06 - Lubricants

1. 06 - Lubricants

2. The intent of this presentation is to present enough information to provide the reader with a fundamental knowledge of different type lubricants and lubrication techniques used within Michelin and to better understand basic system and equipment operations.

3. 06 - Lubricants Principles Of Lubrication And Lubrication Technology Proper lubrication is essential to keeping industrial equipment operating. Almost every machine and tool requires lubrication to protect its moving parts and enhance operation. In almost any situation involving moving parts in a plant, lubricants will be involved. What Is Lubrication? Lubrication is a means of separating moving surfaces under pressure. It is concerned with oils or other substances used to make surfaces slippery. To lubricate means to apply a lubricant, a substance which will provide a smooth, slippery film for moving parts to slide on.

4. 06 - Lubricants Why Lubricate? There are six primary reasons for lubrication: To reduce friction To reduce wear To help dampen shock To cool moving elements To prevent corrosion To seal out dirt and other contaminants Lubricants serve all six primary reasons for lubrication and fall into different classifications and types. The general classifications are : Liquid Semi-solid Solid Gas

5. 06 - Lubricants The selection of a lubricant for any given application will be determined by the nature of the application itself. For example, bearings in a gear box are usually best lubricated by an oil, while bearings in a pillow block usually require a grease. The focus of this text is on oil and grease. Friction When two objects are in contact, there is always resistance to their movement against one another. This resistance to movement is called friction, which is defined as that force which exists between two contact surfaces and which offers resistance to the movement of one object against the other. If both bodies are solids, the force is called solid friction, which can either be sliding friction or rolling friction. If one or both bodies are liquid, the force is called liquid friction. Sliding friction Sliding friction occurs when one solid moves against another one. The figure below gives three such examples:

6. 06 - Lubricants 1. a block sliding on a flat surface; 2. a piston sliding inside a cylinder; 3. a shaft rotating inside a bushing. All the above produce sliding friction if there is no lubricant. Rolling friction The rolling of a cylinder or a spherical object on a flat surface creates rolling friction. The figure below gives examples of rolling friction:

7. 06 - Lubricants a ball rolling on a flat surface; balls rolling inside the track of a ball bearing; 3. block being moved on rollers. The rolling friction is not as strong as the sliding friction. This is why heavy objects are usually moved with the help of rollers rather than skates or ramps.

8. 06 - Lubricants Friction of liquids When the particles that make up a liquid are moving and that the external surface of this liquid is in contact with a solid surface, the liquid develops a number of internal planes, each made up of numerous molecules. The friction created by the sliding of planes against one another and between molecules rubbing against one another is called liquid friction. When a liquid is injected between two solids, one of which is set into motion, this liquid becomes a floating film and breaks down into fine planes of molecules. The combination of the resistance that the liquid opposes to this separation and the tendency of the planes of lubricant to stick or adhere to one another is called the friction of liquids. There is no friction of liquids unless the liquid is set in motion by the movement of at least one solid body that is in contact with the liquid.

9. 06 - Lubricants Causes of friction The cause and scope of friction in any solid or liquid are largely determined by two properties which exist in all matter: COHESION and ADHESION.

10. 06 - Lubricants Cohesion Cohesion is the force which holds together the particles of a substance. To varying degrees, both solids and liquids have properties of cohesion. For instance, the cohesion of steel is greater than that of wood, which is greater than that of grease, which in turn is greater than that of oil, which is greater than that of water, which is greater than that of gasoline, etc. Adhesion On the other hand, solids and liquids obviously have another property or quality regarding friction. This property, ADHESION, makes liquids adhere to solids and solids to one another.

