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Extreme pressure lubrication and wear. The chemical reactivity and the extreme pressure action of two aliphatic disulfides
SYSTEMATIC ABSTRACTS The Detection of Oil Fihne Between Hypoid Gear Teeth Using Contact Resistance Measurements. R. B. Campbell and D. MacDonald. J. Inst. Petrol., 47 (1961) 365-374. The oil films were always very thin or absent where the sliding speed, and consequently the gear surface temperature, was highest. The effect of surface conditioning of the teeth through “running-in” has ,been investigated, and suggestions are put forward as to the role of so-called extreme pressure additives. Lubrication of Rolling Surfaces by a ReeEyring Fluid. J. C. Bell. ASLE Trans., 5 (1962) 160-171, Discussion: p. I6g-171, 4 figs., 4 tables, 15 refs. Recent measurements of thicknesses of lubricant films between cylinders rolling at moderate speeds have agreed reasonably well with the predictions of Grubin’s formula, but at high speeds and with high viscosity lubricants significant disagreements have been observed. Therefore, the elastohydrodynamic theory underlying that formula is reconstructed so to be based,not on a Newtonian model for the lubricant, but on the ReeEyring model which permits shear stress to develop at a lessening rate as shear rate increases. A formula comparable to Grubin’s is derived, and it is shown that the changes in the formula are in the direction needed to explain the observed discrepancies between experimental data and the former theory. Exhaustive examination or use of this new forhula is hampered by lack of data on the Ree-Eyring parameters, so further expenmental work is recommended. The Effect of Temperature in Concentrated Contact Lubrication. F. W. Smith. ASLE Trans.,5 (1962) 142-148, Discussion p. 147-148; 6 figs. I table, 15 refs. Experiments are described on the frictional behavior of a petroleum oil in the contact zone between a spherical steel roller and a cylindrical one moving in combined rolling and sliding at 23 “C, IOO “C, and Igo “C, and at maximum Hertz contact stresses of up to 3go,ooo p.s.i. The coefficient of friction is found to decrease with increasing temperature. The results are interpreted on the hypothesis that the frictional force represents the shearing of a film of essentially solidified lubricant at a shear plane of molecular dimensions. Chemical Changes in Steel Surfaces During Extreme Pressure Lubrication. D. Godfrey. ASLE Trans., 5 (1962) 57-66, Discussion p. 64-65; 3 figs., 3 tables, 47 refs. Films and wear fragments from unfailed test cups from SAE extreme pressure runs with sulfurized mineral oil and films from unfailed
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hypoid gear teeth run in commercial gear oils were analyzed by six methods. The major compound was Fe804 or a similar spine]. Minor constituents were FeS, FeO, and an “iron carbide.” Emission spectrographic analysis showed silicon in much greater concentrations than in the base metal. The beneficial effects of silicon enrichment are discussed and the mechanisms that might cause it to concentrate in the surface. Bench test data are given demonstrating how poly (methylphenylsiloxane) can increase the load-carrying capacity and reduce the wear of gear oils. The Mechanism of Action of Sulfur Compounds During Boundary Lubrication, Using 3% as a Tracer. T. Sakurai, S. Ikeda and H. Okabe. ASLE Trans.,5 (1962) 67-74; II figs., 3 tables, 5 refs. The mechanism of the action of sulfur compounds during boundary lubrication has been studied by using 3% as a tracer. A NACA type friction machine was used to study the chemical reaction between elementary sulfur or sulfur compounds and metals. All additives were added to cetane which was used as a lubricating oil. It has been found that it is possible to study kinetically the formation of the iron sulfide and