Cyrogenics, more questions???

Don I conceed, he's all yours, that kiss on the cheek was a little over the top for me. :D :D

Bill
 
I am a little out of place here and don't know scrap about knifemaking and would not presume to be able to contribute to this discussion, but I work with LOTS and LOTS of liquid nitrogen professionally.

In a smallish dewar LN will not last very long, you would probably need a VERY high quality 10 liter dewar to make it last for a week and that is not counting use. Putting the dewar into a freezer will help only with the insulation but not much. LN is about -200 deg C even if your freezer runs at -20 deg (and that is already a pretty good freezer, most run -10- -15 deg C) the temperature different is still 180 deg C not much difference in comparison to 220 if stored at room temperature.

However, even a simple styrofoam cup, especially a bigger one, like 10 l or so, will store LN for several hours (especially if you put a styrofoam sheet as lid on it). So my suggestion, if you do several knifes in a few weeks would be the following:
You can order from your local specialty gas company a so-called low-pressure gas pack or low-pressure dewar which the gas company should deliver to you. The gas pack contains 240 liters LN at a pressure of 22 psi and costs you about $45 (I just asked our purchasing department). You are probably pay a small delivery fee (unless you live really out of the way) and you may pay a deposit for the dewar which you will get back when the empty dewar is picked up. These are pretty big stainless drums on wheels and they will last you about 3 weeks easily pretty much regardless of use, unless you go through tens of liters per day like we do. All you will need is a transfer line, which consists of a bend copper tube a fitting to connect to the dewar and a splashguard. The splashguard is not cheap, but a whole lot cheaper than a good portable dewar. With this you can draw what ever amount you need and put it into a standard wide mouth thermosbottle (the soup thermos by Stanley works very well).

I hosted a picture of the dewar and the splash guard on imageshack:
http://img409.imageshack.us/my.php?image=dewar1sx.jpg
http://img409.imageshack.us/my.php?image=splashguard3hr.jpg

Hope this was of some help.
 
Oh, I forgot. As to the dry ice contact problem: You can use dry ice in ethanol, makes very good contact and it is dirt cheap. The ethanol actually gets pretty viscous at dry ice temperatures (about -77 deg C). Of course you better wear gloves because the ethanol might light up if you drop a red hot blade into it :p . You can also use some heavier alcohol which will be less flamable such as ethylen glycol (antifreeze is the cheapest, otherwise you are paying about $35 per 2 liter bottle). But antifreeze will get petty syrupy at dry ice temperatures.

Sorry to intrude.
 
I bought a 32 liter dewar off ebay for a reasonable price! They are filling and testing it before shipping it to me. :)

So, Jeff, my friend, you and I are both off the hook. No kisses anywhere, no pansy stuff at all.

Bill can still give you a kiss though, if he wants. I'm outta here.

Thanks to everyone and especially Jeff for reminding me to try Ebay again.

In case this doesn't make sense, the reason is that my groin hernia is hurting me. I've had two beers, two tylenol, and a very big glass of wine so far. :jerkit:
 
I'd drop an oxycontin on top of that and have a really nice night's sleep, Don. But, then, I'm a child of the 60's. :D

Sorry to hear you're hurting there too. :( I hate that pain.
 
Good luck, Don. Hope it heals well once they do surgery. :)
 
When seeing a HT question or post here I always scan down for Mete's responce. That is my bell weather. My limited experience is that I have always shot for about 12 hours in LN cryo. Don't always hit that because this and that can come up to occupy your one man band. I have left them in there for as few as 10 hours and for as many as about, or almost, 20 hour. SO FAR, no bad reports. My gut feeling is once its transformed its transformed and no more time shall hurt. My true belief is that the consistant drop to, and therefore consistant temperature throughout cross section, eliminates shock and therefore much prefered. Unfortunately that adds much more time or equipment expense to the process. I have not that capabilty here. With only a dewar I get it in there as quick as I can. I see two immediate options: To uniformly cool before submerion if your blade is short enough to hang within the dewar but not within the LN good but if not GET her in there now.

