A Brief History of High Power
Pulsed Magnetic Fields and Magneforming
Russian
Nobel Prize winning physicist P. L. Kapitza was the first researcher to generate
and study the effects of ultrastrong magnetic fields, beginning in 1924.
Kapitza initially used specially designed high current lead-acid storage
batteries as power sources, combined with a custom high current switch and
fuse arrangement to briefly apply huge currents (10,000+ Amperes) into robustly
constructed solenoids. Using this arrangement, Kapitza was able to generate
pulsed magnetic fields of up to 500,000 gauss (500 kilogauss) for 3 milliseconds. In later
work, he employed a specially designed flywheel and dynamo combination, and
ultimately used high voltage capacitor banks to develop even higher fields
for even briefer intervals. In all of these experiments a large amount of
stored energy was very quickly applied, briefly driving a huge current into
an air core solenoid. The source of the energy was then removed or discharged
before the coil could overheat and melt. However, his attempts to achieve fields higher than 300 kilogauss always resulted in violent destruction of the solenoid.
The first laboratory application using a capacitor
bank to actually perform electromagnetic metal forming is credited to T. F.
Wall in 1926. Wall was able to achieve fields exceeding 450,000 gauss by
using robustly constructed coils that subsequently exploded. In the mid 1950's, Harold
Furth and Ralph Waniek at the Harvard Cyclotron Laboratory developed special
coil construction techniques which permitted electromagnets to survive the
intense forces associated with transient ultrastrong magnetic fields. In
the late 1950’s these techniques were first applied on an experimental basis
in industry. US Patent #2,976,907, issued to G. F. Harvey and D. F. Brower,
covers the basic process, which is sometimes called Magnetic Pulse Forming
or “Magneforming”. A. P. Langlois reported on electromagnetic forming
using expendable wire coils to swage tubular parts in 1960. Gulf General
Atomic introduced the first commercially available magnetic metal forming
equipment in 1962. This machine had a capacity of 4,500 foot-pounds ( about
6,100 Joules) per shot, and could generate up to 10 pulses/minute. A number
of other aerospace and capacitor manufacturers further evolved the technology,
increasing the power levels during the 70’s and 80’s. These included McDonnell
Douglas, Boeing, LTV Aerospace, Advanced Kinetics, Inc., Republic Aviation,
and General Dynamics, and capacitor manufacturers Maxwell, Cornell Dubilier,
and Aerovox. Power levels were eventually boosted to over 230,000 Joules/shot
on the largest capacitor discharge machines.
The History of
"Quarter Shrinking"
It's
not exactly clear just when magneforming was first adopted to “shrinking”
coins. I first learned about "quarter shrinking" via a posting by Richard
Hull (Tesla Coil Builders of Richmond, VA or TCBOR) on the Tesla Coil Builders
Mailing List back in 1996 or so. Richard described a videotape of coin crushing
made by Jim Goss at University of Wisconsin. On the tape, Jim performed various
coin crushing experiments in a system that used utility Power Factor Correction
(PFC) capacitors. The special HV switch was constructed from a pair of massive
graphite anodes (removed from special purpose electron tubes called ignitrons).
A cannon ball was rolled down a PVC pipe to in order to bridge the
connection between the graphite electrodes, discharging the capacitor bank
into the work coil! Jim's experiments were eventually ended due to capacitor
failure. This is because most capacitors, including PFC caps, are not constructed
to handle the huge magnetic forces and hydrodynamic shock associated with the high
discharge currents used in magneforming.
About a year later (1997), I acquired a batch
of large 54 uF 15 kV GE pulse capacitors off the surplus market. Each were
metal cased with "Frankenstein" insulators, and weighing about 150 pounds.
A veritable Mad Scientist treasure! I used three of these, and a triggered
spark gap made by fellow coiler Rob Stephens from near Ontario, Canada, to
build a combination can and quarter shrinker in early 1998. However, with
continued use, the system suffered from progressive weakening of the internal
capacitor buses, ultimately leading to catastrophic capacitor failures. One particularly destructive failure caused the steel case
to rupture and a couple of gallons of nasty looking blackened oil and capacitor
foil fragments to leak onto the indoor-outdoor carpeting! Needless to say, the wife was NOT
amused by these events!
Upon autopsy, I was able to determine that these so-called "pulse caps" were
actually constructed as PFC capacitors, and it was quite obvious that they
could not withstand the repetitive high current and electromagnetic forces
involved with quarter shrinking. This is why they failed after only 50-100 shots.
