Network Associate’s McAfee Labs. A number of antivirus vendors sell products that block hostile Java applets and Active X controls.
17. TISCO has internationally up-to-date stainless steel production lines, fully integrated,
starting from smelting using hot metal as main charge, refining, hot rolling, cold rolling, capable of cold rolled coils/sheets, hot rolled coils, hot rolled plates, clad plates, bars, wire rods, seamless steel tubes, weld pipes, large castings in different sizes and specifications. It can produce to China National Standard (GB), European Standard, American Standard, Japanese Standard the regular and high-end stainless steel products as of austensitic, martensitic, ferritic, duplex, precipitation hardened series; hot rolled coils made to 20mm thick and 2100mm wide; hot rolled plates 100mm thick and 3000mm wide, and cold rolled sheets 0.4 -8mm thick and 1500-2100mm wide. Steel product can be delivered with finish quality of NO.1, 2B, BA, 2D, NO.3, NO.4 and HL.
太钢拥有国际先进水平的以铁水为主原料的冶炼-精炼-连住铸-热轧-冷轧全流程不锈钢生产线，已形成包括冷轧卷（板）、热轧卷板、热轧中厚板、复合钢板、棒材、线材、无缝管、焊管、大型铸件在内的不锈钢产品系列。可按照中国国家标准、欧标、美标、日标、生产奥氏体、马氏体、铁素体、双相钢、沉淀硬化各系列多规格的不锈钢常规品种及高端品种。可生产20mm厚、2100mm宽的热轧卷板：100mm厚、3000mm宽的热轧中厚板；0.4-0.8mm厚、1500-2100mm宽的宽幅冷轧薄板。可提供no.1、2B、BA、2D、NO3、NO4和HL等各种表面加工等级的板材。
18. China’s stainless steel industry should carry out national policy，follow the worried trend，and realize the maximum conservation and rational use of energy such as coal，oil and gas and electricity as well as resources such as water and meta1．In the mean time，pay attention to environmental protection，reduce the emission of greenhouse gas，and prevent our environment to be polluted by sewage ，solid waste，waste gas and noise．Sustainable development is the natural requirement for us and future generation and it is also the
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