ベントナイト粘結生砂型の結合構造と湿態性質との関係

抄録

  Generally, the bonding structure of green molding sand controls the green properties of sand mold. Many investigators have considered that the bonding material on sand grain surfaces adhered to the surfaces smoothly and uniformly.
    Some investigators have studied the distribution of bonding material on sand grain surfaces and explained that adhesion was not smooth, but they did not go so far as to discuss the relation between green properties and bonding structure of sand mold.
    The authors have considered that the observation of grain surface and its bonding structure by stereoscopic microscope will not be difficult when glass beads are used with water-bentonite mixture as bonding material. Accordingly, we first observed the bonding structure and green properties of glass beads-water-bentonite mixture. Next, we used silica sand and studied the relation between its bonding structure and green properties. The results were as follows:
  (1) Bonding structure of green glass beads mold was observed more easily than sand green mold by stereoscopic microscope, because there was no need to consider the influence of grain size, fineness of sand and distribution of grain size which must be considered for silica sand.
  (2) Surface hardness and green compressive strength increased with the increase of bonding material in a fixed water content of the bonding material. We considered the reason behind this to be the gradual increase of the bonding material in the gaps preventing the movement of grains.
  (3) Bulk density increased according to the increase of bonding material in a fixed water content of bonding material. The reason for this was considered to be the gradual increase of the bonding material in the gaps with the increase of the bonding material.
  (4) Permeability decreased with the increase of water content of the bondig material. We considered the reason to be in that more bonding material got into the gaps with the increase of water content of the bonding material.
  (5) Permeability decreased when there was little water in the bonding material, or when the proportion on fine grains in coarse increased. We considered the reaason to be in that powdered bentonite or fine grains got into the gaps.
  (6) In both glass beads and silica sand, permeability was small when there was plenty of bonding material, but the difference in permeability between abundant and little bonding material was greater when glass beads were used than when silica sand was used.
  (7) When glass beads were used, there was no large difference between three ramming piece and high pressure compacted piece. We reasoned that this was because spherical glass beads were compacted densely with comparatively small pressure.
  (8) When the ratio of coase to fine in the molding sand was almost the same, compactibility of the mixture was greatest in both glass beads and silica sand.