the rate of the wear of its film on the friction surface. Some good analytical results have been obtained. The rate of wear of iron sulfide film for benzyl disulfide is lower than that for the elementary sulfur, because the former may adsorb effectively to the worn surface. The iron sulfide film formed on the friction surface seems to absorb the polar compounds more actively than the surface of iron oxide. These results were revealed from the autoradiography of the adsorption. Extreme Pressure Lubrication and Wear. The Chemical Reactivity and the Extreme Pressure Action of Two AliphaticDisuUides. A. Dorinson andV. E. Broman. ASLE Trans., 5 (1962) 75-90. Discussion p. 89-90; 18 figs., 3 tables, 17 refs. Reaction rates were studied for the action of di-tert-octyl disulfide and di-n-octyl disulfide in white oil on iron powder over the temperature range 165-250 “C. The data were fitted to the Arrhenius equation, and the tertiary disulfide was found to be 1500 times as reactive as the normal disulfide. White oil solutions of the two disulfides were subjected to the Falex test and to the four-ball extremepressure test, and the teriary disulfide was found to be the more effective lubricant additive in these tests. Wear studies were carried out with a pin and disk apparatus under conditions which approximated the above bench tests as regards specimen material, rubbing speed and pressure. The complex Wear, 5 (1962) 408-415
nature of the course of wear made it difficult to compare the two disulfides quantitatively. It was found that the teriary disulfide was 2-20 times as efficacious as the normal disulfide in reducing the terminal steady-state wear rate. By treating the additive action of the disulfides as a competition between the rate of metallic adhesion and the rate of chemical reaction with iron, it is possible to reconcile the wide discrepancy between the relative chemical reactivity and the relative additive action of the two disulfides in a quantitative fashion. Spindle Coupling Lubrication Methods. J. Simon. Lubrication Eng., 18 (1962) 278-282 ; 10 figs., 2 refs. Both automatic and continuous methods of lubrication for the reversing and unidirectional coupling are presented ; modifications of these methods are also described. Nonautomatic methods, some of which have increased slipper life tenfold, are presented. 3.2. Lubricants Proceedings of the Air Force-Navy-Industry Propulsion Systems Lubricants Conference. Book; for abstract see Appl. Mechanics Revs., ‘5 (1962) 4’5. The Behaviour of Lubricants at High Rates of Shear. (in German) Das Verhalten von Schmiermitteln bei hohen Schergefallen R. Schnurmann. ErdBl und Kohle, sg (6) (1962) 451-455; 9 figs., z tables, g refs. A method is described for the generation of high rates of shear, of the order of 106 set-1, by the use of so little power as to raise the temperature of the liquid during shearing by not more than, say, 0.05”C. Only under such conditions of low energy input is it possible to attain high rates of shear without heating the liquid and to maintain laminar flow. It was thus shown that, quite generally, liquids with nonspherical molecules, even straight mineral oils, exhibited the phenomenon of temporary viscosity reduction. Liquids containing very long molecules suffered also a permanent viscosity loss. A liquid which shows temporary viscosity reduction has a smaller viscosity- temperature coefficient while the shearing stress is maintained than at a low rate of shear, whereas permanent viscosity loss is accompanied by an increase of the viscosity-temperature coefficient. Temporary viscosity reduction can be explained by the non-uniform rate of revolution of non-spherical molecules in a laminar stream. However, when the revolving molecules get in one another’s way, molecular turbulence sets in, and the apparent viscosity increases with any further rise in the rate of shear.
