Breakage process of mineral processing comminution machines – An approach to liberation

Mineral liberation and size reduction are the most critical steps before mineral separation. Several investigations showed that mineral liberation degree could be affected by ore texture and/or loading mechanisms. However, varied definitions have been used for the breakage fundamentals as the leading cause of mineral liberation. This review identifies the breakage fundamentals and analyzes them in terms of process and ore breakage behavior. It is highlighted that the breakage fundamentals are essential for optimizing of comminution environments and designing the comminution machines. Three main areas of breakage processes in regard to fundamentals of breakage are classified and addressed as “Loading mechanism”, “Breakage mechanism”, and “Breakage mode”. Despite the fact that many advances have been made in the design of the comminution machines; still, the combined effect of breakage fundamentals and ore properties such as ore texture in a quantitative manner is not fully understood. In this regard, this study identifies and discusses the material and process factors influencing the breakage phenomenon. This potentially paves the way for improving the comminution environment concerning a particular ore type.     

DEM modelling of non-spherical particle breakage and flow in an industrial scale cone crusher

Predictions of particle flow and compression breakage of non-round rock passing through an industrial scale cone crusher are presented. The DEM (Discrete Element Method) particle breakage model is generalised to allow non-round particles to be broken into non-round progeny. Particles are broken in this DEM model when the elastic energy of a contact is sufficiently high to initiate fracture. Progeny size distribution data from JKMRC Drop Weight Test (JKDWT) or JKMRC rotary breakage test (JKRBT) is used to generate the specific daughter fragments from each breakage event. This DEM model is able to predict the production of both coarser progeny which are resolved in the DEM model and finer progeny which are not. This allows the prediction of product down to very small sizes, limited only by the fineness of the fragments measured in the breakage characterisation. The predicted flow of material through the crusher, product size distribution and liner wear are discussed. The generalised breakage model demonstrated here is suitable for modelling all forms of crushers.     

Development of a pilot roller test machine for investigating the pulverizing performance of particle beds

Various types of pulverizers are commonly used in power plants for the purpose of breaking coal particles into fine powders to achieve optimum combustion for the boilers. To investigate the effects of factors that may influence the pulverizing efficiency, this study presents the development of a pilot roller test machine, which can significantly simplify the grinding conditions in actual pulverizers whilst the key variables involved in a rolling compression can be considered. The monitoring and data acquisition systems allow real-time monitoring of the pulverizing induced roller movements. Through parametric numerical analyses on an elastic feed bed of 5–30 mm in thickness and 500–1000 MPa in elastic modulus, it is found that the machine is capable of providing a maximum contact pressure stress in a range of 4.5–17.5 MPa. A series of fundamental tests have been conducted by the developed machine using a type of bituminous coal and typical bound values of roller weight and speed. The size reduction results as well as the measurements of roller movement demonstrate the capability of the machine as a suitable tool for testing grinding performance. Some discussions of the potential extension of the machine are also given in the final part.     

Numerical solution of mixed continuous–discrete population balance models for depolymerization of branched polymers

A simulation technique to describe the depolymerization of branched polymers via bivariate population balance modeling was developed. The polymers were characterized by two internal coordinates: the number of monomer units and branching bonds. Three commonly used mechanisms for depolymerization (random chain, end chain, and random debranching scission) were applied and formulated such that only physically possible polymers were created. The mechanisms and the population balance equation were formulated in a mixed continuous–discrete manner. The population balance equation was solved using the Direct Quadrature Method of Moments (DQMOM). With this algorithm, the time evolution of the distribution with respect to the internal coordinate was computed. In addition, the algorithm was validated through comparison with Monte Carlo simulations. Notably, the accuracy of the mixed continuous–discrete formulation was significantly higher that of the continuous formulation. However, DQMOM was found to be unsuitable for describing the temporal evolution of the distribution for random scission.     

Simulation of Turbulent Emulsification in a Sonolator Mixer: Interpretation of Drop Breakage Time

The simulation of dilute emulsions in a model ACIP2 Sonolator is investigated using computational fluid dynamics and population balance methods. Two breakage frequency models are used that differ in the expression of the drop breakage time. Drop breakage modeling based on homogenous isotropic turbulence (HIT) shows poor agreement of the Sauter mean diameter when compared to the experiments; simulations with the empirical model from Alopaeus et al. yield better agreement. By perturbing the classical HIT spectrum, it is shown that the breakage time in the empirical model corresponds to a non‐isotropic energy spectrum. Such spectra have been observed in the non‐isotropic near field in a model A Sonolator, which provides a plausible explanation of why the empirical model performs better than the HIT‐based model.     

