Nonlinear comminution process modeling based on GA–FNN in the computational comminution system

A new concept named computational comminution is firstly proposed in this paper. Based on information technology, the structure of a computational comminution system (CCS) is built. The study on CCS is very different from the traditional ones for comminution, such as the study based on theoretic models, or the study based on experimental models. As one of the key technologies in CCS, a modeling framework for comminution processes is implemented particularly by employing GA–FNN that can model complex nonlinear processes such as the comminution process of cement by integrating artificial neural networks, fuzzy sets and genetic algorithms. Application results of this modeling method to the Horomill cement comminution process show that the modeling framework discussed in this paper is efficient.     

矿岩粉碎颗粒分形结构与粉碎能耗的关系

用半自动图象分析系统测定了矿岩粉碎后颗粒的周边分形结构,得到粉碎后颗粒表面的分维数在2.033—2.110范围,其分维数随粒度减小而有所增大。按粉碎能耗增量正比?颗粒分形结构的表面积增量原理,得到和Hukki粉碎能耗表达式相同的结果,后者是概括了Rittinger,Kick和Bond三大粉碎能耗学说的共同表达式。     

大红山铜矿二选厂碎磨流程的确定

根据大红山铜矿二选厂所处理矿石的性质,认真分析、借鉴了处理相同类型矿石的大红山铜矿一选厂的生产实践经验,提出几种不同碎磨流程方案,经过详细的技术经济比较和论证,确定了合理的碎磨流程.     

Modeling of shear instabilities observed in cylinder collapse experiments performed on ceramic powders

Brittle materials fail by microcracking and fragmentation when subjected to multiaxial loading. In some cases full comminution occurs and the material behavior becomes governed by the flow of particles. In this work a granular model developed by Anand and co-workers, based on a two-mechanism elastoplastic formulation, is extended to include rate effects and incompressibility at zero void ratio. The model parameters for Alumina and Silicon Carbide ceramic powders are identified using stress histories obtained by means of pressure-shear plate impact experiments. The model is then used to simulate the shear banding mechanism experimentally observed in thick-wall cylinder collapse experiments performed on ceramic powders (Nesterenko and co-workers). The proposed model captures the main physics of the problem and provides valuable insight in the deformation process. Initiation site and speed of propagating instabilities are obtained from the simulations.     

A CONTINUOUS DAMAGE APPROACH TO RELATIONSHIP BETWEEN SIZE REDUCTION AND ENERGY CONSUMPTION DURING ORE COMMINUTION

Based upon the aspect of continuous damaging,the process of ore comminution may be des-cribed as the growth and propagation of the microcracks in the ore grains under external load-ing,and a theoretical expression has been developed on the relationship between the grain sizedistribution and the total energy consumption during entire ore comminution process.The en-ergy consumed totally may be considered consisting of two portions,i.e.with fresh crack sur-faces growth and with crack propagation.The proposed expression seems to be an advanceover previous conventional ones,especially that from the viewpoint of energy distribution.     

Tribotesting system for hardmetal mechanical characterization

Performance of a material in a tribomechanical system can only be determined by a carefully designed simulation in which mechanical elements undergo processes similar to those in a complex engineering environment. In this paper a simple and reliable integrated testing method, in which conjoin actions involving fracture and abrasion of hardmetals together with abradant comminution, is carefully monitored and analysed. The presented system approach to tribotesting enables the mechanical characterization of hardmetals in attrition contact with granular minerals which takes place in e.g. mineral processing or in drilling action. The results from this testing show that by using one apparatus and test specimen shape it is possible to obtain a reliable rating of hardmetals according to both criteria: their fracture toughness as well as their resistance to abrasion in rubbing contact with the abradant. The integrated testing method required a theoretical or empirical model which describes the relationship between fracture toughness, other mechanical properties and the test's fracture indicator. For the range of materials tested, the best correlation received was for the empirical model for the removal of brittle material by lateral cracking.     

Effects of humidity on the flow characteristics of a composite plasma spray powder

The effects of environmental humidity on the flow characteristics of a multicomponent (composite) plasma spray powder have been investigated. Angular and spherical BaF₂−CaF₂ powder was fabricated by comminution and by atomization, respectively. The fluorides were blended with nichrome, chromia, and silver powders to produce a composite plasma spray feedstock. The tap density, apparent density, and angle of repose were measured at 50% relative humidity (RH). The flow of the powder was studied from 2 to 100% RH. The results suggest that the feedstock flow is only slightly degraded with increasing humidity below 66% RH and is more affected above 66% RH. There was no flow above 90% RH except with narrower particle size distributions of the angular fluorides, which allowed flow up to 95% RH. These results offer guidance that enhances the commercial potential for this material system.     