The implications of the shear dependence of the viscosity for the load-carrying capacity of lubricants and the cold starting of engines are discussed. Also, the effect of the lead content of the fuel on permanent viscosity loss of the lubricant is related to the effect of the lead on the shear breakdown of lubricants containing polymer molecules and the chemical reactions of the thus formed free radicals. The Effect of Lubricant Viscosity on Metallic Contact and Friction in a Sliding System. M. J. Furey and J. Ii. Appeldoorn. ASLE Trans., 5 (x962) 149-159, Discussion: p. i.=,TPr5g; 8 figs., 6 tables, 8 refs. Astudy wasmadeof the effect of lubricant viscosity on metallic contact and friction in the transition zone between hydrodynamic and boundary lubrication. The system used was one of pure sliding and relatively high contact stress, namely, a fixed steel ball on a rotating steel cylinder. The extent of metallic contact was determined by measuring the electrical resistance between the rubbing surfaces. Increasing the viscosity of Newtonian fluids (mineral oils) over the range from 2 to 1100 centipoises caused a decrease in metallic contact-the effect becoming progressively more pronounced at higher viscosities. The viscosity here was the viscosity at atmospheric pressure and at the test temperature; neither pressure-viscosity nor temperatureviscosity properties appeared to be important factors. On the other hand, non-Newtonian fluids (polymer-thickened oils) gave more metallic contact than their mineral oil counterparts--suggesting that shear-viscosity is important. However, no beneficial effects of viscoelastic properties were observed with these oils. Friction generally decreased as the lubricant viscosity was increased, probably because of the reduction in metallic contact. Elastic Behavior of Certain HydrocarbonSoap and Other Colloidal Systems. A. H. Nissan. ASLE Trans., 5 (1962) 134141; IO figs., 5 tables, IO refs. Solutions of aluminium soaps in hydrocarbons, and of certain other polymeric liquids, show normal stress phenomena when they are subjected to shear -the so-called Weissenberg Effect. In the present paper the influence of speed, concentration, temperature, molecular weight of solute and of the type of solvent on these phenomena is investigated. The normal stress is also found to correlate with the viscosity of the system. Although it is known that this remarkable phenomenon is related to the free energy changes-or the elastically stored energythere is no comprehensive theory as yet which explains it in terms of the molecules taking part in the straining operation. Wear, j (1962) 408-415
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hypoid gear teeth run in commercial gear oils were analyzed by six methods. The major compound was Fe804 or a similar spine]. Minor constituents were FeS, FeO, and an “iron carbide.” Emission spectrographic analysis showed silicon in much greater concentrations than in the base metal. The beneficial effects of silicon enrichment are discussed and the mechanisms that might cause it to concentrate in the surface. Bench test data are given demonstrating how poly (methylphenylsiloxane) can increase the load-carrying capacity and reduce the wear of gear oils. The Mechanism of Action of Sulfur Compounds During Boundary Lubrication, Using 3% as a Tracer. T. Sakurai, S. Ikeda and H. Okabe. ASLE Trans.,5 (1962) 67-74; II figs., 3 tables, 5 refs. The mechanism of the action of sulfur compounds during boundary lubrication has been studied by using 3% as a tracer. A NACA type friction machine was used to study the chemical reaction between elementary sulfur or sulfur compounds and metals. All additives were added to cetane which was used as a lubricating oil. It has been found that it is possible to study kinetically the formation of the iron sulfide and the rate of the wear of its film on the friction surface. Some good analytical results have been obtained. The rate of wear of iron sulfide film for benzyl disulfide is lower than that for the elementary sulfur, because the former may adsorb effectively to the worn surface. The iron sulfide film formed on the friction surface seems to absorb the polar compounds more actively than the surface of iron oxide. These results were revealed from the autoradiography of the adsorption. Extreme Pressure Lubrication and Wear. The Chemical Reactivity and the Extreme Pressure Action of Two AliphaticDisuUides. A. Dorinson andV. E. Broman. ASLE Trans., 5 (1962) 75-90. Discussion p. 89-90; 18 figs., 3 tables, 17 refs. Reaction rates were studied for the action of di-tert-octyl disulfide and di-n-octyl disulfide in white oil on iron powder over the temperature range 165-250 “C. The data were fitted to the Arrhenius equation, and the tertiary disulfide was found to be 1500 times as reactive as the normal disulfide. White oil solutions of the two disulfides were subjected to the Falex test and to the four-ball extremepressure test, and the teriary disulfide was found to be the more effective lubricant additive in these tests. Wear studies were carried out with a pin and disk apparatus under conditions which approximated the above bench tests as regards specimen material, rubbing speed and pressure. The complex Wear, 5 (1962) 408-415
