Application of grinding kinetics analysis of inorganic powders by a stirred ball mill

The need for ultra fine particles has been increasing in the preparation field of raw powders such as fine ceramics and high functional products. A series of wet grinding experiments were carried out on inorganic powders such as calcite, pyrophyllite and talc by a stirred ball mill. The grinding rate constant K’ in the equation of grinding kinetics was examined based on the grinding kinetics analysis as the same type of function of a previous paper on a vertical type planetary ball mill. The experimental particle size distribution of the ground products was obtained in various grinding conditions. The grinding rate constants K and K’ were expressed by empirical equation involving experimental conditions by a stirred ball mill. The empirical equation on the grinding rate constant was expressed in terms of a function involving the ball diameter of grinding balls, the median diameter of feed material, and Bond’s work index of material, in the experimental conditions. The values of empirical constants C1 and C₂ were 21.13 and 0.0109 on K, while C₁ and C₂ were 120.99 and 0.0192 on K′, respectively. And the particle size distribution of ground products of each test material for a given grinding time was found to be expressing the selection function (the specific rate of breakage) which was obtained from the grinding kinetics analysis. In this study, the grinding rate change on calcite and pyrophyllite was similar at the same experimental operation condition. However, in the case of talc, it was observed that the grinding rate was not increased compared with other samples.     

助磨剂与水泥的适应性及发展趋势

综述助磨剂的定义、种类及作用;分析了不同助磨剂对参加不同混合材的水泥粉磨效率的影响;介绍了助磨剂在水泥生产中的作用及原理,如Rebinde r的强度削弱理论和Mardulier的颗粒分散理论,现代学者提出的薄膜理论等;对水泥助磨剂的发展前景进行了展望.     

不同助磨剂对水泥粉磨效率的影响

选取立窑和回转窑两种熟料,在同一试验条件下掺入不同混合材,在不同掺量下磨制成若干个试样,并采用细度、比表面积及粒度分布等指标来评价不同或同种助磨剂对粉磨普通水泥、矿渣水泥和火山灰水泥的效率,通过对比分析,为助磨剂的选用提供参考依据。     

The crushing of wheat kernels and its consequence on the grinding process

This article presents the results of investigations on the grinding energy requirements for crushed and whole wheat kernels regarding different moisture levels. Two common wheat cultivars Turnia and Slade were used for tests. According to the Single Kernel Characterization System (SKCS) hardness index (HI), Turnia was classified as hard and Slade as a soft wheat (HI = 71 and 32, respectively). The results showed that the crushing of wheat kernels prior to hammer mill grinding had a significant influence on the grinding process. The average particle size of the ground material obtained from the crushed kernels of Slade was always significantly lower than from the whole kernels. A similar situation was observed for Turnia samples, when the moisture of kernels was 12, 14, and 16%. For soft wheat in particular, the highest changes were observed in the fraction of particles below 200 μm, where the crushing caused an increase in this fraction. However, this tendency was not observed for hard wheat. The specific grinding energy of uncrushed kernels ranged from 72.3 to 146.7 kJ·kg^− 1 and from 67.0 to 114.4 kJ·kg^− 1 for Turnia and Slade, respectively. The crushing caused a decrease of specific grinding energy in both cultivars. The total specific grinding energy of crushed kernels (the sum of crushing energy and grinding energy) ranged from 47.6 to 100.5 kJ·kg^− 1 and from 44.6 to 85.3 kJ·kg^− 1 for hard and soft wheat, respectively. In addition, the other grinding energy indices confirmed that crushing of kernels prior to hammer mill grinding considerably reduced the grinding energy requirements.     

Preparation of a novel vitrified bond CBN grinding wheel and study on the grinding performance

The vitrified bond CBN grinding wheels are characterized by high efficiency, high precision, and low environmental pollution. In recent years, the vitrified bond CBN grinding wheel has been widely used in manufacturing industries such as aerospace, automotive, and machine tools. In this study, a novel vitrified bond formulation containing nano SiO₂ and nano CeO₂ is selected to prepare the grinding wheel. The grinding experiments on 45# steel and YG20 alloy indicate that the grinding performance of the nano vitrified bond grinding wheel is significantly better than that of the conventional vitrified bond grinding wheel. The introduction of nano SiO₂ and nano CeO₂ greatly improves the machining performance of the vitrified bond CBN grinding wheel.     

