New Alternative Low-Lead Copper Alloy Shows Promise
C83470 is a viable option to produce castings that will be in compliance with the Safe Drinking Water Act or other standards requiring castings to be low in lead.
AFS Copper Alloy Division
(Click here to see the story as it appears in the February issue of Modern Casting.)
Many alternative low-lead brass and bronze alloys are available to metalcasting facilities for use in producing castings that will be in compliance with the Safe Drinking Water Act or other standards. Recently, a new no-lead alloy has entered the market that provides a combination of improved casting pressure tightness, mechanical strength, machinability (chip-breaking), alloy recyclability and pattern yield when compared to other low-lead alloy alternatives.
The Copper Development Association (CDA) lists a number of low-lead alloys identified by UNS number on its website (www.copper.org) and in print. Most of these alloys are also listed in applicable ASTM standards, specifying their required chemical composition and mechanical property requirements. Each of these alternative alloys have properties that make them unique from the others, and though they are all low in lead, each alloy presents differing challenges to metalcasters and machine shops when chosen to replace traditional lead-bearing alloys.
To date, no low-lead alloy alternative has proven to be an identical replacement for traditional lead-bearing alloys regarding casting, machining, pressure tightness and overall performance characteristics in typical waterworks casting applications.
A new sulfide-bearing tin bronze was developed in the 2000s by Shiga Valve Cooperative, Hikone, Japan, in conjunction with Kansai University, Suita, Japan. The new alloy has since been added to the CDA alloy database and given UNS number C83470.
With the introduction of this new alloy, copper-based casting facilities will have another tool to help meet the needs of the castings produced in no- or low-lead applications.
Learning by Trial
Beginning in 2011, the AFS Copper Alloy Division performed trials at Ford Meter Box Co., Inc., Wabash, Indiana, and A.Y. McDonald Mfg. Co. Inc., Dubuque, Iowa, to study alloy use in North American facilities. Green sand molds were produced with automatic molding machines utilizing warm box and shell cores.
The C83470 material was melted in a coreless induction furnace and a lift-swing furnace. Many different castings were manufactured in a size range consistent with standard casting sizes of these facilities. Casting weights were from 0.25-7.7 lbs., with wall thicknesses varying from 0.10-0.75 in. C83470 appears to be sensitive to high turbulence during pouring. While some existing gating and risering techniques designed for traditional leaded alloys, such as C83600, were successful without modification, other casting geometries required larger ingates. In some cases, due to the higher copper content of C83470, increased riser volumes were needed. In most cases, the thin ingates in a pressurized system resulted in poor casting quality. A non-pressurized gating system, along with generous parting-line venting, tended to result in more favorable casting quality.
Overabundance of superheat can cause problems, so degassing the metal is advised. Targeting the maximum of the zinc range also can be beneficial with degassing. Mixed results were found while purging the furnace with nitrogen gas, while phosphorous additions to the furnace appeared to help in some instances. Gas defects were the leading causes for scrap castings both before and after machining, and additional work with minimizing turbulence, gating design, pouring temperatures, pouring practices and other practices may be needed.
Pouring temperatures in the 2,100-2,275 F (1,149-1,246 C) range were needed to reduce misrun scrap, but may have contributed to higher amounts of centerline shrinkage porosity. These temperatures are 25-50 F higher than the current melting and pouring practices for bismuth alloy (C89833) castings. Different techniques of both horizontal and vertical venting were found to be effective in removing some of the gas.
As experience was gained during the trials, the use of proper mold venting addressed many of the gas issues. With proper venting techniques and minor gating changes, typical degassing methods were suitable.
The C83470 material was poured manually. No issues were found pouring this material, although some gating modifications may help reduce turbulence and gas issues. Some extra slag build-up in the ladles was noticed at times. Air monitoring did not pick up any significant levels of sulfur dioxide during melting or pouring.
Castings were found to have good surface finish when steps were taken to control gas absorption. In some instances, sawing and grinding the material was challenging due to material build-up on the wheels or blades. Additional investigation into cutting wheels and methods is needed. No major concerns were seen with grinding flash or trimming parting lines.
Castings made from the C83470 material (Fig. 1) were machined using both single-point tooling and gang tooling. The chips produced from both processes were larger and longer than those from other traditional plumbing alloys. The gang tooling could not evacuate the large chips easily, causing heat build-up and premature tooling failure. Elevated sulfur content can help break up the chips and reduce the size of the long, curly ribbons. Dye penetrant was used on selected machined castings, and no cracking was found in these castings.
Pressure tests of the C83470 material found it to be pressure tight. After successful pressure testing (up to 150 psi), many castings were fractured to examine the internal grain structure for potential defects. Defects found in these castings had minimal impact on pressure testing. Cold shuts and gas defects, where the defect did not penetrate the entire wall thickness, still allowed for positive pressure test results even with less than desirable metal structure (Fig. 2). The pressure tests resulted in almost no failures for leaking.
Testing of tensile bars poured during the trials resulted in mechanical properties that exceeded the published mechanical properties of C83470. Table 2 shows example tensile bar results from the trials. Castings made from the C83470 material were very ductile.
