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best for every application, the wide variety of alternatives for lead-free copper alloys provides the oppor- tunity to select the best possible lead-free alloy for each specific component. Te selection lies within the pre-


A wide variety of alloys are available as


alternatives to lead-based coppers.


requirements. What performance standard does the component need to meet?


• Corrosion protection. • Alloy cost and availability. Who makes it and how much is avail- able? How available is the alloy in the scrap stream? How abundant are the alloying elements? Among the number of no-lead


casting alloys available today, the most common alloys being used for water components are bismuth brass and bronze, silicon brass and bronze, and low lead sulfur tin bronze. Te following provides some guidelines for using these alloys.


Alloy Selection While no single alloy will work


Popular Sulfur Tin Bronze


• C83470 Copper Tin Zinc Alloy Tis newer sulfur containing alloy has been available in the U.S. for several years and is being used in no-lead water applications.


C83470 Copper Tin Zinc Alloy (U.S. EPA registered antimicrobial) Cu


Pb


Min (%) Max (%)


90.0 96.0


0.09


Sn 3.0 5.0


In determining Cu min, Cu may be calculated as Cu = Ni Copper + sum of named elements 99.5% min Ni value includes Co


Sand Cast Tensile Strength:


Yield Strength: % Elongation:


Note: All properties from ASTM 13584-14 unless otherwise noted.


28 ksi minimum 14 ksi minimum 15 minimum


Casting Considerations In most cases, few pattern changes are required when


switching from leaded alloys. Melting and pouring procedures will not vary greatly from the leaded alloys. Cross contamina- tion is not a concern with this alloy as casting returns can mix with the other alloy groups without causing a problem. Te narrow freezing range of this alloy makes for a better casting microstructure, especially noticeable on large cross sections and heavy walls. Te alloy is not quite as strong as the silicon alloys, but comparable to bismuth alloys. Tis alloy machines


34 | MODERN CASTING September 2016


easier than the other popular options. Tis alloy is not brittle and will not crack during soldering or brazing. It is highly recyclable and does not depend on rare or uncommon elements. If proper de-oxidation procedures are not followed, SO2 bubbles can form in the castings. Cleaning room and machining processes may need to be adjusted. Specifically, the use of gang tooling creates problems evacuating chips and the design and operation of this type of tooling needs to be evaluated.


Zn 1.0 3.0


Fe 0.50 P 0.10 Ni 1.0 Al 0.01 S


0.20 0.6


Sb 0.20 Si 0.01


rogative of the component manu- facturers to decide which alloy will assure the production of the highest quality products at the best possible price. Although component applica- tion and relevant specifications will be the major driving factors when selecting a no-lead alloy, manufactur- ers and designers also will consider the total cost of the final component. Te alloy material cost is a part of the equation, but the total overall component cost also includes the impact of the full manufacturing, finishing and recycling processes. Current market availability and long- term sustainability of the alloy are also factors to consider.


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