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liquid nitrogen dewar


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hey guys so I have been using a THICK Styrofoam cooler to put liquid nitrogen in for cryo treating the stainless I use. good side I don't have to spend a bunch of money on a dewar, down side it only lasts for 2-3 days so I have to profile and get a bunch of blades ready for heat treat and do them all at once other wise I would be going through a lot of liquid nitro gen if I went and did 1 or 2 blades at a time, I have been doing it this way for a lil while but I think I am ready to invest in a dewar so I can keep the liquid nitrogen for a extended period of time so I don't have to run around with a chicken with its head cut off trying to heat treat as many blades as possible before it evaporates...so I did some searching on the web amazon ebay ect.. for dewars and there are so many out there I saw some ones that look decent for around 4-500 bucks wich is ok I am NOT trying to buy one for 1000 bucks most I saw were between 15-25 liters. so I am wondering since I don't know much about this all I know is I think I want at least a 15 liter one and it has to have a wide enough neck to fit the knives through so I am looking for some advice on what any of you guys do wether you know a certain company that would be good or a site that sells them that would be good to look at or even if there is another option besides a dewar to hold the liquid nitrogen ANY help would really be appreciated I am in a lil bit of info overload from looking at so  many different ones,,,,thanks guys

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I would suggest that a THICK Styrofoam cooler could be a bad idea. Drop a hot blade and it will cut that styrofoam cooler open and let all the nitrogen out. Not to mention the damage the liquid could do to shoes, feet, etc

I will default to those with experience in this area of treating blades to provide their advice.

 

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liquid nitrogen is used when the blade is at room temperature.  But a dropped blade can still pierce the styrofoam at certain orientations.

Have you looked for used Dewers from AI?  I see them at the scrap yard infrequently. Since you must live in the same area I do you can probably source one at the same scrapyard I do.

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Any dewar found in a scrap yard is most likely ruined.  A Dewar has an inner and outer shell with a vacuum pulled along with some insulation.  Once the vacuum is lost the containers ability to hold the liquid is less than a styrofoam cooler.  Not that it's legal to transport and carry liquid nitrogen in a cooler, but that's between you and your supplier.  I haven't put the stuff in a cooler for a customer in 20 years, lol.  Any used dewar from a doctors office or semen tank can sometimes be found, but keep in mind that vacuum.  If the tank is mishandles or transported to much it can be lost.  These tanks are repairable, but that cost money.

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glen as Thomas said the kinves are at room temp when the go in the cooler. and I put them in slowly I don't just drop them in and I made a lil home made rack that fits in it to keep them on their spine. I also put that cooler inside a BIG plastic tuperware kinda thing and it is completely surrounded by insulation  I found the insulation on the sides and on top of the cooler helps it keep a lil longer. and will conatin a spill if that happens.  How ever a major problem with this is that everytime there is LN in it it freezes little channels through the Styrofoam and after about 5+ fills it can eat a lil pin hole all the way through this lil pin hole is SMALL its not big enough that you can actually see liquid coming out but it is enough to give a spot for it to evaporate as it comes out and it turns those 3 days I can keep it to about 1 1/2 I have had this happen to 2 coolers so far (another reason I need a dear to much waste)

 Thomas I don't think I would want one from a scrap yard but a used one is a option IF its still in very good condition....you said " have I looked from Al?" what do you mean "Al" ???

JM thanks I didn't think about that contacting a doctors office or a lab and seeing if they have a used one may be a very good idea thank you!

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Just pointing out that we haven't a clue where you are at in the over 150 different countries participating on these forums.  So answers that someone in Australia posts might just be a waste of their time and efforts, Hence the suggestion that people give a general location in their profile.

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The neck is the weak point of insulation so dewars tend to try and keep those small.  Also, the vast majority of people use dewars for transport and pour from them rather than use them directly--again, prompting a smaller neck.

Have you considered a dewar for storage and a secondary container for the actual treatment of blades?  I have seen lab containers for LN2 that have larger flip lids but would not be suitable for transport.  You also might be able to scab your own treatment vessel together with a "hotel pan" (look it up if it doesn't ring a bell) inner plus an outer frame and urethane foam insulation (and lid system).  It'd be the uppity permanent version of the styrofoam system you use now but actual storage would be properly in the dewar.  Hotel pans come in an amazing range of sizes and depths.

Just tossing out some ideas.  I know little about the cryo treat process so don't know other requirements.  

LN2 will cause the O2 in the air to condense into a liquid under certain circumstances so just be aware and careful that you might be making something problematic if the conditions are right.  In the stone age when I worked at the science museum, we used to go through about 50 gallons of LN2 a week--all science play to out-do the other guy, "we don need no steenkin safety measures". 

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the only problem with using a second container for treatment is in the process of pouring from dewar to conainer and then back to dewar if any is left you will loose a lot due to evaporation everytime you pour it into a new container it instantly evaporates until the liquid nitrogen cools that container down to close to its temp wich is exactly what I am trying to prevent if I can put the knives directly into the dewar it will make a HUGE difference due to loss

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I don't use much liquid nitrogen, primarily for the little bit of stainless I do.  I used to take a metal thermos with the cap seal removed so it could vent, and placed in a 5 gallon bucket wrapped with towels.  It used to cost me like 4$ to fill and it'd last a couple of days with blades in it.  Unfortunately Airgas bought out the welding supply where I got it and there a bunch of arrogant jerks and I refuse to do business with them.  They and most other suppliers refuse to fill anything but a LN dewar.  I've got an old one, my father used to AI when he was dairying, it's vacuum has leaked out, but it'll still hold LN for about 30 days, it was a 60 day tank.  Of course that's just sitting, the more you open and put room temp blades in the faster it evaporates.  I've looked at getting a smaller tank with a large mouth, but the prices are insane.

A safety note, don't transport LN or dry ice in an inclosed vehicle, put it in the back of a truck, as it evaporates it displaces oxygen and can suffocate you.  A wreck with LN can also be a very bad thing, there was a driver that filled tanks at different farms and had a wreck, he was a popsicle.

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