After the sand casting frame is poured, it is cooled in the mold cavity until the central riser reaches a certain temperature, and then it is pumped into the heat treatment furnace for heat treatment. The whole simulation ends when the box is pumped and the sand is dropped. In the simulation, the boxing time of sand casting frame is 12 days after pouring, and the change of residual stress in the cooling process of bamboo slips is analyzed.
The figure shows the equivalent stress distribution of sand casting frame at several different times during cooling. Because the sand casting frame takes half of the model in the calculation process and imposes displacement constraints on the symmetry plane, the stress on the symmetry plane is relatively large, which is inconsistent with the actual situation. The stress distribution on the symmetry plane can be ignored in the analysis. In other parts, it can be seen that the root of the large riser is the part with the most concentrated stress. Before box beating and sand dropping, the stress value is the highest, close to 250Mpa. This distribution is very unfavorable to the subsequent cutting riser. Stress concentration also exists in the transition fillet and the root of small riser.
The stress at the root of the large riser may increase sharply during box beating and sand dropping. This is mainly because after the constraint of the sand mold is lifted, the change of the stress at the root of the riser of sand casting is mainly affected by the change of temperature. After sand dropping, the riser root still at a high temperature is equivalent to being subjected to a rapid cooling effect, so the stress will increase sharply by a certain value. The stress level at the transition fillet decreases slowly after the sand mold is released, and the stress value will continue to increase during the subsequent temperature drop. After sand falling, during the process of handling and cutting, the position of stress concentration marked in Figure B must be very careful, and cracks may appear if handled improperly.