Initial Stage Of Grinding Research Articles

Research on the grinding performance of grinding wheel in the initial grinding stage after electric spark dressing of grinding wheel

Research on the grinding performance of grinding wheel in the initial grinding stage after electric spark dressing of grinding wheel

Effect of mechanical grinding time on the particle groups characteristics and activation effect of Yellow River sediment

Yellow River sediment(YRS) is an abundant resource of dredged sediment, and has found wide applications as various construction materials. However, its potential activity has seldom been reported. In this study, the activity of YRS was stimulated by mechanical grinding. The particle characteristics after different grinding times were investigated and the mechanism of activating YRS was illustrated. In the initial grinding stage (within 25 min), the size of YRS was significantly reduced and the particle size distribution (PSD) was uniform. In the ultrafine grinding stage (25–70 min), the particle size and distribution did not change further. Instead, the mineral crystal structure was destroyed, leading to a reduced crystallinity and an increased number of broken bridge oxygen bonds. After YRS was ground for 40 min, the activity index reached the maximum. YRS exhibited significantly improved activity, providing a theoretical basis for its application as supplementary cementitious materials to reduce cement dosage. When the grinding was further increased to 70 min, the activity of YRS decreased due to the reorganization of chemical bonds.

Feed hardness and acoustic emissions of autogenous/semi-autogenous (AG/SAG) mills

In this study, the relationship between acoustic emissions and hardness of different rock types (model quartz, model calcite, and real iron ore) coupled with binary mix ratios of model quartz and iron ore (1:3, 1:1 and 3:1) was investigated in a laboratory-based AG/SAG mill. The acoustic emission response and sensitivity of the mill were compared, along with its product particle size distribution. Features, such as discrete wavelet transform (DWT), power spectral density estimate (PSDE), and statistical root mean square (RMS) were extracted from the mill acoustic emissions. From the results, it was evident that the mill acoustic emission response can be used to classify different rock hardness and their binary mixtures. Model quartz emitted the highest acoustic response, followed by iron ore and model calcite at the initial stages of grinding (5 min). The results further indicated that as the rock feed sizes reduced, the average mill noise also increased as a function of grinding time. Accordingly, the acoustic emission presented a contrasting effect with model calcite and model quartz emitting the highest and lowest noise emission, respectively. The proportions of different mineral types (model quartz and iron ore) were reflected well in the acoustic emissions. The study has demonstrated that the integration of acoustic sensing techniques in AG/SAG mills can serve as a proxy for online measurement of different rock/ore hardness, for example, as a fast track method to determine the hardness of ores in comparison to the traditional ore grindability procedures, such as Bond work index (BWI) and SAG power index(SPI) tests which can be laborious and time-consuming.

Effect of feed size on residence time and energy consumption in a stirred mill: An attainable region method

In mineral processing, stirred mills have become a common device due to their high energy efficiency. In this work, the kinetics of batch wet grinding studies were studied using six mono-sized fractions of quartz. The population balance model (PBM) was used to simulate the evolution behavior of the particle size distribution in a laboratory scale stirred mill. The parameters of PBM were obtained by calculations performed on experimental data. The results showed that the breakage behavior of each class followed a first-order model in the grinding process. Furthermore, the particle size distribution was back calculated from the determined parameters of the PBM. The simulated results were analyzed by the attainable region (AR) method to maximize the volume fraction of the desired size (−45 + 10 μm) in grinding products. The results obtained indicated that the turning point and switch point were largely dependent on the feed size. These results suggest that a finer feed size is a better choice if the objective is to maximize the volume fraction of the desired size in the shortest residence time possible in a grinding circuit with a classifier. In addition, at the initial stage of grinding, the influence of the specific energy input on the yield of the desired size and overgrinding size for different feed sizes was significant.

Морфология и химический состав поверхности титанового сплава на начальном этапе шлифования кругом из кубического нитрида бора

Морфология и химический состав поверхности титанового сплава на начальном этапе шлифования кругом из кубического нитрида бора

Positron annihilation spectroscopic investigation of high energy ball – milling engendered defects in CaCu3Ti4O12

Polycrystalline sample of calcium – copper – titanate (CaCu3Ti4O12) was synthesized by two – steps solid state reaction route and then high energy ball-milled for several hours. Samples collected at different hours of milling were characterized and studied. X-ray diffraction patterns indicated monophase formation in the initial stage of grinding and a few other phases were found being formed with further milling. The elemental analysis indicated the possible presence of defects possibly due to non-stoichiometry, which was subsequently confirmed through positron annihilation studies. The positron trapping defects in the samples were found evolving from monovacancies to larger vacancy clusters and microvoids during increased hours of milling. The concomitant process of reduction of the sizes of the crystallites to nanometre dimensions resulted in the diffusion of thermalized positrons to the nanocrystallite surfaces and subsequent annihilation. The results indicated defects as a strong entity of influence on the structure and properties of CaCu3Ti4O12 and deserving serious consideration when the high dielectric material is sought for use in practical applications.