矿岩粉碎全过程能耗-粒度关系的连续损伤理论研究SCIEI

本文从连续损伤理论的观点出发,将矿岩粉碎过程描述为在外部荷载作用下矿岩颗粒内部微缺陷(损伤)演化和繁衍的过程。导出了粉碎能耗与产品粒度分布的理论表达式。该式包含了所有传统的理论,同时较传统的能量分配观点前进了一步。     

球形烧结态Cr3C2-25%NiCr复合粉末制备研究

试验通过添加高分子分散剂配制Cr3C2-25%NiCr料浆,采用喷雾干燥技术制备球形粉末,在保护气氛下进行液相烧结,气流粉碎分级后形成合适粒度粉末.实验研究了不同分散剂含量对喷雾干燥制备Cr3C2-25%NiCr复合粉末性能的影响,液相烧结工艺对Cr3C2与NiCr合金相之间冶金化结合状态的影响.研究结果表明高分子分散剂能够很好的调解料浆性能,使喷雾干燥粉末具有良好的物性.采用SEM、XRD及化学成分分析表明粉末物理性能与国外粉末相当,超音速火焰喷涂涂层性能较好.     

Effect of particle morphology on flow characteristics of a composite plasma spray powder

The effects of BaF₂-CaF₂ particle morphology on National Aeronautics and Space Administration (NASA) PS304 feedstock powder flowability were investigated, BaF₂-CaF₂ eutectic powders were fabricated by comminution (producing an angular morphology) and by gas atomization (producing a spherical morphology). The fluoride powders were added incrementally to the other powder constituents of the NASA PS304 feedstock, (Ni-Cr, Cr₂O₃, and Ag powders). A linear relationship between flow time and concentration of the BaF₂-CaF₂ powder was found. The flow of the powder blend with spherical BaF₂-CaF₂ was better than that with angular BaF₂-CaF₂. The flowability of the powder blend with angular fluorides decreased linearly with increasing fluoride concentration. However, the flow of the powder blend with spherical fluorides was independent of fluoride concentration. The results suggest that for this material blend, particle morphology plays a significant role in flow behavior, offering potential methods to improve powder flowability and enhance the commercial potential. These findings may be applicable to other difficult-to-flow powders such as cohesive ceramics.     

Microstrain temperature evolution in β-eucryptite ceramics: Measurement and model

Mechanisms of microcracking and stress release in β-eucryptite ceramics were investigated by applying a combination of neutron diffraction (ND), dilatometry and the Integrity Factor Model (IFM). It was observed that the macroscopic thermal expansion of solid samples closely follows the lattice thermal expansion as a function of temperature, and both are dominated by microcracks closing (during heating) and opening (during cooling). Analogous experiments on powders showed that the stresses that manifest peak shift are indeed relieved by comminution, and that the resulting lattice thermal expansion can be considered as unconstrained. By means of Rietveld refinement of the ND data, the evolution with temperature of peak width parameters linked to strain distributions along the basal, pyramidal and axial planes could also be extracted. The peak width parameters S_HKL correlated well with the strains calculated by peak shift and with the model results. Furthermore, while the peak shifts showed that the powders are basically stress free, the S_HKL showed a strong evolution of the peak width. Powders carry, therefore, a measurable strain distribution inside the particles, owing to the thermal expansion anisotropy of the crystallites. The IFM allowed this behavior to be rationalized, and the effect of microcracking on thermal expansion to be quantified. Experimental data allowed accurate numerical prediction of microcracking on cooling and of the evolution of microstresses. They also allowed the derivation of the material elastic modulus from bulk thermal expansion curves through the IFM concept. Ultrasound resonance measurements of the elastic modulus strongly support these theoretical predictions.     

A novel technology of high-voltage pulse discharge for comminution of galena ore

An innovative technology of high-voltage pulse discharge (HVPD) was proposed to investigate the comminution characteristics of galena ore. The optimal experiment parameters were determined as follows: spark gap spacing of 25 mm, pulse number of 120, and voltage of 25 kV. The mass fraction with size <0.074 mm in ground products was improved by the HVPD. Meanwhile, the relative grindability declined with the increase of the grinding time, which indicated that the superiority of HVPD was weakened. The ground products of HVPD were distributed more homogeneously than those of mechanical crushing. The liberation of breakage products was improved by 24.57% via the HVPD. Moreover, the Brunauer–Emmett–Teller (BET) specific surface area, pore volume, and average pore size were increased via the HVPD. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses suggested that obvious grain-boundary breakage and several stomatal traces were observed in the HVPD products.     

