Plasma cutter on nitrogen?

[cweagle]

I have a small plasma, Snap-on model YA2230, aka Century 118-008. It's a 22A output, 220V unit. I've run it fine on regular compressed air before, but right now am in a situation where I can't run a compressor at the same time as it. It would be really really easy to hook up a bottle of nitrogen and use that - but the manual specifically says to use only air, nothing else. Seems odd to me - the atmosphere is 78% N2, 21% O2. My LWS doesn't sell straight air, only N2.

Anybody have any insight to share in this matter? If the consumables weren't so d***ed expensive to risk, I'd just go for it. Various internet research has even said that N2 should _increase_ consumable life... ?! The N2 would be totally dry, too, which increases consumable life as well.

 

[PAToyota]

From the Miller website:

Compressed air is the most popular gas used for plasma cutting. [snip - information about compressed air]

The other gas used is nitrogen, but the only advantages to using it are when cutting stainless steel. You will get a cleaner cut but the cut thickness will be diminished a little. With some exotic metals a gas mixture may be needed.

My Hypertherm manual mentions using air or nitrogen, but no real details so I searched on the net and found the above information.

 

[krusty the clown]

not an expert (disclaimer) but i would think any non inert gas would work especially nitrogen. have you considered running you compressor untill it's full and shutting it off untill the pressure drops to low to be useable? it may be too time consuming but for small projects it may work ( thats assuming the issue is your service wont handle the load of the plasma cutter and the compressor at the same time).

 

[cweagle]

That's exactly the pickle I'm in. My compressor's tank should let the plasma run for maybe a minute. This seems like a lot of hassle.

 

[krusty the clown]

how big of a tank? what pressure are you regulating it to?

 

[cweagle]

OK, ok, make me do the math

26 gal (3.5cf) tank, 150psi max, delivering 4.5cfm at 80psi. Gives about 1.5 minutes.

 

[krusty the clown]

yes the tank is too small to use it like i suggested. IIRC the air supply to the plasma cutter should be regulated down to 35-40 psi, but even that won't help much. maybe time for a new compressor and bigger service to the garage

 

[cweagle]

Right, the plasma has a built-in regulator to take it down to 60-65psi, but you need a little headroom to make a regulator work right. Most will 'blow-through' if the differential gets too low; it depends on the specific model. I've heard some stories (FWIW) of some high-pressure bottle regulatorss set to a few 10's of output PSI, suddenly blowing 100psi when the bottle gets down to that level.

 

[cweagle]

Also - I can't upgrade service due to complicated rental arrangements. And man, I don't want to buy a generator right now...

 

[Speargun]

How about a scuba tank?

Common tank sizes are 80 - 120 cubic feet at 3000 - 3500 psi. You would need a regulator, but once set up, you can easily get refills at any dive shop or, if you have a friend in the fire dept., most fire stations have high pressure compressors.

An average, used, 80cf aluminum tank goes for about $80 - $100 and just about any cheap regulator from ebay could be used since it won't be used for life support.

 

[krusty the clown]

good idea speargun.......in fact you really just need more storage. what if you could find a non working 80 gal compressor just for the tank?

 

[Vicegrip]

80 CF at 4.5 per min then shelp off to get a $10 refill. SCUBA tanks need 1 year VIP and 5 year hydro inspections as well. same issues with Nitrogen once the cylinder is empty you are burning only time driving to get refills.

See if you can find a small compressor that has a good output at the needed pressure in this case 65 psi. I bet there are some 120v compressors that can ether keep up or reduce the stop and catch up times. compressor efficiency drops as the pressure rises so the compressor will make more CFM as the pressor drops.

Do you have any amp headroom?

Non inert gas would be bad news. Nitrogen and Argon while both inert have very different thermal and electrical properties.

 

[cweagle]

80 CF at 4.5 per min then shelp off to get a $10 refill.

Yeah, it's worse than that, as I figure. The 80CF rating is at atmospheric pressure ('gauge pressure' of 0psi; the 4.5CF is at 60psi.

The actual run time for a 300CF tank should be around 15 minutes. Glad I don't have much cutting to do. Also - not all cylinder regulators can flow 1200CFH!

 

[cweagle]

Hmm, wait a minute. This guy at http://www.truetex.com/aircompressors.htm says

"When a compressor pumps one "CFM" (cubic foot per minute), that means the intake port inhaled one cubic foot of "free air" (air at atmospheric pressure). (Note: A CFM does not mean in any sense the compressed volume.) So the unit really measures the mass of air flowing per minute, not volume. Some people labor under a stubborn misundertanding that these units refer to the flow of compressed volume (as opposed to free air volume), but this is flatly wrong. "

So maybe I'm totally wrong. Maybe my 300CF N2 cylinder really will last an hour, and any old regulator can keep up.

Can somebody confirm what CFM really means in an air compressor context?

 

[Vicegrip]

Compressors are most often rated by CFM @ 90 PSI. Yes the intake volume equals the the output volume at atmosferic pressure. or 0 PSI guage. The compressor does not make air it moves it. This movement is sometimes held up a bit and it piles up in the storage tank. The end result always is 100% same amount of air in as out. Now how many CFM can the pump move when pushing at 60 PSI? 90 PSI? 175 PSI. This changes and is graphed as a pumping curve. This curve drops down as the pressures go up. How much depends on the compressor and other variables. Bottom line a compressor will move more air at a constaint 60 PSI than it will at a constant 90 PSI.