Application of artificial neural network method to predict the breakage properties of PGE bearing chromite ore

In the present investigation, systematic grinding experiments were conducted in a laboratory ball mill to determine the breakage properties of low-grade PGE bearing chromite ore. The population balance modeling technique was used to study the breakage parameters such as primary breakage distribution (B_{i, j}) and the specific rates of breakage (S_i). The breakage and selection function values were determined for six feed sizes. The results stated that the breakage follows the first-order grinding kinetics for all the feed sizes. It was observed that the coarser feed sizes exhibit higher selection function values than the finer feed size. Further, an artificial neural network was used to predict breakage characteristics of low-grade PGE bearing chromite ore. The predicted results obtained from the neural network modeling were close to the experimental results with a correlation of determination R² = 0.99 for both product size and selection function.     

Comparative study on NiAl and FeAl intermetallic-bonded diamond tools and grinding performance for Si3N4 ceramic

Metal-bonded diamond tools are widely used for machining hard and brittle materials such as ceramic and stone. The metal bonds are normally based on alloys composed of Fe, Co, Ni, Cu, Sn, Zn, or Cr. However, high heavy metal concentrations are hazardous to the environment and tool operators. Furthermore, the high density of these metal bonds results in excessively heavy tools, requiring high energy and intensive labor during operation. Therefore, we propose two environmentally friendly and lightweight metal bonds based on NiAl and FeAl intermetallics for diamond tools by reactive hot-press sintering. The effect of sintering temperature on the microstructure and mechanical properties of NiAl and FeAl was examined and the tribological behavior of NiAl and FeAl on Si₃N₄ ceramic balls was investigated. Grinding performance of the sintered diamond tools on Si₃N₄ ceramic was also compared. Our results reveal that B2-ordered NiAl and FeAl are obtained at sintering temperatures in the range of 700–1100 °C. The relative density of sintered NiAl is higher than that of FeAl, while the Vickers hardness and flexural strength of NiAl are lower than that of FeAl. Compared with FeAl, NiAl demonstrates higher wear resistance in a friction test against Si₃N₄ ceramic, while FeAl-bonded diamond tools demonstrate a higher grinding ratio than NiAl-bonded diamond tools due to enhanced self-sharpening ability. Nevertheless, diamond tools based on both NiAl and FeAl can be used to grind Si₃N₄ ceramics.     

飞行时间二次离子质谱对矿物表面性质的研究

随着易选矿石的逐步枯竭,低品位、嵌布粒度细等难选矿石的开发利用已成必然趋势。目前,矿物加工已经从实践生产阶段发展到了理论研究指导实践生产的阶段,因此具有分辨率高、信息量大、灵敏快速以及样品用量少等特点的矿物表层研究方法来支撑理论研究是必不可少的。飞行时间二次离子质谱法(TOF-SIMS)是近年来在矿物加工中使用较多的一种矿物表面化学分析方法,具有表面质谱、化学成像、深度剖析、快速灵敏及数据精准的优点,因此总结归纳了近年来TOF-SIMS在矿物加工中应用取得的成果,以期为学者提供可靠的理论依据及技术支持。     

Energy aspects and workpiece surface characteristics in ultrasonic-assisted cylindrical grinding of alumina–zirconia ceramics

Ultrasonic assisted grinding is a novel method for improving the grinding process of difficult-to-cut materials. In the present research a novel setup has been designed and manufactured for utilizing ultrasonic vibrations in external cylindrical grinding. The designed ultrasonic head vibrates a rotating workpiece in axial direction. An alumina–zirconia ceramic (AZ90) has been selected as the workpiece material. Energy aspects and workpiece surface characteristics of ultrasonic assisted cylindrical grinding (UACG) and conventional cylindrical grinding (CG) processes have been analytically modeled and corresponding grinding experiments have been performed. The combined kinematics of the cylindrical plunge grinding process and axial ultrasonic vibrations provide a unique surface treatment conditions, which leads to reduced peak heights and increased valley depths of the surface topography. The main axial vibration mode provides the overlap of the adjacent cutting traces and consequently smoothens the surface topography in cylindrical plunge grinding. It has been analytically and experimentally shown that, applying ultrasonic vibrations, grinding energy can be reduced up to more than 35% depending on the process parameters. The surface characteristics of the ground workpieces have been investigated in terms of four surface roughness parameters and the roundness error.     

Effect of grinding-induced cyclic heating on the hardened layer generation in the plunge grinding of a cylindrical component

This paper discusses the effects of the grinding-induced cyclic heating on the properties of the hardened layer in a plunge cylindrical grinding process on the high strength steel EN26. It was found that a multi-pass grinding brings about a uniform and continuous hardened layer along the circumference of the cylindrical workpiece. An increase of the number of grinding passes, leads to a thicker layer of hardening, a larger compressive residual stress and a deeper plastic deformation zone. Within the plastic deformation zone, the martensitic grains are refined by the thermo-mechanical loading, giving rise to a hardness of 12.5% higher than that from a conventional martensitic transformation. The coupled effects of heat accumulation and wheel wear in the multi-pass grinding are the main causes for the thickening of the hardened layer. A too small infeed per workpiece revolution would result in insufficient grinding heat, and in turn, bring about an undesirable tempered hardened layer and a reduction of its hardness.     

