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Friction in

Friction in Lubrication and the Coefficient of Friction. The lubricants used and values of μ were as follows : Lubricant. Value of μ Soap B. 0.033-0.061 R.O.D. Emulsion 0.064-0.077 Castor Oil 0.069-0.081 Oil Dag 0.088-0.0096 WIRE DRAWING Hypoid 90 0.01 -0.11 (Drawing speed 3.5 ft/niin.; well-polished Widia dies, die semi-angles 2.8°-5.1°; reductions of area 27-48%). A valuable paper on Wire Drawing has been I t was found that with the better lubricants, μ3 de­ published by the Institute of Metals, the authors creases when the die-angle is reduced, but with the being H. G. Baron, M.Sc., and Professor C. Thompson, poorer lubricants the die-angle ha s littl e or no influence. D.Met., M.Sc. With good soap lubricants, the surface finish of the We give herewith a brief synopsis of this paper with dies has little effect on μ, but with the liquid lubric­ some extracts from the conclusions, and recommend ants it has a marked influence. With good lubric­ readers interested in this subject to obtain the com­ plete paper for their records. ants, also, μ decreases when the interfacial pressure is reduced. Results are given of a short investigation of the magnitude of frictional loss in drawing 65:35 brass With good soap lubricants, μ decreases continu­ wire, using carbide dies with and without parallel ously as th e speed is reduced from 3.3 t o 0.001 in/min. extensions. A room-temperature ageing effect was With liquid lubricants μ decreases when the speed is noticed in the C5:35 drawn brass wire under certain reduced from 3.5 ft/min. but at some critical speed, conditions. The 0.2 per cent proof stress, for instance, which is quite low, there is again an increase in μ. decreased when the wire was aged. With good soap lubricants, again, the lubricating A heavy pass is reported to be more economical in film tends to become much thicker when the speed the total work done than are a series of light passes is increased to the region of 1,000 ft/min. With which give the same final diameter. The ratio (work these lubricants μ decreases when the temperature is raised up to 120°C. except when the drawing speed wasted in friction) to (total work done) decreases as is less than 0.01 in/min. the reduction of area is increased. Also, the ratio (work done in the parallel zone of the die) to (total The wire drawing soaps provide a relatively thick work done) decreases as the reduction of area is film of lubricant which behaves hydrodynamically. increased, and eventually becomes zero when the With liquid lubricants the film is thinner and nearer drawing load approaches the breaking load of the to the boundary state, but the best liquid lubricants wire. show some hydrodynamic tendencies. Copies of the complete paper are available from The Institute of Metals, 4, Grosvenor Gardens, Theories of Wire Drawing. London, S.W.I., price 2s. 6d. ea. to non-members. The three wire drawing theories due to Sachs, Davis and Dokos, and Hill and Tupper, respectively, all agree that when friction and redundant work are zero, the work done in drawing is equal to the work done in simple tensile stretching. Sachs's equation fails when the drawing stress becomes greater than the "mean yield stress". Also, the elastic term which Davis and Dokos add to their equation is inaccurate and should be omitted. When this elastic term is neglected and redundant work is small, Davis and Dokos's equation appears to be more accurate than those of Sachs or Hill and Tupper, and can be used to calculate reliable values of μ. The sources of error in Davis and Dokos's equation are small, and tend to make the calculated values of μ too large. Wir e Drawing and Back-Pull. Experiments with back-pull have shown that the relationship between the die load and back-pull is not strictly linear due to the fact that the coefficient of friction decreases as back-pull is increased. It is believed, however, that MacLellan's equation can be used under specified conditions. Back-pull experi­ ments provide the most accurate method of deriving μ when μ is small. Scientific LUBRICATION March. 19SI http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Industrial Lubrication and Tribology Emerald Publishing

Friction in

Industrial Lubrication and Tribology , Volume 3 (3): 1 – Mar 1, 1951

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0036-8792
DOI
10.1108/eb052102
Publisher site
See Article on Publisher Site

