There are three types of slag addition: the first type of coarse slag is 2mg · SiO2 + MGS or + FES; the second type of strip slag is MgO, and the third type of fine slag is MgO + MGS, which are separate or consistent with precipitation. In addition, Al2O3 is mixed in type 1 coarse slag.
Therefore, the preventive measures to be taken are as follows: on the premise of ensuring spheroidization, the amount of residual magnesium should be reduced as much as possible; the content of oxygen and sulfur in the original molten iron must be minimized; the amount of magnesium added and the amount of residual magnesium can be reduced by containing calcium and rare earth in the spheroidizing agent.
Teapot type furnace and ladle are used to separate the slag completely.
When the pouring temperature is low, MgO and SiO2 are produced. They combine to form forsterite, which can also be combined with Al2O3. Therefore, slag addition is formed. Forsterite will be produced rapidly below 1350 ℃. In addition, the turbulent flow of molten iron is easy to oxidize, which promotes these reactions. Therefore, attention must be paid to avoid the turbulent flow in the pouring system and pouring method.
The addition of 0.02-0.1% cryolite powder and sodium fluocarbonate powder on the surface of the spheroidizer can reduce the formation of slag.
A filter screen is arranged at the bottom of the sprue or at the connection part of the cross sprue, or a slag blocking device is arranged in the pouring system. The head must be as low as possible during pouring. If necessary, the runner shall be divided into upper and lower types to reduce the pressure. A slag collecting riser can also be arranged in the cross sprue to float the rotating slag of the molten iron. During in mold inoculation, FeSi reaction should be sufficient to prevent the undissolved FeSi from floating to the surface and forming abnormal structure, which will cause the deterioration of machining performance. It is also possible to extend a section at the top of the transverse sprue as the agent slag section, but the internal sprue shall not be opened here.