PARTICLE SIZE AND SHAPE CHARACTERISTICS OF KEMERBURGAZ QUARTZ SANDS OBTAINED BY SIEVING,LASER DIFFRACTION,AND DIGITAL IMAGE PROCESSING METHODS

The ever-progressing development of industrial processes and products regularly requires significant progress in the development of associated measurement techniques. With the advance of technology, there have been many developments in the mining sector. Mineral particle size is a critical parameter in any process involving the liberation and separation of minerals. In most mineral processing plants, product grade and mineral recovery require sufficient mineral liberation and optimum size distribution. There are many methods of measuring mineral particle sizes. Sieving, sedimentation, microscopy, digital image processing, and laser diffraction are the most common particle size analysis methods. The shape of the particles plays an important role in the assessment of particle size distribution. Most sizing techniques, however, assume that the sample being measured is spherical, as a sphere is the only shape that can be described by a single number. Therefore different techniques can give different results for the same sample depending on this aspect. Within the scope of this study, the particle size distribution of two different sand samples (Sarikum and Senkoy) was assessed by sieving, digital image processing, and laser diffraction techniques. In addition, the convexity and circularity parameters of the samples were measured by a Morphology G device. The particle size distribution results obtained from different techniques for each sample are discussed depending on the values of convexity and circularity of the sample particles.     

Sintered copper–graphite powder compacts forindustrial applications

Abstract

Studies were made on copper/graphite based powders and sintered compacts for industrial applications. The dependence of particle shape on friction in the powder mass, compression ratio, and electrical receptivity of powder metallurgy components was studied using near spherical precipitated copper powders and angular or flakelike powders generated by mechanical comminution. Results reveal that powders with particles that are nearly spherical in shape have lower friction, lower compression ratios, and higher electrical resistivities in sintered compacts than powders with acicular or flakelike particles. Also, the effects produced by the small additions of lead and zinc (up to 2·5 wt-%) on the electrical resistivity and hardness of sintered copper–graphite compacts are also presented, and the influence of variation of briguetting pressure is discussed.     

THE IMPORTANCE OF SURFACE PROPERTIES AND PARTICLE SHAPE IN THE COMPACTION OF GRAPHITE AND MoS2

Abstract

Adsorptive studies of the surfaces of graphite and MOS₂have shown that these consist of two distinct types of site. The sites on the basal-plane surface differ from those on the edge surface with respect to their relative affinities for different organic compounds. These findings led to the development of grinding techniques to produce graphite and MoS₂ powders possessing different ratios of basal-plane:edge-surface area.

Grinding graphite and MoS₂ in the presence of low-viscosity, volatile hydrocarbons produced very thin flake-like powders, consisting predominantly of basal-plane surface. These fine flakes showed a high affinity for long-chain n-paraffins and were therefore termed oleophilic solids. Grinding under reduced pressure also produced very fine powders, having, however, a more granular structure exhibiting a far lower ratio of basal-plane: edge-surface area. These were termed polar solids to distinguish them from the solids ground in liquid hydrocarbons.

The cold-forming properties of the various powders have been compared under uniaxial compaction. The conversion of synthetic and natural graphite powders to the oleophilic form resulted in marked improvements in both compact strength and modulus. Synthetic graphite converted to the polar form would not form a compact at cold-forming pressures up to 800 MN/m².

The cohesive properties of the oleophilic graphite powders were improved by heating to 900°C in hydrogen. Electrical-resistivity measurements showed that cold-formed oleophilic graphite compacts exhibited a marked anisotropy. The improved cold-forming properties of the powders are ascribed directly to improved cohesion via basal-plane site interactions, coupled with the facility of the flake powders to take up a preferential orientation during compaction in order fully to utilize the extensive basal-plane sites available for cohesion.

The differences between the oleophilic and polar forms of MoS₂ were less marked. It is believed that interparticle cohesive junctions are more readily formed via edge/edge interactions, and basal-plane junctions do not play as important a role in the cohesion of MoS₂ as in that of graphite.

The corrosion and abrasion of metal surfaces by graphite and MoS₂ have been examined. In all cases the powders converted to the oleophilic form showed reduced abrasive and corrosive characteristics when compared to similar powders converted to the polar form. These improvements are believed to result from the reduction of the possibilities of edge interactions with the metal surfaces.     

FACTORS AFFECTING THE COMPACTION OF TUNGSTEN POWDERS

Abstract

It is difficult to form tungsten powders into compacts by pressure-forming methods. The brittleness of the powder particles causes them to fracture under pressure instead of producing the typical “point welds” exhibited by more ductile particles. Because of this, the powder characteristics such as particle size, size distribution, and particle shape play a most important role in the compacting of tungsten powders.

Both regular- and irregular-shaped particles of tungsten powder are discussed as regards the formation of strong and dense compacts from these powders. Powders composed of irregular-shaped particles gave stronger, but less dense compacts. The effects of particle size and particle-size distribution are also considered. Each of these factors has individual as well as combined effects. It was found that certain critical particle-size distributions produced the densest compacts.

