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Theory
of Operation:
The Quarter Shrinker uses a technology called high velocity
electromagnetic forming, or "Magneforming". This is a "high energy rate" process that was originally
developed by the aerospace industry in conjunction with NASA, and was popularized by Aerovox,
Grumman, and Maxwell. It involves quickly discharging a high energy
capacitor bank through a work coil to generate an extremely powerful, rapidly
changing magnetic field which then "forms" the metal to be fabricated. The technique uses pulsed power
to generate a very high current pulse over a very short time interval.
Although electromagnetic forming works best with metals that have
relatively high electrical conductivity (such
as copper, silver, or aluminum), it will also work to a limited extent
with poorer conducting metals or alloys such as steel or
nickel.
To
shrink coins, I charge up a large high voltage capacitor
bank consisting of a number of large "energy discharge" capacitors. Each capacitor
is specially designed to reliably store up to 12,000 volts and deliver
100,000 ampere discharges. Each steel-cased capacitor measures 30" x
14" x 8", and weighs 165 pounds. A High Voltage
Double Pole Double Throw (DPDT) relay
is used to connect the capacitor bank to either a high voltage DC
charging supply,
or to a bank of high power "bleeder" resistors. A 15,000 volt high
voltage transformer and
a set of 40 kV rectifiers make up the DC charging supply for the capacitor
bank. The electrical
energy stored in the capacitor bank is proportional to the square of the stored
voltage, and the actual "shrinking" force is proportional to
the energy stored in the capacitor bank.
During shrinking, the
charged capacitor bank is quickly discharged through
a single layer work coil made from two-layer film-insulated 200C magnet wire. The coin is held
firmly in the center of the coil by a pair
of insulated dowel rods so that its axis of rotation is parallel to the
centerline
of the coil. This helps to keep the coin from twisting, and also helps
balance axial forces that might otherwise eject the coin from the coil. The
two ends of the coil
are stripped of insulation, formed appropriately, and then firmly bolted to a pair of heavy copper bus bars. A spark gap is the only affordable
device that can hold off the high voltage and then reliably and efficiently
switch the huge currents involved in the shrinking process (typically 50,000 - 100,000 amperes).
Originally, the high voltage "switch" that discharged the capacitor bank into the
work coil
was a special type of high power triggerable spark gap called a "trigatron". The trigatron switch was "fired" by applying a high voltage
(~50 kV) triggering pulse to the trigger electrode, which in turn
caused the main gap
in the trigatron to ionize and fire. However, I needed to expand the
working voltage range and reduce spark gap maintenance, so I have
converted to a solenoid-driven high current spark gap
switch
that uses 2.5" diameter brass electrodes (similar to those used in the
earlier
trigatron switch). The solenoid drives one electrodes close to the
other,
triggering an arc. However, the movable electrode does not quite
contact the fixed electrode in order to prevent contact welding (a
potential problem
at lower power levels).
When the spark gap fires, current rapidly climbs in
the
work coil, and the rate of change may approach five billion
amperes/second. As the work coil current increases, it creates a rapidly increasing magnetic field within the work coil.
The natural resonant frequency of the LC circuit that's formed by the capacitor bank
and the inductance of the work coil ranges between 8 to 12 kilohertz (kHz). Through electromagnetic induction ("transformer action"), a
huge circulating current is induced within the coin. However, because of skin effect,
most of the induced current is confined to the outermost rim of the coin, typically
penetrating to a depth of only 0.050 inches or less. In clad coins, most of the
circulating
current actually flows within the better conducting copper center of
the clad sandwich
than in the outer layers. This causes the center of clad coins to
shrink a bit more than the outermost layers, leading to an "Oreo Cookie"
effect. Because of Lenz's Law, the magnetic fields of the coin and work coil strongly oppose each
other, resulting in tremendous repulsion forces between
the work coil and the rim of the coin. The
circulating current in the rim of the coin prevents most of the
magnetic field from the work coil from penetrating the interior of the
coin.
