CO₂型の崩壊性におよぼすマグネシヤ添加の影響

抄録

  CO₂ mold was developed by the foundry industry for master molds and cores, but it has a disadvantage in that since it is bonded with sodium silicate, collapsibility is poor. Some properties of CO₂ mold, with the addition of several kinds of MgO systematically differing with calcining condition, such as the compressive strength, surface safety index just after gassing and after 24 hrs. holding, the retained strength after heating for an hour at elevated temperature, and the collapsibility in a practical test, were investigated. The products formed in the CO₂ sand by the addition of activated MgO calcined at low temperature were investigated by means of X ray diffraction.
  The results obtained are as follows:
  (1) Addition of activated MgO calcined at low temperature did not influence the above-mentioned propeties of mold at room temperature, while addition of MgO calcined at temperatures over 1,000°C had bad effect on these properties.
  (2) Addition of activated MgO calcined at low temperature considerably improved the collapsibility of CO₂ mold. However, there was no improvement by the addition of MgO calcined at temperatures over 1,000°C. Therefore, it was confirmed that activated MgO calcined at low temperature was suitable for collapsibility.
  (3) Two compounds of 2MgO·SiO₂ (Folsterite) and MgO·SiO₂ (Clinoenstatite) with high melting points were produced in the CO₂ mold with the addition of activated MgO calcined at low temperature and it seemed that these compounds improved the collapsibility of CO₂ mold because it prevented the sintering of CO₂ sand.