リン酸アルミニウムを粘結剤とする金型用塗型材におけるリン酸クロムの添加効果

  The constitution and porosity changes on heating, wettability on steel surfaces and moisture absorption were investigated on metal mold casting washes using 20% aluminum dihydrogen phosphate solution (PH≃1.5) as a bonding material. Different amounts of chromium phosphate, were added into the solution for the modification of the wash composition. A comparative investigation was made for metal mold casting washes using 15% water glasssolution (Na₂O/SiO₂ mol ratio=1: 2.1) as another bonding material. </br>  The results can be summarized as follows : </br>  (1) Aluminum trimeta- and/or ortho-phosphates are the major constituents of phosphate washes whem the washes are heated up to temperatures of 700-1,000°C. </br>  (2) A non-crystalline state is easily attained by a heat treatment of phosphate washes modified by a suitable amount of chromium cation. The temperature range of the achievement is increased with increasing the cation content. </br>  (3) The crystallization of water glass washes at temperatures below the solidification range can be explained by the concepts of crystal nucleation and growth of super-cooled liquid. </br>  (4) The porosity of phosphate washes is largely increased on heating the washes modified by the chromium cation (>about 0.02 mol per 100g. of 20% dihydrogen phosphate solution) from 300 to 1,000°C. The porosity is increased with increasing the cation content, and with decreasing the content of silica flour included as an aggregate. The temperature range for the attainment of maximum porosity is 700-800°C. </br>  (5) The porosity of water glass washes decreases when the washes are heated to the crystallization temperature range. </br>  (6) The matrix of porous phosphate washes (max. porosity : about 98%) is the noncrystalline solid including finely dispersed pores (dimension??0.1mm). The effectiveness of this matrix in the prevention from chilling a cast iron can be explained by the concept of heat conduction in the system solid and pore components. </br>  (7) The contact angle on a steel surface is smaller for the aluminum dihydrogen phosphate bonding agent than for the water glass bonding agent. The decrease in the angle with time is larger for the former than for the latter : This suggests the easier formation of chemical bonds and leads to give an increased adhesion at the interface of metal mold and wash in the former. </br>  (8) The moisture absorption by the modified phosphate washes is comparatively small. This leads to decrease in the defects caused by water vapor excessively evolved from washes during the casting. process.</br>  The above results suggests the superiority in both thermal insulation and durability of the modified aluminum phosphate washes for the metal mold casting of cast iron.