Why is aluminum not used for electrode material?

By s002bdk Date 08-18-2009 16:43

I am trying to eliminate the use of copper electrodes on a seam welding line for contamination reasons and have not been successful on one of our lines. I have been able on one of the lines to change from Class III copper to Molybdenum and have actually seen better weld results with the material I am welding. Unfortunately when I tried to use Moly on the other line it did not work because of sticking between the electrodes and material being welded. The seam weld wheels are 8 inch diameter wheels. I thought about trying silver tungsten but have not been able to find a supplier that can supply 8 inch diameter wheel that is 3/8 inch thick. I am trying to find another suitable material that does not contain copper that would weld 0.005 inch nickel plated steel to 0.005 inch nickel plated steel. Currently we use CL II electrodes. I was unable to find any other material besides moly and silver tungsten that did not contain copper. I thought of aluminum but have always been told it will not work. Would someone be able to explain why? If anyone knows of any other non copper materials to try please let me know.

Thanks

By G.S.Crisi (****)

Date 08-18-2009 18:49

Aluminum is used as rod in GTAW (popularly known as TIG welding). In this usage, the rod doesn't conduct electricity, i.e., it doesn't make part of the electric circuit.
Aluminum can't be used as electrode because of two reasons:
1st. Much higher electric conductivity than steel.
2nd. Much lower melting point than steel.
Any (or at least most) engineering handbooks will tell you the differences of those physical properties of aluminum when compared to steel.
Giovanni S. Crisi
Sao Paulo - Brazil

By ravi theCobra (**)

Date 08-18-2009 19:15

There was an article in a welding magazine about 30 ( Count 'em ) years ago about how the seams on cans were welded using the

rotating electrodes you describe and a roll of single strand copper wire which is fed thru as the weld seam is made -

Had you considered this mertod of roll seam welding ?

By 803056

Date 08-18-2009 20:59

Aluminum oxidizes easily. I've read that 90% of the maximum oxide thickness forms in the first 24 hours of exposure to air.

While aluminum is an excellent conductor of electricity, aluminum oxide isn't. It actually acts in a fashion similar to a diode in that it allows current to flow easily in one direction, but not the other. This characteristic would have a detrimental affect on any process using AC, such as in the case of resistance welding.

Aluminum is rather soft, so it wouldn't stand up to the forces encountered during seam welding. It would mushroom easily and to the excesss, reducing the current density which would have a negative impact of the welding operation.

I believe I have hit the main reasons for not using aluminum electrodes for resistance welding. There may be some others I haven't thought of. I will be interested in seeing what other folks have to say.

Best regards - Al

By 803056

Date 08-18-2009 21:10

That sounds like resistance brazing where the copper strand serves as the braze filler metal.

I won a free lunch one day when some old codger and I got in to a discussion about brazing and somehow it came about that I bet him lunch that I could braze two pieces of steel together and he wouldn't be able to break them apart. The deal was made.

Now I remember the situation! We had to make an extension for the drill bit so we could access a location we couldn't reach with the regular drill. So I said I could extend the bit using a length of small diameter pipe. He said it would have to be welded because braze wasn't strong enough and we didn't have brazing rod on the job site. I bet him I could braze it with a piece of copper and he said I was full of male cow excrement.

Anyway, I did braze it together with the cutting torch (that's all we had on the job site) and a length of copper wire left behind by the electricians. I striped back the plastic insulation, no flux was used (we didn't have any), and we drilled the several holes that were required, and I got my lunch bought and paid for!

Best regards - Al

By DaveBoyer (*****)

Date 08-19-2009 02:18

I have seen the guy demonstrating the Henrob torch braze with copper electrical wire. Proper joint geometry is key to successful brazing. Some of these codgers don't know there are brazing alloys with well over 100 KSI ultimate strength.

By s002bdk Date 08-19-2009 12:05

Soutec Soudronic makes welders like you mentioned and yes I have looked into them and they would work great but that does not eliminate my copper contamination issues. Are there any other materials available for AC resistance seam welding that do not contain copper?