Abstract
With a view to examine the acceptability of conventional practice of collapsibility testing of the carbon dioxide sand mold, where the standard specimen of the sand mold first heated up to a given high temperature and then cooled down to a room temperature, experiments were conducted by checking the compressive strength. In these experiments, the cores made of the carbon dioxide process were used to obtain several ring casting of different metals with different thicknesses in order to check the process of temperature rise and the casting conditions which result in achievement of four different levels of nearly constant temperature of 250°C, 500°C, 830°C and 1130°C. Then, pouring was carried out to the ring mold, and castings obtained were subjected to cooling down to the room temperature, followed by wedging test, by which the collapsibility of the core was examined, according to the final number of wedge driving for perfect penetration of the wedge. Other measurements were made on the standard specimens of the carbon dioxide mold which have been heated up in an electric furnace in nearly a same process of the temperature rise by heating as in the core during the preceding cast testing, to determine the residual strength. Finally, comparison was conducted with respect to the obtained results between residual strength testing of the standard specimen, and wedging test of the core often test castings and got the following conclusions;
1) Residual strength of the tested standard specimen offers a good guide to estimate the collapsibility of casting core, provided that heating has been made within a temperature range below 830°C, where no substantial sintering is seemed not taking place.
2) The core, checked by the collapsibility test where heating occurer up to high temperature exceeding 1000°C cannot determind with respect to its collapsibility from the residual strength, obtained by testing the standard specimen, because penetration of cast metal sintering of sand grain are likely to take place.
