Handbook of Lubrication Episode 1 Part 13 docx

If no viscosities are known, the critical viscosity may be estimated from the values of P cr , T cr , and molecular weight M, as follows: (6) Table 4 illustrates the application of the two methods to the calculation of the viscosity of nitrogen. For each temperature, T r is calculated from T cr = 126.3 K. Next are listed the Volume II 297 FIGURE 4. Generalized reduced viscosity of gases. (From Hougen, O. A., Watson, K. M., and Ragatz, R. A., C.P.P. Charts, 2nd ed., John Wiley & Sons, New York, 1960. With permission.) Table 4 COMPARISON OF ESTIMATED NITROGEN VISCOSITIES AT 1 BAR 291-300 4/10/06 12:48 PM Page 297 Copyright © 1983 CRC Press LLC values of μ r estimated from Figure 4 from the low density limit curve. Assuming we know the viscosity is 17.9 ×10 –6 Pa·sec at 300 K where μ r is estimated to be 1.00, the value of μ cr is the same and the viscosities at the other temperatures are directly calculated as shown. If no viscosities are known, Equation 6 is used: μ cr = 7.70 ×10 –7 (28.02) 0.5 (34.0) 0.667 (126.3) –0.167 = 19.1 ×10 –6 Values for the other temperatures are calculated directly from the estimated values of μ r . The final column shows the actual viscosities, indicating a reasonable check. For convenience, the following are conversions to the SI system: 1 reyn =1.45 ×10 –10 Pa·sec and 1 P=0.1 Pa·sec. Specific Volume The specific volumes listed in Table 1 indicate the degree of “perfection” of a gas. At 273.1 K and I bar pressure, 1 g-mol of a perfect gas occupies a volume of 22.4 ᐉ. Adjusting this to 300 K gives 24.6 ᐉ. If the specific volumes in Table 1 are multiplied by the molecular weight for each gas, the result is liters per gram mole (ᐉ/g-mol) and also cubic meters per kilogram-mole (m 3 /kg-mol). Values for air, nitrogen, and oxygen are 24.9. Freon 21, Freon 11, and sulfur dioxide are below the perfect gas figure, indicating some degree of association between molecules. Pressure is given here in bars or atmospheres. For use in the SI system, 1 bar is equivalent to 101,300 Pa. APPLICATION OF DATA Hydrodynamic bearings principally require knowledge of the viscosity of the gas at the temperature and pressure involved. When the pressures are very low or the spacing between surfaces is very small, consideration must be given to the mean free path. Hydrostatic bearings involve feeding of gas at an elevated pressure into the bearing film area. Viscosity is required in calculating the flow through the film; thermal properties are required in calculating flow through feed orifices or ports. Sonic velocity sets a limit on flow rate in these situations. Hydrodynamic and Hydrostatic Designs The viscosity enters directly in hydrodynamic calculations through the principal terms in Reynolds equation which are of the form: Because of the usually good heat transfer to the surfaces, hydrodynamic films are treated as isothermal and at the bearing surface temperature. Ambient temperature and pressure conditions are adequate for the determination of operating viscosity from the data in the previous section. In hydrostatic design computations, one is concerned with mass flow through thin slots obeying the equation: (7) where the kinematic viscosity ν=μ/ρ enters. Here h is the slot thickness, ρ is the mass density, and w is the slot width. Where turbulence may be involved, the kinematic viscosity 298 CRC Handbook of Lubrication 291-300 4/10/06 12:48 PM Page 298 Copyright © 1983 CRC Press LLC enters in the Reynolds number: \ (8) where U is the velocity of one surface relative to another a distance h away. Feed restrictors to a hydrostatic gas bearing are more commonly of the orifice type rather than of the laminar flow type. For discharge of a perfect gas through an orifice, (P 1 /P 2 ) α = T 1 /T 2 (9) where T is the absolute temperature. The exponent a is usually expressed in terms of the ratio of specific heats, k = C p /C v , but can also be expressed in terms of the gas constant R, C p , and the molecular weight M: α=(k – 1) /k = R/C p M (10) The limiting pressure ratio at which the throat velocity equals the speed of sound is given by: (11) The key constant α can be calculated directly from Equation 10. As an example, consider the monomolecular gas argon with a molecular weight of 39.94 and a heat capacity at 300 K of C p = 0.522 kJ/kg·deg. For argon at 300 K, α=8.314/ (0.522 × 39.94) = 0.399, and r c = (0.601/0.8005) 1/0.399 = 0.488. This is equal to the theoretical value for a perfect gas of 0.49. Mean Free Path The mean free path is a measure