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Technical English Through Reading 专业英语阅读 王明赞 编 l Machine Design 机械设计机械设计 l Metalwork 金属加工金属加工 l Electrical Motor Control 电机控制电机控制 l Principles of Measurement system 测量系统原理测量系统原理 Technical English Through Reading 1 Contents PART 1 MACHINE DESIGN 1 1.1 INTRODUCTION TO MACHINE DESIGN1 1.1.1 What Is Machine Design.1 1.1.2 Fundamental Background for Machine Design.1 1.1.3 Philosophy of Machine Design 2 1.1.4 Communication of Design4 1.1.5 Piston Engine Versus the Wankel Engine 5 1.1.6 The Four- stroke Automotive Piston Engine 5 1.1.7 Rotary Wankel Engine 6 1.1.8 Major of Machine Design.8 1.1.9 Initial Conception of Design 9 1.1.10 Strength Analysis 9 1.1.11 Selection of Materials .10 1.1.12 Appearance 10 1.1.13 Manufacturing .11 1.1.14 Economy11 1.1.15 Safety .12 1.1.16 Environmental Effects 12 1.1.17 Reliability and Life.13 1.1.18 Legal Considerations 13 1.2 FAILURE ANALYSIS AND DIMENSIONAL DETERMINATION14 1.2.1 Introduction .14 1.2.2 Tensile Static Strength 15 1.2.3 Design Properties of Materials.18 1.2.4 Compression and Shear Static Strength.19 1.2.5 Dynamic Loads20 1.2.6 Dynamic Strength20 1.2.7 FatigueThe Endurance Limit Diagram20 1.2.8 Stress Concentration .23 1.2.9 Allowable Stress and Factor of Safety.23 1.2.10 Creep: A Plastic Phenomenon 25 1.3 LUBRICATION AND JOURNAL BEARINGS.25 1.3.1 Introduction .25 1.3.2 Theory of Friction .25 1.3.3 Journal Bearings26 Contents 2 1.3.4 Lubricant Characteristics28 1.4 ANTIFRICTION BEARINGS.29 1.4.1 Introduction .29 1.4.2 Ball Bearings .29 1.4.3 Life of Antifriction Bearings30 1.5 SHAFTS31 1.5.1 Introduction .31 1.5.2 Shaft Design 32 1.5.3 Critical Speeds of Shafts.34 1.6 FUNDAMENTALS OF GEARS .34 1.6.1 Introduction .34 1.6.2 Gear Terminology35 1.6.3 Gear Drive System37 PART 2 METALWORK .39 2.1 MARKING OUT AND MEASURING .39 2.1.1 Tools in General Use.39 2.1.2 The Vernier Caliper Gauge .41 2.1.3 The Micrometer.42 2.1.4 The Dial Indicator .44 2.1.5 Gauges44 2.2 DRILLING AND REAMING45 2.2.1 Accident Prevention45 2.2.2 Drilling.46 2.2.3 Drilling Machines49 2.2.4 Other Processes .52 2.2.5 Reaming.52 2.2.6 Cutting Fluids54 2.3 THE LATHE .55 2.3.1 The Center Lathe.56 2.3.2 Lathe Sizes.59 2.3.3 Work Holding and Driving .59 2.3.4 Tool Posts.63 2.3.5 Lathe Tools 63 2.4 LATHEWORK67 2.4.1 Turning on Centers67 2.4.2 Screw- cutting in the Lathe69 PART 3 ELECTRIC MOTOR CONTROL.72 3.1 GENERAL PRINCIPLES OF ELECTRIC MOTOR CONTROL.72 3.1.1 Motor Control Installation Considerations72 3.1.2 Purpose of Controller73 Technical English Through Reading 3 3.1.3 Manual Control75 3.1.4 Remote and Automatic Control75 3.1.5 Starting and Stopping77 3.1.6 Speed Control of Motors.78 3.1.7 Protective Features79 3.1.8 Classification of Automatic Motor Starting Control Systems81 3.2 PUSH BUTTONS AND CONTROL STATIONS.81 3.2.1 Push Buttons81 3.2.2 Selector Switches 83 3.3 RELAYS AND CONTACTORS83 3.3.1 Control Relays.83 3.3.2 Solid- state Relay .85 3.3.3 The Transistor as A Switch.85 3.3.4 Surge Protection86 3.3.5 Contactors86 3.3.6 AC Mechanically Held Contactors and Relays .87 3.3.7 Thermostat Relay 89 3.4 TIMING RELAYS90 3.4.1 Introduction .90 3.4.2 Fluid Dashpot Timing Relays.90 3.4.3 Pneumatic Timers91 3.4.4 Magnetic Time Limit Relay91 3.4.5 Capacitor Time limit Relay.92 3.4.6 Electronic Timers 93 3.4.7 Selecting A Timing Relay.93 3.5 TWO- WIRE CONTROLS94 3.6 THREE- WIRE AND SEPARATE CONTROLS.95 3.6.1 Three- Wire Controls .95 3.6.2 Push- to- test Pilot Light.96 3.6.3 Alarm Silencing Circuit97 3.6.4 Separate Control97 PART 4 PRINCIPLES OF MEASUREMENT SYSTEM99 4.1 THE FUNDAMENTALS OF TECHNICAL MEASUREMENT.99 4.1.1 The general measurement system.99 4.1.2 Calibration.101 4.1.3 Types of Input Quantities101 4.1.4 Standards, Dimensions, and Units of Measurement .102 4.1.5 Certainty/Uncertainty: Validity of Results 103 4.2 MEASURING SYSTEM RESPONSE 104 4.2.1 Introduction .104 Contents 4 4.2.2 Amplitude Response104 4.2.3 Frequency Response105 4.2.4 Phase Response .105 4.2.5 Predicting Performance for Complex Waveforms.106 4.2.6 Delay, Rise Time, and Slew Rate.107 4.3 SENSING ELEMENT107 4.3.1 Resistive Sensing Elements108 4.3.2 Capacitive Sensing Elements 111 4.3.3 Inductive Sensing Element.112 4.3.4 Electromagnetic Sensing Elements114 4.4 SIGNAL CONDITIONING ELEMENTS.116 4.4.1 Deflection Bridges 116 4.4.2 Amplifiers118 4.5 SIGNAL PROCESSING ELEMENTS119 4.5.1 Analogue to Digital (A/D) Conversion119 4.5.2 Typical Microcomputer System125 4.5.3 Use of Microcomputer in A