A method to evaluate the overall breakage degree of pre-weakening processing and its applications

The product fineness indicator t₁₀ and the pre-weakening degree indicator percentage change of A * b value (C_Ab) were used to described the two aspects of the breakage result of processing with pre-weakening effect. However, there lacks a method to evaluate the ‘overall’ breakage degree with a single index. It was observed that when the high voltage pulse breakage (HVP breakage or HVPB) induced cracks inside pre-weakened particles were consumed during impact breakage, the breakage characteristics of the progeny particles are the same to raw ore particles. Based on this phenomenon, the concepts of equivalent size S_ie and equivalent size reduction t_10e are proposed. Raw ore particles of size S_ie is ‘equivalent’ to pre-weakened particles of size S_i in terms of their impact breakage product size distribution. Therefore the value of S_i and the consequently derived t_10e can be used to evaluate the overall breakage degree of pre-weakened particles. The calculation procedure of S_ie and t_10e is demonstrated in the context of HVP breakage. It is found that the impact breakage product of pre-weakened particles can be well predicted from S_ie. In addition to the evaluation of overall breakage degree of pre-weakening processing, this method also has potential to apply in the simulation of comminution circuits with pre-weakening processing and the development of breakage model for processing with pre-weakening effect.     

Predicting breakage behavior and particle size of bronze and cast iron machining chips pulverized by jet milling

It has been proposed that the breakage behavior of particulate materials can be described by two material parameters f_mat and W_min. f_mat describes the resistance of the material to fracture in impact pulverization and W_min characterizes the specific energy which a particle can absorb without fracture. It is shown in this study that this concept can be used to quantify breakage behavior of bronze and cast iron chips in jet milling process and also to predict particle size of the jet milled product. Different tin bronze and cast iron chips with varying initial size were pulverized in a target plate jet mill with different velocity. f_mat was found to be in the range of 0.06–0.09 and 0.18–0.25 for bronze and cast iron alloys, respectively. For the cast iron alloys f_mat increased with increasing content of carbon and silicon. Similarly, for the bronze alloys, f_mat increased with increasing tin content. An equation was developed to predict mean particle size of the jet milled chips as a function of the kinetic energy, initial chip size and material parameters. The experimental results of various alloys confirmed that the mean particle size after single and multiple impacts were accurately predicted.     

Degradation model of Gladstone Port Authority's coal using a twin-pendulum apparatus

Single-particle breakage tests of South Blackwater and Ensham coal were conducted by using a computer-monitored twin-pendulum device to determine a parameter which will describe the product size distribution of the breakage product. The size distribution parameter ‘t’₅₀ related to the specific comminution energy [defined as the comminution energy per unit mass which transmitted to a particle during breakage (kWh/t)] of breakage coal particles and described the breakage characteristics of two types of coal. At a specific comminution energy level, the t₅₀ parameter of South Blackwater coal was higher than the t₅₀ parameter of Ensham coal. A degradation model was developed with several parameters for the coal-handling circuits of Gladstone Port. In the degradation model, the raw data of the non-cushioned curve deviates from the model data after a few initial drops because the mass of the sample reduces in successive drops and produced more fines.     

Size reduction performance evaluation of HPGR/ball mill and HPGR/stirred mill for PGE bearing chromite ore

In the present study, size reduction experiments were performed on High-Pressure Grinding Rolls (HPGR), ball mill and stirred mill of PGE bearing chromite ore. The performance of HPGR was evaluated in two stages of size reduction to reduce energy consumption. In the first stage of HPGR, the effect of operating variables such as the gap between the rolls, roll speed, and specific pressing force on product size (P₈₀) and energy consumption (E_CS) was investigated. The process to get the smallest product size was optimized within the experimental range of investigation. The crushed product of HPGR was subjected to grinding in the second stage in a ball mill and stirred mill. The effect of mill speed, grinding time, and ball size on the performance of the ball mill was investigated and the product was further investigated in the second stage. A comparative analysis of the ball mill and stirred mill performance and energy consumption at different grinding time intervals was also performed. It was found that the ball mill consumed 54.67 kWh/t energy to reduce the F₈₀ feed size of 722.2 µm to P₈₀ product size of 275.4 µm while stirred mill consumed 32.45 kWh/t of energy to produce the product size of 235.6 µm. It also showed that stirred mill produced finer product than the ball mill at around 40% lesser consumption of energy. It can be concluded that the HPGR-Stirred mill combination was a more energy-efficient grinding circuit than the HPGR-Ball mill combination for PGE bearing chromite ore.     

