Lubrication Fundamentals 2011 Part 2 potx

deasphalting and extraction. The solvent extraction portion of the Duo-Sol process employs either phenol or cresylic acid as the extraction solvent. C. Furfural Extraction Before discussing furfural extraction and the subsequent processing, it should be pointed out that from this stage on, a lube refinery differs from most fuel refineries in another important aspect. Lube units process very different feedstocks at various times. For example, a furfural extraction unit will process not only the deasphalted oil from the PD unit but the distillate feeds from the vacuum tower as well. These different feedstocks are processed in ‘‘blocked out’’ operation. This means that while one of the feeds is being processed, the others are collected in intermediate tankage and are processed later. Runs of various lengths, from days to weeks, are scheduled so that demands are met and intermediate tankage requirements are not excessive. During the switching from one stock to another, some transition oil is produced and must be disposed of. One other consequence of this blocked-out type of operation is that each section of the process units must be designed to handle the most demanding service. As a unit’s capacity for various stocks may be limited by the requirements imposed on its different sections. Furfural extraction separates aromatic compounds from nonaromatic compounds. In its simplest form, the process consists of mixing furfural with the feedstock, allowing the mixture to settle into two liquid phases, decanting, and removing the solvent from each phase. This can be demonstrated in a glass graduated cylinder, where the more dense furfural dissolves the dark-colored aromatic materials from a distillate, leaving a lighter- colored raffinate product. The resultant product from the furfural extraction shows an increase in thermal and oxidative stability as well as an improvement in viscosity and temperature characteristics, as measured by a higher viscosity index (VI). Figure 2.18 is a simplified flow diagram of a commercial furfural extraction unit. The feedstock is charged to the middle of the extraction column, the furfural near the top. The density difference causes a counterflow in the column; the downward-flowing furfural Figure 2.18 Furfural extraction. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. dissolves the aromatic compounds. The furfural raffinate rises and is removed from the top of the column. The furfural extract is removed from the bottom of the column. Each of the products is passed to the solvent recovery system, with the furfural being recycled as feed to the extractor. The solvent recovery system, which is not discussed here in any detail, is much more complicated than this treatment suggests. The major effect of furfural extraction on the physical properties of a base stock is an increase in viscosity index—an improvement in the viscosity–temperature relationship of the oil. However, equally important, but less obvious, changes in the base stock result. Although oxidation and thermal stability are improved, there is no physical property of the base stock that is easily measurable that can be related to these characteristics. Thus, while viscosity index is sometimes used to monitor the day-to-day operations of a furfural extraction unit, VI is only an indication of the continuity of the operation, not an absolute criterion of quality. The quality of base stocks for a given product (and the refining conditions needed to produce the base stocks) is arrived at by extensive testing, ranging from bench-scale to full-fleet testing programs. Careful control of the operation of the refining units is essential to assure the continuous production of base stocks meeting all the quality criteria needed in the final products. D. Solvent Extraction Another solvent extraction process that has been used employs phenol as the solvent. The capacity and the number of phenol extraction units in operation (if Duo-Sol units are included with phenol) exceed those available for furfural extraction. However, recent trends indicate that the use of phenol extraction will decline. ExxonMobil’s recent solvent extraction units are based on furfural extraction. The action of these solvents on the oil charge is quite similar, although different operation conditions are used with each solvent. Some lube refineries use N-methylpyrrolidone (NMP) as the extraction solvent. E. Hybrid Processing Certain lubricants, used in critical applications, require base stocks with high viscosity indices (Ͼ 105 VI) and very low sulfur contents. While solvent extraction can achieve this VI level with some crudes, raffinate yields are typically very low and sulfur removal is limited to about 80%. An alternative processing route for high VI is to couple hydrotreating with extraction. This is commonly called hybrid processing. While hydrotreating helps to preserve yield, the chemical reactions that occur result in some additional