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Old 06-06-2017, 12:53 AM   #1
bneub
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Default Weld problems

I am having some porosity and contamination in new TIG welds on an old gas welded fuselage.

Weld on the right was away from the old weld. The one on the left is picking up the edge of an old weld.

The fuselage was blasted, wire brushed, and cleaned with acetone. I'm using straight argon, ER80S-D2, and the same techniques as usual on 4130.

I wonder if the old weld filler is causing my problem and open to any ideas.

Yes, that's a hardware store bolt holding things in place while I tack it up.


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Old 06-06-2017, 01:08 AM   #2
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TIG hates zinc. Any chance the bolt's plating has come through the weld from the inside? Is the bolt stuck in the bushing?


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Old 06-06-2017, 01:21 AM   #3
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Benub,
i would take a little more time with a 4" grinder and remove the entire bushing and washer.
Like Bill says, use an uncoated bolt.
You may also have oil contaminated base metal.
Double check your gas or borrow and switch tanks to make sure it is pure argon.
How did it break?
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Old 06-06-2017, 03:24 AM   #4
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The bolt stayed free, I pulled it out with my fingers. Now that it's tacked in, I'll take the bolt all the way out and try some more. It could have gotten hot enough to offgas zinc.

I'm using the same argon bottle I've had for a while. It's about half full and no problems so far.

The plane was set up with a 360 when I bought the project, I'm switching to a 540. The 540 mount from steen is built for 7/16 bolts per the plans. The old mount holes were all off center with the new mount so I drilled them out and slid new bushings in the new lined up holes.
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Old 06-06-2017, 03:30 AM   #5
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A couple of pics of how I cut the new holes. A 9/16" annular cutter with a shaft welded in. I pulled it through from the back side to the washer.
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Old 06-06-2017, 04:10 AM   #6
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I concur... grind away all the old weld filet. I helped my hangar neighbor repair a tailwheel spring bracket that broke loose over the winter months.. got about 2/3 rds done with tig, and then we kept getting something from the tailpost tube contaminating the weld. Had to resort to gas to finish the job, and that was a real trick to keep from damaging the covering material. Judicious use of a water soaked rag to try to keep smoking the fabric. In the end the fabric shrunk back a little ways, but some finishing tape and PVC cement worked out well to repair.
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Old 06-06-2017, 09:58 AM   #7
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I doubt it's the bolt, we use hardware store bolts all the time to hold stuff together during welding. Not just tacking but the complete weld. Just FYI......
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Old 06-06-2017, 12:43 PM   #8
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I have had that happen when the argon is insufficient to shield the weld. Make sure the flow is set correctly.

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Old 06-06-2017, 09:59 PM   #9
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Same thing happened to me, found a small cut in the argon hose leading to torch.
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Old 06-07-2017, 02:58 AM   #10
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I tried a couple of samples on some new scrap tube tonight with the same setup and two different brands of filler.

The bottom bead was .045 Blue Demon filler from Amazon. The top bead was .035 from the welding supply store. Both are ER80S-D2.

The first pic was the raw weld, uncleaned. The second pic was cleaned with a 120 grit bristle brush. I was a little suspicious of the blue demon filler before I cleaned it. The surface didn't look very good. I thought maybe I found my problem. Looks better cleaned.

The local machine shop suggested preheating the problem spot on my fuselage. His logic is that it's ok to preheat 4130 and it could possibly burn off any remaining contaminants. Any thoughts on that suggestion? If it doesn't work, I only have a half day of grinding to do...

Thanks for all the advice. I feel for the builders 30 years ago, no smart phone pics and no internet for advice.
Brian


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