The design principle of the pouring system is that the mold filling is stable, the temperature gradient of the molten metal in the mold cavity is reasonable after the mold filling, the feeding channel of the riser is unblocked, the utilization rate of the molten metal reaches the maximum limit, and the casting pouring mode is generally divided into top injection, bottom injection and step injection. It is concluded that the filling sequence of sand casting and EPC is quite different in the same filling process. At the same time, the energy loss of liquid metal front in EPC is much greater than that in sand casting. When the lost foam casting is poured, the foam pattern fills the sand box. The high temperature molten metal must be decomposed and vaporized by EPS before filling the cavity occupied by the sand box. The main influencing factors of EPC process are as follows;
(1) The decomposition rate of EPS under the action of heat at the flow front of liquid metal filling.
(2) The rate at which the products of EPS pyrolysis escape from the sandbox through the coating.
It has been proved that during the filling process of liquid metal in EPC casting, the high temperature liquid metal is filled from the inner riser to the surrounding and gradually fills the whole cavity. We can use the modeling function of UG software to make several common ways of annotation
There are two forms of shallow injection system: open and closed. Shenyang University of science and technology thinks that the resistance section to control the casting speed of EPC should be in the straight channel, and the section area of the straight, cross and internal channels should gradually increase. Through the throttling of the sprue, the liquid metal starts to fill the casting through the cross sprue and the inner gate. The mold filling can be relatively stable, and the inner diameter of the sprue of the open gating system becomes smaller. In this way, a relatively small amount of liquid metal can be used to establish a higher static head. The high static head is very helpful to reduce the back spraying and improve the casting yield. The characteristics of the open gating system are as follows:, It is the sprue that controls the liquid metal flow, that is, the minimum section of the whole gating system is located at the top of the sprue, and the area of each sprue increases gradually.
However, some scholars think that in EPC, the filling speed of liquid metal should be kept constant during the filling process. During the pouring process, the EPS foam in the sprue can be decomposed quickly and vaporized. The metal liquid can not be filled with straight track in a short time, and a certain static pressure head is established. During the pouring process, the molten metal is also kept in full state, which is conducive to slag blocking. The difference between the closed injection system and the open gating system is the metal liquid flow in the closed gating system. On the inner gate of the minimum section, from the straight gate to the cross sprue to the inner gate, the first level of the cross section becomes smaller.
When the closed type annotation system is filled, the liquid metal can reach a high speed after entering the runner, and has great momentum after reaching the inner gate. After the metal liquid begins filling the cavity, the inner gate is centered and diffused to fill around. The speed is very fast. However, because the filling of the metal liquid on the transverse runner frame is hindered by the pressure of the foam air gap, the liquid metal can not be filled quickly. There is a great difference in the time between the pouring of molten metal and the internal gates. In the near gate, the flow rate of the molten metal is the largest and the filling speed is fast. The internal gate of the runner away from the runner must wait until the foam is decomposed to reach the metal liquid and the flow rate is the smallest. The result of different internal gate flow is the confusion of the metal liquid filling and the release of the EPS decomposition product. Disorderly. However, in the whole filling process, the liquid metal has been continuously filling the whole pouring system, the liquid metal will not break, and the slag blocking effect is the best. The air gap at the front of the liquid metal is very small in the direct sprue. When the mold is filled to the transverse sprue, it begins to increase. After entering the casting cavity, the air gap further increases, and the air gap pressure also increases.
In the process of using the open gating system, the liquid metal can fill the whole cross sprue earlier than the liquid metal in the closed gating system, and the follow-up liquid metal can also fill the area filled by the front metal quickly, which makes up for the heat loss of the front metal. In this way, the temperature of the liquid metal in the sprue drops less. Moreover, the metal liquid at the filling front is limited, and the decomposing gasification and escaping of EPS need a certain pressure and time. Therefore, the filling of metal liquid is relatively gentle, and the filling speed is slow. But in the same way, the filling of molten metal in the inner runner is still in order, and the front of molten metal is chaotic, which is easy to produce entrainment and slag inclusion.
In conclusion, the closed pouring system has good slag retaining effect and fast filling speed. Considering the use characteristics and production beat of production castings, the annual demand is large, so the closed pouring system process is adopted.
