Cryo testing

by the way I checked with my gas guy on helium he won't get it for me it runs about 5 time as much as LN2 I still think it's worth the money if I can get it.
Click to expand...

May not seem like it, but the gas guy is probably doing you a favor.

Please try and talk to, or better, visit, somebody who actually uses liquid He before considering messing around with it. It really is in a whole other league than LN2. You blow off several liters of liquid just to cool the expensive hi-vacuum-jacketed dip-tube needed to transfer it from one dewar to another. No valves for this stuff like LN2. You must move it by pressurizing with dry He gas. Anything else will freeze and plug up. If you're not topping off a dewar that already has Liq He in it, count on using many more liters to cool it enough that it will hold liquid. Keeping "ice" (frozen water and air) from plugging up vents is serious business. Liq He dewars don't have pressure builders like LN2. All thermal contact with outside world is minimized or the stuff just doeasn't hang around at all. To keep it for more than a few days requires double dewars, with an LN2 chamber between. I've maintained such double dewars which required a minimum volume of liq He to cool superconducting magnets and cryogen refills were totally different for liq He and Ln2. You just can't pour a bunch of Liq He around like LN2, at least not at a temperature that humans can tolerate.

One strong blast of the cold gas from the transfer line, before liquid starts to flow, or a vventing dewar, can cause serious damage before you can even jerk your hand away. Guy I knew that happened to lost use of his hand for two or three months. Once the line starts to cool down, it's like a lit torch. The stuff is only a couple degrees above absolute zero and has weird properties, like zero viscosity. It can slosh around in a dewar for hours after being disturbed. It can snow in the room it's being used in, if a lot evaporates at once. If it's humid, things can easily get foggy enough that you really can't see.

It is very hard to keep around without putting warmer things (i.e. everything else) into it, and you'd need large a volume to ensure reproducibilty ... It would be very easy to boil it all away, and not know how cold you'd gotten the blade. Pre-cooling the blade in LN2 is the only way that would make any sense to me. I can't imagine that it would be worth the cost to buy and equipment needed to handle Liq He effectively and safely.
 
I've seen the hospitals get it around there I just want to dip a few blades :( luck guys:) just to satisfy the old beanie.

I need helium .:mad:
hey thanks for the info..it is interesting to say the least :)
 
"I've seen the hospitals get it around there I just want to dip a few blades.."

Since they get it to keep the superconducting magnets in thier MRIs working, they probably aren't gonna let you get near with anything steel that's magnetic.:)

Liq He is only a few degrees above absolute zero, the cessation of all atomic motion, so it's doubtful that much at all can happen at that temp. It would have to happen during cooling down or warming up, and without some fancy stuff, be pretty uncontrollable, let alone doing a "soak".

These guys have equipment for such experimentation, but it is undoubtably very spendy and probably custom to get large enough for blades. Fun to look at though.

http://www.cryoindustries.com/products.htm
 
Firkin's right: "It really is in a whole other league than LN2"

Besides that, it's cost prohibitive considering the support equipment needed for any controllability. I did some experiments once with Raman Spectroscopy of carbon nanotubes, Buckministerfullerenes (C60), and carbon tetrachloride under LN2. It would have been nice to have done the same experiments under Liq He, but even having ornl right next door to the university, it would've been cost prohibitive to do so.

-Darren
 
that's what we're looking for no molecular motion just getting there
will do what I'm looking for the test at least.
:) thanks for the web link...
 
Paul,

I suppose I should assume then, from your last post, I should allow STAINLESS to cool to ambient room temperature after quenching and then immediatly cryo WITHOUT first tempering (???).

Thank you; Roger
 
Looks like your reply came through fine Paul..
How do you like that? Paul calls me to reply cause he was having problems gettting it to go through..
What a great guy huh?:D
 
Thanks for that quick responce (both of you).

I shall follow instruction and cryo stainless before temper.

Roger
 
For Paul and/or Knightsteel:

I just bit the bullet and just became a proud, though now very broke, owner of a 20 liter dewar. No more just using dry ice! Yeah!

I remember over the last year reading here that cryo using LN is usually performed for 8 to 12 hours. My questions are three:

Is that amount of time a good measure???

Can I over cryo a blade at LN temperature (10 hours verses 24 hours as an example)???

Do different steels require different cryo times at LN temperature(simple carbon verses super stainless for example)???

Thanks guys; Roger

I appreciate your kindly wisdom based on experience.
 
Roger,

Sorry, I now see that incomplete information is worse that no information. There seem to be a lot of misconceptions as to what "cryo" even is. But I now see that if I don't explain what I am doing and why, then others will try it expecting similar results and just get it wrong.

