Casting defect of malleable cast iron and prevention method

Defect one: Can’t pour

Features: the casting shape is incomplete, the edges and corners are round, which are commonly seen in thin wall parts.

Reasons:

1. Iron liquid oxygen is serious, carbon and silicon content is low, sulfur content is high;

2. Low pouring temperature, slow pouring speed or intermittent pouring.

Prevention methods:

1. Check whether the air volume is too large;

2. Add relay coke, adjust the height of the bottom coke;

3. Improve the casting temperature and casting speed, and do not cut off the flow during casting.

Defect two: shrinkage loose

Features: the surface of the pores is rough and uneven, with dendritic crystals, concentrated pores for shrinkage, small dispersed for shrinkage, more common in hot nodes.

Reasons:

1. The content of carbon and silicon is too low, the shrinkage is large, the riser feeding is insufficient;

2. The pouring temperature is too high and the shrinkage is large;

3, riser neck is too long, section is too small;

4, the casting temperature is too low, poor fluidity of liquid iron, affecting feeding;

Prevention methods:

1. Control the chemical composition of iron liquefaction to prevent low carbon and silicon content;

2. Strictly control pouring temperature;

3, reasonable design riser, if necessary, with cold iron, to ensure the sequence of solidification;

4. Increase the content of bismuth appropriately.

Defect three: hot crack, cold crack

Features: Hot crack is fracture along grain boundary at high temperature, with tortuous shape and oxidizing color. Internal hot crack often coexists with shrinkage cavity.

Cold crack occurs at low temperature, transgranular fracture, flat shape, metallic luster or slightly oxidized surface.

Reasons:

1, solidification process shrinkage is blocked;

2, the content of carbon in liquid iron is too low, the content of sulfur is too high, and the pouring temperature is too high;

3, liquid iron gas content is large;

4. The complex parts are packed too early.

Prevention methods:

1, improve the type, core of the concession;

2. The mass fraction of carbon should not be less than 2.3%;

3, control the content of sulfur;

4, cupola to fully oven, air volume can not be too large;

5, avoid casting temperature is too high, and improve the cooling speed, in order to refine the grain;

6. Control the packing temperature.