Lubricants Introduction to Properties and Performance

Those working with tribology often have a background in mechanical engineering, while people working with lubricant development have a chemistry/chemical engineering background. This means they have a tradition of approaching problems in different ways. Today?s product development puts higher demands on timing and quality, requiring collaboration between people with different backgrounds. However, they can lack understanding of each other?s challenges as well as a common language, and so this book aims to bridge the gap between these two areas.

Lubricants: Introduction to Properties and Performance provides an easy to understand overview of tribology and lubricant chemistry. The first part of the book is theoretical and provides an introduction to tribological contact, friction, wear and lubrication, as well as the basic concepts regarding properties and the most commonly made analyses on lubricants. Base fluids and their properties and common additives used in lubricants are also covered. The second part of the book is hands-on and introduces the reader to the actual formulations and the evaluation of their performance. Different applications and their corresponding lubricant formulations are considered and tribological test methods are discussed. Finally used oil characterisation and surface characterisation are covered which give the reader an introduction to different methods of characterising used oils and surfaces, respectively.

Key features:

• Combines chemistry and tribology of lubricants into one unified approach
• Covers the fundamental theory, describing lubricant properties as well as base fluids and additives
• Contains practical information on the formulations of lubricants and evaluates their performance
• Considers applications of lubricants in hydraulics, gears and combustion engines

Lubricants: Introduction to Properties and Performance is a comprehensive reference for industry practitioners (tribologists, lubricant technicians, and lubricant chemists, etc) and is also an excellent source of information for graduate and undergraduate students.