The initial energy stored within the capacitor bank is typically in the range of 3,500 - 6,300 Joules (watt-seconds). Because this energy is discharged in approximately 20 millionths of a second, the instantaneous power
is very large and, for a brief instant, is roughly equivalent to the electrical
power consumed by a good sized city. The repulsion forces between the work coil
and the coin create tremendous radial compressive forces that easily overcome
the yield strength of the metal alloys in the coin, causing the coin
to plastically deform into a smaller diameter. The higher the initial energy,
the greater the degree of "shrinkage". Applying a 6,300 joule pulse results
in a quarter whose final diameter is about 0.1" SMALLER than a dime! At the same
time, similar radial expansion forces cause the work coil to explode
in a potentially lethal shower of copper fragments. In addition, there
are also large (but less strong) axial forces that squeeze the work coil
wires together while the coil is simultaneously expanding in diameter. In
all cases, the forces acting upon the coil are in a direction that would tend to
increase its inductance. The coin effectively behaves as a short circuited single turn
secondary in a 10:1 step down transformer, and the current that's induced in the outer rim
of the coin may exceed a million amperes!
The metal forming effect
of huge magnetic fields is sometimes seen on a much larger scale. For
example, repulsive forces between the windings of large utility power
transformers can
literally tear the transformer apart during a high current short
circuit, or rip heavy bus bars from their mounting insulators within electrical substations.
As
the work coil expands, the insulation separates
from the wire (since the film insulation can't stretch as much as the
ductile copper!), the
wire eventually fragments, and pieces of the coil are forcefully
ejected
outward with the force of a small bomb, with small coil fragments
reaching velocities of up to 5,000 fps. For safety, the work coil is
housed
inside a blast shield made from 1/2" Lexan
polycarbonate, the same material used
to make bulletproof windows. Furthermore, the regions in the direct
path of the exploding coil fragments are further reinforced with 1/4"
thick steel plates. Once the
work coil disintegrates,
most of the residual energy in the
system
is dissipated in a ball of blue white plasma.
The Quarter Shrinker is designed so that any residual energy in the
capacitors is safely dissipated by high power bleeder
resistors. The system is triggered from about 15 feet away from
a remote control box. I've found (the hard way!) that 8,000 Joules is
about the maximum energy I can repeatedly use without running a risk of
fracturing
the Lexan blast shield from the shock wave. Under the right conditions,
Lexan
does shatter - I've got the pieces to prove it! Other experimenters
(Rob Stephens, Bill Emery, Phillip Rembold, Ross Overstreet, Brian
Basura, and Ed Wingate)
have resorted to using steel enclosures when running at higher power
levels.
Adding 1/4" steel plates has stopped the Lexan blast shield from
fracturing. However, future designs will use 1/2" thick AR400
steel armor plate to better withstand deformation from repetitive hammering by supersonic coil
fragments.
Results:
The largest coin I've shrunk was a Silver Eagle, a silver
coin that starts out being about 1.6" in diameter, and ends up 1.3" in diameter afterwards.
At 6,300 joules, a silver Morgan Dollar
is reduced from about 1.5" to 1.25" in diameter, and a clad Kennedy half dollar is reduced to a diameter smaller than a
US Quarter.
At 5,000 joules, quarters will shrink to about 80-100 mils smaller than a dime.
During the shrinking process, the current in the coil usually never
makes it to
the first current peak, since the work coil disintegrates first. This
disintegration
prevents the energy discharge capacitors from seeing potentially
damaging
voltage reversals. However, the rapid discharge and tremendous surge
currents
are still very hard on the capacitors. Because of
failures with earlier GE pulse capacitors, I've redesigned the system
to use low inductance, 100 kA/shot Maxwell (now General Atomics Energy Products) pulse caps that are truly
rated
for this type of abuse (300,000 shots at 100,000 amperes/shot). My original capacitors would begin failing
after 50 - 100 shots. The robust Maxwell capacitors have withstood
well over 6,000 shots with nary a whimper.
Examination of the coil fragments show that the wire has
been substantially stretched (#10 AWG looks like #14 AWG afterwards),
it becomes strongly work hardened, and has periodically "pinched" regions and kinks
caused by the copper being stressed beyond its yield strength by the
ultrastrong magnetic field. Many fragments are 1/4" long or less, and all
pieces show evidence of tensile fracture at the ends. Since the wire's insulation
is blown off, most fragments are bare copper. The wire often also shows signs of localized melting
on the inner surface of the solenoid due to current "bunching" from a combination
of skin effect and proximity effect.