Leachate testing was conducted on multiple waterworks ball valve assemblies. The valve sizes ranged between 0.625-2 in., with all passing the NSF/ANSI Standard 61-G requirements.
Recyclability
Comprehensive recyclability of the current low-lead alternative family of alloys has been an industry-wide concern for recyclers, ingot makers and metalcasting facilities. This issue affects quality, cost and value. During the trials, C83470 provided advantages in this regard.
Current available low-lead alloys offer casting solutions, but vary in their ability to be safely and effectively recycled if they should become cross-contaminated with, or cause cross-contamination of, some of the other low lead alloys or the leaded brasses. Currently, the value of the resultant cross-contaminated material may be considerably reduced because this material must be refined or diluted when consumed back either by the facility or an ingot maker. Elements such as lead, bismuth, silicon or aluminum must be either removed by refining or diluted to bring the metal back into specification for reuse.
C83470 contains no lead, bismuth, silicon, aluminum or other element that causes cross-contamination and/or recycling concerns. C83470 will be easier for facilities to manage from this perspective and should potentially be more cost effective to recycle both in the facility and by an ingot maker. Should cross contamination of C83470 with another alloy occur in the facility, the sulfide present in C83470 is less likely to be a detriment to the casting quality, castability and value of returns, such as gates and risers. This is because alloys other than C83470 have significantly higher tolerance for sulfur than other alloying elements. Sulfur is relatively easy to remove by refining during the recycling process, negating the need for dilution with copper.
C83470 directly addresses the big picture of recyclability and the costs of finite natural resources.
Applications
C83470 most likely will be used in applications in the waterworks industry and castings that must meet the requirements of the Safe Drinking Water Act or other international standards restricting lead content. The alloy also can be used in applications that require pressure tightness, whether for air, water, gas or oil. Other viable applications include pump components, water impellors and housings, and small gears.
C83470 also has applicability for continuous cast rod, bar and shapes, as well as potential as a choice for bearings.
Based upon the trials conducted over the last three years, the authors believe this alloy is a viable option to produce castings that will be in compliance with the Safe Drinking Water Act or other standards requiring castings to be low in lead. Standard melting, deoxidation and pouring practices apply with C83470 as with other leaded and non-leaded waterworks and plumbing alloys.
Each facility should thoroughly investigate this alloy and implement the needed controls at each process step to ensure best results. Further research may be needed based on product applications. Results may vary.
This article is based on research conducted by members of the AFS Copper Alloy Division.
ncountering a scenario in which you are forced to suddenly and immediately suspend melting operations for an extended period can be a death sentence for many metalcasting facilities. Small to mid-size businesses are the backbone of the industry, but many do not survive when forced into extended downtime. One disaster-stricken metalcaster, however, found resilience through its own perseverance and a circle of support from peers, friends, suppliers, teams from installation and repair providers, an original equipment manufacturer and even competitors.
Tonkawa Foundry, a third-generation, family-owned operation in Tonkawa, Okla., was entering its 65th year of operation this year when a significant technical failure ravaged the power supply and melting furnaces on January 17. Thanks to the textbook evacuation directed by Operations Manager Carrie Haley, no one was physically harmed during the incident, but the extent of emotional and financial damage, and just how long the event would take Tonkawa offline, was unclear.
Tonkawa’s power supply and two steel-shell furnaces would have to be rebuilt. No part of the reconstruction process could begin until the insurance company approved removal of the equipment from the site. The potential loss of Tonkawa’s employees and customers to competing metalcasters seemed inevitable.
Within two days of the incident, repair, installation and equipment representatives were on site at Tonkawa to survey the damage. Once the insurance company issued approval to begin work, the installation team mobilized within 24 hours to remove the equipment and disassemble the melt deck.
Since the damaged equipment was installed in the 1980s and 1990s, Tonkawa and an equipment services and repair company quickly strategized a plan and identified ways to enhance the safety, efficiency and overall productivity of Tonkawa’s melt deck.
“The most critical issue was for our team to organize a response plan,” said Steve Otto, executive vice president for EMSCO’s New Jersey Installation Division. “We needed to arrive at Tonkawa ready to work as soon as possible and deliver quickly and thoroughly so they could get back to the business of melting and producing castings, and minimize their risk of closing.”
Several years after Tonkawa’s melt deck was originally installed, an elevation change was required to accommodate the use of a larger capacity ladle under the spout of the furnaces. Rather than raising the entire melt deck, only the area supporting the furnaces was elevated. As a result, the power supply and workstation were two steps down from the furnaces, creating a number of inconveniences and challenges that impacted overall work flow in the melt area. Additionally, the proximity of the power supply to the furnaces not only contributed to the limited workspace, but also increased the odds of the power supply facing damage.
The damage to the melt deck required it to be reconstructed. It was determined to be the ideal opportunity to raise the entire deck to the same elevation and arrange the power supply, workstation and furnaces onto one level. The furnace installation company provided the layout concepts, and with the aid of Rajesh Krishnamurthy, applications engineer, Oklahoma State Univ., Tonkawa used the concepts to generate blueprints for the new deck construction. The results yielded a modernized melt system with an even elevation, strategically placed power supply, enhanced worker safety and increased operator productivity.
