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Up Topic Welding Industry / General Welding Discussion / Black lines next to stainless flux core welds?
- - By PlasmaHead2 (***) Date 10-14-2014 01:54 Edited 10-14-2014 02:03
So what exactly are they? Some part of the flux and if so why are they so tightly adhered? The majority of the flux removed it's self in almost one piece.
The opinion my brain formed while scrubbing them off was something like a vapor deposition of the flux ingredients???
They get machined all over and passivated by the customer; My big concern was if those black lines would end up as trapped slag that would show up in machining...
A coworker fit and put a GTAW root pass which I filled in with FCAW. I did my best to be a robot...:twisted:
Attachment: Blacklinesbeforecleaning.jpg (148k)
Attachment: duringcleaning.jpg (146k)
Attachment: selfremovingslag.jpg (167k)
Attachment: cleaned.jpg (147k)
Parent - - By aevald (*****) Date 10-14-2014 14:40
Hello PlasmaHead2, I thought about your question and checked out the photos. Now, I certainly can't specifically identify the "black lines" as to chemical make-up yet, that coloring and the consistency of it looks very similar to the residue that is left when using Solar Flux as a backing for many SS welding operations. It isn't very easy to get off either. Just a hunch, but I believe that you could treat it in a similar fashion to the silica islands that often show up with GMAW welding, in other words, if multiple passes are being employed it would be a good thing to remove prior to adding additional passes. Just my $.02 Good luck and best regards, Allan
Parent - - By PlasmaHead2 (***) Date 10-14-2014 23:25
These were single pass welds so I didn't have to worry too much. I do clean them off when confronted with multipass welds and the quickest way I found to deal with them is a carbide burr bit.
Only down side is trying to make sure the bit doesn't hop around and dig up the rest of the work...
Never tried solar flux but after this I think it would be a weapon of last resort, cleaning that out of the inside of a pipe sounds like WAY more fun that I want to have. Ever.:lol:
Parent - - By aevald (*****) Date 10-14-2014 23:37
Understand about not wanting to clean residue from the inside of a pipe yet, in most instances where this (solar flux) might be used for internal oxidation control I don't believe that it is expected to be cleaned. In those cases it is likely that an Argon purge would be used.

It was too stubborn for a stainless steel wire wheel or wheel-mounted scotch-brite pad? I don't believe that I have ever had that much difficulty with removal of that type of deposit. Well good luck and best regards, Allan
Parent - By PlasmaHead2 (***) Date 10-15-2014 03:13
It took a stiff grip, more than a bit of down pressure, and about 15 to 30 seconds to scuff off the black lines in the picture... Far more effort and time than I thought it should have needed.
Almost seemed like the wire had to dig into the base metal a bit before the lines vanished...
I'll try a scotch bright next time I run flux core, I skipped it on these parts because they were too hot for one of those disks..
On these parts it didn't matter so much but part of my concern is what about a part where the surface finish and or fine dimensions mattered A LOT more? (I know, I know; Use GTAW :wink::lol:)
How could I make them go away without having to use "harsh" abrasives...

I'm lucky and get to use argon on my SS parts :smile:
Parent - - By 46.00 (****) Date 10-14-2014 17:43
Most likely bismuth deposits, added to aid flux removal......
Parent - - By yojimbo (***) Date 10-15-2014 02:02
Plasma-

What surface preparation were you doing before welding?  Have you tried hitting the weld area with a flapper wheel/disc to remove any surface oxides prior to welding?  If nothing else it might make final clean up less difficult.
Parent - By PlasmaHead2 (***) Date 10-15-2014 03:25
The parts were machined by the customer, fitted and root passed with GTAW by a co-worker and handed to me to fill in with FCAW. I cleaned any heat tint from the root with a SS wire wheel and an acetone wipe down. I took a carbide burr to the starts/stops and the toes anywhere I saw the black lines.
If I could upload the "during cleaning" pic at full size you could see some of the lathe tool marks and the spots where the wire wheel wiped them out...
Parent - - By PlasmaHead2 (***) Date 10-15-2014 03:30
Bismuth eh? would that be in your average carbon steel FCAW wire as well?
Is that one of those too small of a percent/weight to mention elements in the wires?
I have one of those science pun pictures about bismuth, but it doesn't show on of the nice "hopper" crystals that bismuth will form, so it doesn't feel right... ya know?:lol::twisted:
Parent - - By Stringer (***) Date 10-28-2014 23:38
Nice looking weld. Heavy stainless welds have always presented nominal oxides and coloring on the sides for me. Wire brush and passivate if you want, but to me it looks like a job well done.
Parent - By 46.00 (****) Date 10-29-2014 18:16
I would agree Stringer, I would consider this normal and easily removed by wire brushing or lite use of flap wheel or other mechanical tools etc. I have included a link to a paper co authored by a very knowledge man I had the pleasure of working with on the development of some FCAW wire many years ago. Anyhow, whilst not related to the OP, it does talk about the effects of Bismuth in S/S FCAW.

http://www.nickelalloys.com.br/Metrode%20CD%202011/Technical%20Literature/General%20Flux%20Cored%20Wire/IIW%20Bismuth%20Position%20Statement%20IX-1974-00.pdf
Up Topic Welding Industry / General Welding Discussion / Black lines next to stainless flux core welds?

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