Chat with us, powered by LiveChat All material surfaces, harder or softer, have many irregularities in the form of asperities (Peaks) and valleys. When two solid surfaces are pressed over each other, the asperities of both | WriteDen

All material surfaces, harder or softer, have many irregularities in the form of asperities (Peaks) and valleys. When two solid surfaces are pressed over each other, the asperities of both

electrical engineering question

lubrlubricant testing
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Program : B.Tech Subject Name: Engineering Chemistry Subject Code: BT-101 Semester: 1st
ENGINEERING CHEMISTRY (BT-101) NOTES UNIT III: LUBRICANTS & LUBRICATION INTRODUCTION: All material surfaces, harder or softer, have many irregularities in the form of asperities (Peaks) and valleys. When two solid surfaces are pressed over each other, the asperities of both the upper surface and lower surface come in contact with each other, it causes some deformation effect on the metal surface which is more in case of ductile metals. This contact causes the weed junction which carries all the loads between the two surfaces. Thus, the true area of contact is only a small fraction of the apparent contact area between the two surfaces. Friction is the relative movement of two surfaces in contact with each other. Generally, there are two types of friction encountered, (i) sliding friction and (ii) rolling friction. Surface wear during sliding is due to shearing of asperities (i) Sliding friction: The friction caused by the sliding two materials of different hardness over one another. Due to this sliding, the peaks of the softer metal gets broken easily then the peaks of the harder metals. The effects of the sliding friction are: (a) Ploughing i.e., cutting out the softer material by the asperities of the harder materials. (b) The interlocking of the surface irregularities. (ii) Rolling friction: It occurs when a load sphere or cylinder rolls over a flat surface of the other body. The coefficient of the rolling friction is usually very low as compared to the sliding friction. Thus, the effect of rolling friction is much lower than the sliding friction, as the effect of rolling friction is caused by elastic deformation of the two surfaces. In case of sliding friction, the coefficient of friction is much larger in static condition than for the kinetic condition. Therefore, the lubricant plays less important role in case of rolling friction than the sliding friction. In case of any friction a considerable amount of frictional heat is released at the rubbing surfaces which is more in case of sliding friction as the contact area of this friction is more. The frictional heat is not uniformly distributed over apparent contact area between the rubbing materials but it is highly localized, particularly at the surface asperities. If this frictional heat reaches the melting temperature of the material, welded junction may be formed. The amount of frictional heat depends upon the nature of the sliding material and the speed of the sliding. Lubricant- A substance which is introduced between two relatively moving surfaces for reducing friction and wear is called lubricants. The process of reducing frictional resistance between moving surfaces by the application of lubricants is called lubrication. Functions of Lubricants: 1. It reduces the loss of energy in the form of heat. 2. It increases the efficiency of machine. 3. It efficiently prevents the interlocking or inter-joints welding at the surface asperities. 4. It increases the smooth motion of the moving parts. 5. It reduces the surface deformation, wear and tear. 6. It reduces the expansion of metal by local frictional heat. 7. It protects the materials from corrosion. 8. Sometimes it stops the leakage of gases or pressures from the cylinder. Mechanisms of Lubrication:- There are mainly three types of mechanism of lubrication. They are: 1. Fluid film or hydrodynamic lubrication. 