كتاب Tribology in Machine Design

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Tribology in Machine Design
T. A. STOLARSKI
MSc, PhD, DSc, DIG, CEng,MIMechE

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Contents
Preface . xi
1. Introduction to the Concept of Tribodesign 1
1.1 Specific Principles of Tribodesign 4
1.2 Tribological Problems in Machine Design 6
1.2.1 Plain Sliding Bearings 6
1.2.2 Rolling Contact Bearings 7
1.2.3 Piston, Piston Rings and Cylinder Liners 8
1.2.4 Cam and Cam Followers 9
1.2.5 Friction Drives 10
1.2.6 Involute Gears . 10
1.2.7 Hypoid Gears 11
1.2.8 Worm Gears . 12
2. Basic Principles of Tribology . 13
2.1 Origins of Sliding Friction . 13
2.2 Contact Between Bodies in Relative Motion . 14
2.3 Friction Due to Adhesion . 15
2.4 Friction Due to Ploughing 16
2.5 Friction Due to Deformation 17
2.6 Energy Dissipation During Friction . 18
2.7 Friction under Complex Motion Conditions . 18
2.8 Types of Wear and Their Mechanisms 19
2.8.1 Adhesive Wear . 19vi Contents
2.8.2 Abrasive Wear . 20
2.8.3 Wear Due to Surface Fatigue . 21
2.8.4 Wear Due to Chemical Reactions . 22
2.9 Sliding Contact Between Surface Asperities 23
2.10 The Probability of Surface Asperity Contact 26
2.11 Wear in Lubricated Contacts . 31
2.11.1 Rheological Lubrication Regime . 33
2.11.2 Functional Lubrication Regime 33
2.11.3 Fractional Film Defect . 34
2.11.4 Load Sharing in Lubricated Contacts 37
2.11.5 Adhesive Wear Equation . 39
2.11.6 Fatigue Wear Equation . 40
2.11.7 Numerical Example . 41
2.12 Relation Between Fracture Mechanics and Wear . 45
2.12.1 Estimation of Stress Intensity under Non-Uniform Applied Loads . 47
2.13 Film Lubrication . 48
2.13.1 Coefficient of Viscosity . 48
2.13.2 Fluid Film in Simple Shear . 49
2.13.3 Viscous Flow Between Very Close Parallel Surfaces . 50
2.13.4 Shear Stress Variations Within the Film . 51
2.13.5 Lubrication Theory by Osborne Reynolds 51
2.13.6 High-Speed Unloaded Journal 53
2.13.7 Equilibrium Conditions in a Loaded Bearing 53
2.13.8 Loaded High-Speed Journal 54
2.13.9 Equilibrium Equations for Loaded High-Speed Journal . 57
2.13.10 Reaction Torque Acting on the Bearing 59
2.13.11 The Virtual Coefficient of Friction 59
2.13.12 The Sommerfeld Diagram . 60
References . 63
3. Elements of Contact Mechanics . 64
3.1 Introduction . 64Contents vii
3.2 Concentrated and Distributed Forces on Plane Surfaces . 65
3.3 Contact Between Two Elastic Bodies in the Form of Spheres 67
3.4 Contact Between Cylinders and Between Bodies of General Shape 70
3.5 Failures of Contacting Surfaces . 71
3.6 Design Values and Procedures . 73
3.7 Thermal Effects in Surface Contacts . 74
3.7.1 Analysis of Line Contacts 75
3.7.2 Refinement for Unequal Bulk Temperatures . 79
3.7.3 Refinement for Thermal Bulging in the Conjunction Zone 80
3.7.4 The Effect of Surface Layers and Lubricant Films 80
3.7.5 Critical Temperature for Lubricated Contacts . 82
3.7.6 The Case of Circular Contact 83
3.7.7 Contacts for Which Size Is Determined by Load 85
3.7.8 Maximum Attainable Flash Temperature 86
3.8 Contact Between Rough Surfaces . 87
3.8.1 Characteristics of Random Rough Surfaces . 87
3.8.2 Contact of Nominally Flat Rough Surfaces . 90
3.9 Representation of Machine Element Contacts . 94
