Chapter- 5 Grease Formulations

Transcription

1 Chapter- 5 Grease Formulations

2 5. INTRODUCTION Contribution of the chapter is toward the application part related to the work apportioned in chapter-3 that is application of depolymerized products (considered as polyols) in the synthesis of lubricant (grease). And the main parameters that encourage us to do this successful attempt are discussed here. The first one is that the lots of attempt made to depolymerize the PET materials and further trans esterify it with variety of oils and considering it as polyols are shown as its application in synthesizing of products such as PU adhesive [1], waterborne polyurethane adhesives [2], urethane oil varnishes[3], foams [4], Epoxy resin [5], etc. and majority of them are focused on the PU based system only. Thus the trend of utilizing depolymerized material (polyol) in polymers application makes us to think to utilize these materials in divers field rather than in different polymer synthesis. On the other hand we found that the lubricating market is now days demanding substitution of petro-based materials preferably by naturalbased renewable one. This becomes the second important parameter for this successful attempt. The third and most valid parameter that makes us select this work is the castor oil, which is the natural, renewable and having inherent lubricity thus all the depolymerized product of chapter-3 having these properties and that can be used in lubricating field as considering base oil. 236

3 5.1 Introduction Lubricants Lubricants are one of the important products derived from crude petroleum. Thought the percentage yield of the lubricating fractions from crude petroleum is relatively low, their value is far greater in terms of their essentiality to industry and other sectors of the economy. Lubricating oils and greases are essential for the proper functioning of nearly every machine, equipment and instruments and their importance cannot be overemphasized. A lubricant is an agent employed for reducing friction and preventing wear between two rubbing solid surfaces where fraction is the resistance that offered due to this mutual rubbing between the parts, while result in loss of material from the surface due to abrasion is termed as wear. It should be noted that friction is not a definite invariable quantity. It depends on load, speed and nature of material. Wear can be minimized by modifying the surface properties of solids by one or more of surface engineering processes or by use of lubricants. The main purpose of a lubricant is to keep the moving/sliding surfaces apart, so that friction and consequent destruction of material is minimized. Apart from the main function a lubricant may also perform various other supplementary functions such as temperature control by conducting away the heat of frication, removal of contaminants, corrosion and rust prevention, elimination of gum and sludge formation, electrical insulation, power transmission, shock reduction and sealing to prevent loss of pressure or entry of dust. [6-11] 237

4 Lubrication is the process, or technique of reducing wear of one or both surfaces in close proximity, which are in motion relative to each another. This can be done by interposing a substance called lubricant between the surfaces to carry or help to carry the load between the opposing surfaces. The lubrication of two surfaces moving relative to each other depends upon a number of factors like load, relative velocity of the surfaces, geometry of the surfaces, physical and chemical properties of lubricants and the metals out of which the surfaces are made. The main purposes of lubrication are (i) to reduce wear and prevent heat loss that results due to contact of surfaces in motion, (ii) to protect it from corrosion and reduce oxidation; (iii) to act as an insulator in transformer applications; and (iv) to act as a sealing agent against dirt, dust, and water. While wear and heat cannot be completely eliminated, they can be reduced to negligible or acceptable levels by the use of lubricants. Because as heat and wear are associated with friction, both effects can be minimized by reducing the coefficient of friction between the contacting surfaces. Any material used to reduce friction in this way is a lubricant. [12-16] Lubricants constitute of more than 600 products within a wide range of viscosities and hence the lubrication sector strives to develop various upgraded products through extensive research and development. Lubricant development is a multidisciplinary work that includes expertise in various fields such as surface science, physics, metallurgy, chemical/mechanical/ automobile engineering, and polymer science and also requires good teamwork to make a sustainable product. 238

5 5.2 Type of Lubricants A lubricant may be in the form of a liquid, semi-solid, solid or gas. The liquid lubricants include petroleum oils, fatty oils, synthetic fluids and emulsion. Semi-solid lubricants are known by the name of greases. Solid lubricants include molybdenum disulfide, graphite powder, tungsten disulfide powder, boron nitride, phenanthrene, copper phthalocynainde, and metal films of gallium, indium, thallium, lead, tin, gold and silver. Many gases such as air, hydrogen, helium, nitrogen, oxygen, uranium hexafluoride, carbon dioxide and argon have been used as lubricants. The lubricants which are major commercial interest and values are usually liquids or greases. However, a variety of solids and some gases are also used as lubricants in specialized application where the conventional liquid and greases are not suitable. The solid substances in combination with the more conventional liquid lubricants provide additional properties or enhance the original properties such as lubricity oiliness and load carrying ability of the standard lubricant. These substances may either assume the primary role of lubrication where the liquid lubricant with which they are compounded serve only in the secondary role Solid lubricants [17-22] Dry lubricants or solid lubricants are materials which despite being in the solid phase are able to reduce friction between two surfaces sliding against each other without the need for a liquid oil medium. A solid lubricant is a material that will separate two moving surfaces under boundary conditions and decrease the amount of wear. Solid lubricants are basically any solid material which can be 239

