Technology & Engineering
Lubricants
Lubricants are substances used to reduce friction and wear between moving parts. They are commonly employed in machinery, vehicles, and industrial equipment to ensure smooth operation and prevent damage. Lubricants come in various forms, such as oils, greases, and solid lubricants, and are selected based on the specific requirements of the application.
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9 Key excerpts on "Lubricants"
No longer available |Learn more- Heinz P. Bloch, Kenneth Bannister(Authors)
- 2020(Publication Date)
- River Publishers(Publisher)
Whether in the form of a liquid, solid or gas, mod -ern Lubricants are pure liquid engineering, and through the blending of additives to a variety of different base stocks they can be designed to perform up to eight func -tions simultaneously whilst operating in a host of differ -ing environments. Webster’s dictionary describes a lubricant as “a substance (e.g. oil, grease, or soap) that when introduced between solid surfaces which move over one another reduces resistance to movement, heat production, and wear (i.e. friction and its effects) by forming a fluid film between the surfaces.” Essentially, a lubricant’s function is to control and minimize the sacrificial harmful effects of moving surfac -es passing over one another under load, and at speed. It does this in the following eight definitive ways: Function 1—Control and minimize friction: The primary function of every lubricant is to control and minimize the effects of friction. When two solid surfaces passing over one another are allowed to come into contact under load, they “rub” together and produce dry friction requiring considerable energy to keep the surfaces moving. With no lubricant present to separate the moving surfaces from one another, surfaces quickly degrade and can weld or lock together resulting in a “seize.” The indiscriminate sacrifices of wear surfaces produces rapid wear and loss of energy to heat resulting in poor performance, reduced reliability, and increased energy use. The introduction of a lubricating film between the two wear surfaces creates a fluid barrier that prevents surface contact. Although a small amount of fluid friction is still present in the lubricant film, the energy required to move the surfaces over one another is but a small fraction of that required to overcome “surface to surface” dry fric-tion.
eBook - PDFEngineering Chemistry
Fundamentals and Applications
- Shikha Agarwal(Author)
- 2019(Publication Date)
- Cambridge University Press(Publisher)
7.1 Introduction A lubricant is a substance introduced between two moving surfaces to reduce friction. This property of reducing friction is termed lubricity or slipperiness and the process of reducing friction between two moving surfaces by the introduction of Lubricants is known as lubrication. Before going into what lubrication is, what a lubricant is and how it functions, we need to know what friction is. Friction is the force that resists the relative motion between two bodies in contact. The surfaces of all material, no matter how smooth they appear, are not truly smooth on an atomic scale. They are rough, with sharp and rugged projections called asperities (Fig. 7.1(a)). When two surfaces come in contact with each other, initially, they only touch at a few of these asperity points (Fig. 7.1(b)). When a small load is applied on a metal surface, local high pressure develops at these points (asperities) of contact, which then tend to interlock, thus developing a resistance to motion. When a metal slides, the peaks get broken resulting in wear and tear of the surfaces. Further, if the pressure is high, the asperities deform plastically increasing the contact area between the two surfaces. A sufficiently high pressure leads to the formation of a welded junction between asperities. Additional force is then required to break these junctions. This further adds to the frictional resistance. Figure 7.1 (a) Magnified view of a real surface. (b) Contact between two surfaces on application of load Lubricants Chapter 7 432 Engineering Chemistry: Fundamentals and Applications Thus, frictional resistance harms the system in three ways. • It causes energy loss. Extra work has to be done to overcome the force of friction. • Friction causes generation of heat in areas in contact. These heated parts may melt and get deformed, leading to seizure (welding of two surfaces due to heat) of the system. • Breaking of asperities brings about abrasion or surface wear and tear.
