1. Too high pouring temperature will greatly increase the proportion of waste products
Excessive pouring temperature can cause the sand mold to expand, especially for complex sand cores in gray iron castings.
If the pouring temperature exceeds 1420°C, it results in increased waste products. At 1460°C, waste products reach 50%.
The temperature of molten iron can be accurately controlled during production by using induction furnace melting.
2. Possible defects when the pouring temperature is too low
(1) Manganese Sulfide Porosity: This type of porosity is typically found below or on the surface of gray iron castings, often exposed after processing. The diameter of the pores typically ranges from 2 to 6mm, sometimes containing a small amount of slag.
A metallographic study has demonstrated that MnS segregation and slag mixing during casting occur due to low pouring temperatures and high levels of Mn and S in the molten iron.
To prevent this defect, a suitable Mn content of 0.5% to 0.65% and S content should be maintained to improve the purity of the molten iron.
(2) Porosity and Porosity caused by Sand Core Gas: These defects are commonly caused by poor sand core exhaust during the core-making process, leading to insufficient vent holes. Additional drilling can be performed after the core has hardened to form vent holes.
(3) Liquid Slag Inclusion: Small holes are found under the surface of gray iron castings after processing with liquid slag inclusion.
The diameter of these holes ranges from 1 to 3mm, with some cases showing only 1 to 2 small holes.
Metallographic studies have shown that this defect appears with a small amount of liquid slag, but no segregation of S is found.
Research has shown that this defect is related to the pouring temperature. The casting will not exhibit this defect when the pouring temperature is above 1380℃, and the pouring temperature should be controlled between 1380℃ and 1420℃.
Changing the design of the pouring system does not eliminate this defect, and it is believed that low pouring temperature and pouring the molten iron in a micro-reducing atmosphere contribute to this defect.
The most common cause of low pouring temperature is the long-term transport and storage of molten iron in an open ladle, resulting in heat dissipation. Using a ladle cover with insulating material can reduce heat loss.