Showing papers in "Powder Metallurgy in 1969"
TL;DR: In this paper, the conditions under which carbide-tipped rock-cutting tools are employed are very much more severe than any experienced under metal-cutting conditions, vibration of the cutting machine being very significant.
Abstract: The conditions under which carbide-tipped rock-cutting tools are employed are very much more severe than any experienced under metal-cutting conditions, vibration of the cutting machine being very significant. Cutting rock also tends to be an intermittent process.Once macroscopic chipping of the cutting edge has been overcome, the predominant mechanism of wear appears to be one of microfracturing of the surface layers, probably a high-strain-fatigue type of failure. For this reason pure WC–Co grades are usually employed for greater fracture-resistance, rather than other grades of cemented carbides. However, other mechanisms of wear are also probably operative, corresponding to abrasive mechanisms, and becoming more important as higher temperatures are generated. Recent hardness measurements indicate that at the temperatures generated in the carbide tip, especially when cutting quartzitic rock, grains of the rock material could well be harder than the tool material. At the wear flat, where a certai...
59 citations
TL;DR: In this paper, the creep behaviour of high-density silicon carbide has been examined under four-point transverse bending in air at temperatures from 1000 to 1300°C Stresses in the range 0·207 GN m−2 (30 000 Ib in−2) to 0·496 GN m −2 (72000 lb in−1) were applied in tests lasting up to 3·6 Msec (1000 h).
Abstract: The creep behaviour of high-density silicon carbide has been examined under four-point transverse bending in air at temperatures from 1000 to 1300°C Stresses in the range 0·207 GN m−2 (30 000 Ib in−2) to 0·496 GN m−2 (72000 lb in−2) were appliedIn tests lasting up to 3·6 Msec (1000 h) the creep strain (ϵp) increased with time (t) as ϵp = Atk where k was between 0·2 and 0·5 The dependence of A on stress (σ) and absolute temperature (T) was found to be with n between 1 and 2 and Q∼230 kJ mole−1 (55 kcal mole−1)These results are compared with estimates of creep in SiC obtained by extrapolation of steady-state creep data from higher temperatures
26 citations
TL;DR: The microstructure of dispersion-strengthened aluminium products manufactured by powder blending has been examined by optical and transmission electron microscopy, and the mechanical properties have been determined at room temperature and at elevated temperatures by tensile- and creep-testing as mentioned in this paper.
Abstract: The microstructure of dispersion-strengthened aluminium products manufactured by powder blending has been examined by optical and transmission electron microscopy, and the mechanical properties have been determined at room temperature and at elevated temperatures by tensile- and creep-testing.Powder variables, such as the size of the aluminium-powder particles and the size, volume concentration, and type of oxide (Al2O3, SiO2, ZrO2) used as the dispersed phase, have been investigated, together with manufacturing variables, such as temperature of the extrusion billet, reduction ratio in extrusion, and heat-treatment after extrusion. Major variables are the size of the aluminium particles and the oxide concentration, and generally it has been found that the strength increases and the elongation decreases for decreasing size of aluminium particles and increasing oxide concentration. The elongation measured after extended creep-testing is, however, practically the same for all products, of the order o...
21 citations
TL;DR: In this article, the deformation of particles and the general process of densification during the roll-compacting of strip from metal powder have been determined by photomicrographic and QTM studies.
Abstract: The deformation of particles and the general process of densification during the roll-compacting of strip from metal powder have been determined by photomicrographic and QTM studies. Observations were made on the expansion of the compacted strip after it had passed the plane joining the roll axes. The effect was related to elastic recovery of the material and the expansion of gases entrapped in the pores between the particles.The production of satisfactory green strip was found to be restricted to a range of thicknesses obtained between certain maximum and minimum roll gaps. These limits were related to roll pressure and strip density. It was also restricted by a maximum rolling speed that was governed by powder flow to the compaction zone.Density variations that occurred across the width and through the thickness of green strip were also determined.
21 citations
TL;DR: In this article, a survey of the existing literature on UAl2-Al dispersions is surveyed and a comparison with similar data for UAl3-al dispersions was attempted.
