The finished American Silver Eagle coin is a masterpiece of art and science – the product of a fascinating series of human and modern technological processes. Here is the story in brief.
Legislative Beginning
The American Silver Eagle coin, like other coins minted in the United States, began its life from legislative bills, in this case initiated by Senator McClure and Representative Craig in 1982 and amended by Senator McClure’s ‘Liberty Coin Act’ in 1985 and signed into law by President Reagan in the same year.
The point of the legislation was to maximize the return on the sale of strategic stockpiles (Defense National Stockpile) of silver (to help balance the Federal Budget) through the production and sale of silver bullion coins. As the stockpiles were being depleted, as intended by the initial legislation, President Bush signed the ‘Support of American Eagle Silver Bullion Program Act’ in 2002 to extend the coinage program through the purchase of silver on the open market.
Senator McClure’s ‘Liberty Coin Act’ stipulated the parameters of the Silver Eagle, including its size, weight, purity, obverse and reverse designs, inscriptions, and edge finish.
Creating the Relief Designs
Ideas for the design of coins come from politicians, citizens, artists and sculptors alike. Once the objectives and concepts of the design are established by all parties, drawings are made of both sides of the coin, including images and textual inscriptions required by law (‘IN GOD WE TRUST’ and ‘E PLURIBUS UNUM’).
The final drawings are approved before sculptors and engravers create and refine their renditions using physical and digital modeling techniques. Physical models used to be made with clay and plaster and digitally scanned into a database for more detailed work. Now, more sophisticated software tools are used to model and finish the designs directly from the original drawings.
The obverse relief on the American Silver Eagle was taken from Adolph Weinman’s ‘Walking Liberty’ design. On the reverse side, the ‘heraldic eagle’ relief was created by John Mercanti.
Making the Dies
Once the digitized coin reliefs have been completed, CAM (Computer Aided Manufacturing) software is used to interpret this data and create instructions for CNC (Computer Numerical Control) machine cutters of different and finer diameters that will mill out each relief on the end of a separate steel ‘hub’. The result is an extremely polished and accurate replica of the coin design faces on these ‘master hubs’, one for the obverse and one for the reverse design of the coin.
Initially, the master hubs that are fabricated are of larger diameter than the legislated coin dimensions. So, a reducing lathe is used to create a master hub of the correct size.
Because dies wear out after a certain number of impressions, the capability to produce enough dies for mass production is met by a succession of master hub to master die steps. The initial master hub of the final correct size is used to create a ‘master die’. The master hub is first hardened by heat treating, while the die material is softened by annealing. The master hub which has a raised design profile is then pressed into the master die material, creating an infuse impression of the coin face in the master die – and as a result is strengthened through the compression of the press. These master dies are then used to create ‘working hubs’ and the working hubs are in turn used to create ‘working dies’. The process is repeated until enough working dies are created for the total production run of coins.
The working dies will be used to ‘strike’ and manufacture the coins from silver blanks.
Punching Out the Blanks
The silver for the American Eagle initially came from the Defense National Stockpile starting in 1986. Since about 2001, when the stockpile became depleted, silver has been purchased from the open market.
The silver is processed to conform to the purity requirements of the Eagle and manufactured into thin strips slightly thicker than the final height of the coin. The coin strips are 1500 feet long by about 13 inches wide and are delivered to the Mint in coils each weighing about 6,000 pounds.
These silver coils feed into high-speed automatic presses that cut out round ‘blanks’. The diameter of the blank is slightly larger than the final coin dimension to account for the formation of the ‘rim’ in a later stage. Its weight is the same as the final weight of the coin. About 25 per cent of the coil material is left over after punching out the blanks. This residual, called ‘webbing’, is recycled to the supplier and melted down for use in new coils.
Now the Silver Eagle is beginning to take shape.