11. 06 - Lubricants Adhesion is the force which makes liquids cling to solids. For instance, oil adheres to metal, water to wood, etc. On the basis of these definitions and these examples of cohesion and adhesion, one can see that: all solids have a high factor of cohesion, but a relatively low factor of adhesion; liquids usually have a high factor of adhesion, but a relatively low factor of cohesion; most substances that have a high factor of one or the other property, have a low one of the other. However, the factor of adhesion varies greatly from one substance to another. This is why mercury does not stick to glass, steel, marble, etc., whereas mineral oil does. This is because mercury has a high factor of cohesion, but a low one of adhesion, whereas the reverse holds for mineral oil. It should be noted that both mercury and mineral oil are considered as liquids. The friction in solids, as well as in liquids, is their tendency to stick together and resist displacement; given the fact that the friction of liquids is less than the sliding and rolling frictions, this difference can be used to reduce friction.

12. 06 - Lubricants Reduction of friction through the introduction of a liquid between two surfaces Friction is diminished through the injection of a liquid between the surfaces of solids moving against one another, which means that the sliding or rolling friction is replaced by the friction of liquids. To achieve the best possible results, the lubrication specialist must take two factors into account: temperature and roughness of the surfaces of solids.

13. 06 - Lubricants Friction always releases heat The quantity of heat released by friction varies greatly depending on the materials involved, but depends overall on the type of friction. When surfaces are lubricated, sliding friction releases the most heat, rolling friction releases less, while the friction of liquids releases the least. If the surfaces of solid bodies moving one against the other are lubricated, the friction of solids is replaced by the friction of liquids. The friction of liquids is the least heat generating because it is the one that requires the least effort to overcome. Therefore, lubricated solids require less force to set them in motion than identical non‑lubricated ones.

14. 06 - Lubricants Causes of friction in metals All metals, however smoothly polished, prove to have a rough surface when examined with a microscope. When force is applied to two pieces of metal that are in contact with one another, their respective surfaces catch where they are contacted, that is where there are opposing asperities. These asperities are the parts of the solids where the adhesion phenomenon takes place. The force required to break this contact is called friction.

15. 06 - Lubricants Reduction of friction through lubrication When liquids are placed between two solids, such as metals, to create a space between the rough surfaces of these metals, they act as a liquid film which allows the two hard surfaces to move against one another without touching. These surfaces are then said to be lubricated. Figure above shows that A, a metallic body, is moving toward the left, while B, another metallic body, is moving toward the right, and that their asperities, detailed in C, cannot catch against each other, or rip each other out, as they would were there no liquid between them. Therefore, lubrication reduces friction.

16. 06 - Lubricants The ability of a liquid to maintain metallic surfaces apart from one another depends greatly on a suitable balance between its properties of cohesion and adhesion. For instance, water is a better lubricant than gasoline, but oil is better than water, because though water and gasoline have superior adhesion properties, they have much less cohesion than oil. This is why when water or gasoline are used as a lubricant they are necessarily broken up by heavy loads. On the other hand, oil has the cohesion that is required to support a load that would break a film of water or gasoline, and its adhesion coefficient is sufficient stick to metallic surfaces. Under similar conditions, the efficiency of a given quantity of lubricant is less under 1000 pounds of pressure than it is under 500 pounds, because the increased pressure forces the lubricant out and reduces its thickness; thus, to a certain extent, pressure determines whether or not the lubricant will be able to keep the rough metallic surfaces apart. Reaction of a lubricant under operating conditions The above figure shows the lubricant as a five‑plane film designated A, B, C, D and E.

17. 06 - Lubricants Planes A and E are in contact with the metallic surfaces and remain relatively stationary as a result of the property of adhesion. Planes B, C and D stick to one another, and to planes A and E as a result of the property of cohesion. If the top metal plate is moved to the right (see the figure below), plane A adheres to it and slides against plane B; plane B, in turn, slides against C; C slides against D, and D against E. Plane E, as is the case for plane A, remains almost immobile because it adheres to the bottom metal plate. Before there can be movement between these various plane, the cohesion force that holds them together must be overcome.