eBook - PDFEngineering Chemistry
Fundamentals and Applications
- Shikha Agarwal(Author)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
7.1 Introduction A lubricant is a substance introduced between two moving surfaces to reduce friction. This property of reducing friction is termed as lubricity or slipperiness and the process of reducing friction between two moving surfaces by the introduction of Lubricants is known as lubrication. Before going into what lubrication is, what a lubricant is and how it functions, we need to know what friction is. Friction is the force that resists the relative motion between two bodies in contact. The surfaces of all material, no matter how smooth they appear, are not truly smooth on an atomic scale. They are rough, with sharp and rugged projections called asperities (Figure 7.1(a)). When two surfaces come in contact with each other, initially, they only touch at a few of these asperity points (Figure 7.1(b)). When a small load is applied on a metal surface, local high pressure develops at these points (asperities) of contact which then tend to interlock, thus, developing a resistance to motion. When a metal slides, the peaks get broken resulting in wear and tear of the surfaces. Further, if the pressure is high, the asperities deform plastically increasing the contact area between the two surfaces. A sufficiently high pressure leads to the formation of a welded junction between asperities. Additional force is then required to break these junctions. This further adds to the frictional resistance. Figure 7.1 (a) Magnified view of a real surface (b) Contact between two surfaces on application of load Lubricants Chapter 7 Lubricants 401 Thus, frictional resistance harms the system in three ways. • It causes energy loss. Extra work has to be done to overcome the force of friction. • Friction causes generation of heat in areas in contact. These heated parts may melt, get deformed leading to seizure (welding of two surfaces due to heat) of the system. • Breaking of asperities brings about abrasion or surface wear and tear.
eBook - PDFTribology
Fundamentals and Advancements
- Jürgen Gegner(Author)
- 2013(Publication Date)
- IntechOpen(Publisher)
Lubricants and Special Fluids. Amsterdam: Elsevier; 1992. [8] Lansdown A.R., Lubrication and lubricant selection: a practical guide. 3 rd Edition. John Wiley & Sons; 2004. [9] Rudnick L. R., editor. Lubricant Additives: Chemistry and Applications, 1st Edition. New York:Marcel Dekker, 2003. [10] March, J., Advanced Organic Chemistry: Reactions, mechanisms, Structure. New York: Wiley-VCH; 1992. Fundamentals of Lubricants and Lubrication http://dx.doi.org/10.5772/55731 53 Chapter 2 Lubrication and Lubricants Nehal S. Ahmed and Amal M. Nassar Additional information is available at the end of the chapter http://dx.doi.org/10.5772/56043 1. Introduction 1.1. Lubrication The primary purpose of lubrication is to reduce wear and heat between contacting surfaces in relative motion. While wear and heat cannot be completely eliminated, they can be reduced to negligible or acceptable levels. Because heat and wear are associated with friction, both effects can be minimized by reducing the coefficient of friction between the contacting surfaces. Lubrication is also used to reduce oxidation and prevent rust; to provide insulation in transformer applications; to transmit mechanical power in hydraulic fluid power applications; and to seal against dust, dirt, and water. 1.1.1. The lubrication regimes The modern period of lubrication began with the work of Osborne Reynolds (1842-1912). Reynold's research was concerned with shafts rotating in bearings and cases this show in Fig. 1. When a lubricant was applied to the shaft, Reynolds found that a rotating shaft pulled a converging wedge of lubricant between the shaft and the bearing. He also noted that as the shaft gained velocity, the liquid flowed between the two surfaces at a greater rate. This, because the lubricant is viscous, produces a liquid pressure in the lubricant wedge that is sufficient to keep the two surfaces separated.
