Ball-milling Media Research Articles

A Review of the Grinding Media in Ball Mills for Mineral Processing

The ball mill is a rotating cylindrical vessel with grinding media inside, which is responsible for breaking the ore particles. Grinding media play an important role in the comminution of mineral ores in these mills. This work reviews the application of balls in mineral processing as a function of the materials used to manufacture them and the mass loss, as influenced by three basic wear mechanisms: impact, abrasion, and corrosion. The effect of grinding media geometries and density on the mill performance was also reviewed to determine what the research has recommended as the most suitable grinding media for different grinding applications. Although considerable work has been carried out in that area, the influence of grinding media shape on the liberation of minerals, as well as the effect of various mill conditions on the performance of mixed grinding media shapes, are still poorly understood. Thus, the review opens up opportunities for further research to improve the grinding processes, especially considering that even a slight improvement in the process efficiency significantly reduces the production costs.

Effect of mechanical ball milling on the electrical and powder bed properties of gas-atomized Ti–48Al–2Cr–2Nb and elucidation of the smoke mechanism in the powder bed fusion electron beam melting process

Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam (PBF-EB) technology. In this study, mechanical stimulation was suggested to suppress smoke of gas-atomized (GA) Ti–48Al–2Cr–2Nb powder using Al2O3 and WC ball milling. The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribution map and contact mechanics simulation. It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture. The variation of surface and electrical properties by mechanical stimulation was investigated via XPS, TEM, Impedance analysis. The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration, despite the increased oxide film thickness, and the capacitive response disappeared in Al-60 and WC-30 via metal–insulator transition. This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation. The smoke mechanism of ball-milled powders was discussed based on the percolation theory. In the smoke experiment, smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50, respectively, despite the longer charge dissipation time. This could be due to the high probability of contact with conductive particles. For the Al-60 and WC-30 powders, smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity. We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.

Factors determining the flowability and spreading quality of gas-atomized Ti-48Al-2Cr-2Nb powders in powder bed fusion additive manufacturing

A high-quality powder bed is necessary for obtaining high-quality products using powder bed fusion-based additive manufacturing. In this study, mechanical ball milling was suggested to improve the flowability and spreadability of gas-atomized (GA) Ti–48Al–2Cr–2Nb powder in the powder bed fusion additive manufacturing process. The deformation mechanism of the GA powder significantly differed depending on the ball milling media. Surface grinding mainly occurred during Al 2 O 3 ball milling, while the pulverization was dominant in WC ball milling because of the higher impact force. The flowability of the GA powder under dynamic conditions was improved after Al 2 O 3 and WC ball milling owing to the decreased cohesive force. The high cohesive force in the GA powder under dynamic conditions was attributed to the electrostatic force caused by charge accumulation on the oxide film. The packing density of GA powder was increased after WC ball milling despite the formation of numerous irregular particles owing to the synergetic effect of rapid energy dissipation, minimized wall effect, and void filling effect. Furthermore, the spreadability of the GA powder was improved by ball milling because of the decrease in the cohesive force. Therefore, it was demonstrated that the flowability and spreadability of the GA powder can be improved via ball milling because of changes in particle size, shape, and surface properties. • Flowability of GA powder under the dynamic condition was improved after ball milling owing to the decreased cohesion force. • High cohesive force in GA powder was mainly attributed to the electrostatic force caused by charge accumulation on the oxide film. • Spreadability of GA powder was improved after ball milling due to the decreased cohesion force.

Efficient Al Recovery from Aluminum Dross with Simultaneous AlN Separation by a Mechanical Method

Aluminum dross (AD) is a hazardous waste that contains valuable metallic Al and reactive aluminum nitride (AlN). The intergrowth of Al and AlN presents a challenge to Al recovery and AlN removal. In the current work, a mechanical milling method was developed to separate Al and AlN. Steel bars and balls were used as grinding media. The AD particle size decreased after milling and was distributed in the ranges 0.425–2 mm, 0.15–0.425 mm, 0.08–0.15 mm, and <0.08 mm. The particle size distribution was affected by the ball milling media and grinding time. Steel ball media had a better grinding effect on particles > 2 mm. After ball milling, the Dp0.08–2 mm size fraction accounted for approximately 90%. With changes in particle size, the element content of AD varied: the fraction of metallic Al decreased, while the fraction of Si increased. Metallic Al mainly existed in particles with size > 0.425 mm, accounting for 48.5%. AlN mainly existed in Dp0.15–0.425 mm, accounting for 64.9%. The optimal milling conditions achieved a 65% Al recovery rate and a 90% AlN separation efficiency. This work provides a promising approach for highly efficient pretreatment for AD recovery and AlN elimination in industrial applications.

