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Generalized characteristics of rheological properties of greases
LITERATURE
AND CURRENT
EVENTS
403
Oil Additives. F. G. Rounds, ASLE Trans., g (1966) 88-100. Dynamic friction and static immersion tests in which oil temperature was varied and dynamic friction tests in which load was varied have been run on steel balls with oil blends containing seven commercial additives. Analyses of the ball surfaces by X-ray fluorescence have shown that significant surface coating formation is initiated at calculated surface temperatures of from 250 to 350°F for most of the additives studied. Although the surface coating “thickness” generally increased with temperature, the rate of increase was generally different for the static and dynamic tests. Both surface temperature and mechanical shearing appear to influence the reactions responsible for the surface coatings. Used oil analyses showed that base oil oxidation, additive decomposition, and, in some cases, sludge formation became detectible at temperatures corresponding to the start of significant surface coating formation. The results suggest that in situ polymerization may be an important phenomenon occurring on rubbing surfaces.
with the eutectics. The viscosities of the four liquid metals measured in a couette-type viscometer vary little with temperature and are always less than the two oil viscosities within the range of temperatures studied. An analysis of the friction heat path of the fourball machine shows that practically all of the calories are dissipated by the balls by convection to the lubricant. The good lubricating properties of the metals can be explained in the light of recent theories which suggest that the sharp increase in wear rate is dependent on a temperature known as the transition temperature, and thus, indirectly in the fourball machine, on the coefficient of heat transfer which is approximately thirty times larger for the eutectics than for the oils.
Some Aspects of the Heat of Adsorption in the Function of a Boundary Lubricant. C. N. Rowe, ASLE Trans., g (1966) IOO-III. The empirical relationship between the rate of adhesive wear and the ratio of load to hardness has been extended to consider the presence of a lubricant film on the surface. The expression contains two parameters, one of which is specific to characteristics of the lubricant and the other specific to characteristics of the sliding metal couple. A model is developed which considers the heat of adsorption as the controlling factor in the effectiveness of the boundary lubricant. The wear rate of a copper pin sliding against a steel disk with n-hexadecane as lubricant was determined as a function of load, sliding velocity, and temperature. Confirmation of the model is observed and the calculated heat of adsorption is I 1.5 kcal/mole. The estimated wear coefficient for that portion of the real area of contact which is metal-metal is about 0.2. This suggests that the probability will be near unity that a wear particle will be formed.
The Effect of Rheological Characteristics on the Bearing Capacity of a Lubricant Layer. (in Russian) S. B. Ainbinder and A. M. Grinshtein, Ref. Zh. Mekhan. (1965) Rev. g. B 548. For abstract see Appl. Mech. Rev., Ig (3) (1966) 282.
Lubrication with Low-melting Liquid metals. (in French) R. Bornemann and M. Godet, Rev. Inst. Franc. Petrole Ann. Combust. Liquides, 20 (IO) (1965) 1575; 27 figs., 3 tables,-31 refs. The wear oroduced with two svnthetic oils between IO; and 25o’C in a four-ball machine is notably higher than that measured with four alloys (eutectics) of Bi, Pb, Sn and Cd. The score load for one of these eutectics is higher than the maximum permissible load of the machine (8,000 N). The sharp change in slope, characteristic of all oils, does not occur
The Rheological Behavior of the Lubricant in the Contact Zone of a Rolling Contact System. J. C. Bell, J. W. Kannel and C. M. Allen, Trans. ASME, 860 (3) (1964) 423-435. (J. Basic Eng.) For abstract see A$@ Mech. Rev., Ig (2) (1966) 184.
Generalized Characteristics of Rheological Properties of Greases. V. P. Pavlov and G. V. Vinogradov, Lubrication Eng., 21 (II) (1965) 479-484; 3 figs., 14 refs. Greases are rheologically-complex, plastic, dispersed systems. Of considerable interest in characterizing them, for many fields of their performance, is the dependence of the shear stress on the deformation and deformation rate when the latter is varied over a very wide range. At very low deformation rates (usually below IO-~ set-1) the flow of greases is of the creep type, obeying the laws of flow of highly (IO~~-IO’~ poises) Newtonian or viscous slightly-structurized liquids. The ultimate shearing strength and the yield value are especially- important parameters determining the rheological properties of greases. As is shown in this paper, they have a distinct physical sense when determined by deformation at a constant rate. After the ultimate strength is surpassed at rates of deformation exceeding creep-shear rates, greases behave like anomalous and superstrongly-structurized systems, anomalous, the range of shear rate under which the viscosity anomaly occurs covering ten or more orders of magnitude. Beginning from a Wear, 9 (1966) 398-409
LITEKATUKE
404 certain sufficiently high deformation rate (usually above 10~ see-1) greases become practically Newtonian liquids m the process of flow, their viscosities being not much above that of the dispersion media. Fundamental Aspects of Grease Bleeding. S. F. Calhoun, NLGI Spokesman, q (IO) (1966)
328-332.