18. V=0 V=0

19. V=0 V=0

20. 06 - Lubricants Planes A and E are in contact with the metallic surfaces and remain relatively stationary as a result of the property of adhesion. Planes B, C and D stick to one another, and to planes A and E as a result of the property of cohesion. If the top metal plate is moved to the right (see the figure below), plane A adheres to it and slides against plane B; plane B, in turn, slides against C; C slides against D, and D against E. Plane E, as is the case for plane A, remains almost immobile because it adheres to the bottom metal plate. Before there can be movement between these various plane, the cohesion force that holds them together must be overcome. This explanation of how a film of lubricant behaves between flat surfaces also applies for the curved surfaces of smooth, fully lubricated bearings, the bearings of electric‑motor rotors or any other kind of machine where a smooth bearing is supplied with enough oil during its operation.

21. 06 - Lubricants Types Of Lubrication Insufficient and excessive lubrication Insufficient lubrication occurs when there is only enough oil to coat the two surfaces with a thin film, their rubbing against each other causes excessive wear, and ultimately breakage. Let’s take the metallic surfaces shown in the figure above, but give them an insufficient amount of oil, so that instead of there being five planes of oil (A, B, C, D and E) there are only two (A and B). The five‑plane simplification was made to illustrate the fact that there is movement between planes inside the oil. A case of insufficient oiling occurs when this kind of motion is either hindered or not possible. Excessive lubrication On the other hand, excessive lubrication, particularly with grease rather than oil, prevents the proper dissipation of the heat created by the movement of the parts, for instance in a bearing. As heat rises in the bearing, so does the internal pressure, which will rupture the seals.

22. 06 - Lubricants Proper lubrication Proper lubrication means that there are enough planes of oil molecules sliding against one another to maintain oil friction, which completely separates the metal surfaces, under normal loads, and prevents the friction of solids. Partial lubrication Partial lubrication means that there are so few planes of molecules in the film that they break up and therefore cannot slide against one another anymore. This occurs when the film is broken by the periodic touching of the contact surfaces. This condition will increase the heat inside the bearing, as if it was being subjected to twice its normal load.

23. 06 - Lubricants Oil Lubrication Principles of lubrication and of the oil wedge Drawing 1 in the above figure shows a shaft (a) at rest, with the oil opening on top; the load is vertical as shown by the arrow; please note that the metal components make contact at A. In drawing 2, the shaft has started rotating in the direction given by the curved arrow. Part of the oil supplied to the bearing from above (low pressure point) sticks to the shaft when it just starts rotating. As the speed increases, the adherence of oil to the shaft pushes the oil film between the shaft and the bearing, and in so doing separates them (hydraulic wedge phenomenon). Once the weight of the shaft is borne by the wedged oil, the combined forces of the shaft and its movement attain a state of equilibrium, which is illustrated in drawing 3.

24. 06 - Lubricants Once the shaft has started rotating, the film of oil at point B in drawing 2 is very thin. As the speed increases, it becomes thicker, acquires greater internal pressure and forces the shaft away from the bearing housing. Then as the speed increases to its operating level the pressure in the oil wedge becomes even greater, which lifts the shaft and forces it to the right (C in drawing 4). The trick in all this is to use an oil whose consistency is just enough to lift the shaft and keep it away from the housing (for ex.: grinder bearings). Oil viscosity The degree of cohesion between the molecules of a given oil determines its viscosity. The more viscous an oil is, the more its molecules stick to one another. Viscosity is the resistance to flow of a liquid at a given temperature.

25. 06 - Lubricants Viscosity varies with temperature: ‑ the colder the oil, the thicker it becomes; ‑ the warmer the oil, the thinner it becomes. There are two ways to express viscosity: kinematic viscosity and absolute (or dynamic) viscosity. Kinematic viscosity is used more than absolute viscosity, and relates to the time it takes for 60 milliliters of oil to flow out of a capillary tube (0.012 in.). The measuring unit is the "centistoke" (cSt) or the "Saybolt Universal Second" (SUS). NOTE: Viscosity varies from one type of oil to another.