2. Thin film or boundary lubrication. Downloaded from be.rgpvnotes.inPage no: 1Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES 3. Extreme pressure lubrication. (1) Fluid film or hydrodynamic lubrication: In this lubrication, two moving surfaces are separated from each other by a thick film of lubricating oil 0 (thickness around 1000A0).Hence it prevents the direct contact between these rubbing surfaces and welding of junctions generally does not occur. This happens because, the lubricating oil cover the irregularities of the Sliding surfaces & forms a thick layer in between them, so that there is no direct contact between the material surfaces. Actually the shaft floats in the lubricant. The resistance to movement of moving parts is only due to the internal resistance between the particles of the lubricant moving over each other. Based on this principle, the lubricant chosen should have low viscosity. Selection of lubricant: In order to maintain a suitable viscosity of the oil, ordinary hydrocarbon lubricants are blended with long chain polymers. At operating condition, hydrocarbon petroleum fractions. Generally contain small quantities of unsaturated hydrocarbons, which get oxidized to form gummy products. To reduce the antioxidants like amino phenols are added. This type of hydrodynamic lubrication gives satisfactory results as the coefficient of friction in such cases is very low. Hydrodynamic friction occurs in the case of a shaft running at a fair speed with a low load. (ii) Boundary lubrication or thin film lubrication: It is done when a thick fluid film cannot be maintained between the two moving surfaces so that direct metal to metal contact is possible. This happens when (i) the viscosity of the oil is low (ii) the load is very high (iii) the speed of the movement is very low and (iv) a shaft starts moving from rest. Under such conditions, the lubricant should be adsorbed physically or chemically on both the metallic surfaces. These adsorbed lubricant layers avoid the direct metal to metal contact. The coefficient of friction in these cases is slightly more than hydrodynamic lubrication. In boundary lubrication, surface asperities contact each other even though the lubricant supports much of the load. Friction depends mainly on the shearing forces necessary to cleave these adhering asperities and wear and friction can be reduced by certain additives. Wear inhibitors and lubricity agents are polar materials that adsorb on a metal and provide a film that reduces metal-to-metal contact. Condition of lubricants: The lubricant used for boundary lubrication should have: (1) Long hydrocarbon chains. (2) Lateral attraction between the chains. (3) Polar groups to promote spreading and orientation over the metallic surfaces at high pressure. (4) Active groups to form chemical bonds with metallic surfaces. In this boundary lubrication the metal surfaces are closer to each other, but still they are well separated by the lubricant. The property of the oil which enhances the adsorption and maintenance of the thin film is called oiliness. High viscosity index, resistance to heat and oxidation, good oiliness and low pour Downloaded from be.rgpvnotes.inPage no: 2Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES point are some of the good qualities of boundary lubricants. Boundary lubrication (i.e., the boundary friction) boundary lubrication is the lubricant from the friction surfaces between the molecules and the internal friction between molecules (i.e., liquid lubrication) the transition to direct contact with the surface friction before the critical state. At this time there is a layer of friction interface adsorption film thickness is typically about 0.1μm, with some lubrication. We call this layer of thin boundary film. Boundary lubrication film depends on the nature of the friction surface; depends on the oil lubricant additives, extreme pressure additives on the friction surface of the metal structure of the boundary film formation with the oil viscosity has little mouth. Generally vegetable and animals oils have all the above mentioned good qualities of lubricant. They are adsorbed (physically or chemically) easily on the, metal surfaces with the active group of -COOH. But they tend to break down at high temperatures. In order to improve the oiliness of the mineral oils, usually little fatty acids are added. (iii) Extreme pressure lubrications: Extreme pressure lubrication are a special case of boundary lubrication, friction is Deputy Commissioner in the override (or high contact stress), speed, temperature conditions, extreme pressure lubricant additives react with the metal friction surface generate a chemical reaction film, separated the two friction surfaces, and play a lower coefficient of friction, reduce wear and tear (or change the direct contact with the metal surface of serious wear and tear), to the role of lubrication, it is called extreme pressure lubrication. When the moving surfaces are under very high pressure and speed, the lubricant may decompose or vaporize or they may not stick on the surfaces because high local temperature is produced. To meet these extreme pressure conditions, special additives called “extreme pressure additives” are added to the mineral oils. Extreme pressure additives are compounds having active groups such as chlorine (chlorinated esters), sulphur (sulphurised oils) and phosphorus (tricresyl, phosphate). At high temperatures, they react with metal giving surface layers like metallic chlorides, sulphides or phosphides. These surface layers have high melting point and serve as good lubricant under extreme pressure and temperature conditions. Extreme pressure (EP) additives are a special class of boundary lubrication additive which react with the metal surface to form compounds with lower shear strength than the metal. Classification of Lubricants:- Lubricants may be broadly classified, on the basis of their physical state as: 1. Liquid Lubricants. (a) Vegetable oils and animals oils. (b) Mineral oils from petroleum. (c) Blended oils or doped oils or compound oils. (d) Synthetic oils. 2. Semi solid lubricants. 3. Solid lubricants. Lubricating Oils/ Liquid lubricants: (a) Vegetable or animal oils: These are most commonly used lubricants. They possess good oiliness and adsorb themselves on the metallic surfaces. However, they decompose at high temperatures and undergo oxidation easy, forming gummy and -acidic hydrolyzed products and get thickened on coming in contact with air. Thereby restricting the smooth movement of the moving surfaces. To overcome such restrictions, usually they are blended with mineral oils (blending agents). (b) Mineral oils: They are obtained by fractional distillation of petroleum. They are the heavier fractions containing long chain hydrocarbons in petroleum oils ranging between 12 to 50 carbon atoms. The shorter chain oils have lower viscosity than the longer chain hydrocarbons. They are widely used as Downloaded from be.rgpvnotes.inPage no: 3Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES lubricants as they possess good stability under service conditions but poor oiliness. The oiliness of these oils can be improved by adding oils like oleic, stearic acids etc. They have impurities like sulphur compounds, gum forming alkenes, asphalt, waxy impurities, other color impurities, reluctant and some other unwanted impurities. All these impurities should be removed to prevent the formation of corrosive and gummy products to decrease the friction. Removal of impurities: A number of processes are used for removing these undesired impurities as follows: (i) Solvent refining: Sulphur compounds, alkenes and other gum products can be removed by this process. In this process, the oil is mixed with a suitable solvent like phenol which is immiscible with oils. But the undesirable impurities are highly soluble in phenol, thereby the liquid separates into two layers (oil goes up and phenol comes down). Oil layer is free from impurities but containing some solvents and the solvent layer contains the impurities. Then the oil layer is distilled out and some additives may be added to improve the lubricating quality of the oil. (ii) Dewaxing: Waxy impurities are removed by treating the lubricants with suitable solvents like propane and then the wax solution is cooled. The wax precipitates, which is removed from the oil by passing the oil wax suspension through a filter. The solvent present in the oil is then recovered by distillation. (iii) Filtration: The colored impurities can be removed by filtration through bauxite or clay. (iv) Acid refining: Sometimes the dewaxed oils contain a number of undesirable impurities. To eliminate these impurities, the dewaxed-oil is treated with concentrated H2SO4 and then agitated so that the impurities dissolve in acid and it is filtered out. This filtrate is neutralized by adding a calculated amount of a base NaOH. (c) Blended lubricating oils: Single oil cannot possess all the good qualities of the lubrication. Therefore to get the satisfactory lubricant with desirable characteristics, specific additives are blended with the oil. These are called blended oils. An additive is a material that imparts a new or desired properties to the lubricating oil It may also enhance a desirable property that the lubricating oil already possess to some degree. Broadly, there are two types of additives chemically active additive & chemically inert additives. Chemically active additive are those which chemically interact with metals (to form protective films) .dispersant, detergents, extreme pressure agents, etc. Chemically inert additives are those additives which improve the physical properties that are critical to the effective performance of the lubricant. Like viscosity index improver, foam inhibitors etc. Greases or Semi solid lubricants:- The most important semisolid lubricants are Greases and Vaseline. Grease: Grease is used to lubricate journal bearings when cooling of the bearing