According to the trial production and simulation results of the two schemes of bottom injection and top injection, the bottom injection filling is stable and easy to discharge slag, but the slag collecting riser should be added at the top of the cylinder, the pouring system solidifies too early, the long fork of nodular cast iron can not get external feeding, and the self feeding of long fork of nodular cast iron can not fully meet the feeding demand; The top injection mold filling is rapid and can maintain a high temperature, but the slag discharge and exhaust conditions are not good. The central riser is connected with the inner sprue to ensure that the inner sprue condenses late and provides a certain feeding for the nodular cast iron long fork. The two square risers do not play a sufficient feeding role. The slag collecting risers of the two trial production schemes are too large, which is easy to reverse the nodular cast iron long fork in the solidification stage. Considering the two schemes comprehensively, it is decided to integrate the advantages of the two trial production schemes, and adopt the double-layer stepped pouring method. The transverse sprue is similar to the central large riser of top injection type, and pouring instead of pouring. A small slag collecting riser is set at the top of the cylinder and the front end of the upper fork arm, without additional feeding riser, and ensure that the slag collecting riser solidifies within 10s after mold filling.
The improved process scheme is shown in the figure. The pouring position is set at the upper and lower large hot joints of the cylinder to artificially change the temperature field distribution in the solidification process of nodular cast iron long fork, trying to realize sequential solidification, so that the final solidification area of nodular cast iron long fork is well connected with the pouring system. A slag collecting riser with a size of 30mm is placed at the top of the cylinder and the front end of the upper fork × 50mm × 20mm； The sprue runner still uses a hollow foam runner with a diameter of 45mm, and the runner height is 250mm. The solid foam runner with hollow hollow runner and vertical placement is 60mm. × 60mm × 240mm, the runner can ensure the late solidification of the inner gate and maintain the feeding at the hot joint; The size of internal sprue is 60mm × 40mm × 40mm. In order to prevent reverse pumping, the variable section form is adopted, and the section size of the inner gate is 40mm × 30mm。
By analyzing the trial production results and simulation results, the improved pouring scheme of nodular cast iron long fork EPC is designed. The compensation measure of embedded ferrochrome cold sand is adopted to remedy the centralized shrinkage and porosity of the improved scheme. Finally, the optimal scheme to minimize shrinkage and porosity is obtained and put into production for verification.