DEM Investigation of Discrete Heat Transfer Behavior of the Grinding Media in Ball Mills

This study presented a numerical model for the quantitative assessment of the heat transfer behavior of grinding media inside a ball mill. Effects of various mill speeds, grinding media filling, and the number of lifters on heat transfer were studied and verified by comparing the experimental results and the numerical simulations calculated by DEM (Discrete Element Method). The results show that the heat transfer of grinding media has a strong sensitivity to the variation of the mill speed, grinding media filling, and the number of lifters. The optimum grinding conditions for heat transfer behavior can be determined in terms of the temperature field of the grinding media. The maximum temperature rise of grinding media occurs at a range from 70% to 80% of critical speed. The maximum average temperature of grinding media up to 295.057 K appears at the grinding media filling 25% and the number of lifters 12. Subsequently, validation experiments are carried out to validate the numerical simulation results. The experimental results are closer to the simulation results, indicating the reasonability of the heat transfer model.

Ball Milling Medium May Tune the Self-Curing Property and Root Canal Microleakage of β-Dicalcium Silicate-Based Cement.

It is still a challenge to overcome the extended setting process of pure Ca-silicate as root canal fillers. We investigated the effects of attapulgite (a basic hydrous silicate of magnesium and aluminum) and ball-milling liquid medium on the self-curing properties of conventional β-dicalcium silicate (C2Si)-based cements. It was shown that a minor amount of attapulgite nanofibers (1–4%) had only a slight influence on setting time but caused a large increase in compressive resistance and structural stability. In particular, the ball milling media with different acetone/water ratios (3:0, 2:1, 1:2, 0:3) could directly influence the particle size distribution of C2Si powders, and the co-existence of liquid media (2:1 or 1:2) may be beneficial for shortening the setting time, enhancing early-stage compressive strength, and significantly improving the anti-microleakage ability of cement. Moreover, the composite cements also exhibited appreciable antibacterial efficacy in vitro. These findings demonstrated that the physicochemical properties of the Ca-silicate powders could be tuned by adding a minor amount of inorganic silicate nanofibers and a simple ball milling condition, and such a facile strategy is favorable for developing novel (pre-mixed) Ca silicate-based cements as root canal sealers.

Green and simple production of graphite intercalation compound used sodium bicarbonate as intercalation agent

In view of the technical difficulties in the preparation of graphite intercalation compound (GIC) such as complex processes, the need to use strong acid reagents, and the product containing corrosive elements. A novel, efficient and simple method used sodium bicarbonate as intercalation agent was developed, which combined with mechanical force and chemical method for the green production of GIC. The production parameters were optimized by the single factor experiments, the optimal conditions were the ball mill speed 500 r/min for 4 h (6 mm diameter of the stainless-steel beads as ball milling media), the decomposition temperature 200 ℃ for 4 h, and 1:1 mass ratio of flake graphite to sodium bicarbonate. SEM results revealed that the prepared product appears the lamellar separation, pores, and semi-open morphology characteristic of GIC. FT-IR results indicated that the preparation method does not change the carbon-based structure, and the sodium bicarbonate intercalant has entered the interlayer of graphite flakes to form GIC. XRD results further showed that the GIC products still maintained the structure of carbon atoms or molecules, and the sodium bicarbonate intercalation agent has entered the interlayer of the graphite, and increased the interlayer distance of the layered graphite. The expandability of GIC products was studied, and the results show that it was expandable, and the expandable volume of GIC products prepared under optimal conditions has reached 142 mL/g. The theoretical basis for large-scale production was provided by studied the mechanism of the preparation method and designed the flow chart. The method has the advantages of simple process, products free of impurities, no use of aggressive reagents, process stable, and does not pollute the environment, being favorable to mass production, and provided new preparation method and idea for two-dimensional nanomaterials with preparation technical difficulties.

