Investigation of the process of grinding reduced sponge iron and development of the technology of producing iron powders of different bulk density

Summary The following grinding technology is recommended for the purpose of increasing the fine-fraction yield of powder: a) grinding of reduced briquets in a hammer mill and the sifting of powder into coarse and fine fractions; b) grinding of the coarse fraction in a ball mill over a period of 16 h and the sifting of powder by means of a vibrating screen; c) mixing of the fine fractions obtained in the first and the second screenings.In order to increase the bulk density of the powder, it is recommended to perform triple grinding of the powder in a hammer mill or to grind it in a ball mill.     

Acceleration of mechanical size reduction of chromium carbide powders and mixtures based on chromium carbide

We have investigated how mechanical activation by rolling on smooth rollers affects the dispersion kinetics of chromium carbide powders and mixtures of chromium carbide powder with nickel in a ball mill. We have shown that preliminary double rolling of chromium carbide powder on a rolling mill accelerates particle size reduction in the ball mill down to a size of 1.4–1.5 μm by a factor of 4.6 compared with unrolled powder. In this case, the size reduction increases from 36 to 91 in relative units. The mean particle diameter for the powders and mixtures decreases exponentially as the grinding time increases from 12 h to 84 h. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 1–8, January–February, 2000.     

论金属矿业粉碎技术的热点问题（续2）

评述近年来国内外金属矿业粉碎工程领域的几个热点问题,内容涉及圆锥破碎机、辊压机（高压辊磨机）、自磨（半自磨）机、球磨机、再磨搅拌磨机等。介绍和评述了目前国际上最先进、最著名和最大规格的粉碎工程设备之最新发展,例如瑞典Sandvik集团的CH系列液压圆锥破碎机、芬兰Metso集团的HP系列圆锥破碎机、我国与俄罗斯的惯性圆锥破碎机,德国Thyssen Krupp Polysius公司和KHD Humboldt Wedag公司的辊压机、我国中信重机公司的自磨（半自磨）机和球磨机、现代自磨（半自磨）实验技术、澳大利亚Mount Isa铅锌矿和德国Netzsch-Fein-mahltechnik公司的Isa搅拌磨机、芬兰Metso集团的VertiMill搅拌磨机等。     

论金属矿业粉碎技术的热点问题（续3）

评述近年来国内外金属矿业粉碎工程领域的几个热点问题,内容涉及圆锥破碎机、辊压机（高压辊磨机）、自磨（半自磨）机、球磨机、再磨搅拌磨机等。介绍和评述了目前国际上最先进、最著名和最大规格的粉碎工程设备之最新发展,例如瑞典Sandvik集团的CH系列液压圆锥破碎机、芬兰Metso集团的HP系列圆锥破碎机、我国与俄罗斯的惯性圆锥破碎机,德国ThyssenKruppPolysius公司和KHDHumboldtWedag公司的辊压机、我国中信重机公司的自磨（半自磨）机和球磨机、现代自磨（半自磨）实验技术、澳大利亚MountIsa铅锌矿和德国Netzsch-Fein·mahhechnik公司的Isa搅拌磨机、芬兰Metso集团的VertiMill搅拌磨机等。     

论金属矿业粉碎技术的热点问题(续4)

评述近年来国内外金属矿业粉碎工程领域的几个热点问题,内容涉及圆锥破碎机、辊压机(高压辊磨机)、自磨(半自磨)机、球磨机、再磨搅拌磨机等.介绍和评述了目前国际上最先进、最著名和最大规格的粉碎工程设备之最新发展,例如瑞典Sandvik集团的CH系列液压圆锥破碎机、芬兰Metso集团的HP系列圆锥破碎机、我国与俄罗斯的惯性圆锥破碎机,德国Thyssen Krupp Polysius公司和KHD Humboldt Wedag公司的辊压机、我国中信重机公司的自磨(半自磨)机和球磨机、现代自磨(半自磨)实验技术、澳大利亚Mount Isa铅锌矿和德国Netzsch-Feinmahhechnik公司的Isa搅拌磨机、芬兰Metso集团的VertiMill搅拌磨机等.     