After considerable hunting, I was able to locate a batch of reasonably priced
(and VERY robust) Maxwell 70 uF 12,000 volt energy discharge capacitors. Each capacitor
is rated at 100,000 Amperes/shot for 300,000 shots(!). I'm now redesigning
the system so that it can deliver up to 24,000 Joules, or about 17,800 foot-pounds
of energy per shot. This is about the same energy as dropping a one ton weight
from a height of 9 feet!
In 1998, a fellow high voltage researcher described an article
that he'd seen in a 1993 issue of "Extraordinary Science" magazine (no
longer published). In this article the author, Gary Hawkins, described using an x-ray
high voltage power supply and a 60 kV capacitor bank to launch rings and plates,
and later on, to crush coins. The article contained a number of pictures
of coins he'd shrunk using coils with different numbers of turns at varying
power levels. I'm attempting to locate a copy to scan in if possible. Until
very recently, this was all that I knew of the brief history of coin crushing.
However, a conversation with William Beaty in 2001 revealed that Quarter
Shrinking actually first appeared in 1991.
Bill Beaty’s fascinating account of what is believed to be the first "Quarter Shrinker"
"Dale
Travous is a sculptor who once had a
big studio space in downtown Seattle, and was making Tesla coils (and
later
a big Tesla Magnifier.) He traded some equipment for some big
caps
around 1990 or so. I think they were 150 kV, maybe 10 uF, six of
them. He was charging them up and using them to destroy pieces of
wire, and I told him about an article I'd seen in the 1970s about an
"optical
shutter" made from a coil of copper rod wound around a soup can with
the
ends removed. When a big laser energy storage capacitor was
discharged
through the coil, the soup can would instantly neck down to close the
aperture." [Note: Recently, one of the Sandia Laboratories pulsed power
scientists who invented this device forwarded me a picture of it, originally taken in 1974].
"He tried this on copper pipe and was making
hourglass effects (even shredding very thick .75" pipe when the necked-down
part would *bounce*.) Then he found that he could distort a penny
with a very thick coil from a 500-amp circuit breaker. Then he found
that he could smoothly shrink pennies to less that 50% of their original
diameter, but the coil would be destroyed after a few shots. Then
he started using coils made from #10 solid copper wire. Eventually
he tried lots of other coins, and settled on using quarters (they were
a bit more impressive than pennies or $.50 coins for some reason.)
I'm pretty sure this was all in 1991. "
"We found more big caps at Boeing Surplus.
Boeing uses them as dent-pullers. I saw what was probably the dent-puller
power supply at auction, a huge thing the size of several refrigerators
with a bunch of big energy storage caps in parallel within. We learned
that many manufacturers also use capacitor discharges to crimp the metal
fittings onto the ends of rubber hoses."
"Gary Hawkins was a co-renter of the lab space,
and he sent an article to the International Tesla Society about the "Quarter
Shrinker" cap bank. They published it in their magazine, see EXTRAORDINARY
SCIENCE, Volume 5 No.3, summer 1993, p10. This magazine was a publication
of the International Tesla Society, Colorado Springs, CO - the group is
now defunct. Email the author at ghawk@eskimo.com, or http://www.eskimo.com/~ghawk
Others who built later Quarter Shrinkers probably saw this article, or
heard about it second-hand."
"Around 1994 or 1995 Dale Travous had some
pieces in an art exhibit at Seattle COCA gallery. One was a series
of about twenty progressively shrunken quarters mounted in a row on a piece
of white Plexiglas. At the same time he stopped shrinking coins and
instead was using the cap bank attached to a steel "watergun", a short
stubby cannon which could explode a cc of water and drive a plastic slug
through a 12" block of clay. Big fun. Later he entered the
cap bank in the "science fair" put on by THE STRANGER adult newspaper.
It was a room-freshener. He was vaporizing cherries, strawberries,
etc. An immense blast like a shotgun going off, and then the room smells
nice."
"Around the same time we got some 100 uF 30
kV Maxwell capacitors free after a government auction, and built a second
quarter shrinker. Lots of people in the Seattle area have coins which
were crushed by this version. Around 1995 I downloaded Mozilla and found
eskimo.com, and posted the article on my beastie that mentioned the quarter
shrinker, http://amasci.com/amateur/capexpt.html.
Much later I added photos of the original capacitor bank. The photos is
still there near the top of the article - go see! All the lab space is
long gone, and the cap banks have been in storage since 1996 or so…”
| If you are aware
of any earlier history, please let me know! |