Abstract: The existing literature on UAl2-Al dispersions is surveyed and a comparison with similar data for UAl3-Al dispersions is attempted. The experimental work included the preparation of a practically single-phase UAl2 compound by induction-melting and its grinding to a predetermined particle size. The blending of UAl2 and aluminium powders into suitable dispersions and their compaction by cold pressing to the densities required for roll-bonding are described. The picture-frame technique was used to clad the dispersions with aluminium to produce test-plates for irradiation experiments.The kinetics of the UAl2 and UAl3 solid-state reactions with aluminium are dealt with on a qualitative basis. Throughout, comparison is made with the known technology of UAl3-Al dispersions, taking into consideration uranium densities, production aspects, pyrophoricity, volume changes, &c.It is concluded that UAl2-Al dispersions have potential applications as fuels for advanced test reactors.
17 citations
TL;DR: In this article, a theoretical approach to the subject is adopted in which the perfect wheel is considered in terms of a balanced system of matrix wear vs. the useful life of the diamond point.
Abstract: The field of metal-bonded diamond grinding wheels and saws is described. The production of these tools is an important part of the industrial-diamond industry, yet methods of construction, formulation and use raise practical problems that have not so far received a comprehensive and fundamental appraisal.A theoretical approach to the subject is adopted in which the perfect wheel is considered in terms of a balanced system of matrix wear vs. the useful life of the diamond point. The discussion emphasizes the close association of grinding with tribology and explains how control of the wear of the metal matrix, together with the correct choice of diamond parameters, plays an important part in the performance of the wheel. It is stressed that lubrication during the grinding operation is the dominant factor in achieving maximum efficiency and economy.The metal matrix is considered with regard to both its wear characteristics and its diamond-retention properties. Some wear data for common matrices are q...
16 citations
TL;DR: The first suggestion that the porous products of powder metallurgy could be used as self-lubricating bearings appears to have been made sometime in the early 1920s as discussed by the authors.
Abstract: The first suggestion that the porous products of powder metallurgy could be used as self-lubricating bearings appears to have been made sometime in the early 1920s. The idea probably originated from attempts to overcome the heat conductivity limitation of oil-soaked wooden bearings. Fortunately, the conventional bearing bronze compositions could be produced by sintering and pressing the copper and tin powders which were then available, and called for nothing spectacular in the way of presses, sintering atmospheres, or furnace equipment. Although these early products were capable of only a fraction of the duty to which porous metal bearings are subjected today, their rapid development was possible because the techniques and principles involved in their manufacture were already available from other applications of powder metallurgy. The current (1964) world production of porous metal bearings is estimated to be about eight millions per day, and is still expanding.
15 citations
TL;DR: The roll-compaction of METAL POWDERS as mentioned in this paper was the first publication of the concept of powder metallurgy, and was published in 1969, Vol. 12, No. 24, pp. 598-612.
Abstract: (1969). THE ROLL-COMPACTION OF METAL POWDERS. Powder Metallurgy: Vol. 12, No. 24, pp. 598-612.
11 citations
TL;DR: In this paper, data acquired from practical industrial experience with several commonly used compacting lubricants have been investigated from the viewpoints of thermal decomposition in relation to sintering conditions (atmospheres, vacuum, temperature); influence on the compactibility of iron powder (improved density) and the reduction of ejection force.
Abstract: Data acquired from practical industrial experience with several commonly used compacting lubricants have been investigated from the viewpoints of: (1) thermal decomposition in relation to sintering conditions (atmospheres, vacuum, temperature); (2) influence on the compactibility of iron powder (improved density) and the reduction of ejection force.On the basis of the results obtained, the paper concludes with several points of guidance regarding the use of lubricants in iron powder metallurgy.
9 citations
TL;DR: In this article, five classes of sinter-based bearing are identified: steel-backed materials with compacted non-porous sintered linings for engine bearings and wrapped bushes; steel backed materials with porous sintering linings impregnated with a plastic, intended for operation dry or with sparse lubrication.