eBook - PDFAutomotive Repair & Maintenance NQF2 SB
TVET FIRST
- Sparrow Consulting(Author)
- 2013(Publication Date)
- Macmillan(Publisher)
The harder you fall, the deeper the scratches on your skin will be. Think about it 174 Module 23: The purpose of lubrication in vehicles Unit 23.2: The function of lubrication Many vehicle parts come into contact with each other when the vehicle functions. This contact often results in wear on vehicle parts. The total heat of the vehicle can also increase a lot, which is not desirable at all. One way to fix these problems is through proper lubrication. Lubrication is the method used to reduce wear of one or both surfaces that are in contact with each other and that are moving. This is done by putting a lubricant between the surfaces to carry, or to help carry, the load between the surfaces. The lubricant can be a solid (e.g. graphite), a solid/liquid dispersion , a liquid or a liquefied gas. In the automotive industry, lubrication is mostly achieved by using highly viscous substances such as various types of oil and grease. Although oil and grease have similar functions, their properties differ. From the above explanation, you can see that the main purpose of lubrication is to reduce wear and heat between surfaces that are rubbing against each other to an acceptable level by reducing the friction between the two surfaces. Lubrication can also be used to: • Reduce oxidation and prevent rust. • Provide insulation in transformer applications. • Transfer mechanical power in hydraulic fluid power applications. • Seal against dust, dirt and water. Lubrication can be further understood by defining the purpose and functions of Lubricants. A lubricant is a mixture of base oils and performance-enhancing additives needed to protect the engine, gear box and other moving areas. Lubrication, on the other hand, refers to the process of applying Lubricants. The functions of a lubricant are to: • Lubricate the sliding contact between vehicle parts. • Provide an oil film between rolling contact surfaces. • Carry away the heat generated by friction in order to cool down the engine.
eBook - PDF- Tedric A. Harris, Michael N. Kotzalas(Authors)
- 2006(Publication Date)
- CRC Press(Publisher)
12 Lubricants and Lubrication Techniques 12.1 GENERAL The primary function of a lubricant is to prevent wear of the rolling and sliding contacts of a bearing through hydrodynamic, elastohydrodynamic (EHL), or boundary lubrication; how-ever, there are many other vital functions, such as: . Minimizing the frictional power loss of the bearing . Acting as a heat transfer medium to remove heat from the bearing, or redistributing the heat energy within the bearing to minimize differential thermal expansions . Protecting the precision surfaces of the bearing components from corrosion . Removing wear debris from the roller contact paths . Minimizing the amount of extraneous dirt entering the roller contact paths . Providing a damping medium for cage dynamic motions No single lubricant or class of Lubricants can satisfy all the requirements for bearing operating conditions, from cryogenic to ultrahigh temperatures, from very slow to ultrahigh speeds, and from benign to highly reactive operating environments. As for most engineering tasks, a compromise is generally exercised between performance and economic constraints. The economic constraints involve not only the cost of the lubricant and the method of application, but also its impact on the life cycle cost of the mechanical system. Cost and performance decisions are frequently complicated because many other com-ponents of a mechanical system also need lubrication or cooling, and they might dominate the selection process. For example, an automotive gearbox typically comprises gears, a ring synchronizer, rolling bearings of several types operating in very different load and speed regimes, plain bearings, clutches, and splines. 12.2 TYPES OF Lubricants 12.2.1 S ELECTION OF L UBRICANT T YPE The selection of a lubricant type for a bearing application is based on several considerations, for example: . Operating temperature . Operating environment . Mechanical properties . Chemical properties . Transport properties 255
eBook - PDF- William F. Gale, Terry C. Totemeier(Authors)
- 2003(Publication Date)
- Butterworth-Heinemann(Publisher)
24 Lubricants 24.1 Introduction Lubricants minimise friction and wear in rubbing contacts by reducing metal–metal contact, remov-ing wear debris, and carrying away frictional heat. They may also prevent rusting and with liquid Lubricants remove heat. Lubricants may be solid, such as graphite, molybdenum disulphide, poly-tetrafluoroethylene and talc; or gaseous, commonly air; but the principal Lubricants are liquids such as mineral oil, or the semi-solid greases formed from liquids by the use of thickening agents. 24.1.1 Main regimes of lubrication HYDRODYNAMIC LUBRICATION (HL) A viscous fluid film between two solid surfaces moving in very close proximity to one another becomes pressurised and holds those surfaces apart, often against considerable loads. During the process, the surface may be deformed elastically (EHL – elastohydrodynamic lubrication) or plastically. HYDROSTATIC LUBRICATION In this case, two solid surfaces are separated by a thick fluid film supplied from an external pressure source, e.g. by an oil pump system. BOUNDARY LUBRICATION When the contact of asperities on sliding couples increases as the load increases, the sliding speed decreases or the fluid viscosity decreases, the friction significantly increases and the load is mainly supported by the asperity contact. Such lubrication condition is known as boundary lubrication. MIXED LUBRICATION This is the situation when several lubrication modes, such as HL and boundary lubrication, coexist. 24.2 Lubrication condition, friction and wear In hydrodynamic lubrication friction is purely viscous and is directly dependent on the area of the film, the rate of shear and the viscosity of the lubricant. Coefficients of friction are as low as 0.001– 0.003 and wear is negligible. When the speed of sliding and the oil viscosity are insufficient for the viscous film to carry the load, contact occurs between asperities on the opposing surfaces.
