Reduction of the porcelain firing temperature by preparation of the raw materials

An innovative way of reduction of firing temperature of porcelain tableware is reached by preparation of raw materials down to submicron- and nanoscaled powder for higher reactivity. In this study a common slurry was ground in an agitator ball mill from d₅₀ = 5.0 μm to 0.9 μm, green bodies were prepared, and glost firing was simulated in a dilatometer. The sintering temperature has been decreased by approximately 180 °C. A reflection between ball mill and agitator ball mill regarding the grinding cost shows no difference which means that the ball mill could be replaced. The energy consumption during the grinding process will be discussed regarding to energy savings resulting from reduced firing temperature. Furthermore a comparison between experimental and literature data will be done. The effect of grinding of raw material is finally evaluated concerning sintering behaviour and material properties.     

Scale-up of power consumption in agitated ball mills

Previous investigations have shown that the specific energy input is the overall parameter of influence on product size during communition in agitated ball mills, from laboratory up to industrial scale. The specific energy input is the introduced energy related to the amount of comminuted material. This parameter can be used for mill scale-up. Consequently, a method had to be found of introducing power into the mill so as to obtain a given specific energy input. For this purpose, stirring tests with purely Newtonian liquids were carried out in absence of solids and hence, without comminution. Mathematical models are presented which describe the power consumption in agitated ball mills in absence of grinding beads. In addition, tests with grinding beads filling were also performed, leading to scale-up guidelines with respect to power consumption. Finally, the influence of size and material of grinding beads was investigated.     

Intensive grinding of powders in an electro-magneto-mechanical mill

The paper presents the results of high-energy grinding in the electro-magneto-mechanical (EMM) mill. Ground powder is treated in a very specific and intensive way owing to several field forces operating simultaneously in the EMM mill. The grinding power in the centre of the mill's working chamber is in the order of 2 MW/m³, which is much more than in ordinary mills. Therefore, the grinding time is very short, i.e., several tens of seconds. The self-disintegrated Fe–Al–Si powders of 155 μm on average undergo size reduction to 8 μm after 120 s. Over 25% of the total weight get the size of less than 1.3 μm. Very hard materials, such as SiC and B₄C reduce their grain size over 30 times after 120 s of grinding in the EMM mill. The results of the grinding of Fe₂O₃ powder are even better. In ball mills, vibration and planetary mills, similar results can be achieved after a period several hundreds times longer. The treatment of Fe–Al–Si powder presented here is intended as the preparation procedure for sintering, plasma spraying or laser surface alloying.     

The effect of ball and mill diameters on grinding rate parameters in dry grinding operation

For dry ball mill grinding operation, the effect of ball and mill diameters on grinding rate parameters of the size-discretized population balance model has been investigated for quartz, limestone, a soft cement clinker and a hard cement clinker. Experiments were performed in three mills of 29.2, 40.6 and 61.0 cm diameter. The diameter of the balls used ranged from 1.27 to 3.81 cm. The particle size range covered was $\text{8}\text{10}$ to $\text{100}\text{150}$ mesh. The rate parameter values were determined very accurately using a special technique. It has been shown that the particle size exponent α in equation S_i = Ax_i^α is independent of ball and mill diameters. Based on this fact, a new correlation has been developed to describe the effect of ball and mill diameters on the rate parameters. The various constants in this correlation are strongly material dependent.     

Scale-up method of planetary ball mill

The objective of this paper is to investigate the scale-up method of the planetary ball mill by the computational simulation based on Discrete Element Method. Firstly, the dry grinding of a gibbsite powder by using four different scales of planetary mill was developed to compare the grinding rate with the specific impact energy of balls calculated from computational simulation. The grinding rate is well correlated with the specific impact energy in all mills; and its relationship is expressed by a linear correlation. It points out that the specific impact energy is very useful for estimation of the grinding rate and optimization for the operational conditions. Secondly, the scale-up method for the planetary mill was established by evaluating the impact energy. The impact energy is proportional to the cube of the diameter of the pot, the depth of the pot and the revolution radius of the disk, respectively. When the planetary mill is scaled-up in geometrical similarity, the impact energy of the balls is proportional to 4.87 power of the scale-up ratio.     