大掺量石灰石复合水泥专用高效助磨剂的研究

对适合大掺量石灰石复合水泥的专属性高效复合水泥助磨剂进行研究是水泥工业节能减排技术开发内容之一。结合水泥粉磨与水泥水化理论,成功研制了以烷醇胺、乙基麦芽酚及脂肪酸钠等为主要组分的适合于大掺量石灰石复合水泥生产的高效水泥助磨剂,多次工业性试验表明,其效果良好。     

The effect of mill speed on kinetic breakage parameters of clinker and limestone

In this study, the effect of mill speed was investigated on the limestone and the clinker samples of Gölta? Cement Factory (Isparta, Turkey) at batch grinding conditions based on a kinetic model. For this purpose, first, six different monosize fractions were carried out between 0.850 and 0.106 mm formed by a two-sieve series. Then, S_i and B_i,j equations were determined from the size distributions at different grinding times, and the model parameters (S_i, a_T,α,γ, and φ_j) were compared for five different mill speed (fractional of mill critical speed; 55%, 65%, 75%, 85%, and 95%).The effect of the fraction of mill critical speed (φ_c) on the grinding for model parameter a_T was found to be different for two different samples: a_T=0.0344 exp(0.00301 φ_c) for clinker and a_T=0.0225 exp(0.06183 φ_c) for limestone. Additionally, it was found in this study that optimum grinding occurs at φ_c=85%, in contrast to the 70% of critical speed of the ball mill in the cement factory.     

白土矿物超细磨中助磨剂的研究

对某地白土矿超细磨助磨剂的研究结果表明，四种表面活性剂的助磨效果顺序是石油磺酸钠＞ＴＦ２７９＞三乙醇胺＞油酸钠。当石油磺酸钠用量为０．１５５％时，其－５００目产率可由７６．５％提高到８４．９％，增量为８．４％。ＮａＯＨ、Ｎａ２ＣＯ３和六偏磷酸钠三种无机盐对白土矿物亦有一定的助磨效果，当碳酸钠加入量为０．１５％时，其－５００目产率增加了７．４％。助磨剂能明显提高粉磨效率。     

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

The specific rate of breakage (S_i) 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 (S_i) 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.     

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.     

助磨剂的助磨作用及对粉体流变性能的影响

选用五种助磨剂，对四种有代表性的物料进行了助磨实验，同时测试了磨后物料粉体的流变特性。分析了助磨效能、粉体流变性能和助磨机理三者的关系。研究结果显示：当助磨剂使粉体的流动性增强、堆积密度增大时，助磨效果趋于增强     

助磨剂在开发与应用中的几个问题

助磨剂对颗粒表面起作用而达到助磨的效果。不仅要重视助磨剂的改性和降低成本的研究,还应加强复合助磨剂和生料助磨剂的研究。使用者不仅要明确掺入助磨剂的目的、用量和质量,还要从工艺上用好助磨剂,才能达到降耗增产的目的。     

Effect of motive gases on fine grinding in a fluid energy mill

A research program spanning over 30 years in DuPont has concentrated on fundamental understanding of the fluid mechanics in confined vortex fluid energy mills. Extensive internal reports and patents have documented numerous accomplishments. Direct visualization and measurement of velocity profiles, computational fluid dynamic modeling, in-line particle size measurement, and experimental study of gas molecular weight effect have resulted in optimized operation and improved energy efficiency. This paper will only discuss the effect of motive gases on the grinding performance. Helium, steam, air, and CO₂ are studied as motive gases to provide a broad range of molecular weight that determines the gas specific sonic velocity and resultant kinetic energy. The experimental results indicated that a fully developed flow in the grinding chamber is needed for the built-in air classification to control the product top size. The shape of particle size distributions is not significantly affected by the properties of motive gases. The gas/solid ratio or the energy intensity does not determine the grinding limit, rather how fast the limit is reached. It is very clear, however, that the motive gas with the lighter molecular weight has the capability to reach a finer grinding limit. Simply, helium gas will be able to grind finer than steam, steam grinds finer than compressed air or nitrogen, and they are all better than CO₂.     

Finite element analysis of grinding process of long fiber reinforced ceramic matrix woven composites: Modeling,experimental verification and material removal mechanism

A Finite element analysis (FEA) modeling method for grinding wheel and long fiber reinforced ceramic matrix woven composites (LFRCWCs) specimen was integrated and proposed in this paper. This method was adopted to analyze the grinding process of a 2.5D woven quartz fiber reinforced silicon dioxide ceramic matrix (SiO₂/SiO₂) composite. Relevant grinding experiments were conducted, whose results verified the accuracy of the FEA method. Based on the FEA and experimental investigation, material removal mechanism in the grinding process of this material was discussed and the following conclusions can be drawn: 1) the modeling method that sets the interface of fibers and matrix with the same mechanical configuration as the matrix can obtain a pretty high simulation precision; 2) ceramic matrix can be easily broken and removed by fiber squeezing caused by grinding forces thus reducing the surface quality. To alleviate this damage, grinding directions should be selected as along with the fiber orientation which generates shear stress on fibers; 3) fiber debonds are caused by the inconsistent deformations of the warp and weft fiber bundles. Grinding across the axis of the wefts is a better choice to alleviate this damage.     