Crystallographic Features of Nanosized Titanium Carbide Produced from Titanium and Carbon in a Planetary-Ball Mill

Structural changes that occur in titanium during grinding of a powder mixture of titanium and carbon in an AIR-015M planetary-ball mill are studied. Grinding of the powder mixture results in the formation of titanium carbide single crystals with particles 7–50 nm in size over the entire reaction zone. At the initial stage of grinding, texturing of titanium occurs and the titanium lattice cell increases in volume, thus inducing internal stresses. Based on these data, it is suggested that the introduction of carbon into the strained titanium particles leads to stacking faults in the titanium hcp lattice, acting as nuclei of fcc titanium carbide in the titanium sites fragmented. Single-crystal TiC 10–20 nm nanoparticles are formed in these sites. The length of titanium–carbon contacts naturally increases with grinding time, giving rise to more nuclei of the new fcc phase. This promotes a mechanically induced self-propagating reaction. The heat generated in the reaction contributes to the sintering of titanium carbide nanoparticles. This results in the formation of particle aggregates 0.1–0.5 μm in size.

Dechlorination of polyvinyl chloride by its grinding with KOH and NaOH

Abstract —Polyvinyl chloride (PVC) powder was ground with one of two dried alkaline additives, i.e. KOH and NaOH, pellets in air by a planetary ball mill to investigate the dechlorination reaction during the grinding. Grinding of the mixture causes the size reduction of PVC, with causing its mechanochemical reaction with the additive to form partially dechlorinated PVC and chloride (KCl or NaCl), respectively. In both reaction systems, the dechlorination yield increases with an increase in grinding time and amount of additive. The C C bonds in the PVC ingredient are created in its structure with decreasing molecular weight (MW). The MW of the polymer ground with KOH is higher than that ground with NaOH. The dechlorination speed of the polymer ground with KOH is faster than that ground with NaOH in the initial stage of grinding, but this is reversed during prolonged grinding.

メカノケミカル・レドックス・プロセスによるマグネタイト微粉末の合成

Direct mechanochemical synthesis of γ-Fe3O4 powders with a planetary-mill from metallic-Fe and FeO(OH)(1:2) in H2O2-containing acetone is proposed. At the initial stage of grinding, FeO(OH) particles are kneaded into deformable metallic-Fe forming composite particles. When the metallic-Fe is oxidized to FeO by H2O2, the FeO immediately reacts with FeO(OH) to form γ-Fe3O4. Almost singlephase γ-Fe3O4 is obtained by the grinding at 5s-1 for 5.0h. The heat of oxidation of iron promotes the formation of γ-Fe3O4. The γ-Fe3O4 particles are dispersed into the grinding liquid without adhesion to the grinding media. The small amounts of residual Fe and FeO(OH) further react under heat-treatment at 300°C in Ar. The primary particle size of the synthesized γ-Fe3O4 is 13-17nm. α-Fe2O3 does not form when excess amounts of H2O2 are added (H2O2/Fe=3.17). Although H2O as a substitute of H2O2 produces γ-Fe3O4, the addition of small amounts of oxidation reagents effectively promote the synthesis reactions.

Influence of grinding on the structure and colour properties of talc, bentonite and calcite white fillers

AbstractThe influence of grinding on colour and particle-size properties of talc and smectite from a white bentonite were studied and compared with a fine-grained calcite from a chalk. Grinding decreased the grain size of all three minerals. The crystallite size and structure of smectite was not affected but the crystallite size of talc decreased. The Si–O–Mg and Mg–O bonds of talc were disrupted and cation exchange capacity increased with increasing grinding. Delamination of talc crystallites was observed in the initial stages of grinding, whereas with more intense treatment, amorphous material was formed. Comminution improved the colour properties of all three minerals, namely brightness, L* (lightness) and ΔE*ab (deviation from perfect white diffuser). Grinding time exerts greater influence on the reflectance from calcite surfaces than from clay minerals. This difference is attributed to continuous formation of progressively smaller diffuse reflection units forming a smoother calcite surface. Decrease of grain size does not form considerably smaller diffuse reflection units in clay minerals unless delamination takes place. With prolonged grinding, amorphization forms additional diffuse reflection units and a smoother surface due to comminution.