Empirical and scale-up modeling in stirred ball mills

Stirred ball mills are frequently used for ultrafine- and nanogrinding in food, pharmaceutical and chemical industry, but only few investigations have been published on empirical or scale-up modeling of stirred ball mills. Experiments have been carried out with a laboratory scale stirred ball mill. During the experiments the main technical parameters such as stirrer speed, grinding media, filling ratio, grinding time and the solid mass concentration have been systematically adjusted. The particle size distribution of mill products can be well estimated by empirical functions, so an empirical model has been prepared for the laboratory mill. The relation between the grinding fineness, grinding time and specific grinding work was represented for several materials such as pumice, andesite, limestone and tailings of ore mining industry. The power consumption of the stirred ball mill for scale-up was determined by a method based on the dimensional analysis. A new scale-up model has been presented as well by with industrial size stirred ball mills can be designed on the basis of the laboratory measurements.     

Changes in the structure of hematite by extended dry grinding in relation to imposed stress energy

The effect of extended dry milling in different mills on the structural changes of hematite concentrate has been investigated using a combination analysis of XRD line broadening, BET and particle size measurements. Structural changes were followed by XRD line broadening analysis using integral breadth method and Warren-Averbach approach. For analysis, the stress energy was estimated by considering different grinding variables in different mills and changes in the structure discussed in terms of stress energy.Within comparable range of stress energy, lower BET surface area was produced by grinding in the vibratory mill. The maximum surface area increased to 18,400 m²/kg in the vibratory mill after releasing 51,300 kJ/kg energy. The conversion of the 80% of initial hematite to amorphous phase during extended dry grinding by tumbling, planetary and vibratory mills, needs 4000, 8500 and 50,000 kJ/kg energy respectively. It was understood that vibratory mill introduces the minimum lattice strain and gives the largest crystallites when applying the same level of stress energy. The smallest crystallites with grinding in tumbling, vibratory and planetary mills were obtained about 17.3, 13.5 and 5.6 nm after releasing 5230, 51,300 and 15,600 kJ/kg respectively. For these levels of stress energy, in turn, the microstrain <ε_L=10 nm²>^1/2 exceeds 4.4 × 10^− 3, 3.9 × 10^− 3 and 5.3 × 10^− 3.It was further revealed that higher concentrations of defects (Amorphization and excess energy) per unit surface area were induced by grinding in the planetary and tumbling mills. A theoretical calculation of the energy contribution to the long-lived defects indicated that products from tumbling and planetary mills have higher excess energy compared to the products from vibratory mill for the same stress energy. The maximum theoretical excess energy was estimated about 75.4, 80.0 and 81.3 kJ per mole of the ground hematite with tumbling, vibratory and planetary mills after releasing 5230, 51,300 and 15,600 kJ/kg of stress energy respectively. Grinding in vibratory mill needs much more energy to reach the same effect as the other used mills. A comparison of specific energy input and stress energy among the used mills points out that for generation of the same levels of stress energy, the planetary mill consumes more energy than the other used mills.     

关于大型球磨机的设计

球磨机中研磨体的运动方式主要有抛落式和泻落式两种。研磨体的抛落式运动已经有了比较深入的研究并作为设计中小型球磨机的理论基础.对于大型球磨机研磨体的运动方式应采用泻落式.本文对研磨体的泻落式运动进行讨论并给予数学描述,在此基础上为大型球磨机的设计提供了理论依据.     

Trajectories and impact velocities of grinding bodies in planetary ball mills

The motion of grinding bodies in conventional ball mills has been repeatedly investigated, both theoretically and experimentally. It is well-known that, depending on mill filling and speed of rotation, different motion patterns occur and some of these patterns, especially that of cataracting, can be described by simplified theories. This contribution presents such a theory of the cataracting motion of grinding bodies in a planetary ball mill. An analytical method for the evaluation of trajectories is given which permits an iterative calculation of the time and impact location of the grinding bodies on mill shell or mill filling. This leads to the determination of the impact velocity of grinding bodies and its component normal to the mill shell. On the assumption that this component is decisive for the grinding effect, conditions for an optimal design of a planetary ball mill are deduced.     

Optimization of variables in grinding brass particles for paint and pigment industry

Flaky metal powders commonly used as paint and pigments, are generally produced by grinding in ball mills or vibration mills. The key to good quality powder production is to optimize the processing parameters. In the present work grinding of brass particles is studied in detail in a laboratory size ball mill to determine the optimal levels of the ball to material ratio, type and amount of additives, mill speed, ball load, etc. The quality of the powder is assessed on the basis of water coverage, degree of flattening and luster by visual inspection. Preliminary results in a 35 cm diameter ball mill with 30% ball load show that a material to ball ratio of 0.067 with a 0.1% dosage of stearic acid is required for good quality powder. For determining optimal mill speed and ball size a 2² factorial design of experiment has been followed. It has been determined that to achieve best powder quality the mill must run at 70% critical speed and the ball size must not exceed 20 mm. The quality of the powder assessed through SEM study for surface morphology and particle size analysis compares very well with the industrial samples.     

