Lubricants

Introduction to Properties and Performance

Marika Torbacke, Åsa Kassman Rudolphi, Elisabet Kassfeldt

• Publisher: Wiley
• Year: 2014
• Print ISBN:
  9781118799741
• Edition: 1
• eBook ISBN:
  9781118799710
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

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.

Part One
Lubricant Properties

1
Introduction to Tribology

When surfaces move relative each other, friction and wear arise. Tribology is the science and technology of interacting surfaces in relative motion and covers the three subjects of friction, wear and lubrication. Practical examples of tribology are found anywhere. This can be a slippery shoe on ice or a piece of soap in a wet hand, but also a well lubricated smoothly running machine or mechanical system.

Baldos, a unique car built by students at Luleå University of Technology, is an excellent example of development of new machines with a focus on design for low energy losses (see Figure 1.1). Baldos has been invited to different worldwide events in, for example, Washington DC, Stuttgart and Monaco.

Figure 1.1 Baldos – a machine with low energy losses

The term ‘tribology’ is derived from the Greek word tribos, which means rubbing [1]. Friction, wear and lubrication can be treated separately, each of them with its own underlying questions, but in order to understand tribology a system approach is required [2–5].

The subject of tribology is visualized in Figure 1.2. Friction and wear can be investigated on their own in unlubricated or lubricated contacts. Lubrication is supplementing the areas of friction and wear. In this book, examples from hydraulics, gears and combustion engines are used.

Figure 1.2 The different areas of tribology: friction, wear and lubrication

Tribology is highly important for sustainable growth of industry and society. High levels of friction and wear will lead to high energy consumption and in the worst case will shorten the life of the system. Sustainable growth implies, for example, reducing consumption of raw materials and toxic or environmentally harmful surface materials and lubricants. This means that even minor reductions in friction and prolonged life of lubricated systems yield large monetary and environmental savings.

The impact of environmental demands is exemplified by the emission legislation placed on the automotive segment regarding emissions of both particulate matter and greenhouse gases. Improved tribological performance can make vehicles more energy efficient. Both reduction in friction and improved wear resistance have significant effects on fuel consumption and thus also on greenhouse gas emissions. Good tribological performance is therefore of great importance in order to meet the increasingly tougher demands for emissions from cars and trucks.

General trends in the development of products and processes aim at higher power density, reduced friction losses, longer wear life, reduced lubricant consumption, less toxic or environmentally damaging lubricants and additives, reduced use of environmentally harmful surface treatment processes and reduced weight of components.

This chapter will introduce the reader to the most important tribological phenomena, covering the tribological contact followed by friction, wear and lubrication.

1.1 Tribological Contacts

A tribological contact is defined as two solid bodies in contact under relative motion. It can be either unlubricated or lubricated. The tribological contact is characterized by its operating conditions (e.g. velocity, load and type of motions), material parameters (e.g. surface material, surface roughness and hardness), environmental conditions (e.g. temperature and humidity) and, in the lubricated case, lubricant properties (e.g. viscosity) (see Figure 1.3).

Figure 1.3 Tribological contacts are affected by different conditions

The tribological contact can be observed at different scales, that is at macroscopic scale (or macroscale) or at microscopic scale (or microscale) (see Figure 1.4). The macroscale will give global information of the contact, while the microscale will give local information within the contact. For example, a contact that appears smooth at macroscale may appear very rough and uneven at microscale. The real contact area between the surfaces is the sum of a large number of small areas where surface peaks from the two surfaces get into contact. As a consequence, the apparent contact area at the macroscale is much larger than the real contact area between the two surfaces in contact.

Figure 1.4 The tribological contact can be observed at macroscale (left) or at microscale (right). Surfaces appearing smooth at macroscale still show roughness at microscale

In engineering systems, as machines, the solid bodies are usually made of steel. Consequently, most contacts are steel–steel contacts. However, yellow metal (e.g. bronze), polymeric materials and ceramics are also used. In these cases the contact is often steel–yellow metal, steel–polymeric material or steel–ceramics. Steel–steel contacts almost always require lubrication while the other examples may be run either unlubricated or lubricated.

1.1.1 Macroscale Contacts

The shape of the bodies in contact determines the overall geometry of the contact, which strongly influences the operating conditions and performance of the contact [6]. A contact is said to be conformal if the surfaces of the two bodies fit exactly or closely together, such as two flat surfaces in contact. If the two bodies have dissimilar ...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• List of Symbols
• Part One Lubricant Properties
• Part Two Lubricant Performance
• Index
• End User License Agreement