O2 on air plasma

[Karl_T]

I'm painting my plasma cutter next week. Yea. Mechanical fabrication complete, tons o' wiring left.

I'm thinking of adding oxygen ablility to the cutter by running two air lines out to the unit and solenoids for both lines. Most of my parts will have an outline that could use air and then several holes for bolts or tapping. The hardening from the air would be a real PITA. This route would allow a switch to O2 for hole popping.

My question, will an old Innerlogic air cutter be able to use O2 and produce HAZ free edge?

Karl

[slammedxonair]

I'm pretty sure you cant run o2 to a regular air plasma only nitrogen.

[jimcolt]

I would suggest that you do not use oxygen on any plasma torch that is designed for air. The Innerlogic air torches (they have a 45 amp and a 100 amp unit) are essentially copies of Hypertherm's old HT40 and Max100 air torches....these torches use a composite swirl ring, as well as composite (plastic) internal insulation within the torch body.....by using pure oxygen with this material in the torch you will eventually create a situation that will support combustion within the torch and leads. I have seen these oxygen fires that will destroy the torch....and sometimes will actually burn back the torch leads a few feet!

Plasma torches that are designed for oxygen cutting use completely different internal materials....and the swirl rings are made of (usually) volcanic lava....which looks like ceramic.

The air cutting process actually produces a chemical effect on the edge known as "nitriding".....this is a form of case hardening related to the approximately 80% nitrogen content in air. Oxygen plasma systems minimize the HAZ (heat affected zone) by minimizing the amount of nitrogen that comes in contact with the molten steel on the cut edge.....

Jim Colt Hypertherm

[Karl_T]

Jim, thanks for the explanation. Don't need a repeat of the Apollo 1 incident.


You seem so knowledgable. I'm curious, why is CO2 not a good choice for plasma gas? No nitriding, no oxidation of equipment. Must be another problem cause its WAY cheaper than O2.

Karl

[jimcolt]

C02 is often used as a shield gas....it simply does not work well as a plasma gas....I believe that it causes difficulty with arc starting due to it's ionization properties. Typical plasma gas combinations in order of their popularity: 1. Air (because low cost air plasma systems are designed for use with this gas....and users think that air is free) 2. Oxygen (by far the best way....and usually the least expensive way to cut steel due to it's ability to cut faster, cleaner...resulting in more parts and less secondary grinding...in recent years technology with high end systems such as high definition plasma...has further improved consumable life, cut quality and speed for this process gas) 3. Nitrogen (usually used with a shield gas of C02....or water, or water injection for best cut quality on stainless steel) 4. Argon/hydrogen in a 35% hydrogen mix (used for excellent cut quality on stainless and aluminum thicker than 3/8") 5. Nitrogen/Hydrogen in a 5% hydrogen mix (used with high definition class cutting of thin stainless for a metalurgically superior cut edge suitable for weldability).

Most air plasma torches are only compatible with either air or nitrogen....it is dangerous to use other gases if the system is not designed for their use. Most air plasma torches also are a single gas torch.....so a shield gas cannot be utilized as in high end industrial torches.

Apollo 1....as a kid I was infatuated with the space program....when Grissom, Chaffee and White were killed on the launch pad (oxygen supported fire) I was devastated...

Jim

[Karl_T]

Jim, I wish I'd met you before i went to that auction. Oh well, life is a learning experience. The Inner Logic unit is not going to meet my needs. I'll use it to shake down my refit table and then replace it.

We fabricate in steel 0.070 to 0.500 inch. Cut speed is not an issue but being able to tap a hole with only a quick drill reem is. Most of the plate stock sees the press brake and then becomes part of a weldament. We went for a plasma over an oxy torch unit to have capability for aluminum.

So, what unit will you sell me?

Karl

[quisman]

You've got a PM.

[WSS]

Originally Posted by jimcolt Apollo 1....as a kid I was infatuated with the space program....when Grissom, Chaffee and White were killed on the launch pad (oxygen supported fire) I was devastated... Jim

A few years ago my wife had the opportunity to do a level 4 session in a recompression chamber, part of the program was on and off of oxygen at intervals (4hrs) which meant a high percent of oxygen in the chamber. It was not planned so we had not eaten for about 8hrs. The chamber had a small equalizing trap door to transfer food into. The food couldn't have oil or paper (potato chips were not allowed) and all sorts of rules due to the pressurized oxy. Poor thing, she had a really dry sandwich. Even the fire suppression system had to have extra psi to counter the high psi inside. It was really very interesting, had my adrenal gland not been acting up, I would have got more out of the experience.