Mechanical Engineering-Tribology In Machine Design Episode 1 pdf

www.GetPedia.com * The Ebook starts from the next page : Enjoy ! Tribology in Machine Design This page intentionally leJ blank Tribology in Machine Design T. A. STOLARSKI MSc, PhD, DSc, DIC, CEng, MIMechE EINEMANN 1 OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01 801-204 1 A division of Reed Educational and Professional Publishing Ltd -@ A member of the Reed Elsevier plc group First published 1990 Reprinted 2000 0 T. A. Stolarski 1990 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England WIP OLP. Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN 0 7506 3623 8 Printed and bound in Great Britain Contents Preface Introduction to the concept of tribodesign Specific principles of tribodesign Tribological problems in machine design 1.2.1. Plain sliding bearings 1.2.2. Rolling contact bearings 1.2.3. Piston, piston rings and cylinder liners 1.2.4. Cam and cam followers 1.2.5. Friction drives 1.2.6. Involute gears 1.2.7. Hypoid gears 1.2.8. Worm gears Basic principles of tribology Origins of sliding friction Contact between bodies in relative motion Friction due to adhesion Friction due to ploughing Friction due to deformation Energy dissipation during friction Friction under complex motion conditions Types of wear and their mechanisms 2.8.1. Adhesive wear 2.8.2. Abrasive wear 2.8.3. Wear due to surface fatigue 2.8.4. Wear due to chemical reactions Sliding contact between surface asperities The probability of surface asperity contact Wear in lubricated contacts 2.11.1. Rheological lubrication regime 2.1 1.2. Functional lubrication regime 2.11.3. Fractional film defect 2.1 1.4. Load sharing in lubricated contacts 2.1 1.5. Adhesive wear equation 2.1 1.6. Fatigue wear equation 2.1 1.7. Numerical example vi Contents Relation between fracture mechanics and wear 2.12.1. Estimation of stress intensity under non-uniform applied loads Film lubrication 2.13.1 Coefficient of viscosity 2.13.2. Fluid film in simple shear 2.13.3. Viscous flow between very close parallel surfaces 2.13.4. Shear stress variations within the film 2.13.5. Lubrication theory by Osborne Reynolds 2.13.6. High-speed unloaded journal 2.13.7. Equilibrium conditions in a loaded bearing 2.13.8. Loaded high-speed journal 2.13.9. Equilibrium equations for loaded high-speed journal 2.13.10. Reaction torque acting on the bearing 2.13.1 1. The virtual coefficient of friction 2.13.12. The Sommerfeld diagram References Elements of contact mechanics Introduction Concentrated and distributed forces on plane surfaces Contact between two elastic bodies in the form of spheres Contact between cylinders and between bodies of general shape Failures of contacting surfaces Design values and procedures Thermal effects in surface contacts 3.7.1 Analysis of line contacts 3.7.2. Refinement for unequal bulk temperatures 3.7.3. Refinement for thermal bulging in the conjunction zone 3.7.4. The effect of surface layers and lubricant films 3.7.5. Critical temperature for lubricated contacts 3.7.6. The case of circular contact 3.7.7. Contacts for which size is determined by load 3.7.8. Maximum attainable flash temperature Contact between rough surfaces 3.8.1. Characteristics of random rough surfaces 3.8.2. Contact of nominally flat rough surfaces Representation of machine element contacts References Friction, lubrication and wear in lower kinematic pairs Introduction The concept of friction angle 4.2.1. Friction in slideways 4.2.2. Friction stability Contents vii Friction in screws with a square thread 4.3.1. Application of a threaded screw in a jack Friction in screws with a triangular thread Plate clutch - mechanism of operation Cone clutch - mechanism of operation 4.6.1. Driving torque Rim clutch - mechanism of operation 4.7.1. Equilibrium conditions 4.7.2. Auxiliary mechanisms 4.7.3. Power transmission rating Centrifugal clutch - mechanism of operation Boundary lubricated sliding bearings 4.9.1. Axially loaded bearings 4.9.2. Pivot and collar bearings Drives utilizing friction force 4.10.1. Belt drive 4.10.2. Mechanism of action 4.10.3. Power transmission rating 4.10.4. Relationship between belt tension and modulus 4.10.5. V-belt and rope drives Frictional aspects of brake design 4.11.1. The band brake 4.11.2. The curved brake block 4.11.3. The band and block brake The role of friction in the propu!sion and the braking of vehicles Tractive resistance Pneumatic tyres 4.14.1. Creepofanautomobiletyre 4.14.2. Transverse tangential forces 4.14.3. Functions of the tyre in vehicle application 4.14.4. Design features of the tyre surface 4.14.5. The mechanism of rolling and sliding 4.14.6. Tyre performance on a wet road surface 4.14.7. The development of tyres with improved performance Tribodesign aspects of mechanical seals 4.15.1. Operation fundamentals 4.15.2. Utilization of surface tension 4.15.3. Utilization of viscosity 4.15.4. Utilization of hydrodynamic action 4.15.5. Labyrinth seals 4.15.6. Wear in mechanical seals 4.15.7. Parameters affecting wear 4.15.8. Analytical models of wear 4.15.9. Parameters defining performance limits 4.15.10. Material aspects of seal design viii Contents 4.15.1 1. Lubrication of seals References Sliding-element bearings Derivation of the Reynolds equation Hydrostatic bearings Squeeze-film lubrication bearings Thrust bearings 5.4.1. Flat pivot 5.4.2. The effect of the pressure gradient in the direction of motion 5.4.3. Equilibrium conditions 5.4.4. The coefficient of friction and critical slope Journal bearings 5.5.1. Geometrical configuration and pressure generation 5.5.2. Mechanism of load transmission 5.5.3. Thermoflow considerations 5.5.4. Design for load-bearing capacity 