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help for oxy acetylene welding aluminized exhaust pipe

Posted: Mon Jun 15, 2015 10:26 am
by Dan Timberlake
When patching together "custom" exhaust parts for various vehicles I often use sections harvested from cars with OEM heavily aluminized exhausts. Lately I've been having problems with achieving fusion with the aluminized parts. Removing the coating with abrasives works OK, but a convenient wire wheel seems to just smear the aluminum. Previously I could "break up" the aluminum coating by manipulating/dabbing the filler rod when the steel was molten, but recently that has not worked particularly well.

On a welding bulletin board someone suggested that the copper coated Oxy acetylene filler rod was part of the problem, and uncoated filler would work much better. I think someone claimed that coat hanger was a great filler for exhaust work, but I am reluctant to start using that unknown stuff.

Over on eng-tips the common recommendation is dip the end of the pipe in drano etc to eat the aluminum off the pipe.
Is there a quick, easy, cheap magic way to work with the aluminum coating in place?

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Mon Jun 15, 2015 3:02 pm
by Dave Koehler
No easy way around it. Welding 101. You have to get rid of the coating. The hanger wire is the worst metal on earth. Might have been fine for oxy/acet waaay back in the day before WW2.
Tape off a nice circle and get out that draino. That wont take long to accomplish.

Even better and likely wiser both in looks and finances is to acquire a box of bent pieces from one of the header people.

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Mon Jun 15, 2015 11:51 pm
by joe 90
Copper coated filler rod is mig welding wire.

The filler rods I've always used for oxy acetylene have never been coated.
Coat hangers are galvanised, they give off horrible fumes that you don't want to breathe.

Steel pipe with aluminium coating, it should oxidise when you get it hot enough then come off with a wire brush.

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Tue Jun 16, 2015 9:35 am
by Dan Timberlake
joe 90 wrote:Copper coated filler rod IS mig welding wire.
Hi Joe,

I find I have to be careful when using the word "IS" .
I am not alone.
https://www.youtube.com/watch?v=j4XT-l-_3y0

https://www.forneyind.com/store/results ... ory_id=682
http://airgas.com/product/Welding-Produ ... 1060503POP

I may get some bare steel gas welding rod to try next.

thanks,

Dan T

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Tue Jun 16, 2015 9:47 am
by Dave Koehler
I suspect the real problem is what "IS" the aluminum coating made of. It can't be just aluminum. There just about has to be some kind of binder in the mix, yes? The Other is what is causing the problems.

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Tue Jun 16, 2015 11:14 am
by Dan Timberlake
RE: Binder in the mix.

Could be, I don't know.
For various reasons what I think gives me the most trouble is OEM Volvo, whose heavily coated systems from the 90s are just now failing here in rusty Massachusetts, and then mostly at the welds.
https://volvo850wagon.files.wordpress.c ... cn7940.jpg

That makes me think -
1 - The OEM systems were made by welding aluminized pipe and mufflers together
2 - They successfully welded them without removing the aluminizing, probably with MIG.

On my most recent project joining a NAPA Soundmaster low end muffler for a Camaro and NI exhaust adapters and hunks of consumer grade pipe from Autozone etc all gave me unexpected fusion trouble (Oxy-acetylene neutral flame, copper plated real OA steel filler) until I sanded off the "aluminum." I would not have expected that the aftermarket exhausts would have started using better or thicker aluminizing, but that is kind of how it acted.

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Fri Jun 19, 2015 12:40 am
by modok
I know the question was Flame welding, BUT, this may be a useful clue.
I found mig with co2 shielding welds aluminized tubing very well. Not sure why. The c02 may be helping to burn it off.

The adapters at my local autozone seem to be galvanized(zinc), and that sucks big time. Even grinding a lot of it off it still sucks to weld, and fumes probably taking time off my life.

I have heard some confusion about galvanized vs aluminumized, but it seems clear to me. Zinc burns off leaving white strings everywhere and raining down on me and fumes, while the aluminum... it seems to more or less disappear.

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Sat Jun 20, 2015 2:12 pm
by Dan Timberlake
I'm not sure galvanized exhaust components are going to be long lasting.
In the presence of hot water (around 150 F) the electrochemical polarity reverses, and the zinc no longer sacrifices itself (corrodes/oxidizes) for the steel. Instead the steel oxidizes to save the zinc.

About 20 years ago i had stopped spraying exhaust stuff with zinc rich primer due to poor results. About that time I read something like this, but on the Dow website in regards to Coolant for Commercial water systems in cooling towers etc. They warned about using galvanized components.

http://www.hdgasa.org.za/infoSheet/HDGA ... 0Water.pdf
"... at hot water temperatures there is a reversal of electrochemical polarity and the steel becomes anodic
to the zinc. With most tap waters reversal occurs at about 65Ç."

Re: help for oxy acetylene welding aluminized exhaust pipe

Posted: Sun Jun 21, 2015 12:11 am
by modok
yes, IMO paint is more durable than zinc