论金属矿业粉碎技术的热点问题（续1）

评述近年来国内外金属矿业粉碎工程领域的几个热点问题,内容涉及圆锥破碎机、辊压机（高压辊磨机）、自磨（半自磨）机、球磨机、再磨搅拌磨机等。介绍和评述了目前国际上最先进、最著名和最大规格的粉碎工程设备之最新发展,例如瑞典Sandvik集团的CH系列液压圆锥破碎机、芬兰Metso集团的HP系列圆锥破碎机、我国与俄罗斯的惯性圆锥破碎机,德国ThyssenKrupp Polysius公司和KHD Humboldt Wedag公司的辊压机、我国中信重机公司的自磨（半自磨）机和球磨机、现代自磨（半自磨）实验技术、澳大利亚Mount Isa铅锌矿和德国Netzsch-Fein-mahltechnik公司的Isa搅拌磨机、芬兰Metso集团的VertiMill搅拌磨机等。     

Particle size dependent sinterability and magnetic properties of recycled HDDR Nd-Fe-B powders consolidated with spark plasma sintering

The dependence of the magnetic properties on the particle size of recycled HDDR Nd-Fe-B powders was investigated,with the aim to assess the reprocessing potential of the end-of-life scrap magnets via spark plasma sintering(SPS).The as received recycled HDDR powder has coercivity(H_(ci))=830 kA/m and particles in the range from 30 to 700 μm(average 220 μm).After burr milling,the average particle size is reduced to 120 μm and subsequently the H_(ci) of fine(milled) powder was 595 kA/m.Spark plasma sintering was exploited to consolidate the nanograined HDDR powders and limit the abnormal grain coarsening.The optimal SPS-ing of coarse HDDR powder at 750℃for 1 min produces fully dense magnets with H_(ci)=950±100 kA/m which further increases to 1200 kA/m via thermal treatment at 750℃for 15 min.The burr milled fine HDDR powder under similar SPS conditions and after thermal treatment results in H_(ci)=940 kA/m.The fine powder is further sieved down from 630 to less than 50 μm mesh size,to evaluate the possible reduction in H_(ci) in relation to the particle size.The gain in oxygen content doubles for 50 μm sized particles as compared with coarser fractions(200 μm).The XRD analysis for fractionated powder indicates an increase in Nd_2O_3 phase peaks in the finer(100 μm)fractions.Similarly,the H_(ci) reduces from 820 kA/m in the coarse particles(200 μm) to 460 kA/m in the fine sized particles(100μm).SPS was done on each HDDR powder fraction under the optimal conditions to measure the variation in H_(ci) and density.The H_(ci) of SPS-ed coarse fraction(200 μm) is higher than 930 kA/m and it falls abruptly to just 70 kA/m for the fine sized particles(100 μm).The thermal treatment further improves the H_(ci) to1000 kA/m only up to 100 μm sized fractions with90% sintered density.The full densification(99%) is observed only in the coarse fractions.The loss of coercivity and lack of sinterability in the fine sized particles(100 μm) are attributed to a very high oxygen content.This implies that during recycling,if good magnetic properties are to be maintained or even increase the HDDR powder particles can be sized down only up to≥100 μm.     

True Flotation and Entrainment of Kaolinitic Ore in Batch Tests

A new method for true flotation and entrainment evaluation is proposed and compared with three renowned methods. Therefore, reverse froth flotation tests were conducted in a laboratory Denver cell with a kaolinitic ore. The evaluation of entrainment and true flotation was based on the recoveries of iron, titanium, and manganese oxides (FeO, TiO₂, and MnO), and the contributions of each oxide on kaolin minerals determined by electronic microprobe. The effect of particle size in the flotation process was analyzed by particle size distributions of four fractions (<25 µm; +25–45 µm, +45–63 µm; and >63 µm). The contribution of entrainment is similar for the three oxides and the degree of entrainment decreases with increasing particle size; however, the recovery by true flotation is different because of its discriminatory effect on minerals. MnO has the greatest recovery, as a consequence of the major contribution of its hydrophobic minerals, while FeO has the lowest recovery values. The results of the proposed method, developed for fully liberated feeds, are coherent with those obtained by the other three methods, despite the slightly overestimated contribution of entrainment in the case of fraction greater than 63 µm.     

