한국주조공학회

The behavior of sand and mold at high temperatures was generally agreed to importantly affect the quality of castings made. By changing water content through 2,4,6 and 8%, and bentonite content through 5,7,9 and 11%, specimens have been made according to the respective composition. Specimens have been subjected to hot compressive strength and thermal expansion at 400, 600, 800 and 1000℃ respectively. The results obtained were as follows ; 1. At each temperature, thermal expansion decreased and hot compressive strength increased with the increase in water content. 2. After thermal expansion was peaked at approximately 1000℃ the contraction and maximum hot compressive strength appeared. 3. At each temperature, maximum hot compressive strength appeared 2%, 4,6% and 8% water content for 7%, 9% and 11% bentonite content respectively. 4. When 2% H_2O was added, though bentonite content was increased, hot compressive strength did not rarely change. 5. Until the thermal expansion was completed the required time was 15-18 minutes at 400℃ and 600℃, and 10-13 minutes at 800℃. At 1000℃, the required time was 7-9 minutes in order to gain the maximum expansion, after that, contraction proceeded during 3-4 minutes before expansion was completed.