In this paper, the author concludes that better homogenization and dispersion of the grease thickener in the liquid component will increase both of the oil-retaining forces, and thus reduce bleeding. The Effect of Variations in the Viscosity and Type of the Mineral-oil Component on the Permeability Coefficients of Lithium-Calcium and Baragel Greases. J. L. Zakin and E. H. Tu, XLGI Spokesman, 29 (ro) (1966) 333-337. 3.3. Solid lubricants Preferential Adsorption of Compound8 with Long Methylene Chains on Cast Iron, Graphite, Boron Nitride, and Molybdenum Disulfide. A. J. Groszek, ASLE Trans., 9 (1966) 67-76. Several layered solids, which are effective solid lubricants, have a strong affinity for methylene groups. This leads to preferential adsorption on the solids of those paraffinic molecules that can form the maximum number of contacts with the surface and with each other. Thus the strength of adsorption of mineral oils increases with their average molecular weight. The strong affinity of the surfaces of the solid lubricants and cast iron for paraffine hydrocarbon is expected to influence their loadcarrying capacity, in that it should be higher for the oleophilic sliding surfaces than for surfaces such as those of plain steel, which are devoid of this property. So far, however, this has not been confirmed experimentally. For MoSz dispersed in mineral oils, indications have been obtained that the strong attachment of oil molecules to the surfaces of the dispersed solid reduces its EP effectiveness. Friction and Wear of Graphite and Molybdenum Disulphide. E. R. Braithwaite, Sci. Lubrication, 18 (4) (1966) 13, Part I; ibid., 18 (5) (1966) 17. Part 2; 16 figs., 4 tables, 23 refs. Part I : Experimental evidence for, and hypotheses on, the influence of adsorption of vapours on friction and the significance of intercrystalline forces, are presented. Part 2: Evidence of contact lubrication is given. The Effects of Reactor Radiation on Three High-temperature Solid-f&n Lubricants. R. H. McDaniel, Lubrication Eng., 21 (II) Wear, 9 (1966)
398-409
ANT) CUKKEN’f
EVEXI’S
463-473; I I figs., 7 tables, II refs. Experiments were performed to tleterminc the effects of reactor radiation on the wear life of three high-temperature, solid-film lubricant-PbS + MOSS I- BgOB, CaFy .i oxide frit, and MoSe + graphite + sodium silicate. Test specimens were irradiated under static conditions to an average gamma dose of 2.2 x loll ergs/g (C) plus associated neutrons of 5.2 x 1016 n/cm2 (E > 2.9 Me\‘). Subsequent tests with a double-rub, shoetype, sliding-wear tester were made with a load of IIO lb. per rub shoe and at a sliding speed of 128 ft./min. Tests were performed at several temperatures up to 1500’F. Based on the data obtained in this experiment and the statistical treatment employed (Weibull plots and ranking of data), it was concluded that static exposure to reactor radiation had no significant effect on the wear life of the PbS + MO& $ Hz03 film nor on the CaFz coating. The MO& + graphite 1~ sodium silicate film suffered a decrease in wear life at 80”F, but it displayed improved wear life at (loooF and izoo°F after irradiation. (1965)
Fluoride Solid Lubricant8 for Extreme Temperature8 and Corrosive Environments. H. E. Sliney, Th. N. Strom and G. P. Allen, ASLE Trans., 8 (1965) 307-322. Fluorides of the alkali metals and the alkalineearth metals have an interesting combination of properties that make them promising candidates as solid lubricant materials for use at high temperatures and in corrosive environments. They are chemically inert in strong oxidizing or reducing environments; they are relatively soft and non-abrasive; and some of them, such as CaF2, have planes of perfect cleavage in their crystal structure suggesting low shear strength and good friction properties. Thin, fused fluoride coatings (0.001 inch) were applied to nickel chromium alloys by spraying water slurries of the fluorides on the bearing surface, drying it, then firing it in a hydrogen atmosphere. Coatings of CaFz-LiF mixtures and of CaFz-BaFs mixtures were effective as solid lubricants in hydrogen to 1500°F and in air to 1200’F. The CaFs-BaFz coatings were effective solid lubricants in liquid sodium at 1000°F and a sliding velocity of sooo ft./min. Vapor-deposited, Thin Gold Films as Lubricants in Vacuum (lo-” mm Hg). T. Spalvins and D. H. Buckley, XASA Th-D-3040.
