DEM modelling of the dynamics of mill startup

Speed is one of the important parameters in tumbling ball mills because it affects the dynamic motion of the balls within the mill. In turn the motion of the balls affects the distribution of the forces and thus the power draft of the mill. The main objective of this work is to model the dynamics of mill startup using the discrete element method (DEM). To achieve the experimental objective speed and torque as a function of time during mill startup were measured experimentally. A 0.55 m diameter mill was used to perform the experimental analysis. Load volume, J of 0% and 20% and mill speed of 70%, 100%, 120% and 150% of the critical are analyzed in detail. The DEM software, MillSoft (by Rajamani) was used to model the experimental results. During the experiments, the mill was allowed to ramp from rest until it reached the setpoint; after this it continued at constant speed. We have developed good dynamic models of mill speed. The experiments show that torque is the same for all conditions up to the point where each attains steady state, because the ramp rate is constant. The final torque for speeds greater than 100% of the critical speed (experiments and simulations) is not zero because only one layer of balls centrifuges in the time used. The experimental and the simulated torque compare well. Overall the dynamics of mill startup can be modelled with semiquantitative accuracy using DEM.     

颗粒层受压破碎过程的试验研究

在刚性金属容器-活塞压力设备中,进行颗粒层受压破碎过程的试验研究。通过不同最大压力下不同厚度、不同粒径散体颗粒层的受压破碎试验,得到破碎颗粒恢复力位移曲线和产品粒度分布曲线,并分析其对颗粒层破碎的影响规律。进一步试验,分别得到能量吸收与位移、压强的关系曲线,以及能量吸收与颗粒粒径对破碎比的影响曲线。通过对所得曲线进行对比分析可知能量吸收是决定破碎比的最主要因素,能量吸收的多少直接影响颗粒的破碎效果。     

放矿口尺寸对放矿效果的影响

无底柱分段崩落法是金属矿山地下开采应用较多的一种高效采矿方法，在覆盖岩层下进行放矿，矿石损失贫化大、回收效果差的问题非常突出。为了解决这一问题，国内外的大量研究集中在放矿理论、结构参数、覆盖层形成和出矿工艺等方面。无底柱分段崩落法放矿中，放矿口尺寸的大小对放矿效果有着显著的影响，是造成无底柱分段崩落法损失贫化大的一个不可忽视的因素。为了进一步研究放矿口高度和宽度对放出矿石量、废石混入的影响，采用单进路单分段 物理放矿模型，进行了12种不同放矿口尺寸的物理放矿实验。结果表明：适当扩大放矿口宽度或降低高度，会增加放出纯矿石量、提高矿石回收率、降低贫化率，且放矿口宽度小于5 m，高宽之比在0.7~1之间时，混入废石率较小。     

Ball motion,axial segregation and power consumption in a full scale two chamber cement mill

Grinding of clinker for cement production is often performed in a two chamber ball mill. In the first shorter chamber, raw feed is ground using media consisting of large balls. The ground product of the first chamber exits through a discharge grate and enters the second longer chamber. Here smaller balls are used to grind the product material even finer. In this paper we analyse the charge motion, short term ball segregation processes and energy utilisation in a 4 m diameter cement ball mill using DEM. The power draw predicted is consistent with the rated power of the mill. The energy dissipation in the mill is dominated by shear interaction. The gentle liner profiles ensure that few balls move on cataracting trajectories. The distribution of energy utilisation between the different size media fractions is explored as are differences in the collisional environment between the two mill chambers.     

带式输送机转载溜槽试验设计研究

为了合理选择转载溜槽的几何参数,保证料流的畅通同时降低物料与边界的磨损量,对转运溜槽中的物料运动进行了分析,建立了物料在转载溜槽中的流动模型。根据试验设计理论对溜槽的相关参数进行了试验设计,利用直观分析法获得了较优方案。结果表明:直线段和圆弧段的任意组合溜槽中,当圆弧半径5.5m、入口角度18°、总高度3m和出口角度33°时,无量纲磨损数最小。     

磨矿介质形状对橄辉岩型钒钛磁铁矿磨矿动力学影响研究

为了更深入地研究橄辉岩型钒钛磁铁矿磨矿行为,采用钢球、钢锻作为磨矿介质在不同磨矿时间下进行了分批次磨矿试验,研究了点、线不同接触方式对橄辉岩型钒钛磁铁矿磨矿动力学过程与产品分布,重点考察了磨矿动力学参数、比破碎速率、磨矿产品分布特性。研究结果表明：两种介质下的磨矿动力学均符合标准动力学方程,相关参数k与m值均与粒径呈指数函数关系;钢锻介质更适合选择性磨矿,钢球介质下的细粒级产品较钢锻介质多,磨矿时间越大,产品分布越均匀,短时间内,钢锻介质对粗颗粒的破碎效果要优于钢球介质;以上研究结果可为橄辉岩型钒钛磁铁矿磨矿工艺参数提供一定的理论基础与参考价值。     

