How The Copper Industry Helps Solve Corrosion Problems

H.T. Michels, Copper Development Association Inc.

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Alloy Development Program - A Substitute for Leaded Brass Plumbing Casting

Lead has traditionally been used in cast brass plumbing fixtures to improve machinability and to ensure pressure tightness. The latter is achieved because lead fills intradendritic voids in castings, which may interconnect and form a path from the inner to the outer surfaces through which small amounts of water may weep. Thus lead prevents weeping of water through the walls of castings. Cast red and yellow brasses contain a fine dispersion of lead particles within their microstructure. This dispersed lead improves machinability of brass castings by acting as a cutting tool lubricant. The presence of lead provides weak points or notches in otherwise continuous chips, which facilitate their breakages into smaller segments and thus are easily cleared away. This allows machines to run at high speeds and therefore keeps machining costs per unit low. Thus any substitute for lead must fill intradendritic voids, act as a cutting tool lubricant and also introduce notches so chips break easily.

The most common plumbing brass, UNS Alloy C84400, a semi-red brass, is known as 81 metal or 81-3-7-9 where the 3, 7 and 9 represent the nominal amounts of tin, lead and zinc in the alloy. The most popular red brass, UNS Alloy C83600 is known as 85 metal or 85-5-5-5. In this alloy, the tin, lead and zinc contents are equal and are 5% each. A yellow brass, UNS Alloy C85800, is a permanent mold die-casting alloy, which is widely used in the manufacturing of plumbing fixtures. It contains 1.5% each of lead and tin and 31 to 41% zinc. The mechanical and physical properties of these alloys are located in our Standards & Properties section.

The 1996 amendment to the 1986 (U.S.) Safe Drinking Water Act, which includes the regulation of leaded plumbing fixtures and fittings, provided the impetus to identify a substitute for lead in cast brasses used in potable water systems. All end-point devices, which include faucets, ice makers and water coolers, must satisfy National Sanitation Foundation (NSF) Standard 61, Section 9, which sets limits for the amount of lead that maybe released to drinking water. Any device, to be certified under NSF 61, is filled with pH8 test water and samples are withdrawn and analyzed over 19 days. In order to pass, the data must insure, with 90% confidence, that 75% of the products examined leach less than 11 ppb lead. Note that this is less than the 15 ppb of lead limit of the Lead and Copper Rule in that the (U.S.) EPA assumes that up to 4 ppb of lead could potentially originate from other sources. In fact, a California Proposition 65 consent judgment has set a lower limit of 5 ppb of lead in that state, as measured according to the NSF 61 test procedure.

Please note that devices, and not alloys, are certified under NSF 61. This is because devices, which are constructed of alloys in various designs and configurations, vary in the surface area of any lead-containing alloy exposed to the test water. Thus the various designs of devices, even when made of the same alloy, can leach varying amounts of lead. Find additional information on The Safe Drinking Water Act, as well as details related to NSF 61 by using our site search.

Bismuth and Selenium

The concept of utilizing bismuth and selenium as a lead substitute in brasses originated at the ASARCO Technical Center in Salt Lake City, Utah. The alloy development was pursued by a consortium, which consisted of the CDA, American Foundrymen's Society, the Brass and Bronze Ingot Manufacturers Association and the Canadian Material Technology Laboratory (CANMET).

Bismuth is adjacent to lead in the Periodic Table of the Elements and has a melting point of 56 C and like lead, is virtually insoluble in copper. In contrast to lead, bismuth is not known to be toxic to humans, and in fact is a major component of a popular stomach medication. Selenium, in combination with bismuth reduces the amount of bismuth needed to achieve the desired properties. In addition, selenium, like copper, is an essential nutrient for humans.

Three alloys have been developed, EnviroBrass® I, II and III, which are Alloys C89510, C89520 and C89550. The original designation of these alloys, SeBiLOY®, which reflects the addition of selenium and bismuth, is a foundry oriented description. However, their new name emphasizes increasing awareness of health and the environment. The compositions of the three new alloys are listed in Table 1.

