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29th Dec 2014, 08:57 AM #1Senior Member
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Advice, tips re. removing duragal for a weld?
I'm TIG welding a Duragal door and frame with quite a few small section welds to a 65x35 perimeter frame. Any ideas, other than grinding to remove the gal coating. No problem doing ends of sections I just stand them in Hydrochloric acid for a few minutes but on the side of a long length is a different issue. I thought of the possibility of mixing up a flour paste with Hydrochloric and putting it exactly where I want it. I find the grinding messy and time consuming. Thanks
woodworm.
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29th Dec 2014, 09:17 AM #2Most Valued Member
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Hi there,
I'm certainly not the best welder in the world and I have never done TIG welding. I rarely bother removing the light gal coating when I weld duragal using arc or mig. it's a messier weld though.
My understanding from your post is that TIG requires a much cleaner surface, is that correct? A hydrochloric acid paste made from flour sounds like a clever idea.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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29th Dec 2014, 09:37 AM #3Senior Member
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I do prefer TIG for these jobs, very neat results, but yes if not cleaned of the coating, the zinc leaps happily onto the electrode which then needs to be re sharpened, plus there is the messier weld also. I got the flour paste idea from paint stripping where it's used to slow drying out of strippers while they do their work.
woodworm.
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29th Dec 2014, 09:57 AM #4Golden Member
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I've found the gal gives off a nasty vapour if welded plus can make the electrode fizz.
I would strongly recommend grinding it off.
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29th Dec 2014, 10:41 AM #5Senior Member
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29th Dec 2014, 12:06 PM #6Golden Member
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Dipping the ends in hydrochloric will promote rust formation in side the end of the tube. I'd never do this for this reason. I like the paste idea - not sure if the HCl would react with flour or not. Another option is just paper towel soaked in HCl, then dab as required? I'm not clear on why you can't just grind the required areas?
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29th Dec 2014, 12:24 PM #7Senior Member
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Yes, hydrochloric can cause rusting inside but in this case my welds are all closed up and the remaining zinc plating does it's job as an anode anyway. Also, I do flush the parts thoroughly with water.
I tried the flour mix and it doesn't work. No reaction with the flour though, just too prone to dripping off but could be ok on a flat surface. Needs to something with a more sticky effect.
You are right I could grind it off, it's just that I was looking for a more precise result, eg. taking off only the required amount of coating. I do have Nitric acid but definitely reluctant to use that for this.woodworm.
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29th Dec 2014, 12:52 PM #8Senior Member
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If you use one of those die grinders, you can grind fairly accurately.
I use arc for duragal, no grinding, just weld it, seems to come out reasonably neat.Regards
Bradford
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29th Dec 2014, 02:56 PM #9Golden Member
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How about pickling paste? the paste for cleaning up stainless steel. Use a simple paintbrush or one of those foam brushes?
I persisted a long time with tigging gal sections (by grinding through the gal to steel - you can tell you have got through all the zinc by the change in spark pattern/colour) , but in the end I found I got good results just stick welding (gemini 12 rods) on thin duragal for all positions except overhead fillets - where I'd get punished for any gaps in the fit up. In those cases, I'd grind out the mess and tig over the top (since the gal had burned away). The trouble with TIG was that any full penetration would tend to bring zinc and other crap in from the back side of the weld and ultimately back onto your tungsten.
How thick is your duragal?
When I was faced with a job with about 300 duragal joints, I bit the bullet and bought at MIG, which is the perfect tool for the job.
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29th Dec 2014, 03:40 PM #10Most Valued Member
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Anyone using pickling paste needs to be fully aware of just how nasty it is.
Put it this way, if you get it in your eyes, you stand a better than average chance of permanent damage, quite possibly blindness, even if you wash it out immediately. There are a couple of hideously expensive products that neutralise it. Oh, by the way, did I mention that it leaches the calcium out of your bones too, so don't get it on your skin either. Treat pickling paste with as much respect as you would treat a nuclear reactor in your workshop.
I am told that very shortly, pickling paste will be a regulated substance, meaning that you will need a licence complete with detailed plans to capture and dispose of the effluent produced.
Methinks that a flap disc sounds far safer and more practical for zinc removal if you must use a TIG for this job. Duragal is only very thin anyway, so it just about comes off when you look at it.
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29th Dec 2014, 04:09 PM #11Most Valued Member
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I know very little about pickling paste but your description of it makes me think it has Hydrofluoric acid (HF). This is a particularly nasty acid indeed.
If this is certainly the case, I would be steering very clear of it. Of course it sounds like it used pretty widely and so I dare say that if the correct precautions are followed and the correct PPC used then it must be "reasonably" safe. HF is also created as a product of combustion with such fires as cars etc. from the plastics etc.
HF put the fear of god into me!
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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29th Dec 2014, 04:23 PM #12Golden Member
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Yes it does (or at least some do) contain HF and agreed it not something to be taken lightly. It's one of the few acids that can dissolve sand and hence has some special uses in the laboratory and is one of the few acids where the fear of god was really drummed into us.
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29th Dec 2014, 04:30 PM #13Senior Member
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Ah well, in the end I gave up procrastinating grabbed an 80grit flap-disc put it on the variable speed grinder set at 3 speed and got stuck into it. Worked a treat. I've had mixed feelings about flap-discs in the past but took me around 10 or so minutes to do 20 separate areas. All tacked up and no electrode contamination. Duragal is 1.6 and 2.0mm and and I always grind until I see it's colour change from silvery to dark.
woodworm.
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29th Dec 2014, 04:35 PM #14Senior Member
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29th Dec 2014, 08:18 PM #15Banned
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If you want to try the Hydrochloric Acid again. Take a bar of velvet soap. Run it through a chesse grater, and mix your HCI with that. The soap is some what neutral, but will make a nice paste that wont run or sag.
Regards Phil.
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