What are the reasons for the shrinkage of ductile iron castings?

Some foundry manufacturers or customers will want to know what are the reasons for the shrinkage of ductile iron castings, and the following supreme machinery manufacturers will take you to understand what are its influencing factors.

1. The modulus of ductile iron castings. The casting module is greater than 2.5, and it is easy to realize riser-free casting. However, there are also experts who are skeptical about this limit. Generally speaking, thick castings are easy to cast without shrinkage due to graphitization expansion. At this point, the carbon equivalent should not exceed 4.5% to avoid graphite floating. However, small castings with scattered hot spots are prone to shrinkage porosity, which can be solved by quenching, chrome ore or local internal risers. Particular attention is paid to the feeding and shrinkage of the pouring riser system. In general, hot risers should be used whenever possible to avoid cold risers.

2. Pay full attention to the rigidity of the sand box and the hardness of the sand mold. In terms of the rigidity of the sand box and the compactness of the sand mold, the setting should not be too full.

3. The rationality of the pouring and riser process design. Try to use hot risers and quenching, cold risers have poor feeding effect.

4. Casting mold cooling rate.

5. Reasonable choice of pouring temperature and speed. For some thick castings, appropriately increasing the pouring temperature and extending the pouring speed can solve the problem of shrinkage porosity. At the same time, it is conducive to the secondary oxidation slag floating castings and increasing the qualification of flaw detection.

6. Reasonable selection of chemical composition and appropriate residual magnesium and rare earth content.

7. Under the cooling condition of sand mold, striving for more graphite balls is conducive to reducing the shrinkage porosity and improving the mechanical properties.

8. In order to obtain better raw materials and good molten iron metallurgical quality, special attention should be paid not to keep the molten iron at high temperature for too long before tapping, and pretreatment should be carried out before tapping to increase the graphite crystal nucleus of molten iron, which can increase the number of graphite balls and reduce shrinkage porosity.