References 96
4. Friction, Lubrication and Wear in Lower Kinematic Pairs 97
4.1 Introduction 97
4.2 The Concept of Friction Angle . 98
4.2.1 Friction in Slideways . 98
4.2.2 Friction Stability . 100
4.3 Friction in Screws with a Square Thread . 103
4.3.1 Application of a Threaded Screw in a Jack 105
4.4 Friction in Screws with a Triangular Thread . 109
4.5 Plate Clutch - Mechanism of Operation . 111
4.6 Cone Clutch - Mechanism of Operation 114
4.6.1 Driving Torque . 115
4.7 Rim Clutch - Mechanism of Operation 116viii Contents
4.7.1 Equilibrium Conditions 117
4.7.2 Auxiliary Mechanisms 119
4.7.3 Power Transmission Rating 120
4.8 Centrifugal Clutch - Mechanism of Operation . 120
4.9 Boundary Lubricated Sliding Bearings . 121
4.9.1 Axially Loaded Bearings 123
4.9.2 Pivot and Collar Bearings 124
4.10 Drives Utilizing Friction Force 127
4.10.1 Belt Drive . 128
4.10.2 Mechanism of Action . 129
4.10.3 Power Transmission Rating 132
4.10.4 Relationship Between Belt Tension and Modulus 133
4.10.5 V-Belt and Rope Drives 134
4.11 Frictional Aspects of Brake Design . 136
4.11.1 The Band Brake 136
4.11.2 The Curved Brake Block . 138
4.11.3 The Band and Block Brake . 144
4.12 The Role of Friction in the Propulsion and the Braking of Vehicles 145
4.13 Tractive Resistance . 150
4.14 Pneumatic Tyres . 151
4.14.1 Creep of an Automobile Tyre 152
4.14.2 Transverse Tangential Forces 152
4.14.3 Functions of the Tyre in Vehicle Application . 154
4.14.4 Design Features of the Tyre Surface . 154
4.14.5 The Mechanism of Rolling and Sliding 155
4.14.6 Tyre Performance on a Wet Road Surface . 157
4.14.7 The Development of Tyres with Improved Performance 159
4.15 Tribodesign Aspects of Mechanical Seals 160
4.15.1 Operation Fundamentals 161
4.15.2 Utilization of Surface Tension . 162
4.15.3 Utilization of Viscosity . 162Contents ix
4.15.4 Utilization of Hydrodynamic Action 163
4.15.5 Labyrinth Seals 164
4.15.6 Wear in Mechanical Seals 164
4.15.7 Parameters Affecting Wear . 168
4.15.8 Analytical Models of Wear . 169
4.15.9 Parameters Defining Performance Limits 170
4.15.10 Material Aspects of Seal Design . 170
4.15.11 Lubrication of Seals 172
References 173
5. Sliding-Element Bearings 174
5.1 Derivation of the Reynolds Equation 174
5.2 Hydrostatic Bearings 178
5.3 Squeeze-Film Lubrication Bearings . 181
5.4 Thrust Bearings . 183
5.4.1 Flat Pivot 184
5.4.2 The Effect of the Pressure Gradient in the Direction of Motion . 186
5.4.3 Equilibrium Conditions . 188
5.4.4 The Coefficient of Friction and Critical Slope . 188
5.5 Journal Bearings 189
5.5.1 Geometrical Configuration and Pressure Generation 189
5.5.2 Mechanism of Load Transmission . 192
5.5.3 Thermoflow Considerations 194
5.5.4 Design for Load-Bearing Capacity . 196
5.5.5 Unconventional Cases of Loading . 197
5.5.6 Numerical Example 199
5.5.7 Short Bearing Theory - CAD Approach . 201
5.6 Journal Bearings for Specialized Applications . 204
5.6.1 Journal Bearings with Fixed Non-Preloaded Pads . 205
5.6.2 Journal Bearings with Fixed Preloaded Pads . 205
5.6.3 Journal Bearings with Special Geometric Features 207
5.6.4 Journal Bearings with Movable Pads 207x Contents
5.7 Gas Bearings . 210
5.8 Dynamically Loaded Journal Bearings . 212
