A METHOD FOR DETERMINING THE SIZE DISTRIBUTION OF MICRO-PORES IN POWDER PARTICLES

Abstract

Determination of particle density by the displacement method, with different liquid media, can be used to assess the size distribution of micropores in powder particles. Certain errors and assumptions are involved.     

THE EFFECT OF COPPER ON THE PROPERTIES OF LUBRICANTS

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.     

THE PRODUCTION OF METAL POWDERS FROM AQUEOUS SOLUTIONS

Abstract

The principles involved in producing metal powders by hydrogen reduction of metal ions in aqueous solutions are discussed from the thermo-dynamic and the kinetic standpoint. The influence of nuclei and of surface-active agents on the nature of the powders are considered in relation to the production of nickel, cobalt, and copper.

A survey is made of the scale and technology of current processes and the uses to which metal powders may be put are described, with particular reference to the manufacture of metal strip and plates, dispersion-hardened nickel, and composites.

The practicability of controlling the conditions of reduction to yield powders with widely varying combinations of properties is a most valuable attribute of hydrometallurgical methods.     

THE POWDER METALLURGY OF TITANIUM–TIN ALLOYS CONTAINING UP TO 15% TIN

Abstract

Density measurements and data on the mechanical properties of titanium–tin alloys, fabricated by powder metallurgy from sodium-reduced titanium, are reported.

Low porosities were achieved after a single pressing and sintering operation. A typical set of preparation conditions involved compacting at 40 tons/in.² and sintering, in vacuum, at 1300° C. for 1 hr. With tin contents above 5%, evaporation of tin during sintering could prove troublesome.

The presence of tin strengthened titanium markedly. The addition of 15% tin increased the ultimate tensile stress at room temperature by ～90%, with a corresponding, though less marked, reduction in ductility.     

TECHNIQUES FOR THE EVALUATION OF POWDERS. III.—OBSERVATIONS ON COMPACTS

Abstract

A large number of tests based on observations made on compacts have been devised to evaluate the pressing and sintering characteristics of metal powders. These are summarized under four headings: behaviour during pressing, properties of the green compact, behaviour during sintering, and the properties of the sintered compact. The specifications which set down standard testing techniques are described and reviewed. The principles involved in the various proposed tests are given, together with any limitations or precautions that need special consideration. In a number of cases there is obvious scope for further study and research, and these are pointed out.     

Evaluation of drilling parameters effects on machinability of PM materials using ANOVA

Abstract

The aim of this paper is the machinability analysis, in different drilling conditions, of sintered metals filled with a machinability enhancer. The cutting parameters involved in the study are: rotating velocity, feedrate and coating of the tool. To reduce the number of experimental tests required, a 2^k–1 fractional design of experiment with three two level factors and two replications for each run was employed. The experimental design was repeated for three sintered metals with different hardnesses or densities. The obtained results show new insight into the machining mechanism of sintered material and into the influence of the cutting parameters on the machining forces.     

The restart of TKS Plate Mill,Duisburg

Abstract

The recent upgrading by VAI of automation equipment at the 3·9 m plate mill of ThyssenKrupp Stahl (TKS) in Duisburg-Süd, Germany involved the installation of new equipment during regular maintenance shut-downs and caused no additional loss of production. To maintain full production capabilities, a switch-over unit was used to provide a seamless transition to the new automation system.     

THE FABRICATION OF COMPONENTS FROM ALUMINIUM REINFORCED WITH SILICA FIBRES

Abstract

The salient fabrication parameters involved in the hot pressing of composites of aluminium reinforced with silica fibres have been studied and their effects evaluated. The roles of temperature, atmosphere, and time in promoting bonding are much as would be anticipated from general powder-metallurgy considerations. The effect of pressure is modified by mechanical damage to the fibres at high pressures. This damage can be minimized by ensuring good fibre alignment.

Methods have been developed, analogous to those used with fibre reinforced plastics, for the fabrication of simple filament-wound shapes, such as rings, and of more complex shapes. A few trials have been made on pressure-welding and soldering techniques for forming lap-joints between pieces of aluminium-silica.     

