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On 1/8/14 6:00 AM, David Rieben wrote:
OTOH, I would not want to trust "containment" of a possible RSG "come-apart" to acrylic
(plexiglas), as plexi does not do too well with impacts compared to polycarbonate. Tungsten
is quite dense (19.3 gm/cm3), about equal to gold in density, but a heckuva lot harder! Those
flying electrodes could be hurled at over 100 mph from the disc should it break during operation!
I think you mean 100 *km/hr* <grin>
1800 RPM, 12"(30cm) diameter disk has a tangential velocity of 94 ft/sec
(29 m/s, 64 mi/hr, 103 km/hr)
Seems to me if the RSG is designed properly with adequate surface area of the metallic hardware
for supporting the stationary electrodes, the rate of heat dissipation, which would be further assisted
by the air flow "wind" generated by the flying electrodes, should be sufficient to prevent
the said parts from reaching ignition temperature of the poly (580C).
Indeed..
As for the flying electrodes,
at least "mine" are mounted to an epoxy-fiberglass composite (G-10) disc, as poly will indeed
melt at a much lower temperature (140-150C) than its igniton temp. http://www.tcforensic.com.au/docs/article10.html
And most epoxy glass laminates will "char" long before they "burn"..
But moving back to the original incident.. there are varying stories on
the web about speculative "root cause"
Hot electrode landing somewhere and smoldering?
Electric motor overheat and smolder?
MMC overheat and smolder?
The common thread is "something starting and sitting latent, and then
bursting into flame later"
I'm not sure any of the above 3 are really plausible.
And, is this the kind of thing that people who are designing for
permanent installations (e.g. museum coils) should bear in mind, and
potentially design for?). Many, many years ago, I was involved in UL
testing for a piece of office automation equipment (what would, today,
be called a file server), and they required us to show that even if
something caught fire inside, that
a) it would be contained within the box (no dripping flaming embers or
plastic onto the carpet underneath)