There appear irregular cracks on some tooth casting, which are called the heat cracks. Then how the heat cracks come about?
The heat cracks appear during the process of solidification, when the casting is in the plastic property and deformation state. The shape of these cracks is tortuous and irregular. And its formation is mainly caused by the uneven shrinkage of the forming components. In the filling process of the parts, the matters such as the uneven distribution of mold temperature field, a relatively low forming pressure, and ineffectively feeding, will cause the uneven shrinkage of the forming parts. In the casting process, the solidification time of different casting parts are not the same, due to which there will exists two tensile stress in the opposite direction during the core pulling. If the two tensile stresses is greater than the stress effect of material under high temperature, the bucket tooth workpiece will break in the weak point, and then the heat cracks come about.
