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Up Topic Welding Industry / Technical Discussions / AC GTAW on Steel
- - By PlasmaHead2 (***) Date 07-08-2015 01:40 Edited 07-08-2015 02:59
In an effort to keep from rambling on and on... Numbered short questions!:grin:
So with AC GTAW on plain old steels:
1: Why does it not stabilize... even with an inverter (miller dynasty 350) shifted to 99% EN @5-10 amps *EP at 500hz freq...
2: Is the AC wave removing mill scale as it would the oxide surface of Al or Mg?
3: Is the manner of how the AC wave removing the oxides(if it is...) the reason it doesn't stabilize?

I will gladly elaborate at a later time as to how these questions came about... it mostly involves me forgetting to hit a button after doing some quick Al tacks for a shop fixture then going back to steel... Provided anyone is interested.

Thanks,
Clif
*typing too fast...
Parent - - By kcd616 (***) Date 07-08-2015 01:57
Clif.
very interested
the Kent stupid post
no idea
I think your correct
I will let smarter people like Al Moore, Lawrence
answer this
sincerely,
Kent
Parent - By PlasmaHead2 (***) Date 07-08-2015 03:07
Kent,
Correct about which part? :lol:
BTW, I feel like I owe you a 6 pack of your favored beverage for that iron/carbon diagram... Well played good Sir :smile:
Parent - - By Lawrence (*****) Date 07-09-2015 12:48
Mill scale will never be something that GTAW can adapt to... No matter how fancy your power supply.

It's quite a bit thicker than aluminum oxide and puts a ton of oxygen into the arc/puddle when you GTAW over it.

We have done trials years ago with AC asymmetric GTAW that was heavily balanced toward EN with 400hz...  It was able to lift oxidation off of Inconel and Hastelloy hot sections pretty impressively....

I think the proof is that when you grind your steel to brite metal you will have a stable arc (assuming the steel is killed).

Sorry I couldn't be a bit more helpful

tell us more of your story :)
Parent - - By PlasmaHead2 (***) Date 07-11-2015 17:11
I have pictures and a better story to tell... and no time at the moment to tell it.
Ill try and get on here later tonight.
Parent - - By aevald (*****) Date 07-11-2015 22:08
Hello Clif, I'll be staying "tuned" for the rest of your story. Regards, Allan
Parent - - By PlasmaHead2 (***) Date 07-14-2015 00:13 Edited 07-14-2015 00:39
So the fun started one day after lunch. Me and a coworker went to the Chinese buffet... it was a terrible idea. Delicious but terrible for the whole having to function thing. Lucky for me I did all the hard work of fitting and tacking all my parts Before I put my self into a food coma.
All was going along well, maybe a little slower than normal but going well none the less.
Then a random shop job pops up, tacking a few various thickness of Aluminium plates together to make a locating fixture for the spot welder. Simple enough, push a button on the Dynasty and off I go. (I Love shop fixture jobs...)
So the coworker wanders away with his part attached and I lean back into the part I was welding on and *BZZZZAPPPPP!!* :eek:
Well that Wasn't the nice *POP* Whoosh of the DC arc I wanted... *$%!@*&#
Fix the W, hit the button, off I go back into the robot mode/food coma :lol:
The part that started all of this was how the arc etched away some of the scale...
I grind off what I can when I have the chance... I dont always get to tack them together.
The have lately listened to me and got the plate sand blasted by the distributor... so life is good.
So later on I tried setting the machine to roughly what Lawrence mentioned, and running a bead right over the scale on a scrap plate. The arc never seemed to stabilize and crackled roughly around a 1/2" dia from the weld pool...
Thanks for the replies
Clif
Parent - By aevald (*****) Date 07-14-2015 05:08
Thanks Clif, sounds interesting enough allright. Best regards, Allan
Parent - By PlasmaHead2 (***) Date 07-14-2015 00:35
I remembered reading one of your post about welding Inconel's with asymmetric GTAW... thought I would try it on AR235... It didnt work out so well...the results were... weird. The scale kinda etched away but the puddle was really rough and was basically like welding through the scale (gee I wonder why...:roll::lol:) That was a little while ago.
So with the first questions answered I tried another test...

After this post I tried it again but this time I ground the mill scale off.
Thanks to the Dynasty's memory functions I ended up some where near my original "test"
I was around 200 amps En, 90 amps Ep, 99%En, 400hz.
Plate was ground shiny, W was clean with a slight taper and a blunted end (2%cer 3/32), #7 gas lens. I forgot to check which scale the flow meter was at... I believe cfh but the ball was right around 20.
I couldn't bring the AC weld above half power without the puddle developing a bright green glow and lots of porosity and the W suffered quite a bit of deterioration. It really didn't seem to like it at all... I think the original test over full scale fared better...
So I switched back to DC and ran a bead on the other side of the plate to make sure something else wasn't wrong.
Apart from outrunning my gas coverage the DC bead ran fine.
I have more pictures if anyone wants, and the same sample.
I have a feeling I set the Ep side too high on the AC side... I'll try again later.
Thanks for the replies
Clif
Attachment: 064r.jpg - start of AC weld (185k)
Attachment: 065r.jpg - AC weld (172k)
Attachment: 066r.jpg - DC weld (191k)
Attachment: 074r.jpg - AC weld 2 (165k)
Up Topic Welding Industry / Technical Discussions / AC GTAW on Steel

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