Abstract: Five classes of sinter-based bearings are identified: steel-backed materials with compacted non-porous sintered linings for engine bearings and wrapped bushes; steel-backed materials with porous sintered linings impregnated with a plastic, intended for operation dry or with sparse lubrication; unbacked porous sintered-metal parts impregnated with oil to form self-lubricating bearings; unbacked non-porous sintered metal parts incorporating graphite; sintered polytetrafluoroethylene parts incorporating powdered metals. Methods of manufacture are outlined.Techniques of bearing evaluation are described, the most useful being sophisticated, flexible test-rigs which approach closely the conditions of actual bearing applications.The relative fatigue strengths of sintered engine-bearing linings are given and sintered copper-lead is shown to be equivalent in fatigue strength to cast linings.The impregnation of sintered bronze linings with PTFE and lead yields a material with good un lubricated wear-resista...
9 citations
TL;DR: Sintered friction materials as mentioned in this paper are complex metal-based composites that represent excellent examples of the principles of powder metallurgy and can be used for both wet and dry applications.
Abstract: Sintered friction materials are complex metal-based composites that represent excellent examples of the principles of powder metallurgy The production methods employed are compared with those of conventional powder metallurgy and the formulation of the materials is briefly described Some typical applications, both wet and dry, are given and comparisons with the equivalent organic-based materials are made
TL;DR: Turning and drilling tests have been carried out on nine different materials as mentioned in this paper, and the most critical factor in turning is the breakouts at the corners of the test-specimen, especially at low densities.
Abstract: Turning and drilling tests have been carried out on nine different materials.The most critical factor in turning is the breakouts at the corners of the test-specimen, especially at low densities. These can be eliminated by adopting a lower feed and smaller depth of cut. The best surface finish is achieved with the highest possible speed and low cut depth. Alloying iron with 0·5% sulphur resulted in the lowest recorded specific cutting force, a good surface finish, and the longest tool life attained. The density had no influence on the tool wear.Tool life in drilling can be improved considerably by using: (a) a 40° helix angle for soft power-metallurgy materials; (b) extra-short drills. Burrs can be eliminated by shortening the chisel edge or increasing the point angle to 185°. The use of sulphur-alloyed iron resulted in a tool life many times higher than that for plain iron of the same density.Machining recommendations are given for turning and drilling the various materials.
TL;DR: In this article, the dispersion-strengthening of carbonyl iron by alumina and zirconia has been found to be sensitive to particle morphology, which is interpreted in terms of the variation of particle morphology with production history.
Abstract: The dispersion-strengthening of carbonyl iron by alumina and zirconia has been found to be sensitive to particle morphology. This has been studied by optical and electron microscopy in samples representing each stage of various production sequences.In the case of alloys that had been sintered at 1350°C and then forged and cold rolled, alumina had a greater room-temperature-strengthening effect than did zirconia; whereas for alloys sintered at the same temperature but tested in the extruded condition there was no such difference. Furthermore, sintering at 1200°C followed by forging and cold rolling produced a similar degree of dispersion-strengthening for each of the two dispersoids. These observations are interpreted in terms of the variation of particle morphology with production history.Tensile properties were also determined in the range 20–600°C for alloys that had been sintered at 1350°C and extruded. The dispersion-strengthening effect decreased with increasing temperature in a manner that i...
TL;DR: In this paper, the wear processes that are significant on those parts of the interface where seizure is complete are considered separately from those in areas where contact is localized and intermittent Examination of worn tools suggests that two major wear processes take place on cemented carbide under each of these sets of conditions.
Abstract: The stress, strain, and temperature at the interface between tool and work material during metal cutting are such as to promote seizure Conditions of seizure normally exist over part of the interface during most metal-cutting operations The wear processes that are significant on those parts of the interface where seizure is complete are considered separately from those in areas where contact is localized and intermittent Examination of worn tools suggests that two major wear processes take place on cemented carbide under each of these sets of conditions It is believed to be unlikely that abrasion plays a major role in the wear of cemented carbide tools except in special circumstances The influence of powder-metallurgical processing variables in the production of cemented carbide tools is considered in relation to each of the main wear processes
TL;DR: In this article, the effects of composition, shrinkage, atmosphere, time, and temperature of sintering, and compacting pressure on the tensile strength of sintered and maraged steels were examined.
