Converting to Low-Lead Copper Casting: Three Foundries' Experiences.
Copper-based foundries are forced to deal with lead and its ensuing government regulations, such as NSF Regulation 61. As regulations change or are enforced more strictly, foundries may consider converting to low and no-lead copper alloys.
This conversion can be attractive from a safety standpoint. Using low and no-lead copper components eliminates potential concerns about lead leaching into potable water. These alloys also negate worries about affecting the health of employees working with leaded alloys. In addition, low and no-lead alloys render irrelevant issues about hazardous waste disposal.
However, the difficulties that arise from a conversion to low and no-lead alloys provide a set of challenges that, while not health-related, can seriously affect a foundry. When switching to low and no-lead copper alloys, foundries will have to alter their casting and machining methods to compensate for differences in the alloy chemistries (see sidebar, "LowLead Copper Alloy Casting Checklist').
To examine the issue of converting from a lead alloy to a low or no-lead alloy operation, following are two case studies from foundries that have converted (see sidebar, "Aurora Metals: An Early Converter" for information on a third foundry's conversion). Each chose to deal with lead in its own way and describes the decisions and challenges faced with its method.
Globe Valve, Delphi, Indiana, casts a red brass alloy (6% lead), CDA848, using green sand molds and a low-lead yellow brass alloy (1.2% lead), CDA857-10 B2, using a low-pressure permanent mold process. This captive foundry has 250 employees and casts kitchen and bath faucets and related plumbing components.
Until 1994, Globe Valve dealt solely in red brass castings. During a heavy demand period, the foundry arranged for an outside permanent mold casting supplier to fulfill a few of the foundry's orders. The foundry learned that these permanent mold castings had a higher quality level and a lower scrap yield. In addition, these castings had less surface porosity than the foundry's red brass sand castings. Intrigued, it examined adding permanent mold casting to its processes.
Globe Valve continued using the red brass sand molds for its "under-the-counter" or "behind-the-wall" work and switched to a low-lead yellow brass alloy using the permanent mold process for finer surface finish faucets and other cosmetic plumbing castings. With this addition, Globe Valve established two separate operations--one for lead and one for low-lead--sharing the same coreroom.
In setting up the low-lead operation, Globe Valve faced several challenges.
First, the foundry needed copper beryllium dies for the permanent mold process. It chose these dies because copper beryllium has a high heat transfer rate and is resistant to heat damage. The die is able to pull heat out of the molten metal at a fast speed, leading to quick solidification.
Next, the foundry needed to find a core process that would work with both casting processes. The foundry chose coldbox coremaking because the low binder percentage of the cores results in less evolved gas, keeping gas-related casting defects to a minimum.
After settling on the coldbox cores, Globe Valve turned to its gating system design. Copper beryllium dies transfer heat from molten metal at such a fast rate that gating must be designed carefully to avoid instant solidification. The foundry learned that gating for the yellow brass permanent mold castings needed to be three times the size of gating for the red brass sand castings. The size of the gates, risers and vents requires them to be sawed off for finishing. The thinner red brass gates, risers and vents simply can be broken or sheared off.
Another problem was that rapidly solidifying castings in the permanent mold process potentially can cause shrink-related defects. Globe Valve focused on this problem through design to ensure uniform wall thickness in castings. While learning to deal with these new challenges, the foundry chose to tool its dies and design its gating in-house to gain the expertise.
Globe Valve also needed to alter its machining and finishing processes for low-lead castings. It was able to use the same equipment to service both types of castings, but needed to apply a misting coolant to permanent mold castings to compensate for the lubrication lead provides. The yellow brass castings have a high cosmetic appeal, so they are ground, polished, buffed; chrome-plated and buffed again to a high finish luster. The red brass castings, hidden and designed for function, do not require this labor-intensive process and retain their as-cast finish.
Mike Regelbrugge, director of engineering at Globe Valve, says the fine appearance of the yellow brass permanent mold castings has helped his foundry's business as the quality level expected of plumbing castings has "ratcheted up over the last 100 years to the point that faucets are viewed as bathroom jewelry."
LA Pump and Valve Products
LA Pump and Valve Products, Huntington Park, California, casts pumps, valves and other large aluminum bronze castings in nobake molding for the petrochemical, offshore oil and gas, and marine industries. Founded in 1950, the 35-employee shop is gradually transitioning from a jobbing shop to a captive foundry and its own OEM.
In 1986, the foundry began a two-year study of no-lead alloys because it felt that leaded alloys were too great of a liability. Joe Pinto, president of LA Pump and Valve, examined six alloy candidates before settling on the 952 and 953 aluminum bronze no-lead alloys.
LA Pump and Valve chose these alloys because they could replace leaded brass without a monetary impact for its customer base. Even though the no-lead alloy is more expensive, the cost remains unchanged because the 953 alloy is 14% lighter by volume than the foundry's original alloy of choice, 836 leaded brass. Castings weigh 14% less, and this weight difference between the metals means that customers receive a lighter (less costly) casting, which balances out the ingot price difference.
Because of the extensive research, converting the foundry's castings to the aluminum bronze alloy proceeded smoothly. The new alloy required a higher pouring temperature. The foundry needed to make changes in the gating and risers to accommodate the voids in the casting surface that lead usually fills in. The greatest change was that the size of the risers doubled to ensure that enough metal flowed into the mold.
LA Pump and Valve also worked with its customers to adjust the machining process. The no-lead aluminum bronze alloys produced higher tensile strength castings that proved much harder to machine. To compensate, the machine shop must take smaller cuts into the casting, lengthening the machining process.