of the average distance between collisions of the gas molecules. It is a function of the volume density of the gas and is given by: λ=1/(1.414μσ 2 n) (12) where σ is the molecular diameter and n is the molecular density in molecules per cubic centimeter. The number of molecules per gram-mole is Avogadro’s Number, 6.02 × 10 23 . As an example, the molecular density of argon at 273 K is n = 6.02 × 10 23 /22,440 = 2.69 × 10 19 The molecular diameter is approximately 2.9 × 10 –8 cm. Applying Equation 12: λ=1/ [1.414π (2.9 × 10 –8 ) 2 × 2.69 × 10 19 ] = 9.9 × 10 –6 cm The value estimated in the Handbook of Chemistry and Physics is 9.0. This accuracy is quite sufficient for low pressure or very thin film bearing design. Speed of Sound Speed of sound in a gas is a function of temperature, molecular weight, heat capacity at constant pressure, and the gas constant: Volume II 299 291-300 4/10/06 12:48 PM Page 299 Copyright © 1983 CRC Press LLC (13) Applying this data to oxygen, Table 1 lists M =32.00, and C p = 0.920 kJ/kg·K. Using this data in Equation 13 yield 329 m/sec, as compared with the value of 353 m/sec listed in Table 1. NOMENCLATURE C = Temperature, C C p = Specific heat at constant pressure, kJ/kg·K C v = Specific heat at constant volume, kJ/kg·K P = Pressure, N·m –2 T = Absolute temperature, K T B = Boiling point, K U = Surface velocity, m/sec h = Film thickness, m M = Molecular weight w = Width of leakage path, m ν=Kinematic viscosity, m 2 /sec λ=Mean free path, m μ=Absolute viscosity, Pa·sec ρ=Mass density, kg/m 3 Φ=Sonic velocity, m/sec REFERENCES 1. Vargaftile, N. B., Tables on the Thermophysical Properties of Liquids and Gases, 2nd ed., John Wiley & Sons, New York, 1975. 2. Bird, R. B., Steward, W. E., and Lightfoot, E. N., Transport Phenomena,, John Wiley & Sons, New York, 1960. 3. Uyehara, O. A. and Watson, K. M., Natl. Pel. News, 36, 764, 1944. 4. Hougen, O. A., Watson, K. M., and Ragatz, R. A., C.P.P. Charts, 2nd ed., John Wiley & Sons, New York, 1960. 300 CRC Handbook of Lubrication 291-300 4/10/06 12:48 PM Page 300 Copyright © 1983 CRC Press LLC LUBRICATING OILADDITIVES J. A. O’Brien INTRODUCTION The modern history of lubricant additives began in the early 20th century with the use of fatty oils and sulfur in mineral oils to improve lubrication under high loads. World War II provided a major impetus to the development of lubricant additives as the military, engine builders, and machine manufacturers demanded more performance from their equipment. Consumption of lubricant additives in the U.S. increased from 127 thousand metric tons in 1950 to 710 thousand metric tons in 1978. 1 Lubricants for internal combustion (IC) engines account for 72% of the market. Total free-world consumption of lubricant additives is estimated to be about three times that of the U.S. The unique feature of IC engine lubricants is their exposure to combustion products from blow-by, fuel combustion products which leak past piston rings and contact the lubricant. Blow-by contains unburned fuel, reactive intermediates of fuel oxidation, fixed nitrogen in the forms of nitrogen oxides, and their fuel reaction products, soot, products of fuel additives, sulfur oxides, carbon monoxide, carbon dioxide, and water. IC engine lubricants require extensive additive treatment to counteract the effects of blow-by, such as internal engine rust, bearing corrosion, surface deposits which interfere with engine clearances, sludge formation which blocks lubricant passages, and lubricant decomposition. Some industrial lubricants, such as those used in a steel or paper mill, also encounter severe environments and contamination. External and internal environments may subject lubricants to severe oxidizing conditions, extreme pressures and temperatures, water, dust, metal catalysts, and active chemicals. ADDITIVE FUNCTIONS Many minerals are used as lubricant additives, far too many to list in detail. Ramney published three texts 2,3,4 listing recent additive patents. This chapter discusses some of the more widely used additives, emphasizing their primary performance characteristics. Chem- ical structure and manufacture of some major lubricant additives are included in the Appendix. Boundary Lubrication Additives 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. Table 1 lists common boundary lubrication additives. Wear inhibitors and lubricity agents are polar materials that adsorb on a metal and provide a film that reduces metal-to-metal contact. 