is not a factor, typically if the bearing operates at relatively low speeds. Grease is also beneficial if shock loading occurs or if the bearing frequently starts and stops or reverses direction. Grease is almost always used to lubricate pins and bushings because it provides a thicker lubricant than oil to support static loads and to protect against vibration and shock-loading that are common in many of these applications. Lithium soap or lithium complex thickeners are the most common thickeners used in greases and are excellent for most journal bearing applications. Grease is a semisolid combination of a petroleum product and soap. It is obtained by saponification of fat (fatty acids etc.) with alkali like NaOH followed by adding hot Lubricating oil under agitation. The amount of mineral oil added determines the consistency of the finished grease. Soaps are gelling agents which can interconnect with the added oil. Therefore, the structure of the lubricating greases is like gel. Downloaded from be.rgpvnotes.inPage no: 4Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES Soaps dissolve in the oil at higher temperatures so that the interconnecting bonds will be broken out and the grease liquefies. To improve the heat resistance of grease; inorganic solid thickening agents like clay, colloidal silica, carbon black etc. are added to it. Advantages of greases: 1. Greases have higher frictional resistance than oil. 2. Because of the presence of soap in oil, greases stick well on the surfaces. 3. Greases are used in situations where oil film cannot be remaining in its position machine working under high pressures at slow speed. 4. Greases can support heavier load at low speed. 5. Greases can be used in bearing and gears that work at high temperatures. 6. They are used in situations where sealing is necessary against entry of dust, dirt, grit or moisture. 7. Greases are used in situations, where dripping or spurting of oil is undesirable; therefore it can be used in textile and good products manufacturing industries. 8. They also do not require much attention as oils. Disadvantages of greases: l. They have high co-efficient of friction. 2 They have a tendency to separate into oils and soaps. . 3. On long use, oil in the grease may evaporate. 4. Greases cannot effectively dissipate heat from the bearing. Greases are classified based on the soap used in their manufacture as below: (a) Lime or calcium soap grease or cup greases: They are the emulsions of petroleum oil with calcium soaps. They are insoluble in water, so water resistant. Above 65?C they cannot be used because oil and soap separates out above this temperature. They are widely used as they are the cheapest. (b) Sodium soap greases: They are sodium soaps dispersed in petroleum oils. They are water soluble, so they are not water resistant. They can be used up to 1750 C because of its high melting point and fibrous structure. They are suitable for use where the lubricants get heated due to friction. (c) Lithium soap greases: They are petroleum oils, thickened by mixing lithium soaps. They are water resistant, high temperature withstanding, good mechanical stability and low oxidation tendency. They are suitable for use at low temperature about 15?C only. They are used in multipurpose. (d) Aluminum soap greases: They are aluminum soaps dispersed in oils. Due to its low soap content, they are water proof. They cannot be used above 90?C. (e) Axle greases: They are the resin greases. They are separated by adding slaked lime to the mixture of soluble resin oil and fatty oils. They are allowed to react at 58?C. The mixture is thoroughly mixed and allowed to stand, when grease flats as stiff mass called cold set grease. Filters like talc and mica are also added to these greases. They are water resistant and suitable for use as axle greases and for heavy equipments. Solid Lubricants: Solid lubrication between the friction surface materials into the solid lubricant powder also can play a good lubricating effect. Friction between the two surfaces of solid lubricant, its shear resistance is very small, slight external force, will have a slip between molecules. This put the two outside the friction between the grinding into a solid lubricant in friction between molecules. There are two necessary conditions for solid lubricant, the first is a solid lubricant molecules should have a low shear strength, it is easy to slip; followed with solid lubricant to the friction surface has a strong affinity, in the friction process, always has maintained that the surface friction layer of solid lubricant, and a layer of solid lubricant which does not corrode the surface