For the purpose of the shear test free of friction between a powder and a cell wall, at a high temperature, a direct shear tester with two parallel plates and electric heaters has been developed. The performance of the tester has been evaluated, and the effect of temperature on the powder yield locus has been investigated. The reproducibility of experimental data obtained by this tester is satisfactory, and the experimental procedure at a high temperature as well as at room temperature is simple. The results of the shear test at various temperatures show that the friction coefficient of powder decreases, and the cohesion of powder increases with increasing temperature.

View full abstract

The operation of the continuous thickener which was employed as a washing process for the recovery of useful chromite, was studied by use of a batch settling curve instead of a solid flux curve. The feed concentration, the feed rate and the amount of coagulating agent were fluctuated greatly during the actual operations. It was suggested that the suitable amount of coagulant was 0.2% of feed slurry from the analysis of twenty-four batch settling curves obtained over the period of a week.
In order to eliminate the inefficient use of a filter which is now employed for dewatering underflow sludge from the thickener, two-parallel settling tanks are proposed, and their operations are investigated by a batch settling curve. Since the complete solid flux curve can not be obtained in slurries with widely variable amounts of coagulant, the use of a batch settling curve may be advantageous to analyze the operation of the continuous thickener.

View full abstract

The light-weight aggregates production process aimed at the utilization of inorganic residues in municipal refuse resulted the development of pellets which were very weak. The effects of operational process conditions on pellet strength were examined, and the following results are obtained.
(1) Hydrogen gas was found to have evolved due to the reaction of water with fine aluminum metal which existed in the refuse and was ground during the grinding process. The evolved gas is considered to partly break down the pellet structure so that the pellet becomes very weak.
(2) The pellet strength is strongly dependent on the amount of water in the wetting process and the curing time thereafter. A water content of more than 10wt.% in the wetting process as well as more than a one day curing time was required to obtain a transportation resistive pellet having more than 2kg/cm² in strength.
(3) Precipitation of solutes or Al(OH)₃ is considered to contribute to an increase in the pellet strength as the curing time becomes longer.

View full abstract

Airborne dust particles from a fluidized bed and those dispersed by a high-speed air stream through a small pipe were observed by a scanning electron microscope and measured by a cascade impactor. The powder material used in this study is ultra-fine powder of kanto loam for industrial testing (JIS Z 8901, standard dust No. 11).
Airborne dust particles from a fluidized bed are mostly aggregated. A high-speed air stream can well disperse these aggregated particles. Where the pipe diameter is 1.5mm∅ and the air velocity is 57m/sec, the particle size distribution of the dispersed airborne dust closely corresponds to that specified by the JIS. But observation by a scanning electron microscope showed that this well-dispersed airborne dust still contained aggregates. Besides it seemed that these aggregates conld be dispersed into small particles without limit. Therefore, if this dust is dispersed by too large of a dispersing effect, it is in danger of over-dispersion. For instance, the size distribution of dust dispersed by the air stream through a 1.1mm∅ pipe with a 104m/sec air velocity, in which the dispersing effect is much larger than the above-mentioned condition, was smaller than that specified by the JIS.
Therefore, when powder, such as kanto loam, which has the possibility of being dispersed into small particles without limit, is used for industrial testing powder, it is necessary to carefully examine the method of dispersing it. The method using a high-speed air stream through a small pipe is very effective for dispersing powder such as kanto loam, because airborne dust can be dispersed into the equilibrium size according to the condition of the air stream, The resulting size distribution of that is very stable.

View full abstract