Morphology and wear of high chromium and austempered ductile iron balls as grinding media in ball mills

High chromium balls are recognized as better grinding media in terms of wear rates than forged steel balls, which are conventional grinding media in the milling process of iron ore. In this research work, the wear rate of high chromium balls and austempered ductile iron (ADI) balls as crushing media in a ball mill are compared. ADI are prepared by austenitizing the spheroidal graphite (SG) iron balls at 920 °C for one hour, and step austempering heat treatments were given, which includes the first step austenitizing at 300 °C for 15 min, followed by a second step austenitizing at 400 °C for 60 min. The wear rates were estimated when both balls were used separately by maintaining the same machining conditions and when the balls are mixed. The grinding wear conduct of both materials is evaluated for wear loss in wet grinding conditions. The experimental results reveal that the performance of ADI balls is better than high chromium balls when tested separately and mixed. Results also indicate that the wear rates/revolutions will decrease when the operating period increases.

Influence of powder mixing processes on phase composition, microstructure, and mechanical properties of α/β-SiAlON ceramic tool materials

α/β-SiAlON composite ceramics using powders mixed through different processes were prepared via spark plasma sintering. Effects of different powder mixing methods (ball-milling and ultrasonic vibration with mechanical stirring), ball-milling media (Al2O3 and Si3N4 balls), and mixing times (12 and 24 h) on the components and morphology of mixed powders, phase composition, microstructure, and mechanical properties of α/β-SiAlON ceramics were studied. Results indicate that additional oxides are mixed to powders when ball-milled with Al2O3 balls, leading to an increase in the amount of amorphous glass and a decline in α/β ratio and mechanical properties. These effects were reduced when powders were ball-milled with Si3N4 balls, and α-SiAlON content and fracture toughness increased significantly. Moreover, α/β-SiAlON ceramics that underwent ultrasonic vibration with mechanical stirring exhibited the highest hardness and oxidation resistance at high temperature, and their α/β ratio was close to expected value.

Drying characteristics of sludge in a rotary drum for fast-drying application

High temperature metallurgical slag (temperature, >1450?C) and high moisture sludge (moisture content, >80 wt.%) are common wastes with huge outputs. Many problems, such as high cost, low level of harmlessness, and low efficiency, are encountered in current treatment methods. If these wastes can be recycled, they can be valuable secondary resources. Therefore, using the drum apparatuses to treat these two kinds of wastes is proposed. The process uses waste heat of slag to dry sludge with high moisture content and is a kind of alternative circulation treatment technology in which steel balls are used as ball milling media and intermediate heat carriers. Besides, this technology can break up slag or sludge in real time, thereby ensuring high heat or mass transfer rate. This study presents an experimental investigation of the dynamic drying process of wet sludge mixed with hot steel balls in a rotary drum. The relationship of operation parameters (including sludge moisture content, sludge treatment mass, steel ball diameter, and rotary speed of drum) and drying effect is obtained. There are three kinds of final drying results: completely dried to powder, few sludge agglomerations, and sludge-to-wall adhesion. If the operating parameters are set well, the sludge could be efficiently and completely dried and eventually in powder form.

Effect of Forming Technology on the Properties of Quartz Sands Porous Materials via Dry Pressing Method

The effect of forming technology on the properties of quartz sand porous materials were researched with the low grade quartz sand along the Yangtze River via the pressureless sintering method in this paper, which lay technology foundation for researching new heat insulating materials. The wear of ball milling media is investigated through adjusting the ball milling parameter via the weigh methods. The results are shown that the porosity of quartz sand porous materials are decreased with increasing a forming pressure. The porosities of Φ30 and Φ50 materials are decreased with increasing a holding pressure time, however, the porosity decreasing rate of Φ30 is slower than that of Φ50. The porosity of Φ50 is higher than that of Φ30 under same forming conditions. Through optimized the forming conditions, the porosity of sintered Φ50 quartz matrix porous materials reaches 54.52% under the forming pressure for 5MPa and the holding pressure time for 5min.

