Transitioning to No-Lead Copper
No-lead copper alloys solidify differently than leaded alloys, so metalcasters must gather information and test the materials to make the switch successfully. SAM SCOTT, ESI NORTH AMERICA, FARMINGTON HILLS, MICHIGAN
copper alloys, which are commonly considered a health risk. Why is the transition tricky? One primary reason: no-lead alloys shrink nearly 3% more during solidifi cation (Fig. 1). When transitioning a casting design from a
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leaded copper component to a no-lead component, the metalcaster must ask: • Will I have more porosity locations? • Do I need to feed new areas? • How much should I increase riser size to account for more shrinkage?
• Will current acceptable shrink locations no longer be acceptable? In order to understand the eff ects of the
change of alloy, experiments and material testing can be performed, or quick, inexpensive and accurate material property calculations can take their place. T e required thermo-physical and some mechanical properties can be determined using knowledge of the alloy composition and solidifi cation path. T e data that can be gathered in this manner includes conductivity, density, specifi c heat, latent heat (or enthalpy), fraction solid and viscosity. T e diff erence in shrink exhibited by no-lead
alloys was not common knowledge as little as fi ve years ago. Now, most metalcasters are aware that when they transition to a no-lead part, they may need to make changes to their pat- terns to account for the shrink discrepancy. Particularly in cases where some shrink already occurred, the no-lead alloy can lead to unacceptable porosity levels. In other cases, the location of the resulting porosity will dictate that no changes are necessary. If the porosity level is unacceptable, the metalcaster should
proceed with pattern changes, including the use of larger ris- ers, additional risers, altered gate locations, or modifi ed pro-
Fresno Valves converted this 4-lb. boiler head casting from C83600 to C87500 no-lead copper.
cess parameters, such as pouring temperature or rate. If the part is going to feed substantially diff erently, riser location changes or part design changes also may need to be made. For a boiler head casting produced by Fresno Valves & Castings Inc., Selma, Calif., in C87500 copper alloy, none of this was necessary. Via solidifi cation modeling, the com-
November 2011 MODERN CASTING | 41
or more than half a decade, metalcasters and researchers have been working to ease the transition away from leaded
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