From single particle impact behaviour to modelling of impact mills

An approach to quantify the impact grinding performance of different materials is presented. Based on a dimensional analysis and on fracture mechanical considerations two material parameters, f_Mat. and W_m,min, are derived from theoretical considerations. f_Mat. characterises the resistance of particulate material against fracture in impact comminution. W_m,min gives the mass specific energy which a particle can absorb without fracture. Using this approach various materials in a wide size range, e.g. different polymers, crystalline substances, glass and limestone, can be characterised quantitatively. The derived material parameters are applied to the systematic and multi-scale modelling of grinding in impact mills. A population balance model is presented and the results of the simulation for two different impact mills are shown. The developed model allows for a clear separation of the influence of material properties, mill specific features and operating conditions, thus enabling a deeper understanding of the impact grinding process.     

Naßmahlung in Rührwerksmühlen

Wet grinding in agitated ball mills. To ensure certain product qualities it is necessary to have very fine particles or a narrow particle size distribution. For this process agitated ball mill grinding can be used as well as crystallisation and precipitation. Cost effective grinding of very fine products to a narrow particle size distribution requires that the effects of variation of strain intensity, frequency of impacts, residence time distribution, size of grinding media, viscosity of liquid and concentration of feed material should be known. The most important parameters and their effects on the grinding result are demonstrated, as well as explained by a model, and the consequences for the operating conditions of agitated ball mills are presented. By using small grinding media in agitated ball mills the production rate can be increased, or at the same energy level smaller particles can be obtained by grinding or deagglomeration. At high flow rates and a narrow residence time distribution the feed material becomes more homogeneous. These facts require the development of new or modified types of agitated ball mills.     

几种典型水泥粉磨系统的比较

水泥粉磨系统已由早先的球磨机系统逐步发展到现在的球磨机+辊压机系统和立磨系统。通过分析流程和主要配置及运行参数,归类出比较典型的七种水泥粉磨系统的技术性能持点。其中,立磨终粉磨系统流程最简单,能耗最低,是水泥粉磨方案的首选;辊压机+球磨(带涡流选粉机)组成的联合粉磨系统及立磨和球磨组成的联合粉磨系统流程相近,能耗相近,可作为水泥粉磨系统的优选方案;辊压机和球磨机组成的开流及半开流系统缺点最多,应尽量避免选用。     

Analysis of energy-size reduction relationships in batch tumbling ball mills

A theoretical energy-size reduction relationship is derived for tumbling ball mills based on a solution of the integro-differential equation of comminution kinetics, in which the proportional relationship is applied between the grinding rate constant and the net mill power. The derived formula is similar to an empirical energy law, dW ∝ dx_r/x_rⁱ, where W is the specific energy input, x_r is the particle size of product and the exponent i is shown to be a variable depending upon the ground material, the type of mill and the method to measure energy. Derived results are confirmed with reported data in reasonable agreement. Also, the Bond's energy law is examined and a method for the correction of the Bond work index is discussed.     

A Comparative Study on a Vertical Stirred Mill Agitator Design for Fine Grinding

Comminution is an energy intensive process. A small change in efficiency can lead to substantial benefits in an overall economy of the process plant. This study focused on the comparison of vertical stirred mill agitator designs. A double helical screw agitator was designed for this purpose. A series of stirred mill experiments were performed with two types of agitator designs a standard pin type and CSIRO’s designed double helical screw stirrers. The effects of operating parameters such as grinding time, stirrer speed, and pulp density on grinding performance was investigated using a magnetite concentrate. Grinding performance was analyzed by considering the product fineness and the energy consumption. The test results show that the grinding time and stirrer speed played a significant role; however, the pulp density had little impact on grinding performance in both cases of agitator designs. The 80% passing target product size of 38 μm was obtained with double helical screw agitator in 20 min of grinding with an expend of 10.53 kWh/t specific energy, whereas, the target product size of 38 μm was achieved with the pin type stirrer at the rate of 21.73 kWh/t. It is evident that grinding in a vertical stirred mill with a double helical screw is more efficient than that using a pin type stirrer in terms of the product size distribution and the specific energy consumption. It is concluded that the double helical screw design provides better energy efficiency compared to the pin type stirrer design. The models were developed for the responses P₈₀ and E_cs. Both models show high regression coefficients thus ensuring a satisfactory of models with experimental data. The model equations developed were then optimized using a quadratic programming to minimize the P₈₀ size at minimum specific energy.     

