Some studies have pointed out that the cross-sectional area of each component of lost foam casting gating system, the size and quantity of inner gate have no obvious influence on mold filling. The minimum cross-sectional area of the lost foam casting gating system should be appropriate. On the one hand, it is necessary to ensure that the liquid metal at the front of the mold filling speed is fast enough to avoid losing the mold filling capacity due to excessive temperature drop. On the other hand, it is not allowed to make the flow rate of liquid metal in the lost foam casting gating system too fast to avoid sand flushing defects. At present, there is no theoretical formula for the design of lost foam casting gating system. In practice, analogy method is generally used to design lost foam casting gating system.
Increasing the static head of liquid metal in lost foam casting can not only improve the driving force of liquid metal filling and pattern decomposition products escaping from the coating, but also increase the flow life of liquid metal filling front, so as to improve the filling ability of liquid metal in lost foam casting. Increasing the sprue height can improve the static pressure head of the lost foam casting, but the runner is also filled with foam pattern. Only when the foam gasification in the sprue disappears, can the liquid metal in the lost foam casting reach the inner gate. Therefore, the increase of sprue height will increase the heat loss at the front of liquid metal in lost foam casting, reduce the overheating during mold filling, and then reduce the mold filling capacity of liquid metal in lost foam casting. The influence of sprue height on liquid metal filling ability of lost foam casting is different under different conditions. When the superheat, density and heat capacity of liquid metal in lost foam casting are relatively high, increasing the height of sprue can improve the mold filling capacity of liquid metal in lost foam casting. On the contrary, increasing the height of sprue will reduce the mold filling capacity of liquid metal in lost foam casting. In the presence of negative pressure, the influence of sprue height on mold filling speed is greater than that without negative pressure.
Besides, the filling and solidification of lost foam casting is also affected by foam pattern, permeability of the coating and shape and temperature of molding sand. In a word, the appearance of foam pattern makes the decomposition speed and the escape velocity of decomposition products become the dominant factor in the mold filling process of lost foam casting. When there are defects related to mold filling capacity such as cold shut and insufficient pouring in the actual production of lost foam casting, the main factors leading to this result should be found out and solved according to the production results and the filling and solidification characteristics of lost foam casting, rather than blindly applying the experience of traditional casting, otherwise, it is difficult to achieve the expected purpose.