viscosity loss. By properly targeting the correct distillate viscosity, extraction severity, and hydrotreating severity, high VI base stocks can be produced at economic yields. Another application of hybrid processing consists of mild furfural extraction and lube hydrocracking to produce base stocks from crudes of marginal quality. F. MEK Dewaxing The next process in lube base stock manufacture is the removal of wax to reduce the pour point of the base stock. Figure 2.19, a simple representation of the process, shows the waxy oil being mixed with MEK–toluene solvent. The mixture is then cooled to a temperature between 10ЊF(מ12ЊC) and 20ЊF(מ6ЊC) below the desired pour point. The wax crystals that form are kept in suspension by stirring during the cooling. The wax is then Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. One other distinctive feature of this cooling train is the use of scraped-wall, double- pipe heat exchangers, which consist of a pipe inside a pipe. The inner pipe carries the solvent–oil–wax mixture; the outer pipe the cooling medium, either cold product or refri- gerant. The inner pipe is equipped with a set of scraper blades that rotate and scrape away any wax that plates out on the walls of the inner pipe. This action is necessary to maintain a reasonable rate of heat transfer. Although the method is efficient, scraped-wall, double- pipe heat exchangers are expensive and costly to maintain. The cooled slurry is passed to filter feed surge drum and then to the filter itself, where the actual separation is accomplished. Rotary vacuum filters used in dewaxing plants are large drums covered with a filter cloth, which prevents the wax crystals from passing through to the inside of the drum as the drum rotates in a vat containing the slurry of wax, oil, and solvent. A vacuum applied inside the drum pulls the solvent–oil mixture (filtrate) through the cloth, thus separating the oil from the wax. Figures 2.21–2.24 illustrate the operation of this type of filter: by looking at the end of the drum in each one, we can follow a single segment as the drum rotates through one revolution. In Figure 2.21, the segment is submerged in the slurry vat and is building up a wax cake on the filter cloth. The filtrate is being pulled into the interior of the drum. As the drum rotates through the slurry, the wax cake will increase in thickness and, as the segment leaves the vat, the vacuum state is maintained for a short period to dry the cake and remove as much oil and solvent as possible for the wax cake. Figure 2.22 shows the cold wash solvent being applied to the cake, displacing more of the oil in the cake. The wash portion of the cycle is followed by another short period of drying. The wax cake (Figure 2.23) is lifted from the filter by means of flue gas. This is accomplished by applying a positive pressure to the inside of the drum. As the drum rotates, the wax cake is guided from the drum by means of a blade (Figure 2.24), which directs it to a conveyor and then to the solvent recovery system. This segment of the drum is then ready to reenter the vat and continue with another cycle of pickup, dry, wash, dry, cake lift, and wax removal. Figure 2.21 Dewaxing cycle filtration. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. Figure 2.25 Catalytic dewaxing process flow diagram. Figure 2.26 Lube hydrofinishing process. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. structure of the color bodies and unstable components in the oil, resulting in a lighter colored oil that is improved in certain performance qualities. The process operates similarly to processes that are used to desulfurize kerosenes and diesel fuels. Hydrofinishing represents relatively mild operation at relatively low temperatures and pressures. It will also saturate residual olefins to form paraffins. This process stabilizes base stock color and improves demulsibility and air release characteristics. Slight improvement in oxidation resistance may also result. J. Hydrotreating Hydrotreating represents a more severe set of operating conditions than hydrofinishing. At higher pressures and with selected catalysts, the aromatic rings become saturated to become naphthenes. In addition to converting aromatics, hydrotreating can remove most of the sulfur and nitrogen. This also has a positive effect on oxidation stability and deposit control. ExxonMobil uses a proprietary hydrotreating process to manufacture very high quality (VHQ) stocks for severe turbine applications. This process allows retention of selected aromatic compounds to provide the desired additive and contaminant solvency in the finished product, while maintaining good oxidative stability. K. Hydrocracking Lube hydrocracking is an alternative to solvent refining for producing lube base stocks. In solvent lube processing, the main objective is to remove undesirable low VI components in crude via liquid–liquid extraction. Lube hydrocracking may be employed to convert the undesirable components into valuable