以疏水絮团形式从铁矿石中磁选细粒赤铁矿和褐铁矿

本文研究了絮团磁选 (FMS)法 ,即以絮团形式磁选细粒弱磁性铁矿石 ,以代替强磁选机或高梯度磁选机处理细粒弱磁性铁矿石。本研究用细磨至微米级的赤铁矿和褐铁矿进行 ,添加油酸钠和煤油引起疏水絮凝 ,形成大的絮团。试验结果表明 ,与相同条件下的常规磁选相比 ,FMS法可用中场强磁选机有效地回收细粒赤铁矿和褐铁矿 ,并且获得高的分选效率。FMS法处理铁品位为 30 5 %的赤铁矿矿石时 ,获得的精矿铁品位为 6 4%,回收率为 82 %。研究发现 ,FMS法的分选效率与疏水絮凝主要参数 (油酸钠用量、搅拌时间和煤油用量 )密切相关。这表明 ,FMS法具有高的分选效率可归因于疏水絮团的形成 ,使得磁场作用在细粒铁矿物的磁力增大 ,在磁选机中细粒铁矿物更易附着在齿板上 ,从而进入磁性精矿中。

芒特艾萨矿铅/锌选矿厂铅回路中细粒方铅矿回收问题的探讨 第一部分 磨矿介质效应

对芒特艾萨矿铅/锌选矿厂铅二段粗选和扫选槽进行了生产调查。调查样品的粒度分析表明,选厂这一段中总铅回收率的一个主要限制因素是-5μm粒级部分细粒方铅矿的回收率下降。对铅二段粗选给料的现厂样品和棒磨给料矿样进行了分批浮选试验。这些实验的矿物回收率-粒度数据表明,细粒方铅矿的浮选行为同现厂生产所观察到的类似。增加捕收剂用量既不能提高细粒方铅矿的最大回收率,也不能提高其浮选速率常数,反而降低了方铅矿对闪锌矿的选择性。改变磨矿介质即从高碳钢改为高铬合金钢,将会使细粒方铅矿的最大回收率和浮选速率常数显著提高。用高碳钢介质所测得的EDTA(乙二胺四醋酸)可提取铁的量同现厂所测得的结果相同,但要高于那些用高铬合金钢介质所测得的值。无论在实验室里还是在现场生产中,细粒方铅矿上氧化铁亲水层表面浓度的增大是降低其浮选行为的一个可能原因。

淮北选煤厂细粒煤泥分选实践

为探索煤炭精细分级分选,优化生产系统,淮北选煤厂对煤泥重介质旋流器及粗煤泥振动弧形筛进行了优化,通过采用大直径煤泥重介质旋流器,改变弧形筛工艺参数,增加筛面喷水,稳定斜管浓缩机溢流等措施,加强重介分选环节对>0.25 m m粒级煤炭的精选,降低了重介系统分选下限,有效控制了粗精煤灰分、水分;降低了浮选入浮量、粒度、灰分,减轻了浮选系统的压力。同时通过采用“2+2”浮选工艺,降低了浮选精煤灰分,避免了重介精煤“背灰”现象,实现了精煤产率最大化。

通过分散处理改善萤石矿石的浮选

在本工作中,通过粒度分析和扫描电镜(SEM)测量,研究了墨西哥一矿山萤石矿浆中的多相凝聚。试验结果表明,在pH9.0时在萤石矿浆中有一个矿泥包覆形式的强多相凝聚,它可归因于水溶液中萤石/石英和方解石/石英颗粒之间双电层的吸引,以及水溶液中萤石/方解石颗粒之间很弱的双电层排斥。此外,通过使用化学分散剂CMC(羧甲基纤维素)或水玻璃研究了这种多相凝聚的消除,以改善萤石矿石的泡沫浮选。试验结果表明,用CMC作分散剂的这种分散处理能有效改善萤石浮选,在相同的精矿CaF2品位98%时,萤石的回收率从72%提高到78.5%。