Magnetic Properties of Mechanically Alloyed and Annealed Powders Fe100 – XCX(X = 5 and 15 at.%)

The effect of the structural state and the phase composition on the magnetic hysteresis properties of Fe(95)C(5) and Fe(85)C(15) powders after mechanical alloying and annealing is investigated. It is shown that in the initial stage of grinding in a ball planetary mill the coercive force of the Fe–C powders is determined by the degree of defectiveness of the α-Fe phase and the relative volume and dimensions of nonmagnetic graphitic inclusions in iron powder particles. As the grinding time increases, the α-Fe phase goes over into a nanostructure state and carbon from graphite inclusions goes over into an amorphous Am(Fe–C) phase. After annealing on the temperature interval 300–600°C, the amorphous Am(Fe–C) phase is transformed into Fe3C ferric carbide. The coercive force of the Fe3C phase strongly depends on the degree of distortion of its crystal lattice and amounts to ∼ 80 A/cm for the phase with distorted lattice and ∼ 240 A/cm for the phase with equilibrium undistorted lattice. The magnetic characteristics of the powder after mechanical alloying and subsequent annealing are determined by the type, amount, and structural state of the phases containing in the samples.

A study on the specific rate of breakage of cement materials in a laboratory ball mill

The specific rate of breakage (Si) in the widely accepted first-order expression of grinding rate is one of the important factors required to evaluate a grinding process, particularly for the initial grinding stage in various mill types.In this study, the effects of ball diameter and feed size on the specific rate of breakage were investigated on limestone, trass and clinker samples at batch grinding conditions based on a kinetic model. Eight different monosize fractions were prepared between 1.7 and 0.106 mm, using a √2 sieve series. The specific rates of breakage (Si) were determined from the size distributions at different grinding times, and the specific rates of breakage were compared for three different ball diameters (41, 25.4 and 9.5 mm).The results indicated that the variation of the specific rate of breakage with feed size of cement materials could be expressed. For the specific rate of breakage of each material, empirical equations were developed to express it as a function of feed size and ball diameter.

Experimental study on the grinding rate constant of solid materials in a ball mill

The grinding rate constant, in the widely accepted first-order expression of grinding rate, is one of the important factors required to evaluate a grinding process particularly for its initial grinding stage of various mill types. In this study, we conducted grinding tests on silica glass, limestone and gypsum using a laboratory ball mill, and measured the grinding rate constant of the feed size reduction. We investigated the effects of feed size and ball diameter on the grinding rate constant of the materials used when the mass of balls, mass of feed, and the mill's rotational speed were constant. The results indicate that the variation of the grinding rate constant with feed size of the materials can be expressed by revising the equation proposed by Snow. For the grinding rate constant of each material, empirical equations were developed to express it as a function of feed size and ball diameter.

Material characteristics and the breakage parameters in a circular fluid energy mill

Towards analyzing the breakage behavior of materials with respect to their physical properties in the context of simulation and modeling of the process of comminution in a circular fluid energy mill, the present work was taken up to characterize the effect of material hardness on the breakage process of the mill. The breakage parameters of a range of materials, chosen based on their hardness, were analyzed by estimating them using the G-H solution for the size discretized batch grinding equation, with corrections to account for the deviation from first-order kinetics during the initial stages of grinding and a back-calculation scheme. All the operating variables of the mill were kept the same while collecting the primary breakage data using a single-size feed for six successive passes through the grinding chamber of the mill. The breakage distribution values could be related to particle size with the sum of two power function equations, while the breakage rate could be expressed as a power function of the dimensionless particle size and the top size interval disappearance. The coefficients of these functions for different materials indicated inconsistent behavior with respect to the hardness for softer materials, while medium and harder minerals showed specific trends.

転動ミルの粉砕速度定数に関する実験的検討 フィード粒子径，媒体径の影響

The grinding rate constant is one of the important factors needed to estimate or evaluate a grinding process. It has been found that the decreasing rate of the feed size was described by a first-order equation in the initial grinding stage of various mills.In this study, grinding tests were carried out on silica glass using a ball mill, and the grinding rate constant of feed size decrease were measured. The effects of the ball diameter and the feed size on the rate constant were investigated when the mass of balls, the mass of feed and the rotational speed of the mill were constant.As the result of the tests, the grinding rate constant could be expressed by modifying the equation which was proposed by Snow as the function of ball diameter and feed size.