26. 06 - Lubricants Viscosity index The viscosity index is the measure of the viscosity change in function of temperature. The smaller the variation caused by temperature, the greater is the viscosity index. Example: An oil which is viscous at 100oC and remains so at 0oC has a greater viscosity index than another oil which is viscous at 100oC but congealed at 0oC. NOTE: Lubricants have a number of properties. Extra thick oil The term "thick" applies to an oil whose cohesion factor between molecules is very high. The force with which the outer planes adhere to the mobile parts is not sufficient to break the strength of the film. This leads to incomplete and insufficient lubrication because the wedging process cannot produce an oil film that will separate in enough planes. Under such conditions, the bearing lacks oil and deteriorates.

27. 06 - Lubricants Extra thin oil When the oil is too thin, it cannot lubricate a bearing properly because the cohesion between the planes of the oil film is too weak. This means that the oil film is not strong enough to carry the weight of the shaft and provide proper lubrication under normal loads. The planes then break apart, lubrication becomes insufficient and the bearing starts deteriorating

28. 06 - Lubricants The viscosity of a given oil is appropriate when the force holding the molecules together is such that the counter force developed by the shaft while it is rotating inside the bearing will not break the molecular planes of the oil film. An appropriate oil is the one which allows for an equilibrium between the forces of cohesion and adhesion. When choosing an oil, it is important to take into account 1. the operating speed, 2. the fitting of parts (play required for proper operation) and 3. the loads, since all these factors have great influence on the operation of the components. Proper viscosity

29. 06 - Lubricants Major properties of oils low volatility during operation; satisfactory pouring characteristics within the operating range of temperatures; capacity to conserve its operating characteristics for long enough a period; compatibility with other substances in the system. Pour point The pour point is the temperature at which the surface remains immobile for five seconds. NOTE: The pour point is the lowest temperature at which an oil is sufficiently fluid to be pumped or poured.

30. 06 - Lubricants Flash point and fire point Oil will burn if hot enough. At the flash point temperature petroleum oils will release enough vapors to ignite or explode, about 300° F for light oils to about 500° F for heavy oils. Well below its flash point, an oil will become too thin to lubricate properly. The fire point is the temperature at which the oil catches fire. Qualities Required Of Gear Oils Extreme pressure (EP) properties Extreme pressure EP properties are needed when gear mechanisms feature combinations of high‑load hypoid and spiral bevel or worm gears. Straight gears and spiral bevel gears under moderate loads do not call for such additives.

31. 06 - Lubricants Resistance to oxidation Gear lubricants must be chemically stable in order to resist oxidation and the accumulation of sludge under prolonged use at temperatures in the 200 to 240 oF range, with vigorous agitation in the presence of air. Overall, the base oils used to make gear oils are considered as more resistant to oxidation and deterioration than the additives that are designed to ensure maximum protection with maximum stability. Resistance to corrosion EP additives are chemically active by nature and protect gear teeth through a controlled type of corrosion. However, they must not be corrosive to the point of weakening the metal. The discoloration of gears and internal components is frequent and is not a sign of abnormal corrosion. Resistance to foaming This is a must in gear oils since there is violent agitation. An additive incorporated into gear oil keeps the formation of air bubbles down, therefore prevents the occurrence of froth.

32. 06 - Lubricants Viscosity index Given the great amplitude between ambient temperature and the temperature of the gear housing, it is advisable to use oil with a viscosity index of at least 80. Pour point It must allow for lubrication at the lowest temperatures that can be expected. Low viscosity gear oils have a pour point of at least ‑50oF. Channeling temperature Gear oils must be sufficiently fluid, at the lowest operating temperatures, to flow and coat mobile components, rather than create some preferential channel in which gear components can move without lubricant. The channeling temperature can be 15oF lower that the pour point specified for a product.

33. 06 - Lubricants • Synthetic oils • Synthetic lubricants are only partly derived from petroleum. Rather, they are a mixture of chemicals and certain bases obtained from petroleum. There are a number of major ones, of which: • synthetic hydrocarbons; • organic esters; • phosphaticesters; • silicones; • polyglycols. • Qualities of synthetic lubricants • Synthetic lubricants can solve most lubrication problems, reduce operating costs and prolong the working life of lubricants. In short, they keep on performing when other lubricants have already broken down.