(1965)
13 PP.
Thin gold films were vapor-deposited on nickel, nickel-chromium, and nickel-rhenium surfaces to be used for lubrication purposes. The durability of the film was determined by friction characteristics. Durability and strong bonding (adhesion) between the film and the substrate are essential when thin
AND CURRENT
EVENTS
403
Oil Additives. F. G. Rounds, ASLE Trans., g (1966) 88-100. Dynamic friction and static immersion tests in which oil temperature was varied and dynamic friction tests in which load was varied have been run on steel balls with oil blends containing seven commercial additives. Analyses of the ball surfaces by X-ray fluorescence have shown that significant surface coating formation is initiated at calculated surface temperatures of from 250 to 350°F for most of the additives studied. Although the surface coating “thickness” generally increased with temperature, the rate of increase was generally different for the static and dynamic tests. Both surface temperature and mechanical shearing appear to influence the reactions responsible for the surface coatings. Used oil analyses showed that base oil oxidation, additive decomposition, and, in some cases, sludge formation became detectible at temperatures corresponding to the start of significant surface coating formation. The results suggest that in situ polymerization may be an important phenomenon occurring on rubbing surfaces.
with the eutectics. The viscosities of the four liquid metals measured in a couette-type viscometer vary little with temperature and are always less than the two oil viscosities within the range of temperatures studied. An analysis of the friction heat path of the fourball machine shows that practically all of the calories are dissipated by the balls by convection to the lubricant. The good lubricating properties of the metals can be explained in the light of recent theories which suggest that the sharp increase in wear rate is dependent on a temperature known as the transition temperature, and thus, indirectly in the fourball machine, on the coefficient of heat transfer which is approximately thirty times larger for the eutectics than for the oils.
Some Aspects of the Heat of Adsorption in the Function of a Boundary Lubricant. C. N. Rowe, ASLE Trans., g (1966) IOO-III. The empirical relationship between the rate of adhesive wear and the ratio of load to hardness has been extended to consider the presence of a lubricant film on the surface. The expression contains two parameters, one of which is specific to characteristics of the lubricant and the other specific to characteristics of the sliding metal couple. A model is developed which considers the heat of adsorption as the controlling factor in the effectiveness of the boundary lubricant. The wear rate of a copper pin sliding against a steel disk with n-hexadecane as lubricant was determined as a function of load, sliding velocity, and temperature. Confirmation of the model is observed and the calculated heat of adsorption is I 1.5 kcal/mole. The estimated wear coefficient for that portion of the real area of contact which is metal-metal is about 0.2. This suggests that the probability will be near unity that a wear particle will be formed.
The Effect of Rheological Characteristics on the Bearing Capacity of a Lubricant Layer. (in Russian) S. B. Ainbinder and A. M. Grinshtein, Ref. Zh. Mekhan. (1965) Rev. g. B 548. For abstract see Appl. Mech. Rev., Ig (3) (1966) 282.
Lubrication with Low-melting Liquid metals. (in French) R. Bornemann and M. Godet, Rev. Inst. Franc. Petrole Ann. Combust. Liquides, 20 (IO) (1965) 1575; 27 figs., 3 tables,-31 refs. The wear oroduced with two svnthetic oils between IO; and 25o’C in a four-ball machine is notably higher than that measured with four alloys (eutectics) of Bi, Pb, Sn and Cd. The score load for one of these eutectics is higher than the maximum permissible load of the machine (8,000 N). The sharp change in slope, characteristic of all oils, does not occur
The Rheological Behavior of the Lubricant in the Contact Zone of a Rolling Contact System. J. C. Bell, J. W. Kannel and C. M. Allen, Trans. ASME, 860 (3) (1964) 423-435. (J. Basic Eng.) For abstract see A$@ Mech. Rev., Ig (2) (1966) 184.
Generalized Characteristics of Rheological Properties of Greases. V. P. Pavlov and G. V. Vinogradov, Lubrication Eng., 21 (II) (1965) 479-484; 3 figs., 14 refs. Greases are rheologically-complex, plastic, dispersed systems. Of considerable interest in characterizing them, for many fields of their performance, is the dependence of the shear stress on the deformation and deformation rate when the latter is varied over a very wide range. At very low deformation rates (usually below IO-~ set-1) the flow of greases is of the creep type, obeying the laws of flow of highly (IO~~-IO’~ poises) Newtonian or viscous slightly-structurized liquids. The ultimate shearing strength and the yield value are especially- important parameters determining the rheological properties of greases. As is shown in this paper, they have a distinct physical sense when determined by deformation at a constant rate. After the ultimate strength is surpassed at rates of deformation exceeding creep-shear rates, greases behave like anomalous and superstrongly-structurized systems, anomalous, the range of shear rate under which the viscosity anomaly occurs covering ten or more orders of magnitude. Beginning from a Wear, 9 (1966) 398-409
LITEKATUKE
404 certain sufficiently high deformation rate (usually above 10~ see-1) greases become practically Newtonian liquids m the process of flow, their viscosities being not much above that of the dispersion media. Fundamental Aspects of Grease Bleeding. S. F. Calhoun, NLGI Spokesman, q (IO) (1966)
328-332.