Abstract

Lubrication and the Coefficient of Friction. The lubricants used and values of μ were as follows : Lubricant. Value of μ Soap B. 0.033-0.061 R.O.D. Emulsion 0.064-0.077 Castor Oil 0.069-0.081 Oil Dag 0.088-0.0096 WIRE DRAWING Hypoid 90 0.01 -0.11 (Drawing speed 3.5 ft/niin.; well-polished Widia dies, die semi-angles 2.8°-5.1°; reductions of area 27-48%). A valuable paper on Wire Drawing has been I t was found that with the better lubricants, μ3 de­ published by the Institute of Metals, the authors creases when the die-angle is reduced, but with the being H. G. Baron, M.Sc., and Professor C. Thompson, poorer lubricants the die-angle ha s littl e or no influence. D.Met., M.Sc. With good soap lubricants, the surface finish of the We give herewith a brief synopsis of this paper with dies has little effect on μ, but with the liquid lubric­ some extracts from the conclusions, and recommend ants it has a marked influence. With good lubric­ readers interested in this subject to obtain the com­ plete paper for their records. ants, also, μ decreases when the interfacial pressure is reduced. Results are given of a short investigation of the magnitude of frictional loss in drawing 65:35 brass With good soap lubricants, μ decreases continu­ wire, using carbide dies with and without parallel ously as th e speed is reduced from 3.3 t o 0.001 in/min. extensions. A room-temperature ageing effect was With liquid lubricants μ decreases when the speed is noticed in the C5:35 drawn brass wire under certain reduced from 3.5 ft/min. but at some critical speed, conditions. The 0.2 per cent proof stress, for instance, which is quite low, there is again an increase in μ. decreased when the wire was aged. With good soap lubricants, again, the lubricating A heavy pass is reported to be more economical in film tends to become much thicker when the speed the total work done than are a series of light passes is increased to the region of 1,000 ft/min. With which give the same final diameter. The ratio (work these lubricants μ decreases when the temperature is raised up to 120°C. except when the drawing speed wasted in friction) to (total work done) decreases as is less than 0.01 in/min. the reduction of area is increased. Also, the ratio (work done in the parallel zone of the die) to (total The wire drawing soaps provide a relatively thick work done) decreases as the reduction of area is film of lubricant which behaves hydrodynamically. increased, and eventually becomes zero when the With liquid lubricants the film is thinner and nearer drawing load approaches the breaking load of the to the boundary state, but the best liquid lubricants wire. show some hydrodynamic tendencies. Copies of the complete paper are available from The Institute of Metals, 4, Grosvenor Gardens, Theories of Wire Drawing. London, S.W.I., price 2s. 6d. ea. to non-members. The three wire drawing theories due to Sachs, Davis and Dokos, and Hill and Tupper, respectively, all agree that when friction and redundant work are zero, the work done in drawing is equal to the work done in simple tensile stretching. Sachs's equation fails when the drawing stress becomes greater than the "mean yield stress". Also, the elastic term which Davis and Dokos add to their equation is inaccurate and should be omitted. When this elastic term is neglected and redundant work is small, Davis and Dokos's equation appears to be more accurate than those of Sachs or Hill and Tupper, and can be used to calculate reliable values of μ. The sources of error in Davis and Dokos's equation are small, and tend to make the calculated values of μ too large. Wir e Drawing and Back-Pull. Experiments with back-pull have shown that the relationship between the die load and back-pull is not strictly linear due to the fact that the coefficient of friction decreases as back-pull is increased. It is believed, however, that MacLellan's equation can be used under specified conditions. Back-pull experi­ ments provide the most accurate method of deriving μ when μ is small. Scientific LUBRICATION March. 19SI

Journal

Industrial Lubrication and TribologyEmerald Publishing

Published: Mar 1, 1951

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