Analyses of the energy-size reduction of mixtures of narrowly sized coals in a ball-and-race mill

Mixture breakage of particles in various sizes is common in industrial mills, and breakage behavior is influenced by size composition. But studies on particle breakage are conducted to narrowly sized samples. In this paper, tentative works are made to investigate interaction among super clean coal in mixture breakage from aspects of breakage rate, energy consumed characteristics and energy split factors. Experimental results demonstrate that breakage rate of coarse particles in mixture breakage increases if compared with that in single breakage. Particle size is modelled into classical breakage equation, and the modified model is successfully applied to mixture breakage. Energy split factor of component is determined based on the balance of specific energies of components in heterogeneous breakage and energy-size equation, and consumed energy (W) of component in multi-component grinding is calculated. Calculated energy split factors of components are all above one in various mixed conditions, so energy efficiency (value of product t₁₀ at the same specific energy) decreases if compared with that of single breakage. Energy split analyses are also conducted for mixture breakage of middling coals, which illustrates that the method is robustness for energy-size reduction process influenced by associated minerals in coal.     

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.     

Influence of high-pressure grinding rolls on physical properties and impact breakage behavior of coarsely sized cement clinker

ABSTRACT

High-pressure grinding rolls (HPGR) are widely used in cement clinker grinding prior to ball milling. The efficiency of HPGR was previously related to two capabilities: (a) efficient stressing mechanism and (b) weakening of particles which lead to finer product sizes after subsequent ball milling. This study aimed to investigate the influence of HPGR on the impact breakage behavior of coarsely sized cement clinker. Drop weight tests were conducted on three single-size samples from both feed and product streams of an industrial HPGR, so as to obtain impact breakage parameters: breakage probability and impact breakage functions. Radiographic, Vickers micro-hardness, BET, SEM, XRD, XRF, and image processing methods were utilized to explain the variations in impact breakage parameters. The product samples were found to have less porosity than feed samples but they contained HPGR-induced micro-cracks. Those cracks are believed to be responsible for lower hardness and higher breakage probability of product particles than of feed ones under impact. However, fragments generated from the product samples by drop weight tests were coarser than those generated from feed samples. That was due to elimination of pores by HPGR action. At excess energy levels, both samples were broken to same extent regardless of structural differences.     

Influence of Al2O3 particle pinning on thermal stability of nanocrystalline Fe

Second-phase particle pinning has been well known as a mechanism impeding grain boundary (GB) migration, and thus, is documented as an efficient approach for stabilizing nanocrystalline (NC) materials at elevated temperatures. The pinning force exerted by interaction between small dispersed particles and GBs strongly depends on size and volume fraction of the particles. Since metallic oxides, e.g. Al₂O₃, exhibit great structural stability and high resistance against coarsening at high temperatures, they are expected as effective stabilizers for NC materials. In this work, NC composites consisting of NC Fe and Al₂O₃ nanoparticles with different amounts and sizes were prepared by high energy ball milling and annealed at various temperatures (T_ann) for different time periods (t_ann). Microstructures of the ball milled and annealed samples were examined by X-ray diffraction and transmission electron microscopy. The results show that the addition of Al₂O₃ nanoparticles not only enhances the thermal stability of NC Fe grains but also reduces their coarsening rate at elevated temperatures, and reducing the particle size and/or increasing its amount enhance the stabilizing effect of the Al₂O₃ particles on the NC Fe grains.     

Simulation of particle bed breakage by slow compression and impact using a DEM particle replacement model

The present work introduces a particle replacement model implemented in the commercial software EDEM to describe breakage of particles. Several model parameters were initially estimated on the basis of single-particle breakage tests on iron ore pellets. The model was then used to simulate breakage of particle beds by both slow compression and impact. Model predictions were compared to experiments in terms of compressive force versus packing density, breakage probability of the particles versus compressive force applied to the bed, and the product size distribution in compression and impact. The model showed the expected trends as well as some agreement with the measured product size distributions both from confined and unconfined stressing conditions of the bed of particles, being a simple and effective approach to describe breakage in systems where particles are stressed as assemblies.     

