Classification of Oolitics by Different Calcination Temperatures of Bentonite and Its Relationship to Green Sand Properties

Abstract

  The generation of oolitics confers green sand with special characteristics such as water absorbency, anchoring, and cushioning effects, enabling it to be used as molding sand. As the form of the oolitics varies according to the temperature at which they are generated, each of these characteristics is thought to manifest at a different temperature, which was investigated in the present research.

  Oolitics generated at various temperatures were prepared in a bentonite calcination test and observed by scanning electron microscopy and X-ray diffractometer. The water absorbency, anchoring, and cushioning effects of green sand with the prepared oolitics were then determined.

  This led to the following findings.

  1) Water absorbency effects were demonstrated by water absorption to porous sites within the oolitics. Two porous forms were detected in this study. Below approximately 717℃, bentonite becomes partially inactive and turns into oolitics, which can easily be peeled off.

  In this oolitics, water was absorbed into gaps in the oolitics film. In contrast, in oolitics generated at temperatures from around 717℃ to 1160℃, water moved into sites that had undergone foaming.

  2) Cushioning effects were observed from around 717℃ to 1300℃ when oolitics underwent foaming in fusion tests.

  3) Anchoring effects were observed from around 717℃ when oolitics adhering to the casting sand were generated, up to around 1160℃ where the sand vitrified and became smooth.