機(jī)械專業(yè)英語

1、Part 2: Machine Elements and Mechanisms2.1 Introduction Machine elementsMachine elements refer to an elementary component of a machine. They include: structural components such as bearings, axles, keys, fasteners, seals, and lubricants.Mechanisms such as gear trains, belt or chain drives, linkages,

2、cam and follower systems, including brakes and clutchesControl components such as buttons, switches, indicators, sensors, actuators and computer controllers. Machine elements are basic mechanical parts and features used as the building blocks of most machines.Figure 2.1 Machine elements are the buil

3、ding blocks of most machines2.2 Fastenings2.2.1 Introduction A fastener is a device used to connect or join two or more components. Traditional forms of fastening include nuts, bolts, screws and rivets. They are frequently used and most of them have been standardized with their shapes and sizes. The

4、 importance of fasteners in a machine2.2.2 Thread TerminologyFigure 2.2 Screw threads(b) Left-hand thread.(a) Right-hand thread. Figure 2.3 Specialist terminology used for describing threads.2.2.3 Thread Forms3. Square thread1. Metric threads2. Acme threads4. Buttress threadsBasic pipe thread with 5

5、5 angle.5. Pipe thread2.2.4 Power ScrewFigure. 2.9 A worm-gear screw jack . A power screw, also known as a leadscrew (or lead screw) or translation screw, is a device used in machinery to change angular motion into linear motion, and, usually, to transmit power.The advantages of a leadscrew are： Lar

6、ge load carrying capability Compact Simple to design Easy to manufacture; no specialized machinery is required Large mechanical advantage Precise and accurate linear motion Smooth, quiet, and low maintenance Minimal number of partsMost are self-locking The disadvantages are that most are not very ef

7、ficient. Leadscrew efficiency is typically between 25 and 70%A higher performing but more expensive alternative is the ball screw.Figure 2.10 Ball screws.2.2.4 Bolts, Studs, Nuts and Plain WasherFigure 2.11 Bolts and screws. 1. Bolts2. StudsFigure 2.12 Studs.Figure 2.13 Standard nuts. 3. Nuts4. Wash

8、ersFigure 2.14 Washers.2.2.5 Alternative Screw Heads and End PointsFigure 2.15 Alternative screw heads.90。 SlottedcountersunkSlottedround headSlottedcheese headSquareheadSlottedfillister headSlottedinstrumentheadSlotted headHexagonsocketheadPhillips headFigure 2.16 Alternative screw points.FlatDogCo

9、nical RoundCup2.2.6 Selection of Screwed FastenersSelection criteria for the screw materials ： temperature； required strength； resistance to corrosion； joint material and cost ； assembly considerations.2.2.7 Systems for Specifying the Dimensions of Screws1. ISO metric screw thread2. British Standard

10、 Whitworth3. British Association screw thread4. Unified Thread Standard2.2.8 Applications of Screwed FastenersFigure 2.17 Applications of screwed fasteners.Name all parts and fasteners in the drawing 2.3 Keys and Pins (a) Parallel keys 2.3.1 Keys (b) Semicircular keys Figure 2.19 Parallel key joints

11、. （1-Shaft. 2-Hub, 3-Key, 4-Nut, 5-Washer） (c) Tapered keys Figure 2.18 Keys. Figure 2.20 Semicircular keys.Figure 2.21 Tapered keys. 2.3.2 Pins (a) Taper pins(b) Parallel pins(C) split pinsFigure 2.22 Pin joints. 2.4 Riveted Joints Figure 2.23 Conventional rivet before and after setting 2.5 Welded

12、Joints Welding can be described as the process of joining material together by raising the temperature of the surfaces to be joined so that they become plastic or molten. Types of Welding : ungsten inert gas welding (TIG)submerged arc welding (SAW)metal inert gas welding (MIG)manual metal arc weldin

