h a l f b a k e r y"Bun is such a sad word, is it not?" -- Watt, "Waiting for Godot"
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In a manner similar to a tile-saw, a thin stream of liquid nitrogen is squirted at the blade contact point to cut(/break/chisel) through metals that embrittle at cryogenic temperatures. The blade itself won't get cold because of the rapid spinning, short exposure time and usual friction.
Works for
drills too but requires special hollow bits.
[link]
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Making metal more brittle will not lead to a smooth cut,
and may actually detract from the viability of the cut
edges. For a smooth cut with machine tools or saws, you
actually want the metal in a ductile state so that very thin
layers are peeled away by the teeth. Think of trying to cut
a block of cheese or butter; frozen, it will crumble, but at
room temp it cuts cleanly. |
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As for drills, get ready to snap some bits. Also, hollow drill
bits designed for a number of different porpoises are
WKTE. |
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Wellll... the application I thunk it for was cutting through safes (saves?) where a smooth edge isn't requisite. |
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"Say lad, what you got there?" |
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I am not sure it would work on metals that you are simultaneously subjecting to lots of frictional heating. Heat transfer coefficients are too high in metals. You seem to want to create the brittleness of a ceramic in the metal, at point of "cutting". It might be better to cool the rest of the safe with the nitrogen, to prevent those Greek bonds from burning whilst you are gaining access. |
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// cutting through safes // |
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You should have said so. In that case, what you want is
impact, not removal or abrasion. Find the weak point of
the safe, freeze it, then smack it with a sledgehammer
until it shatters. Not to belabor the point, but trying to cut
or drill cryofrozen metal will damage the cutting tool as
much as or more than the metal, since carbide tips are
already a bit brittle to begin with. You also run the risk of
injury when the blade breaks or jams. |
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There exist portable circular saws specially made for
cutting steel without lubricants; they are known in my
trade as 'dry saws'. Milwaukee* makes a particularly fine
one. If you are careful, you can make a plunge cut through
a 1/2" plate with one. |
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*to amend a statement I made in another recent post, only
Milwaukee _grinders_ suck. They make good tools
otherwise. |
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// create the brittleness of a ceramic in the metal // |
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Ceramic is a composite material with very different cutting
properties than metal. It's not just a horse of a different
color, it's not even a horse at all. |
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Way I see it, the idea is to freeze a thin layer at the surface then break it off with the flat edge of the blade. Heat induced by friction would be at the very top of the frozen layer. |
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//Ceramic is a composite material with very different cutting properties than metal.// That is what I was implying. Turning a ductile, malleable substances into a brittle structured lattice composite with fault weaknesses, and low shear strength. It also appears to be what the idea is implying. |
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Yep, that's it in a nutshell. Thus my suggestion of impact
vs. cutting; frozen and/or brittle materials do not deal
well with deformation. |
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I am still not convinced (with the shearing off of top layers). It may be possible at very small scales/increments. But by the time you have worked through the lattice at those rates, those Greek bonds in the safe might be junked. Oh wait. |
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I still propose cutting normally and then cooling the rest of the safe off. Or water jets, they work. For that matter, just liquid nitrogen jets, leave the saw behind. |
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//it's not just a horse of a different color, it's not
even a horse at all// |
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I'm with [4whom]. At low temperatures, you
reduce the ductility of metal by reducing the
mobility of dislocations. This, in turn, makes it
more brittle - more like a ceramic, where
dislocations are immobile in the first place. |
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There was a possibly mythical story that bicycle D-
locks could be shattered by freezing them with
liquid nitrogen and then whacking them with a
hammer. Or perhaps it was steel cable locks. |
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The only thing mythical about those reports was the continuity. See Jub spray liquid nitrogen. See Jub strike lock. See Jub run. In fact, it was filmed on three seperate days. They chose Jub because he only changes clothes in months including "r". |
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Working on the railroad, one sometimes encounters locks
that must be opened, but nobody has the key, usually on a
siding switch way the hell out in the middle of nowhere.