6 placed between two bearing surfaces and which will shear more easily under a given load than the bearing materials themselves. The coefficient of friction in dry lubrication is related to the shearing force and the bearing load. They are preferred where (1) the operating conditions are such that a lubricating film cannot be secured by the use of lubricating oils or grease (2) contamination (by the entry of dust particles) of lubricating oils or grease is unacceptable (3) the operating temperature or load is too high, even for grease to remain in position and (4) combustible lubricants must be avoided. They are used either in the dry powder form or with binders to make them stick firmly to the metal surfaces while in use. They are available as dispersions in nonvolatile carriers like soaps, fats, waxes, etc. and as soft metal films. Solid lubricants are either applied as surface coatings or as fillers in self-lubricating composites. The solid film lubricant provides the dual advantage of dry and clean lubrication and in many instances can replace the use of greases and fluid lubricants, particularly where slow sliding movements are involved. In addition solid film lubricants can be used in combination with fluid or pastes. Solid film lubricants enhance the lubrication of components in the boundary friction region, when there is no hydrodynamic lubrication and direct contact between the surfaces occurs. For convenience, the various types of solid lubricant are divided into various classes as follows: a. Structural lubricants. b. Mechanical lubricants. c. Soaps. d. Chemically active lubricants. 240

7 e. Development materials Liquid Lubricants A liquid lubricant prevents friction between moving surfaces by providing a film of lubricant between the substrates. These liquid lubricants are of animal or vegetable, mineral oil and synthetic sources Liquid lubricants are further classified as: a. Vegetable oils. b. Animal oils. c. Mineral oils. d. Blended oils. e. Synthetic oils. (a) Vegetable oils: Vegetable oils were the primary lubricants for machinery and transportation vehicles for thousands of years until the discovery of petroleum. Vegetable oils are extracted from their seeds by two methods namely solvent extraction and crushing. The extracted oil is then further purified and used for its respective purpose. Their chemical structure comprises of triglyceride of fatty acids. Vegetable oils have a property of oiliness by virtue of which they are absorbed on the tenaciously and fulfills the need of lubricant by forming a film. Research has been carried out on using vegetable oils as lubricating oil and from them: 241

8 Canola oil has been practiced as Hydraulic oils, tractor transmission fluids, metal working fluids, food grade lubes, penetrating oils and chain bar lubes while as a in grease, gear lubricant and in cosmetic application, castor oil, Soybean oil, Palm oil, Olive oil, and Rapeseed oil have been practiced. Also Jojoba oil, Crambe oil, Sunflower oil and Cuphea oil are used in application of Grease, intermediate chemicals, surfactants, diesel fuel substitutes and motor oil. (b) Animal oils: Chemically fats and oils are the same terminology but still they differ by their thermal properties. Fats tend to solidify at 20 C, while oil remains in liquid state during same temperature range. Animal oils are extracted by rendering process. In this process the oil containing tissues are broken by treatment with steam and the oil is collected. Some common animal oils are as follows. Whale oil is obtained by distillation of different parts of sperm whale flesh. It is thin pale yellow liquid having specific gravity of It is used as lubricant for light machines. Lard oil is obtained from fats, kidneys and intestines of pigs. It is colorless and used in ordinary machines for general purpose. Tallow oil is obtained by compression of cattle fat under high pressure. It is used for low speed machines working under high pressure. Neat foot oil is obtained by boiling foot of neat in water. It is a pale yellow liquid of specific gravity It is used as lubricant for delicate articles such as watches, clocks, sewing machines etc. In 18 th century it was also used medicinally as a topical application for dry scaly skin conditions. (c) Mineral oils (Petroleum oils) 242

9 They are most widely used as they are abundantly available, quite stable and fulfill the requirements for the lubrication purpose. Chemically mineral oils based lubricants comprises of chains of hydrocarbons ranging from C12-C50. Mineral oil based lubricants are obtained by distillation of crude oil under reduced pressure. The lube fractions are obtained in three classes namely the light fraction, medium fraction and heavy fraction. These fractions of oils cannot be used as such for the lubrication purpose as they contain many impurities like wax, asphalt, various colored substances and other oxidizable impurities which need to be removed before application. Wax interferes with lubricating properties as they tend to solidify at lower temperatures. Wax can be removed from lube fraction by chilling the oil fraction. The asphaltic impurities leaves carbonaceous impurities on the engine parts, asphaltic impurities can be removed by extraction with solvents. The colored impurities can be removed by filtration using Fuller s earth or activated clay. The oil has to be refined by treatment of hydrogen in presence of nickel as catalyst to remove sulfur compounds and to transform unsaturated compound into saturates. Mineral oil based lubricants are used for wide range oil application like automotive lubricants, aviation lubricants, heavy motor lubricants, hydraulic oils, tractor transmission fluids, metal working fluids, food grade lubes, penetrating oils, chain bar lubes, cutting oils, gear oils, marine lubricants etc. (d) Blended oils; No single oil serves as the most ideal lubricants and hence depending on their properties and keeping an eye on application, lubricating oils has to be tailored to make them specific for desired applications. Various additives like 243