A tabulation of the mechanical properties of the three new alloys is presented in Table 2. The mechanical properties of the C89510 and C89520 are similar to the standard leaded semi-red and red plumbing brasses, as listed in Table 2, although they are somewhat lower in elongation. Alloy C89550 is nominally equivalent to leaded yellow brass although its ductility is marginally lower. The net result is that plumbing fittings and fixtures do not have to be radically redesigned when cast in EnviroBrass compositions.

Machinability

Alloy C36000, a free machining wrought brass bar alloy, is considered the industry standard and is assigned a machinability rating of 100. Alloy C89520 has a machinability rating of 85, which is comparable to that of Alloy C83600, as listed in Table 3. The machinability rating of Alloy C89550 (with 0.7% Bi) is 75, which is slightly less than that of Alloy C85800, the leaded yellow brass it may be substituted for, as shown in Table 3. Increasing the bismuth level of Alloy C85800 to 1.1% increases its machinability rating to 97, as is also listed in Table 3. Thus the three new alloys can be machined very much like the traditional leaded brasses. However, slightly higher tool wear is seen when compared to the traditional leaded alloys.

Polishing

The three new alloys can be polished and readily achieve a high luster. In color, Alloy C89510 and Alloy C89520 are nearly identical to the standard red brass alloys and Alloy C89550 is comparable to cast yellow brass in color.

Platability and Corrosion

Platability is also fully equivalent and the substitution of selenium and bismuth does not alter their excellent corrosion resistance in potable waters, when compared to traditional leaded brasses.

Castability

These three new alloys have been fully evaluated in commercial foundaries and have casting properties which are similar to leaded red and yellow brass, as listed in Table 4.

Health and Environmental Benefits

Since no lead is intentionally added to the new selenium and bismuth containing alloys, lead levels are dramatically reduced in foundry sand and baghouse dust. Foundry worker exposed to airborne lead is sharply lower, as are sand reclaimation and disposal costs. Airborne lead levels in machine shops are also lower and therefore worker lead exposure is reduced.

Properties, Specifications and Standards

A data sheet containing the properties of the three EnviroBrass alloys is available as hard copy¹, as well as on Industrial Applications section. There is neither a royalty nor a licensing fee associated with these three alloys. Alloy C89520 is listed in ASTM Specification B 30 and B 584. At present, Alloys C89510 and C89550 are awaiting ASTM action. For a given design, devices made of the EnviroBrass alloys, to which no lead is intentionally added, more easily achieve NSF 61 certification than the leaded alloys they are designed to replace. The reason for this is that no lead is intentionally added to the EnviroBrass alloys, which results in a significantly lower lead content, and a corresponding lower level of lead release, when exposed in the certification NSF 61 test.

Conclusions from the EnviroBrass Alloy Development Program

In summary, the three new EnviroBrass alloys:

• are modern, health and environmentally friendly alloys.
• are non-leaded by virtue of no intentional addition of lead.
• release less lead than the traditional leaded alloys they are designed to replace.
• can assist component and device manufacturers in meeting the current potable water purity regulations and achieving NSF 61 certification.
• have the potential to reduce waste disposal and regulatory costs and improve worker health in foundries and machine shops.
• are similar to their leaded counterparts in machinability and pressure tightness characteristics.
• have similar mechanical properties and casting characteristics, when compared to leaded brasses.
• can be substituted for traditional leaded brasses without the need for radical redesign of castings and potable water devices in which castings are major components.
• should be considerer for applications beyond potable water because of the advantages of lower waste disposal costs and the potential to improve worker health in foundries and machine shops.

References

1. Alloy Data Sheet, EnviroBrass® (SeBiLOY®), Non-Leaded Red Brass and Yellow Brass Casting Alloys, Publication Number A1032-95/00, The Copper Development Association Inc., New York, 2000