古代中国和印度的金粉制造技术和应用

古代中国和印度采用机械法和化学法制造金粉,其金粉技术和应用都有久远的历史,但也有若干差异。印度梵文文献中记载了一种被蚂蚁采集的自然金粉。用金叶生产金粉是一个重要的技术进步,它产生于公元２世纪的中国和公元４世纪的印度。用汞齐技术分又是金粉技术一个 的里程碑在中国它与机械法几乎同时诞生,而在印度则对公元９世纪。在古印度,金粉主要用于医药和涂料领域;在古代金主要用于医药、油漆和丝绸工业。中国的金粉制造技     

The effectiveness of oxides in reducing sliding wear of alloys

During like-on-like reciprocating sliding in air (amplitude 2.5 mm, load 1.5 kg, speed 500 double traversais per minute), the formation of oxides can have considerable influence on the friction and wear characteristics of high-temperature alloys, such as Jethete M152 and Rex 535. In particular, above a certain transition temperature, between 200 and 300°C for these alloys under these conditions, an adherent, smooth wear-protective oxide layer is developed on the load-bearing surfaces. At lower temperatures, oxide debris reduces the extent of metal-metal contact, thereby reducing the friction and wear rate, but does not eliminate it completely. The oxide debris is produced by two processes; one involves transient oxidation of the metal surfaces, removal of such oxide during each transversal, and reoxidation of the exposed metal; the other involves the formation, fracture, comminution, and oxidation of metal debris particles. At temperatures above the transition temperature, the oxide debris is compacted and comminuted between the sliding surfaces to develop the wear-protective oxide layer. This paper considers the reasons for the effectiveness of such oxides in terms of the influence of the hydrostatic pressures generated on plastic deformation of the very fine oxide particles or asperities in the surface. The resulting friction during sliding is less than during metal-metal contact because only limited asperity junction growth occurs before the asperities become sufficiently large and the hydrostatic pressures sufficiently reduced to allow fracture within the oxide-oxide junctions. The oxide-wear debris produced is recompacted into the surface, resulting in only very low wear rates. It has been shown that the number of asperity-asperity contacts during sliding of wear-protective oxide layers is relatively high, typically 5×10³/mm² of apparent contact area, while the mean surface flash temperature rise is low, typically 2°C. Consideration is given to some of the conditions that favor development of wear-protective oxide layers.     

纳米材料的进步及应用

简述国外和国内有关纳米材料的研究概况和所取得的成果 ,并分别介绍纳米磁性材料、纳米金属材料、纳米复合材料、纳米硬质合金材料及纳米航空材料等应用方面所取得的成果。     

Near-surface phenomena occurring in cemented carbides with different binders during rotary-percussive drilling of reinforced concrete: FE simulation and microstructural investigations

Rotary-percussive drilling through steel rebar in reinforced concrete subjects drill bits to intensive thermomechanical loading and wear. Significant microstructural changes occur in near-surface regions. These include, but are not limited to, micro- and mesoscopic cracking; fracture at WC-binder interfaces; WC comminution; partial WC dissolution and rearrangement; surface decarburization; binder depletion and pore formation; and the creation of secondary phases within the binder [1–4].Cemented carbide drill bits with three different binders (Co, CoNi and Ni) were drilled in steel reinforced concrete. After sectioning the drill bits, numerous analysis methods were employed to identify the type and composition of phases present; to characterize microstructural changes and wear phenomena; and to locally measure the properties of the modified surface microstructure. Noticeable differences between the binder types are evident.A variety of finite element (FE) simulation methods were used to describe the thermo-mechanical loading spectrum acting on the drill bits. Transient (dynamic) impact loading and quasi-static indentation simulations calculated the stresses and temperatures generated in the application. The magnitude, orientation vectors and spatial distribution of the simulated stress and temperature fields were correlated with the experimental findings regarding crack initiation sites and regions experiencing thermo-mechanically induced surface microstructural and compositional modification. This paper presents some of these findings from extensive experimental and simulation studies.     

锂离子电池新型LiFeSO_4F正极材料的研究进展

与LiFePO_4材料相比,LiFeSO_4F正极材料理论上具有更稳定的结构、更高的电压平台和离子电导率,有望成为动力锂离子电池的热门正极材料,具有更好的应用前景。介绍了LiFeSO_4F正极材料的结构,综述了近年来LiFeSO_4F正极材料的合成及掺杂改性方面的研究进展,重点对LiFeSO_4F正极材料的制备方法和掺杂进行了总结和探讨,并对LiFeSO_4F正极材料的发展前景进行了展望。     

Three-Dimensional Visualization of Material Flow During Friction Stir Welding of Steel and Aluminum

Material flow is a key phenomenon to obtain sound joints by friction stir welding (FSW), and it is highly dependent of the welded material. It is well known that the optimal FSW condition depends on the welded material. However, the material flow during FSW has not been totally clarified in spite of many researches. Especially, the material flow of steel during FSW is still unclear. It seems difficult to understand the material flow by the traditional method such as the tracer method or observation of the microstructure in the stir zone. Therefore, in this study, the material flow of steel was three dimensionally visualized by x-ray radiography using two pairs of x-ray transmission real-time imaging systems, and was then compared with the material flow of aluminum. The result revealed the effect of the welded material on the material flow during FSW.     

PAP-D型铝塑复合材料热老化研究

复合材料一般由多种成分组合而成,温度的升高会引起各组分的膨胀,如果各组分的膨胀系数不一样,会引起复合材料的热应力疲劳.对PAP-D型铝塑复合材料进行了热老化试验,分析了温度对复合材料性能的影响.并以试验所得数据为基础对该材料在正常条件下的使用寿命进行评估,其寿命大于30年.