自動車用鋳鉄鋳物の砂膨張欠陥に及ぼす鋳物砂の焼結効果

抄録

  Expansion defects such as scab or fin are mostly studied from the standpoint of binder contents and properties. In this paper, these defects in gray cast iron for automobiles were examined with green sand molds and shell molds, particularly from the point of view of feldspar content in silica sand.
  Hot toughness of molding sands increased by increasing the feldspar content in silica sand. This increase in hot toughness was caused by sintering of feldspar grains. It was effective for scab defects in green sand molds and shell molds. Where metal penetration and finning appears on the surface of shell cores which are surrounded by heavy metal sections, feldspar additions have cured the problem in most casess. For example, adding 11% feldspar to silica sand reduced scabs on surfaces of shell cores which were used for transmission cases (about 25kg in weight). In the case of water jacket cores for cylinder heads and diesel engine blocks, it was necessary to add up to 11-37% where most severe finning and penetration occured. When these castings had extremely few holes for ejecting core sands, it was necessary not to add more than 27% of feldspar, because the jacket cores became less collapsible as a result of graze caused by fusion of the feldspar.