I. Too High Casting Temperature will Greatly Increase its Rejection Rate.
Too high casting temperature will make sand moulds inflate, especially for theses gray iron foundry with complicated sand cores. When the casting temperature reaches ≥1420℃， corresponding rejection rate will begin to increase. And when the temperature is up to 1460℃, the rate will access to 50%. During the manufacture, adopting electric induction furnace melt can better keep corresponding casting temperature.

II. Low Casting Temperature is Likely to Form Casting Defects.

i. Manganese Sulfide Gas Holes

This kind of gas holes generally form on the upper place beneath the surface of gray iron casting and exposed after the machining process. Their diameters reach 2-6mm. Sometimes, a small number of molten slags can be seen in these gas holes.

ii. Gas Holes Resulting from Core Gas

Porosities and gas holes defects come from poor exhausts from sand cores among gray iron foundry. As sand cores treat with the harding process in core boxes in the process of creating cores, it often makes insufficient exhaust holes happening there.
iii. Liquid Slag

There will form some single small-size gas holes beneath the surface of gray iron foundry once the completion of machining. The diameters of holes are 1-3mm generally. Large amount of studies prove that the kind of defects also have some relation with the casting temperature. When the temperature reaches 1380℃, it’s hard to find the kind defects in gray iron foundry. It is worth mentioning that in the case of changing gating system design, it still cannot decrease the number of these defects.