mechanical design - peter r. n. childs

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Mechanical Engineering


Mechanical DesignThis book is dedicated to Hazel,Tabitha and AngusMechanical DesignSecond editionPeter R. N. ChildsBSc (Hons), DPhil, CEng, FIMechE, MIED, ILTM, Mem ASMEUniversity of Sussex, UKAMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORDPARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYOElsevier Butterworth-HeinemannLinacre House, Jordan Hill, Oxford OX2 8DP200 Wheeler Road, Burlington, MA 01803First published 1998 by ArnoldSecond edition 2004Copyright 2004, Elsevier Ltd. All rights reservedNo part of this publication may be reproduced in any material form(including photocopying or storing in any medium by electronic meansand whether or not transiently or incidentally to some other use of thispublication) without the written permission of the copyright holderexcept in accordance with the provisions of the Copyright, Designs andPatents Act 1988 or under the terms of a licence issued by the CopyrightLicensing Agency Ltd, 90 Tottenham Court Road, London, England W1T 4LP. Applications for the copyright holders written permission toreproduce any part of this publication should be addressed to the publisherPermissions may be sought directly from Elseviers Science and TechnologyRights Department in Oxford, UK; phone: (44) (0) 1865 843830;fax: (44) (0) 1865 853333; e-mail: mayalso complete your request on-line via the Elsevier homepage(, by selecting Customer Support and thenObtaining PermissionsBritish Library Cataloguing in Publication DataA catalogue record for this book is available from the British LibraryLibrary of Congress Cataloguing in Publication DataA catalogue record for this book is available from the Library of CongressISBN 0 7506 5771 5Typeset by Charon Tec Pvt. Ltd, ChennaiPrinted and bound by Great BritainFor information on all Elsevier Butterworth-Heinemannpublications visit our website at http://books.elsevier.comDisclaimer While the content of this book has been obtained from avariety of reliable sources and has been checked carefully, the author andthe publisher accept no responsibility for any loss, damage or under-achievement arising out of the use of the material presented.CONTENTSPreface ixAbout the author xiAcknowledgements xiii1 Design 11.1 Introduction 11.2 The design process 21.3 Total design 51.4 Product design specification 91.5 Conceptual design 121.6 The technology base 161.7 Conclusions 18References and sources of information 18Nomenclature 19Worksheet 192 Mechanical engineering 222.1 Introduction 222.2 Thermodynamics 252.3 Mechanics 272.4 Materials 272.5 Conclusions 29References and sources of information 29Nomenclature 293 Machine elements 303.1 Introduction 303.2 Tribology 313.3 Bearings 323.4 Gears, belts and chains 333.5 Seals 343.6 Clutches and brakes 353.7 Springs 363.8 Fasteners 363.9 Enclosures 373.10 Conclusions 38References 38Nomenclature 384 Bearings 394.1 Introduction 394.2 Sliding bearings 404.3 Rolling contact bearings 634.4 Conclusions 71References and sources of information 72Nomenclature 73Worksheet 745 Shafts 795.1 Introduction 795.2 Shafthub connection 825.3 Shaftshaft connection couplings 845.4 Critical speeds and shaft deflection 855.5 ASME design code for transmission shafting 945.6 Conclusions 101References and sources of information 102Nomenclature 102Worksheet 1036 Gears 1076.1 Introduction 1076.2 Construction of gear tooth profiles 1136.3 Gear trains 1166.4 Tooth systems 1226.5 Force analysis 1226.6 Simple gear selection procedure 1246.7 Conclusions 133References and sources of information 133Nomenclature 134Worksheet 1347 Detailed gear stressing 1377.1 Introduction 1377.2 Wear failure 1387.3 AGMA equations for bending and contact stress 1397.4 Gear selection procedure 1487.5 Conclusions 150References and sources of information 150Nomenclature 151Worksheet 1518 Belts and chain drives 1548.1 Introduction 1548.2 Belt drives 155Contentsvi8.3 Chain drives 1668.4 Conclusions 173References and sources of information 173Nomenclature 175Worksheet 1759 Seals 1779.1 Introduction 1779.2 Static seals 1789.3 Dynamics seals 1829.4 Conclusions 188References and sources of information 188Nomenclature 190Worksheet 19010 Clutches and brakes 19210.1 Introduction 19210.2 Clutches 19410.3 Brakes 20310.4 Conclusions 220References and sources of information 220Nomenclature 221Worksheet 22211 Springs 22511.1 Introduction 22511.2 Helical compression springs 22911.3 Helical extension springs 23911.4 Helical torsion springs 24111.5 Leaf springs 24211.6 Belleville spring washers 24411.7 Conclusions 247References and sources of information 247Nomenclature 249Worksheet 24912 Fastening and power screws 25112.1 Introduction to permanent and non-permanent fastening 25112.2 Threaded fasteners 25112.3 Power screws 25812.4 Rivets 26112.5 Adhesives 26712.6 Welding 27012.7 Snap fasteners 270Contentsvii12.8 Conclusions 272References and sources of information 272Nomenclature 27313 