U.S. Mint reports experimental metal findings
- Published: Jun 7, 2019, 5 AM
The U.S. Mint’s latest biennial report to Congress on its research into alternative compositions for circulating coins includes potentially seamless options incorporating manganese with varying percentages of copper and nickel.
The Mint terms alternatives that would not require retrofitting of vending equipment as “seamless” options, while options that would require vending machine updates are termed “co-circulating” in the report.
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The lowest cost option for the 5-cent coin is a homogenous nickel-steel alloy that could bring the combined production and associated costs below face value for the first time in more than a dozen years.
The lowest cost alternative for the current copper-nickel clad dime is nickel-plated steel; for the quarter dollar, a clad alternative with lower percentages of copper and nickel but additional zinc and manganese would lower cost.
The current cent’s planchet has a composition of 99.2 percent zinc and 0.8 percent copper plated with pure copper. The current 5-cent coin is made of a homogenous alloy of 75 percent copper and 25 percent nickel. The dime and quarter dollar planchets are each composed of outer layers of 75 percent copper and 25 percent nickel bonded to a core of pure copper.
The U.S. Mint’s testing of co-circulating options resulted in the development of two “unique” alternatives, involving according to the 2018 report.
The 2018 report is the fourth mandated under The Coin Modernization, Oversight and Continuity Act of 2010, Public Law 11-302.
Previous reports were submitted to Congress in December 2012, December 2014 and June 2017 (for 2016). The 2018-dated report was submitted in April 2019. No formal recommendations were made to adopt any of the options developed.
The 2012 report outlined six potential alloys to replace the current compositions.
The 2014 report addressed which alloys would not work for U.S. coinage and contained recommendations for further research.
The results of that refined research are included in the 2016 report.
Two different potentially seamless composition options involving manganese could be useful for the 5-cent, dime and quarter dollar denominations.
An 80/20 option for the 5-cent denomination would comprise a homogenous composition of 77 percent copper, 3 percent manganese, and 20 percent nickel.
The lowest cost option for the 5-cent denomination, based on test results, was nickel-steel, combining nickel, iron and manganese, at a cost of 4.72 cents. The nickel-steel option is not seamless, however.
The dime and quarter dollars could use the same 80/20 composition for the two outer layers and bond them to a core of pure copper.
The 80/20 option for the dime tested out at 3.3 cents per coin. The least expensive option for the dime, nickel-plated steel, while not seamless, cost 2.29 cents per coin.
The second potentially seamless composition, C99750T-M, contains 50.75 percent copper, 14 percent nickel, 33 percent zinc and 2.1 percent manganese.
Test results showed the C99750T-M option to be the least expensive option for the quarter dollar, at 7.98 cents, 3.16 percent lower than the current costs for its copper-nickel clad composition.
Additional testing is required to confirm whether one or both of the potentially seamless options are viable, according to the 2018 report.
Additional testing would also be needed to assess the feasibility of five co-circulating composition options — three that could potentially be used for both the 5-cent and dime denominations, and two for the 5-cent coin only.
The three co-circulating options for the 5-cent and dime are:
??Multi-ply plated steel (MPPS)
??Nickel-plated steel (NPS)
??Nickel-plated silicon steel — a unique option developed by the Mint as an alternative to the nickel or multi-ply plated steel commonly used by other world mints. This alloy would co-circulate with a distinguishable electromagnetic signature for vending machine recognition.
Two additional co-circulating options for only the 5-cent denomination are:
? R52 stainless steel
??Nickel steel — a monolithic alloy uniquely developed by the U.S. Mint. Not attracted to magnets, it is a less expensive co-circulating option than stainless steel. The nickel concentration would be 25 percent, with the balance of the alloy being lower cost iron and some manganese.
Testing was conducted using the various options with machinery from three major coin acceptor manufacturers — Cummins, CPI and Suzohapp (Scancoin).
Production improvements during the research and development process include extending die life for producing 5-cent coins through modification of the upset profiles (the method to form a raised rim on blanks before striking).
Improvements also involve slight tweaking of the coin designs.
“Matching planchet upset and die curvatures will reduce coining pressures around the coin edge, producing more uniform normal pressures,” according to the report.” This “matched system” would enable coining presses to use less stamping force and still obtain optimal detail in the coins produced using current coinage materials. Less stamping force results in longer die life. Production testing confirms the effectiveness of this approach, and larger scale testing is currently in progress. Once completed, these refinements can be incorporated into the standard 5-cent design, and testing can move forward to transition the approach to other denominations.
According to the report, “Matching planchet and die curvatures will also be beneficial when considering alternative materials, which in many cases are harder than current cupronickel. Greater hardness increases the coins’ wear resistance, but the striking tonnage must be increased to get the same level of detail in the new coins as in the old ones. This greater striking pressure would reduce the die life and increase the stamping process cost. After the upset and die modifications, these harder new materials could be stamped to get the same image detail with the same tonnage as current production.”
Testing has been executed using blanks both punched from cold-rolled coils supplied to the Mint by outside vendors, with the blanks then annealed for the upsetting process, and from push-back blanking. The push-back blanking involves the Mint punching blanks from coils already annealed by a supplying vendor.
“The Mint contracted with an independent company to perform a study on the formation of the coins’ rims in the optimized design,” according to the 2018 biennial report. “The contractor used a prototype upsetting tool and tested several different profiles and methods of upsetting blanks and determined that a tapered upset with a concave facing formed the best rims of coins, and that tapered upset with a convex facing was nearly as good. Continued testing and evaluation are in progress.”
No options have been found in any of the experimental phases to bring the combined costs for cent production below face value.
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