10 anti-oxidants, anti-wear, anti-corrosion; extreme pressure additives etc. can be incorporated to improve their characteristics. Such type of derived oils as known as blended oils which confers the desired properties of lubricant required for particular machinery. (e) Synthetic oils Synthetic oils are easy to use under challenging conditions like high speed machineries, wide variation in temperature conditions, fire risk and heavy load. Synthetic oils perform even below -30 C and above 130 C. It is possible to synthesize lubricants with molecular structure that can cope with specific operating conditions. Dibasic esters, poly glycol ethers, fluoro and chloro hydrocarbons, organo phosphates, silicones and silicate esters etc. are currently used as synthetic lubricants. Di-esters derived from adipic and sebacic acids esterified with C8-C9 branched alcohols are used in jet engines and military equipment s. These lubricants work over a wide range of temperature as they have low pour point and high flash point. Phosphate esters are fire resistant and are used as hydraulic fluids. Silicates esters are used as high temperature hydraulic fluids. They have high viscosity index. [23-28] Semi-solid Lubricants [29-35] Greases are typically applied in areas where a continuous supply of oil cannot be retained, such as open bearings or gears. The modern definition of lubricating grease is it is a solid or semi-solid product obtained by the dispersion of a thickening agent in a liquid lubricant. This system may also include other ingredients that impart special properties. Grease contains mainly three ingredients i.e. base oil, thickener and additives. The majority of greases on the 244

11 market are composed of mineral oil blended with a soap thickener. Most grease produced today use mineral oil as their fluid components. These mineral oilbased greases typically provide satisfactory performance in most industrial applications. The thickener gives grease its characteristic consistency and is sometimes thought of as a three-dimensional fibrous network or sponge that holds the oil in place. Additives enhance performance and protect the grease and lubricated surfaces. (a) Base Oil: Most grease produced today use mineral oil as their fluid components. These mineral oil-based greases typically provide satisfactory performance in most industrial applications. There are five specific categories of base oils. These categories define the type of base stock the oil is formulated from. The categories are as follows. i. Group I: Group 1base oils are the least refined of all the groups. They are usually a mix of different hydrocarbon chains with little or no uniformity. While some automotive oils on the market use Group I stocks, it s generally used in less demanding applications. Group I base stocks contain less than 90 percent saturates and/or greater than.03 percent sulfur and have viscosity index greater than or equal to 80 and less than 120. ii. Group II: Group II base oils are common in mineral based motor oils currently available on the market. It have fair to good performance in lubricating properties such as volatility, oxidative stability and flash/fire points. It gives fair performance in 245

12 areas such as pour point, cold crank viscosity and extreme pressure wear. Group II base stocks contain greater than or equal to 90 percent saturates and less than or equal to.03 percent sulfur and have viscosity index greater than or equal to 80 and less than 120. iii. Group III Group III base oils are subjected to the highest level of mineral oil refining of the base oil groups. Although it is not chemically engineered, it offers good performance in a wide range of attributes as well as good molecular uniformity and stability. They are commonly mixed with additives and marketed as synthetic or semi-synthetic products. Group III base oils have become more common in America in the last decade. Group III base stocks contain greater than or equal to 90 percent saturates and less than or equal to.03percent sulfur and have viscosity index greater than or equal to 120. iv. Group IV Group IV base oils are chemically engineered synthetic base stocks. Poly alpha olefins (PAO's) are a common example of a synthetic base stock. Synthetics, when combined with additives, offer excellent performance over a wide range of lubricating properties. They have very stable chemical compositions and highly uniform molecular chains. Group IV base oils are becoming more common in synthetic and synthetic-blend products for automotive and industrial applications. v. Group V Group V base oils are used mainly in the creation of oil additives. Esters and poly esters are both common Group V base oils used in the formulation of oil 246

13 additives. Group V oils are generally not used as base oils themselves, but add beneficial properties to other base oils. Most grease is formulated using Group I and II mineral oil base stocks, which are appropriate for most applications. However, there are applications that might benefit from the use of synthetic base oil. Such applications include high or low operating temperatures, a wide ambient temperature range, or any application where extended re-lubrication intervals are desired. (b) Thickeners: Lubricating greases has very complex structure and can comprise of varieties of components depending on the application. Nevertheless the most important component in lubricating grease is the thickener. The thickener consist various metal soaps of Li, Na, Ca, Ba, Al, etc. Non-soap thickeners include carbon black, silica gel, poly-urea and other synthetic polymers, clays, etc. The primary objective of the thickener is to supply a solid structure to keep its consistency during non-operating conditions but it also provides mechanical stability to the grease both over time and under the influence of different forces e.g. shear stress. (c) Additives: Lubricating greases of today are, as mentioned before, based on scientific grounds and almost all greases contains some form of additive viz. anti-wear, extreme pressure, corrosion inhibitor, friction reducers, drop point enhancer, anti-oxidants, tackifiers etc. Additives contribute with the final touch to the grease in terms of optimal performance. The most important feature of additives is solubility and compatibility with the base oil. Depending on the compatibility 247