Breakage behaviour of single rice particles under compression and impact

Grain breakage is mainly caused by impact and compression load in harvest and processing. At present, the mechanism of grain breakage under loading, especially the statistics of breakage characteristics, is not clear. The analysis of breakage process of single particle provides a foundation for the understanding of breakage mechanisms. This paper aims to examine breakage behaviour of a single rice particle under compression and impact experiments. Firstly, the equivalent diameter (D_p) and moisture content (MC) of rice particles were regarded as important factors that may affect breakage. Then, by performing quasi-static compression and dynamic impact experiments under different values of D_p and MC, the detailed compression failure force, rice strength, breakage modes, breakage probability, and the breakage probability models were analyzed comprehensively. Furthermore, breakage processes of rice particles under these two breakage experiments were compared and discussed. Finally, the Weibull distribution of the compression breakage characteristics, the “non-size effect” of compression and impact breakage, the tensile failure forms, velocity threshold of impact breakage and the close relationship between the breakage characteristics under impact and compression were mainly found. The findings are useful for providing guidance for the revelation of breakage mechanism and optimizing related agricultural equipment design.     

The kinetics and efficiency of batch ball grinding with cemented tungsten carbide balls

Cemented tungsten carbide balls (hereafter abbreviated as WC balls) are commonly applied in grinding of wasted tool steel for reuse owing to their extraordinary surface hardness (89.5 HRA) and high density (14.5 –14.9 g/cm³). In this study, grinding tests were conducted with WC balls on quartz ore to estimate comminution kinetics. Compared with steel balls, they provided high breakage rates, lower energy-specific breakage rates, and finer breakage distributions due to their high density. Simulations were conducted using an energy-based population balance model. The simulated results demonstrated that WC balls had higher throughput for coarse particles and lower energy efficiency for fine particles. Subsequently, a preliminary criterion for ball selection was established and indicated that WC balls could be substituted for steel balls to certain particle size ranges.     

Evaluation of Particle Degradation Due to High-Speed Impacts in a Pneumatic Handling System

Particle degradation can be a significant issue in particulate solids handling and processing, particularly in pneumatic conveying systems, in which high-speed impact is usually the main contributory factor leading to changes in particle size distribution (comparing the material to its virgin state). However, other factors may strongly influence particles breakage as well, such as particle concentrations, bend geometry, and hardness of pipe material. Because of such complex influences, it is often very difficult to predict particle degradation accurately and rapidly for industrial processes. In this article, a general method for evaluating particle degradation due to high-speed impacts is described, in which the breakage properties of particles are quantified using what are known as “breakage matrices.” Rather than a pilot-size test facility, a bench-scale degradation tester has been used. Some advantages of using the bench-scale tester are briefly explored. Experimental determination of adipic acid has been carried out for a range of impact velocities in four particle size categories. Subsequently, particle breakage matrices of adipic acid have been established for these impact velocities. The experimental results show that the “breakage matrices” of particles is an effective and easy method for evaluation of particle degradation due to high-speed impacts. The possibility of the “breakage matrices” approach being applied to a pneumatic conveying system is also explored by a simulation example.     

颗粒碰撞阻尼的时效性研究

颗粒碰撞阻尼是一种被动式振动控制器,其中颗粒材料在冲击过程中的尺度和形貌变化必然对其减振性能产生重要影响。文中初次探讨了带有中值粒度为35微米的锌颗粒的颗粒碰撞阻尼器在96小时内对正弦激励悬臂梁的阻尼减振的时效性。研究证明,主系统的响应在所考察的时间历程内出现了三次微幅上升,它是锌颗粒材料在冲击作用下结构和能态变化的结果。首先,随着冲击的进程,颗粒的冷焊效应阻碍了冲击器的运动速度,降低了冲击器的动量交换功能。第二,颗粒应变能和层错能的下降降低了系统的不可逆能耗。第三,颗粒的细化使其本身缺陷减少,进一步细化的难度增加,也使得系统内的不可逆能耗不断减小。这是主系统的响应随着振动历程出现了两次阶跃性微幅上升的主要原因。     

