GETTING THE LEAD OUT One of copper’s more appealing characteristics is its resis-
tance to corrosion, which can result in increased fl ow capacity. Because of this, plumbing components in North America traditionally have been made from leaded red and semi-red brasses (alloys C83600 and C84400) via green sand molding. Certain elements are added to copper-based alloys to maintain their desirable characteristics while remaining a viable metalcasting option. Lead is among these additives, because it improves machinability and helps ensure pressure tightness. But lead has been linked to a variety of adverse health concerns. Ingesting lead paint chips or dust is the most well-known source of lead exposure. But plumbing fi xtures also can be a source of lead in drinking water. The 1996 Amendment to the Safe Drinking Water Act, which limits the amount of lead in drinking water, encour- aged metalcasters to fi nd a replacement for lead in brass castings in potable water systems. Since then, all faucets, drinking fountains, water coolers and other drinking water conveyance devices have had to pass a national standard for certifi cation (National Sanitation Foundation Standard 61). The application of non-leaded brass castings (which
also may be described as low-lead alloys because no lead is intentionally added to them) is an important approach being taken to reduce the lead intake in drinking water. A variety of other approaches have been attempted or are being utilized, including the use of coatings, the chemical
removal of interior surface lead and reducing internal surface areas by design changes. Most lead-free alloys contain bismuth as the major al-
loying element, because it can replace lead in the copper alloys and contribute to the machinability and pressure tightness characteristics. Similar to lead, bismuth almost is completely insoluble in copper and has a low melting point. Additionally, it is not known to be toxic to humans. Some lead-free alloys also contain selenium as the
alloying element due to its effect on machinability. Ini- tial research has shown that selenium, in combination with bismuth in brass casting applications, consider- ably increases the machinability. This also reduces the total amount of bismuth in the alloy. Selenium, similar to copper, is an essential nutrient for humans. Copper-based castings are at their best when the end use calls for a component that can hold pressure tightness while delivering good corrosion-resistant characteristics. Combined, the lead-free alternative alloys have displaced as much as 10% of the market traditionally dominated by leaded red brass. As the metalcasting industry continues to move away from leaded metals, these bismuth- and selenium-containing copper-based alloys have shown that they can move into an already established waterworks marketplace without compromising casting quality.
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quired an alloy that was capable of complexity while remaining conduc- tive. T e highly conductive C011 alloy met both specifi cations. T ick to thin section design
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34 | METAL CASTING DESIGN & PURCHASING | Mar/Apr 2015
becomes an even larger problem for copper-base alloys with wide freezing ranges such as red brasses, tin bronzes and, to some extent, the medium freezing range alloys such as the yellow brasses. T ese alloys, which account for the highest level of casting production, do not solidify directionally. While proper risering helps combat this, it doesn’t have the same eff ect as direc- tional solidifi cation. With these alloys, shrinkage defects normally are internal and often found during machining, leading to scrapped castings. To counteract the solidifi cation issues with wide-freezing range copper alloys, metalcasters use chills and chro- mite and zircon sand cores to promote the proper solidifi cation. Chilling these sections can be more eff ective than using a riser, though each of these tools increases the cost of a fi nished casting.
Copper Alloy Processing Castings often require further
processing after cleaning and fi nish-
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