Influence of rare earth Tb4O7 addition on the densification, abrasion resistance and microstructure of alumina ceramics

This study aimed to improve the purity and performance of alumina ceramics used as ball milling media. High-alumina ceramics (> 96 wt% Al2O3), with high densification and excellent abrasion resistance, were fabricated by the cold isostatic pressing method. The effects of adding the rare earth Tb4O7 on the densification, abrasion resistance, crystalline phase, micro-morphology and grain size of the ceramics were studied. The experiment results showed that the densification and abrasion resistance of the samples increased with Tb4O7 addition. The sample with 0.8 wt% Tb4O7 sintered at 1625 °C exhibited the best performance, with a linear shrinkage, relative density and abrasion rate of 22.28%, 95.70% and 0.103‰, respectively. The abrasion resistance improved by 27.5% compared with the sample without Tb4O7. X-ray diffraction analysis indicated that the primary phases of the samples were corundum, spinel, CaAl12O19 and α-quartz, and a small quantity of Tb3Al5O12 was generated when more than 0.4 wt% Tb4O7 was added. Furthermore, some Mg2+ and Ca2+ ions in the liquid phases dissolved into Tb3Al5O12 crystalline grains during the sintering process, which enhanced the grain boundary cohesion of the materials. Scanning electron microscopy indicated that the existence of Tb3Al5O12 at grain boundaries reduced the average size of the corundum grains. This helped transform inter-granular fractures into trans-granular fractures, thereby improving the abrasion resistance of the ceramic materials.

Kinetic parameters of grinding media in ball mills with various liner design and mill speed based on DEM modeling

The article presents analysis of the experiments in the ball mill of 0.5x0.3 m with four different liner types based on DEM modeling. The numerical experiment always complements laboratory research and allow obtaining high accuracy output data. An important property of the numerical experiment is the possibility of visualization of the results. The EDEM software allows calculating trajectory of the grinding bodies and kinetic parameters of each ball for the relative mill speed and the different types of mill’s liners.

A new method for few-layer graphene preparation via plasma-assisted ball milling

We report a new method for few-layer graphene (FLG) preparation via plasma-assisted ball milling with carbide, nitride or oxides as ball-milling media and expandable graphite raw material. Scanning electron microscopy, transmission electron microscopy and Raman spectroscopy were applied to characterize the FLG. FLGs prepared by using different ball-milling media such as boron nitride (BN), tungsten carbide (WC), zinc oxide (ZnO), iron oxide (Fe2O3) and germanium oxide (GeO2) were used to determine the relationship between the FLG layer number and inductive capacity of the ball-milling media. Parameters for the synthesis of high-quality FLGs were also optimized.

A Cross Wedge Rolling Process for Forming 70 mm Diameter Balls from Heads of Scrap Railway Rails

The paper describes an innovative technique for producing balls which are used as grinding media in ball mills. With this method, balls are formed from heads of scrap railway rails. The proposed two-stage technique is based on cross wedge rolling. First, a rail head is formed into a cylindrical bar with a diameter of 52mm. Next, the bar is formed into four balls, each with a diameter of 70mm. Given the two-stage design of the process, an innovative flat-wedge reversing mill had to be designed. The paper presents the design of such a mill. In addition, it also reports the numerical findings and experimental results of producing balls by the proposed technique.

A Study of Preparation and Characterization of Nano-Sized SiC Powder Using High Energy Ball Milling

This study investigated the preparation of nanosized crystalline SiC powders from micro sized Silicon Carbide powder at room temperature through high energy ball milling. Silicon carbide was milled with hardened steel balls and ball milling media under identical conditions of ball mass to powder mass ratio 10:1 and target milling times of 60 h. The sample was taken out after every 20 hours of milling and it was characterized for its crystalline size, lattice strain, and percentage of crystalline by using X-Ray Diffractometer (XRD). It was found that for the 60 hours The size, shape and texture of the fresh as well as nanostructured Silicon carbide powder were studied using Scanning Electron Microscopy (SEM). The raw Silicon carbide powder particles were mostly angular in shape. The shape of the 60h milled particles is irregular and the surface morphology is rough.