Influence of particle breakage on the dynamic compression responses of brittle granular materials

The dynamic compression responses of dry quartz sand are tested with a modified spilt Hopkinson pressure bar (MSHPB), and the quasi-static compression responses are tested for comparison with a material testing system. In the experiments, the axial stress–strain responses and the confining pressure of the jacket are both measured. Comparison of the dynamic and the quasi-static axial stress–strain curves indicate that dry quartz sand exhibits obvious strain-rate effects. The grain size distributions of the samples after dynamic and quasi-static loading are obtained with the laser diffractometry technique to interpret the rate effects. Quantitative analyses of the grain size distributions show that at the same stress level, the particle breakage extent under quasi-static loading is larger than that under dynamic loading. Moreover, the experimental and the theoretical relationships of the particle breakage extent versus the plastic work show that the energy efficiency in particle breakage is higher under quasi-static loading, which is the intrinsic cause of the strain-rate effects of brittle granular materials. Using the discrete element method (DEM), the energy distributions in the brittle granular material under confined compression are discussed. It is observed that the input work is mainly transformed into the frictional dissipation, and the frictional dissipation under dynamic loading is higher than that under quasi-static loading corresponding to the same breakage extent. The reason is that more fragmentation debris is produced during dynamic breakage of single grains, which promotes particle rearrangement and the corresponding frictional dissipation significantly.     

Ore impact breakage characterisation using mixed particles in wide size range

The Drop Weight Tester (DWT) for ore impact breakage characterisation uses particles in five narrow size fractions, and the JKMRC Rotary Breakage Tester (JKRBT) uses four size fractions, both with three impact energy levels for each size fraction. It is time consuming to prepare these narrowly sized particles and to carry out size analysis on the 15 DWT or 12 JKRBT products, so a Wide-size JKRBT characterisation method was developed. In this method, the mixed particles in 13.2–45 mm size range are tested as one size class in the JKRBT by single-particle breakage mode. The wide-size feed is then divided into several virtual narrow size fractions by simulation, based on which the impact product size distributions are calculated using a size-dependent breakage model. Four sets of measurement data, consisting of two feed samples in the 13.2–45 mm size range with different size distributions tested with two impact energy levels, are adequate to determine the three model parameters. In the case where a benchmark ore of known breakage characteristic parameters is available, one Wide-size JKRBT impact treatment can determine the ore competence change parameter using a t₁₀-based model.     

纬纱和织轴回潮率对织造效率的影响

以新疆某棉纺织厂织布车间生产的14．5／14．5378／378137细布2001年全年车间温湿度与纬纱和织轴回潮率数据为基础，采用计算机为工具，用统计学的方法来分析温湿度与回潮率的关系及回潮率对织造效率的影响。认为纬纱回潮率控制在5％～6．5％时对纬纱断头无明显影响，织轴回潮率控制在9％～10％时经纱断头少且保持稳定。     

风力烟丝输送系统的改进

为解决使用过程中存在的烟丝造碎大和烟丝组分分离及烟丝填充能力降低等问题,对风力烟丝输送系统进行了改进:确定合理的风速;采用变频调速技术,以及设置瞬间补风装置削减风速峰值等方式,提高风速的稳定性;吸丝管风速实现独立调节;改进吸丝管的用料;采用无振动转塔式喂料机,防止烟丝分层;提高电控系统的自动化程度。改进后风力烟丝输送过程中烟丝造碎率降低了0.94%,每年可节约成本约500万元。     

竹浆纤维羊绒混纺纱的开发及其拉伸性能的研究

测试在不同混纺比例下纱线断裂强力及断裂伸长等性能，得出由于混纺比例的不同，纱线的性能也有所差异，从而确定比较合适的混纺比例。实验测试得出竹浆纤维50％，羊毛35％，山羊绒15％的混纺纱，合股并施加150T／m的捻度后，具有较好的机械性能。