ASPECTS OF THE VOLUME PRODUCTION OF GREEN POROUS BEARING COMPACTS

Abstract

The history and method of manufacture of self-lubricating porous metal bearings are briefly outlined. The importance of achieving appropriate quality at each stage of manufacture, and particularly during compacting, is emphasized and the qualities desired in a green bearing compact are detailed. Various factors relating to the economic large-scale manufacture of green bearing compacts are then considered. The virtues of elemental powders and the influence of lubrication upon powder mix properties and pressing and ejection of compacts are discussed. The special powder flow problems associated with long, thin-walled bearings and the advantage, in this respect, of a moving core rod are described. The particular difficulties encountered in compacting such bearings are stated and special consideration is given to the ejection problems involved. It is concluded that limitations of bearing length and wall section must be accepted.     

Laser wire casting

Abstract

A new technique has been developed for the production of solid wire or rods from powder by laser melting. Three techniques have been developed to ensure that the molten powder solidifies as a rod or wire rather than a series of droplets. The straight rods or wires produced in this way have near-circular cross-section, are several millimetres in diameter and can be pore free. The techniques can be used to produce welding rods, tensile test samples and other solid pieces from a wide range of powder mixes. The rapid thermal cycle involved means that it is now possible to produce hitherto difficult mixtures and alloys in the solid form in seconds.     

A Review of Recent Studies on Copper Smelting

Abstract

A review of more important studies on Cu smelting which have appeared in the literature since 1950. The works reviewed comprise studies of the physicochem. systems pertaining to the smelting and converting operations and accounts of recent advances in technology.

The essential physicochem components are Cu, Fe, O, S and SiO₂, and a considerable body of knowledge has accumulated of 2-, 3- and 4-component systems involved in slag;matte equilibria. The distribution of Cu between the 2 liquid phases is strongly influenced by the O potential and silica activity. Much less attention has been given to the kinetic aspects of-cop.per smelting, namely the rates of chem. reactions and of heat and mass transfer; the importance of these phenomena in relation to Cu losses is discussed.     

Porous Media

Abstract

A review is presented of the postulated neck formation and growth mechanisms involved in the high-voltage discharge process for forming high aspect ratio powder metallurgy bodies. Together with the results of recent work this allows a mechanism of liquid-phase weld formation and growth to be outlined which is confirmed by scanning electron micrographs of welds found with a variety of materials. PM/0202     

From trial and error to computer modelling of thermomechanical processing

Abstract

Since the 1950s, thermomechanical processing in the iron and steel industry has progressed from being skills based, using results from trial and error development work, to being science based, using computer modelling for process optimisation and control, and prediction of product properties. Some of the steps in this evolution are illustrated in the lecture, using hot rolling, as the main example, because The University of Sheffield has been involved in research in this field over the whole of the period. As basic understanding of the physics of the microstructural changes, and the speed of computing have increased, there has been a continuing trend for more complex models to be used for offline optimisation and for online control and property prediction. Such models are now accepted as an economically valuable tool for thermomechanical processing.     

Two-dimensional heat transfer model for secondary cooling of continuously cast beam blanks

Abstract

A two-dimensional heat transfer model was developed for the secondary cooling system during beam blank continuous casting. The finite element method was used to calculate the heat transfer. Accurate cooling boundary conditions in the secondary cooling zone are involved, including spray water cooling, water evaporation cooling, radiation cooling and roll contact cooling in the casting direction and non-uniform distribution of spray water flow density in the cross-section. The causes of longitudinal crack at the fillet during Q235 steel continuous casting were analysed on the basis of the simulation of the developed model, and then the spray water flow and the transverse nozzle layout were optimised. Practical results show that the surface quality of the beam blank improved after optimisations. Numerical results from the present model were validated using previous experimental measurements, which show good agreement.     

