What factors affect nodular cast iron?

The influence factors of ductile iron castings

1, riser and chill: if the gating system, riser and chill is set properly, can not guarantee the order of solidification of liquid metal; in addition, the number, size and riser castingconnection when not, will affect the feeding effect of riser.

P: 2, the phosphorus content in liquid iron high, the solidification range is enlarged, and the low melting pointeutectic solidification of phosphorus in the last do not supply, and make the casting shell is weak, therefore has the tendency of shrinkage hole, shrinkage porositygenerated. The general factory to control the phosphorus content of less than 8%.

3, rare earth and rare earth magnesium: residual amount is too high will deteriorate the graphite shape, reduce thenodularity, so rare earth content should not be too high.And magnesium is a strongly stable carbide elements,retards the graphitization. This shows that the residual magnesium content and residual rare earth content will increase the ductile iron chill tendency, the expanded graphite was reduced, so when they were higher, will also increase the shrinkage tendency.

4, the wall thickness after forming crust of casting surface,temperature of liquid metal internal is higher, the greater isthe liquid contraction, shrinkage volume not only the absolute value increases, the relative value also increased.In addition, if the wall thickness changes too suddenly, thick section isolated not feeding, the shrinkage tends to increase.

5, temperature: high temperature casting, is conducive tofeeding, but too high will increase the liquid shrinkage, toeliminate the shrinkage is adverse, so should be selected according to the pouring temperature of the specific circumstances, generally 1300 to 1350 degrees is appropriate.

6, sand compactness: if the sand compaction is too low oruneven, so that after casting metal static pressure or expansion force, produce the phenomenon of cavityexpansion, resulting in the original metal not feeding andlead to the casting shrinkage Kong Suosong.

7, carbon equivalent: raising the carbon content, increase the graphitization expansion, can reduce the shrinkage. In addition, improve the carbon equivalent, also can improve the liquidity of ductile iron, conducive to feeding. Empirical formula for production of high quality castings for C%+1/7Si%>3 9%. But the increase of carbon equivalent,should not make the nodular cast iron graphite floating and other defects.