Speed Measurement System 128 Technical English Through Reading 1 PART 1 MACHINE DESIGN 1.1 INTRODUCTION TO MACHINE DESIGN 1.1.1 What Is Machine Design Machine design is the application of science and technology to device new or improved products for the purpose of satisfying human needs. It is a vast field of engineering technology which not only concerns itself with the original conception of the conduct in terms of its size, shape and construction details, but also considers the various factors involved in the manufacture, marketing and use of the product. A product can be defined as any manufactured item, including machines, structures, tools, and instruments. People who perform the various functions of machine design are typically called designer, or design engineer. Machine design is a creative activity Basically. However, in addition to being innovative, a design engineer must also have a solid background in the fundamentals of engineering technology. 1.1.2 Fundamental Background for Machine Design A design engineer must have working knowledge in the areas of mechanical drawing, kinematics, material engineering, strength of materials and manufacturing processes. The following statements will indicate how each of these basic background subjects relates to machine design: (1) Mechanical drawing. Detailed drawings must be prepared noting the exact shape, size and material composition for each component, assembly drawings showing how the total product is put together by fastening each part in proper sequence are also needed. (2) Kinematics. Knowledge of this subject, for example, would permit analysis of the motion of the internal mechanism of “Smarty Bird“ This analysis would include the attainment of the desired eye- rolling action. Normally, the very creation of the toy and its internal mechanism would occur during this initial phase of machine design called kinematics. (3) Mechanics. Use of this subject provides an analysis of the forces which, for example, act upon a lawn chair when a person is seated in it. Obviously, a person can damage the lawn chair by carelessly jumping on the seat. This motion, in effect, applies dynamic loading instead of the gradually applied loading taken into consideration when the lawn chair was designed. The result of this misuse is excessively large forces that can cause permanent damage. Therefore, using the laws of mechanics, a reasonable amount of dynamic loading should be taken into Part 1 Machine Design 2 account during the early design phase. (4) Materials of engineering. Because the lawn chair is commonly used in an outdoor environment, the tubing is made of aluminum to resist corrosion. The webbing is made of a plastic material that will not readily deteriorate with sustained exposure to sunlight and moisture. Obviously, the proper selection of materials is a vital area of machine design. (5) Strength of materials. The subject concerns itself with whether or not a part is strong enough to sustain the forces it will experience evaluated from mechanics. For example, the size and shape of the aluminum tubular sections of the lawn chair are determined in such a way, that failure will not occur (under normal use) due to excessive stresses and deflections. The magnitude of stresses and deflections depends on the size and shape of a given part as well as on its material, composition, and actual loads. (6) Manufacturing processes. “Smarty Bird“ is no simple toy. How each component is produced and how the entire toy is assembled are established by using methods learned in manufacturing technology. It is here that a designer comes to grips with the reality of costs. The flexible shafts are used in “Smarty Bird“ because they simplify of manufacturing by eliminating expensive parts and by cutting the labor costs of installing and aligning rigid shafting. In conjunction with the use of the processing fundamentals, there are many significant considerations, which must be detail with in the general field of machine design. Among these are safety, environmental effects, appearance, and economy. 