Frames, casings and enclosures 27513.1 Introduction 27513.2 Designing to resist bending 27613.3 Designing to resist torsion 27813.4 Designing to provide adequate ventilation 27913.5 Safety 28113.6 Conclusions 281References and sources of information 281Nomenclature 28114 Sensors and actuators 28314.1 Introduction 28314.2 Sensors 28414.3 Actuators 29114.4 Conclusions 297References and sources of information 297Nomenclature 29715 Engineering tolerancing 29915.1 Introduction 29915.2 Component tolerances 29915.3 Statistical tolerancing 30715.4 Conclusions 319References and sources of information 319Nomenclature 319Worksheet 32016 Design management and case study 32216.1 Introduction 32216.2 Management of design 32616.3 Costing 32916.4 A guide to design literature and sources of information 33516.5 Case study 33616.6 Conclusions 346References and sources of information 346Nomenclature 347Worksheet 348Index 351ContentsviiiPREFACEThe overall aims of this book are to introduce thesubject of total design and the design and selec-tion of various common mechanical engineeringcomponentsandmachineelements. Thesepro-videbuildingblocks withwhichthedesignerand engineer can practise their art.Theapproachadoptedfordefiningdesign followsthatdevelopedbytheSEED(SharingExperienceinEngineeringDesign)programmewheredesignisviewedasthe thetotalactivity necessary to provide a product or process to meet a market need. Within this framework the text isconcentratedondevelopingdetailedmechanicaldesignskillsintheareasofbearings, shafts, gears,seals, beltandchaindrives, clutchesandbrakes,springs and fasteners. Where standard componentsare available from manufacturers, the steps necessaryfor their specification and selection are developed.The framework used within the text has been toprovide descriptive and illustrative information tointroduceprinciplesandindividualcomponentsand to expose the reader to the detailed methodsand calculations necessary to specify and design orselectacomponent. Toprovidethereaderwithsufficientinformationtodevelopthenecessaryskills to repeat calculations and selection processes,detailedexamplesandworkedsolutionsaresup-plied throughout the text.Thisbookisprincipallyayear/level1and2undergraduate text. Prerequisite skills include someyear 1 undergraduate mathematics, fluid mechan-ics and heat transfer, principles of materials, staticsand dynamics. However, as the subjects are intro-duced in a descriptive and illustrative format andas full worked solutions are provided, it is possiblefor readers without this formal level of educationto benefit from this book. The text is specificallyaimed at automotive and mechanical engineeringdegreeprogrammesandwouldbeofvalueformodules in design, mechanical engineering design,design and manufacture, design studies, automo-tivepower-trainandtransmissionandtribology,as well as modules and project work incorporat-ing a design element requiring knowledge aboutany of the content described.The aims and objectives described are achievedbyshortintroductorychaptersontotaldesign,mechanicalengineeringandmachineelementsfollowedbyninechaptersonmachineelementscovering: bearings, shafts, gears, seals, chainandbelt drives, clutches and brakes, springs and fasten-ers. Chapters13and14introducecasingsandenclosures and sensors and actuators, key featuresof most forms of mechanical technology.The sub-ject of tolerancing from a component to a processlevel is introduced in Chapter 15.The last chapterservestopresentthesubjectofdesignmanage-ment and an integrated design using the detaileddesignaspectscoveredwithinthebook. Thedesign methods where appropriate are developedto national and international standards.The first edition of this text served to introduceavarietyofmachineelementsasbuildingblockswithwhichdesignofmechanicaldevicescanbeundertaken. Thematerialcoveredbythisfirst editionisstillvalidandtheapproachadoptedofintroducing and explaining the aspects of techno-logy by means of text, photographs, diagrams andstep-by-stepprocedureshasbeenwellreceived.Anumberofimportantmachineelementswereomittedinthefirsteditionsuchasfasteners,springs, sensorsandactuators. Theyareincludedhere. Reworkingofaspectsoftheoriginaltextincludestheintroductorychapterscoveringtotaldesign, thescopeofmechanicalengineeringandmachineelements. Anewchapterisincludedoncasingsandenclosuresandthefinalchapter hasbeenrewrittentoprovideanintegratedapproach. Theuseofmultipleworkedexamplesandcompletedsolutionshasbeenmaintainedasthese proved to be both useful and popular in thefirst edition.Peter R. N. ChildsPrefacexABOUT THE AUTHORPeter Childs is a Reader in Mechanical Engineer-ing at the University of Sussex and lectures in cre-ative styling, engineering design, fluid mechanicsand engine testing. His research interests includedesign, air-breathingenginesandinstrumenta-tion. He is actively involved in research and devel-opmentwithprojectsincludingworkforFord,Rolls-Royce, Siemens, Alstom, DaimlerChryslerand Volvo. HeisafellowoftheInstitutionofMechanical Engineers and in 1999 was