plasma cutter question

[shade tree welder]

Does anyone out there know if you can use your oxygen bottle as air supply for the plasma cutter? i use my compressor at the shop, but out in the field i was wondering about the oxy, mite not last to long as per volume or what the oxy will do when mixed with the plasma arc.

[SkidSteerSteve]

I've never tried it, but one thing I would be very leary about would be if there has been any residual oil build up from the shop air supply. Fuel + Oxidizer + Pressure + Spark......SSS

[Scott V]

Back to the Hyper guy again. You can use bottled air or nitrogen for aluminum,
Stainless steel. Read the last line first. Second post.

The majority of manual (designed for hand cutting operations) and about 30% of machine (designed for mechanized cutting) plasma systems in the world use compressed air as the plasma forming gas. Many industrial plasma systems today use oxygen as the plasma gas and compressed air as the shield gas.



Here are the normal plasma gases used for cutting different materials:



Compressed Air…..used on all materials. Compressed air is easily accessible….and produces relatively fast cuts with good edge appearance on most materials….especially carbon steel. Air is comprised of (approximately) 20% oxygen and 80% nitrogen. The oxygen provides an exothermic reaction with easily oxidized materials such as carbon steel….which reduces dross and increases cutting speed. Unfortunately…the nitrogen content in air produces a nitriding effect on steel that provides a very hardened surface….and the nitride finish can create weld porosity if the raw cut surface is directly welded. When cutting stainless steels with air…expect a brown discolored cut edge…..this is an oxide layer from the oxygen…..and this layer can affect some welding processes.



Oxygen…..Used only on plasma systems that are specifically designed for oxygen use. Oxygen produces the best cut speed, cut quality, and metallurgical finish on carbon steels. Oxygen will cut other materials such as stainless and aluminum…..but it is not normally used for anything but steel. The edge finish is relatively soft….can be easily welded and machined. Drilling, reaming or tapping of an oxygen plasma cut hole is possible on steel.



Nitrogen ….Nitrogen was the most popular plasma gas up until about 15 years ago when technology improvements in power supply and torch designs allowed the use of air and oxygen as plasma gas. Nitrogen is still used on some older plasma systems that are not designed for air or oxygen use. Nitrogen, if used for cutting carbon steel, will produce a very hard nitrided edge finish, will cut at dramatically slower speeds (as this is simply a thermal process with no exothermic reaction as with oxygen or air), and it is common to experience heavy, hard to remove dross on the bottom of the cut plate. Nitrogen can help to minimize oxidation on stainless steel when either nitrogen or carbon dioxide is used as a shielding gas, or when the plate is submerged under water so that ambient air cannot contact the cut face in the vicinity of the arc. High purity nitrogen, when used with the proper tungsten insert electrode….can provide very long electrode life as compared to some air or oxygen cutting systems.

[Scott V]

35% Hydrogen/65%Argon…this gas is used only on plasma systems that are specifically designed for the use of this gas mixture. This gas is pre-mixed and stored in a high pressure cylinder…..and it is usually used with a nitrogen shield gas for cutting stainless steel and aluminum over 3/8” (9.5mm) thick. If this gas mixture is used on thinner stainless steel…it will produce very tenacious, hard to remove dross. This gas mixture is often used for plasma gouging (metal removal) applications for very good results…..often replacing carbon arc gouging applications.



5% Hydrogen/95% Nitrogen...This process is relatively new….and is used for high quality cutting of stainless steel on materials thinner than ¼” (6mm).



Each of the above gas mixes should only be used with specific combinations of consumables (nozzles, electrodes, swirl rings, etc.) and flow rates and pressures as recommended by your plasma system manufacturer.



Using oxygen in a torch that was designed for air cutting could cause a serious fire and injury…..consequently, the use of an explosive mixture such as Hydrogen/Argon in a system that wasn’t designed to use these gases could cause an explosion. Be careful, follow the manufacturers directions!



Best regards, Jim Colt

[jamlit]

Ok after reading the above posts and believeing that nitorgen was still used out int the feilds. What is the recommended gas that can be bottled and used on today's plasma cutters for mild steel. I have a new Thermdynamics cutmaster 38 and might be buying a cutmaster 101. I have nevered needed to go out of the shop yet but now am very interested in this question incase in need to.

[Scott V]

What is the recommended gas that can be bottled and used on today's plasma cutters for mild steel.

They bottle plain old air for that. You probably will not like the price though.

[wldrman]

I've used a contractors compressor with pretty good results. You need to find one that has good make up air capabilites. I also run a cutmaster 38.

[Stick]

Re: Nitride

Hello,
I can't find seem to pin down how far back does one have to grind the edge of air plasma cut steel to eliminate the nitride.
Thanks.

[bialecki]

Get a Portable Air Compressor for Field Plasma Work

Does anyone out there know if you can use your oxygen bottle as air supply for the plasma cutter? i use my compressor at the shop, but out in the field i was wondering about the oxy, mite not last to long as per volume or what the oxy will do when mixed with the plasma arc.

Best and safest bet is get a gasoline powered air compressor for the field. I am sure their (the plasma cutter company) R&D spent time and money investigating how to best design their equipment with compressed air.

[DSW]

You can get Hp bottled air. It not inexpensive and you will need to get the fitting to match the bottle. CGA 346 or 347 depending on the tank you get most likely. You could also use a SCUBA cyl. Most are 80 cf alum cyl. and use a yoke style valve. You can get adapters for them to hook up a reg. As they are SCUBA specific they arn't the easiest to find and aint cheep! I can get them if you really need one.

I have several SCBA cyl. these are for the fire dept air packs. They use a std CGA 346 or 347 ftg. Most fire co have the ability to fill them but probably wont unless you know some one. Scuba shops could fill them but they definately wont have the adapter.

I build Hp gas fill systems for the dive industry / technical divers. Regularly mix and blend O2, He and air, service and O2 clean dive gear. I would not recomend putting air in a dedicated O2 bottle. I won't even put air in my dive tanks from a SCUBA shop that I am unfamiliar with, as my tanks will regularly see 100% O2 in the mix process. I have seen an O2 fire up close and personal in my last work location and have no interest in refreshing my memory.

[flukecej]

Use of air cylinder bottles not wirth the trouble

A few years ago when I first started looking for a plasma torch, I came across a used Miller Spectrum 375 down at the LWS. I asked how much for the unit. It was being sold on consignment for $1400.00. It had only been used once and the guy didn't like it. So, he was trying to resale the unit back through the LWS where he had purchased it.

This is what he was trying to do with it. He was cutting thin sheet metal steel, like one would use for flashing, duct work, or light galvanized tin that you might use on a shed or barn. Whether he cut one sheet or several sheets at a time, he could not get the cut quality he was looking for, nor the increase in speed that plasma would offer. He was not using an air compressor, he was using 220 CF bottle with either compresses air and even used Compressed Nitrogen Gas in a bottle. Even though the bottle was at 2200 PSI when full, and properly regulated to provide the correct CFM and Input Pressure to the Miller 375 Cutter, it would not cut very long before using the contents of the nitrogen bottle up. He even tried using more cylinders in combination to get longer cuts, it still didn't work.

Your best bet is with a continuous air source, such as an air compressor. Just make sure you have the right PSI and CFM for your plasma cutter and make sure that air is clean and dry.

The Oxygen systems mentioned by others responding are more industrial in scope, not portable what so ever. Look at the industrial systems over at Hypertherm on their website, the oxygen systems don't look very portable, the machines are large and heavy, and the actual equipment runs on 400-600Volt 3 Phase power.