Some experimental observations are presented here worked on models concerning the relationship betwen the packing characteristics and the shrinking behavior of the packed bodies, constructed of contractile powder and non-contractile powder, and subjected to special treatment such as drying or sintering.
Steel balls each of 1.43cm in diameter were used as models for non-contractile powder, and sugar balls each of 1.39cm in diameter as models for contractile powder.
The mixed bodies having the 1-x volume parts of steel balls and the x volume parts of sugar balls, where x is varied as 10, 20…90 respectively, were kept in the measuring container illustrated in Fig. 1 and Fig. 3.
Three types of regular packing arrangements, cubic, orthorhombic, and double-nested, were chosen in these tests as shown in Fig. 3 and Fig. 5.
When the experiment was started, the water was regulated at constant temperature, and was poured into the container vessel to dissolve the contractile model powder (Sugar balls). The regular arrangement in the packed bed was affected and the heights of the bed were brought to contract.
These contracting actions varied according to the dissolving action of the water to the sugar balls, that is in proportion to the dissolubility of the sugar balls and the temperature of the dissolving water. The resulting contraction is remarkable.
The mathematical statement in these behaviors can be expressed as (6) where εx' is contracting strain of the packed bodies, ε'mx the theoretical strain calculated from the additivity of two components, Va' the ratio of packed volume to real volume of the powders, and V'ma the same ratio of additional value.
Based on the above equation (6) the following argument is possible. The cubic arrangelnent could be destroyed easily, but the double-nested arrangement is stable on account of the bridge forming properties, and the orthorhombic arrangement lies midway, that is the latter could be more liable to distruction than the double-nested structure, and more stable than the cubic structure.
These numerical statement are shown in Fig. 10-12.