friction. Generally attached to the metal surface, a mechanical, but there are also form a chemical combination. The nature of the solid material with many, such as graphite, molybdenum disulfide, talc and so on. For non-layered structure for the Downloaded from be.rgpvnotes.inPage no: 5Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES solid lubricant, or soft metal, mainly for its low shear stress, play a role of lubrication, then it attached to the friction surface lubricating film. For the already formed solid lubricating film lubrication mechanism of boundary lubrication mechanism can explain the lubrication approximation. The two most usual solid lubricants employed are graphite and molybdenum disulphide. These lubricants are used either in the dry powder form or mixed with water or oil. The solids fill up the low spots in the surfaces of moving parts and form solid films, which have low frictional resistance. The usual coefficient of friction between solid-lubricants is between 0.005 and 0.01. Advantages of solid lubricants: l. They are used in heavy machineries working at very high loads and slow speeds. 2. The operating temperature is too high. 3. Liquid lubricants and greases are easily contaminated with dust which is unaccountable, for example, in commutator blades of electric motors and generators, because proper films cannot be maintained. 4. Combustible lubricants must be avoided. l. Graphite: Graphite is most widely used of all solid lubricants. In graphite, carbon atoms are arranged in hexagons in several flat layers, which are held together by only weak bonds so that the force to shear the crystals parallel to the layers is low. Each carbon atom in a layer is surrounded by three other carbon atoms. Lubricating action of graphite: It is very soapy, non flammable graphite is mainly used at high temperature in the absence of air and high pressures. Graphite is used either in dry powder form or dispersed in oil (oil dag) or in water (aqua dag) or as graphite grease. Oil dag is found particularly useful in IC engines, because it forms a film between the piston rings and the cylinder and gives a tight fit contact, thereby increasing compression. Water dag is used in food industries, where a lubricant free from oil is needed. Graphite grease is used at high temperature. Uses: It is used as lubricant in air compressors, lathes, general machine-shop works, food stuffs industry, railway track joints etc. 2. Molybdenum disulphide: It has sandwich like structure ‘Mo’ and ‘S’ are separately arranged in different layers and are sandwiched alternatively. Lubricating action of molybdenum disulphide: Poor inter laminar attraction is responsible for low shear strength in a direction parallel to the layers. It is stable up to 400?C and is used at high temperatures. It possesses very low coefficient of friction. It can be used as a dry powder or oil-dag or aqua-dag or grease. A solid film made from 70% MoS2, 7% graphite and 23% silicate is used in space vehicles which can withstand high temperature and even nuclear radiation. The other commonly used solid lubricants are talc, mica, soap stone etc. Teflon acts as a lubricant in gear pumps, periscope etc. Synthetic Lubricants: These are synthesized specially to meet the severe operating conditions. The synthetic lubricants can perform well over a wide range of temperatures from-50″C upto260″C.These lubricants possess low freezing points, high viscosity index and non flammable. Polyalkene glycols, silicones, chlorinated and fluorinated hydrocarbons; organic amines, imines and oxides are the important synthetic oils. Advantages of synthetic lubricants 1. They possess high thermal stability at high operating temperatures. 2. They have viscosity index and high flash points. 3. They are chemically stable and having low freezing points. Downloaded from be.rgpvnotes.inPage no: 6Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES (a) Polyalkene glycols: Polyalkene glycols like polyethylene glycol, poly-propylene glycol etc. can be used as both water soluble and water insoluble lubricants in rubber bearings and joints. They have all the three advantages mentioned above. (b) Silicones: These synthetic lubricants are not oxidized below 2000C and possess high viscosity index. At temperature above 2000C, silicones are oxidized quickly and undergo cracking process at about 230?C. Therefore such lubricants are used for low temperature lubrication purposes but not employed for high temperature applications. (c) Chlorinated and fluorinated hydrocarbons: They are not decomposed by heat, not easily oxidisable and chemically inert and resistant to chemicals etc. (d) Organic