1.1.3 Philosophy of Machine Design An unknown author wrote the following poem called “The designer.” It relates that a design engineer may enjoy making a design so complex that manufacturing of the product is virtually impossible. THE DESIGNER The designer bent across his board Wonderful things in his head wore stored. Said he as he rubbed his throbbing bean, “How can I make this tough machine? Now if I make this part just straight I know that it will work first rate, But thats too easy to shape and bore It never would make the machinist sore. So I better put an angle there Then watch those babies tear their hair. And there are the holes that hold the cap Ill put them down where theyre hard to tap. Now this wont work, Ill bet a buck, Technical English Through Reading 3 It cant be held in a shoe or chuck, In cant be drilled and it cant be ground, In fact, the design is exceedingly sound.” He looked again and cried: “At last! Success is mineit cant even be cast.” Obviously, the foregoing poem is a satire. However, it clearly emphasizes the importance of a design engineer in establishing the manufacturability of a product. As stated previously, the purpose of machine design is to produce a product that will serve a need for man. Inventions, discoveries and scientific knowledge by themselves do not necessarily benefit people; only if they are incorporated into a designed product will a benefit be derived. It should be recognized, therefore, that a human need must be identified before a particular product is designed. Sometimes a human need may be recognized, but a decision is reached to do nothing about it. The reason could simply be that, at the moment, the rewards do not justify the time and effort that must be expended. If, however, the decision is reached to satisfy the human need by manufactured product, the entire project must be clearly defined. Machine design should be considered to be an opportunity to use innovative talents to envision a design of a product, to analyze the system and then make sound judgments on how the product is to be manufactured. It is important to understand the fundamentals of engineering rather than memorize mere facts and equations. There are no facts or equations, which alone can be used to provide all the correct decisions, required producing a good design. On the other hand, any calculations made must be done with the utmost care and precision. For example, if a decimal point is misplaced, an otherwise acceptable design may not function. Good designs require trying new ideas and being willing to take a certain amount of risk, knowing that if the new idea does not work the existing method can be reinstated. Thus a designer must have patience, since there is no assurance of success for the time and effort expended. Creating a completely new design generally requires that many old and will- established methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques, and attitudes. A design engineer should constantly search for ways to improve an existing product and must decide what old, proven concepts should be used and what new, untried ideas should be incorporated. New designs generally have “bugs” or unforeseen problems which must be worked out before the superior characteristics of the new designs, can be enjoyed. Thus, there is a chance for a superior conduct, but only at higher risk. It should be emphasized that, if a design does not warrant radical new methods, such methods should not be applied merely for the sake of change. During the beginning stages of design, creativity should be allowed to flourish without a great number of constraints. Although many impractical ideas may arise, it is usually easy to eliminate them in the early stages of design before manufacturing requires firm details. In this Part 1 Machine Design 4 way, innovative ideas are not inhibited. Quite often, more than one design is developed, up to the point where they can be compared against each other. It is entirely possible that the design that is ultimately accepted, will use ideas existing in one of the rejected designs that did not show as overall promise. Psychologists frequently talk about trying to fit people to the machines they operate. It is essentially the responsibility of the design engineer to strive to fit machines to people. This is not an easy task, since there is really no average person for which certain operating dimensions and procedures are optimums. However, many human operator features must be considered including the following: (1) Size and locations of hand wheels, knobs, switches, and foot pedals; (2) Space allocations for working areas; (3) Ventilation; (4) Colors and lighting; (5) Strength of operator; (6) Safety features; (7) Monotonous operator motions; (8) Operator acceptance. 