Abstract: Maraging steels based on 18 and 12% nickel, and containing cobalt, molybdenum, silicon, copper, chromium, titanium, and aluminium in various proportions, were prepared in sintered form under varied processing conditions The mechanical properties of the steels have been examined with particular reference to the effects of: (1) composition; (2) degree of shrinkage; (3) atmosphere, time, and temperature of sintering; and (4) compacting pressure The influence of the type of iron-powder base was also studiedThe results demonstrate the possibility of producing, in the sintered and maraged condition and with only slight shrinkage on sintering, tensile strengths of the order of 95–110 kgf mm−2 (60–70 tonf in−2) Two compositions appear promising for further development as high-strength materials, and another to provide enhanced ductility In all cases impact properties are similar to those characteristic of conventional sintered steels
TL;DR: In this paper, a new method for lubricating the tools of a pelletizing press is described, based on the use of dry lubricants mixed with polystyrene balls as a carrier.
Abstract: A new method for lubricating the tools of a pelletizing press is described, based on the use of dry lubricants mixed with polystyrene balls as a carrier. The solid lubricant is introduced into the die, applied to the walls of the compacting chamber by the movement of the punches, and then ejected following the normal pelletizing cycle. Hence, a very thin film of lubricant remains on the walls and makes it possible afterwards to pelletize a uranium dioxide powder. The process has been applied to a double rotary press in which one half is used to “pelletize” the lubricant and the other half to obtain the required production of UO2 pellets. Pellets have been fabricated from a loose virgin powder which had not been granulated. The process does not lead to contamination of the UO2 pellets because the deposit of lubricant is very thin and uniform. It is applicable whatever the shape and the dimensions of the pellets may be, owing to the good flow rate of the polystyrene balls. Moreover, the polystyrene compact ...
TL;DR: In this article, it is shown that metal powders can be precipitated directly by reducing with hydrogen some organic phases produced by liquid-liquid extraction of aqueous solutions containing several metals.
Abstract: Nickel, cobalt, copper, and iron powders can be manufactured by hydrometallurgical processes. It is possible to use a wide variety of materials, including waste solutions, as the metal-containing feed. Estimates of the capital cost of reduction autoclaves and ancillary equipment show the advantage of increasing the scale of the operation from 2 to 50 tons of metal produced per day.A major factor in the economics of producing the powders is the cost of purifying the solutions to give a liquor from which metal of the desired purity can be precipitated. Liquid–liquid extraction does not appear to have been used so far in a refinery in which metal is precipitated by hydrogen. The possible application of the technique is examined briefly.Metal powders can be precipitated directly by reducing with hydrogen some organic phases produced by liquid–liquid extraction of aqueous solutions containing several metals. A suitable solvent mixture is acarboxylic acid with hydrocarbon diluent. The total pressure nec...
TL;DR: In this paper, a review of the use of porous materials for externally pressurized gas-bearing restrictors is presented, together with an explanation of the properties of the porous restrictor relative to orifice and capillary restrictors.
Abstract: A review of published work on the use of porous materials for externally pressurized gas-bearing restrictors is presented, together with an explanation of the properties of the porous restrictor relative to orifice and capillary restrictors.Areas in which further work on porous materials is required are stated and a material considered suitable for gas-bearing applications is defined.
TL;DR: In this paper, wear and friction studies have been carried out on pressed and sintered composites of 75-95% theoretical density, and the wear-resistance correlates well with the ratio of the volume fraction of tungsten carbide to that of graphite (WC/graphite); there is a minimum in weight loss at a ratio near unity.
Abstract: Wear and friction studies have been carried out on pressed and sintered composites of 75–95% theoretical density. Carbonyl nickel and tungsten carbide, both with a particle size of 5 μm, and natural crystalline flake graphite with an approximate size of 1·1 μm were used. The wear specimens were run against a rotating (100 rev/min) steel cylinder. The wear-resistance correlates well with the ratio of the volume fraction of tungsten carbide to that of graphite (WC/graphite); there is a minimum in weight loss at a ratio near unity. This effect is explained in terms of powder coating with graphite during blending, which affects grain-boundary formation and grain growth during sintering; supporting metallographic evidence is given. The wear-debris particle size produced is related to wear; the wear rate increases with increasing particle size. Residual porosity in the materials reduces wear-resistance. The wear rate does not correlate with hardness or coefficient of friction; the results of wear tests ...