amines: They are good synthetic lubricants, since they possess low pour points and high viscosity index. They can be used under temperature conditions of -50″C to 250″C. Lubricating Emulsions: – An emulsion is a heterogeneous system consists of disperse phase and dispersion medium. In this emulsion, the two phases are immiscible liquids. The liquid being dispersed as fine droplets (dispersed phase) into a fairly coarse dispersion medium. The size of dispersed phase should be within the range of l micron to 6 micron. As the two immiscible liquids is inherently unstable, it is prepared by vigorous stirring and addition of emulsifier or emulsifying agent to make it more stable. The emulsifying agents contain polar and non- polar groups and they are classified as hydrophilic end and hydrophobic end depending on their affinity towards water molecule. The hydrophilic end emulsions have greater affinity towards water while the hydrophobic ends do not have any affinity towards water, rather they are preferred to wet by oil. The emulsifier molecule is adsorbed at the interface of the two phases, resulting in formation of a protective film around the dispersed droplet. For example, soaps of different types, detergents, long chain sulphonic acids, lyophillic colloids etc. act as emulsifying agents in different cases. A certain large number of droplets of a liquid into another liquid increases the surface area and hence requires large amount of energy. The required energy would be less if the surface tension is decreased. The function of the emulsifying agents is to diminish the surface tension. Emulsions are broadly classified into two types (I) Oil in water type in which the disperse phase is the oil in water medium (2) Water in oil type in which water droplets are dispersed in oil. The type of emulsion produced depends upon the nature of the emulsifying agents used. For example, when sodium oleate is used as an emulsifier, oil in water emulsion is formed. But if soap with a bivalent cation is employed, say calcium oleate, water in oil type emulsion is obtained. In order to ascertain the type of given emulsion, a small quantity of water is added with stirring and the effect is observed under a microscope. If the emulsion is oil in water type, water would mix freely with the excess medium, the droplets remaining undisturbed. If it is water in oil type, the addition of oil to the emulsion would produce similar effect. Properties and Testing of lubricating oils 1. Viscosity and Viscosity index 2. Flash Point and Fire Point 3. Cloud Point and Pour Point 4. Aniline Point 5. Steam Emulsion Number 6. Neutralization Number 7. Saponification Number 8. Iodine value 9. Carbon residue Downloaded from be.rgpvnotes.inPage no: 7Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES 1. VISCOSITY: – It is the property of a fluid that determines its resistance to flow. It is an indicator of flowability of a lubricating oil, the lower the viscosity, greater the flowability. It is mainly, due to the forces of cohesion between the molecules of lubricating oil. Absolute viscosity may be defined as “the tangential force per unit area which is required to maintain a unit velocity gradient between two parallel layers; It is denoted by eta (η). Its unit in C.G.S. System is poise and its dimensions are ML-1T -1 Absolute Kinematic viscosity is the ratio of absolute viscosity to ‘density for any fluid. It is denoted by v. Its unit in C.G.S. system is stokes and its dimensions are L 2 T-1 Effect of temperature on viscosity. Like any other fluid, viscosity of lubricating oil is inversely proportional to temperature. i.e., with increase of temperature, viscosity decreases. This is due to the decreases in intermolecular attraction. At higher temperatures oils must have sufficient viscosity to carry loads. Hence, heavier oils are used at higher temperatures. Similarly, light oils are used at low ambient temperatures. Effect of pressure on Viscosity Lubricating oils are subjected to extreme pressure at the interface between gears and between rolling element and race in a rolling bearing.. At such high pressures, viscosity of lubricating oils increases considerably. Significance of Viscosity. Viscosity helps in the selection of good Lubricating oil. For instance, Light oils have low densities and easy f’lowability. These oils i.e., generally used on parts moving at high speed promotes the formation of a good oil film. Moreover, light oils do not impose much drag on high-speed parts. Diagram (from manual): In contrast, Heavy oils are used on parts moving at slow speed under heavy loads as they resist being squeeze out. Light oils are not