This is second hand info...
When I was setting up a beam welder in our shop with Ken Rorie from KENTEX, he told me a story about a past customer of his that was having similar trouble. He described it as very large intermittant holes in SAW fillet welds made by a beam welding machine. They first suspected cutting slag left over from the plasma table process, but continued to have the problem after implementing a procedure that required all cut egdes to be ground. They finally fixed the problem by changing from nitrogen fed plasma cutting to compressed air. It doesn't really seem logical, but that's what he said happened.
Are you using Nitrogen?
Tim
Update : 1/9/08
My old friend Ken Rorie sent me an email to let me know my memory is fried. I should know better than to try to quote from a 5 year old conversation...
Anyway, here's what I meant to say:
"I have a customer in Arkansas (this has since happened with other customers since this original encounter) who was experiencing large pin holes in his continuous fillet welds when welding with Twinwire, 1/16" electrode diameter and subarc process. He said the problem was intermittent and could not figure out what was causing it. I even hired 2 consultants to look at the problem and they could not determine the cause. He was plasma cutting his webs using an MG plasma cutter and shop air for gas. The holes were as large as 3/8" diameter and were intermittent. You might not see a hole for 18-24", then four holes in a row at 2" centers, etc.
We discovered that the problem only occurred on thin webs (typically less than 3/16" thickness). This was evidently related to the higher speeds used in cutting the thin webs. We determined the use of shop air as the plasma gas left nitrite deposits on the cut edge. When the subarc fillet weld was being made, the nitrite deposits were turned back into nitrogen gas and bubbled up through the deposited weld metal. Changing to oxygen as the plasma gas solved the problem. I recently had another customer encounter the identical problem. Their small, home made plasma cutter could not utilize oxygen as the plasma gas, so we used a grinder to clean the cut edge of the web material and the problem disappeared. The important thing was the clean the cut edge of the thickness, not the flat surfaces on either side of the web material. I thought this further explanation might help explain the problem and what we discovered for a fix. "
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