Softening the Blanks – Annealing
The Eagle blanks are heated in an annealing furnace to a very high temperature – around 1,000 degrees Fahrenheit – to change their molecular structure and soften them in preparation for creating the rim and edging, and ‘pressing in’ the coin’s designs.
After annealing, the blanks are quenched or cooled in a liquid solution and then dried.
Cleaning
The annealing process oxidizes the finish on the blank material. Consequently, the softened blanks must be chemically washed to remove these oxides and any other residual tarnish and contamination.
The result is a clean and bright blank that is ready for the next stages of coin production.
Burnishing the Uncirculated Silver Eagle
In 2006, the American Silver Eagle Uncirculated (or Burnished) coin was introduced. This coin differs from the bullion and proof versions by its particularly shiny background achieved by an extra step in the preparation of blanks for coining – ‘burnishing’.
Blanks are tossed in a drum with steel pellets that texture the surfaces to eliminate visual defects, close porosity and produce a very bright shiny background to the coin’s obverse and reverse designs that will be ‘pressed in’ during a later stage.
Fashioning the Rim – Upsetting
To finish the sizing of the coins, softened, cleaned and burnished blanks undergo an ‘upsetting’ process that creates a rim on each of the surfaces. The rim is made by forcing the blank through a smaller diameter opening that downsizes the diameter to specifications while raising the thickness on both sides in a small band on the outside circumference of the blank.
Presto, the blank has become a ‘planchet’.
The ‘upsetting’ pressures result in a hardening of the material at the outside edge of the coin, giving it more resilience to damage, and protecting the design surfaces from wear and tear. The rim height is designed to be higher than any of the relief patterns on the coins inner surfaces to prevent the patterns from contact when the coin is lying flat.
Finished planchets are inspected for defects (for example, gouges that are unlikely to survive the coining process) and, if found unacceptable, are rejected to a ‘waffler’ that physically defaces them and returns them to the silver supplier for recycling.
The Coining Process
The ‘piece de resistance’ in this entire minting operation is the ‘coining’ process.
Here, the ‘planchets’, with their finished surfaces and rims, are fed into the stamping presses and are struck with literally tons of force to impress the obverse and reverse die patterns on both surfaces at the same time. Usually the anvil or stationary part of the press is the reverse (or ‘tails’) die, while the hammer or striking part of the press is the obverse (or ‘heads’) die. The reeded edge on the planchet is also formed during the same striking process from a reeded collar affixed inside the coining press.
American Silver Eagle bullion and uncirculated coins are struck once each in multiple die presses, while proof coins are struck in single die presses multiple times.
Inspecting, Counting and Packaging
The coining process is designed with sophisticated quality control mechanisms. Batch samples are inspected automatically and manually for adherence to quality specifications and the entire batch accepted or rejected on the basis of the inspection. Rejected coins, like defective planchets, are sent to the ‘waffler’ for destruction and recycling.
All coins that pass inspection continue on to counting and packaging areas.
Bullion coins are packaged and shipped in bulk to authorized purchasers in green plastic ‘monster boxes’ – each box contains 500 coins packaged in twenty-five 20-coin plastic tubes. These bullion coins are sold to the public through the purchasers’ distribution network.
Silver Eagle proof, uncirculated and special issues are all available directly from the US Mint. The proof and uncirculated coins are packaged individually in protective plastic and mounted in a satin-lined, velvet-covered presentation case along with a certificate of authenticity.
That is how the American Silver Eagle coin is made.
If you are interested in collecting or investing in the American Silver Eagle or just want to become more enlightened, drop by my blog at: AmericanSilverEagleCoins.org
I am very busy there building up a repository of interesting articles and references to guide you along. Enjoy the tour!
Tim MacKenzie is a Professional Engineer in Ontario, Canada. He spent many years in scientific research and building information systems. His focus now is on Internet communications.
Article Source: http://EzineArticles.com/?American-Silver-Eagle-Coins—How-They-Are-Made&id=4623815
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