Optimum milling parameters for production of highly uniform metal-matrix nanocomposites with improved mechanical properties

In the present paper, a system dynamic model is presented to predict the final particle size of milled powder during ball milling process. The presented model is used to obtain the optimum ball size, milling speed and milling time that achieve the best particle size reduction of metal-matrix nanocomposites. Parametric study is performed using the presented analytical model to study the influence of ball size and milling speed on the milling efficiency. The predictions of the presented model are validated with experimental results done during this work for Cu-5%ZrO₂ nanocomposite and others available in the literature. The results show that the milling time required to achieve the steady state condition for Cu-5%ZrO₂ nanocomposite is 15?h. At 15?h of milling, ZrO₂ particles are highly uniform distributed in Cu matrix and the microhardness is increased from 75.4 HV for Cu to 197.6 HV for Cu-5%ZrO₂ nanocomposite. After 15?h, the particle size reduction rate is too low and the hardness improvement rate is too low as well (204.1 HV after 20?h milling) which make the milling process after 15?h is not appreciable.     

Analysis of grinding kinetics in a laboratory ball mill using population-balance-model and discrete-element-method

Grinding processing consumes a lot of energy in mineral processing, but it is a low-efficiency process in which only approximately 1% of the total energy is used to reduce the actual particle size. Therefore, an efficient operation in the grinding process increases the competitiveness of the production and is an essential for enhancing the energy efficiency of the entire mineral processing procedure.Therefore, the study will focus on to finding a different method to predicting the particle size distribution of the ball mill, by using the PBM which reflects the actual size distributions of ground product and the DEM which can understand the internal particle behavior in the mill chamber. First, the grinding parameters were calculated by applying size distributions of ground product under various conditions to PBM and the behaviors of the particles inside the ball mill obtained through DEM were analyzed to predict the distribution of the impact energy used for grinding. Next, the relational expression between the grinding rate parameter and the normal force applied to the grinding materials was derived. Using the relational expression derived from this study, it was confirmed that the size distributions in other conditions can be predicted.     

Wet Grindability of Calcite to Ultra-Fine Sizes in Conventional Ball Mill

An experimental practice on the ultra-fine wet grinding of calcite ore in a conventional batch ball mill is reported. In this study, the effect of wet grinding conditions on the production of fine particles was researched. The influence of operating parameters such as operation speed (% of critical speed), ball filling ratio, calcite filling ratio, pulp density, ball size distribution, and grinding time on the grindability of calcite ore was systematically examined. Experimental results were evaluated on the basis of d₈₀ product size. As a result of this study, optimum experimental conditions were found to be 80% of critical speed for operation speed, 35% for ball filling ratio, 15% for calcite filling ratio, 75% for pulp density, 50% (1 cm) and 50% (2 cm) for ball size distribution, and 60 min for grinding time. It was found that the best product has d₁₀ = 1.51, d₅₀ = 12.53, and d₈₀ = 30.02 µm particle size and its steepness factor is 3.75. The outcomes indicate that the wet grinding technique in conventional ball mill for calcite ore is effective to obtain ultra-fine size products.     

Effects of grinding aids on the grinding kinetics and surface morphological characterization of quartz

The kinetic parameters of a grinding process can be used to study the variations in particle size reductions and grinding efficiencies. Appropriate grinding aids usually change the surfaces of a material and the properties of the pulp, thus improving the grinding efficiency. In this paper, pure quartz samples with mixed particle sizes and single particle sizes were selected as the raw materials. The effects of different sodium tripolyphosphate (STPP) and citric acid (CA) dosages on the dynamic parameters k, selection function S₁ and breakage function B for quartz grinding were studied. The results showed that the STPP and CA enhanced the grinding process of the quartz. In other words, the parameter k, the selection function S₁ and the breakage function B were all increased to varying degrees. The results of SEM, BET and contact angle measurements showed that the surfaces of the quartz particles became rounder, the specific surface area and average pore size increased, and the surface hydrophilicity increased. As a result, the grindability of the quartz increased, and the grinding kinetic parameters changed. Finally, the results showed that the improvements in the quartz grindability were consistent with the influence of grinding aids on the kinetic parameter k, selection function S₁ and breakage function B_i,1.     