喷射磨矿机磨矿时磨矿参数对产品细度的影响

研究了喷射磨矿机磨矿时一些参数对产品细度的影响,试验设备采用了实验室规模的螺旋型喷射磨矿机。喷射磨矿机磨矿中,最重要的变量是给料速率、磨矿空气体积流量和使磨矿在恒定压力下进行的内分级管高度。结果表明,内分级管(涡流测高器)的高度在喷射磨矿机磨矿中也是一个相关的变量,在过程最佳化时应予考虑。在最小给料速率、最大磨矿空气流速和最短分级管时得到最细的产品粒度。

Numerical simulation of acoustic pressure field for ultrasonic grain refinement of AZ80 magnesium alloy

Ultrasound with different intensities was applied to treating AZ80 alloy melt to improve its solidification structure.The average grain size of the alloy could be decreased from 303 to 148 μm after the ultrasound with intensity of 30.48 W/cm2 was applied.To gain insight into the mechanism of ultrasonic treatment which affected the microstructure of the alloy,numerical simulations were carried out and the effects of different ultrasonic pressures on the behaviors of cavitation bubble in the melt were studied.The ultrasonic field propagation in the melt was also characterized.The results show that samples from different positions are subjected to different acoustic pressures and the effect of grain refinement by ultrasonic treatment for these samples is different.With the increase of ultrasonic intensity,the acoustic pressure is increased and the grain size is decreased generally.

Grain refinement of pure aluminum by direct current pulsed magnetic field and inoculation

The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.

Effects of grain refining and modification on mechanical properties and microstructures of Al-7.5Si-4Cu cast alloy

Al-7.5Si-4Cu cast alloy melt modified by Al-5Ti-B, RE and Al-10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners and modifiers on the mechanical properties, microstructures, grain refining and modification, and intermetallic compounds of the alloy. The results show that the mechanical properties and the microstructures of Al-7.5Si-4Cu cast alloys are improved immensely by combining addition of 0.8%Al-5Ti-B, 0.1%RE and 0.1%Al-10Sr grain refiners and modifiers compared with the individual addition and cast conditions. For individual addition condition, addition of 0.8%Al-5Ti-B master alloy can obtain superior tensile strength, Brinell hardness and finer equiaxedα（Al） dendrites. The alloy with 0.1%RE master alloy shows the highest improvement in ductility because the rare earth can purify the molten metal and change the shape of intermetallic compounds. While the alloy with 0.1%Al-10Sr modifier shows only good improvement in yield strength, and the improvement of other performance is unsatisfactory. The Al-10Sr modifier has a significant metamorphism for the eutectic silicon, but will make the gas content in the aluminum alloy melt increase to form serious columnar grain structures. The effects of grain refining and modification on mean area and aspect ratio have the same conclusions obtained in the mechanical properties and the microstructures analyses.

Improving in plasticity of orthorhombic Ti_2AlNb-based alloys sheet by high density electropulsing

In order to optimize the ductility of orthorhombic Ti2AlNb-based alloys sheet,Ti22Al27Nb sheet was treated by high density electropulsing（J max =6.80 7.09 kA/mm2,tp =110 μs） under ambient condition.Microstructures were observed by SEM,and the tensile properties were also studied using uniaxial tension tests.The experimental results show that electropulsing can refine the microstructures of Ti22Al27Nb sheets.The specimen with the fine and homogeneous microstructures has good plasticity,and its elongation reaches 19.4%.The mechanism about the effect of electropulsing treatment on the microstructure of Ti22Al27Nb sheets was discussed.It was thought that the increase in nucleation rate during phase transformation and a very short treating time were regarded as the main reasons of producing smaller grains and increase in the plasticity by electropulsing.