“Eliminating the steps and relocating the power supply farther from the furnaces was a significant improvement to our melt deck,” Tonkawa Co-Owner Jim Salisbury said.
Within four days of insurance company approval, all damaged equipment had been removed and shipped for repair.
The insurance company required an autopsy on the damaged furnace before any repair work could begin. The forensic analysis was hosted by EMSCO in Anniston, Ala., in the presence of insurance company personnel, as well as an assembly of industry representatives from the companies who had received notices of potential subrogation from the insurance company.
Tonkawa’s furnace was completely disassembled while the insurance company’s forensic inspector directed, photographed, cataloged and analyzed every turn of every bolt on the furnace over a nine-hour workday. The coil was dissected, and lining samples were retained for future reference.
While the furnace sustained extensive damage, it did not have to be replaced entirely.
Structural reconstruction was performed to address run-out damage in the bottom of the furnace, a new coil was fabricated and the hydraulic cylinders were repacked and resealed. Fortunately, the major components were salvageable, and ultimately, the furnace was rebuilt for half the cost of a new furnace.
“The furnace experienced a significant technical failure,” said Jimmy Horton, vice president and general manager of southern operations, EMSCO. “However, not only was the unit rebuilt, it was rebuilt using minimal replacement parts.”
Though work was underway on the furnaces, Tonkawa was challenged with a projected lead time of 14 weeks on the power supply.
When accounting for the three weeks lost to insurance company holds and the time required for installation, Tonkawa was looking at a total production loss of 18-20 weeks. From the perspective of sibling co-owners Sandy Salisbury Linton and Jim Salisbury, Tonkawa could not survive such a long period of lost productivity. After putting their heads together with their furnace supplier, it was determined the reason for the long turnaround on the power supply could be traced to the manufacturer of the steel cabinet that housed the power supply.
The solution? The existing cabinet would be completely refurbished and Tonkawa would do the work rather than the initial manufacturer. This reduced the 14-week lead time to just five weeks.
Tonkawa is the single source for a number of its customers. Although lead-time had been significantly reduced, the Tonkawa team still needed a strategy to keep the single source customers in business as well as a plan to retain their larger customers.
Tonkawa pours many wear-resistant, high-chrome alloys for the agriculture and shot blast industries. Kansas Castings, Belle Plaine, Kan., which is a friendly competitor, is located 50 miles north of Tonkawa. Kansas Castings offered Tonkawa two to three heats every Friday for as long as it needed.
“We made molds, put them on a flatbed trailer, prayed it wasn’t going to rain in Oklahoma, and drove the molds to Kansas Castings. We were molding, shot blasting, cleaning, grinding and shipping every Friday,” Salisbury Linton said.
Others joined the circle of support that was quickly surrounding the Tonkawa Foundry family.
Modern Investment Casting Corporation (MICC) is located 12 miles east of Tonkawa in Ponca City, Okla. Though MICC is an investment shop and Tonkawa is a sand casting facility, MICC’s relationship with Tonkawa dates back years to when Sandy and Jim’s father, Gene Salisbury, was at the helm.
“Gene was always willing to help you out,” said MICC owner, Dave Cashon. “His advice was invaluable for us over the years, so when the opportunity arose to support Sandy and Jim, we volunteered our help.”
MICC offered to pour anything Tonkawa needed every Friday in its furnace. Tonkawa brought its alloy, furnace hand and molds, while MICC provided its furnace and a furnace hand for three heats. Many of the specialty parts Tonkawa produces were completed with MICC’s support.
When Salisbury Linton approached Cashon and asked him to issue her an invoice to cover the overhead Tonkawa was consuming, Cashon told her if she brought in six-dozen donuts every Friday morning they’d call it even.
“We’re all kind of like family,” Cashon said. “We’re all part of the same industry and though we may be friendly competitors at times, you don’t want to see anybody go through what they’ve gone through and it could have just as easily been our furnace that failed. While we all take the appropriate measures and perform maintenance to prevent these scenarios from occurring, they unfortunately still occur from time to time in our industry.”
Tonkawa had recently added steel work to its menu of services and Central Machine & Tool, Enid, Okla., was able to take Tonkawa’s patterns and fulfill its steel orders so it would not fall behind with those customers, while CFM Corporation, Blackwell, Okla., took three of Tonkawa’s employees on a temporary basis and kept them working during the downtime. Additionally, a couple of Tonkawa’s major suppliers extended their payables terms.
Thanks to Tonkawa’s suppliers, friends and its personnel’s own passion, persistence and dedication, the business is up, running and recovering—placing it among the few shops of its size to overcome the odds and remain in business after facing calamity.
Nearly eight months after that devastating Saturday evening in January, Salisbury Linton reflected on the people and events that helped Tonkawa rise from the ashes. “We certainly would not have the opportunity to see what the future holds for Tonkawa if it weren’t for all the kind-hearted people who cared about what happened to us. Everyone still checks in on us.”