5.5.5. Unconventional cases of loading 5.5.6. Numerical example 5.5.7. Short bearing theory - CAD approach Journal bearings for specialized applications 5.6.1. Journal bearings with fixed non-preloaded pads 5.6.2. Journal bearings with fixed preloaded pads 5.6.3. Journal bearings with special geometric features 5.6.4. Journal bearings with movable pads Gas bearings Dynamically loaded journal bearings 5.8.1. Connecting-rod big-end bearing 5.8.2. Loads acting on main crankshaft bearing 5.8.3. Minimum oil film thickness Modern developments in journal bearing design 5.9.1. Bearing fit 5.9.2. Grooving 5.9.3. Clearance 5.9.4. Bearing materials Selection and design of thrust bearings 5.10.1. Tilting-pad bearing characteristics 5.10.2. Design features of hydrostatic thrust bearings Self-lubricating bearings 5.1 1.1. Classification of self-lubricating bearings 5.11.2. Design considerations References Friction, lubrication and wear in higher kinematic pairs Introduction Loads acting on contact area [...]... even indispensible, branch of machine design and, therefore, of mechanical engineering in general In any attempt to integrate tribology and tribodesign into mechanical engineering and machine design, it is advantageous to start by visualizing 2 Tribology in machine design the engineering task of mechanical engneers in general, and of machine designers in particular The task of a mechanical engineer... bearing 1. 1 Specific principles of tribodesign Two principles, specific to tribodesign, that is, the principle of preventing contact between rubbing surfaces, and the equally important principle of regarding lubricant films as machine elements and, accordingly, lubricants as engineering materials, can be distinguished In its most general form the principle of contact prevention is also taken to embody inhibiting,... failure The loading conditions ofcams are never steady and this fact should also be considered at the design stage 10 Tribology in machine design 1. 2.5 Friction drives Friction drives, which are being used increasingly in infinitely variable gears, are the converse of hypoid gears in so far as it is the intention that two smooth machine elements should roll together without sliding, whilst being able to... above that certain general principles, typical for machine design, are also applicable in tribodesign However, there are certain principles that are specific to tribodesign, but still hardly known amongst machine designers It is hoped that this book will encourage designers to take advantage of the results, concepts and knowledge offered by tribology 1. 2 Tribological problems in machine design The view... tribology 1. 2 Tribological problems in machine design The view that tribology, in general, and tribodesign, in particular, are intrinsic parts of machine design can be further reinforced by a brief review of tribological problems encountered in the most common machine elements 1. 2 .1 Plain sliding bearings When a journal bearing operates in the hydrodynamic regime of lubrication, a hydrodynamic film develops... application is tribodesign, which is regarded here as a branch of machine design concerning all machine elements where friction, lubrication and wear play a significant part In its most advanced form, tribodesign can be integrated into machine design to the extent of leading to novel and more efficient layouts for various kinds of machinery For example, the magnetic gap between the rotor and stator in an electric... results and ideas in terms of principles and concepts that are directly accessible and appealing to the design engineer It is hoped that the procedures and techniques of analysis explained in this book will be found helpful in applying the principles of tribology to the design of the machine elements commonly found in mechanical devices and systems It is designed to supplement the Engineering Science Data... in the contact zone Hysteresis losses Rolling friction Lubrication of cylinders Analysis of line contact lubrication Heating at the inlet to the contact Analysis of point contact lubrication Cam-follower system References Rollingcontact bearings Introduction Analysis of friction in rolling-contact bearings 7.2 .1 Friction torque due to differential sliding 7.2.2 Friction torque due to gyroscopic spin... helped me in many different ways to continue my research in this subject Finally, special thanks are due to my wife Alicja for her patience and understanding during the preparation of the manuscript Brunel University T.A.S I Introduction to the concept of tribodesign The behaviour and influence of forces within materials is a recognized basic subject in engineering design This subject, and indeed the... goes on High alkaline oil is more apt to cause abnormal wear and this is attributed to a lack of spreadability at high temperatures Machined finishes are regarded as having more resistance to scuffing than ground finishes because of the oil-retaining characteristics of the roughened surfaces The use of taper face rings is effective in preventing scuffing by relieving the edge load in the earliest stages . engineering and machine design, it is advantageous to start by visualizing 2 Tribology in machine design the engineering task of mechanical engneers in general, and of machine designers in. Plain sliding bearings 1. 2.2. Rolling contact bearings 1. 2.3. Piston, piston rings and cylinder liners 1. 2.4. Cam and cam followers 1. 2.5. Friction drives 1. 2.6. Involute gears 1. 2.7. Hypoid. tribodesign is an obvious, and even indispensible, branch of machine design and, therefore, of mechanical engineering in general. In any attempt to integrate tribology and tribodesign into mechanical