14 the formulated grease shows the desired property. Some lubricating greases demands active additives on the metal surface to compete with polar molecules in the soap structure. 5.3 Mechanism of Lubricants When two metal surfaces come in contact with each other, bonds between atoms of both surfaces are established and adhesion takes place. If a roughness of one metal is slid across a flat surface of the other the adhesion between them can lead to transfer of material from one to the other, the process known as adhesive wear and is the most pervasive wear process which can never be eliminated [36]. Lubricants are applied on such working which minimizes the contact area between the metal surfaces. The mechanism of a lubricating surface can be classified in three types: Thick-film lubrication Thin-film lubrication Extreme pressure lubrication Thick-Film Lubrication It is also known as fluid-film lubrication or hydrodynamic lubrication. In this type of mechanism one of the rubbing surfaces is slightly displaced in relation to the other and a wedge shaped film of the lubricant is formed between the two surfaces rubbing each other against each other. Thus, the pressure developed in the wedge shaped film supports the load and prevents the direct contact between the rubbing surfaces. The lubricating film fills the surface irregularities of the sliding surfaces and forms a thick layer between them. Due to formation of thick film surfaces does not come in direct contact with each 248

15 other and reduces the wear considerably. The friction generated between the surfaces depends upon the dimensions of the film and the viscosity of the lubricant. The thickness of the film is about 1000 A. In this type of lubrication the lubricant has the minimum viscosity under working condition and hence it manages to penetrate between the moving parts of metal. Co-efficient of friction in thick film lubrication lies in the range of to Thin-Film Lubrication It is also known as boundary lubrication. Such type of lubrication takes place when either a bearing suddenly comes in motion or when excessive pressure is exerted on the bearings. When two metal surfaces come in contact with the lubricant, a thin film of lubricant gets adsorbed on the metal surface and is held by Van der Waal s force of attraction. This thin layer of lubricant prevents direct metal-to-metal contact. Friction generated in this type of lubrication mainly depends on chemical nature of lubricant and the metal surface irregularity. Co-efficient of friction in thin film lubrication ranges from 0.05 to Lubricants used for boundary lubrication must have long hydrocarbon chain, a polar group which promotes formation of wedge in the metal surfaces. High viscosity index, resistance to heat and oxidation, good oiliness, low pourpoint are the desirable properties for boundary lubrication Extreme Pressure Lubricants When the moving/sliding surfaces are under very high pressure and speed, a high local temperature is attained under such conditions, liquid lubricants fail to stick and may decompose and even vaporize. When the motion of metals is subjected to constant load, a considerable amount of friction heat is 249

16 generated which causes the liquid lubricant to drip out or may sometimes decompose due to high temperature. To overcome this problem some additives like organic phosphorus, sulphur and chlorinated esters are added in the mineral oil. These are called extreme pressure additives. These additives react with the metal surface at higher temperature to form durable films of phosphates, sulphides and chlorides which helps in reducing friction. The lubrication phenomenon is affected by through this chemical action and hence a noticeable amount of wear on the metal surfaces is expected to occur. [37-45] 5.4 Properties and Testing of Lubricants Lubricant must possess many physical and chemical properties in order to function properly. The physical and chemical methods of testing lubricants can be broadly divided in to three groups: test for the determination of physical constaints, test related to application and test related to composition Physical test a. Viscosity: The most important property of lubricating oil is its viscosity. Viscosity of a fluid is that property which determines its resistance to shear or flow. It not only determines the flow characteristics of lubricating oil but also controls its frictional and thermal effects. It is the most important single property of any lubricating oil, because it is the main determinant of the operating characteristics of the lubricant. If the viscosity of the oil is too low, a liquid oil film cannot be maintained between two moving/sliding surfaces. On the other hand, if the viscosity of the oil is too high, excessive friction will result.three common viscometers in use in industrial laboratories are the Saybolt, the Redwood and 250

17 the Engler viscometers. All the three viscometers measure the time of flow of a specified volume of fluid through an orifice of fixed diameter; the volume of fluid and the diameter of the orifice being different for different viscometer. Viscosity of liquids decreases with increasing temperature and, consequently, the lubricating oil becomes thinner as the operating temperature increases. Hence, viscosity of good lubricating oil should not change much with change in temperature, so that it can be used continuously, under varying conditions of temperature. The rate at which the viscosity of lubricating oil changes with temperature is measured by an arbitrary scale, known as Viscosity Index (V. I). If the viscosity of lubricating oil falls rapidly as the temperature is raised, it has a low viscosity index. On the other hand, if the viscosity of lubricating oil is only slightly affected on raising the temperature, its viscosity index is high. [46-47] b. Density and Specific Gravity: Density and specific gravity values must be known whenever weight and volume factors are of concern. To some extent density and gravity values coupled with the viscosity index will provide an indication of the base stock from which the lubricant is blended. Hydrometer measurements are employed when more rapid approximation is acceptable as in routing testing. Specific gravity of a lubricant is sometimes expressed as API gravity, in API degree. [48] c. Flash and Fire Points: The flash point is the lowest temperature at which an oil or fuel gives off sufficient vapor to form an ignitable mixture under standard condition, while the fire point is the lowest temperature at which an oil or fuel vaporizes rapidly enough to sustain burning after ignition at standard test condition. In most cases, 251