34. 06 - Lubricants • Advantages of synthetic lubricants • less frequent lubrication; • lower consumption; • less maintenance; • reduction in replacement or repair costs (parts and labor); • improved performance; • reduced wear; • longer working life of parts; • lower fire risk, which leads to lower insurance premiums; • reduced inventory; • single lubricant for multiple uses; • excellent fluidity at low temperatures.

35. 06 - Lubricants NOTE : When Disposing of used oil - SAFETY FIRST Each plant has its own regulations regarding the safe disposal of used or contaminated oils. These regulations must meet environmental laws. Whatever the applicable regulations and laws, be encouraged to follow them. Nature's life supporting systems will suffer more and more if workers are not aware of environmental problems stemming from improper disposal of contaminated products.

36. 06 - Lubricants • Grease Lubrication • What are greases • Greases are solid or semi‑solid lubricants. They are made by dispersing thickeners in a liquid lubricant. • Types of greases • There are usually two grease types on the market: • ordinary greases; • complex greases. • Ordinary greases are mineral oils that have been thickened with metallic soap, which is obtained by combining fats (animal or vegetable) with a metal or mineral. The most frequently used elements for this purpose are calcium, sodium, lithium and aluminum. However, grease manufacturing requires the use of a third component: organic or inorganic additives.

37. 06 - Lubricants The following chart presents the major components of greases:

38. 06 - Lubricants How grease lubricates When the mobile components of a bearing come into contact with the grease, a small quantity of oil expressed from the grease ensures the lubrication of the bearing surface. This oil gradually breaks down due to oxidation or is lost by evaporation or under the effect of the centrifugal force. The separation of oil from grease on the contact surfaces must be minimized to ensure efficient lubrication. A bearing cannot continue to function properly unless the grease keeps on supplying a lubricating oil to the surfaces which rub against one another. After a while, all greases oxidize and the oil they contain wears out on the contact surfaces. However, an appropriate grease will slow down the separation of oil and prolong its working life. The lubrication process is also made easier when soap has been added to the oil, thanks to the excellent adhesion characteristics of this component. This property helps maintain the grease in its proper place inside a bearing, which cuts leaks down and enhances water tightness and prevents contamination. Moreover, soap increases the load‑bearing capacity.

39. 06 - Lubricants • Operating conditions • It takes a wide range of greases to meet a vast array of operating conditions. The operating conditions are dictated by the physical characteristics of a mechanism, the type of movement and the degree of water tightness, or by the need for the lubricant to also be a tightening agent to prevent lubricant loss or foreign substance penetration. • Since they are solid, greases do not cool nor cleanse as an oil does. Beyond these limitations, greases have virtually all the other functions of lubricating fluids. For a given application, a grease must: • provide appropriate lubrication to reduce friction and the wear of surfaces that come in contact; • protect against corrosion; • be a tightening agent by preventing the penetration of water and foreign substances; • prevent leaks, scaling and other losses from lubricated surfaces; • resist unacceptable structure or consistence changes due to mechanical constraints during prolonged use;

40. 06 - Lubricants • resist hardening which causes extra resistance to the movement of components during cold spells; • offer physical characteristics suitable for the method of application; • be compatible with elastomer joints or with other lubricated components in the mechanism; • tolerate some contamination, such as humidity, without losing its major characteristics. • Classification of greases • Greases are usually identified according to the NLGI consistency classification (National Lubricating Grease Institute). • The grades are defined as ranges of the 60‑stroke worked penetration at 25oC, as determined by ASTM penetration test.

41. 06 - Lubricants While viscosity is the basic property of a lubricating oil, consistency is that of a grease. It is expressed in terms of ductility or stiffness, that is the degree of resistance a grease opposes to deformation under an applied force.

42. 06 - Lubricants Measuring consistency Consistency is measured in terms of the penetration (tenths of a millimeter) or the depth to which a normal cone subject to gravity sinks into a sample of grease undergoing the ASTM D217 penetration test. The greater the penetration at the testing temperature, the greater the ductility of the grease. Shown to the left is a Penetrometer KEY a = dial indicator, graduated in millimeters b=penetration cone c=sample.