The effect of micronization on kaolinites and their sorption behaviour

The effect of micronization on the crystalline structure of kaolinite clay mineral and the role of this mechanically modified kaolinite structure on the adsorption/ion-exchange properties of toxic heavy metals are discussed. Two methods of micronization (ball milling and oscillatory milling) were used for the purpose. Micronization using a ball mill was found to be a slow process where dry grinding proved to have some effect compared to wet grinding. But grinding in an oscillatory mill could produce almost complete destruction of the clay structure (amorphization) within one hour of grinding time. The ground samples were characterized using XRD, IR spectrometry, TGA, DTA, SEM, surface area and pore volume measurements and particle size analysis. Adsorption kinetics for Cd and Cu show a slight improvement during the initial stages of grinding (i.e., from 4.24 – 4.68 meq/100 g for Cd and 2.79 to 3.45 meq/100 g for Cu at a grinding time of 10 min) brought in by the delamination after which the rate of adsorption decreases (1.024 meq/100 g and 1.09 meq/100 g for Cd and Cu respectively). For lead ions, there is an increased sorption and also it was observed that it takes a longer period for attaining equilibrium compared to cadmium and copper.

Effect of dry grinding on ion-exchange characteristics of synthetic mordenite

The changes in ion-exchange characteristics of synthetic mordenite ground by a planetary ball mill under dry conditions were investigated using radioisotopes of 137Cs and 85Sr as tracers. The self-diffusion of Cs + in the mordenite sample was facilitated in the initial stage of grinding, while it was leveled off for the further operation. The relative amount of Cs + immediately exchanged in the mordenite sample was gradually styptic to a constant value with increase in grinding time after showing a rapid reduction in amount in the early stages of grinding. High selectivity of the mordenite sample for Cs + against Sr 2+ observed in acidic solution diminished obviously with an increase in grinding time.

セラミック原料の湿式粉砕におけるコンタミネーションについての一考察

The problem of contamination has become the centre of interest in the technique for the preparation of a high-purity powder, especially the milling process of the starting powder in high performance ceramics. In this report, the increasing tendencies in the amount of impurity in TiO2 powder during wet alumina ball milling are described.The results obtained are summarized as follows:(1) Impurity (intermixture into the ground TiO2 powder), caused by wear of the grinding ball and the mill liner, was mainly included in the finer size range of the ground productt in the initial grinding stage. Also, the size of intermixture was distributed widely throughout the full size range of the ground product in the final grinding stage.(2) The intermixture concentration was influenced considerably by the viscosity and the specific gravity of the slurry.(3) The size of the wear debris was distributed into a finer size range of the ground product. Then, in the closed circuit wet milling process, it was estimated that the impurity was concentrated in the fine grinding product that was collected by the classifier.

Solution and experimental validation of a mathematical model for vibrational milling of metal powders

A population balance model for grinding of metal powders incorporating three size change, mechanisms, namely flattening, attrition and breakage, is presented. Analytical solution is obtained for the simplified case of pure flattening and pure attrition. The predominance of pure flattening has been observed in the initial stages of aluminum grinding. The pure attrition model is found to be valid only in the case of brass and during the initial stages of grinding of copper. The validity of the pure breakage model towards the latter part of grinding of aluminum has been established.

Effect of Mixed Grinding of Kaolinite-Gibbsite Mixture on Formation of Mullite.

Effect of mixed grinding of a kaolinite-gibbsite mixture on formation of mullite has been investigated by the X-ray diffraction method, DTA, SEM and surface area determination of powders. The both structures of individual specimen and their mixture are transformed easily into an amorphous state within about 60 minutes grinding by a planetary ball mill under dry condition. The amount of amorphous phase in the ground specimen increases with increasing grinding time. Accordingly, there has been a rapid decrease in the density of the mixture in the beginning of grinding and a leveling off with the progress of grinding. The specific surface area of the mixture increases sharply at the initial stage of grinding, then decreases gradually with an increase in grinding time, because of the coagulation. The mixed grinding has resulted in the formation of mullite directly from spinel phase without formation of corundum and cristobalite phases during sintering at more than 1223K. The ratio of formation of mullite has increased with an increase of grinding time and sintering temperature.