18 the fire points are 5 C to 40 C higher than the flash points. The flash and fire do not have any bearing with lubricating property of the oil, but these are important when oil is exposed to high temperature service. A good lubricant should have flash point at least above the temperature at which it is to be used. This safeguards against risk if fire, during the use of lubricant. There are three instruments used for the determination of flash and fir points of lubricants: Cleveland Open Cup, Tag Closed Cup and Pensky-Martens closed tester. [49-50] d. Penetration Value: Penetration value is a number indicating the relative consistency (softness or hardness) of the grease. It is equal to the depth (expressed in units of 0.1 mm.) to which a weighted core penetrates the grease in 5 second. A proper consistency will make the grease stay in the bearing without generating too much friction. Hardness or softness of lubricating greases can be checked using ASTM D Penetration value measurements are usually taken in both worked and unworked conditions. [51] e. Dropping Point: The dropping point is the temperature at which grease changes from a quasisolid to a liquid state under prescribed conditions. This change in state is typical of grease containing as thickeners soaps of conventional types. The droping point does not indicate the ability of greases to withstand high temperature operation. However the dropping point obviously, is a practical limit to applications designed to use greases in the quasi-solid state. [52] f. Dielectric Constant: 252

19 In the pure state, free of any contaminants, lubricating oils are extremely poor conductors of electricity and good insulators. Because of the sensitivity to water, the test has been found useful in other application such as checking the dryness of refrigerator oils. ASTM describes the system generally applied for the measurement of the electrical insulating properties of petroleum base oils. [48] g. Evaporation loss: In many lubricant applications, high temperature has a controlling influence on the resultant performance. Neglecting oxidative and stability aspects, considerable amount of more volatile constituents of a lubricant may be lost due to evaporation. Due to the evaporation losses oils ultimately become tarry and greases approach the condition that essentially only the thickener remains. The generally accepted method for the measurement of evaporation losses of lubrication oils and greases is described in ASTM D (1968). [48] h. Colour: The colour of oil is determined by comparing a layer of the oil in a standard glass cell with a number of standard coloured slides. Test for colour are only useful in connection with refining practice. The apparatus most commonly used for colour determination is ASTM union colorimeter, in which the colour of oil is matched against those of a series of standard glasses. The ASTM method of colour determination is described in ASTM D 155. [48] Application Test a. Cloud and pour point: 253

20 When the lubricant oil is cooled slowly, the temperature at which it becomes cloudy or hazy in appearance, is called its cloud point; while the temperature at which the lubricant oil cease to flow or pour, is called its pour point. Cloud and pour points indicate the suitability of lubricant oil in cold conditions. Lubricant oil used in a machine working at low temperatures should possess low pour point; otherwise solidification of lubricant oil will cause jamming of machine. It has been found that presence of waxes in the lubricant oil raise pour point. [53] b. Flock Point: The flock point of oil is the temperature at which paraffin wax or other materials normally dissolved in oil separate as a flock in a mixture of the oil and 90% refrigerant. The flock point is applied specifically to those oils which are used to lubricate refrigerator compressors. [48] c. Corrosion test: Depending on the classification or application of the lubricants, several types of corrosion test may be carried out. Lubricants are normally not corrosive unless chemically active ingredients such as chlorine and sulphur are present in the lubricant. It is not feasible to discuss the entire corrosion test. [49] The ASTM tests for corrosion are: i. Copper corrosion or strip test: (D ) ii. Rust preventing (steam turbine oil): (D ) iii. Effect of grease on copper: (D ; 1968) iv. General Corrosive test for lubricating oil: ( Federal Test Method ) Composition Analysis 254

21 Composition analysis of a lubricant does not refer to the determination of the individual compounds present but rather to determination of certain values characteristics to a given compound group. a. Neutralization Number: The neutralization number of a lubricant expresses the acidity or basicity of the material. Generally two methods are used for the determination of neutralization number: potentiometric titration or titration with colour indicator. b. Aniline point: Aniline point determination is applicable to only hydrocarbon type lubricants. The aniline point of a lubricant is the temperature at which equal volumes of the lubricant sample and aniline become mutually soluble. The test for aniline point is described in ASTM D 611, ASTM D 1012 and Federal Test Method c. Carbon Residue: The carbon residue value of motor oil, while at one time regarded as indicative of the amount of carbonaceous deposits a motor oil would form in the combustion chamber of an engine, is now considered to be of doubtful significance due to the presence of additives in many oils. For example, an ashforming detergent additive may increase the carbon residue value of oil yet will generally reduce its tendency to form deposits. [54-55] d. Saponification number: 255