A larger diameter work coil, operating at lower power
levels, is used to crush aluminum cans. An aluminum soft drink can ends up looking
like an hourglass as the center is shrunk to about half its original diameter.
In this case, the coil does not disintegrate due to its more massive design
(3 turns of #4 AWG solid wire) and the system is fired using a lower energy
level than that used for coin crushing. At higher power levels the can is
ripped apart from the combination of the air inside the can suddenly being
compressed, and the heating of the can from the induced currents. Can crushing
also works with steel cans, but the can undergoes greater heating and reduced
shrinkage because of steel's lower conductivity. The "skin depth" is also
much thinner due to the ferromagnetic properties of the steel alloy. Since
the work coil is not destroyed during can crushing, the capacitor bank and
spark gap are stressed by a damped oscillatory ("ringing")
discharge.
The capacitor bank voltage must be reduced to avoid damaging the caps.
Since most of the capacitor bank's energy ends up being dissipated as
heat
in the spark gap, can crushing causes significant electrode heating and
erosion in the
HV switch.
The
Quarter Shrinker works well on clad dimes, quarters, half dollars,
Eisenhowers, silver Morgan and Peace Dollars, Susan B. Anthony,
Sacagawea, small Presidential dollars, and most foreign coins.
It works less well with nickel and nickel-copper coins, but
only slightly works with plated steel coins. It also works well with
older
bronze and copper-zinc alloy pennies. However, since mid 1982, US
pennies
have been made using a zinc core with a thin copper overcoat. During
shrinking,
the thin copper layer vaporizes and the zinc core melts, leaving an
unrecognizable
disk of molten zinc accompanied by a messy shower of zinc globules
throughout the
blast chamber.
Because of the greater hardness and much poorer electrical conductivity
of nickel-copper alloys, the shrinking process doesn't work as well
with US
nickels, only shrinking them by only about 10% even at 6,300 Joules.
A
shrunken coin weighs exactly the
same as before, and its density also remains unchanged. The coin becomes
thicker
as its diameter is reduced, but the overall volume of the coins
stays the same. Certain bimetal foreign coins (with rings and
centers made from different alloys) may show different degrees of
shrinkage based
upon the electrical conductivity and hardness. In some cases, the
center portion
may shrink a bit more, freeing it from the outer ring. This occurs with older
Mexican, UK, and French bimetals, and newer Two Euro bimetal coins.
Because
of the extremely high discharge currents
and fast current rise times, energy discharge capacitors are fabricated
to
have low inductance and use special internal construction techniques to
safely handle the mechanical shock created by magnetic and dielectric forces
during high current pulse discharges. Unfortunately, the GE
pulse
capacitors that I previously used were simply not designed to withstand
this abuse, and they began to fail catastrophically. One actually
ruptured its metal
case, hemorrhaging stinky, arc-blackened capacitor oil all over the floor.
This was a real hit with the wife! Our Maxwell energy discharge capacitors have proven to be true
"Timex's" - they "take a lickin' and keep on
tickin'".
Is Wire Fragmentation Consistent with EM Field Theory?
Copper wire fragments from the work
coil clearly indicate that the wire has been subjected to large tensile stresses.
Most of the observed effects on the wire can be explained by hoop stresses
from magnetic pressure
within the work coil solenoid, Lenz's Law repulsion
between the coil and the coin, and periodic conductor pinching
("sausage" instability). The latter is a phenomenon that magnetic
pinching forces are sufficient to cause the conductor to temporarily
behave as though it were a conductive fluid. However, there is also a
curious ridge which shows
up under microscopic examination of the coil fragments that may hint of
other
effects as well. This artifact was first noticed by Richard Hull of the
Tesla
Coil Builders of Richmond, Virginia (TCBOR) when reviewing similar wire
fragments
from another researcher (Jim Goss). It seems that when an extremely
high
current flows through a solid or liquid metallic conductor, certain
effects
begin to appear which may not be fully explained by existing EM field
theory
and Lorentz forces. One very interesting example involves forcing a very large
current pulse very quickly through a straight piece of wire. Under appropriate
conditions, the wire does not melt or explode. Instead, it fractures into
a series of roughly equal length fragments, each fragment showing unmistakable
evidence of impact tensile failure. Each segment has literally been pulled
apart from neighboring fragments with little or no evidence of necking down
or melting. Clearly large tensile forces were set up within the wire during
the brief time that the large current flowed. But, per existing EM theory,
no tensile forces should exist!