Ultra-fine grinding mechanism of inorganic powders in a stirred ball mill

Recently, in various industrial processes, the need for fine particles, especially submicron-sized particles, has increased in the field of preparing raw powders such as fine ceramics and high value added products. Therefore, the research in fine grinding has gained more importance, especially, in submicron grinding. In the previous paper, a series of wet grinding experiments using inorganic powders by a stirred ball mill were performed. The grinding consumption power was measured, and the grinding rate constant, K, in the grinding kinetics equation was examined, based on a grinding kinetics analysis of experimental specific surface area with particle size distribution of ground products obtained under various grinding conditions. Also the effect of grinding aids on grinding rate constant K was investigated. It was confirmed that the grinding rate constant K, when using grinding aids improved by 1.95% and 25.6% for a 60 wt% and 70wt% slurry concentrate, respectively, when compared with the case of the absence of grinding aids. It was found that grinding aids have an important effect on increasing the grinding rate, especially for a slurry of high concentration.     

Synthesis and electrochemical characterization of orthorhombic LiMnO2 material

Well-defined orthorhombic LiMnO₂ was synthesized using LiOH and γ-MnOOH starting materials at 1000 °C in an argon flow by quenching process. X-ray diffraction (XRD) revealed that the compound showed an orthorhombic phase of a space group with Pmnm (a=2.806 Å, b=5.750 Å, and c=4.593 Å). The prepared compound was composed of particles of about 5-15 μm diameter with a bar-shape and small spherical one of about 1-2 μm. It showed very small initial discharge capacity of about 34 mA h g⁻¹ in the (3+4) V region at room temperature. However, after 12 h grinding, the LiMnO₂ delivered 201 mA h g⁻¹ in the first cycle and still delivered 200 mA h g⁻¹ after 50 cycles at room temperature. We found that the initial discharge capacity of LiMnO₂ agreed well with its specific surface area by Brunauer, Emmett and Teller (BET) analysis. Especially, the grinding treatment played an important role to activate the lithium insertion-extraction into the LiMnO₂ layer in the 3 V region.     

水泥粉磨工艺外加剂—额外效益

助磨剂的主要作用是减小破碎的阻力、防止结块、减少糊球和降低磨机内的填隙率。使用助磨剂能增加水泥产量，降低水泥生产成本，改善水泥性能。阐述了普通助磨剂与球磨机内部状况两者之间的关系，指出磨机系统以及研磨的物料特性不同，使用的助磨剂的品种及用量也不同，需要进行工业性试验，才能确定。     

Investigation of the effects of fatty acids on the compressive strength of the concrete and the grindability of the cement

In cement industry, a great energy consumption has been observed during grinding of clinker. To reduce this consumption, some waste products have been used as grinding aids.In this investigation, the effects of sunflower oil (SO), oleic acid (OA), stearic acid (SA), myristic acid (MA) and lauric acid (LA) on the fineness and strength of the cement have been examined. These aids were added into clinker in certain ratios based on the cement clinker weight and the grinding has been done for a definite time at the same condition.All of the fatty acids used increased the fineness as compared with the cement without the grinding additives. SO and OA decreased the strength significantly, LA decreased it to a lesser extent and SA increased it definitely according to the common cement. But MA did not alter the strength of the cement as much as SA. In addition, the covering of the balls influences the grinding of cement clinker unfavourably.     

CGA560增强助磨剂在水泥粉磨中的应用研究

研究了CGA560增强助磨剂在水泥粉磨中对台时产量和水泥质量的影响。试验结果表明:在磨机状况不改变的条件下,CGA560增强助磨剂的加入可提高磨机产量10%-30%;同时可有效减少过粉磨现象,优化水泥颗粒级配,提高了水泥粉磨细度及比表面积;因而使水泥强度等性能得到了明显改善和提高。     

水泥助磨剂组分对水泥与减水剂相容性的影响

讨论了助磨剂不同组分对水泥与减水剂相容性的影响,分析认为,助磨剂主要通过影响水泥水化进程和减水剂分子在水泥颗粒上的有效吸附两种方式,使相容性变差或改善,据此提出选择与减水剂相容性好的助磨剂的几点建议。