Freezing and smashing is a method I've seen employed
several times in the absence of an oxyfuel torch. |
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More appropriately, where (on the lock) did you freeze them? I have the same trick with a padlock and two spanners, no freezing. Manufactures of padlocks tend to over temper the metals, telling you it is harder. Yes, and more brittle. |
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// How did you freeze them? // |
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With pressurized nitrogen, either from small bottles that
track crews keep handy for this express purpose (because a
20 lb. nitrogen bottle is more portable than a torch rig and
doesn't carry the risk of starting a brushfire), or from
larger cylinders carried on trucks, used in mixing shield gas
when when welding manganese-steel rail. It's not as cold
as liquid nitrogen, but when released under high pressure
it gets the job done. |
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We usually froze the top of the shackle (aka bolt), right at
the u-bend where it's weakest, and then one guy would
hold a rail fork or something one side as an anvil while his
partner cracked the lock with a drilling hammer (this will
work without freezing, but you'll be beating on it for a
while). It also helps to have the anvil-holder or a third
person to hold the lock steady with a pair of channel-locks. |
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Once I
was on a job where we had to break one of those disc-
shaped high-security locks; after several unsuccessful
attacks on the minimally exposed shackle, we squirted
nitrogen into the key slot and shattered the barrel with a
large punch. It took three attempts before things inside
were pulverized enough to tip all the pins and tumblers
out. |
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So, just to be clear. No portable witch's teat? |
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Nope, just bottled N1. Any pressurized gas will come out
cold enough to give you frostbite, but nitrogen will freeze
your skin solid (or so I've been told). It all has to do with
thermodynamics somehow. I could go get a textbook and
refresh my education on exactly how this works, but I'm
comfy and I don't feel like getting up. |
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It's Boyle's Law. If you direct pressurized nitrogen at your skin, you get boils. |
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//just bottled N1// Argonne Labs uses a 45kv spark chamber for generating N1; not sure that it's patient enough to be chilled and/or bottled. I think N2 might be more likely. |
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Sorry, my mistake. Industrial nitrogen is N2. I'm pretty sure
all of the 'straight' gases I use--oxygen, helium, hydrogen,
nitrogen, argon--are in stable molecular form. I think. It's
been a tragically long time since I did any serious welding
work, but thankfully my recovery is nearly over. Soon I can
go down to the shop and start remembering these things
again. |
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O2, H2, N2, but He and Ar - the noble gases are stable in monoatomic form; everybody else holds hands. |
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I once worked with some guys trying to repair a valve on an earthfill dam; it was down a 40 foot shaft, and somebody had to go down on a cable. Lacking anything solid to attach to, they found an old piece of rail (very light, mine-shaft style rail) and shoved it through some vent-holes of the headhouse, leaving about a 10-foot span. They threw a short chain over the rail, attached a pulley, and started lowering a 200-pound fellow down the hole. |
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All fine and good, except the ambient temperature was about -35 deg. F. |
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I was expecting the rail to break, and mentioned it to some - and got soundly ridiculed. It didn't break. |
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Until they started using the cable to apply lift to a stuck valve plate. There were some very surprised people there - especially the guy who found out how unpleasant it is to get dropped into freezing water on a freezing day and have 40 feet of cable and a couple pieces of steel rail dropped on your head. |
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Yeah, that sounds about right. The railroad approach to
workplace safety is best summed up by the words 'nobody
saw that, so it didn't happen'. You just get the fuckin' job
done and don't get hurt. If I started listing off all of the
dangerous misuse of tools and equipment we got up to, I'd
fill [jutta]'s server. |
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Hence the term "railroaded". And we don't have to give those goddam greeks a dime!! |
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They do have an awfully good subway system,
courtesy of the EU, that is woefully overstaffed and
underutilised. |
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