- Wayne Kilcollins(Author)
- 2012(Publication Date)
- Cengage Learning EMEA(Publisher)
All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 4 Lubrication 79 TYPES OF Lubricants Lubricants are classified in several different categories according to their origin. These include animal, vegetable, mineral, petroleum-based, and synthetic. Animal and veg-etable oils have been used for thousands of years. Animal oils have been harvested directly from carcasses in such forms as whale oil or through the rendering of animal fat to pro-duce oils or grease. Vegetable oils have been processed for centuries as well. These oils are from plant varieties such as olives, sunflowers, castor beans, and soy beans, along with other grains or nuts. These oils were useful in the develop-ment of many ancient technologies because they were read-ily available and easy to process. Several early civilizations, such as the Egyptians and Romans, used grease formulated from animal and vegetable oils to improve the efficiency of mechanical components. The Romans processed olive oil with ground limestone to produce grease to lubricate wheel sleeves and other mechanisms. Further discussions on mod-ern grease formulation will be presented later in the chapter. Animal- and vegetable-based Lubricants were used ex-tensively up through the Industrial Revolution. Even today, some applications use vegetable-based Lubricants. These ap-plications include food processing because of the nontoxic nature of vegetable oils.
eBook - PDFIndustrial Tribology
The Practical Aspects of Friction, Lubrication and Wear
- M.H. Jones, D. Scott(Authors)
- 1983(Publication Date)
- North Holland(Publisher)
In order t o approach lubricant selection r e a I i s t i c a l l y , we should be clear as t o what are the objects o f lubrication. The primary object o f l u b r i c a t i o n i s t o reduce f r i c t i o n o r wear, o r usually both f r i c t i o n and wear. This i s the factor which defines a material as a l u b r i -cant . There are i n addition three secondary functions o f a lubricant:- ( i ) To act as a coolant. I n some systems t h i s w i l l be a v i t a l function o f the lubricant because f r i c t i o n a l o r process heat must be removed and no a l t e r n a t i v e cooling f l u i d can be used. To remove wear debris o r other contaminants, o r t o prevent other contami- nants from entering the system. ( i i i ) To protect metals against corrosion. ( i i ) There i s no good reason why a 224 lubricant should be expected t o provide such protection, but because min- eral o i l s are very e f f e c t i v e corrosion preventives, many designers have come t o expect the same o f a l l Lubricants. The lubricant w i l l often s a t i s f a c t o r i l y f u l f i l a l l these tasks, but where the available choice o f Lubricants i s limited, it may be necessary to choose the lubricant only t o meet the f r i c t i o n and wear requirements, and t o use other techniques t o solve the cooling, contamination and corrosion problems. 9.2 SELECTING THE LUBRICANT TYPE Lubrication systems as such are outside the scope of t h i s chapter, but the problem o f lubricant selection cannot e n t i r e l y be separated from that o f selec- t i n g the lubrication system. The most straightforward way t o select both lubricant and lubrication system i s probably t o s t a r t w i t h the simplest technique and t o progress from that only as f a r as i s necessary t o ensure satisfactory operation. The simplest technique w i l l usually have the lowest i n i t i a l cost, and w i l l often also be the most re1 iable.
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