It can be found from the analysis that simply changing the height of the pouring riser of nodular cast iron has limited effect on improving the shrinkage and porosity casting defects of nodular cast iron, and the process needs to be further optimized. Previous studies have shown that simply changing the diameter of nodular cast iron pouring riser can not effectively improve the feeding capacity of nodular cast iron pouring riser. Therefore, it is considered to change the diameter of nodular cast iron pouring riser and the length of riser neck at the same time to further overcome the barrier function of riser neck, that is, expand the diameter of nodular cast iron pouring riser and shorten the length of riser neck at the same time, The thermal effect of nodular cast iron pouring riser on riser neck is enhanced and the solidification speed of riser neck is reduced.
Therefore, keep the height of nodular cast iron pouring riser HR middle = 70 mm and HR side = 90 mm unchanged. Design optimization scheme 3: the diameter of middle riser is increased by 5 mm, the diameter of side riser is increased by 4.5 mm, that is, Dr middle = 60 mm, Dr side = 54.50 mm, and the riser neck is shortened by 2.5 mm; Optimization scheme 4: the diameter of middle riser is increased by 8 mm, the diameter of side riser is increased by 7.3 mm, that is, Dr middle = 68 mm, Dr side = 57.3 mm, and the riser neck is shortened by 4 mm;
Figure 1 shows the temperature distribution during solidification of process schemes 1, 3 and 4. It can be seen from the figure that the temperature of riser neck in scheme 1 (Fig. 1 (a)) without changing the diameter and length of nodular cast iron pouring riser is 1176 ℃, while the temperature of nodular cast iron pouring riser neck in schemes 3 and 4 is 1178 ℃ and 1176 ℃ respectively. This shows that the design of scheme 3 increases the temperature of riser neck and reduces the cooling rate of feeding channel in the same period of solidification, but scheme 4 does not produce this effect. Combined with the prediction results of shrinkage and porosity distribution simulated in schemes 3 and 4 in Fig. 2, it is found that both schemes eliminate the shrinkage and porosity casting defects in scheme 1. Especially in scheme 3, because the temperature of the pouring riser neck of nodular cast iron is increased, the cooling speed of the riser neck is reduced, and the action time of the pouring riser of nodular cast iron is prolonged, the volume of shrinkage casting defects in nodular cast iron is significantly reduced. Although scheme 4 also effectively eliminated the shrinkage casting defects originally located in the overlapping action area of the middle and side risers, the area near the connecting hole of the upper control arm of nodular cast iron deviated from the riser feeding channel and failed to be fully fed, resulting in large shrinkage casting defects (Fig. 2 (b)).