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. This low-shear compound provides the lubrication. Friction modifiers can either adsorb or react with the surface to reduce friction by forming a very low shear-strength film. For example, Figure 1 demonstrates the effect of a friction modifier in an automatic transmission fluid. Without a friction modifier, the friction coef- ficient in the transmission would increase at low-sliding velocity where surface asperities make contact. This would result in rough shifting and lead to high-transmission loading and driver discomfort in vehicles. The friction modified fluid now in common use permits smooth shifting at low speeds while it maintains adequate friction under normal driving to prevent Volume II 301 301-315 4/10/06 12:51 PM Page 301 Copyright © 1983 CRC Press LLC or (2) deactivate corrosive contaminants in the lubricant. Certain additives that inhibit cor- rosion in some environments can actually cause corrosion in others. For example, zinc dithiophosphates inhibit copper-lead bearing corrosion in an oxidative environment, yet cause silver bearing distress from sulfidation. When used in high concentrations, zinc dialkyldi- thiophosphates can also pit some ferrous metals. Oxidation Inhibitors Oxidation, the most common form of lubricant deterioration, proceeds through free-radical reactions which are accelerated by heat and catalyzed by metals. In hydrocarbon lubricants, free-radicals react with oxygen to form peroxy free-radicals which attack hydrocarbons to form new free-radicals and hydroperoxides. Free-radicals are formed faster than they are used and the rate of oxidation increases. Some hydroperoxides decompose into aldehydes, ketones, carboxylic acids, and other oxygen-containing hydrocarbons. The oxygen compounds polymerize to form viscous soluble materials (lubricant thickening) and insoluble materials (sludge and deposits.) Some of the oxygen compounds are active, polar materials that accelerate rust and corrosion. Volume II 303 FIGURE 2. Effect of friction modifier in engine crankcase lubricant. Table 2 CORROSION INHIBITORS 301-315 4/10/06 12:51 PM Page 303 Copyright © 1983 CRC Press LLC Oxidation inhibitors (Table 3) generally function by one or more of three mechanisms: free radical inhibition, peroxide decomposition, or metal deactivation. Each mechanism inhibits oxidation at a different link in the chain reaction. Hindered phenols, such as 2,6- di-t-butyl-para-cresol (DBPC), are effective free-radical oxidation inhibitors because they react with free-radicals to form nonfree-radical compounds. Some sulfur compounds de- compose peroxides into stable compounds. Some selective polar additives react with metal ions and surfaces to inhibit their catalytic activity and are known as metal deactivators. Detergents and Dispersants Both detergent and dispersant additives (Table 4) are polar materials which provide a cleaning function. Detergency is a surface phenomenon of cleaning surface deposits. Dis- persancy is a bulk lubricant phenomenon of keeping contaminants suspended in the lubricant. Detergent and dispersant additives each perform both of the above functions and differ in their relative ability to function at the machine surface or in the bulk of the lubricant. Viscosity Modifiers Viscosity index (VI) improvers (Table 5) are polymers that cause minimal increase in 304 CRC Handbook of Lubrication Table 3 OXIDATION INHIBITORS Table 4 DETERGENTS AND DISPERSANTS Table 5 VI IMPROVERS 301-315 4/10/06 12:51 PM Page 304 Copyright © 1983 CRC Press LLC lubricant viscosity at low temperature, but considerable increase at high temperature. Table 6 demonstrates the effects of a VI improver. Atypical 100 VI SAE 40 viscosity grade oil has proper viscosity (14 cSt) for engine lubrication at 100°C, but is too viscous (15000 cP) to permit engine starting at –18°C. Atypical 100 VI SAE 10Woil would permit engine starting at – 19°C, but is not viscous enough to protect the engine from wear at 100°C. By adding a VI improver to the SAE 10Woil, the product can permit engine starting at –18°C and still protect the engine from wear at 100°C. Many of the same chemicals are also used as thickeners to increase the viscosity of products for special applications such as gear oils. Molecular weight may be varied to optimize specific performance characteristics. Viscous petroleum fractions, such as bright stocks, are also used as thickeners but are not considered additives. PourPoint Depressants Petroleum oils contain paraffinic wax which crystallizes in a lattice-like structure as the lubricant cools and prevents the lubricant from