In this paper, the author concludes that better homogenization and dispersion of the grease thickener in the liquid component will increase both of the oil-retaining forces, and thus reduce bleeding. The Effect of Variations in the Viscosity and Type of the Mineral-oil Component on the Permeability Coefficients of Lithium-Calcium and Baragel Greases. J. L. Zakin and E. H. Tu, XLGI Spokesman, 29 (ro) (1966) 333-337. 3.3. Solid lubricants Preferential Adsorption of Compound8 with Long Methylene Chains on Cast Iron, Graphite, Boron Nitride, and Molybdenum Disulfide. A. J. Groszek, ASLE Trans., 9 (1966) 67-76. Several layered solids, which are effective solid lubricants, have a strong affinity for methylene groups. This leads to preferential adsorption on the solids of those paraffinic molecules that can form the maximum number of contacts with the surface and with each other. Thus the strength of adsorption of mineral oils increases with their average molecular weight. The strong affinity of the surfaces of the solid lubricants and cast iron for paraffine hydrocarbon is expected to influence their loadcarrying capacity, in that it should be higher for the oleophilic sliding surfaces than for surfaces such as those of plain steel, which are devoid of this property. So far, however, this has not been confirmed experimentally. For MoSz dispersed in mineral oils, indications have been obtained that the strong attachment of oil molecules to the surfaces of the dispersed solid reduces its EP effectiveness. Friction and Wear of Graphite and Molybdenum Disulphide. E. R. Braithwaite, Sci. Lubrication, 18 (4) (1966) 13, Part I; ibid., 18 (5) (1966) 17. Part 2; 16 figs., 4 tables, 23 refs. Part I : Experimental evidence for, and hypotheses on, the influence of adsorption of vapours on friction and the significance of intercrystalline forces, are presented. Part 2: Evidence of contact lubrication is given. The Effects of Reactor Radiation on Three High-temperature Solid-f&n Lubricants. R. H. McDaniel, Lubrication Eng., 21 (II) Wear, 9 (1966)
398-409
ANT) CUKKEN’f
EVEXI’S
463-473; I I figs., 7 tables, II refs. Experiments were performed to tleterminc the effects of reactor radiation on the wear life of three high-temperature, solid-film lubricant-PbS + MOSS I- BgOB, CaFy .i oxide frit, and MoSe + graphite + sodium silicate. Test specimens were irradiated under static conditions to an average gamma dose of 2.2 x loll ergs/g (C) plus associated neutrons of 5.2 x 1016 n/cm2 (E > 2.9 Me\‘). Subsequent tests with a double-rub, shoetype, sliding-wear tester were made with a load of IIO lb. per rub shoe and at a sliding speed of 128 ft./min. Tests were performed at several temperatures up to 1500’F. Based on the data obtained in this experiment and the statistical treatment employed (Weibull plots and ranking of data), it was concluded that static exposure to reactor radiation had no significant effect on the wear life of the PbS + MO& $ Hz03 film nor on the CaFz coating. The MO& + graphite 1~ sodium silicate film suffered a decrease in wear life at 80”F, but it displayed improved wear life at (loooF and izoo°F after irradiation. (1965)
Fluoride Solid Lubricant8 for Extreme Temperature8 and Corrosive Environments. H. E. Sliney, Th. N. Strom and G. P. Allen, ASLE Trans., 8 (1965) 307-322. Fluorides of the alkali metals and the alkalineearth metals have an interesting combination of properties that make them promising candidates as solid lubricant materials for use at high temperatures and in corrosive environments. They are chemically inert in strong oxidizing or reducing environments; they are relatively soft and non-abrasive; and some of them, such as CaF2, have planes of perfect cleavage in their crystal structure suggesting low shear strength and good friction properties. Thin, fused fluoride coatings (0.001 inch) were applied to nickel chromium alloys by spraying water slurries of the fluorides on the bearing surface, drying it, then firing it in a hydrogen atmosphere. Coatings of CaFz-LiF mixtures and of CaFz-BaFs mixtures were effective as solid lubricants in hydrogen to 1500°F and in air to 1200’F. The CaFs-BaFz coatings were effective solid lubricants in liquid sodium at 1000°F and a sliding velocity of sooo ft./min. Vapor-deposited, Thin Gold Films as Lubricants in Vacuum (lo-” mm Hg). T. Spalvins and D. H. Buckley, XASA Th-D-3040.
(1965)
13 PP.
Thin gold films were vapor-deposited on nickel, nickel-chromium, and nickel-rhenium surfaces to be used for lubrication purposes. The durability of the film was determined by friction characteristics. Durability and strong bonding (adhesion) between the film and the substrate are essential when thin