Effects of adding overspray powder on microstructures and mechanical properties of spray deposited 8009 aluminium alloy

Abstract

Under normal condition the cooling rate in a spray deposition process is too low to form 8009 aluminium alloy. In order to increase the cooling rate, overspray 8009 aluminium alloy powders were added. The effects of adding overspray powder on microstructures and mechanical properties of the spray deposited 8009, with and without addition of the overspray powders, were studied. It is shown that adding proper content of overspray powders significantly improves the mechanical properties of the spray deposited 8009 alloy. The mechanism involved in modification of the microstructures and the mechanical properties of the spray deposited 8009 alloy produced with the overspray powder addition approach was discussed.     

Phase transformations in reactive sintering of tungsten

Abstract

It has been demonstrated recently that tungsten (T _m = 3410±20°C) can be sintered by reactive sintering in a reductive atmosphere such as hydrogen. This alternative technique to the conventional sintering (T _s>2000°C) makes use of a small amount of aluminium addition which acts as a sintering aid and hence lowers the sintering temperature significantly (T _s1200°C). This study explores the phase transformations that take place during reactive sintering of tungsten in view of the mechanisms involved. DSC, SEM and TEM have been used for a fundamental understanding of this system.     

Sintered Magnetically Hard Materials: Present and Future

Abstract

Sintering is an essential step for producing many permanent magnets, from the low-cost high-tonnage hard ferrites to the low-tonnage high-properties rare earth-cobalt magnets. Shaping those magnets from powders through a sintering step is not only a matter of densification to a solid and precise part, it must often retain, improve, or confer the essential magnetic property, i.e. coercivity. Present understanding of the relationship between microstructure and hard magnetic properties is briefly covered, with attention focused mainly on the particle size law. The paper reviews the technologies involved in the three main grades of sintered permanent magnets, Alnicos, ferrites, and rare earth-cobalt magnets; except for the first quality, grain growth must be avoided or controlled during sintering. Possible directions for future development of magnetically hard materials are discussed. PM/0252     

HIP processing of materials for offshore (energy) applications

Abstract

The Particulate Engineering Committee (PEC) of IOM3 held its long anticipated workshop on hot isostatic pressing (HIP) of materials for offshore (energy) applications on 16 April in Aberdeen, UK. Hosted by TWI and supported by EPMA, the one day meeting attracted about 30 delegates that filled comfortably the premises to its capacity. It was an opportunity for end users from the oil and gas sector and those involved in powders, consumables, engineering services and other end user communities to come together to capture the latest developments in the field of PM-HIP for offshore and energy applications.     

THE EXTRUSION OF ATOMIZED ALUMINIUM POWDERS

Abstract

More than a hundred experiments have been performed to investigate the extrusion mechanism involved and the effect of process variables on the structure, substructure, and mechanical properties of the extrude when processing atomized aluminium powder of varying mesh size. It is demonstrated that extrusion pressure is largely independent of the final properties and that the ductility of the extrude may be controlled by the process variables. A mechanism that agrees with experimental observations is suggested to explain the extrusion mechanics. Transmission and scanning electron microscopy results also support the theses presented.     

Unidirectional Solidification of Eutectic Cast Iron

Abstract

High intrinsic damping in alloys finds many applications in the elimination of unwanted vibrations and reduction of acoustic noise. The increasing interest in these materials has resulted in the development of a new class of engineering alloys, the HIDAMETS (high-damping metals), specifically tailored for use in vibration-resistant structures. Numerous different physical mechanisms (usually controlled by the alloy microstructure) can be responsible for the level of internal friction or damping in a candidate alloy for a particular application. Consequently, alloy selection depends mainly upon the conditions to be encountered in service, i.e. temperature, frequency of vibration, amplitude of vibration, magnetic field, etc. Characterization of the internal friction in high damping alloys is described and some of the mechanisms involved are discussed. Results obtained for two different alloys are presented. The first is a commercial Mn-Cu alloy used for marine propellers and the second is a die-cast Zn-Al alloy with possible application in the automotive industry.