Thread: Must be doing something wrong

Unlikely, as I wiped the parts down before taking them together. With all the mucking around finding clamps etc, there was plenty of time for the acetone to evaporate before it might have been trapped.

Michael

A frustrating day welding today, because I couldn't manage to get anything to go wrong
First, the warm up piece - a 2mm piece of Al. Violates Green's law for beginner welders - the best looking welds are the ones people don't see. The Al sheet behind it is the top of my welding table. It was directly on that surface and nothing came up through the joint. The wonky edge shows I do need practice with the plasma cutter though.
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I milled a piece of scrap black steel with some 1mm steps in it, chasing my theory that it might be the oxide reacting. The second photo shows two beads running up the steps - one with filler (top), one without (btm).
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The next photo is the other side of the piece. Oxide taken off with a flap wheel. Again, 2 beads one with (top) and without filler (btm)
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Getting really frustrated with this lack of failure, I tried a bead directly on an un-dressed piece of steel and while the oxide bubbled around a bit, no porosity.

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I checked for drafts too. This is the layout in the shed when I weld. The duct (for the A/C) is around 2 metres from the weld table. I normally only have it on for stick (blow the fumes away).

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I ground all the welds away after welding but no holes.
Things that didn't change were cup size, gas flow rate, post flow, technique, gas, hose connections, filler metal (and amount of cleaning). The only significant thing that I didn't do was wipe things down with acetone. Maybe that was the issue - things were too clean???

Michael

That's a good set of tests.

Maybe your acetone had stuff dissolved in it? Been doing any fibre-glassing lately?

I went back and looked at your original photos - I have to admit that I've never had that result before, so I'm having trouble working out what might have caused it. Pretty hard if you can't re-create the issue. Maybe if it occurs again (you said it comes and goes?) then run through all those things identified in this thread and see if any of them make a difference.

Good luck

- Mick

I'm just a diy hack, so take this with a pinch of salt, but I think the steel itself can be contaminated occasionally. I've had something similar to your results just three times, in very small areas. All while welding a bigger project with no difference in prep or anything. In fact it happened just this weekend. It all looks ok, until maybe you hit a bit and it all goes to pot and spread eveywhere if you try to "run it in". In the picture you can see where it happened and how much I ground away before trying again. I cleaned off the brown soot with acetone before welding (this picture was to help me see if I had got any obvious impurites when I blew it up, to see if i needed to grind out more).
It stated welding fine again, but then weld wrong as soon as the weld hit the top bit of the 10mm plate. Not the join but the bit that wasn't ground (grinded?). Then it just spreads everywhere and I've learned you've just got to stop. All the steel here is from the scrapyard, so could have been used for anything, however I had the same thing on a small section when I bought all new steel to build an A frame to lift my lathe. I was welding for hours and just one bit caused problems. It happens so rarely I've decided it must be the steel and best to grind it all away as much as possible and start again.

An intermittent fault could still conceivably be a cracked gas line.....