The development of a CFD model of a submerged arc furnace for phosphorus production

A computational fluid dynamics (CFD) based model of a submerged arc furnace for the production of phosphorus was developed. The model was constructed to investigate the influence of changing operating conditions on energy distribution within the burden and reaction characteristics such as the position of the solid–gas reaction zone. Two user-developed models generate a volumetric distribution of the mass sources and energy sinks within the packed bed region. Boundary conditions, initial values and material specifications are provided by industrial measurements, laboratory experiments and a combination of empirical and thermodynamical data. The results provide three-dimensional furnace characteristics of gas flow, energy distribution and chemical reactions that will give decision support for a predictive, Dynamic-CFD hybrid model [Scheepers, E., Yang, Y., Reuter, M., Adema, A., 2006. A dynamic-cfd hybrid model of a submerged arc furnace for phosphorus production. Minerals Engineering 19 (3), 309–317].     

Modelling comminution patterns within a pilot scale AG/SAG mill

The patterns of rock comminution within tumbling mills, as well as the nature of forces, are of significant practical importance. Discrete element modelling (DEM) has been used to analyse the pattern of specific energy applied to rock, in terms of spatial distribution within a pilot AG/SAG mill. We also analysed in some detail the nature of the forces, which may result in rock comminution.In order to examine the distribution of energy applied within the mill, the DEM models were compared with measured particle mass losses, in small scale AG and SAG mill experiments. The intensity of contact stresses was estimated using the Hertz theory of elastic contacts. The results indicate that in the case of the AG mill, the highest intensity stresses and strains are likely to occur deep within the charge, and close to the base. This effect is probably more pronounced for large AG mills. In the SAG mill case, the impacts of the steel balls on the surface of the charge are likely to be the most potent. In both cases, the spatial pattern of medium-to-high energy collisions is affected by the rotational speed of the mill.Based on an assumed damage threshold for rock, in terms of specific energy introduced per single collision, the spatial pattern of productive collisions within each charge was estimated and compared with rates of mass loss. We also investigated the nature of the comminution process within AG vs. SAG mill, in order to explain the observed differences in energy utilisation efficiency, between two types of milling. All experiments were performed using a laboratory scale mill of 1.19 m diameter and 0.31 m length, equipped with 14 square section lifters of height 40 mm.     

大空间采场覆岩结构特征及其矿压作用机理

特厚煤层开采形成的采场空间大,覆岩扰动范围广,采场顶板来压具有明显的大小周期来压及强矿压显现特点。大空间采场覆岩扰动层位多、岩层间作用机制复杂,顶板破断块体间的作用力及方向多变,导致大空间采场覆岩结构理论分析存在较大难度。为从理论上揭示特厚煤层大空间采场覆岩结构特征及其矿压作用机理,在实测分析得到大空间采场覆岩结构特征基础上,基于能量变分原理建立了大空间采场覆岩结构力学模型,揭示了大空间采场覆岩结构的矿压作用机制;建立了大空间采场覆岩结构条件下的“煤体-支架”协同承载模型,得到了采场支架围岩的相互作用关系。研究表明,特厚煤层开采形成的大空间采场覆岩具有显著的“低-中-高”层位结构特征,是采场复杂矿压显现的直接诱因,“中-低”位顶板结构失稳形成采场大小周期来压,高位顶板结构的失稳联动是诱发大空间采场强矿压显现的主要因素;覆岩结构的失稳运动还受到采空区矸石支撑、顶板有效位能作用及高位顶板悬长等的制约,是采场来压强弱的重要影响因素;大空间采场条件下“煤体-支架”协同承载,所得理论研究成果与基于实测反演分析得到的支架围岩关系研究结论具有较好的一致性,验证了大空间采场覆岩结构理论的正确性。     