Kinetic spraying deposition behavior of bulk amorphous NiTiZrSiSn feedstock

A kinetic spraying process, which is basically a solid-state deposition process, was used for the formation of a fully amorphous coating. By using a pre-heating system for the powder carrier gas and using helium for the process gas, it was possible to form an amorphous coating. The main process parameters evaluated during this study were gas species [N₂ and He] and pre-heating temperature [RT (below T_g) and 550 °C (liquid metallic region)]. Aside from the empirical approach, in-flight particle velocity within the kinetic spraying process was measured using a SprayWatch-2i system. The deposition behavior of a NiTiZrSiSn bulk amorphous powder was observed when it was sprayed using the kinetic spraying process. In order to predict the temperature-dependent deformation behavior of the bulk amorphous material during impact, Vickers microhardness, as an indirect method, was measured at various temperatures.While the bulk amorphous feedstock material was being coated, both the kinetic and thermal energies of the in-flight particles were important. The former affected the deposition of the bulk amorphous coating, while the latter had more effect on the mechanical properties of the coating. Particle deposition behavior was considered from the viewpoint of the environmental effect, such as particle–energy combination, on the deposition behavior. The bonding of the impacting NiTiZrSiSn bulk amorphous particle was primarily caused by temperature-dependent deformation and fracture (local liquid formation) behavior.     

Energy dissipation in collision of two balls covered by fine particles

A new fine particle impact damper (FPID) is composed of a spherical impactor and a small quantity of fine particles as damping agent. The model of energy dissipation in the collision between two balls covered by fine particles is necessary to investigate the mechanism and performance of FPID. In this study, a simplified model verified by FEA simulations is proposed to estimate the energy dissipation in collision between two balls covered by fine particles. In addition, the energy dissipation in the collision between two balls covered by fine particles is compared with that in the impact between two balls without fine particles, by means of theoretical predictions. FEA simulations are also carried out to discuss the effects of diameter ratio of particle to ball, particle material and particle amount on the energetic expression of the elastic–plastic loading (EPL) index (EPL_E). The results from the FEA simulations agree well with the estimations from the model proposed in this paper. It is concluded that the energy dissipation in the collision between two balls covered by fine particles can be predicted by classical collision models of two particles through the substitution of several parameters from balls; the plastic deformation of fine particles affixed on balls can exhaust much more energy than that of the two balls without particles, which is the reason for the good performance of FPID; the diameter ratio of particle to ball and the material of particles do not have significant effects on the EPL_E when the ratio is limited to the range of [1/200 – 1/10]. A correlation of the EPL_E and dimensionless initial relative velocity is also found for the collisions between two balls, which is independent not only of the particle size and material properties but also of the particles presence.     

Dilute phase pneumatic conveying of whey protein isolate powders: Particle breakage and its effects on bulk properties

Breakage of dairy powder during pneumatic conveying negatively affects the end-customer properties (scoop uniformity and reconstitution). A dilute phase pneumatic conveying system was built to conduct studies into this problem using whey protein isolate powder (WPI) as the test material. Effects of conveying air velocity (V), solid loading rate (S_L), pipe bend radius (D), and initial particle size (d) on the level of attrition were experimentally studied. Four quality characteristics were measured before and after conveying: particle size distribution, tapped bulk density, flowability, and wettability. The damaged WPI agglomerates after conveying give rise to many porous holes exposed to the interstitial air. V is the most important input variable and breakage levels rise rapidly at higher airspeeds. The mean volume diameter D[4,3] decreased by around 20% using the largest airspeed of 30 m/s. Powder breakage is also very sensitive to particle size. There appears to be a threshold size below which breakage is almost negligible. By contrast, S_L and D show lesser influence on powder breakage. Reflecting the changes in particle size due to breakage, tapped bulk density increases whereas wettability decreases as a result of an increase in conveying air velocity. However, breakage does not show a significant effect on powder flowability as powder damage not only decreases particle size but also changes the particle’s surface morphology.