Casting is a relatively hot metal processing technology that we master earlier. Casting is casting liquid metal into the casting cavity that is suitable for the shape of the parts, and after cooling and solidifying, it can get part or blank. The cast material is mostly solid but heated to liquid metal (for example, copper, iron, aluminum, tin, lead, etc.), and the mold material can be sand, metal and even ceramics. There are different ways to use different requirements. The high pouring temperature can cause the increase of sand type, especially the gray iron with complex sand core. When the pouring temperature is more than 1420 degrees C, the waste products are increased and the casting temperature is 1460 degrees centigrade, and the waste quality is 50%. In production, induction furnace smelting can control the temperature of molten iron better.
2. Defects that may be formed when pouring temperature is too low
(1) stomatal stomata and porous stomata caused by sand core gas are often caused by poor sand core exhaust. Because the core of sand is hardened in core box, which often makes the number of sand core vent holes insufficient. In order to form vent holes, drill holes can be added after core hardening.
(2) the pores of manganese sulfide are located below the epidermis of gray iron and often on the top. They are often exposed after processing, and the diameter of the pores is about 2~6mm. Sometimes a small amount of slag is contained in the hole. The metallographic study shows that the defect is composed of MnS segregation and slag, which is due to low pouring temperature and high content of Mn and S in the molten iron.
Such S content and suitable Mn content (0.5%~0.65%) can significantly improve the purity of molten iron and effectively prevent such defects.
(3) after the liquid slag is processed, a single hole can be found beneath the surface of gray cast iron, and the diameter of the hole is generally 1~3mm. In individual cases, there are only 1~2 small holes. Metallographic studies show that these small pores appear together with a small amount of liquid slag, but no segregation of S is found. The research shows that this defect is related to the pouring temperature. When the pouring temperature is higher than 1380 C, this defect is not found in the casting, so the pouring temperature should be controlled at 1380 - 1420 degrees C. It is worth mentioning that the design of the gating system is changed and the defect can not be eliminated. Therefore, the defects can be considered to be due to the low pouring temperature and the casting of the molten iron in a small reduction atmosphere.
The most common reason why pouring temperature is too low is the long time transportation and retention of molten iron in the open ladle before pouring. The heat loss can be significantly reduced by using the ladle cover with insulation material.