22 The saponification number of oil is expressed as the mg of KOH that will react with the ingredient in 1 g of the lubricant, under reflux conditions for a fixed period of time and it is determined by the ASTM D 94. Properties: A lubricant has to meet various regimes of tribology apart from reducing friction between the moving substrates. An ideal lubricant should have following characteristics. It should have a high viscosity index. It should have flash and fire points higher than the operating temperature of the machine. It should have high oiliness. The cloud and pour points of a good lubricant should always be lower than the operating temperature of the machine. The volatility of the lubricating oil should be low. It should deposit least amount of carbon during use. It should have higher aniline point. It should possess a higher resistance towards oxidation and corrosion. It should have good detergent quality. 5.5 Lubricant Classification Systems [56] Professional societies and organizations have established classifications for oil and grease. The most widely encountered systems are those of the following organizations: SAE (Society of Automotive Engineers) API (American Petroleum Institute) 256

23 AGMA (American Gear Manufacturers Association) ISO (International Standards Organization) NLGI (National Lubricating Grease Institute) 5.6 Lubricating Greases Grease is essentially a solid or semi-solid lubricant consisting of a gelling or thickening agent in a liquid lubricant. Other ingredients such as fillers and additives may also be incorporated to impart special properties. A typical grease composition contains 60 95% base fluid (mineral, synthetic, or vegetable oil), 5 25% thickener (common thickeners are fatty acid soaps and organic or inorganic non-soap thickeners), and 0 10% additives (antioxidants, corrosion inhibitors, anti-wear/extreme pressure, antifoam, tackiness agents, etc.). Additives enhance performance and protect the grease and lubricated surfaces. [57] Base fluid (Mineral or veg.) 60 to 90% Thickener (Metal Soap) 5 to 25% Additives 0 to 10% Grease 257

24 There are two main processes used for producing lubricating grease: i. Lubricating Grease with the soap thickener produced in situ, within the desired lubricating fluid. ii. Lubricating Grease with a pre-made soap thickener or inorganic thickener added to the lubricating fluid. All too often, lubricating greases are looked upon as thick oils, a perception that can inevitably lead to problems in application. Greases are the bulk which not only has the lubricating property but also has the tendency to absorb the contaminants such water and debris, without reduction in its lubrication ability. The solid state of the grease simplifies the choice of conventional seals and helps to keep contaminants from penetrating into the surfaces that are to be lubricated. This not only prevents detrimental particles getting access to the surface but also gives good protection against corrosion. Considering all said above, lubricating greases should be regarded as high technology products. Since the beginning of the 50 s, so called multi-purpose greases have been available. These were lubricating greases that can meet most lubrication demands and is true, in about 80% of all applications. With the increasing technical development of applications, the use of multi-purpose greases eventually decreased as they seems to be more quantitative than being qualitative. The development of grease technology took gradually by trial and error, use of various thickeners, changing the base oils and incorporating additives as per desired applications gave rise to application based greases [58]. The use of proper lubrication will not only reduce costs, but also effect the natural environment in a positive way. By using an appropriate lubricant in any given application, the demand for the 258

25 energy needed to drive the equipment can be reduced and the machinery can give a higher reliability (less standstill time for maintenance and unexpected breakdowns). The lifetime will be appreciably extended and effective output of the equipment increased. There have been calculations made, which show that billions of dollars in savings every year could be made by changing to the appropriate lubricant for currently running equipment Grease vs. Oil Generally speaking oil lubrication is more versatile than grease lubrication, however, there are a number of application where grease lubrication offers advantages over oil lubrication. Because of their many advantages over oil, greases are now the first choice for the lubrication of ball and roller bearing in electric motors, household appliances, aircraft accessories, automotive wheel bearings, railroad apparatus etc., they are also used for the lubrication of small gear drives and for many slow-speed sliding applications. [59] Advantages: Greases are handier lubricants than oils. Grease lubrication gives batter protection under extreme operating conditions such as extreme pressures, low speeds, shock load and bearings operating intermittently or reversing. Grease lubrication provides more effective sealing against contaminants such as water and dirt. Greases lubrication permits simplified design of housing and enclosure because grease clings to metal surface more easily and more firmly. Grease reduces possible damage to the process or product from leakage. 259

26 Grease lasts longer than oil and therefore, requires less frequent maintenance or replacement than oil lubrication. 5.7 Relevance of Study Worldwide consumption of lubricants in 2005 was around 40 million metric tonnes and it was estimated to increasing with 4% rate per year and approximately 30% of them ended up or will end up in ecosystem. Present production of biodegradable lubricant is only 1% of the total production, among them today the global grease consumption is estimated at 1,296 KT of which industrial applications accounts for 691 KT. Mineral oil based greases account for close to 90% of the global demand, while 9 % of synthetic esters is used and only 1% of bio degradable base oils are used for manufacturing of greases. It is assumed that global consumption of grease in industrial application will be up to 758 KT till The base oil used for the formulation of grease is environmentally hostile mineral oil. Formulation of environment friendly grease depends primarily on the biodegradability of the base oils. Thus search for environment friendly substitutes to mineral oils as base oils in formulation of greases has become a frontier area of research in the lubricant industry in the new paradigm of sustainable technology development caused by the alarms of environmental degradations. The demand for biodegradable lubricants is due to a growing concern for the impact that technology is making to the environment. This concern is occurring both as the result of combination of local and national regulations, and as well as a result of consumer influence. Vegetable oils are perceived to be alternatives to mineral oils for lubricant base oils because of certain inherent technical properties and their ability for 260

