Questions about soldering Galvanized sheet metal

I am trying to make some small boxes from 28 gauge galvanized steel. I want
to assemble them by soldering. I am using a 120 watt soldering iron,
tin-lead solder and Nokorode brand flux. The flux says it can be used on
galvanized steel but I am having a lot of trouble. I am cleaning the parts
with a SS wire brush, I then apply flux and brush again, then I solder.
Some time the solder will wet the metal properly but if it doesn't no amount
of cleaning and fluxing works.
I think I need a more active flux. Does anyone have any suggestions?
Reply to
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Try swabbing the contact areas with muriatic acid immediately before soldering. Muriatic acid is a 30% concentration of hydrochloric acid in water. Very corrosive and dangerous to skin and eyes. Best to work outdoors, and keep open container away from precision tools - they will rust if contact with the vapor. Does your soldering iron provide enough heat? The solder should run freely. Maybe a propane torch will work better.
Reply to
David Anderson
If you use gas to heat - drink some milk beforehand to avoid headaches. EG. saturate your body with calcium instead of zinc. :-)
Work outdoors.
Reply to
You might find the liquid flux to be better than paste. Even the folks soldering the copper foil for stained glass are using 250w irons. Flux is mostly just zinc in hydrochloric acid, with the noncorroding ones having all zinc chloride and no acid left.
Reply to
The few times I've done this on gutters, I used zinc chloride paste flux and one of those large soldering heads for a propane torch. Probably one of those old-time plumber's soldering coppers would have been a better choice, the heat off that soldering tip was marginal. A 120 watt soldering iron is a non-starter except for really small pieces. You didn't say what sort of solder you're using, 50-50, 60-40 or what, that can make a big difference, too. I'm not sure if you can get the zinc chloride flux from Home Despot, the local real hardware still has it, last time I looked. I think that Nokorode stuff has ammonium chloride in it, I inherited some cans of it from my grandfather, but the containers were in such bad shape I disposed of them. The stuff I have now is Kester brand. Oh, another thing, you need bright metal to solder to, some of that galvanizing gets oxidized, gray and dusty, you can't get a good joint when it's like that. If it's new metal, that shouldn't be a problem, if it's salvage, it is.
Reply to
Stan Schaefer
Muriatic acid will remove the galvanizing.
Ordinary tinner's fluid works well on galvanized steel. One brand name is Harris Staykleen, available at welding stores.
Try using a silverbearing solder as sold in the plumbing department at Home Depot. It's only about $1 more a spool and it wets and flows nicely.
120 watts may not be enough heat for your job.
Reply to
Don Foreman
Another possibility with new galvanized steel is that it might have a light coat of oil or other preservative on it. You must remove any such coating with solvent or detergent before soldering. Failure to do so would cause the problems you're seeing: once that stuff burns or bakes on it's tough to remove.
I think Nokorode has oil in it to prevent post-soldering corrosion of copper plumbing. That could also be a problem. Use straight soldering fluid, and clean the work after soldering to remove flux and prevent subsequent corrosion.
Reply to
Don Foreman
If the pieces have to be soldered, can you use brass or copper sheet, or unetched copper PCB instead?
If you have to use Galvanized, why not just use, say, rivets to make the joints?
Reply to
Tim Shoppa
Muriatic acid will remove the galvanizing if you immerse the parts in muriatic acid. If a quick wipe with muriatic on a piece of rag takes off all the galvanizing, there wasn't enough there to amount to anything anyway. One thing I believe is worth doing is to thoroughly clean up after soldering galvanized, especially zinc chloride containing flux. Neutralize if you've used acid core solder and clean well. Otherwise, you'll see corrosion down the road.
bob g.
D> Muriatic acid will remove the galvanizing.
Reply to
Robert Galloway
Your 120W iron is probably too small, but the wattage of the iron is less important than it's mass. A roofer's iron will have a copper tip that's about 1 inch in diameter and about 3 or 4 inches long. If you frequent swap meets, look for old roofer's irons that were heated in a fire or a flame. The iron should be tinned with sal salamoniac and solder. I have no experience with acid cored solder on galvanized; my dad taught me how to solder using the acid pot and bar solder.
Regards, Ed
Reply to
Ed Bailen

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