石こう鋳型による銅合金鋳物の鋳はだについて

抄録

  In the previous report, effect of various alloying elements in the copper-base binary alloys on the thermal decomposition temperature of gypsum which are made to contact with these alloy melts were investigated by the differential thermogravimetric equipment with 20°C/min heating rate and by the decolorization of KIO₃ solution due to SO₂ generating from gypsum. In order to confirm these results under the casting condition, 80×80×5mm specimens of pure Cu and Cu-base binary alloys with various concentration of alloying elements were cast varying the pouring temperature into the plaster mold, and compared the appearance and roughness of casting surfaces.
  The promotion of the reaction between pure Cu and Cu-base binary alloy melts and plaster molds including more than 60% of alpha gypsum were clearly recognized and the casting surfaces coarsened, when the pouring temperature exceeded the thermal decomposition temperature of gypsum which was investigated in the previous work. Cu-2%Be, Cu-5%Al and Cu-5%Si alloys little reacted with the plaster mold by the formation of stable oxide films in a short period when the pouring temperature was as high as 1,250°C. In the case of Cu-40%Zn and Cu-10%Sn alloy, as a result of insufficient difference between the temperature of thermal decomposition of gypsum and melting point of alloy, the pouring temperature for obtaining good casting surface with the plaster mold was restricted within a certain temperature range where neither the thermal decomposition of gypsum nor the miss-run of melt occur. In the case of Cu-Pb alloy which included 5-10% of Pb, because the thermal decomposition temperature of gypsum and the melting point of alloy was close together to bring about either thermal decomposition of gypsum or miss-run of melt, it was considered that it was impossible to use this alloy with a plaster mold.