flowing. The lowest temperature at which the lubricant flows is called the pour point. Pour point depressants co-crystallize with the paraffinic wax, modify growth of the lattice-like structure, and permit flow at temperatures below the pour point of the unmodified lubricant. Common pour point depressants include: polymethacrylates, wax alkylated naphthalene polymers, wax alkylated phenol polymers, and chlorinated polymers. Emulsion Modifiers Emulsifiers give stable emulsions of water-in-oil or oil-in-water. They are used where high amounts of water improve cooling due to the high specific heat and thermal conductivity of water. Lubricants which contain water are increasingly being used to conserve petroleum base stocks. Demulsifiers make emulsions unstable, which permits separation of water and lubricant. They are particularly important where water contamination can damage the lubricant in marine or industrial applications. Emulsion modifiers change the interfacial tension of oil and water. Low-interfacial tension permits stable emulsions. Table 7 lists emulsion modifiers. Foam Decomposers Excessive lubricant foaming can cause an overflow of the lubricating system, displace lubricant in pumps, increase response time of hydraulic systems, and disrupt the lubricant supply. Two theories predominate on the function of foam decomposers. The first is that they increase gas-lubricant interfacial tension to the point where the bubbles collapse. The second is that these partially soluble compounds with low-surface tension cause openings in the bubbles which allow the gas to escape. Foam decomposers function at concentrations from 1 to 50 ppm. High concentrations can lead to excessive foaming, more than the original lubricant, and increased air entrainment. Common foam decomposers include: polysiloxanes (silicones), polyacrylates, organic co- polymers, and candellilla wax. Volume II305 Table 6 EFFECT OF VI IMPROVER 301-315 4/10/06 12:51 PM Page 305 Copyright © 1983 CRC Press LLC rust inhibitors function by adsorbing on metal surfaces and they compete for the same surface. The wear inhibitor can displace the rust inhibitor on the surface and be detrimental to rust inhibition. Likewise, the rust inhibitor can displace the wear inhibitor. Meeting Performance Requirements Universal engine lubricants meet the performance requirements of passenger car gasoline engines, as well as turbocharged two-stroke cycle and four-stroke cycle truck diesel engines. The additive package requires a very careful balance because it deals with diverse, complex quality requirements. Passenger car engine lubricant requirements in the U.S. are defined by a series of laboratory engine tests designated SF 8 by the American Petroleum Institute (API). The SF designation signifies that the lubricant passed the tests shown in Table 8. Truck diesel engine lubricant requirements in the U.S. are designated CD. 9 To obtain the CD designation, the lubricant must pass the tests shown in Table 9. Most engine lubricant requirements outside the U.S. also require SF or CD performance plus additional local performance requirements. Each SF and CD test stresses certain performance aspects of the lubricant and has been correlated with field experience. The IID test simulates short-trip winter driving, which is the most severe rust-forming condition. The IIID test simulates high-speed, high-load, and high-temperature driving conditions, such as towing a camper-trailer across the desert in the summer at high speed, which are severe for oxidative thickening and wear. The VD test simulates continuous stop-and-go city driving with an overhead cam engine — a severe condition for sludge and varnish formation and cam wear. The 1-G2 test simulates a heavily loaded, turbocharged, four-stroke diesel using high-sulfur fuel. The L-38 test stresses pro- tection of copper-lead bearings from corrosion. In addition to passing all SF and CD tests, a universal engine oil must also have less than 1% sulfated ash to be compatible with two- stroke cycle diesel engine performance. Lubricant formulation involves handling all of these conditions with the same lubricant. Volume II 307 Table 8 SF ENGINE LUBRICANT TESTS 8 Table 9 CD ENGINE LUBRICANT TESTS 9 301-315 4/10/06 12:51 PM Page 307 Copyright © 1983 CRC Press LLC [...]... 