Silver soldering zinc plated steel

Does anyone know whether it's possible/advisable to silver solder BZP mild steel as it is, or does one need to strip off the zinc plating first?

Thanks - Rowan

Hi Rowan

Best to strip it off, the zinc burns off with nasty white fumes that do you no good at all, concrete cleaner does a good job of getting zinc plating off, or some drain cleaners that contain Hydrochloric acid.

I believe there is a condition called metal fume fever that breathing in zinc smoke brings on, sounds unpleasant!

Stay Safe

Dave

Take care if you smoke as this will give off inflammable hydrogen and you may discover a new way that smoking is bad for your health!

The good news is that the used acid will probably make an excellent Zinc Chloride soft soldering flux.

At what temperature does the zinc burn off? I'm silver soldering at one end of a piece of BZP studding. Do I need to take all the plating off, or only within 1cm of where I am soldering, or what?

Thanks - Rowan

Malt vinegar saturated with table salt will remove zinc over night.

Don't know how much Zinc to remove in your particular situation but Zinc melts at 431C and boils at 907C but it will oxidise into very dodgy Zinc Oxide even at room temperature - heat only increases the rate of reaction

Just near where the metal gets hot. Zinc melts at about 420C and boils at about 900C, so it will misbehave at Silver Solder temperatures. The main problem is contaminating the soldered joint, so give that part a good clean. Zinc fume is an industrial hazard, not awful in hobby workshp quantities, but avoid breathing it in and keep exposure low. Work outside if possible.

many years ago I had to arc weld some galv section together. I'd ground it off where the weld would be, but the stuff adjacent fumed off. I felt proper poorly that evening even after only a couple of hours exposure

Metal fume fever can be fatal! Metal fume fever

Hi Rowan

As I understand it, you are not welding. You are brazing with a "silver solder". Big difference!

See p.m.

I am not about to turn down my heating nor dispose of (responsibly) all the brass in my home and workshop!

Cup Alloys , sorry to butt in on this thread but when I click the link for your

HT5 Kit all I get is a Internal Server Error.

Yes, I'm silver soldering. Does this mean that I don't have to strip off the zinc? Or that I only need to strip it off the part where I am brazing? Or that I need to strip it off the whole part?

I guess there are two issues:

1. The zinc evaporating or burning with attendant health issues.

2. Does the presence of zinc prevent a good braze?

Thanks - Rowan

+1 for remove the plating first.

Does it have to be silver solder?

Soft solder takes to zinc and mild steel using Bakers Fluid as flux but of course its a lower strength joint and useless for high temperature applications.

Hi Rowan.

Check your personal messages. The chances are that your brazing alloy contains a significant amount of zinc!

Or email your phone number and I will ring you.

Regards

Keith

Hi David.

Thanks for the note and apologize for the blip.

I don't know what the problem is, but I will inform Glenn and Shaun today.

Can I suggest that you give them a call tomorrow?

Regards

Keith.

There doesn't seem to be a PM. E-mail me at rowan(at)sylvesterbradley(dot)org.

Thanks - Rowan

Does this mean that I don't have to worry about a bit of zinc in the plating damaging the braze?

I'm using CuP Alloys EF Starter Pack for these joints.

Thanks - Rowan

Hi Rowan.

Correct!

Keith

Another thing I thought I knew for sure turns out to be wrong! I've got a convincing list of Silver Solders and very few of them contain Zinc.

But Keith is right - a little research shows most modern Silver Solders contain Zinc, often lots of it. Seems my list is badly out-of-date, or maybe for some specialised industry. Can't be many hobbyists using pure Indium solder...

Thanks Keith!