1.1.4 Communication of Design Another important point which should be recognized, is that a design engineer Must be able to communicate ideas to other people if they are to be incorporated. Initially, the designer must communicate a preliminary design to get management approval. This is usually done by verbal discussions in conjunction with drawing layouts and written material. To communicate effectively, the following questions must be answered: (1) Does the design really serve a human need? (2) Will it be competitive with existing products of rival companies? (3) Is it economical to produce? (4) Can it be readily maintained? (5) Will it sell and make a profit? Only time will provide the true answers to the preceding questions, but the Product should be designed, manufactured, and marketed only with initial affirmative answers. The design engineer also must communicate the finalized design to manufacturing through the use if detail and assembly drawings. Quite often, a problem will occur during the manufacturing cycle. It may be that a change is required in the dimensioning or tolerance of a part so that it can be more readily produced. This falls in the category of engineering changes that must be approved by the design engineer so that the product function will not be adversely affected. In other cases, a deficiency in the design may appear during assembly or testing just prior to shipping. These are always a better way that to do it and the designer should constantly strive towards finding that better way. One Technical English Through Reading 5 reality that needs to be kept in mind is that many of the products that will be in existence ten years from now have probably not yet even been conceived. 1.1.5 Piston Engine Versus the Wankel Engine The automobile, without a doubt, has had one of the most profound influences on people in the twentieth century. Powered predominantly by the conventional reciprocating piston engine during the first seven decades of the twentieth century, the automobile has been the basis for the largest industry in the world. Most people in the United States who are old enough to obtain a license own automobiles. This, however, has contributed to the new problem of “air pollution,“ which, stated simply, means that the atmosphere is gradually accumulating more and more chemical contaminants harmful to human life. One of the results of increasing air pollution has been a hard look at other types of engines which promise to provide fewer pollutants in exhaust emissions. One such engine recently receiving a great deal of development is the Wankel engine. It is a very possible replacement for the piston engine. A second, concurrent problem is a shortage of available crude oil from which gasoline is derived. Thus, there is also a need for a much more efficient engine as well as one which produces far fewer pollutants. Surprisingly enough, the first four stroke piston engine was built in 1866 by Nickolaas August Otto and Euger Langen of Germany. The present- day piston engine works on basically the same principles as the one built by Otto and Langen. In fact, the thermodynamic process operating in the modern piston is called the Otto cycle. On the other hand, the Wankel rotary engine was not invented until 1954, when Felix Wankel, also of Germany, discovered that he could reproduce the Otto cycle with a purely rotary- type engine. From an efficient point of view, the Wankel engine is superior because it is simpler, contains fewer parts and operates more quietly. It wasnt, however, until the 1960s that much effort was put into the development of the Wankel engine. The main reason for this was that the piston engine was already a proven, reliably working power plant. It was the human needs for an engine with far less polluting exhaust emissions, which apparently spearheaded new engine developments in the early 1960s. In 1967, Toyo Kogyo of Japan was manufacturing Wankel- powered Mazda automobiles and the United States began to witness the impact by the early 1970s. Recognizing the great potential of the Wankel engine, General Motors in 1971 signed a $50 million licensing agreement with Wankel patent holders (Wankel Gmb H and Audi NSU and the U. S. licensee, Curtiss Wright). From 1971 to 1975, General Motors is to pay the $50 million and develop the Wankel engine for is own conduction. After 1975, General Motors can use its own designed Wankel engines without paying any additional licensing fees. Next, let us examine the design and operation of the piston and Wankel engines. 1.1.6 The Four- strok