27 biodegradability. Compared to mineral oils, vegetable oils in general possess high flash point, high viscosity index, high lubricity and low evaporative loss. Therefore due to these nontoxic and biodegradable characteristics of vegetable seed oils and esters that can substitute mineral oil as base fluid in grease making. Also they exhibit excellent lubrication properties due to unbalanced electrical charges which make them attach to metal surfaces. The presence of a polar group with a long hydrocarbon chain makes vegetable oil amphiphilic in nature, allowing it to be used as a boundary lubricant. The molecules have strong affinity for and interact strongly with metal surfaces. The long hydrocarbon chain is oriented away from the metal surface to form a monomolecular layer with excellent boundary lubrication properties. When the molecule is adsorbed on the metal surface, two types of interactions occur. The adhesive interaction between the ester group and metal is very sensitive to the type and number of functional groups. The lateral interaction caused by dipole-dipole and dispersive interaction between the hydrocarbon chains is sensitive to structural properties including chain length, unsaturation, and stereochemistry. Vegetable oils that are extensively used for biodegradable grease preparations are soybean, rapeseed, sunflower, and castor oil. Other vegetable oils used are olive, peanut, palm, corn, cottonseed, safflower, lesquerella, coconut and linseed. Today, greases are expected to work under extreme operating conditions, including shock load, wide temperature range, varying pressure, surface material and environment. 5.8 Definition of the Problem 261

28 Crude oil dependent industries are having the major problem related to crude oil replacements; this is due to finiteness of crude petroleum also due to its detrimental effects over environment. This makes everyone look towards renewable resources as they are easily available, environmentally friendly and hence sustainable indeed. Utilization of the vegetable oils in recycling and feedstock sector by different industries is the main approach of the current scenario. In the previous work we utilized the castor oil as recycling material and thereby formed product is used as feedstock for the grease formulation in the present work. 5.9 Objective of the Study The present work is envisaged; 1. Make an effort to utilize the castor oil: PET based recycled product as base oil in the formulation of greases without additives. 2. To evaluate the tribological properties using standard tests and procedures of the thereby formed greases. And compare it with stander mineral oil based one. 3. Providing the new field for absorption of the PET recycled product Materials and Methods Base oil, Mineral oil based grease and Thickener: The castor oil based depolymerized PET products obtained in the previous work is used as such as base oil without giving further any treatment and purification. According to the PET: CO ratio i.e. 1:3 to 1:7 based depolymerized products are further coding as base oils CC3 to CC7 respectively. 262

29 SN-500, all purpose grease was used as standard to evaluate performance properties of formulated grease. Sodium stearate was used as thickener in the formulation of grease and was procured from SD Fine chemicals Ltd. Baroda, Gujarat Formulation of grease: Grease was formulated using the depolymerized product as base oil. Sodium stearate was used as a thickener to formulate, vegetable oil based grease. Thickener was thermo-mechanically dispersed in the oil matrix, using a high speed stirrer. Concentration of the thickener was maintained at 10% (w/v) of the total volume of oil. Initially 60% of the total volume of the oil was charged in the reactor and heated up to 120 C. Then 50% of the soap was added and the stirred vigorously for intimate mixing. Temperature was gradually raised to 150 C and a part of base oil (20%) was added and the temperature was increased to 200 C along with stirring. At 200 C the remaining oil and soap was added and the stirring speed was increased to 1500 rpm. Base oil and the thickener were vigorously stirred for 30 minutes at 200 C, and then the temperature was lowered gradually. 263

30 Stirring was continued while decreasing the temperature to avoid settling of soap, with decrease in temperature it was observed that the viscosity of oil increases. Till reaching the room temperature the viscous oil turned into semisolid grease. No additives were incorporated in the formulation of grease. Properties of both vegetable based formulated grease and mineral grease were evaluated and compared Characterization Unlike formulation of grease, its testing also takes plays a crucial role in its application. Combination of two Greek words Tribo and Logos is become tribology having meaning rubbing and logic respectively and defined as the science and technology of interacting surfaces in relative motion. It covers all the fields of wear, lubrication, friction and the Science associated with surfaces, which interacts with each other in a relative motion. Thus formulated greases were thought to characterize for tribological characteristics. Tribological properties of the formulated grease such as roll stability, cone penetration, drop point, co-efficient of friction by pin on disc method and weld load were evaluated by ASTM D1831, ASTM D1403, ASTM D566, ASTM D2266 and ASTM D2596 respectively. All the test samples were taken as raw; no additives were added in any of the samples. I. Drop point: 264

31 The dropping point of grease is the temperature at which the thickener loses its ability to maintain the base oil within the thickener matrix. This may be due to the thickener melting or the oil becoming so thin that the surface tension and capillary action become insufficient to hold the oil within the thickener matrix. Drop point of all the test samples was determined using ASTM D566 method. [52] II. Cone penetration: Lubricating greases consistency is measured by ASTM D 1403 method, and is reported in terms of various NLGI grades ranging from 000 for semi fluid to 6 for solid block greases. [51] 265

