Yoshiteru Kanda

Relationships between particle size and fracture energy or impact velocity required to fracture as estimated from single particle crushing

Abstract The relationships between fracture energy and compressive strength of sphere have been theoretically studied from the viewpoint of fracture mechanics using experimental results of crushing of spheres. Two kinds of glassy and five kinds of natural materials were examined. Specimen diameter ranged, from 0.5 to 3 cm. Combining the above with the size effect of strength reported in the previous papers, the authors obtained a new equation for the change in fracture energy with size. The specific fracture energy increased with a decrease in size and, with natural materials, when size was less than 500, μm, the specific fracture energy increased rapidly. Even if the kinetic energy of a particle with a size of 100 μm was converted completely into fracture energy, the impact velocities required to fracture were calculated to be 13 ∼ 225 m/s for the samples used in this report.

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

Abstract 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 mills 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.

A consideration of grinding limit based on fracture mechanics

Abstract In general, it is well known that the energy efficiency of a grinding process decreases with decrease in produced particle size, increase in grinding time, or increase in input energy. In this paper, based on the experimental results of single particle crushing, we define the size reduction energy as the elastic strain energy which is stored in the solids up to the instant of fracture. Assuming that the kinetic energy of a grinding medium was converted completely into fracture energy, the efficiency of size reduction evaluated by the produced specific surface area has been calculated.

A fundamental study of dry and wet grinding from the viewpoint of breaking strength

Abstract The preparation of fine powders by grinding may be accomplished by either a dry or a wet process and the differences between these have been discussed. In general, it is well known that there are many mechanical properties which have direct effects upon the grindabilities of solids. Breaking properties, especially, are related to the grindabilities. A practical grinding process involves every breaking condition and these are complex and cannot be measured directly. In addition, the difference in breaking strength in different atmospheres is also known. In this paper, bending tests were carried out on glass material in order to investigate the difference between dry and wet grinding. The quantitative effects of water on bending strength, and of crack propagation on glass surface, and the relationship between the bending strength and the number of cracks were studied fundamentally. As a result, it was found that the wet strength is less than the dry, the crack length in water is larger than that in air and a wet grinding process is useful from the point of view of strength of solids.

Study on industrial catalyst for bituminous coal liquefaction

Abstract The catalyst activities and the grinding characteristics of natural iron compounds and sulfides were investigated with the aim of preparing an industrial coal liquefaction catalyst for the NEDOL process large-scale plants. From the viewpoint of economy, since these plants are to be located at coal mining sites, it is economical to utilize a natural compound produced in the vicinity of plant site as the catalyst raw material. The coal liquefaction, using an electromagnetic agitation type autoclave, suggested that iron sulfide (pyrite) is the best raw material for the catalyst, because it contains higher iron and sulfur for producing pyrrhotite, an active component under the reacting conditions, and thereby, it needs no pollutant sulfur addition. However, taking into consideration the grinding characteristics, iron sulfide is not thought to have good grinding characteristics in a fine particle zone. Co-pulverization, using iron sulfide and coal, improves the grinding efficiency, the abrasion and the catalyst activities, so that the industrial catalyst preparation can be realized by means of the co-pulverization method.

Chapter 12 Comminution Energy and Evaluation in Fine Grinding

Publisher Summary This chapter highlights comminution energy and evaluation in fine grinding. The purposes for comminution are to liberate minerals for concentration processes, to reduce the size, to increase the surface area, and to free the useful materials from their matrices. Comminution is an old mechanical unit operation for size reduction of solid materials and an important operation in the field of mineral processing, the ceramic industry, the electronics industry and so on. The energy efficiency of comminution is very low and the energy required for comminution increases with a decrease in feed or produced particle size. Research and development to find energy saving and the energy required in comminution processes have been performed. In design, operation and control of comminution processes, it is necessary to evaluate the comminution energy of solid materials. In general, the comminution energy (i.e., the size reduction energy) is expressed as a function of the particle size of feed and product. In addition, the chapter also presented various Laws of comminution energy including Rittingers law Kicks law Bonds law, and Holmess law.

The compressive crushing of quartz in a powder bed—the effect of feed size on grindability

Abstract In this paper, stress conditions in a roller mill were simulated by slow compression of quartz powder beds between parallel platens and compressive crushing of powder beds was also carried out to gain an understanding of the action of a roller mill. The effect of the feed size on the crushing resistance was investigated when the applied load and mass of feed were constant. It was found that the specific energy to produce the crushed products increased essentially with a decrease in the feed size.

A compressive crushing of powder bed — a consideration of size distribution of product and specific energy to produce fine particles

Abstract Roller mills have come to be actively used for preparation of fine particles. In this paper, stress conditions in roller mill were simulated by slow compression of quartz powder beds between parallel platens and compressive crushing of powder beds was also carried out to gain an understanding of the action of a roller mill. The effect of the mass of feed and the applied load on both the probability of crushing and the size distribution of crushed product were studied. We define the crushing energy as the energy input in a powder bed and the specific crushing energy to produce fine particles was calculated experimentally. It was found that the mean size of crushed product decreased with decrease in the mass of feed and with increase in the applied load (probability of crushing), but the probability of crushing with the maximum specific energy to produce fine particles was observed.

An examination of ultra-fine grinding by preferential grinding

Abstract Laboratory-scale ball mill tests were carried out for the purpose of quantitative investigation of the grindability and preferential grinding of each component of a binary mixture of materials having different properties. The samples used were limestone and quartz. Limestone was selected as the less resistant and quartz as the more resistant material to be used. In a simultaneous grinding of these materials, it was found that the overall rate of simultaneous grinding and those estimated for the mixture were almost the same, but the grindability of limestone was higher when it was ground in a mixture than when it was ground separately. Quartz was useful for ultra-fine grinding of limestone.

Effects of cracks on bending strength of glass

Abstract In general, it is well known that there are various mechanical properties which have direct effects upon the grindabilities of materials. Breaking properties, especially, are related to grindabilities. A practical grinding operation involves every breaking condition. These conditions are complex and cannot be measured directly. In this paper, bending tests were carried out on glass material in order to investigate the relationships between the bending strength and the number of cracks. As a result, it was found that the strength decreases with an increase in not only the crack length but also the number of cracks.