Improvement of Silver Extraction by Ultrafine Grinding Prior to Cyanide Leaching of the Plant Tailings of a Refractory Silver Ore

Ultrafine grinding (UFG) was proposed as a pretreatment method prior to cyanide leaching of old plant tailings of a refractory silver ore. Direct cyanidation of the as-received tailings (d₈₀: 100 µm) led to a low silver extraction of only ≤43% over 24 h. A size-based diagnostic study has demonstrated that the refractoriness of the tailings is essentially physical in character. Therefore, effects of particle size/UFG (d₉₉: 5–75 µm), concentrations of NaCN (0.75–2.25 g/L) and Pb(NO₃)₂ (0–500 g/t) on the extraction of silver were investigated using a Box–Behnken design. The statistical analysis of the experimental data (%Ag extraction at 1 h) revealed that particle size/UFG was the most significant parameter for the extraction of silver, which was substantially improved after UFG. A positive effect of increasing the concentration of NaCN was also observed particularly at finer particle sizes while the effect of concentration of Pb(NO₃)₂ was insignificant. Almost complete extraction for silver (i.e., ≥99%) was demonstrated to be possible at even higher concentrations of cyanide (>2.25 g/L NaCN) when using the finest material (d₉₉: 5 µm) over only 1 h of leaching. Albeit, the consumption of cyanide tended to increase with UFG or increasing the initial concentration of cyanide. The findings showed that UFG can be used as a suitable and environmentally sound pretreatment method to improve the extraction of silver from the refractory silver ore tailings. The diagnostic approach adopted in the current study has proved to be a useful analytical tool to determine the amenability of the ore to ultrafine-grinding as a pretreatment process.     

Scenario-Based Multi-Objective Genetic Algorithm Optimization of Closed Ball-Milling Circuit of Esfordi Phosphate Plant

The main goal of this article is to demonstrate an approach based on integration of process simulation and Multi-Objective Genetic Algorithm (MOGA) concepts to solve a real grinding circuit optimization problem by finding the best operating condition under which process objectives can be achieved. Esfordi phosphate plant is located near city of Bafgh at Yazd province of Iran and produces 5 Mt of phosphate annually. The fine particles (nearly ?20 µm) in hydrocyclone underflow which contain a high grade of iron are subjected to over grinding. In addition to electrical energy loss, this causes problems in the downstream process, i.e., flotation stage. The main goals of this study were to solve this problem by adjusting operating condition so that (a) hydrocyclone overflow particle size can be increased from 94.2 µm to 100 µm and (b) increase hydrocyclone underflow particle size from 205 to 500 µm. The second process objective will decrease fine particles in hydrocyclone underflow stream. First, plant sampling campaigns were carried out to calibrate ball mill and hydrocyclone models to be used for performing simulation trials. Then, full circuit simulations were done and optimized by MOGA search process to find the best operating condition that produces hydrocyclone overflow and underflow streams with predefined particle sizes simultaneously. The results indicate that there are various solutions that can be recommended for plant testing and performance improvements. The results of plant implementation of one solution for scenario No. 4 showed improved circuit performance and also validated simulator predictions.     

Grain-Size Composition and Coercive Force of Nd2Fe14B Alloy Powder in a Finely Divided State

The change in grain-size composition and magnetic properties of powder prepared by grinding cast alloy Nd₂Fe₁₄B in a ball mill for different times is studied. It is shown that during grinding the coercive force of the powder increases uniformly at first reaching a maximum, and then it decreases. It is established that this phenomenon is not due to powder oxidation during grinding but a reduction in the level of particle uniaxial anisotropy caused by deformation of their surface layer during grinding. The change in coercive force of Nd ₂Fe₁₄B alloy powder on grinding obeys the same features that are observed with mechanical grinding of other uniaxial magnetic materials.     

