CO
2 Process sands with different fundamental materials and different additives were prepared and their residual strengths after baking were examined. On the other hand, variation of void, free thermal expansion contraetion, and microscopic deformation of bonding structure were examined.
In this investigation the author tries to clarify the cause of collapse deterioration through analysis of the deformation of bonding structure and plans the improvement of collapsibility.
The results obtained were as follows.
(1) Residual strength was maximum at about 200°C, 800°C in baking temperature. The peak on the lower side occurred through vaporization of moisture, and the peak on the upper side did as follows:
Sand grains were coated with molten binder at high temperature, succeedingly, bonding bridge was narrowed and the contact point increased, during the cool moulding sands were not cracked.
(2) About CO
2 process sands, the expansion contraction curves were compared with the fundamental type. (Fineness grade No. 6 Silica Sand, Molecular ratio≒2.0 sodium Silicate binder).
It was found from the contraction state in the curves that the residual strength was decreased when the fluidity of sand grain with molten binder was checked as well as when it was accelerated.
The former contributes to the separation of bonded point, and the latter is due to the formation of non-uniform structure through severe sintering and void enlargement.
(3) For an over-all improvement of collapsibility a combination of hygroscopic and mineral additives appears to be the most effective.
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