The dipping technique of cryo REDUCES toughness and breaking strength by about 40% due to thermal shock, uneven contraction and expansion, and micro-cracking. While many still use this, I think that overall it is detrimental to the steel.

To get the kind of results that my tests have shown require precise temperature control throughout the process. We use a vacuum insulated heat exchange cryo unit with a computer controller and built in heating unit built by Applied Cryogenics. There is never any contact between LN2 and the steel.

The chilling and cooling rates between -100F and -300F should not exceed 1 degree per minute for small parts. Larger parts require slower rates and incremental plateaus for temperaure equalization.

Daniel Watson
 
Originally posted by knightsteel
Roger,
The dipping technique of cryo REDUCES toughness and breaking strength by about 40% due to thermal shock, uneven contraction and expansion, and micro-cracking. While many still use this, I think that overall it is detrimental to the steel.
Daniel Watson
Click to expand...

has any of you other guys done any bend/brake tests
before and after the dipping method most of us use..?

Ed Have you any testing results on this,, this is an interesting thread
 
Today I ordered a group of 440C blades from K&G to do some testing. I plan to show the results here. We will do Rockwell and bend/break on 2 blades in each of several catagories: 1) as recieved, 2) double tempered, 3) dip cryo and double temper, 4) my basic process (-120F 8hrs., temper, -300F 20hrs., double temper) 5) my best process (-120F 8hrs., temper, -300F 20hrs., temper, -300F 20hrs., double temper) 6) available for suggestions from the list.

Now everyone knows my process !!!

:eek: :footinmou :o :( :rolleyes:

Daniel
 
Daniel if you get those blades and don't do the full heat treat yourself in think you'll be
working with an unknown factor.who did what to it before you
got them type deal.
if the Rockwell is the same on all of them maybe oK
but you still don't know the
treating temperatures the blades went through right?:(
I would think it may influence your testing to the point that we/you still
won't know for sure:( just food for thought and my 2 cents
 
Graymaker and Epsilon,

We will certainly test all the pieces for RC beforehand to check for consistancy. I just don't want to make a dozen knives then break them. Any way around this?

Notice series #2 in the test, in which 2 blades will get double tempered without cryo.

Daniel
 
Daniel
I would re-heat threat them yourself or have
someone do it you know and do all at the same time for
less chance to very from each other., at least
you'd get closer to the bottom or (start).
factory ground blades sent to you soft would give
you possibly more uniform Blades and control of the testing..
just 2 more cents:)
 
Swamp Rat and Busse are sister companies. I believe that the very hush hush nature of their thermal cycles means that there are also doubling it's usefulness as a marking strategy. I appreciate seeing how Daniel and Paul share their valuable knowledge and vast experience with us so that we can also improve our knives.
 
I too appreciate how Paul Bos and Daniel (now) share their knowledge and processes. However, I can appreciate the nature of doing business and keeping trade secrets for different processes as well. Having said that, I don't think Daniel or Paul will lose any business by releasing their heat treat schedule as I don't think most of us will invest in the equipment necessary to do the job like they do, I mean, we've got discussions on here about how hard it is to throw away used belts! ...let alone spend the cash to set up a processing arrangement! :)

Daniel, I'll reiterate, some micrographs would be golden. I'd really like to see some empirical data to back up the results of your breakage tests, I think this is really important. I appreciate the journal references you posted for me earlier. When I get back from Batson's Symposium I plan to start studying everything I can find on cryogenic processing to come up to speed.

How about this for an experiment...just thinking out loud...and really haven't put too much thought into it yet. Get enough steel from the same mill run to make up three data sets of 12 knives each. For all three sets compare the following: Non-cryo, cryo using your equipment, cryo using the dip method. Data set 1: just profile the same blade shape 12 times and do the tests, don't distal taper it or grind the bevels. Data set 2: profile and grind the knives being very careful with the steel in the process (i.e., keep it cool at all times). Data set 3: Profile and grind the knives and abuse the steel in the process (i.e., wear gloves and overheat it and abuse it). To save on grinding time maybe just grind a bevel on one side. Like I said, not much thought about it just an initial idea. I'd be willing to pitch in a few dollars to help cover your steel and LN2 cost, hopefully others would as well. (any interest from anyone else?)...of course, Daniel would have to agree to do this (I don't want to volunteer him!) and we'd all have to discuss the best experiments to do...it always helps to brainstorm for ideas in this regard. But I'd definitely want to see some SEM images of the broken pieces so we could have some hard data. Any interest Daniel? Anyone else? :)

-Darren
 
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