Everything you wanted to know about Air-Carbon-Arc Cutting & Gouging
Air-Carbon-Arc Cutting & Gouging is a very usefull metal removal process. It differs signicantly from both oxy-fuel cutting and plasma cutting. The process uses a carbon electrode, a standard Constant Current Welding power source, and compressed air to melt the metal and blow it away. This process will work on anything that can conduct electricity and be melted with an arc. Steel, cast iron, stainless steel, copper, brass, aluminum, magnesium alloy all can be destroyed with air-carbon-arc.
It is not a common process among hobby metalworkers, and is typically only found in industrial environments. This is unfortunate becuase it is a process that can be of great value to us. After reading this post, you will know everything you need to get started.
The main purpose for air-carbon-arc is gouging and removal of old or defective welds so that they can be redone, or the equipment dismantled. It will allow you to remove the minimum possible amount of material so that the joint can be re-welded. Oxy-fuel and plasma cutting are capable of gouging, however, neither does it as well as air-carbon-arc.
It can be used for cutting too. Oxy-fuel cutting is pretty much limited to steel, and plasma equipment can be very expensive when compared to air-carbon arc. Depending on the thickness of the material you may have to take multiple passes. If you have a cutting situation where mechanical means are not suitable, and plasma/oxy-fuel is not available, it may just be your solution.
With some practice, an operator can very accurately remove metal in a controlled fashion, and applications besides weld removal will soon be discovered. I have used it to destructively remove bolts and nuts, make quick and fast bolt holes, heavy demolotion, you name it.
A little history lesson:
Air-carbon arc cutting and gouging was invented during WWII when, while building a warship, a very long stainless steel weld was done incorrectly and had to be removed. The labor costs of grinding and chipping were cost prohibitive, not to mention the time it would have set the job back. At the time, they didn't have air-carbon-arc torches, so the operator held a carbon electrode in a welding stinger, and an assistant followed the arc with a compressed air nozzle. The gentleman who came up with the idea invented the first air-carbon-arc torch, patented it, and started the "Arcair" company that Thermadyne now owns.
Equipment and consumables needed
First, let's discuss the power source. Air-carbon-arc cutting requires use of a standard Constant Current (CC) SMAW (stick welding) power source.
Remeber that post I made that discusses electricity? No? Well go read it now. The reason I made that post is actually so you can understand why the following is true: Single phase DC Welding power sources will NOT work with DC carbon electrodes.
Don't even try it, it ain't going to happen. The reason is that DC carbons do not have the same chemicals found in welding electrode fluxes, and therefore do not have the same arc stabilization properties. The capactiors are not quite enough to smoothe out the waveform to make a stable arc with DC carbons.
You will require a machine powered by 3 phase power, or an engine driven welding machine. For most hobby metalworkers, 3 phase is out of the question and the best option of course is to go the engine driven route. (Tell your wife, girlfriend, husband, or boyfriend that it's a backup power generator, and you won't be lying.)
Now you have to be carefull when you go to buy your engine driven machine. Some lower end machines generate single phase power and rectify it, just like you would with line powered machines and aren't suitable. The mid to higher range machines will generate 3 phase power or pure DC internally for the welding circuit, and these are what you want. (The machine I use for my air-carbon-arc cutting is an old, used, Lincoln Weldanpower)
(Note: They do make AC carbons that would in theory work OK on single phase power, however they do not make these in all sizes, and I have not yet had a chance to personally try them myself. When I do, I will post about it.)
Well, how many amps do I need?
I'm glad your asked that question! Air-carbon-arc cutting and gouging uses significatnly more amps then welding of the same sized electrode does. For most of the type of stuff you and I do, an 1/8 carbon is the most usefull size, with 3/16" coming in a close second. 1/4" and above is really too big for our needs. Here's a nifty chart:
Note: I've found when using engine driven machines (both mine, and ones at work), that I need more amps to accomplish the same cut as compared to 3 phase powered machines.
What else do I need?
Obviously you need the air-carbon-arc torch! My one and only recomendation to you is the Arcair K2000 torch by Thermadyne products (Same people who make Victor gas-apparatus.) Anything larger then that is over kill for our needs, and also requires very large air compressors. The other brands of air-carbon-arc torches I've seen, I have not been impressed at all with, I think Arcair is the best. The K2000 will run you anywhere from $200-350 retail. I got a great deal on mine in "new" condition from Ebay for $95 plus shipping.