19 79 7 Davis, B T et al., Fuel Economy benefits from Modified Crankcase Lubricants, Paper presented at American Society of Lubrication Engineers, 34th Annual Meeting, St Louis, Mo., 19 79 8 SAE Handbook 19 81, SAE J183 preprint, Society of Automotive Engineers, Warrendale, Pa, February 19 80 9 SAE Handbook 19 79, Society of Automotive Engineers, Warrendale, Pa., 19 79, 13 .02 10 ASTM Special Tech Publ 315 G,... synthetic oils Copyright © 19 83 CRC Press LLC 3 01- 315 4 /10 /06 12 : 51 PM 312 Page 312 CRC Handbook of Lubrication 11 Phosphosulfurized Pinene Variations — R is derived from either alpha or beta pinene or a turpentine mixture Manufacture — Pinene is reacted with P4S10 Application — Antioxidant and anticorrosion additives 12 Dilaurvl Selenide C12 H 25 – Se – C12 H 25 Manufacture — Lauryl chloride heated with... Interdisciplinary Approach to Liquid Lubricant Technology, NASA SP 318 , NTIS N74 -12 219 -12 230, Ku, P M., Ed., 19 73, 433 Copyright © 19 83 CRC Press LLC 317 -333 4 /10 /06 12 :59 PM Page 317 Volume II 317 METAL PROCESSING — DEFORMATION John A Schey INTRODUCTION In manufacturing, the desired shape of individual parts is often obtained by plastic deformation Some 85 to 90% of all steel and other technically important metals... be any of a variety of metals, including zinc and molybdenum R is C4 to C10 x is a function of the metal valence Manufacture — Secondary amines are reacted with carbon disulfide and caustic solution The sodium dithiocarbamate is then reacted with the metal chloride Application — Antioxidants and antifriction additives Copyright © 19 83 CRC Press LLC 3 01- 315 4 /10 /06 12 : 51 PM Page 311 Volume II 311 7 2,4-Ditertiarybutyl-p-Cresol... LLC 3 01- 315 4 /10 /06 314 12 : 51 PM Page 314 CRC Handbook of Lubrication Applications — Dispersants are widely used in crankcase motor oil The alkyl succinic anhydrides and acids are used as rust inhibitors 18 Alkyl Hydroxyl Benzyl Polyamine Variations — R is from an olefin polymer, e.g., polybutene, mol wt 500 to 2000 x is 2 to 5 Stoichiometry may be varied to yield 2 phenols: I amine or 2 amines: 1 phenol... is a mixture of normal and iso-paraffin groups Mol wt is 10 ,000 to 50,000 Manufacture — Polymerization of mixed methacrylie esters Application — Viscosity modifiers (VI improvers) and wax crystallization modifiers (pour point depressants) for petroleum lubricants, especially crankcase motor oils 21 Polyisobutylene Copyright © 19 83 CRC Press LLC 3 01- 315 4 /10 /06 12 : 51 PM Page 315 Volume II 315 Variations...3 01- 315 4 /10 /06 308 12 : 51 PM Page 308 CRC Handbook of Lubrication Table 10 EXAMPLE OF ADDITIVE EFFECTS IN UNIVERSAL ENGINE LUBRICANT Note: Key: + + + , very beneficial; + + , beneficial; + , slightly beneficial; = , no effect; – , detrimental; and – – , very detrimental Table 10 shows how the additives commonly used in universal engine oils perform in the major aspects of the SF and CD... cellosolve carbonate is decomposed with water in the presence of a sulfonic acid In other processes the basic or neutral soap, together with a suspension of the metal oxide or hydroxide, methanol, water, and a promoter such as ammonia or amine, is blown with carbon dioxide Copyright © 19 83 CRC Press LLC 3 01- 315 4 /10 /06 12 : 51 PM Page 313 Volume II 313 Application — Detergents, alkaline agents, and rust inhibitors... Philadelphia 11 ASTM Special Tech Publ 315 H, Part III, American Society of Testing and Materials, Philadelphia, in press 12 ASTM Special Tech Publ 509, Single Cylinder Engine Texts for Evaluating Performance of Crankcase Lubricants, American Society for Testing and Materials, Philadelphia 13 Smalheer, C V and Smith, R K., Lubricant Additives, The Lezius-Hiles Co., Cleveland, Ohio, 19 67 14 Smalheer,... this reason, friction, lubrication, and wear in metalworking have been of great interest .1- 13 EFFECTS OF FRICTION IN METAL DEFORMATION Mathematical Representation of Friction In the absence of plastic deformation, the coefficient of friction is (1) where P is normal force; F, frictional force; p, interface pressure; and τi, interface shear stress; all referred to apparent total area of contact, A In plastic . oils. 21. Polyisobutylene 314 CRC Handbook of Lubrication 3 01- 315 4 /10 /06 12 : 51 PM Page 314 Copyright © 19 83 CRC Press LLC Variations — Copolymers with butene -1. Mol wt vary from 1, 000 to 1, 000,000. Manufacture. Mo., 19 79. 8. SAE Handbook 19 81, SAE J183 preprint, Society of Automotive Engineers, Warrendale, Pa, February 19 80. 9. SAE Handbook 19 79, Society of Automotive Engineers, Warrendale, Pa., 19 79, 13 .02. 10 Liquid Lubricant Technology, NASA SP- 318 , NTIS N74 -12 219 -12 230, Ku, P. M., Ed., 19 73, 433. Volume II 315 3 01- 315 4 /10 /06 12 : 51 PM Page 315 Copyright © 19 83 CRC Press LLC METALPROCESSING — DEFORMATION John