5.8.1 Connecting-Rod Big-End Bearing 213
5.8.2 Loads Acting on Main Crankshaft Bearing . 213
5.8.3 Minimum Oil Film Thickness . 214
5.9 Modern Developments in Journal Bearing Design 217
5.9.1 Bearing Fit . 218
5.9.2 Grooving 219
5.9.3 Clearance 219
5.9.4 Bearing Materials . 220
5.10 Selection and Design of Thrust Bearings 221
5.10.1 Tilting-Pad Bearing Characteristics 223
5.10.2 Design Features of Hydrostatic Thrust Bearings 225
5.11 Self-Lubricating Bearings 226
5.11.1 Classification of Self-Lubricating Bearings . 226
5.11.2 Design Considerations 228
References 230
6. Friction, Lubrication and Wear in Higher Kinematic Pairs 232
6.1 Introduction 232
6.2 Loads Acting on Contact Area . 233
6.3 Traction in the Contact Zone . 233
6.4 Hysteresis Losses 234
6.5 Rolling Friction . 235
6.6 Lubrication of Cylinders 238
6.7 Analysis of Line Contact Lubrication 242
6.8 Heating at the Inlet to the Contact 244
6.9 Analysis of Point Contact Lubrication 245
6.10 Cam-Follower System 246
References 247
7. Rolling-Contact Bearings . 248
7.1 Introduction 248Contents xi
7.2 Analysis of Friction in Rolling-Contact Bearings 248
7.2.1 Friction Torque Due to Differential Sliding 249
7.2.2 Friction Torque Due to Gyroscopic Spin . 250
7.2.3 Friction Torque Due to Elastic Hysteresis 251
7.2.4 Friction Torque Due to Geometric Errors 252
7.2.5 Friction Torque Due to the Effect of the Raceway . 252
7.2.6 Friction Torque Due to Shearing of the Lubricant 252
7.2.7 Friction Torque Caused by the Working Medium . 253
7.2.8 Friction Torque Caused by Temperature Increase 254
7.3 Deformations in Rolling-Contact Bearings 254
7.4 Kinematics of Rolling-Contact Bearings . 256
7.4.1 Normal Speeds 256
7.4.2 High Speeds 258
7.5 Lubrication of Rolling-Contact Bearings 259
7.5.1 Function of a Lubricant 259
7.5.2 Solid Film Lubrication 260
7.5.3 Grease Lubrication 261
7.5.4 Jet Lubrication . 262
7.5.5 Lubrication Utilizing under-Race Passages 263
7.5.6 Mist Lubrication . 264
7.5.7 Surface Failure Modes Related to Lubrication 265
7.5.8 Lubrication Effects on Fatigue Life . 265
7.5.9 Lubricant Contamination and Filtration . 266
7.5.10 Elastohydrodynamic Lubrication in Design Practice 266
7.6 Acoustic Emission in Rolling-Contact Bearings . 268
7.6.1 Inherent Source of Noise 268
7.6.2 Distributed Defects on Rolling Surfaces 269
7.6.3 Surface Geometry and Roughness 269
7.6.4 External Influences on Noise Generation . 270
7.6.5 Noise Reduction and Vibration Control Methods . 271
References . 272xii Contents
8. Lubrication and Efficiency of Involute Gears . 273
8.1 Introduction 273
8.2 Generalities of Gear Tribodesign . 273
8.3 Lubrication Regimes 275
8.4 Gear Failure Due to Scuffing . 278
8.4.1 Critical Temperature Factor 280
8.4.2 Minimum Film Thickness Factor . 281
8.5 Gear Pitting 282
8.5.1 Surface Originated Pitting . 283
8.5.2 Evaluation of Surface Pitting Risk . 283
8.5.3 Subsurface Originated Pitting . 284
8.5.4 Evaluation of Subsurface Pitting Risk . 284
8.6 Assessment of Gear Wear Risk 285
8.7 Design Aspect of Gear Lubrication 286
8.8 Efficiency of Gears 288
8.8.1 Analysis of Friction Losses 289
8.8.2 Summary of Efficiency Formulae 293
References 294
Index 295

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