Microstructure and electrical conductivity in shape and size controlled molybdenum particle thick film

We study the effects of particle morphology on the microstructure and electrical conductivity of Mo particle thick films. In our study, the shape and size of molybdenum (Mo) particles are modified by mechanical ball-milling and atomic layer deposition (ALD). As the total number of collisions between Mo particles and ball-milling media increases, Mo particles are deformed, and the shape of Mo particles changed from irregular polyhedrons to thin flakes. In the ball-milling process, stress frequency is an important processing parameter governing the deformation and breakage of Mo particles. In addition, ALD-grown TiO2 layer is found to significantly suppress the growth of Mo particles at high temperature. After 1000 °C annealing, the particle size of the TiO2 layer-coated film is only half of that of bare Mo particle films. The shape of the particles changes electrical conductivity of the Mo thick films. Large contact area between flake shape particles can increase the carrier mobility of the film and the 5-nm thick TiO2 layer can provide the inter-particle carrier transport path via a tunneling mechanism. Our results show that the combined use of the ball-milling and the ALD coating leads to Mo thick films with high electric conductivity and large surface area.

Characteristic and dispersion of a treated AlN powder in aqueous solvent

Abstract Characteristic and dispersion of the aluminum nitride (AlN) treated by phosphoric acid were studied in aqueous solvent. The treated AlN powder displayed a good stabilization in aqueous ball-milling media. After 72 h ball-milling, the oxygen content of AlN powder with DP270, NH4PAA and without a dispersant were 1.84, 1.92 and 2.08 wt.%, respectively. The isoelectric points were 3.9, 3.5 and 3.35, respectively, for the treated AlN without dispersant, with NH4PAA and DP270. These two dispersants were proved to be effective dispersants by the apparent viscosity and sedimentation tests and could play a dual role in preparation of aqueous AlN suspensions. A dispersant is needed in aqueous suspensions of AlN powder treated by phosphoric acid.

Energetics of collision between grinding media in ball mills and mechanochemical effects

This paper describes the physical and chemical changes such as decomposition, double decomposition, oxidation, and phase transformation reported in the literature as a consequence of solid surfaces coming into contact under mechanical forces. These changes, generally termed mechanochemical and chemomechanical effects, occur in the near-surface regions when surfaces come into contact as in abrasion between solid surfaces and repeated collisions among grinding media in ball mills. For understanding mechanochemical effects in ball mills, the normal impact between two grinding balls is quantified in terms of collision force, contact radius, contact time, and collision energy. These measures are quantitied as a function of ball sizes (diameters varying between 1 and 4 cm), ball material (steel and alumina), and collision velocity (0.4–4 m/s), using expressions developed by previous investigators from the principles of continuum mechanics.

Mechanisms of corrosive wear of steel balls in grinding hematite ore

Much work has. been done on wear of grinding media in ball mills; however, infornlation available is mostly related to abrasive wear, and data concerning corrosive wear are rather limited. Norman and Loeb (1) conducted wear tests on grinding balls. They found that during wet grinding of ore, steel balls showed an increase in rate of wear when the mill atmosphere was changed from air to pure oxygen. When the mill was operated in air atmosphere with pulp that had been Inade alkaline, a reduction in rate of wear was obtained. They reported that this variation in wear rate was due to the influence of an oxide film. Bond (2) attributed the increase in wear when changing from dry to wet grinding to dissolution of iron from active metal surfaces produced in grinding. Sobering and Carlson (3) also found that by converting from wet grinding to dry grinding of hematite ore at their Wabush Mines Plant, ball consumption was reduced by as much as 60% by avoiding the corrosive wear during wet grinding. In a similar manner, Bombled (4) concluded from his wear mechanism studies that the total wear of grinding media in ball mills is equal to the sum of surface abrasion, mass impact and corrosion by oxygen and moisture. By a different approach, Hoey (5) demonstrated the important role played by corrosive wear in the total wear of steel balls during wet grinding of ores in laboratory ball mills. Corrosion inhibitors were used in sulphide ore and iron ore slurries, and corrosive wear was reduced significantly. The role of corrosive wear in the total wear of steel balls was recognized both in the plant and in the laboratory; however, the corrosive wear mechanism has not been investigated. In this paper, ~. mechanism of corrosive wear of steel balls during wet grinding of hematite ore and an extrapolation method for the estin1ation of corrosive wear are presente~J