Abstract
It has been stated that the defects of castings such as buckle, scab and rat tail are caused by cracking of molds which is resulted by excessive thermal expansion and contraction at the mold-metal interface. However, cracking of molds is also introduced by the high hot-strength of molding sand, gas pressure created in the mold and the properties of washing materials and etc.
This study was made on the relation between cracking of core sand and its strength at high temperatures.
Results obtained were shown in the followings :
1. Under the same testing condition, natural silica sand shows higher hot-strength and less cracking than the synthetic.
2. The sand having wide range of grain distribution and containing much moisture and clay has shown high hot-strength and less mold cracks.
3. Bentonite bonded sand gives higher hot-strength and less cracks than in clay bonded.
4. Generally speaking, increasing of hot-strength will reduce the degree of expansion and the occurence of cracks.