lube molecules. Hydrocracking is the most severe hydroprocessing operation and is less dependent on feedstock than solvent refining. However, feedstock can have a significant impact on the product properties. Hydrocracking vacuum distillate usually targets base stocks in the 95–105 VI range. Higher operating severities can increase this up to 115ם VI, but with loss of yield. Use of a high wax (paraffin) content feed will result in an even higher VI (130ם). Hydrocracking produces predominantly lower viscosity base stocks (80–500 SUS) owing to the cracking of larger, heavier molecules. Thus hydrocracked base stocks cannot be used in many heavy industrial and engine oil products. They must be blended with solvent-refined base stocks and/or other thickening agents to achieve the higher viscosity required in some products. Hydrocracking is a well-established process in the refining industry. It has been widely used for many years in fuels manufacture and its use in lube manufacture is currently expanding. This growing interest for lube manufacture stems from several advantages hydrocracking offers versus solvent processing: 1. Higher lube yields: converts undesirable components to lubes. 2. Broader feedstock flexibility: permits production from lower quality, cheaper crudes. 3. Higher quality base oils: can produce base stocks meeting emerging standards for high performance such as API groups II and III. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. 3 Lubricating Oils I. ADDITIVES The preceding chapter discussed refining processes and base stock manufacturing. The lube oil base stock is the building block with respect to which appropriate additives are selected and properly blended to achieve a delicate balance in performance characteristics of the finished lubricant. It is important to mention again that the various base stock manufacturing processes can all produce base stocks with the necessary characteristics to formulate finished lubricants with the desirable performance levels. The key to achieving the highest levels of performance in finished lubricants is in the understanding of the interactions of base stocks and additives and matching those to requirements of machinery and operating conditions to which they can be subjected. Additives are chemical compounds added to lubricating oils to impart specific properties to the finished oils. Some additives impart new and useful properties to the lubricant, some enhance properties already present, while some act to reduce the rate at which undesirable changes take place in the product during its service life. Additives, in improving the performance characteristics of lubricating oils, have aided significantly in the development of improved prime movers and industrial machinery. Modern passenger car engines, automatic transmissions, hypoid gears, railroad and marine diesel engines, high speed gas and steam turbines, and industrial processing machinery, as well as many other types of equipment, would have been greatly retarded in their development were it not for additives and the performance benefits they provide. Additives for lubricating oils were used first during the 1920s, and their use has since increased tremendously. Today, practically all types of lubricating oil contain at least one additive, and some oils contain additives of several different types. The amount of additive used varies from a few hundredths of a percent to 30% or more. In addition to their beneficial effects, additives can have detrimental side effects, especially if the dosage is excessive or if interactions with other additives occur. It is the responsibility of the oil formulator to achieve a balance of additives for optimum performance, and to ensure by testing that this combination is not accompanied by undesirable Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. side effects. When this is achieved, it is usually unnecessary and undesirable for the oil user to add oil additive supplements. The more commonly used additives are discussed in the following sections. Although some are multifunctional, as in the case of certain VI improvers that also function as pour point depressants or dispersants or antiwear agents that also function as oxidation inhibitors, they are discussed in terms of their primary function only. A. Pour Point Depressants Certain high molecular weight polymers function by inhibiting the formation of a wax crystal structure that would prevent oil flow at low temperatures. Two general types of pour point depressant are used: 1. Alkylaromatic polymers adsorb on the wax crystals as they form, preventing them from growing and adhering to each other. 