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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.

FlyingToaster, May 02 2012

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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.   

       As for drills, get ready to snap some bits. Also, hollow drill bits designed for a number of different porpoises are WKTE.
Alterother, May 02 2012

       Wellll... the application I thunk it for was cutting through safes (saves?) where a smooth edge isn't requisite.
FlyingToaster, May 02 2012

       "Say lad, what you got there?"   

       "It's a cold saw."
4whom, May 02 2012

       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.
4whom, May 02 2012

       // cutting through safes //   

       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.   

       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.   

       *to amend a statement I made in another recent post, only Milwaukee _grinders_ suck. They make good tools otherwise.
Alterother, May 02 2012

       // create the brittleness of a ceramic in the metal //   

       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.
Alterother, May 02 2012

       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.
FlyingToaster, May 02 2012

       //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.
4whom, May 02 2012

       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.
Alterother, May 02 2012

       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.   

       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.
4whom, May 02 2012

       //it's not just a horse of a different color, it's not even a horse at all//   

       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.   

       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.
MaxwellBuchanan, May 02 2012

       Both. Not mythical.
Alterother, May 02 2012

       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".
4whom, May 02 2012

       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.
Alterother, May 02 2012

       How did you freeze them?
4whom, May 02 2012

       portable witch's teat.
FlyingToaster, May 02 2012

       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.
4whom, May 02 2012

       // How did you freeze them? //   

       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.   

       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.   

       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.
Alterother, May 02 2012

       So, just to be clear. No portable witch's teat?
4whom, May 02 2012

       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.
Alterother, May 02 2012

       It's Boyle's Law. If you direct pressurized nitrogen at your skin, you get boils.
4whom, May 02 2012

       //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.
lurch, May 02 2012

       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.
Alterother, May 02 2012

       O2, H2, N2, but He and Ar - the noble gases are stable in monoatomic form; everybody else holds hands.   

       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.   

       All fine and good, except the ambient temperature was about -35 deg. F.   

       I was expecting the rail to break, and mentioned it to some - and got soundly ridiculed. It didn't break.   

       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.
lurch, May 02 2012

       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.
Alterother, May 02 2012

       Hence the term "railroaded". And we don't have to give those goddam greeks a dime!!
4whom, May 02 2012

       They do have an awfully good subway system, courtesy of the EU, that is woefully overstaffed and underutilised.
UnaBubba, May 03 2012


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