The figure shows the numerical simulation diagram of mold filling and solidification process of sand casting with central top injection Pouring Scheme. When the pouring time t = 0.2S, the molten metal just fills the pouring system. It can be observed that the sprue nest has an obvious buffer effect on the molten metal. Compared with the initial pouring speed at the gate, the molten metal speed at the front end of the mold filling has slowed down significantly; When t = 1s, the metal liquid enters the sand mold and begins to fill the mold cavity. The three metal liquids injected into the mold cavity in three internal sprues have converged. It can be seen from figure (b) that there is no splashing and entrainment of metal liquid when the three metal liquids converge, indicating that the flow rate of metal liquid at the confluence is not high and the mold filling is stable; At this time, the tooth shaped part at the bottom of the cavity has been basically filled, and the liquid level rises with the circumferential flow of liquid metal in the cavity, which is beneficial to the floating of impurities in the liquid metal; When t = 2S, the mold cavity of the gear blank casting has been completely filled with liquid metal, and the liquid metal begins to flow into the three insulation risers at the same time. The filling process of the sand casting takes only 2S. By observing this figure, it can be seen that the metal filling process basically follows the order from bottom to top, and the filling process is fast and stable, which is conducive to reducing the oxidation of the liquid metal; When t = 2.3S, the riser has been filled with liquid metal, and the pouring and filling process is over.
Figures (E) and (f) show the cooling and solidification process of sand castings; When t = 190s, except for the area near the riser, other parts of the metal of the sand casting have been cooled and solidified; It shows that sand castings solidify from far to near along the riser direction, and there is sufficient liquid metal in the riser to supplement the volume shrinkage space of sand castings; When t = 503s, the sand casting and riser molten metal are completely solidified. The solidification process shows that the riser position arrangement is reasonable and the feeding effect is good, which verifies the rationality of the designed riser.