Sintering and magnetocaloric properties of gas atomised LaFe11.0Si1.2Co0.8

ABSTRACT

The sintering behaviour of LaFe_11.0Si_1.2Co_0.8 powder produced by gas atomisation was examined to provide a basis for the application of powder metallurgical shaping technologies to magnetocaloric La(Fe,Si)₁₃-alloys. The aim was to establish sintering parameters for attaining both high densification and good magnetocaloric properties for the investigated particle sizes <10 µm and <25?µm. Dilatometry measurements and sintering trials were carried out and density, microstructure and entropy change ΔS of the sintered samples were analysed. For the fine particles <10?µm, the lowest investigated sintering temperature 1150°C results in a relative density of 97%, a low α-Fe content and a high ΔS?=??5?J?kg^?1?K^?1 (ΔH=2?T). For powder <25?µm, a two-stage process is required to achieve similar properties.     

Transient liquid phase sintering of high density Fe3Al using Fe and Fe2Al5/FeAl2 powders Part 1: Experimentation and results

Abstract

High density Fe₃Al was produced through transient liquid phase sintering, using rapid heating rates of greater than 150 K min^-1 and a mixture of prealloyed and elemental powders. Prealloyed Fe₂Al₅/FeAl₂ (50Fe/50Al, wt-%) powder was added to elemental iron powder in a ratio appropriate for producing an overall Fe₃Al (13·87 wt-%) ratio. The heating rate, sintering time, sintering temperature, green density and powder particle size were controlled during the study. Heating rate, sintering time and powder particle size had the most significant influence upon the sintered density of the compacts. The highest sintered density of 6·12 Mg m^-3 (92% of the theoretical density for Fe3Al) was achieved after 15 minutes of sintering at 1350°C, using a 250 K min^{- 1} heating rate, 1-6 μm Fe powders and 5·66 μm alloy powders.

SEM microscopy suggests that agglomerated Fe₂Al₅/ FeAl₂ particles, which form a liquid during sintering, are responsible for a significant portion of the remaining porosity in high sintered density compacts, creating stable pores, larger than 100 μm diameter, after melting. High density was achieved by minimising the Kirkendall porosity formed during heating by unbalanced diffusion and solubility between the iron and Fe₂Al₅/FeAl₂ components. The lower diffusion rate of aluminium in the prealloyed powder into the iron compared with elemental aluminium in iron, coupled with a fast heating rate, is expected to permit minimal iron-aluminium interdiffusion during heating so that when a liquid forms the aluminium dissolves in the iron to promote solidification at a lower aluminium content. This leads to a further reduction in porosity.     

复合助磨剂对钢渣超微粉助磨效果

以乙二醇与三乙醇胺为原料、无水乙醇为溶剂配制复合助磨剂。将复合助磨剂分别与滚筒渣、脱硫渣和热闷渣进行混合后,利用行星式球磨机进行粉磨。研究钢渣的化学成分与矿物组成、不同助磨剂对钢渣超微粉粒度分布的影响、复合助磨剂对钢渣超微粉的作用机理。结果表明,当乙二醇、三乙醇胺与无水乙醇按体积比2∶2∶2配制复合助磨剂,以钢渣∶复合助磨剂质量体积比为450 g∶6 mL时,钢渣超微粉的粒度分布最佳,即d90为9.14~9.28、d50为3.31~4.20、d10为0.99~1.04和d90-d10为8.11~8.24 μm,其中复合助磨剂对脱硫渣的助磨效果最佳。     

Effect of phase composition of Geksanit-A grinding powder on the operating properties of abrasive tools

Conclusions This investigation has demonstrated that the instability of the operating characteristics of abrasive disks from Geksanit-A grinding powder is linked with the latter's phase composition: The greater the amount of BN_s in a Geksanit-A grinding powder, the better are the service properties of abrasive tools from this material; the presence of more than 4% of BN_g has a marked deleterious effect on the properties of Geksanit-A abrasive tools. Geksanit-A should contain not less than 60% of BN_g and not more than 4% of BN_s. To improve the service performance of Geksanit-A abrasive disks, it is necessary to develop methods of synthesis enabling the BN_s content of the material to be raised to 90–95%. Geksanit-A abrasive disks are effective in the operations of finishing and grinding of flat faces of high-speed steel tools without the use of a cooling lubricant. Geksanit-A is particularly suitable for the manufacture of abrasive disks of grain size of 125/100m or more, and these should be used at cutting depths of up to 0.04 mm.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 85–88, May, 1982.     

