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Thread: Zinc coated steel?

  1. #1

    Default Zinc coated steel?

    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:

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    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

  2. #2

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

  3. #3
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    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?
    DaveO
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  4. #4

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    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

  5. #5

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    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

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    Quote Originally Posted by posixPilot View Post
    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
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  7. #7
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    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.
    Last edited by DaveO; 01-27-2012 at 07:44 PM. Reason: T joint info
    DaveO
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  8. #8
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    If that coating is in fact cadmium, the abstract at this site, section 1.6, says: avoid avoid avoid.
    http://www.astm.org/Standards/B696.htm
    DaveO
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  9. #9

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    Most bolts, nuts fasteners, and other hardware with a silver color to them are cadmium plated. This is common. Neither are great to breath, but unfortunately, most of us will weld on those sooner or later. Keep you head out of the fumes, and your mind in the game to reduce any poisoning risk. Fortunately galvanized poisoning is rarely fatal or causes long term damage because of the fact that Zinc is a necessary element used by the body. It will eventually be eliminated from the body. Before the body recovers, though, it isn't any fun. Been there, and had to do that.

  10. #10
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    Quote Originally Posted by performance View Post
    Before the body recovers, though, it isn't any fun. Been there, and had to do that.
    Sorry to hear that- from the reading I did, it sounds like a day or two of severe flu symptoms, including "fever rarely higher than 102*".
    Last edited by DaveO; 01-27-2012 at 08:48 PM.
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  11. #11

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    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.
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  12. #12
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    Both Zinc and Cadmium are often used to plate steel for some additional corrosion resistance, and both have low vaporization temperatures. So when welding, not only do these substances liquify, they will actually phase change to metal gas. The metal gasses then combine with oxygen and make "smut" - tiny little particles that look like powder, (often black like soot but other colors are possible as well.) If you weld this stuff, use good ventilation, hold your breath until you're out of the fumes, etc. Don't suck it in. The smut can often kind of harmlessly brush off the surface though. Removal before welding is not a bad idea. Flap wheel on an angle grinder comes to mind. You might want to restore the corrosion resistance lacking in the weld areas with some cold galvanized spray can (9x% zinc content)

    PS - although less common, nickel can also be used to plate metals. It has a high vaporization temperature, and does not need to be removed before welding to avoid "smut." However, due to its high cost, it is not very common. I have seen it on some applications (typically high heat and/or high end.)
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  13. #13

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    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
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  14. #14
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    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.
    Last edited by jakeru; 01-28-2012 at 08:17 PM.
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  15. #15

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    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.
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  16. #16

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    Quote Originally Posted by DaveO View Post
    Sorry to hear that- from the reading I did, it sounds like a day or two of severe flu symptoms, including "fever rarely higher than 102*".
    Ah. Only if you're skerd.

    To the OP: Do you have a cutting torch? (not an Everlast plasma cutter) If so, get a nice cutting flame going and burn that galvanized off there, weld it up using 6010 or 6011, the spray some primer over it.

    Seriously, those fumes may be poisonous, but we're talking LOTS of fumes to kill someone, and those fumes burn going down your nose - so it isn't likely you're going to stand there and keep snorting the stuff. It ain't like crack - you're not going to want a second or third toke.

    I built a gate for a guy once.



    I had a lot of fun with that PROJECT and always told myself I'd build one for myself.

    Never did, though.

  17. #17

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    You didn't build a gate for a guy you built a gate for a king. Holy crap that property looks like it is the whole state of Texas.
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  18. #18

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    LOL - Its kind of funny. See that drive way with the fencing on either side? That's all of the land this pilot owned until you got back to his house, which opened up to the 3 acre plot with his house and shop.

    The hardest part was getting the arc in that top piece. I was able to find a machine shop about 40-miles away, and it seems like they charged around $50 to put that slow bend in that one piece of 2x2 square tubing. You should have seen that little Toyota truck with the 20-foot length of tubing tied to the edge of that flat bed. It looked like it was ready for the joust! No way for a passenger to get IN or OUT through the side door, though.

  19. #19

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    Its up to you how you want to handle the fumes, just use commonsense. I don't like breathing in metals or fumes. I have had asthma when I was young and now my lungs get hurt easy. Last time a guy in my shop welded on zinc, the fumes in the shop hurt my lungs and gave me bronchitis. I was coughing bad for 3 weeks. Grinding off the zinc is the way to go at the debris flying off are still a solid not a gas. Its easier to filter out big particles than smaller ones.
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  20. #20

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    Good point about the Asthma. I don't have that problem.

    If you are outside, the cutting torch (with flame facing away from you) will quickly burn the galvanize off like burning off paint.

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