A father and son team, Dr.'s Peter and Neal Graneau (who
are coauthors of "Newtonian Electrodynamics" and "Newton Versus Einstein")
theorize that internally developed "Ampere' tensile forces" can fully account
for the observed behavior of this, and other high current experiments.
While Ampere' tensile forces are predicted by classical electromagnetic
theory, they have long been removed from all modern textbooks, being replaced
instead by modern field theory and Lorentz forces. Interestingly, even though Ampere' forces
are no longer an accepted part of current EM theory, their existence appear to be experimentally
verifiable in exploding wires or high DC current flow within molten metals (such as aluminum refining).
In their books, the Graneau's give many other thought provoking
experiments
that appear to support Ampere' Tension forces. More recently, other
scientists have proposed that high current wire fragmentation may actually be
caused by a combination of flexural
vibrations and thermal shock. This is an area that's
still ripe for future research and experimentation...
But Isn't Mutilating Money a Federal Offense?
Federal law specifically forbids
the "fraudulent mutilation, diminution, and falsification of coins" (see
US
Code, Title 18 - Crimes and Criminal Procedure, Part I - Crimes, Chapter
17 - Coins and Currency, Paragraph 331). The key word is Fraudulent.
Although
it recently became illegal to melt pennies or nickels or to export them
to reclaim their value as scrap metal, you can otherwise do pretty much
anything else to them as long as you don't alter then with an intent to defraud. This includes squishing
them on railroad tracks, flattening them into elongated souvenirs at tourist
traps, or crushing them with powerful electromagnetic fields. I take great pains to
tell folks exactly what they are receiving and how the process was accomplished.
This is also why those vending machines in tourist traps that squash pennies
into elongated souvenirs or "funny" stamped pennies with Lincoln smoking
a cigar are indeed legal (although they can't be used as currency anymore). The
official position
of the US Mint is that although they "frown on the despicable practice" of
altering
coins, they also agree that it is indeed legal to shrink coins.
Note that this may not be the case within other countries, such as the
UK and Australia, where defacing the Queen's image on a coin used to be considered a punishable offense. Here is an interesting example of fraudulent "coin shrinking" that was prosecuted by the US Secret Service (way back in 1952!).
Paragraph
332 deals with debasement of coins; alteration of official scales,
or embezzlement of metals. Since the coins involved are all made from base
metals, this section does not apply. However, since the density, metal content,
and weight remain unaltered during the shrinking process, coin shrinking
is legal even when applied to precious metal coins. Gold and
90%+ silver coins shrink very well.
So Who Invented this Crazy Device?
No, it wasn't me! For the history of coin
shrinking as presently reconstructed, check out The
Known History of "Quarter Shrinking"
References and More Fun Reading:
Following are various references for the serious researcher.
Also, check the "Out of Print Books Information" and "In Print Book Sources" sections of the Links Page, or check with your local technical college library system.
A. Electromagnetic Metal Forming and Magneto-Solid Mechanics:
1. ASM, "Metals Handbook, 8th Edition, Volume 4, Forming", American Society for Metals
- see section on Electromagnetic Forming (out of print)
2. Wilson, Frank W., ed., "High Velocity Forming of Metals", ASTME,
Prentice-Hall, 1964, 188 pages (out of print)
3. Bruno, E. J., ed., "High Velocity Forming of Metals", Revised, edition,
ASTME, 1968, 227 pages (out of print)
4. NASA, "High-Velocity Metalworking, a Survey, SP-5062", National Aeronautics
and Space Administration, 1967, 188 pages (out of print)
5. Moon, Francis C., "Magneto-Solid Mechanics", John Wiley & Sons, 1984, ISBN 0471885363, 436 pages (out of print)
6. Murr, L. E., Meyers, M. A., ed., et al, "Metallurgical Applications
of Shock-Wave & High-Strain-Rate Phenomena", Marcel Dekker, 1986,
1136 pages, ISBN 0824776127 (in print)
7.
