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, in particular are related to the grindabilities.
In this paper, creep tests were carried out continuously for three hours on glass material under a bending condition in order to investigate the difference between dry and wet grinding. A crack was formed on the center of the tension side of the test piece by the Vickers diamond of the Micro Hardness Tester with an automatic loading system. The quantitative effects of water on the crack propagation on the glass surface and the creep property of glass were investigated.
The results are summarized as follows:
1) The crack length in water is larger than that in air.
2) The ratio of both varied with the hold time and the bending stress.
3) Based on the above, it could be presumed that there is a bending stress at which the specimen willl fracture in water but not in air.

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The power requirement characteristics of an agitating impeller in a spherical agglomeration tank were investigated. Two spherical agglomeration systems were adopted in the experiment: coal-heavy oil-water; and CaCO₃-CaCl₂aq. soln. -CCl₄. The uniform suspension in the tank was maintained through the agglomeration process.
During the progress of spherical agglomeration, the particle size distribution of agglomerates shifted to the large size range, and the compaction of the agglomerates was promoted. The power requirement increased with increasing mean agglomerate size, with the bulk volume of agglomerates in the slurry, and with the density of the agglomerate.
The empirical equation, which shows the relationship between the ratio of the power number in the spherical agglomeration to that in the agitation of the disperse medium without agglomerates and the suspending conditions of the agglomerates, was obtained.

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To investigate the shape effect of particles on their static and dynamic characteristics, the void fraction ε of a packing bed in a cylinder and the discharge rate V_o of particles through a circular orifice were measured by using many kinds of materials differing in particle shape, size d_p and density ρ.
The particle shapes for each material were evaluated by a pair of shape indices φ and ζ. These indices were defined as a measure of circularity and smoothness of a particle profile in our previous paper. The experimental results were discussed using the multiple regression analysis.
The following experimental results were obtained: (1) The void fraction ε depended on the microscopic shape index ζ of each particle rather than on the macroscopic one φ.: (2) The term V_o/(√gd_p^2.5), which represents the discharge characteristics of particles through an orifice, could be correlated as a function of ζ^5.94 and (D_o/d_p)^2.8, regardless of φ.
As a result, it was confirmed that the static and dynamic behavior of particles was closely connected with the surface roughness of each particle.

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