It is well known that powder characteristics of high-performance ceramics have great influence on the sintering activity of the powders and the properties of the final products. Since grinding process is essential for such materials in many cases, it is important to grasp the change in powder characteristics by grinding. In this study, Si3N4 powder was ground with a vibration ball mill under several experimental conditions to examine grinding characteristics such as wear behavior of a mill and grinding media, particle size distribution, specific surface area, and X-ray diffraction intensity. Consequently the following results were obtained; ultra-fine grinding of Si3N4 was possible using a vibration ball mill and grinding behavior was considerably affected by the materials constructing the mill and the grinding media (especially by the hardness of the materials).
†This report was originally printed in J. Soc. Powder Technology, Japan, 20(2), 82-85 (1983) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
The effects of particle shape and operating conditions on the sieving process were experimentally studied and the passing characteristics were discussed. Cylinder particles of unity in aspect ratio were batchwise sieved by a reciprocal shifter. The retention on a woven wire sieve of square mesh was measured and the sieving rates were obtained. The behaviour of retention with sieving time were classified into two types according as the cylinder diameter D was near the mesh size a or D « a. In the latter case, the cylinder was easily screenable and the retention exponentially decreased with sieving time. The sieving rate coefficient was independent of the initial charge. On the other hand, in the former case, the sieving rate was initially influenced by the particle mass charged on the sieve and the sieving process deviated from the exponential decrease. The sieving rate was quantitatively associated with the geometrical shape of cylinders. The sieving rate coefficients of easily screenable cylinders or in the earlier period of sieving were inversely proportional to the third power of the cylinder length. The probabilities of the cylinder passing through an opening were calculated by use of geometrical probabilities and compared with the experimental results. The number of trials of passing per unit time was almost inversely proportional to the cylinder length. Furthermore, the sieving characteristics of a set of sieves were analyzed on the basis of the rate coefficient obtained previously. It was possible to predict the change of each retention with sieving time, sufficiently. The correlation between the equivalent spherical diameter of cylinder and 50%-separation diameter measured by the multistage sieving gave that the separation diameter mainly depended on the cylinder diameter. In the vicinity of centrifugal effect of 1.3, the sieving rate was maximum and the empirical relationship presented by previous workers for the optimum shifting conditions was applicable to the cylinder particles.
†This report was originally printed in J. Soc. Powder Technology, Japan, 20(1), 8-14 (1983) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
The flow behavior of particles was studied with particular attention to the effect of the inclination of a storage vessel and/or turn table of a table feeder. The effect of a converging hopper of the storage vessel and the effect of scrappers were also studied. It was found that the particle flow was intensely distorted by slight inclination (as small as two degrees) of the storage vessel or the turn table. The distortion is found to be more intense for the vessel inclination than for the table inclination, and becomes more intense as the inclination increases. The discharge rate of the feeder increases exponentially with the angle of inclination. The flow distortion was, however, controlled by using scrapers at suitable positions. It was also found that a new theoretical equation for a cylindrical vessel was successfully adapted for estimation of the effect of skirt clearance on the discharge rate of a table feeder.
†This report was originally printed in J. Soc. Powder Technology, Japan, 20 (8), 479-485 (1983) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Pneumatic conveying of granular materials generally requires a great deal of power consumption in spite of its excellent advantages which are not obtainable with other transport methods. The purpose of this study is to examine the behavior of pneumatic conveying systems from both theoretical and experimental perspectives and find out an optimum way of reducing power consumption. It is concluded that the application of vibration to pipes or bends is effective for this purpose. In addition several improvements to obtain economic conditions are discussed.
A new apparatus for the measurement of particle size distribution based on the unbalance caused by centrifugal sedimentation was made on an experimental bases. The size distributions obtained by this method with a constant revolution of the rotor were compared with those measured by other methods using the same sample. Furthermore, in order to shorten the measuring time and expand the measuring size range, some additional attempts were conducted with a linear acceleration followed by a constant revolution of the rotor. They gave similar results of size distribution to the measurements at a constant revolution.
There are many works that refer to the history of grinding implements1～6), but they are restricted mainly to the origin of Western wheat flour milling technology as a professional activity, and do not always pay attention to domestic use. It is an interesting fact that almost all the ancient grinding implements devised by humans throughout history have continued to be used domestically even after the advent of more efficient specialized ones. We can find many examples of this in Japan as well, and some of them have survived to the present day. On the other hand, owing to the recent dramatic change in our life-style, the familiarity of these implements is being rapidly lost in Japan. Therefore, the present work is an attempt to record them in an intelligible form, and to collate them with the Chinese and European ones from the historical viewpoint. Another point to be cited is the very old, traditional grooving of the rotary quern which survives now in Japan. The so-called "counterclockwise revolving, eight-quarter grooving pattern" is the same as that which existed in Europe and China during the Roman period. Though we do not know where and when it originated as yet, this fact is decisive proof of its transmission.
Adhesion forces generated at a contact point between spherical and plate specimens of potassium halides, commercial soda-lime glass and Pyrex glass were estimated by using an electrobalance, and adsorption isotherms of water vapor and methyl alcohol on these samples were also measured. The thickness of a liquid bridge and the pressure at which a capillary condensation occurs for the first time have been investigated using porous glasses each of which has a monodispersed pore radius. The following conclusions have been deduced from the comprehensive comparison of the obtained results. The adhesion forces under low and high water vapor pressures are suggested to be ascribed to hydrogen bond and liquid bridge, respectively. A marked increase of adhesion force observed in the pressure range 0.6 < P/P0 < 0.85 is due to a transformation from hydrogen bond to liquid bridge and due to a change in the physical property of condensed liquid. The thickness of the liquid bridge at P/P0 = 0.6 is presumed to be 29-37Å
As one of the methods of measuring the pore distributions, the equilibrium moisture content curve of porous powder was investigated owing to the facility in the measurement. A simple and reasonable method was developed for calculating the distribution from an adsorption isotherm. It was shown that the distribution could be evaluated by an equation which contained two coefficients. The coefficients depend only on the characteristics of adsorbate, and these values can be calculated from a t-curve. Since it seemed impossible to measure t-curve on the equilibrium moisture content, the t-curve on water vapor adsorption was determined instead of that on moisture content. It was then shown feasible to apply the curve for pore distribution analysis by the equilibrium moisture content curve.
The dynamic mixing power required for mulling process of green mold sands was measured by using various types of kneaders and binding materials. A series of tensile tests for the green mold sands were carried out. The surface structures of the sands were also observed by a scanning electron microscope. The state of mulling of the sands was found to be successfully correlated with the tensile strength, the tensile breakup energy and the compression characteristics of the sands. It was also found that the completeness of mulling process could be assessed by observing the steadiness of the power for mulling, and that it could be evaluated in terms of the tensile breakup energy. The more the power for mulling was required, the better the state of mulling was.