The issue of toxic lead in brass alloys used for casting water valves and plumbing fixtures is a low-level debate: foundries producing products for that market segment have settled on alternative alloys, but there is a general sense that better options may be available
Adding lead improves the machinability of nonferrous alloys, notably copper alloys, and for brass products cast for use as water-handling and treatment lead solves the problem of continuous shrinkage porosity that develops because of the wide freezing range in many of those alloys. In short, lead makes casting brass easier.
But, lead in the castings may poison the water they contact. Lead poisoning is commonly associated with mental and behavioral developmental disabilities, but it also may cause abdominal and digestive issues, blood disorders, and other problems. The federal Safe Drinking Water Act (2011) required that all cast copper components used in potable water applications must contain less than 0.25% lead.
In short, regulators have set the allowable lead content for plumbing products so low that its effectiveness in the casting process is canceled.
Manufacturers of water and plumbing products have moved on from lead, identifying effective alternatives and shifting their casting production to those approved alloys. But the search continues for alternative alloys that are easy to use and affordable. Two recent research reports suggest some new alloys that may have commercial impact.
Late last year Australian researchers reported their development of a lead-free brass alloy, they call “bright brass.” Dr. Kevin Laws of the University of New South Wales School of Materials Science and Engineering explained he and colleagues developed a ‘high-entropy’ alloy system very similar to brass and bronze, in 2014. The elements of their formulation were not revealed.
The Australian researchers have formed a company called Advanced Alloy Holdings and were awarded a government research grant to commercialize the new alloy system: machining and manufacturing trials have been planned, and Laws indicated last fall that the bright brass castings may be available soon.
A separate line of research has played out at Purdue University, where a series of copper-manganese alloys have been found to provide greater strength and castability than the common non-lead alloy options for brass foundries, such as bismuth.
“Our alloys have been shown to have superior overall mechanical properties compared to other cast, lead-free alternatives,” stated Prof. Kevin Trumble, professor of materials engineering at Purdue and director of the Purdue Center for Metal Casting Research.
“We are helping to meet the growing need for new alloys with superior mechanical properties, especially amid an increasing amount of government regulation requiring industries to reduce the lead content they use,” Trumble added.
The Purdue researcher noted the new copper-manganese formulations “solidify over a very narrow temperature range and are completely free of microscopic shrinkage porosity, and have higher strength, so thinner-walled castings can be used compared to their counterparts.”
Trumble also said that, in addition to their metallurgical and mechanical advantages, copper-manganese alloys are more affordable than other lead-alternative materials.
He said the Purdue research team had proven the alloys’ effectiveness to be feasible, cost-effective alternatives for water pumps and marine-industrial components, and “now we are turning our attention to many other potential applications for our discovery.”
As for what those applications may be, the Purdue researchers are testing the new alloys for various plumbing valve applications, as well as fittings and fixtures.