立式磨在苏丹BERBER项目水泥粉磨系统的应用

在新型干法水泥生产线的设计中,国内水泥粉磨系统基本上采用单独球磨机或者球磨机加辊压机系统,球磨机虽然可靠,但能耗相对较大。苏丹BERBER项目水泥粉磨系统的设计采用了立式磨粉磨水泥的方案,重点介绍该系统的特点、工艺流程等,对今后辊磨的发展,认识及设计应用均有帮助。     

用莱歇辊式磨粉磨水泥熟料和高炉矿渣

本文提出了一种关于莱歇磨料磨房水泥和粒化高炉矿渣的新设计思路。在保留水平研磨盘的同时府，新设计的莱歇水泥磨用了4个辊子。其中两个作为研磨辊，另外两个则作为研磨床预挤压的预压辊，这样不仅可大幅度提高研磨辊相单位辊压力，同时可在低磨振操作的情况下保证水泥的性能。新为设计简单可靠、研磨元件的使用寿命大于10000h，运转率高。产品质量稳定，其单位电耗显著低于管磨。且优于带高压辊压机预粉磨的管磨系统。     

Method of grinding as a factor in the rheological and technological properties of alumina suspensions

Conclusions Suspensions of alumina wet-ground and dry-ground in a ball mill are characterized by viscosity changes typical for firm systems with static {ie365-01} and dynamic (Bingham) {ie365-02} fluidity limits.These suspensions are thixotropic; the viscositygh _m of their fully broken up structure is higher and their zeta potential lower than for suspensions of vibro-ground alumina, the explanation being the considerably longer grinding time in a ball mill and the fact that in wet grinding a vigorous interaction proceeds between the solid and liquid phases directly in the grinding process.Alumina wet-ground in a ball mill contains more impurities after washing than alumina dry-ground in a vibro mill. The suspension of the former gives a faster rate of casting but the density and strength of the product are lower.Fired commercial alumina to be used for the production of high-quality dense-sintered refractory corundum ceramics should be dry-ground in a vibratory mill.Translated from Ogneupory, No. 6, pp. 44–51, June, 1977.     

Impact of pressure in static and dynamic pressing of ultrafine plasmochemical ZrO2 (Y)-Al2O3 powders on compact density and compaction efficiency during sintering

The effect of different methods of pretreatment and compacting of ultrafine alumina-zirconia powders of composition (in mass%): 20 Al₂O₃-80 (ZrO₂-Y₂O₃) on densification processes during pressing and subsequent calcination has been studied. Ultrafine powders were prepared by plasma-chemical method. It was found that the initial nanocomposite is a mechanical mixture made up of zirconia nanoparticles and amorphous alumina in a thermodynamically nonequilibrium state. Grinding of powders did not affect their phase state. Powder compacts were produced by means of uniaxial static pressing and magnetic pulse compaction. The impact of mechanical processing of powders on ceramics density was studied. It was shown that dry grinding of powders in a planetary ball mill does not increase the ceramics density. The best and virtually identical results were obtained using preliminary static pressing of powders at increased pressure P?=?900?MPa and their subsequent grinding in a ball mill. Dilatometric studies showed that double-action magnetic pulse compaction provides the maximum shrinkage rate at lower temperatures in comparison to that observed under static pressing. The ceramic density achieved is higher than that obtained using other pressing methods.     

Radial mixing of particles in a dry batch ball mill

Poor mixing in dry ball mills can lead to insufficient presentation of fine particles to the classifying air, overgrinding of particles and wastage of energy in a ball mill. A video capture method has been used to study radial mixing kinetics in a dry batch ball mill. Experiments were conducted in a ball mill with PVC plastic powders being used as particles so that the effect of size reduction could be neglected. Radial mixing in ball mills was studied at typical industrial speeds of 75%, 80% and 90% of critical. The rate of particle mixing was observed to increase with increasing mill speed. A simplified mathematical model is presented that can be used to predict the radial mixing of particles in a ball mill. A parameter, k, was used to quantify the kinetics of mixing as affected by the mill's speed.