Liquid Nitrogen... for freezing... anyone have any thoughts?

[SPYDERLK]

I first thought hot wire knife too, made out of nickel chrome.

I have a Fanuc Robodrill 5 axis machine at work. I also have vertical mills (3 axis). Before investing much, I'd freeze a small piece and try to cut it.

We also have large amounts of Nitrogen at work. You will need what is called a Dewar to handle it. It is the cheapest way to get and store it. Not sure how you would keep an entire pillow sized piece frozen. Ice quickly attracts to where you spray the LN.

I see open cell foam with scallops and other shapes, so I know somehow it is getting cut or molded. Maybe you should try to make a mold by machining, and then make the pillow. What ever you do don't buy machineable foam.. that stuff is nasty, gets all over the place and sticks to everything. I won't let anyone cut it anymore in our shop.

Many regular shapes are done by deforming the foam, making a straight cut, and then return to relaxed form.

 

[jimmysisson]

How about studying the way some packaging is made so the foam flows around the object. My son works with a guy who accomplishes the same thing with fungi. Tight enough for you? The male mold would be a lot easier to form than the pillow if you got the foam consistency right.
Jim

 

[Egon]

Soak the foam in water, freeze and shape frozen???

 

[GLyford]

Please keep in mind a few things.

LN2 expands to a gas at about 700 to 1, or 700 gallons of air for a gallon of LN2. In a 10x12 room, that's about 10% of the vapor in the room. Your 5 gallons will fill half that room...or reduce the oxygen in it by half. You need about 20%, thinking processes decline by 18%, 10% is easily in the "you lose consciousness" range.

Because air is already about 78% nitrogen, your body does not react to it at all. When that nitrogen thins out the oxygen in the room you don't feel a thing but tired, if you have time to feel anything at all. If you manage to get out of the area, you will get a killer headache...this is a sign that your brain has already been damaged. Because it is still cold, it will also sink, so if you are working in a basement, the effect is worse.

A breathable oxygen alarm is a very good idea. This is not the same as a CO alarm which senses hydrocarbons, but the lack of breathable oxygen (there are some that do both).

It is very cold, like instant frostbite cold, and wet. So you have to have protection from both the cold (insulation) and the wet. Cryo gloves do both and are cheap insurance.

Spatter in your face can freeze your eyes. Wear a splash shield or wrap around goggles. No they are not fun to work in...do it anyway. Long sleeves at the minimum, too.

Even though a dewar helps keep the LN2 cold, it is still constantly boiling and venting LN2 to help keep it cold. Do not keep a dewar in an enclosed or sunken space, because it will be surrounded by a constant stream of nitrogen with no oxygen in it. Also, because it is constantly venting, do not plan on using some, then storing it for a long while, then using some more. Also known as static hold time. The bigger the dewar, the longer the hold time. Our department cryoguns just sitting there are empty after a day or less. The big roll around ones can last for weeks. Buy it when you need to use it, or your money will just float away.



So with that said...have you looked into machining foam with abrasives, rather than sharp blades?

 

[Dadnatron]

Soak the foam in water, freeze and shape frozen???

Thought of that, and its not out of the realm. But I'm trying to see if just freezing the foam will work first. I just need to get close... a bit that will cut, even roughly, will allow me to move forward.

I've seen some YouTube videos of flatbed CNC cutting softer foam. I know/believe, it can be done by me in a way that will work. However, the foam I need is different than the foam they are using in those videos.

My real question here is any alternative to purchasing a dewar of the size I need in order to get the amount of LN to test what I need.

My plan was to pour a 1" layer in the bottom of a small tote, place the foam in it, remove it and see if I can immediately mill it. I'm sure there will have to be variations before I get something to work, but that is my goal at this moment.

Also... does anyone have any ideas about how I could gain access to a flatbed CNC router, doesn't need to be 4D, just a regular 'sign' router would work, in order to test these bits? It would be much closer to what I will ultimately be using (theoretically using I should say). I really just need a few hours and someone who can program a few different cuts back and forth on several samples of foam. Any ideas about who might have something like that available? I know a sign shop would, but all the shops around me are pretty big outfits who don't want to do anything 'outside' of core business. I don't blame them.

 

[IslandTractor]

Have you tried dry ice? Conceivably, porous foam could be impregnated w/o damage and just outgas as you machine. It would definitely stay cold. Because of the double phase change latent heat is huge. CO2 sublimes at atmospheric pressure holding at about -75C.

X2

Dry ice is easier and safer to work with. Cheaper too. Why not give it a try?

 

[SPYDERLK]

Thought of that, and its not out of the realm. But I'm trying to see if just freezing the foam will work first. I just need to get close... a bit that will cut, even roughly, will allow me to move forward.

I've seen some YouTube videos of flatbed CNC cutting softer foam. I know/believe, it can be done by me in a way that will work. However, the foam I need is different than the foam they are using in those videos.

My real question here is any alternative to purchasing a deward of the size I need in order to get the amount of LN to test what I need.

My plan was to pour a 1" layer in the bottom of a small tote, place the foam in it, remove it and see if I can immediately mill it. I'm sure there will have to be variations before I get something to work, but that is my goal at this moment.

Also... does anyone have any ideas about how I could gain access to a flatbed CNC router, doesn't need to be 4D, just a regular 'sign' router would work, in order to test these bits? It would be much closer to what I will ultimately be using (theoretically using I should say). I really just need a few hours and someone who can program a few different cuts back and forth on several samples of foam. Any ideas about who might have something like that available? I know a sign shop would, but all the shops around me are pretty big outfits who don't want to do anything 'outside' of core business. I don't blame them.

Have you checked to see if someone can freeze your foam into a block of dry ice.

 

[Dadnatron]

X2

Dry ice is easier and safer to work with. Cheaper too. Why not give it a try?

I haven't really thought about dry ice. That might be a good starting point. If it works, then it would certainly be much easier. AND... I can get it at my local weld shop with just a cooler.

I'll give it a try.

 

[Dadnatron]

Have you checked to see if someone can freeze your foam into a block of dry ice.

I have not, but dry ice isn't made that way. I can't see any way that I could have it frozen in and around the foam, given the way dry ice is produced. But it might be cold enough to solidify the foam long enough to test. Which is all I am after at this point.

 

[RobS]

Waterjet cutter. Will cut the foam without added abrasives and no need to freeze. Pairs well with CAD. Not cheap but maybe someone local to you has one?