Effect of Si-addition as a grain refiner on microstructure and properties of Ti-6Al-4V Alloy

Two different Ti alloys were cast in a graphite mould using vacuum induction skull melting furnace. The first alloy was Ti-6Al-4V and the second was Ti-6Al-4V 0.5Si. Silicon as a grain refiner was added into Ti-6Al-4V alloy, and the effects of Si-addition on the microstructure and properties of the as-cast and swaged alloys were investigated. Hot swaging at 900 °C was performed on the cast samples and then two different thermal treatments were applied. The first treatment was done by heating the swaged samples at 1050 °C to produce fine lamella structure, while the second treatment was carried out at 1050 °C and then decreased the temperature to 800 °C for getting coarse lamella structure. An addition of 0.5% Si to Ti-6Al-4V alloy decreased the grain size of the as-cast sample from 627 to 337 μm. There was an increase in ultimate tensile strength of about 25 MPa for the as-cast Ti-6Al-4V 0.5Si alloy compared to Ti-6Al-4V due to the refinement effect caused by Si addition. A maximum ultimate tensile strength of 1380 MPa and a minimum corrosion rate （1.35×10 6 mm/a in Hank’s solution and 5.78×10 4 mm/a in NaCl solution） were reported for the heat treated fine lamella structure of Ti-6Al-4V 0.5Si alloy. The wear rate was decreased to about 50% by adding 0.5% Si at low sliding speeds and to about 73% at high sliding speeds.

Effect of trace boron on grain refinement of commercially pure aluminum by Al-5Ti-1B

The effect of boron content on grain refinement of commercially pure aluminum by Al-5Ti-1B was quantitatively assessed.When the boron content is less than 0.03 wt.%,the refining performance of Al-5Ti-1B gradually is weakened as the boron content increases,which is attributed to the reaction of boron with the Al_(3)Ti interlayer on TiB_(2)and the consumption of solute Ti.On the contrary,when the boron content exceeds 0.03 wt.%,the refining performance of Al-5Ti-1B gradually recovers with increasing boron content,which is related to the formation of primary AlB_(2)particles that provide additional nucleant substrates.

Microstructure and mechanical properties of fine grained uranium prepared by ECAP and subsequent intermediate heat treatment

The microstructure and mechanical properties of fine grained uranium prepared by equal channel angular pressing(ECAP)and subsequent intermediate heat treatment were investigated systematically by the confocal laser scanning microscope(CLSM),electron backscatter diffraction(EBSD)and split Hopkinson pressure bar(SHPB).The results show that the initial coarse grained uranium was refined from about 1000 to 6.5μm prepared by ECAP at 3 passes and subsequent heat treatment,and the corresponding dynamic yield strength increased from 135 to 390 MPa.For the ECAPed uranium samples,the relationship between grain size and yield strength could be described by classical Hall−Petch relationship,and the fitting Hall−Petch relationship for the fine grained uranium samples prepared by ECAP was drawn.

Production of grain-refined AC7A Al-Mg alloy via solidification in ultrasonic field

The objective of the current study was to investigate the use of ultrasonic melt treatment technology in the production of grain-refined billets of the AC7 A alloy, which was intended for subsequent use as a feedstock in forming operations. The experiments included the application of ultrasonic vibrations to the molten alloys via direct and indirect techniques. Several process parameters such as pouring temperatures(several temperatures between 740 and 660℃), and treatment time(from 12 min down to 2 min) were investigated. The experiment included continuous ultrasonic treatment from the liquid to the semisolid states. The results showed that both treatment techniques were viable for producing billets with the desirable microstructural characteristics. The optimum treatment conditions were the short treatment time(2 to 3 min), from about 660℃ down to 615℃ for the indirect treatment technique, and from 660℃ to 635℃ for the direct treatment technique. The resulting microstructures, at three positions along the height of the ingot, were characterized by fine, non-dendritic α(Al) grains in the order of a hundred microns, as compared to few thousands of microns for the conventional cast ingots. The intermetallic particles were also refined in size and modified in morphology by the ultrasonic treatment. The operating mechanisms by which the ultrasonic vibrations altered the ingot microstructures were discussed and analyzed.