32 Unworked penetration test All the samples of grease were subjected to penetration test. Grease cup, cylindrical in shape with 50ml capacity at 25 C, was filled completely with grease and its surface was smoothened and placed on the penetrometer. Then penetrometer cone was released and allowed to sink in the grease cup under its own weight for 5 seconds. The depth the cone has penetrated is then measured, in tenths of a millimeter. Deeper the cone penetrates in the grease cup, higher is its penetration result and the softer the grease. 266

33 Worked penetration test The worked penetration test was carried out in the same manner as that of un-worked penetration test, but prior to penetration the sample was being subjected to 60 double strokes in the ASTM grease worker. In this method, the disturbance of the grease was standardized by the prescribed working process and is more reliable than Un-worked penetration test because the grease has been subjected to a work load of double strokes.unworked and the worked penetration tests were performed to determine the consistency of grease and its resistance to deformation when subjected to force. Significant difference in penetration of the cone within un-worked and worked grease indicates its poor shear stability. III. Roll stability of greases: Mechanical stability of the grease was evaluated using ASTM D 1831 roll stability worker. 267

34 In the Roll Stability Test grease is rolled at 165 rpm for a 2hrs at 25 C using a steel cylinder which contains a 5 kg heavy round steel block. The change in cone penetration is used to measure mechanical stability. Due to the small size of the sample, working and penetrations are performed on ASTM D 1403 onequarter or one-half scale equipment. [60] IV. Co-efficient of friction: Co-efficient of friction of all the formulated greases was performed using the pin on disc method [61]. The setup of the method comprises of a pin with spherical surface as the tip and a circular rotating disk which is placed at a perpendicular with respect to the spherical pin surface. The diameter of the pin (aluminium) is 10mm and the length is 35mm. The disk is made of hardened steel on which the pin is held with a jaw in the apparatus and rotation is provided to disk which causes wear of the pin on a fixed path on disk. The pin is pressed against the surface of the disk with load being applied with the arm 268

35 attachment provided to the apparatus. Machine is attached with a data acquisition system and WINDUCOM 2010 software which gives result values and graphs. Working Parameter: Weight (load) applied : 3 Kg Rotation disc: 2000 r. p. m. Time duration: 10 min. Pin Size: 10 mm dia. And 35 mm length Sliding distance: 1000mm V. Weld load: The test is used to determine the load carrying properties of a lubricant at high test loads. Four-Ball Test measures a lubricant s extreme pressure properties under Hertzian contact in sliding or rolling motion. Weld load of grease is tested in a four ball system where a rotating ball slides over three stationary balls. This test is run at higher loads till the test balls are welded together. Test is considered to be failed if the rotating ball is welded with any of the three stationary balls. [62] 5.11 Result and Discussion Viscosity and drop point: Viscosity is one of the important properties of the base oil for the formulation of grease which is measured by GBT viscometer. In this method each sample of base oil was fill up to the mark in a blank sample test tube and was compare with the standard measured viscosity samples in a grade wise until 269

36 getting the same flow. Te results are depicted in Table-30. It is clearly seen from the data that the viscosity of the base oil formed by 1:3 concentration is higher and going to decrease by increasing the concentration of castor oil up to 1:7 for the depolymerize the used cloths. Decreasing the viscosity is may be due to the attachment of lower molecular fraction of PET oligomers on the castor oil compare to the attachment while the concentration is 1:3. Droping point of the greases is the temperature at which the thickener loses its ability to maintain the base oil within the thickener matrix. This may be due to thickener melting or the oil becoming so thin that the surface tension and capillary action become insufficient to hold the oil within the thickener matrix. Drop point of all the formulated grease is also depicted in Table-30. From the results we resolve that formulated greases from the base oil based on 1:3 to 1:4 having higher drop point, while based on 1:6 and 1:7 having comparatively lower droping point than SN-500, all purpose grease. Increasing in the droping point is due to the presence of higher molecular oligomers of PET and its aromatic nature in the base oil, in contrast to that decreasing the drop point is due to the presence of lower molecular fraction of PET and may be due to the non-uniform matrix of the soap in the base oil. 270

37 Table 30: Viscosity and drop point PET:CO Base oil Gardner tube Drop code viscometer point Type Stock ( C) 1:3 CC3 Z :4 CC4 Z :5 CC5 Z :6 CC6 U :7 CC7 W SN-500 All purpose grease Mineral oil Cone Penetration Penetration test was performed on all the formulated grease in order to determine the stiffness of grease. In the case of lubricating greases its consistency is termed as its measure of the relative hardness or softness and has some relation to its rheological properties. A proper consistency will make the grease stay in the bearing without generating too much friction. The P0 for unworked and P60 for worked penetration followed ASTM-D 1403 method for half & Quarter scale. The penetration test begins with the grease at temperature 25 C ± 1 being leveled into a cup. Using a penetrometer the cone was drop to the cup for 5s creating hole in grease and its depth was measured in tenths of 271