Preface xi

About the Authors xiii

List of Symbols xv

List of Tables xix

Part One Lubricant Properties

1 Introduction to Tribology 3

1.1 Tribological Contacts 5

1.1.1 Macroscale Contacts 6

1.1.2 Microscale Contacts 8

1.2 Friction 8

1.2.1 The Coefficient of Friction 8

1.2.2 Lubrication Regimes 10

1.3 Wear 12

1.3.1 Wear Rate 13

1.4 Lubrication of the Tribological System 14

1.4.1 The Purposes of Lubricants 14

1.4.2 Reducing Friction and Protecting against Wear 15

1.4.3 Semi-Solid Lubricants 16

1.4.4 Solid Lubricants and Dry Lubricants 16

References 17

2 Lubricant Properties 19

2.1 Performance Properties 20

2.1.1 Viscosity 20

2.1.2 Low and High Temperature Properties of Lubricants 27

2.1.3 Air and Water Entrainment Properties 29

2.1.4 Thermal Properties 32

2.2 Long Life Properties 33

2.2.1 Total Acid Number (TAN) 34

2.2.2 Total Base Number (TBN) 35

2.2.3 Oxidation Stability 35

2.2.4 Hydrolytic Stability 37

2.2.5 Corrosion Inhibition Properties 37

2.3 Environmental Properties 40

2.3.1 Environmentally Adapted Lubricants 40

2.3.2 Market Products with a Reduced Environmental Impact 41

2.4 Summary of Analyses 42

References 44

3 Base Fluids 45

3.1 General Hydrocarbon Chemistry 45

3.2 Base Fluid Categorization 48

3.3 The Refining Process of Crude Oils 50

3.3.1 The Refining Process 51

3.3.2 Influence of the Refining Process on the Oil Properties 52

3.4 Base Fluids Originating from Crude Oil 53

3.4.1 Paraffinic Base Oils 53

3.4.2 Naphthenic Base Oils 53

3.4.3 White Oils 54

3.4.4 Very High Viscosity Index Base Oils 54

3.4.5 Polyalphaolefins 54

3.4.6 Gas-to-Liquid Base Fluids 55

3.4.7 Re-Refined Base Oils 56

3.5 Base Fluids Originating from Renewable Raw Materials 56

3.5.1 Vegetable Oils (Natural Esters) 57

3.5.2 Synthetic Esters 57

3.6 Nonconventional Synthetic Base Fluids 59

3.7 Properties of Base Fluids 59

References 61

4 Additives 63

4.1 Fundamental Concepts and Processes 63

4.1.1 Atoms and Reactions 63

4.1.2 Intermolecular Forces 64

4.1.3 Chemical Potential 66

4.1.4 Surfaces 66

4.1.5 Mass Transfer 67

4.1.6 Adsorption 68

4.1.7 Chemical Characteristics of Surface Active Additives 70

4.2 Additive Exploration 71

4.3 Surface Active Adsorbing Additives 73

4.3.1 Corrosion Inhibitors 73

4.3.2 Friction Modifiers 75

4.3.3 Antiwear Additives 75

4.3.4 Extreme Pressure Additives 76

4.3.5 Activation of Antiwear and Extreme Pressure Additives 77

4.3.6 Competition for Surface Sites by Surface Active Additives 78

4.4 Interfacial Surface Active Additives 79

4.4.1 Defoamers 79

4.4.2 Emulsifiers and Demulsifiers 80

4.5 Physically Bulk Active Additives 81

4.5.1 Viscosity Modifiers 81

4.5.2 Pour Point Depressants 82

4.5.3 Dispersants 84

4.6 Chemically Bulk Active Additives 85

4.6.1 Detergents 85

4.6.2 Antioxidants 87

4.7 Additive Summary 88

References 89

Part Two Lubricant Performance

5 Formulating Lubricants 93

5.1 General Aspects of Development 93

5.1.1 Formulations 93

5.1.2 Development Work 96

5.1.3 Material Compatibility 96

5.1.4 Miscibility 97

5.1.5 Interactions in a Lubricated Contact 97

5.2 Quality of the Lubricated Tribological Contact 98

5.2.1 Lubricant Film Regime 99

5.2.2 Maintaining a High Quality Contact 101

5.3 Hydraulics 101

5.3.1 Description of a Hydraulic System 101

5.3.2 Formulating Hydraulic Oils 102

5.4 Gears 104

5.4.1 Description of Gears 104

5.4.2 Formulating Gear Oils 105

5.5 Combustion Engines 107

5.5.1 Description of Combustion Engines 107

5.5.2 Formulating Combustion Engine Oils 108

References 110

6 Tribological Test Methods 113

6.1 Field, Bench and Component Tests 113

6.2 Model Tests 115

6.2.1 Strategy for Selecting and Planning a Model Test 115

6.3 Lubricant Film Thickness Measurements 117

6.3.1 Electrical Methods 117

6.3.2 Optical Interferometry Method 118

6.4 Tribological Evaluation in Mixed and Boundary Lubrication 121

6.4.1 The Pin-on-Disc Tribotest 121

6.4.2 The Reciprocating Tribotest 123

6.4.3 The Twin Disc Tribotest 124

6.4.4 The Rotary Tribotest 128

6.5 Selection of Model Tests to Simulate Real Contacts 128

6.5.1 Hydraulics 129

6.5.2 Gears 129

6.5.3 Combustion Engines 131

6.6 Summary of Tribotest Methods 131

References 132

7 Lubricant Characterization 133

7.1 General Characterization Concepts 133

7.1.1 Planning 133

7.1.2 Basic Mixing Theory 134

7.1.3 Sampling 135

7.1.4 Diluting the Sample 136

7.1.5 Collecting Analysis Data 137

7.1.6 Calculations and Evaluation 138

7.2 Condition Analyses of Lubricants 138

7.3 Nonused Oil Characterization 140

7.3.1 Development 140

7.3.2 Production 141

7.3.3 Application Examples 142

7.4 Used Oil Characterization 142

7.4.1 Selection of Analyses 143

7.4.2 Analysis Examples of Selected Applications 144

7.5 Summary of Used Oil Analyses 146

References 148

8 Surface Characterization 149

8.1 Surface Characterization of Real Components 151

8.1.1 Examination of Nonused Surfaces 151

8.1.2 Examination of Used Surfaces 151

8.1.3 Characteristics of Application Examples 152

8.2 Microscopy Techniques 153

8.2.1 Visual Inspection 153

8.2.2 Light Optical Microscopy (LOM) 154

8.2.3 Optical Interference Microscopy 154

8.2.4 Atomic Force Microscopy (AFM) 154

8.2.5 Scanning Electron Microscopy (SEM) 155

8.2.6 Focused Ion Beam (FIB) 158

8.2.7 Transmission Electron Microscopy (TEM) 159

8.3 Surface Measurement 159

8.3.1 Statistical Surface Parameters 161

8.3.2 Contacting Stylus Profiler 162

8.3.3 Microscopy Techniques 163

8.4 Hardness Measurement 163

8.4.1 Macro and Micro Hardness 163

8.4.2 Nanoindentation 163

8.5 Surface Analysis Techniques 163

8.5.1 Selected Methods 164

8.5.2 Analysis Performance Parameters and Terminology 165

8.5.3 Depth Profiling and Chemical Mapping 167

8.5.4 Energy Dispersive X-Ray Spectroscopy (EDS) 169

8.5.5 Auger Electron Spectroscopy (AES) 170

8.5.6 X-Ray Photoelectron Spectroscopy (XPS) 173

8.5.7 Secondary Ion Mass Spectroscopy (SIMS) 176

8.5.8 Fourier Transform Infrared Spectroscopy 178

8.6 Summary of Surface Characterization Methods 179

8.6.1 Microscopy and Surface Measurement 179

8.6.2 Surface Analysis 179

References 182

Index 185

Marika Torbacke has a PhD in chemical engineering and has held a position as an adjunct Professor at Luleå University of Technology in Tribochemistry for six years. She has been the development manager for automotive lubricants at Statoil Lubricants and the company representative in ATIEL. She has also worked with development of industrial lubricants with a focus on environmentally adapted lubricants. Apart from her extensive experience of lubricant development work, she has been lecturing and teaching in the areas of lubricants with a focus on environmentally adapted lubricants, elastomer compatibility and soft metal corrosion.

Åsa Kassman Rudolphi is an Associate Professor in Materials Science at Uppsala University. Her field of research is tribology and surface engineering, with focus on materials science aspects. The work includes design and interpretation of experimental studies, surface imaging and analysis for friction and mechanism studies, and evaluation of new material solutions for different applications. She has a long experience of collaboration with industrial partners and industrial applications. She is also frequently teaching and developing courses in the areas of materials engineering and materials characterization.

Elisabet Kassfeldt is a Professor in Machine Elements at Luleå University of Technology. Her field of research covers lubricant properties and performance, including testing and evaluating both lubricated single components and full mechanical systems and industrial applications. Performance of environmentally adapted lubricants is a special area of interest. She has done extensive research work in this field, often in cooperation with industrial partners. In addition, she has a wide experience of teaching in Mechanical Engineering, including courses in machine design, hydraulics and tribology.