Soldering galvanized ductwork

[Nitpicker]

Can ductwork galvanized steel sheet be soldered? What I want involves soldering some curves as well as soldering tabs after bending. If possible I plan on using a jewelers acetylene torch. Is there any special flux or solder to use? Thought I'd ask BEFORE cutting the material.

 

[Falcon67]

Can't help you on that but best be aware of issues with galvanized steel and heat

http://www.nakedwhiz.com/weldinggalvanized.pdf

 

[mayday0017]

no, you do not solder them or weld them.... Bend and uses screws and apply proper mastic.

 

[StingRay]

Yes Galv can be soldered. I've never done it myself so I don't know the process exactly but that's how gutters were done in the old days. My buddy with a rad shop has all kinds of Galv stuff around the shop he's soldered together. Google it and you'll find the answers you need.

 

[mayday0017]

Looks like I was wrong, my apoligies. I knew you could "weld" galvanized but it produces poisionous gas. It also kills the galvanization in the heat effected zone. Didn't know you could solder it.

Learn something every day

 

[readhead]

Galvanized solders very well. Use muratic acid for flux. Would suggest an iron rather than a torch. A torch tends to get the material to hot to fast.

 

[WWIIjeep]

This ^^^^

In addition to muriatic acid, zinc chloride flux is very commonly used for soldering galvanized iron. It's a mixture of muriatic acid and zinc and is slightly less corrosive after the fact. They are both liquid fluxes.

However, if you have vertical surfaces to solder, it will be easier and neater if you use a paste flux instead of a liquid flux. Two common brands of paste soldering flux are Rubyfluid and Nokorode.

Whether you use a torch or an iron, heat the base metal so that it melts the solder and pulls it into the joint; same as sweating copper pipe. Don't melt the solder directly with the torch or the iron because it won't flow into the joint that way.

As redhead said, a soldering iron would be easier and better than a torch for doing flat sheet metal seams.

Practice on some scrap first before the real thing.

 

[ed_h]

Yes, galvanized steel soft solders well with ordinary fluxes. Also, the temps are low enough that there aren't really any toxic fume issues.

Silver soldering would probably cause the same issues as welding, though.

 

[Tucko]

Can ductwork galvanized steel sheet be soldered? What I want involves soldering some curves as well as soldering tabs after bending. If possible I plan on using a jewelers acetylene torch. Is there any special flux or solder to use? Thought I'd ask BEFORE cutting the material.

Clean the area with muriatic acid, applied with a small brush before soldering. But soldering is for waterproofing, why do you want to solder ductwork?
You need soldering irons to do a proper job.

 

[Tucko]

Can ductwork galvanized steel sheet be soldered? What I want involves soldering some curves as well as soldering tabs after bending. If possible I plan on using a jewelers acetylene torch. Is there any special flux or solder to use? Thought I'd ask BEFORE cutting the material.

Clean the area with muriatic acid, applied with a small brush before soldering. But soldering is for waterproofing, why do you want to solder ductwork?
You need soldering irons to do a proper job, a torch would distribute the heat too much, but an iron will pull the solder into the seam
I've soldered thousands of feet of galvanized over the years. Make sure to clean up the seam with a rag and clean water.

 

[Nitpicker]

This is for a "trade" sign. The sign is will be hung over a barn/shed for a tinsmith. I'd use any thin metal but all I can locate is 20gauge galvanized or copper.