Analysis of mold filling and solidification process of injection gating system in sand casting of tractor box

As shown in Figure 1, it shows the filling flow state and temperature distribution at different times when the intermediate injection gating system is adopted for the sand casting of the tractor box. It can be seen from Figure 1 that the total time of the whole filling process is 1.05s. The molten metal first fills the sprue. At 0.068s, the molten metal flows into the cavity through the transverse sprue and inner sprue under the action of gravity. Because the position of the sprue is biased towards the base of the box, the molten metal first passes through the inner sprue on the right.

At 0.173s, the metal liquid flowing from the upper end of the box and the metal liquid flowing through the boss cavity of the shaft installation converge. Because the inner sprue at the upper end of the box is far away from the sprue, the speed of the metal liquid entering the cavity is lower than that passing through the boss cavity; When the two metal liquids converge, the filling is relatively stable, which promotes the gas between the two metal liquids to be discharged from the riser, and there is no air entrainment. After 0.193s, the liquid metal flows to the rectangular boss cavity of the base under the action of gravity, and flows upward along the circular boss under the action of pressure; At 0.354s, the large plane and rectangular boss on the lower side are filled with liquid metal, and the liquid metal flows into the riser on the rectangular boss and the riser on the circular boss; At 0.488s, the large plane on the upper side is basically filled with liquid metal, and the liquid metal on the large plane finally converges at the riser and flows into the riser. It shows that in this scheme, the riser position is set correctly and the circular boss is basically filled. At marks 1 and 2 in Figure 1 (f), the molten metal converges at the intersection of the boss wall, and there are two air entrainment positions. It is predicted that casting defects will appear at this position; When the riser is not filled, only 0.05s is left. In this process, the riser set on the circular boss and rectangular boss has insufficient pouring, which may reduce the feeding function.

As shown in Figure 2, the temperature field image of the solidification process of the sand mold casting of the tractor box is shown. The solidification situation from 1.05s to 184s after the mold filling is studied. After the mold filling is completed, the liquid metal temperature begins to decrease at 1.54s and basically ends at 184s. The temperature change during solidification of sand mold casting of tractor box is an important factor affecting casting defects. It can be seen from the temperature change of the casting solidification process that at 1.54s, the temperature of the contact position between the mold cavity and the mold of the sand mold casting of the tractor box first decreases. Before 15.4s, the temperature of the molten metal in the mold cavity is between the liquidus and the solidus, and the temperature of the molten metal at the inner sprue and riser is in a high temperature state. During this period, under the action of gravity, The metal liquid in the riser and inner gate can realize the obvious feeding of the thick parts of the sand mold casting of the tractor box. It can be found from Fig. 2 (c) and temperature curve Fig. 3 that the temperature at marks 1 and 3 in the figure is greater than that at marks 2 and 4. The temperature at marks 2 and 4 decreases rapidly and solidifies before marks 1 and 3. The riser on the rectangular boss does not play a role in feeding positions 3 and 4. The post solidification of marks 3 may cause casting defects at the junction of large planes on both sides and bosses, and position 1 plays a role in feeding positions 2. As can be seen from Fig. 2 (d), since the large plane of the plates on both sides is thin, the temperature decreases the fastest, so it solidifies first; The middle part of the box body solidifies before the top. Because the sprue is far from the upper end of the tractor box body sand casting, the middle part of the tractor box body sand casting fills the mold cavity before the upper end of the casting, and the temperature drops first, which also leads to the insufficient plane feeding capacity of the liquid metal of the sprue to the upper end of the box body, which is predicted to cause casting defects on the large plane of the side plate. At 60.45s, the temperature of the upper shaft support plate inside the box is significantly higher than that of the lower shaft support plate. After the top support plate solidifies, the metal liquid in the shaft mounting boss feeds and shrinks the support plate; It is found from Figure 2 (f) that when the shaft mounting boss solidifies, the metal liquid in the sprue and the metal liquid in the riser feed and shrink the shaft mounting boss at the same time. The whole solidification process is not an ideal sequential solidification, and the riser on the rectangular boss does not play the role of feeding, resulting in shrinkage cavity and shrinkage porosity casting defects at position 3 marked in Figure 2, which reduces the quality of sand casting of tractor box.

Fig. 4 is the schematic diagram of the later solid rate in the solidification process of the mid injection Pouring Scheme. The yellow part in the figure is the last solidification part. It can be seen that the design riser at the circular boss does not fully feed the boss, so the size of the riser should be increased. It can be seen from Figure 1 (H) that there is insufficient pouring at the riser here. Therefore, it is necessary to improve the pouring system to prevent the occurrence of insufficient pouring. The solid rate of the inner sprue and transverse sprue at the shaft mounting boss is greater than that of the sprue. It can be seen that the feeding capacity of the sprue to the sand casting of the tractor box is weakened in the later stage of solidification. The solid rate of the side plate and the riser on the plate is greater than that of the internal support plate, so the feeding of the riser to the support plate is insufficient, and it is predicted that there will be casting defects on the support plate.

Observe the location and size of casting defects after solidification of sand mold casting of tractor box, as shown in Figure 5. Shrinkage porosity and shrinkage cavity casting defects mainly appear at the connection of boss, flat plates on both sides and internal support plates, which is consistent with the above prediction results. This scheme can successfully realize mold filling and solidification, but there are some shortcomings in the process scheme. In order to reduce the occurrence of casting defects such as shrinkage, measures such as improving the gating system and changing the structure of sand casting of tractor box can be taken.

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