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Grease Lubrication in Rolling Bearings

ISBN: 978-1-118-35391-2
472 pages
February 2013
Grease Lubrication in Rolling Bearings (1118353919) cover image

The definitive book on the science of grease lubrication for roller and needle bearings in industrial and vehicle engineering.

Grease Lubrication in Rolling Bearings provides an overview of the existing knowledge on the various aspects of grease lubrication (including lubrication systems) and the state of the art models that exist today. The book reviews the physical and chemical aspects of grease lubrication, primarily directed towards lubrication of rolling bearings.

The first part of the book covers grease composition, properties and rheology, including thermal and dynamics properties. Later chapters cover the dynamics of greased bearings, including grease life, bearing life, reliability and testing. The final chapter covers lubrications systems – the systems that deliver grease to the components requiring lubrication.

Grease Lubrication in Rolling Bearings:

  • Describes the underlying physical and chemical properties of grease.
  • Discusses the effect of load, speed, temperature, bearing geometry, bearing materials and grease type on bearing wear.
  • Covers both bearing and grease performance, including thermo-mechanical ageing and testing methodologies.

It is intended for researchers and engineers in the petro-chemical and bearing industry, industries related to this (e.g. wind turbine industry, automotive industry) and for application engineers. It will also be of interest for teaching in post-graduate courses.