43. 06 - Lubricants • Penetration test: • The penetration test on a given type of grease consists in allowing a weighted metal cone to sink into the surface of the grease. The grease is classified on the basis of the depth of the indentation made by the cone, and assigned an NLGL number. • A very soft, in fact practically fluid grease, is assigned the number 0, while a very hard one, resembling a bar of soap, is given the number 6. • Soap classification • There are a number of kinds of grease which are classified according to the composition of their soap. The major kinds are: • simple soap; • mixed soap; • complex soap; • non soap; • multipurpose; • extreme pressure (EP).

44. 06 - Lubricants Simple soap greases Simple soap greases contain only one type of soap. Mixed soap greases These greases are a compromise between quality and price. For example: A mixture of calcium and sodium enhances water resistance (calcium) and performance at high temperature (sodium).

45. 06 - Lubricants • Complex soap greases • These greases resist oxidation and softening at high temperatures. • Non Soap greases • These greases can function in the presence of acids (Ph < 7) and alkalines (Ph > 7). They are made with special thickeners such as: • carbon black • silica gel • alkyd ureas • modified clays • NOTE: Water has a Ph of 7.

46. 06 - Lubricants • Multipurpose greases - These greases are designed for use on a number of machines with different greasing processes. They help bring costs down, for example, the properties of complex soap greases with lithium are: • extreme pressure • anti-wear • resistance to oxidation • resistance to shearing • wide range of temperatures, under both humid and dry conditions • Extreme pressure greases • These greases are used when unit pressures are high or shock loads may be encountered. Agents used for such greases are chlorine, sulphur or phosphorus. • Compatibility of greases • The compatibility of greases is determined case by case. It usually increases as temperatures do. Compatibility exists when two kinds of greases can be mixed without giving rise to problems. See the following chart for examples.

47. 06 - Lubricants Major properties of greases Dropping point - The temperature at which it switches from the semisolid form to the liquid form. This is an important test which helps decide on the type of grease to use for a specific application.

48. 06 - Lubricants Pumpability - The lowest temperature at which a grease remains pumpable. Grease is useless if it remains rigid at operating temperatures. Consistency - Measures the oiliness or hardness, or the resistance to deformation of grease when a force is applied. Resistance to shearing - The capacity of an oil to maintain its consistency under mechanical constraints. As speed increases, the structure of the grease changes to the point that its consistency is modified. Bleeding - It is used to determine the percentage of oil which separates, at rest, from its soap base. It does not measure the separation under dynamic conditions. High temperature stability - The capacity to maintain its consistency, structure, and performance under high temperatures. Resistance to oxidation - The capacity of a grease to resist to chemical reactions involving oxygen. Oxidized oils contain waterproof resins which darken greases and can make them corrosive for certain metals; Low temperature pumping - The capacity of a grease to flow and ensure proper lubrication under low temperature operation.

49. 06 - Lubricants Wear resistance - The capacity of a grease to protect against abrasion stemming from metal-to-metal contact under overload conditions. Extreme pressure - The capacity to protect metallic surfaces, while they are sliding against one another and bearing heavy loads, against seizure, thus against wear. Resistance to water - Under homogenizing conditions, water can severely alter oil structure and will dilute and liquefy the grease. In such cases, grease should include some calcium or lithium soap which will not dissolve in water. Resistance to corrosion - The capacity to protect surfaces against the chemical attacks of water or other contaminants.

50. 06 - Lubricants • Comparative advantages of oils and greases • Advantages of oil • It humidifies surfaces because of its fluidity; • it can remove contaminants and dirt (with filters); • it evacuates heat produced by bearings; • it is ideally suited for lubrication. • Advantages of grease • It simplifies the design on component housings; • it does not require reapplication as often; • it does a better job of keeping contaminants out; • it slowly releases the liquid lubricant, thus reducing friction and wear; • it protects against water and abrasives; • it maintains its consistency under mechanical stress; • it sticks to mechanical components; • it protects against corrosion; • it enhances water tightness.