"Electromagnetic
Forming Handbook" - Currently the BEST Electromagnetic Forming Text, Translated
from Russian and ON LINE.
8. "Pulsed Magnet Crimping" by Fred Niell, straightforward explanation of magnetic forming (fairly technical)
B. Capacitor Discharges, High Magnetic Fields, Pulsed Power/Switching, and Wire Fragmentation:
1. Frungel, F., "High Speed Pulse Technology", Vol. 3, Academic Press,
1976, 498 pages (Capacitor Discharge Engineering, out of print)
2. Schaefer, Gerhard, "Gas Discharge Closing Switches", Plenum, 1991,
569 pages (out of print)
3. Martin, T. H., et al, "J. C. Martin on Pulsed Power", Plenum, 1996,
546 pages (out of print)
4. Knoepfel, H., "Pulsed High Magnetic Fields; Physical Effects &
Generation…", Elsevier, 1970, 372 pages (out of print)
5. Fowler, C. M., Caird, Erickson, "Megagauss Technology and Pulsed
Power Applications", Plenum; 1987; 879 pages (out of print)
6. Vitkovitsky, Ihor, "High Power Switching", Van Nostrand Reinhold,
1987, 304 pages
(out of print)
7. Pai, S. T, & Zhang, Q., "Introduction to High Power Pulse Technology",
World Scientific, 1995, 307 pages ( in print)
8. Sarjeant, W. J. & Dollinger, Richard E., "High Power Electronics",
Tab Professional & Reference Books, 1989, 392 pages (out of print)
9. Shneerson, G. A., "Fields & Transients in Superhigh Pulse Current
Devices", Nova Science, 1997, 561 pages (out of print)
10. Parkinson, David H., Mulhall, Brian E., "The Generation of High
Magnetic Fields", Plenum, 1967, 165 pages (out of print)
11. Chace, W. G., Moore, H. K, "Exploding Wires", Volume 1, Plenum, 1959, 373 pages) out of print)
12. Chace, W. G., Moore, H. K, "Exploding Wires", Volume 2, Plenum, 1962, 321 pages) out of print)
13. Chace, W. G., Moore, H. K, "Exploding Wires", Volume 3, Plenum, 1964, 410 pages) out of print)
14. Chace, W. G., Moore, H. K, "Exploding Wires", Volume 4, Plenum, 1967, 348 pages) out of print)
15. Mesyats, Gennady A., "Pulsed Power", Springer, 2004, 568 pages, ISBN 0306486531 (in print)
C. Special Reading for those wishing to delve deeper into more esoteric areas of EM Field Theory and Wire Fragmentation:
1. Graneau, Peter & Neal, "Newtonian Electrodynamics", World Scientific,
1996, 288 pages (in print)
2. Graneau, Peter & Neal, "Newton Versus Einstein, How Matter Interacts
with Matter", Carlton Press, 1993, 219 pages ( in print)
3. Jefimenko, Oleg, "Causality, Electromagnetic Induction, and Gravitation",
Electret Scientific, 1992, 180 pages ( in print)
4. Lukyanov, A., Molokov, S., "Why High Pulsed Currents Shatter Metal Wires?",
Pulsed Power Plasma Science, 2001, Digest of Technical Papers, Volume 2,
pages 1599-1602
5. Lukyanov, A., Molokov, S., Allen, J. E., Wall, D., "The Role of Flexural
Vibrations in the Wire Fragmentation", Pulsed Power 2000, IEE Symposium ,
pages 36/1 -36/4
6. Wall, D. P., Allen, J. E., Molokov, S., "The Fragmentation of Wires
by Pulsed Currents: Beyond the First Fracture", Journal of Physics D: Applied Physics.
36 (2003) 2757–2766
D. Web-Accessible Sources of Information on Ampere' tension forces:
http://www.df.lth.se/~snorkelf/Longitudinal/Slutdok.html
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