露天矿平硐溜井井壁初始碰撞位置理论计算

露天矿山平硐溜井运输系统中,矿石在溜井壁上的初始碰撞破坏较大,确定矿石的初始碰撞位置对于井壁的防护具有重要意义。根据运动学理论,建立矿石运动模型,以某露天矿为例,分析碰撞恢复系数、滑移滚动摩擦系数和临界系数对初始碰撞位置的影响,基于伪随机算法,确定初始碰撞位置的范围。结果表明：随着法向恢复系数、滚动滑移摩擦系数增大,切向恢复系数、临界系数减小,初始碰撞位置距井口的距离变大,滚动滑移摩擦系数是影响初始碰撞位置的主要因素;运动状态的改变对于初始碰撞位置的影响较小;碰撞范围内初始碰撞位置的分布符合指数分布,距离井口6～9 m范围内的井壁需要重点防护。     

刮板输送机中锰钢中部槽的自强化抗磨机理及应用

针对煤矿刮板输送机中部槽的耐磨难题,研究了热轧中锰耐磨钢和马氏体耐磨钢的冲击磨损性能,分析了中锰钢的自强化耐磨机理,介绍了中锰耐磨钢在煤矿刮板输送机中部槽的应用实例。试验结果表明,热轧中锰钢比传统马氏体耐磨钢表现出更好的抗冲击磨料磨损性能,磨损表面硬化层厚度约1 000μm,最高显微硬度达531HV,对应的洛氏硬度达52HRC,表现出优良的耐磨强化效果。研究发现,中锰耐磨钢的耐磨强化机理随冲击功的不同而变化,由较低冲击功的马氏体相变、位错和层错复合强化机制,演变为较高冲击功时的马氏体相变、位错和形变孪晶复合强化机制。实际应用表明,热轧改性中锰耐磨钢的抗磨损性能优于Hardox450耐磨钢,可显著降低中部槽磨损,大幅度延长刮板输送机可靠运行寿命。     

减震防磨损溜槽在山东京杭水铁联运中的应用

溜槽作为煤炭运输中连接运输设备和储煤设施的重要部件，其设计的合理性直接影响到整个生产系统。尤其落差大的溜槽在使用过程中，不仅噪声大，磨损快，而且还会对下一级胶带冲击很大。实际生产中，溜槽维护成本高，严重影响煤炭运输正常作业。结合山东京杭水铁联运项目中溜槽运量大、落差高的特点，阐述了常用的防冲击、减震防磨损的方法以及在实际使用中的优缺点。并结合设计经验，提出了新的应用设计，通过计算机头落煤曲线，得出机头溜槽物料大概落煤点，设计堆煤网格，形成集料槽；在溜槽底板设置阻尼层，并用螺栓固定，起到缓冲减震降噪的作用。同时也起到了保护下一级胶带和落煤点缓冲托辊的作用。     

螺旋溜槽内二次环流分布特性及其分选作用研究进展

近年来,为了响应国家节能减排,建设绿色矿山的政策,解决矿物原料需求大于供给的问题,国内外各大选厂一方面逐渐开始革新现有的设备,另一方面也在逐渐使用重选代替其他的选别方法。重选作为一种古老的选矿方法,因其绿色,成本低在当今社会又一次展现了勃勃的生机。螺旋溜槽作为重选设备的一种,因其入选粒度范围宽、单位面积处理量大、结构简单、无运动部件、易于维护以及独特的结构和优良的分选性能等优点而被广泛应用于国内外选矿厂。目前国内外对于螺旋溜槽的研究多集中在对理论公式及模型的优化上,对二次环流的研究则较少。本文对国内外二次环流的研究现状以及螺旋溜槽参数对分选效果的影响进行了总结,分析了二次环流的研究方向。     

不同长径比煤样动力学特征及本构模型

为研究冲击荷载下不同长径比煤样的动力学性能,借助改进的霍普金森压杆实验装置(?75 mm),开展6个冲击等级(4.18~8.03 m/s)、4种长径比(0.33~1.33)下的冲击压缩实验,并结合灰色关联理论分析动力学参数与长径比之间的关联性,建立基于力学机制、Weibull分布、D-P准则的4参数单轴煤岩强度型统计损伤模型。研究表明:①煤样长径比与应变率、动抗压强度、耗散能均呈二次函数关系,且耗散能随长径比增加而降低; 与电磁能呈一次函数关系,且保持正相关。②煤样长径比对动力学参数的影响排序为:电磁能(0.88)>动抗压强度(0.84)>耗散能(0.81)>应变率(0.78)。③基于Weibull分布、D-P准则构建初始本构模型,并借助动抗压强度σ_max与应变率、长径比n的关系修正,进而对比实验应力-应变曲线,验证模型可靠性(R2>0.91)。     