nature of the course of wear made it difficult to compare the two disulfides quantitatively. It was found that the teriary disulfide was 2-20 times as efficacious as the normal disulfide in reducing the terminal steady-state wear rate. By treating the additive action of the disulfides as a competition between the rate of metallic adhesion and the rate of chemical reaction with iron, it is possible to reconcile the wide discrepancy between the relative chemical reactivity and the relative additive action of the two disulfides in a quantitative fashion. Spindle Coupling Lubrication Methods. J. Simon. Lubrication Eng., 18 (1962) 278-282 ; 10 figs., 2 refs. Both automatic and continuous methods of lubrication for the reversing and unidirectional coupling are presented ; modifications of these methods are also described. Nonautomatic methods, some of which have increased slipper life tenfold, are presented. 3.2. Lubricants Proceedings of the Air Force-Navy-Industry Propulsion Systems Lubricants Conference. Book; for abstract see Appl. Mechanics Revs., ‘5 (1962) 4’5. The Behaviour of Lubricants at High Rates of Shear. (in German) Das Verhalten von Schmiermitteln bei hohen Schergefallen R. Schnurmann. ErdBl und Kohle, sg (6) (1962) 451-455; 9 figs., z tables, g refs. A method is described for the generation of high rates of shear, of the order of 106 set-1, by the use of so little power as to raise the temperature of the liquid during shearing by not more than, say, 0.05”C. Only under such conditions of low energy input is it possible to attain high rates of shear without heating the liquid and to maintain laminar flow. It was thus shown that, quite generally, liquids with nonspherical molecules, even straight mineral oils, exhibited the phenomenon of temporary viscosity reduction. Liquids containing very long molecules suffered also a permanent viscosity loss. A liquid which shows temporary viscosity reduction has a smaller viscosity- temperature coefficient while the shearing stress is maintained than at a low rate of shear, whereas permanent viscosity loss is accompanied by an increase of the viscosity-temperature coefficient. Temporary viscosity reduction can be explained by the non-uniform rate of revolution of non-spherical molecules in a laminar stream. However, when the revolving molecules get in one another’s way, molecular turbulence sets in, and the apparent viscosity increases with any further rise in the rate of shear.
The implications of the shear dependence of the viscosity for the load-carrying capacity of lubricants and the cold starting of engines are discussed. Also, the effect of the lead content of the fuel on permanent viscosity loss of the lubricant is related to the effect of the lead on the shear breakdown of lubricants containing polymer molecules and the chemical reactions of the thus formed free radicals. The Effect of Lubricant Viscosity on Metallic Contact and Friction in a Sliding System. M. J. Furey and J. Ii. Appeldoorn. ASLE Trans., 5 (x962) 149-159, Discussion: p. i.=,TPr5g; 8 figs., 6 tables, 8 refs. Astudy wasmadeof the effect of lubricant viscosity on metallic contact and friction in the transition zone between hydrodynamic and boundary lubrication. The system used was one of pure sliding and relatively high contact stress, namely, a fixed steel ball on a rotating steel cylinder. The extent of metallic contact was determined by measuring the electrical resistance between the rubbing surfaces. Increasing the viscosity of Newtonian fluids (mineral oils) over the range from 2 to 1100 centipoises caused a decrease in metallic contact-the effect becoming progressively more pronounced at higher viscosities. The viscosity here was the viscosity at atmospheric pressure and at the test temperature; neither pressure-viscosity nor temperatureviscosity properties appeared to be important factors. On the other hand, non-Newtonian fluids (polymer-thickened oils) gave more metallic contact than their mineral oil counterparts--suggesting that shear-viscosity is important. However, no beneficial effects of viscoelastic properties were observed with these oils. Friction generally decreased as the lubricant viscosity was increased, probably because of the reduction in metallic contact. Elastic Behavior of Certain HydrocarbonSoap and Other Colloidal Systems. A. H. Nissan. ASLE Trans., 5 (1962) 134141; IO figs., 5 tables, IO refs. Solutions of aluminium soaps in hydrocarbons, and of certain other polymeric liquids, show normal stress phenomena when they are subjected to shear -the so-called Weissenberg Effect. In the present paper the influence of speed, concentration, temperature, molecular weight of solute and of the type of solvent on these phenomena is investigated. The normal stress is also found to correlate with the viscosity of the system. Although it is known that this remarkable phenomenon is related to the free energy changes-or the elastically stored energythere is no comprehensive theory as yet which explains it in terms of the molecules taking part in the straining operation. Wear, j (1962) 408-415