温度对轧辊磨损测量结果的影响

现场实测了涟钢CSP热连轧厂Φ600 mm×2 000 mm材质为(%):3.50C-1.20Si-1.20Mn-2.10Cr-4.50Ni-0.80Mo高铬高镍铸铁CVC轧辊的磨损情况。结果表明,轧辊的磨损呈现典型的箱形,温度对轧辊磨损的影响较大,影响最大部分位于箱底中部,最大差值达85.1μm。因轧辊磨床的磨削精度≤10μm,因此轧辊在磨削前应冷却至10℃以下。     

Production of cord steel at the Magnitogorsk Metallurgical Combine

Studies of the wire rod currently being made at the MMK revealed the presence of nondeformable nonmetallic inclusions as large as 52 µm. The rod was also found to contain aluminates with an Al₂O₃ content greater than 50% and particle sizes greater than 5 µm (6 and 8 µm). Such rod does not meet the requirements established for metal cord. A collaboration with specialists at the company Kordinvest made it possible to determine the requirements that must be met when cord steel is deoxidized with ferroalloys and other materials. In terms of the purity of these materials, the main restrictions are on the allowable concentrations of S, P, Al, and Ti and the gases N and H. A new technology has been developed for making cord steel and treating it outside the furnace, and a trial batch of this steel was made and cast on a continuous section caster in an “open” stream. The company Uralkord has used a trial batch of cord-grade wire rod to make metal cord 15L24. The cord meets all the existing specifications.     

Mechanical activation of the reactive sintering of titanium carbide

This paper describes the mechanical alloying of Ti and C powders by intensive grinding in a planetary mill. The effect of milling conditions and initial composition on the compositional homogeneity and properties of powders and samples consolidated by hot-pressing was studied by x-ray diffraction, scanning electron microscopy, and surface area measurement. The diffraction patterns indicated that a powder mixture ground for 24 hours transforms to TiC after sintering for only one minute at 600°C under a pressure of 3 GPa. Materials Science Instiute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 32–38, May–June, 1998.     

Effect of Rheology of Grinding Efficiency in the Laboratory Scale Continuous Classifying Mill

Abstract

Different ores containing soft minerals as the main components were ground in a continuously operating ball mill at laboratory scale. The effect of grinding conditions was studied by changing the solids feed rate, the feed slurry density, the weight of ball charge and the mill rotation speed. The optima of these variables in terms of energy consumption and production rate of fine fractions were determined individually for each tested ore. The grinding efficiency with this mill, equipped with a screen as a grate and a classifier at the discharge end, could be improved by lowering the slurry density to 25% solids by weight, which is significantly lower than traditionally used in laboratory tests or industrial practice.

The flow properties of the mineral slurries in question were studied as a function of percent solids for a better understanding of the phenomena observed in the grinding testwork. The viscosities of the mill discharge slurries were measured with different slurry densities. Tracer tests were conducted with different water/solids ratios in the mill feed for measuring the residence times of bulk solids, various size fractions and water, The maximum discharge rates of slurries from the mill were also measured with various slurry densities. The grinding results are discussed based on the conclusions drawn from these measurements.     

Some features of the manufacture of R-100F-1 carbonyl iron powder

Conclusions Raising the temperature in the reactor increases the concentrations of carbon and nitrogen impurities in a carbonyl iron powder, the increase in the nitrogen content being greater than that in the carbon content. A rise in reactor temperature increases both the goodness factor Q_reland the temperature coefficient of magnetic permeability TC. Increasing the rate of feed of ammonia to the decomposition reactor brings about a growth in the concentration of nitrogen in a carbonyl iron powder, which lowers the TC of the powder and at the same time slightly decreases its goodness factor Q_rel. The optimum conditions for the manufacture of a starting R-100 powder of lower TC. (not more than 80·10^–6 1/deg C) are: upper, middle, and lower zone temperatures of 311, 306, and 337°C, respectively, an ammonia concentration in the decomposition products of 9 vol. %, and an iron pentacarbonyl feed rate of 32 liters/h. For the manufacture of R-100F-1 powder, the fine powder fractions from cyclones 2, 3, and 4 are used. The quantitative yield of carbonyl iron powder is 1.5–1.7%.Translated from Poroshkovaya Metallurgiya, No. 5 (221), pp. 1–5, May, 1981.