If the static head is increased, the feeding at the later stage of pouring is increased, and the pouring head is too low and the feeding amount is insufficient at the later stage of pouring, the casting shrinkage will be produced. According to the principle of proportional solidification, the feeding of molten iron in the riser (sometimes the riser is replaced by the sprue) does not depend on the static pressure produced by the height of the riser or the sprue, but by the suction effect caused by the liquid shrinkage of the casting, resulting in the volume deficit and pressure reduction. The molten iron in the riser or runner flows into the casting with the help of the static pressure. Here, the real meaning of increasing the static head is to increase the liquid iron storage of the sprue. In view of this purpose, we increase the static head of the sprue from 50 ~ to 90-10 OM, and expand the diameter of the static head of the sprue to 80 ~, which means that this part acts as a riser.



In this way, although the sprue is far away from the shrinkage area, the feeding route between the two is Yang Tong (in continuous liquid phase state). Therefore, according to the equilibrium solidification theory, the sprue should be able to play a feeding role, which has been proved by practice.



If the pouring temperature is lowered properly and the pouring temperature is too high, the liquid shrinkage of the metal in the mold will be increased, which makes the pouring system designed according to the normal pouring temperature unable to provide enough molten metal for feeding. Therefore, when the exit temperature is too high, it is necessary to reduce the pouring temperature of the casting

① A few pieces of smaller and thinner returning materials are added into the ladle to cool down.

② Other thin and small pieces are poured with molten iron with higher temperature in the first half ladle. The casting can be poured when the temperature of molten iron is suitable.



That is to say, on the premise of ensuring spheroidization, the monthly amount of spheroidizing agent should be reduced as much as possible. If the amount of spheroidizing agent is too large, the tendency of chill of molten iron will increase, and the graphitization expansion ability during solidification will be reduced. Therefore, the apparent shrinkage of casting will be increased, and the defects such as shrinkage cavity, shrinkage porosity and shrinkage depression will be easily produced. According to the conditions of pig iron, coke and nodularizing agent used, the amount of spheroidizing agent is reduced and fixed at about 1.7%. Under normal conditions, the nodularizing effect of more than 3 grades can be guaranteed on castings.



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