Zinc coated steel?

[posixPilot]

Hi everyone,

I am getting ready to install a gate operator on a wrought iron gate, and I will need to weld the brackets in place. I just pulled the hardware out of the box, and noticed that the brackets have a shiny silver finish, which I assume is galvanized zinc:



Does this look like a zinc coating, and if so, then preparation would be to grind the coating off where I plan to weld, correct?

Thanks
Mike

[performance]

It looks either galvanized, which I'd expect not to be as shiny, or cadmium plated.

[DaveO]

I have a project in mind that also involves welding on parts with a zinc coating, so I'm following for interest.

Is your gate actually wrought iron, and does that present a dissimilar metals challenge? Or is it steel made to look like wrought iron?

[posixPilot]

Yes, steel not wrought iron ... my dad always used to call it wrought iron, so I guess I do too . The gate is pretty much all square tube, aside from the decorative bits. However, I think the tube is a relatively thin wall, so I'm going to have to practice with some thin walled sq tube to make sure I don't blow holes in the gate.

Cheers
Mike

[DaveO]

I think the tube is a relatively thin wall, so I'm going to have to practice with some thin walled sq tube

You might drill a small hole in an inconspicuous place to find out exactly what you're dealing with.

My plan for the zinc parts is to use the brush wheel side of the bench grinder, but I'm pretty sure the shiny coating is thin enough that it would burn off in an arc. The fumes are unpleasant though, you don't want to breathe them.

That "I'm pretty sure" part of the sentence bothers me, though, I'd prefer a more experienced voice to chime in!

[DaveO]

Here's an article that discusses welding over zinc galvanizing: it discusses avoiding the fumes.
http://www.sperkoengineering.com/htm...Galvanized.pdf

Some interesting points:
~ You can weld over zinc galvanizing as you would over mild steel, although some adjustments to weld set-up conditions (amperage etc) may be required.
~ Avoid filler metals with high silicon content, such as ER70S-6, because the silicon will cause zinc to penetrate the weld and cause cracking.
~ Change the root's geometry in T-type butt joints so zinc vapors can escape, or they will cause porosity.
~ In avoiding fumes, don't attempt to breathe compressed shop air because the oil can coat your lungs and cause "irreversible death". As opposed to reversible death?

Still not sure about shiny metal coverings: I'm going to check the AWS site.

[Cippee]

Metal fume fever is a name for zinc poisoning. You can mig braze galvanized. I use a spool gun with silicon bronze if it doesn't have to be tig welded. I makes a nice weld but it takes a little to getting used to. The lower melting point of bronze doesn't fume as much of the zinc. I don't know if it is true but I've heard drinking milk helps prevent the zinc poisoning.

[posixPilot]

I think it must be cadmium then ... I googled a few pictures, and the finish looks very similar. So, is the preparation the same? (i.e. grind it and wear a respirator)

Thanks
Mike

[Spike]

Cadmium poisoning from welding is bad, and cumulative, and after enough causes permanent nerve damage.
Zinc poisoning is not as bad on the initial poisoning, but it sits in the lungs and causes cumulative damage to lung and nerve tissue. While these metals are necessary in the body, they are not meant to be absorbed through the lungs as a gas like that.

GRIND THOSE HINGES FIRST!
They are flat, uncomplicated shapes, and it's just too easy not to. It's not a thing to gamble with.
Cheap insurance. Plus, it'll be easier to weld, and you won't have the cracking problem from weld contamination. Weld off the grind area, and then an extra inch or so to clear the zinc away from the heat affected zone.

To me, it looks like zinc coating. It's certainly the cheaper of the two coatings. cadmium usually has a much more 'uniform' surface finish. If these were cheapy hinges from the local hardware store, then they're almost certainly zinc.

[posixPilot]

Thanks everyone. So, grind it, ventilate and wear a respirator.

As a related question, I use a half mask respirator with a 3M P100 (magenta) cartridge. The cartridge is marketed for welding, and I noticed that specs mention cadmium as a particulate that it will capture ( which i suppose is good). However, I notice that if I get my head in the plume while using the P100, I still get a lung full of fume. I was wondering if any of the other types of vapor canisters might be useful for welding. They all seem to be marketed towards other specific hazards (paint vapor, ammonia, etc). Anyone have any experience with this?

Thanks
Mike

[jakeru]

If you can smell something when welding, do not further inhale until you can remove your head to fresh air. (That's what I do, at least.) Although, nothing wrong with a safety respirator. (Better safe than sorry!) Usually the fumes rise upwards from the weld area (because heated air rises.) Often, you can reposition where your head is to avoid having it in the fumes. Have it off to the side, and further away (if you know there are going to be fumes), is best. Also of course, taking it outside is best, if there are going to be fumes.

If your welding mask gets powdery stuff on it while welding... that means you had your head in a pretty bad place fumes-wise. Be careful. Even if you hold your breath, the fumes may irritate your eyes and probably not good for your skin either.

Welding potmetal can emit zinc fumes also. (Potmetal is essentially a combination of aluminum + zinc.)

Here is an example of something Nickel plated, (which welded cleanly, despite not removing the plating)
http://www.everlastgenerators.com/fo...e-)-TIG-welded

Cad plating can often/usually have a greenish, yellowish, or blueish coloration. Zinc, pretty much always grey. Electroplated zinc (thin layer) is often shiny and smooth. Cold dipped zinc (thick layer, formed by the steel part being immersed in a vat of molten zinc with additional special process/ingredients to make it "stick") is usually more of a matte texture and a dull grey color.

Chrome plating (which I think most everyone knows what it looks like) also does not weld cleanly by the way, but it's usually only a very thin layer of chrome on the surface. (Nickel and copper layers are usually underneath the thin chrome layer.) Remove all three layers for best weld strength.

As a general rule of thumb, for the best weld strength, remove all platings in the area to be welded, and weld together known base metals with the proper alloy filler rod. Otherwise, any liquid plating metals can mix into your weld puddle and make an "unknown" alloy having "unknown" properties.

-----
Edit: on closer up view of those hinges, I would say they are either electroplated (thin) zinc, or cadmium plating. Given their color and shininess, I'd place my vote towards the electroplated zinc.

[posixPilot]

Grinding off the zinc is the way to go at the debris flying off are still a solid not a gas.

I plan on grinding it down.

Cheers
Mike

[dyethor]

Mixing chemicals are no joke. Unfortunately people don't know what they are doing and get hurt.

[posixPilot]

I plan on grinding it down.

So, I finally welded this piece last weekend (it was actually two separate brackets). I ground them, but I couldn't really tell where the coating stopped and the steel began. Used a respirator and a fan when I welded them, but I still sucked in some of the fumes. I wasn't feeling that great on Sunday night, and by Monday morning I had convinced my self I had zinc poising. Fortunately, when I got to the office, I found out that a number of folks I work with caught a cold, including me. Score one more for the hypochondriacs .

Cheers
Mike