A specific energy-based size reduction model for batch grinding ball mill

A particle size reduction model has been developed as the first component of an upgraded ball mill model. The model is based on a specific energy-size reduction function, which calculates the particle breakage index, t₁₀, according to the size-specific energy, and then calculates the full product size distribution using the t₁₀–t_n relationships and the mass-size balance approach. The model employs an ore-specific and size-dependent breakage function, whose parameters are independently measured with a fine particle breakage characterisation device, the JKFBC. This has effectively overcome the limitation of using a default breakage appearance function for all ores in the perfect mixing ball mill model. Since the ore-specific characteristics and the machine-related specific energy parameters are mechanistically incorporated in the size reduction model, it has the capability to predict size reduction in response to changes in the ball mill feed breakage characteristics and the operation-related specific energy.     

钢球配比及充填率的对比试验研究

针对云南某铅锌矿一段磨矿细度及磨机充填率不达标的问题,进行了不同磨矿介质配比和充填率的对比试验。根据云南某铅锌矿矿石力学性质和磨矿产品循环的粒度筛析分布,利用球径半理论公式精确计算出补装球荷尺寸为Φ80∶Φ60∶Φ40∶Φ30=20∶25∶25∶30。实验室试验结果表明,-0.010mm级别的产率较现场生产降低3.83个百分点,中间可选级别0.15～0.010mm产率提高了4.72个百分点。因为钢段同时具有钢球和钢棒的作用且减轻过磨现象,为考察充填率对磨矿效果的影响,按照重量相等的原则使用了钢段,确定钢段配比为:Φ60×70∶Φ50×60∶Φ35×40∶Φ25×30=20∶25∶25∶30。当钢段充填率增至33%,维持磨矿细度与推荐钢球方案大致相当(即不会降低处理量)的情况下,中间可选级别0.15～0.010mm产率与中间易选级别0.10～0.028mm比现场生产分别提高2.98、0.57个百分点,过磨减轻了2个百分点,达到了优化磨矿产品粒度的目的。     

Regression analysis of surface roughness and micro-structural study in rotary ultrasonic drilling of BK7

Ceramic materials have tremendous demand in manufacturing sectors. However, poor machinability impedes their widespread applications on an industrial scale. BK-7 falls in the same category and is normally processed by ultrasonic machining. But nowadays rotary ultrasonic machining is overtaking the ultrasonic machining for processing difficult to cut materials because of its superlative material removal mechanism. Current study aims to improve the surface quality of BK7 by studying the effect of input factors on surface roughness during rotary ultrasonic machining. Response surface methodology has been used to observe the effect of input variables ― spindle speed, feed rate and ultrasonic power ― on surface roughness (SR). Thereafter, central composite design was employed to estimate the regression coefficients of quadratic model for surface roughness. Fitness of developed quadratic model was checked by ANOVA test, which also revealed that all the model terms of input factors were significant except feed and speed interaction. Feed has the maximum impact over surface roughness descended by moderate impact of power and spindle speed. The study was further reinforced on observing the surface integrity of processed surfaces using scanning electron microscopic images. Mixed flow of material was observed to occur at lower feed rate and higher levels of rpm and ultrasonic power.     

Cu-SiC磨具制备及其性能表征

笔者描述了铜-碳化硅磨具的制备过程,采用热压成形法制备了Cu-SiC磨具。该磨具主要由铜粉、酚醛环氧树脂和碳化硅磨料组成。研究了树脂、碳化硅与辅助磨料的种类、组成对磨具性能的影响。结果表明:当加入适量铜粉,复合材料磨损率会下降、耐磨性能会提高,被磨削表面不易出现凹痕、孔洞;但是铜粉添加过量时,磨具磨损率会增加。较佳配方组成为:35wt%树脂、45wt%碳化硅、15.56wt%铜粉、4.44wt%白刚玉。     

云南某铜矿快速浮选新技术研究

针对云南某铜矿嵌布粒度粗细不均、嵌布关系复杂、部分铜矿物易过磨损失,从而导致铜精矿中铜和伴生金、银回收率低的技术难点,通过采用铜选择性捕收剂BK901G和"铜快速浮选—中矿再磨再选"工艺流程,获得了较好的选矿指标,其中铜精矿中铜的品位和回收率分别达到23.79%和93.66%;伴生金、银的回收率分别达到43.92%和67.93%。该工艺技术可为同类型矿山提供借鉴。