TL;DR: In this paper, the die wear of small cylindrical iron powder compacts has been determined, as influenced by powder type, compacting pressure, compact density, type and hardness of die steel, and punch/die clearance.
Abstract: Small cylindrical iron powder compacts have been produced in series of ∼ 75 000 specimens, using an automatic compacting press running at a speed of 33 strokes/min. Die-wear rates were determined, as influenced by powder type, compacting pressure, compact density, type and hardness of die steel, and punch/die clearance. Simultaneously, the ejection forces were continuously recorded.No substantial difference was found between the die-wear rates of common iron powder grades of an atomized or a sponge type, but an electrolytic grade of especially compact particle structure gave a lower rate. Die wear increases in roughly linear proportion both with the number of compacts and with the compacting pressure.Steel type and hardness of the die had a pronounced influence upon die-wear behaviour, dies of higher hardness yielding lower wear rates. Unsuitable heat-treatment can cause high wear rates even though it might produce high die hardnesses.A punch/die clearance of 10 μm resulted in the most favourable ...
TL;DR: In this paper, the impact-resistance of silicon carbide at room temperature and 1000°C was evaluated using two different criteria: (1) stored energy; (2) Hertzian contact stress.
Abstract: This paper describes work carried out to determine the impact-resistance of silicon carbide at room temperature and 1000°C. Samples of SiC were selected for testing that would fracture according to two different criteria: (1) stored energy; (2) Hertzian contact stress. The literature is extensively reviewed for impact-failure mechanisms but other appropriate work on SiC is shown to be sparse. Equations are developed that describe the main impact-resistance criteria and the influence of microstructure on impact cracking is discussed.
TL;DR: In this paper, the development of vacuum-sintered ferrous materials that can be used for high-strength structural parts is discussed. Butler et al. describe the reasons for choosing this production route, and the development from simple iron-carbon alloys to more complex iron−carbon−nickel−chromium alloys.
Abstract: The work described is concerned with the development of vacuum-sintered ferrous materials that can be used for high-strength structural parts. The reasons for choosing this production route are given, and the development of the materials is traced from the simple iron–carbon alloys to the more complex iron–carbon–nickel–chromium alloys. The metallography of the various series of alloys is included and the mechanical properties are fully reported. Tensile strengths > 70 tons in −2 were obtained after heat-treatment. An indication of the dimensional changes that took place during sintering is also given.
TL;DR: In this paper, three types of carbide powder and six types of graphite, different in size, shape, and structure (one in each group being nickel-coated) were studied to varying degrees.
Abstract: Pure nickel and nickel-based binary and ternary materials containing tungsten carbide and graphite dispersions have been studied. Three types of carbide powder and six types of graphite, different in size, shape, and structure (one in each group being nickel-coated) were studied to varying degrees. The smallest carbide powder (0·35 μm) possessed the best wear-resistance and the lowest coefficient of friction. The larger and coated types of graphite are somewhat superior; however, considerable amounts (∼ 40 vol.-%) are needed to improve wear-resistance substantially and reduce the coefficient. Use of the coated type of carbide leads to rather high coefficients (0·58-0·76) under dry testing conditions. Several effects of the presence of a small amount of oxygen in the sintering atmosphere are discussed; a most interesting result is the marked improvement in the wear-resistance of pure nickel treated to produce a dispersion of nickel oxide. With some powders blending can lead to reduced wear-resistan...
TL;DR: In this article, a reversion to methods of double cold pressing and sintering, which have been facilitated by the enhanced ductility gained from modifications to composition and microstructure, is described.
Abstract: From the earliest incorporation of graphite with metal oxides or metal powders to form porous bearings of low mechanical strength, progressive improvements led to the production of intentionally non-porous graphited metal bearings containing relatively high volumes of finely distributed graphite. These higher-strength bearing materials were achieved in the middle of this century by the employment of hot-pressing techniques.The latest development in this range of materials has seen a reversion to methods of double cold pressing and sintering, which have been facilitated by the enhanced ductility gained from modifications to composition and microstructure. The resultant bearings are produced to finished dimensions without machining, thus affording economies over hot-pressed materials.Some details regarding the properties of such bearings are given and typical applications are described.