2. Polymethacrylates cocrystallize with wax to prevent crystal growth. The additives do not entirely prevent wax crystal growth, but rather lower the temperature at which a rigid structure is formed. Depending on the type of oil, pour point depres- sion of up to 50ЊF (28ЊC) can be achieved by these additives, although a lowering of the pour point by about 20–30 FЊ (11–17 CЊ)ismore common. B. Viscosity Index Improvers VI improvers are long chain, high molecular weight polymers that function by causing the relative viscosity of an oil to increase more at high temperatures than at low temperatures. Generally this result is due to a change in the polymer’s physical configuration with increasing temperature of the mixture. It is postulated that in cold oil the molecules of the polymer adopt a coiled form so that their effect on viscosity is minimized. In hot oil, the molecules tend to straighten out, and the interaction between these long molecules and the oil produces a proportionally greater thickening effect. Note: Although the oil–polymer mixture still decreases in viscosity as the temperature increases, the decrease is not as great as it would have been in the oil alone. Among the principal VI improvers are methacrylate polymers and copolymers, acry- late polymers, olefin polymers and copolymers, and styrene butadiene copolymers. The degree of VI improvement from these materials is a function of the molecular weight distribution of the polymer. The long molecules in VI improvers are subject to degradation due to mechanical shearing in service. Shear breakdown occurs by two mechanisms. Temporary shear breakdown occurs under certain conditions of moderate shear stress and results in a temporary loss of viscosity. Apparently, under these conditions the long molecules of the VI improver align themselves in the direction of the stress, thus reducing resistance to flow. When the stress is removed, the molecules return to their usual random arrangement and the temporary viscosity loss is recovered. This effect can be beneficial in that it can temporarily reduce oil friction to permit easier starting, as in the cranking of a cold engine. Permanent shear breakdown occurs when the shear stresses actually rupture the long molecules, converting them into lower molecular weight materials, which are less effective VI improvers. This results in a permanent viscosity loss, which can be significant. It is generally the limiting factor controlling the maximum amount of VI improver that can be used in a particular oil blend. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. VI improvers are used in engine oils, automatic transmission fluids, multipurpose tractor fluids, and hydraulic fluids. They are also used in automotive gear lubricants. Their use permits the formulation of products that provide satisfactory lubrication over a much wider temperature range than is possible with straight mineral oils alone. C. Defoamants The ability of oils to resist foaming varies considerably depending on type of crude oil, type and degree of refining, and viscosity. In many applications, there may be considerable tendency to agitate the oil and cause foaming, while in other cases even small amounts of foam can be extremely troublesome. In these cases, a defoamant may be added to the oil. Silicone polymers used at a few parts per million are the most widely used defoamants. These materials are essentially insoluble in oil, and the correct choice of polymer size and blending procedures is critical if settling during long-term storage is to be avoided. Also, these additives may increase air entrainment in the oil. Organic polymers are sometimes used to overcome these difficulties with the silicones, although much higher concen- trations are generally required. It is thought that the defoamant droplets attach themselves to the air bubbles and can either spread or form unstable bridges between bubbles, which then coalesce into larger bubbles, which in turn rise more readily to the surface of the foam layer where they collapse, thus releasing the air. D. Oxidation Inhibitors When oil is heated in the presence of air, oxidation occurs. As a result of this oxidation, both the oil viscosity and the concentration of organic acids in the oil increase, and varnish and lacquer deposits may form on hot metal surfaces exposed to the oil. In extreme cases, these deposits may be further oxidized to form hard, carbonaceous materials. The rate at which oxidation proceeds is affected by several factors. As the temperature increases, the rate of oxidation increases exponentially. A rule of thumb is that for each 10ЊC (18ЊF) rise in temperature, the oxidation rate of mineral oil will double. Greater exposure to air (and the oxygen it contains), or more intimate mixing with it, will also increase the rate of oxidation. Many materials, such as metals, particularly copper and iron and organic and mineral acids, may act as catalysts or oxidation promoters. Although the complete mechanism of oil oxidation is not too well defined, it is generally recognized as proceeding by free radical chain reaction. Reaction chain initiators are formed first from unstable oil molecules, and these react with oxygen to form peroxy radicals, which in turn attack the unoxidized oil to form new initiators and hydroperoxides. The hydroperoxides