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INCLUSIONS


Causes: • Sand or slag (above) trapped on the surface.


• Mold failure inclusions and edge disintegration (below) occur with too brittle or weak sands.


Remedies:


• Improve the venting of core gases. • Ensure even sand distribution in the flask.


• Avoid adhesion problems due to excessive local compaction.


• Increase the taper on the pattern and mold.


• Use a release agent.


EROSION & SWELLING


Causes:


• Erosion (above) appears as thickening near the gate, often combined with inclu- sions, caused by improper compaction.


• Swelling can be attributed largely to sand properties. Shown (below) is a thick- ening of undercompacted areas next to the flask wall.


Remedies:


• Improve sand distribution. • Reduce sand compactibility. • Improve core compaction. • If necessary, reduce satura- tion of iron to decrease graphite expansion.


SURFACE ROUGHNESS


Causes: • Sand grain size. • Burnt-on sand.


Remedies:


• Use finer sand or additives. • Improve mold compaction. • Improve gates to avoid local overheating.


March 2014 MODERN CASTING | 55


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