I’ve asked around on the various machinist’s boards and no one there has any clues as to how it could, a buddy of mine has checked with folks he knows, and they can’t see it working, either. They’ve hired this new executive at work (named “Brad” and everyone other than the owner pronounces his name with the same kind of inflection and tone that Kevin Spacey used in American Beauty) and he’s got this “brilliant” idea for getting the castings off the trees. What we’ll do, after the trees have cooled down is dunk them into liquid nitrogen, and then we’ll simply be able to snap the parts right off.
I can’t for the life of me figure out how we’re supposed to be able to get just the gate to snap. I’ve not played with LN, but lord knows I’ve seen enough demonstrations of the kinds of embrittlement that happens when you dunk something into a liquid so cool. It seems to me that entire tree would shatter when you tried to break the part off (assuming some of the halfwit employees didn’t manage to freeze themselves in the process). Any possible way this could work?
I suppose you could try it, but I can’t for the life of me figure out how this is supposed to be better than simply cutting the parts off. What is the material you’re casting, anyway? The main problem I see is that you’d also be making the parts brittle, too,which might result in a higher wastage. Clumsy fingers in gloves, you know.
It’s 1020 steel, though presumably, if they manage to pull this off, they’ll use it for everything else we cast. Why they can’t simply buy a plasma cutter or a high speed waterjet cutter is beyond me.
Freezing hot metal seriously effects it’s microcrystalline structure, and generally tends to make it brittle (among other things). Does this guy have any background in materials science, or is this just some neato notion he cooked up?
How big are these trees? Liquid nitrogen isn’t cheap, and if you boil off more than a bit of it, you’re going to have to worry about keeping the air in the workplace breathable.
Oh… heee. Not like Oak or Elm trees. Took me a bit to figure out what the hell you where talking about. Still, not sure. But I assume your boss is not trying to super freeze trees. Course, one never knows, I’ve had bosses like that.
When your boss is ‘golden’ about all you can do is…
I don’t believe using liquid nitrogen on metal would make it that brittle - or at least not without seriously damaging it. My understanding is that organic substances (like flowers or bananas or whatnot) become brittle at these temperatures because the water inside them freezes. Thus, they shatter instead of bending or flexing. Metal doesn’t have water inside it, though, (or at least not a significant amount) so it wouldn’t react the same way.
An article I read in a Job Shop magazine spoke of supercooling to more evenly achieve a martensitic state-are the castings critical regarding hardness? I’d think that a quick LN plunge would make small mass brittle while leaving larger mass effectively unchanged.
You can see trees like what I’m talking about here.
danceswithcats, they’re hinges, and the hardness is a bit of an issue since they have to be machined and then have a hole tapped. They’re really nice and thin, while the tree is thick.
Alloys and metals have phases which have different molecular arrangements. They can and do change phases as the metal moves through critical temperature points. Sometimes this is beneficial, sometimes it is not, depending on the phase, the speed at which it changes, etc. Think for example of tempering and annealing.
I answered your query on my Board, Tuckerfan; no one wants to see me copy & paste it here and waste space.
I just saw a new buisness highlighted on a local TV station.
They freeze metal parts (liquid nitrogen)to harden them. The three examples I saw were what looked like a auto rotor (read brake disc) a golf club and a baseball bat.
I didn’t know you could do that having only hardened using heat .
Another manufacturing engineer jumping in… Dunking the steel in LN is called Cryogenic Tempering and it will definitely change the metal’s structure. The process is properly used in conjuction with a heat treatment following the freezing. It must be tightly controlled. Good luck. Maybe you won’t have to put up with Brad very much longer.
Not much insight, I mainly advised about the issues of the phase changes and the problems of radical changes in manufacturing techniques without some pretty serious testing and QC. I mentioned a bus load of nuns going over a cliff too…I was just saying to Tuckerfan (since he asked his question on my place) that I wasn’t going to repeat myself here and waste database space. Like I am now. Cripes, I did it again. And again! Arrrrgh!