13、g (MMA)resistance weldinggas welding 2.6 Springl Clampl Store elastic energy l Reduce shock. Functions of springs:(a) Helical compression springs. (b) Helical extension springs. (c) Torsion springs.(d) Spiral torsion springs.(f) Leaf springs.2.7 Bearings2.7.1 Bearing classificationJournal bearingDee

14、p groove ball bearingsTypes:Figure2.26 Bearing classification.Factors for consideration when selecting bearings：(1)Load(2) speed(3) location(4) size(5) cost(6)starting torque(7) noise(8)lubrication supply 2.7.2 Bearing type selection2.27 Bearing type selection by load capacity and speed.Table 2.9 Co

15、mparison of bearing performance for continuous rotation Table2.10 Merits of different rolling contact bearings 2.8 Clutches and Brakes Clutches and brakes provide frictional, magnetic, hydraulic or mechanical connection between two machine elements, usually shafts. In reality, the same device can fu

16、nction as a brake or clutch by fixing its output element to a shaft that can rotate or to ground, respectively.The similarities between clutches and brakes?Figure 2.28 Idealized friction disc clutch or brake. DrivingdiscActuatorPusher discstogetherDrivendiscFrictionmaterialOutputInputFigure 2.29 Typ

17、ical applications of clutches and brakes.Method ofengagementMagneticPneumaticand hydraulicMechanicalElectricalOverrunningPositivecontactFrictionMagneticFluidcouplingSquare jawSpiral jawToothedDiscDrumConeRollerSpragSpring woundMagnetic particleHysteresisEddy currentDry fluidHydraulicClutch classific

18、ation:2.9 Shafts and CouplingsCommonly used shafts： (b) Stepped shafts. （a）Plain shafts. (c) Crankshafts.Shaft design considerations include:1. size and spacing of components (as on a general assembly drawing), tolerances;2. material selection, material treatments;3. deflection and rigidity: bending

19、 deflection; torsional deflection; slope at bearings; shear deflection;4. stress and strength：static strength；fatigue；reliability;5. frequency response;6. manufacturing constraints.Figure 2.32 A typical shaft arrangementName parts in the drawing 2.9.2 ShaftHub ConnectionFigure 2.30 Alternative metho

20、ds of shaft-hub connection.（a）Pin jointsPinShaftHub（b）Key joints（c)Set screw jointsFunctions of couplings 2.9.3 ShaftShaft Connection Couplingstransmit power from one shaft to another.Two general types of coupling: Rigid couplingsUniversal jointsFlexible couplings2.10.1 Introduction 2.10 Belts and C

21、hains（a）Belt driveBelt and chain drives consist of flexible elements running on either pulleys or sprockets.(b) Chain driveThe advantages and disadvantages of a belt over gears and chains:1. Consequence of Failure.2.Versatility in Shaft Connection.3.Effect on Shaft Bearing Life.4.Speed Ratio.5.Cost.

22、 6.Noise and Vibration. 7.Speed and Power.8.Maintenance. Types: 2.10.2 Belt Drives（a）Flat belt drives. (b) Round belt drives.(c) V belt drives(d) Synchronous belt drives.Types:Figure 2.39 Various belt cross-sections.Figure 2.40 Pulley configuration.A chain is a power transmission device consisting o

23、f a series of pin-connected links 2.10.3 Chain Drives(a)Simple chainFigure 2.41 Roller chain. (b) Duplex chain （c）Triplex chainFigure 2.42 Simple chain drive. Chain types:Figure 2.43 Chain types.ChainsSilentConveyorLeafRollerBritish standardrangeStandardseriesDoublepitchBushchainANSIrangeStandardseriesHeavyseriesFigure 2.44 Roller chain components.Figure 2.45 Conveyor chainFigure 2.47 Silent chain Figure2.46 Leaf chainFigure 2.48 Sperber gear box, silent chains 2.11.1 Introduction 2.11 GearsFigure 2.49 Spur gear schematic showing principle terminology. Gears are