1、 Technical English Through Reading 专业英语阅读 王明赞 编 l Machine Design 机械设计 l Metalwork 金属加工 l Electrical Motor Control 电机控制 l Principles of Measurement system 测量系统原理 Technical English Through Reading 1Contents PART 1 MACHINE DESIGN 1 1.1 INTRODUCTION TO MACHINE DESIGN1 1.1.1 What Is Machine Design.1 1.1.
2、2 Fundamental Background for Machine Design.1 1.1.3 Philosophy of Machine Design2 1.1.4 Communication of Design4 1.1.5 Piston Engine Versus the Wankel Engine5 1.1.6 The Four-stroke Automotive Piston Engine5 1.1.7 Rotary Wankel Engine6 1.1.8 Major of Machine Design.8 1.1.9 Initial Conception of Desig
3、n9 1.1.10 Strength Analysis9 1.1.11 Selection of Materials.10 1.1.12 Appearance10 1.1.13 Manufacturing.11 1.1.14 Economy11 1.1.15 Safety.12 1.1.16 Environmental Effects12 1.1.17 Reliability and Life.13 1.1.18 Legal Considerations13 1.2 FAILURE ANALYSIS AND DIMENSIONAL DETERMINATION14 1.2.1 Introduct
4、ion.14 1.2.2 Tensile Static Strength15 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
5、Creep: A Plastic Phenomenon25 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 21.3.4 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
6、 1.5 SHAFTS31 1.5.1 Introduction.31 1.5.2 Shaft Design32 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 Calip
7、er 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 Si
8、zes.59 2.3.3 Work Holding and Driving.59 2.3.4 Tool Posts.63 2.3.5 Lathe Tools63 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
9、Purpose of Controller73 Technical English Through Reading 33.1.3 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 CO
10、NTROL STATIONS.81 3.2.1 Push Buttons81 3.2.2 Selector Switches83 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 Relay89
11、 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 Timers93 3.4.7 Selecting A Timing Relay.93 3.5 TWO-WIRE CONTROLS94 3.6 THREE-WIRE AND SEPARATE CONTROLS.95 3
12、.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 Quantit
13、ies101 4.1.4 Standards, Dimensions, and Units of Measurement.102 4.1.5 Certainty/Uncertainty: Validity of Results103 4.2 MEASURING SYSTEM RESPONSE104 4.2.1 Introduction.104 Contents 44.2.2 Amplitude Response104 4.2.3 Frequency Response105 4.2.4 Phase Response.105 4.2.5 Predicting Performance for Com
14、plex 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 Elements111 4.3.3 Inductive Sensing Element.112 4.3.4 Electromagnetic Sensing Elements114 4.4 SIGNAL CONDITIONING ELEMENTS.116 4.4.1 Deflection Bridges116
15、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 System128 Technical English Through Reading 1PART 1 MACHINE DESIGN 1.1 INTRODUCTION TO MACHINE DESIGN 1.1.1 What
16、 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, s
17、hape 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 a
18、re 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 eng
19、ineer 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 dr
20、awings 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 o
21、f 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 thi
22、s 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 c
23、onsideration 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 2account during the early design phase. (4)
24、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 selecti
25、on 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
26、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. “Sma
27、rty 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 simplif
28、y 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 t
29、hese 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
30、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 m
31、achinist 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 3It cant be held in a shoe or chuck, In cant be drilled a
32、nd 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
33、. 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 b
34、e 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
35、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 s
36、ound 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 th
37、e 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 d
38、oes 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
39、 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
40、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
41、 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
42、 this Part 1 Machine Design 4way, 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 des
43、igns 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 whi
44、ch 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; (
45、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. Initia
46、lly, 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
47、? (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 mar
48、keted 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 t
49、olerance 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 5reality that needs to be kept in mind is that many of the products that will be in existence ten years fro