RL
 
Hey Big Jim

I'm sure HoB didn't take offence. We all offer advice without expectation of acceptance or recognition. The only way to guarantee a reaction is to insult IG :D

BTW, I just bought an old dewar from a nearby rancher. 20 litres and at $1.20 a litre this is going to be WAY cheaper than dry ice. I was paying $70 for a cooler of dry ice pellets. I like it because it is relatively safe to work with, but it's gone in a few days nomatter what you wrap it in. The rancher says he gets holding time of about 2 months with the 20 litre dewar. Since I do heat treat about once a week, that will save me between 4 - 6 trips to town (3 hr round trip) for dry ice per tank of LN - and it will be here when I need it unexpectedly.

Bonus!

Rob!
 
Big Jim I agree with what you posted and I apologize to HOB for not thanking him for his shared info. I started this thread and was the one looking for more info on the subject and he graciously came in and offered his experiences to help educate me on the matter and I thank him for it. I got a little busy and when no one posted on it for a couple days I let the thread slip by me without thinking much more about it, that was no excuse and again I appreciate all the info that was shared by all, you've all helped me a great deal.
Thank you BJ for bringing this back to my attention.

Bill
 
Well, the first dewar I told you about buying on Ebay was a bust. The seller agreed to test it before shipping and it lost the LN overnight. He returned my PayPal money right away.

So I won another that has just been rebuilt by the manufacturer and is guaranteed. Should have it by Friday.

It's a lot smaller but I don't need 30 liters at a time anyway. This one is insulated and vacuum sealed, so it should work great.

I hope!!!:rolleyes:

It's getting really hard to find dry ice down here when I need it.

I just had a brilliant marketing idea!! When I get the dewar I can fill it with my sperm and sell the sperm on Ebay. Probably make enough to retire!!!:jerkit:
 
In the 70's artificial insemenation was a trend in cattle breeding. Almost every rancher with a herd over 100 animals had an AI tank. Mine was labled with the American Breeders Society acronym, ABS, go figure. I set my tank, about 20 liters on 2 inches of closed cell foam insulation. I usuall get 45-70 days until evaporated.

My tank new was priced at $450 plus. I advertised and bought a dewar for $150. And it was full of straws of 30 year old rotten bull semen. I made ear rings and Christmas tree ornaments out of the glass straws after they turned green from reaction to the light they hadn't seen in 30 plus years. The ear rings were a joke and I sold a few pairs for $25. One of these pairs won first prize in an ugly jewelery contests and netted the owner a $650 diamond pendant.

These tanks can be repaired for about $100 if they are not damaged.

Phil Wilson has spent much time working with these cryo treatments and CPM steels. I pay close attention when Phil speaks on these topics. Phil's engineering and scientific background precludes Phil from anything but the scientific method. I also highly reccommend reading Phil's articles in Knives Illustrated on CPM steels. I have and use a Wilson fillet knife, they are the best on the market in design execution and heat treatment....Take Care...Ed
 
I have hoarded my supply of rotten bull semen. Bruce I will make you a custom set if you let me do the piercing. I'm sure I can find a used needle out of a sharp pack disposal station. Anything to accommodate my friends...Take Care...Ed
 
Rlinger, Yes it is important to get the blade fully submersed in the LN2 as quick as possible in one fluid motion. Uneven cooling can cause some stress but the most stress can come from the transformation to martensite. If there is a lot of retained austentite and the blade is only partially immersed then the transformation in this one area contrasted to no transformation in the area next to it can cause huge stresses. This can crack a blade easily. As a point of intrest has any one noticed how long a blade remains soft and can be bent easily in the hands even though the hardness can be in excess or 60 or so? This is especially noticeable with a fillet blade. Phil
 
Steel is soft and can be bent by hand until it cools below around 400 degrees.

If a blade is noticeably bent after removing it from the furnace it's possible to give it an interrupted quench (after it shows no red heat remove it from the quench) and quickly straighten it, then place it back in the quench until it reaches room temperature. :)

Usually bending and returning to straight after heat treating and tempering is a factor of thickness, not hardness.:)
 
Don, what I am observing is the ability to bend the steel in my hand and have it stay bent, after the quench to room temp and even after 2 hours in the LN2. The hardness at that point is 60 or more. It has to be almost all martensite at that point. After a couple of tempers then it will no longer do this. I have asked metalurgists like Dick Barber about this and he just kind of looks at me sidewise. I am not crazy, this is real, just wondered if any one else has observed this and knows why this is possible.. Phil
 
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