suitable in this case as they have low viscosities and it is not possible to maintain lubricant film between the moving surfaces. Subsequently, excessive wear will occur. To sum up, in hydrodynamic lubrication, that lubricant is selected which should have a sufficient high viscosity to adhere to the bearing and resist being squeeze out due to high pressure and get fluid enough to resist excessive friction due to the shearing of oil itself. Thinner oil can easily dissipate the frictional heat because of good oil circulation. Measurement of viscosity of lubricating oil There are many instruments for measuring viscosity and are known as viscometers (or viscosity meters). For examples, Kinematic& Saybolt universal viscometers used in the United States and the Redwood viscometers are commonly used in England. The Saybolt Viscometer It consists of cylindrical brass cup in the bottom of which is an orifice of specified dimension. This cup is surrounded by constant temperature oil both. A desired bath temperature can be obtained by adjusting the temperature regulator. When the sample of lubricating oil reaches test temperature. The time required for 60 mL of the oil to run through the orifice is measured. The oil sample flow by gravity under a standard falling head and at a temperature of 100?F and 210? F. A calibrated standard flask collects the liquid sample. The time of efflux is measured in seconds and are reported as Saybolt Universal Seconds (SUS); for example, 260 SUS, at 100? F. For heavy lubricating oi1s with high viscosities, a large orifice is used in the same apparatus, and the results are reported in Saybolt Furol Seconds (SFS) at a Specified temperature. The kinematic Viscometer It is a U-type of glass apparatus having respectively cone and two bulbs at its two sides. At the bottom portion of two bulb side, capillary tube is attached. It is used for the determination of Kinematic Downloaded from be.rgpvnotes.inPage no: 8Follow us on facebook to get real-time updates from RGPV
ENGINEERING CHEMISTRY (BT-101) NOTES viscosity. The four simple measurements steps are shown. For a fixed volume of sample, time is measured for the sample to flow through a calibrated capillary under an accurately reproducible head of liquid and at a constant temperature. From the measured efflux time, the kinematic viscosity is calculated. Kinematic viscosity in centistokes (CST) = C x t Where C = Viscometer constant and. t = Observed flow time in seconds. The Redwood Viscometer: It is of two types: (a) Redwood viscosity No. I-Universal and (b) Redwood viscosity No.2-Admiralty. The essential differences between the two are: (a) (b) Dimensions of Orifice. Length: 10 mm Diameter: 1.62 mm 50 mm 3.80 mm Useful for Low viscous oils Higher viscous oils Receiving flask has Smaller mouth Larger mouth The Redwood No. 1 apparatus consists of a cylindrical brass oil cup (90mm in height and 46.5 mm in diameter) that holds the test sample of lubricating oil. Bottom of the oil cup is fitted with a polished-agate discharge tube containing an orifice of specified dimension. The oil cup is surrounded by water bath for adjusting the temperature. A calibrated receiving flask (known as Kohlrausch flask) is provided for receiving the oil from polished-agate discharge tube. It is shown in when the sample reaches test temperature the time for 50mL of the sample flow through the orifice is measured. Results are reported in seconds. For example, Redwood Viscosity No. 1 at 1400F, 350 seconds. Conversion Formulas: Let time of efflux =t seconds, Saybolt: cSt = 0.22 t – 180ft Redwood: cSt =0.26 t -171ft. Significance of viscosity measurements. Viscosity is the property of lubricating oil that determines its ability to lubricate. Viscosity values are used in evaluating load carrying capacity, in denoting the effect of temperature changes, for establishing uniformity in shipments and for determining the presence of contaminants in used oil during absolute Viscosity values are required for use in all-bearing design calculations and other lubrication Engg. Technical design problems. Kinematic values are applied in oil blending procedures. Viscosity Index -With changes in temperature, the viscosity of lubricating oil varies, the higher the temperature, the lower the viscosity and vice-versa. The rate of variation of Viscosity with temperature is different for different base oils or fluids. For example, in petroleum oils, the viscosities of naphthenic base oils vary more over the same temperature range than those of paraffinic base oils. The rate at which the viscosity of oil changes with temperature i


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