It is concluded that interlocking of particles, which is brought about by surface irregularities, and interfit, which is determined by correct particle-size distribution, are the determining factors in the compaction of tungsten powders.     

THE INFLUENCE OF PREFORM SHAPE ON MATERIAL FLOW,RESIDUAL POROSITY,AND OCCURRENCE OF FLAWS IN HOT-FORGED POWDER COMPACTS

Abstract

In the hot forging of powder compacts into items of complicated shape, proper preform design is critical. In particular, in cases where items having sections of different lengths in the forging direction are to be produced in tools with undivided punches, the risk of cracking, overlapping or residual porosity in one or several of the sections is great. This paper presents results from hot-forming experiments with a variety of preform shapes and discusses possibilities of overcoming some typical preform design problems.     

Investigation of iron ore particle size and shape on green pellet quality

ABSTRACT

Particle size and shape of iron ore concentrate are effective parameters in the production of quality green pellets. In this research, the effect of particle morphology on green pellet quality was studied. It was concluded that pellet quality improved with increasing specific surface area. Drop number and green compression strength of pellets ground by HPGR were found to be superior over those ground in the ball mill. The chief reasons were related to particle shape and the fraction of fine particles. Smaller particle size results in a higher order of bonding between particles and therefore the formation of a stronger system. Also, the rougher and less circular shape of particles resulted in higher strength. According to the breakage model in the particle-moisture system, pellet failure occurs because of crack propagation in the solid–liquid interface. The effects of roughness on capillary force and wettability have been explained mathematically. In addition, the effects of roughness and aspect ratio on breakage path and increase of required energy for pellet failure have been modelled.     

FACTORS CONTROLLING THE SHAPE REGULARITY OF SINTERED U02 PELLETS

Abstract

As explained mathematically, the magnitude of the ‘diabolo’ effect in sintered nuClear-fuel pellets is a function of the slope and position of the sinterability curve and the density gradient existing in the green pellets. If sinterability is representedby a straight line passing through the origin, the diabolo effect is negligible; this condition can be fulfilled when using a deactivated powder.

In any other case, the density gradient must be kept as low as possible to produce sintered pellets of regular shape. This is discussed as a function of powder roughness, lubricant quality, lubrication technique, and compaction characteristics.

When the sinterability curve cannot be adapted and powder quality and lubrication conditions are fixed, the possibility still exists of minimizing irregularities in sintered diameter by using a single-action press and compacting the powder in an adapted conical die with a moving lower punch.     

THE VIBRATORY PACKING OF POWDERS

Abstract

The objective, in packing particles by vibration, is to increase the density of packing. The main factors affecting the packing of particles in this way are the characteristics of the powder (size distribution, shape, surface condition) and the vibration variables (frequency, amplitude, time). Other factors include segregation by size and shape and also, for a multicomponent powder, by particle density. The wall effect of the container might also be expected to influence the packing in its vicinity. An experimental investigation of some of these variables is here reported.     

EFFECTS OF PARTICLE SIZE ON THE SINTERING KINETICS IN TUNGSTEN POWDER

Abstract

An experimental study has been made of the effects of initial particle size on sintering kinetics in tungsten powder within the temperature range 1100–1500°C. Particle size, compacting pressure, sintering time and temperature all influence the rate of sintering. Isothermal changes in density and volume have been measured. The results indicate grain-boundary diffusion as the mechanism principally responsible for material transport in the case of particle sizes <4 μ Surface diffusion appears to bethe mechanism of material transport in compacts with particle sizes of 14– 16 μ The temperature-dependence of the rate of sintering is characterized by activation energies of 101± 2 and 72± 2 kcal/mole for fine particles (< 4 μ) and coarse particles (14–16 μ), respectively.     

热轧板带钢板形控制技术

介绍了国内外热轧板带钢板形控制的有效方法，即液压弯辊，轧辊横移式四辊轧机、ＰＣ＋ＯＲＧ轧机以及板形在线检测与控制技术状况；分析了传统四辊轧机的固有缺陷，提出了轧机改造的最佳方案，并针对攀钢的实际情况提出了建议。     

安钢低碳贝氏体钢生产的板形控制

安钢生产的低碳贝氏体钢出现瓢曲现象主要是在冷却过程中形成.出现瓢曲的主要原因是钢板在通过层流冷却系统时,在厚度方向和横向方向冷却不均匀造成的.本文分析板形缺陷,研究纵向、厚度方向及纵向的板形控制方法,并制定了相应的措施,达到了改善板形的目的.     

四辊轧机轴向移位变凸度辊型的研究

利用工作辊轴向相对移动来改变辊缝形状的四辊轧机是一种很有前途的板带轧机。决定这种轧机板形控制能力的一个重要因素是工作辊的辊型。本文给出这种辊型的构成方法,并利用它对CVC和UPC两种辊型进行分析,最后给出两种实用辊型——简单的3次辊型和应用广泛的复合辊型。     

SOME ASPECTS OF THE MILLING OF CEMENTED CARBIDE POWDER

Abstract

Cemented carbide powders milled for various times have been studied with respect to the shape and internal structure of the grains. The shrinkage of powder compacts during heat-treatment was recorded dilatometrically. The major effects of milling seem to be to alter the grain size and morphology of the powder and to form a fine dispersion of small particles of Co₃O₄.     