The foundry now casts only in the 953 aluminum bronze alloy. At the time of the transition, the foundry approached its customers, explaining its anti-lead position and citing the benefits of the new alloy. It feels comfortable having distanced itself from the lead and potable water issue and believes that the alloy provides customers with added strength benefits--double that of leaded alloys. This increased strength allows customers' engineers to redesign parts to reduce the thickness of the walls, producing stronger, thinner castings for additional cost savings. Occasionally customers request a leaded alloy, but LA Pump and Valve details the benefits of its "upgraded" alloy and converts the customer to no-lead copper casting.
Joe Pinto says, "Lead makes copper castings easier to pour and makes the foundry workers' jobs easier. Converting to no-lead alloys eliminates any health and safety issues regarding lead and potable water. The change to no-lead alloys takes time to get the foundry running up to speed, but for a foundry to experience long-term success, it should distance itself from lead."
The Road to Lead Regulation
The development and increased use of low and no-lead alloys has been fueled by several regulations. As these regulations come into effect, foundries have taken steps to eliminate the hazards of lead or eliminate lead from their alloys. Listed are several regulations that drive foundries to consider converting to low and no-lead alloys and other precautionary safety measures.
* OSHA 1910.1025--This set a strict standard for exposure to lead, lowering it from previous regulations to 0.05 mg/cu m of air and adding other provisions such as mandatory medical tests, exposure monitoring and change rooms.
* Hazardous Waste/Solid Waste Regulations--Leaded alloys cast in sand may produce hazardous waste sand that requires special disposal in a hazardous waste landfill.
* NSF Standard 61, Sections 8 and 9--This establishes maximum lead leaching levels (11 ppb) for faucets or other end-point devices used in potable water delivery systems. It also details testing procedures to make this determination.
* California Proposition 65-The Right-to-Know Act in California requires manufacturers to inform the public if a product contains a known carcinogen or a material that causes adverse affects on the reproductive system. This originally applied only within the state boundaries, but it expanded to include products made elsewhere and sold in California.
Aurora Metals: An Early Converter
Located in Montgomery, Illinois, Aurora Metals Div., LLC, produces 95% of its castings using traditional gravity pour permanent mold and a proprietary vacuum-cast permanent mold process (the remaining 5% is sand cast). The foundry uses a variety of no-lead silicon brasses and bronzes, aluminum bronzes and nickel aluminum bronzes to produce components for the pump and valve, electrical, mechanical, agricultural and transportation industries.
The foundry stopped using leaded alloys when it shut down its shell mold line in 1983. The castings previously produced through the shell mold process were converted to permanent mold and vacuum permanent mold processes. Aurora Metals wanted to distance itself from lead because of the environmental issues regarding both employee health and lead leaching into potable water. The leaded alloys also didn't pour well into the steel permanent mold dies, making gating a more complex task.
Alloy choices at Aurora Metals were derived from customer specifications. The foundry collaborated with its customers to change over to no-lead alloys that were both safer and responded well to permanent mold casting.
Aurora Metals continued to build some patterns in its tool room and purchased others from qualified vendors. The company learned that the gates and risers, had to be redesigned to alleviate flowability issues with the no-lead alloy. Risers had to be created substantially larger to allow for progressive solidification that chased out shrinkage.
The foundry avoided problems with porosity through its vacuum permanent mold casting process. The process provides stability by pulling gas out through the specially-designed center risers.
Aurora Metals relied heavily on its past experience with the permanent mold process and no-lead alloys when changing over to make the entire foundry lead-free. Says Aurora Metals President Jim Pearson, "Customers choose Aurora Metals for the material characteristics present in the chosen alloys, including higher strength. We have been very satisfied with the no-lead alloys, and so have our customers."
Low-Lead Copper Alloy Casting Checklist
When foundries convert to a low or no-lead copper alloy, they often experience problems during the production process because of different properties the new alloy possesses. Following is a checklist of some of the issues the conversion may bring to light.
* Castability. It may be necessary to reconsider how the metal travels through the mold or change the pouring temperature because of a smaller melting range before solidification. No and low-lead alloys may require an increase in temperature to prevent misruns.
* Porosity. Alloys with low lead content can raise concerns about the casting's ability to pass a leak test because low-lead castings can experience microscopic porosity.
* Cross-Contamination. Foundries running both leaded and low or no-lead alloys must prevent cross-contamination in furnace linings, ladles and the sand system.
* Shot-Blast Contamination. The surface of low and no-lead alloy castings can be contaminated in the blasting unit. Foundries should replace the shot after blasting leaded castings or use separate blast units. They also must be concerned that the liner of their blast unit may be coated with lead, causing contamination.
* Ladle Additions. Low and no-lead alloys may require different additions for grain refinement to keep the casting from cracking. Grain refining also may aid machining.
* Gating System. Because of flowability and slag issues, foundries may need to redesign the casting gating systems for new alloys.
* Mechanical Properties. Leaded alloys offer greater ductility. The absence of this ductility may require alterations to the design or alloy.
* Machining Lubricant. Because lead acts as a lubricant during machining, low and no-lead alloys may need a coolant to machine well. This also may change machining processes.
* Machinability. Low and no-lead alloys require reduced machining speeds, feeds and leads.
* Finishing and Polishing. Leaded alloy substitutes are more prone to spots or cracks. Castings with lead have fewer spots because the lead solidifies last and fills in voids. Castings without lead are more likely to have these spots, as well as cracks due to a brittle phase during cooling.
* In addition to these manufacturing issues, cost plays a significant role when considering switching from leaded to low or no-lead copper alloys. Lead alloys are substantially less expensive then low or no-lead counterparts. The described manufacturing issues increase the cost of low and no-lead copper alloy casting. These castings can require more time initially in the design, casting and machining stages.
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|Date:||Oct 1, 2001|
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