Core Age
The effect of core age within the first 24 hr after strip had no effect on porosity formation. Castings poured with cores used immediately after strip or after overnight aging performed similarly.
If cores made with unbalanced systems were aged several days under ambient conditions, the severity of the defects increased slightly. This is related to atmospheric humidity combining with unreacted material in the polyisocyanate and forming urea structures. These substances readily break down into ammonia derivatives at high temperatures and later dissociate into nascent H and N.
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