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Possible Cause Casting removal is


too slow because of poor mechanical operation or improper cycling.


Suggested Action See that all opening and


ejecting mechanisms operate smoothly, the cycle is properly timed and the mold is at the proper temperature.


Possible Cause Casting removal is delayed


because oversized risers or feeders solidify slowly.


Suggested Action Increase the freezing rate in


risers and feeders by thinning the mold coating or decreasing their size and depending more on chilling or cooling.


Possible Cause Solidification is


uncontrolled, leaving unfed hot spots while the rest of the casting is contracting.


Suggested Action Use chills at hot spots or


change risering to feed these areas and control directional solidification.


Defect: Hot Cracks ▼


Possible Cause Sharp internal


corners or abrupt section changes in a design may cause hot spots. Weak areas or design may cause early contraction stresses in thinner sections.


Suggested Action


Use ample fil- lets at inside corners. Increase the thickness of thin sections as they approach heavier ones. Add ribs to thin sections or add removable exterior fins.


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Possible Cause Ejection pin is


bearing on a weak section of the casting or is exerting pres- sure on an extended section parallel to parting lines.


Suggested Action Pins should bear


on sections vertical to parting lines, which are most inclined to seize in the mold cavity.





Possible Cause Stresses may result


from faulty use of tongs or hoists in removing castings.


Suggested Action Tongs or lift hooks


should grip a stronger part of the casting.


Possible Cause


Rapid or uneven cooling occurs after casting removal, or the castings are stacking improperly while hot.


Suggested Action


Hot castings should not be laid flat on metal plates or cold floors and should not be stacked.


February 2012 MODERN CASTING | 43


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