are unstable and divide, forming new initiators to expand the reaction. Any materials that will interrupt this chain reaction will inhibit oxidation. Two general types of oxidation inhibitor are used: those that react with the initiators, peroxy radicals, and hydroperoxides to form inactive compounds, and those that decompose these materials to form less reactive compounds. At temperatures below 200ЊF (93ЊC), oxidation proceeds slowly and inhibitors of the first type are effective. Examples of this type are hindered (alkylated) phenols such as 2,6-ditertiary-butyl-4-methylphenol (also called 2,6 ditertiary-butylparacresol, DBPC), and aromatic amines such as N-phenyl-␣-naphthylamine. These are used in products such Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. as turbine, circulation, and hydraulic oils, which are intended for extended service at moderate temperatures. When the operating temperature exceeds about 200ЊF (93ЊC), the catalytic effects of metals become important factors in promoting oil oxidation. Under these conditions, inhibitors that reduce the catalytic effect of the metals must be used. These materials usually react with the surfaces of the metals to form protective coatings and for that reason are sometimes called metal deactivators. Typical of additives of this type are the dithiophosphates, primarily zinc dithiophosphate. Since the dithiophosphates also act to decompose hydroperoxides at temperatures above 200ЊF (93ЊC), they inhibit oxidation by this mechanism as well. Oxidation inhibitors may not entirely prevent oil oxidation when conditions of exposure are severe, and some types of oil are inhibited to a much greater degree than others. Oxidation inhibitors are not, therefore, cure-alls, and the formulation of a satisfactorily stable oil requires proper refining of a suitable base stock combined with careful selection of the type and concentration of oxidation inhibitor. It should also be pointed out that other additives can reduce oxidation stability in performing their design functions. Proper formulation requires the balancing of all the additive reactions to achieve the desired total performance characteristics. E. Rust and Corrosion Inhibitors A number of kinds of corrosion can occur in systems served by lubricating oils. Probably the two most important types are corrosion by organic acids that develop in the oil itself and corrosion by contaminants that are picked up and carried by the oil. Corrosion by organic acids can occur, for example, in the bearing inserts used in internal combustion engines. Some of the metals used in these inserts, such as the lead in copper-lead or lead-bronze, are readily attacked by organic acids in oil, as illustrated in Figure 3.1. The corrosion inhibitors form a protective film on the bearing surfaces that Figure 3.1 Heavily corroded copper-lead bearing. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. Figure 3.2 Satisfactorily protected copper-lead bearing. prevents the corrosive materials from reaching or attacking the metal (Figure 3.2). The film may be either adsorbed on the metal or chemically bonded to it. During combustion in gasoline or diesel engines, certain materials in the fuel, such as sulfur and antiknock scavengers, can burn to form strong acids. These acids can then condense on the cylinder walls and be carried to other parts of the engine by the lubricant. Corrosive wear of rings and cylinder walls, and corrosion of crankshafts, rocker arms, and other engine components can then occur. It has been found that the inclusion of highly alkaline materials in the oil will help to neutralize these strong acids as they are formed, greatly reducing this corrosion and corrosive wear. These alkaline materials are also used to provide detergency. See the detailed discussion in Section I.F, Detergents and Dispersants. Rust inhibitors are usually compounds having a high polar attraction toward metal surfaces. By physical or chemical interaction at the metal surface, they form a tenacious, continuous film that prevents water from reaching the metal surface. Typical materials used for this purpose are amine succinates and alkaline earth sulfonates. The effectiveness of a properly selected rust inhibitor is illustrated in Figure 3.3, where specimen 9 is rust free and the other specimens display varying degree of corrosion. Rust inhibitors can be used in most types of lubricating oil, but the selection must be made carefully to avoid problems such as corrosion of nonferrous metals or the formation of troublesome emulsions with water. Because rust inhibitors are adsorbed on metal surfaces, an oil can be depleted of rust inhibitor in time. F. Detergents and Dispersants In internal combustion engine service, a variety of effects tends to cause oil deterioration and the formation of harmful deposits. These deposits can interfere with oil circulation, build up behind piston rings to cause ring sticking and rapid ring wear, and affect clearances and proper functioning of critical components, such as hydraulic valve lifters. Once formed, such deposits are generally hard to remove except by mechanical cleaning. The use of Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. [...]