Also, you will need an air compressor. The K2000 requirse 40 PSI at 8 CFM.
The K2000 features a coaxial air hose/conductor. This hose accounts for about half the cost of the torch, so take damn good care of it. Running too many amps, stepping on the hose, melting the hose, kinks, etc., will all ruin your day.
Here's a pic of the torch setup:
You'll want to add an air hose, and welding lead pigtails with quick connects to the coaxial hose. Not using quick connects is a royal pain in the ass. (I keep my welding stinger on a 5 foot long pigtail and quick connect as well.) The rubber boot slides over the connection points to keep from arcing against crap.
Air-carbon-arc cutting and gouging is a very dangerous process. The arc is much brighter and more intense then a welding arc. It is an EXTREMELY loud process, and hearing protection is NOT optional. (Also, don't forget, not only do ear plugs save your hearing, they keep spatter out of the ear canal.) Heavy welding gloves, and leathers are also reccomended.
I do NOT reccomend using auto-darkening hoods with air-carbon-arc cutting. Use a standard hood with a glass filter. Make sure you pick a shade filter # that is approiate for the amount of amps you are running.
Also, this process presents a very large fire hazard. It is capable of blowing molten metal through the air up to 15-20 feet away if the trajectory is right, so make sure you have a good clear path, and DO NOT do this inside your shop.
Electrocution is also a concern. Don't do this (or weld) if it's wet on the ground, you clothes are dripping from sweat, etc. The worst electrical shock I've had in my lifetime happened at work, last summer, sitting on top of a railcar on a hot sweaty day while using air-carbon-arc to trim a piece for fit up. I shocked myself, and was thrown back about 4 feet. I'm lucky I did not fall off of the car, and the electricity didn't pass thru any organs.
Another considerion is your neighbors. Trust me, they will be able to see and hear you, so keep them in mind.
Can you quit blabbing and get on to it, buddy?
First of all, these carbons are BRITTLE, and expensive ($0.30-$1 a piece), be careful with them.
You want your electrode stick out to be no more then 6" for the larger electrodes, and 3" for the smaller ones. As the electrode wears away, you simply loosen the clamp and slide it further out.
Most DC carbons have a thin copper coating on them to improve the electrical contact between the carbon and the torch.
Make sure the air holes are pointing the right direction! (That's towards the work, buddy.)
The piece that has the air holes swivels 360 degrees so you can put it at any angle you like.
Striking the arc is a little bit different (and easier) then with a welding electrode. Just LIGHTLY touch the electrode to the work, let the arc start, and slowly move it where you want it to go. This requires a special touch, and to be honest, I don't know how else to describe it. Some practice time will quickly teach this to you, as well as how fast you should travel. This really is easier then welding, however, like welding you will get better with practice.
You want to hold the electrode at about a 45 degree angle. You want to use a "push" direction*. Make sure the air holes are BETWEEN the electrode and the work, not over top of the electrode. THIS IS IMPORTANT. Also, don't forget to open the valve! You will make a big mess if you don't. The valve is that black button on the torch handle.
*(same meaning as with MIG welding.)
Note: if you are having trouble starting an arc, try increasing the amps. Don't worry if this takes you past the limits of what the chart says above, or the box of carbons' documentation. Just use enough amps to get the job done, and no more. However, make damn sure you don't exceed the rating of the K2000!!!
Note2: DC carbons use DC Electrode Postivie polarity.
Here's a picture of what a gouge looks like, half way thru a weld.
Here's an action shot. Note the intensity of the arc vs welding. To the right of the arc, you can see the molten metal flying to my right. (The electrode is traveling left to right.)
Here's the completed gouge.
Then you can take a grinder and clean it up. If you look very carefully on the bottom piece, you can see where I gouged the surface a little bit. This can be filled in with weld metal and ground smooth, before re-welding the joint. Nobody will know the difference.
Here's an action shot of welding it back together.
And here's the completed welded, gouged, and re-welded coupon. Yeah, yeah, my heat was screwed up on the beggining of the weld. If I did that on a jobsite, I'd have to gouge it out (again) and fix it!
Well that's about it. Feel free to ask questions.
Air-carbon-arc cutting is a really usefull process, and I hope you enjoy using it. With the large amount of amps, the intense sound and light, the fact you can cut thru metal like butter, and flying molten metal all make this a really awesome process, that is really fun to do (Until you have to do it out of position on a jobsite, and give yourself minor burns every 2 seconds.)