As indicated in the graphs showing each of the three binders tested, PUCB systems have a strong secondary strengthening effect, EACB systems have the quickest loss of strength, and resin coated systems exhibit an initial strengthening and then degrade over the range of temperatures used in casting.


Resin Coated Sands Results


R


esin coated shell sands had the lowest thermal degradation of the three sands tested. Since the sand is thermosetting, it was expected there would


be little if any thermoplastic deformation at elevated temperatures. The samples were almost unaffected at 212F (100C) and retained a large quantity of their original strength until complete thermal degradation occurred. A slight strength increase occurred at 392F (200C). All other temperatures showed a slight but constant degradation of tensile properties with extended times. Although no increase in tensile strength as a result of temperature was observed, an increase in modulus did occur. This increase in modulus almost doubled the original stiff- ness of the test sample, although the strength was ap-


proximately 55%. Because the system is thermosetting, a linear relationship between the modulus and the elevated temperature tensile strength did not exist.


The Bottom Line Resin coated systems exhibit high strengths and stiff-


ness over a wide temperature range and then degrade quickly as temperature exceeds 752F (400C).


Who Should Use Them? Metalcasters seeking greater dimensional accuracy


benefit from resin coated sands, as they maintain their strength throughout the casting process. Heavy iron or steel sections may not be possible due to the quick breakdown at temperatures exceeding 752F (400C).MC


42


MODERN CASTING / February 2010


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