... VG VG VG 2 3 5 7 10 15 22 32 46 68 100 150 22 0 320 460 680 1000 1500 Midpoint viscosity [cSt (mm2/s)] at 40.0ЊC 2. 2 3 .2 4.6 6.8 10 15 22 32 46 68 100 150 22 0 320 460 680 1000 1500 Kinematic viscosity limits [cSt (mm2/s)] at 40.0ЊC Minimum 1.98 2. 88 4.14 6. 12 9.00 13.5 19.8 28 .8 41.4 61 .2 90.0 135 198 28 8 414 6 12 900 1350 Maximum 2. 42 3. 52 5.06 7.48 11.0 16.5 24 .2 35 .2 50.6 74.8 110 165 24 2 3 52 506 748... mind Kinematic viscosity (cSt) at 100ЊC maxd High shear viscosity (cP), at 150ЊC and 106 s 2, mine 3.8 3.8 4.1 5.6 5.6 9.3 5.6 9.3 12. 5 12. 5 16.3 21 .9 — — — — — — Ͻ 9.3 Ͻ 12. 5 Ͻ 16.3 Ͻ 16.3 Ͻ 21 .9 Ͻ 26 .1 — — — — — — 2. 6 2. 9 2. 9f 3.7g 3.7 3.7 All values are critical specifications as defined by ASTM D 324 4 ASTM D 529 3 c ASTM D 4684 Note that the presence of any yield stress detectable by this method constitutes... viscosity grade 0W 5W 10W 15W 20 W 25 W 20 30 40 40 50 60 Low temperature (ЊC) cranking viscosity (cP, max)b 325 0 3500 3500 3500 4500 6000 at ‫03מ‬ at ‫ 52 ‬ at ‫ 02 ‬ at ‫ 52 ‬ at ‫ 02 ‬ at ‫5 מ‬ — — — — — — Low temperature (ЊC) pumping viscosity (cP, max, with no yield stress)c 60 60 60 60 60 60 000 at 000 at 000 at 000 at 000 at 000 at — — — — — — ‫04מ‬ ‫53מ‬ ‫03מ‬ ‫ 52 ‬ ‫ 02 ‬ ‫51מ‬ a Kinematic viscosity... 3 .2 Axle and Manual Transmission Lubricant Viscosity Classification-SAE J306* SAE viscosity grade 70W 75W 80W 85W 90 140 25 0 Maximum temperature for viscosity of 150,000 cP (ЊC) Minimum Maximum ‫55מ‬ ‫04מ‬ ‫ 62 ‬ 21 מ‬ — — — 4.1 4.1 7.0 11.0 13.5 24 .0 41.0 — — — — 24 .0 41.0 — Copyright 20 01 by Exxon Mobil Corporation All Rights Reserved (cSt) Viscosity at 100Њ Celsius Table 3.3 Viscosity System for Industrial... 100ЊF but was converted to viscosities measured at 40ЊC in the interests of international standardization In this form, the system now appears as ASTM Standard D 24 22, American National Standard Z11 .23 2, (British Standards Institution Standard BS 423 1, Deutsches Institut fur Normung) (DIN) No 51519, and International Standards ¨ Organization (ISO) Standard 3448 The ISO viscosity ranges and identifying grade... combustion engine oils 2 Axle and Manual Transmission Lubricant Viscosity Classification SAE Recommended Practice J306 classifies lubricants for use in automotive manual transmissions and drive axles by viscosity measured at 100ЊC (21 2ЊF), and by maximum temperature at which they reach a viscosity of 150,000 cP (150 Pa⋅s) when cooled and measured in accordance with ASTM Standard D 29 83 (Method of Test... ASTM 445 e ASTM D 4683 or ASTM D 4741 f 0W-40, 5W-40, and 10W-40 grades g 15W-40, 20 W-40, 25 W-40 and 40 grades b Copyright 20 01 by Exxon Mobil Corporation All Rights Reserved use where low ambient temperatures will not be encountered Multigrade oils are used for year-round service in automotive engines except for some 2 two-stroke diesel engines An example of a multigrade oil is as follows: oils can... a sample of oil containing iron oxide as a catalyst is aged by being held at 20 0ЊC (3 92 F) for 24 h while air is bubbled through it At the end of the test, the evaporation loss and the Conradson carbon residue (CCR) of the remaining sample are determined The evaporation loss is significant only in that it must not exceed 20 %, so the main criterion is the CCR value The test is believed to correlate... Abrasive wear is caused by abrasive particles, either contaminants carried in from outside or wear particles formed as a result of adhesive wear In either case, oil properties do not have much direct influence on the amount of abrasive wear that occurs, except through their ability to carry particles to filtering systems that remove them from the circulating oils 2 Corrosive or Chemical Wear Corrosive... Table 3 .2 Multigrade oils such as 80W-90 or 85W-140 can be formulated under this system This limiting viscosity of 150,000 cP was selected on the basis of test data indicating that lubrication failures of pinion bearings of a specific axle design could be experienced when the lubricant viscosity exceeded this value Since other axle designs, as well as transmissions, may have higher Table 3 .2 Axle and . 20 5.6 — — 25 W 6000 at מ 560000 at מ15 9.3 — — 20 — — 5.6 Ͻ 9.3 2. 6 30 — — 9.3 Ͻ 12. 5 2. 9 40 — — 12. 5 Ͻ 16.3 2. 9 f 40 — — 12. 5 Ͻ 16.3 3.7 g 50 — — 16.3 Ͻ 21 .9 3.7 60 — — 21 .9 Ͻ 26 .1 3.7 a All. max d 10 6 s 2 , min e 0W 325 0 at מ30 60 000 at מ40 3.8 — — 5W 3500 at 25 60 000 at מ35 3.8 — — 10W 3500 at 20 60 000 at מ30 4.1 — — 15W 3500 at 25 60 000 at 25 5.6 — — 20 W 4500 at 20 60 000 at 20 . wax removal. Figure 2. 21 Dewaxing cycle filtration. Copyright 20 01 by Exxon Mobil Corporation. All Rights Reserved. Figure 2. 25 Catalytic dewaxing process flow diagram. Figure 2. 26 Lube hydrofinishing

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