TL;DR: In this article, a procedure for accumulating data on the friction index and compression ratio of a copper powder at different stages of oxidation and of screened fractions of a stainless-steel powder was described.
Abstract: A procedure is described for accumulating data on the friction index and compression ratio of a copper powder at different stages of oxidation and of screened fractions of a stainless-steel powder. The dimensionless and nameless powder property, friction index divided by the compression ratio, was constant under certain conditions for a regular series of size fractions of stainless-steel powder. Calculations were made of the coefficient of compression and the limiting value of the degree of volume change by the method due to Kawakita.
TL;DR: In this paper, chromium, with and without 4 vol.-% thoria, and nickel powders were ground to fine powder sizes by ball-milling in gaseous hydrogen halides.
Abstract: Chromium, with and without 4 vol.-% thoria, and nickel powders were ground to fine powder sizes by ball-milling in gaseous hydrogen halides. After reducing the milled chromium in flowing hydrogen under pulsating pressure at ∼680°C, submicron-size powders with 4–500 ppm residual halogens were obtained. The compacted chromium–thoria alloys had interparticle spacings ranging from 2·1 to 6·5 μm. After 100 h at 1318°C the interparticle spacing of the 2·1-μm alloy increased to 5·2 μm. Submicron-size chromium and nickel powders were also obtained by pulsating hydrogen reduction of their chlorides.
TL;DR: In this article, an air-blown porous-metal turner bar is used to support web-transport by supporting the web as it passes over the turner, on an externally pressurized air-bearing, and thus eliminating the friction effects.
Abstract: Problems are often encountered in the printing and packaging industries when running webs of paper or plastics on machines, arising from the friction effect between the web and the turner bars used for altering the direction of web travelMany of these web-transport problems may be greatly eased by supporting the web, as it passes over the turner bar, on an externally pressurized air-bearing, and thus virtually eliminating the friction effects The paper presents details of the design of an air-blown porous-metal turner bar suitable for this purpose Advantages to be gained from the installation of such bars, together with their limitations in use, are discussed
TL;DR: The energy of relatively cheap explosives is being used on an increasingly wide scale in different branches of technology, including the technique of powder metallurgy for compacting briquettes and products made from metallic and nonmetallic powders as discussed by the authors.
Abstract: The energy of relatively cheap explosives is being used on an increasingly wide scale in different branches of technology, including the technique of powder metallurgy for compacting briquettes and products made from metallic and non-metallic powders.A brief description is given of some of the results obtained from compacting iron and aluminium/alumina powders (SAP) by means of high explosives. Data for normal “static” compacting and compacting by dynamic loading are included for comparison.
TL;DR: The results of previous studies of frictional properties of sintered iron-based brake linings containing additions of graphite, molybdenum disulphide, lead, corundum (Al2O3), and barytes (BaSO4) are summarized in this article.
Abstract: The results of previous studies of frictional properties of sintered iron-based brake linings containing additions of graphite, molybdenum disulphide, lead, corundum (Al2O3), and barytes (BaSO4) are summarized.Interpretation of qualitative topography and of quantitative analysis by means of electron-microprobe analysis supports the idea of the formation of BaAl2O4 in the regions of direct contact between BaSO4 and Al2O3.Further results concerning the behaviour of sulphur, obtained by means of electron-microprobe analysis, are also discussed.
TL;DR: In this paper, the effect of copper on the properties of mineral oil, polyglycol, aliphatic esters, and silicone fluids has been examined in relation to the case of self-lubricating bearings.
Abstract: The effect of copper on the properties of mineral oil, polyglycol, aliphatic esters, and silicone fluids has been examined in relation to the case of self-lubricating bearings. The various oxidation mechanisms involved are considered, together with specific examples of the part which additives may play in the reduction of deposit formation, inhibition of oxidation, and prevention of copper corrosion.