多段螺旋溜槽的研究

多段螺旋溜槽由五圈两种不同断面结构的螺旋槽组成。其选别机理是每圈为一段选别作业，设备内部两种螺旋槽各圈之间组成多段选别流程结构，矿浆在多段螺旋溜槽内形成分级分选和贫富分选流程。试验结果证明：多段螺旋溜槽是一种高效的重选设备，不但精矿回收率高，且尾矿丢废率也高，主产中采用多段螺旋溜槽不仅单机效率高，且可简化流程。多段螺旋溜槽是螺旋选矿设备５０年发展史上的重大革新。     

菱镁矿粉体颗粒摩擦荷电实验与仿真研究

为了对粉体颗粒摩擦荷电过程进行数值模拟,以菱镁矿粉体颗粒为研究对象,利用离散元模型和电荷转移模型对粉体颗粒运动过程和摩擦荷电过程分别进行理论建模。在EDEM仿真软件中建立了适用于粉体颗粒摩擦荷电仿真的计算模块,并应用该模块进行菱镁矿粉体摩擦荷电仿真分析,考察给料量和滑槽倾斜角度对摩擦荷质比的影响,同时利用振动槽摩擦荷电装置进行菱镁矿粉体颗粒摩擦荷电对比实验研究。结果表明,菱镁矿粉体摩擦荷质比随给料量的增加而减小,随滑槽倾斜角度的增大而减小。试验结果得到了与仿真结果相似的变化趋势,验证了所建粉体颗粒摩擦荷电数值模型的准确性。本文研究结果对更精确粉体颗粒摩擦荷电模型的建立和粉体颗粒摩擦带电的进一步应用具有重要意义。     

DEM validation of media shape effects on the load behaviour and power in a dry pilot mill

Simulations were carried out in Metso’s DEM simulator so as to draw up an understanding of the effects the various ways of defining media shapes within the simulator have on the load behaviour and mill power draw. Wits University made available the load behaviour and mill power draw experimental results for the spherical balls, worn balls and cylpebs so as to validate the DEM simulations. The spherical media were defined by a regular spherical shape model and a multi-faceted polyhedron model. Worn balls were defined by super quadric models. A comparison was made between spherical media shapes, non-spherical single media shapes and a distribution of non-spherical media shapes and sizes in representing a load comprised of worn balls. The effect of increasing angularity of non-spherical media shapes on mill power was investigated. The cylpebs were modelled using a regular cylindrical shape model and the effects of friction on the power drawn were determined.     

莫桑比克某重砂矿重选与筛分粗选对比试验研究

针对莫桑比克某重砂矿原矿有价金属矿物品位低、主要金属分布集中和单体解离度高等特点,开展了螺旋溜槽和高频振动细筛粗选工业对比试验研究。分别考察了螺旋溜槽设备类型、给矿浓度和处理能力等因素对粗选螺旋溜槽分选效果的影响,高频振动细筛筛孔尺寸、给矿浓度和处理能力等因素对粗选筛分效果的影响,并进行了二者最优条件的粗选工业对比试验。对比试验结果表明,粗选螺旋溜槽分选指标优于高频振动细筛,螺旋溜槽获得的粗精矿TiO2品位比高频振动细筛粗精矿TiO2品位高20.96%,尾砂抛除率比高频振动细筛高35.07%,且粗选螺旋溜槽设备投资仅占高频振动细筛设备投资的43.48%。该研究成果为莫桑比克某重砂矿资源开发利用粗选工艺选择提供依据和技术支持。     

溜井储矿段矿石流动特性的影响因素分析*

溜井中矿岩散体的流动特性关系到溜井放矿的安全和可靠。为确保溜井放矿的顺畅性，在分析矿石流动性对溜井放矿影响的基础上，从理论上分析了影响储矿段矿石流动特性的因素。主要包括矿岩结块性、矿岩散体的粒度及分布特征、矿岩含水量、溜井结构、矿石流对井内储料的冲击夯实作用和溜井贮矿高度6个方面。结合部分矿山实践经验，提出了缩短矿岩在溜井中的停滞时间、改善矿岩爆破效果、优化溜井结构参数、控制含水量和粉矿含量、减轻运动矿岩对井内储料的冲击夯实等改善矿岩流动性的针对性解决措施，对于防范溜井储矿段堵塞问题具有重要的作用。     

钢球摩擦吸能器作用机理的力学分析

对钢球摩擦吸能的作用机理进行了初步分析, 基于冲击凿入系统的钎头端受力和钢球变形特性给出了钢球摩擦吸能的等效弹性模量和阻抗特性; 应用波动理论得出了钢球体的反射特性、断面最佳适配、吸能效率和合理球柱长度。该研究可为钢球摩擦吸能器设计提供参考。