(Stoneridge Engineering) The Quarter Shrinker uses a technique called high velocity electromagnetic metal forming, or “Magneforming”. This technique was originally developed by the aerospace industry in conjunction with NASA, and has been popularized by Aerovox, Grumman, and Maxwell. It involves quickly discharging a high energy capacitor bank through a work coil to generate a very powerful and rapidly changing magnetic field which then “forms” the metal to be fabricated. While it works best with metals of relatively high electrical conductivity such as copper or aluminum alloys, it will work to a more limited extent with poorer conductors such as sheet steel.
A close-up of view of Washington’s shrunken head. Although the pattern is basically maintained, there is some relative shifting between some of the features. The radiating lines on the shrunken coin are called “Luder’s Lines”. These are created as the coin is plastically deformed, and are parallel to the direction of the applied shrinking force. The lines clearly show the radial forces that were applied to the coin.
Shrunk by fellow coin shrinker in New Mexico, Peter Ledlie, here’s a “before” and “after” shot of a square brass coal token. The greater shrinkage in the flat section of the token was not anticipated beforehand.
More About the Process
The Quarter Shrinker uses a technique called high-velocity metal forming to ?electromagically? ? shrink coins. This process creates an invisible, but extremely powerful, pulsed magnetic field which literally ?hammers? the coin with the equivalent of a powerful shock wave, forcing it to change its physical shape in the blink of an eye. Energy stored within a high voltage capacitor bank is suddenly discharged into a coil of insulated wire, forcing over 100,000 amperes of current to surge through the coil?s winding, and inducing perhaps one million amperes of current to flow within the coin. The instantaneous power going into the work coil is comparable to the electrical power consumed by a large city! In addition, this huge current is also rapidly changing, and a phenomenon called ?skin effect? forces this immense current to flow within a thin outer circular rind in the perimeter of the coin, penetrating less than 50 thousandths of an inch into the coin.
The magnetic fields created by the work coil and circulating current in the coin oppose each other, creating tremendous repulsion forces between the two. The resulting compressive forces on the coin easily overcome its yield strength, and the coin is symmetrically ?crushed? into a smaller diameter, becoming thicker in the process. The shrinking process is all over in instant – about 25 millionths of a second. At an energy level of 5,000 Joules, a quarter shrinks to a diameter a bit smaller than a dime. But it still retains all its surface features! Higher energies result in smaller quarters. There?s no magic or violations of physics involved ? a shrunken coin still weighs same as before, and its density also remains unchanged.
Similar forces also act upon the work coil, causing it to explode in a violent shower of copper fragments. Early in the shrinking process, the work coil rapidly expands, stretching and ultimately fragmenting from irresistible tensile stresses. The wire?s insulation can?t stretch to the same degree and is blown off, leaving bare wire. After fragmenting, pieces of the coil are forcefully ejected with the force of a small bomb! For safety, the work coil must be confined within a bulletproof blast shield. Once the coil disintegrates, residual system energy is transformed into a blinding ball of bluewhite plasma and a shockwave (a very loud BANG!). Every shrunken coin requires its own hand-wound work coil, which is explosively destroyed during the shrinking process.
The Quarter Shrinker works for most coins. It?s especially effective on US ?clad? coins, since these coins use a highly conductive copper core sandwiched by a nickel copper alloy having a higher melting temperature. Sacagawea (“Golden Dollars?) also shrink quite well, since these utilize a pure copper core sandwiched between layers of a manganese/brass alloy. It also works well with copper pennies made before 1982. However, newer pennies use a thin copper layer plated over an easily melted zinc core ? during shrinking, the copper layer vaporizes, leaving an unrecognizable and partially vaporized glob of zinc. In addition, because of the harder nickel/copper alloy and lower electrical conductivity, shrinking doesn’t work very well with US nickels and other nickel-copper coins.
Bimetal coins (coins with rings and circular centers made from different alloys) often show different degrees of shrinkage based upon electrical conductivity and hardness. In some cases, the center portion may be freed from the outer ring, separating the coin into two pieces. Coins with a hole in the center often close the hole. Silver coins also shrink quite well, but energy levels must be reduced since the silver/copper alloy has a lower melting temperature.
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