A STUDY OF THE FACTORS CONTROLLING GRAIN SIZE IN SINTERED HARD-METAL

Abstract

Previous experimental work concerning the grain growth observed during the sintering of tungsten carbide–cobalt alloys is reviewed. Particle-sizing methods suitable for the examination of hard-metal powders are described, and techniques for the evaluation of the carbide grain size in the sintered compacts are discussed.

By using a Model A Coulter Counter to examine the size distribution of the carbide grains (obtained from the milled hard-metal powders by dissolution of the cobalt with hydrochloric acid), and by counting techniques on electron photomicrographs of carbon replicas of the sintered compacts, it has been established that the increase in grain size during sintering is quantitatively related to the carbon content of the material after pre-heating. The results presented indicate that the cobalt content exerts little influence on the average grain size of the sintered structures A cobalt content >10% by weight is shown to exert a strong damping effect on the rate of comminution during milling.

The linear relationships between the specific surface area of the carbide grains in milled powders (obtained using a Perkin–Elmer Sorptometer) and the specific surface of the carbide phase in sintered compacts are given. The influence of sintering temperature and time on average grain size and contiguity in a commercial alloy is shown. Some preliminary work indicates that the morphologies of the initial carbide powders may be important factors with respect to the grain size of sintered hard-metal.     

METHOD OF PRODUCTION AND SOME PROPERTIES OF A NEW TYPE OF ULTRAFINE PARTICLES

Abstract

A micro-rolling method for the production of fine metallic particles in the size range 0.05–5μm is described, together with ancillary equipment for the separation and collection of predetermined size fractions. The material produced is a flake form of high (up to 100: 1) breadth :thickness ratio and is suitable for applications such as dispersion-hardening and for many operations that involve pressing and sintering procedures.

Details are given of particle shape and size distribution for two typical products, aluminium flake and tungsten flake. Some physical properties of specimens produced from these materials are also cited. Reference is made to other products of the mill, both metallic and non-metallic, and to future development work in relation to these materials.     

THE COMPACTION OF METAL POWDERS BY ROLLING. I.—THE PROPERTIES OF STRIP ROLLED FROM COPPER POWDERS

Abstract

The investigation described is an extension of earlier work (“Symposium on Powder Metallurgy 1954”, p. 131. 1956: London (Iron and Steel Institute), and Sheet Metal Ind., 1955, 32, 589) which described the effect of rolling pressure and sintering conditions on the mechanical properties of strip rolled from copper powders. The directional variation of U.T.S. and of elongation of sintered strip are shown to be the same as those of solid copper with a similar microstructure, at least for material with up to 16% porosity. The shape of powder particles and the particle-size distribution have a marked effect on the strength of sintered strip by virtue of their effect on the shape and size of the pores in the sintered material. Measurements of electrical resistance reveal a linear relationship between conductivity and porosity over wide ranges of porosity in both “green” and sintered strip. The conductivity increases rapidly during the first few minutes of sintering at 1000° C. Measurements of the resistance in the rolling direction and in the transverse direction, which are independent of local variations in density, have been made on green sheet; the resistance in the rolling direction is the higher. A correlation between this result and the mode of particle deformation is proposed, and is elaborated in Part II of this paper.     

THE STRUCTURE AND PROPERTIES OF SOME INTERNALLY OXIDIZED ALLOY POWDER COMPACTS

Abstract

The advantages of internally oxidized structures produced by powder-metallurgical techniques are briefly reviewed and discussed. A metallographic survey of the structures of some internally oxidized copper alloy and nickel alloy powder compacts is presented, and the effect of pressing and sintering variables upon the density and hardness of the product is established. Hot-hardness data up to 800°C, and also some tensile data up to 620°C, are presented for certain alloys.

It is concluded that although dispersion-hardened structures can be prepared by the pressing, sintering, and internal oxidation of appropriate alloy powders, and although the methods described offer a valid comparison of the properties of the various alloys studied, optimum mechanical properties are undoubtedly developed only after the powders are hot worked. The latter treatment densifies the product, removes any porosity in the structure, and increases the stored energy in the material.     

四辊轧机板形测,控系统的设计

介绍东北大学轧制技术及连轧自动化国家重点实验室三机架四辊冷连轧机板形检测与控制系统的设计，并对板形的测，控原理进行了阐述，通过板形测，控系统的使用，使被轧带杜板形质量有了较大的程度的提高。     

闪速炉反应塔炉衬内形的检测系统研究

针对闪速炉反应塔炉衬内壁形状检测诸方法中存在的不足．提出了采用红外点温仪对炉衬外壁连续扫描测温来判断内壁形状的检测方法。