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Preface xvii

List of Abbreviations xix

1 Introduction 1

1.1 Why Lubricate Rolling Bearings? 1

1.2 History of Grease Lubrication 2

1.3 Grease Versus Oil Lubrication 3

2 Lubrication Mechanisms 5

2.1 Introduction 5

2.2 Definition of Grease 6

2.3 Operating Conditions 6

2.4 The Phases in Grease Lubrication 7

2.5 Film Thickness During the Bleeding Phase 8

2.6 Feed and Loss Mechanisms During the Bleeding Phase 10

2.7 Film Thickness and Starvation (Side Flow) 11

2.8 Track Replenishment 12

2.9 Grease Flow 13

2.10 Wall-Slip 15

2.11 Oxidation 16

2.12 EP Additives 16

2.13 Dynamic Behaviour 17

2.14 Grease Life 17

3 Grease Composition and Properties 23

3.1 Base Oil 24

3.2 Base Oil Viscosity and Density 41

3.3 Thickener 49

3.4 Additives 61

3.5 Solid Fillers/Dry Lubricants 66

3.6 Compatibility 67

3.7 Polymer Grease 67

4 Grease Life in Rolling Bearings 71

4.1 Introduction 71

4.2 Relubrication Intervals and Grease Life 71

4.3 The Traffic Light Concept 72

4.4 Grease Life as a Function of Temperature in the Green Zone 75

4.5 SKF Relubrication and Grease Life 76

4.6 Comparison Grease Life/Relubrication Models 78

4.7 Very Low and High Speeds 82

4.8 Large Rolling Bearings 85

4.9 Effect of Load 86

4.10 Effect of Outer-Ring Rotation 90

4.11 Cage Material 90

4.12 Bearing Type 91

4.13 Temperature and Bearing Material 92

4.14 Grease Fill 94

4.15 Vertical Shaft 95

4.16 Vibrations and Shock Loads 96

4.17 Grease Shelf Life/Storage Life 97

5 Lubricating Grease Rheology 99

5.1 Visco-Elastic Behaviour 99

5.2 Viscometers 102

5.3 Oscillatory Shear 108

5.4 Shear Thinning and Yield 112

5.5 Yield Stress 118

5.6 Wall-Slip Effects 122

5.7 Translation Between Oscillatory Shear and Linear Shear Measurements 125

5.8 Normal stresses 126

5.9 Time Dependent Viscosity and Thixotropy 128

5.10 Tackiness 133

6 Grease and Base Oil Flow 137

6.1 Grease Flow in Pipes 137

6.2 Grease Flow in Rolling Bearings 149

7 Grease Bleeding 157

7.1 Introduction 157

7.2 Ball Versus Roller Bearings 158

7.3 Grease Bleeding Measurement Techniques 158

7.4 Bleeding from the Covers and Under the Cage 159

7.5 A Grease Bleeding Model for Pressurized Grease by Centrifugal Forces 161

8 Grease Aging 171

8.1 Mechanical Aging 172

8.2 Grease Oxidation 179

8.3 The Chemistry of Base Oil Film Oxidation 181

8.4 Oxidation of the Thickener 183

8.5 A Simple Model for Base Oil Degradation 184

8.6 Polymerization 186

8.7 Evaporation 186

8.8 Simple Models for the Life of Base Oil 186

9 Film Thickness Theory for Single Contacts 191

9.1 Elasto-Hydrodynamic Lubrication 192

9.2 Contact Geometry and Deformation 198

9.3 EHL Film Thickness, Oil 202

9.4 EHD Film Thickness, Grease 205

9.5 Starvation 212

9.6 Spin 225

10 Film Thickness in Grease Lubricated Rolling Bearings 227

10.1 Thin Layer Flow on Bearing Surfaces 228

10.2 Starved EHL for Rolling Bearings 234

10.3 Cage Clearance and Film Thickness 239

10.4 Full Bearing Film Thickness 241

11 Grease dynamics 245

11.1 Introduction 245

11.2 Grease Reservoir Formation 245

11.3 Temperature Behaviour 246

11.4 Temperature and Film Breakdown 249

11.5 Chaotic Behaviour 249

11.6 Quantitative Analysis of Grease Tests 253

11.7 Discussion 254

12 Reliability 257

12.1 Failure Distribution 258

12.2 Mean Life and Time Between Failures 261

12.3 Percentile Life 264

12.4 Point and Interval Estimates 265

12.5 Sudden Death Testing 275

12.6 System Life Prediction 281

13 Grease Lubrication and Bearing Life 283

13.1 Bearing Failure Modes 283

13.2 Rated Fatigue Life of Grease Lubricated Rolling Bearings 285

13.3 Background of the Fatigue Life Ratings of Grease Lubricated Bearings 289

13.4 Lubricant Chemistry and Bearing Life 296

13.5 Water in Grease 304

13.6 Surface Finish Aspects Related to Grease Lubrication 306

14 Grease Lubrication Mechanisms in Bearing Seals 309

14.1 Introduction 309

14.2 Lubrication Mechanisms for Radial Lip Seals 309

14.3 Sealing Action of Grease 312

14.4 Softening and Leakage 319

14.5 Compatibility 320

14.6 A Film Thickness Model for Bearing Seals 320

14.7 Importance of Sealing Grease Inside the Bearing 324

15 Condition Monitoring and Maintenance 327

15.1 Condition Monitoring 327

15.2 Acoustic Emission 328

15.3 Lubcheck 330

15.4 Consistency Measurement 331

15.5 Oil Bleeding Properties 332

15.6 Oil Content 332

15.7 Particle Contamination 332

15.8 Spectroscopy 333

15.9 Linear Voltammetry 334

15.10 Total Acid Number 335

15.11 DCS – Differential Scanning Calorimetry 335

15.12 Oxidation Bomb 336

15.13 Water 336

16 Grease Qualification Testing 339

16.1 Introduction 339

16.2 Standard Test Methods 339

16.3 Some Qualification Criteria for Grease Selection 374

16.4 Pumpability 375

17 Lubrication Systems 377

17.1 Single Point Lubrication Methods 379

17.2 Centralized Grease Lubrication Systems 380

17.3 Pumps 382

17.4 Valves 384

17.5 Distributors 386

17.6 Single-Line Centralized Lubrication Systems 386

17.7 Dual-Line Lubrication Systems 393

17.8 Progressive Lubrication Systems 394

17.9 Multi-Line Lubrication System 397

17.10 Cyclic Grease Flow 397

17.11 Requirements of the Grease 398

17.12 Grease Pumpability Tests 402

A Characteristics of Paraffinic Hydrocarbons 413

References 415

Index

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Piet M. Lugt
SKF, The Netherlands
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