How does galvanising work?

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I picked up something this morning from the galvaniser.When I dropped it off last Friday, it was my first visit to a galvaniser. There were acres of dirty, rusting steel sitting in precarious piles. Each would have been a 'job'. And some were huge.Mine was a small job - fishpond surround out of 5mm x 100mm flatbar - but it had taken me most of the morning to put together.The buildings aut there were grimy. The guys were filthy, and not terrible chatty. I gave them my name and phone number. I said: 'Do I get an order number or something?' They said: 'Nope.' I said only half joking: 'You won't lose it, will you?' They just looked at me. When I drove off, I wasn't sure I'd ever see it again.Then I got a phone call yesterday to say it was ready. The pick-up zone was on the other side of the building. The yard was just as big, but everything was gleaming. Even the side of the building seemed cleaner and newer. The guys out there had clean uniforms because they weren't handling dirty steel. It was probably my imagination, but they were also much more pleasant.And there was my little job! A guy picked it up with the biggest forklift I've ever seen because workplace laws would not permit them to lift steel over a certain weight. It made me laugh. He brought it over to me and I picked it off the forklift and tossed on top of the car.So how does the process work?I gather they dip it into something to clean it up, and then into another bath that coats it. It's not just a paint, though, is it?Why is it better than paints?How does it compare to paintable cold gal?How does it compare to the 2 pack epoxys around today?So many questions...Scott
Reply:Well the dirty, grungy guys do all the work while some guy in nice clean clothes gets all the "ooooh wow thank you". I'd be grumpy too. http://www.corrosion-doctors.org/Def...alvanizing.htm
Reply:you see Scott the guys doing the work prolly all hate their jobs but do them well.  Plus they are prolly all going to die of brain tumors and lung cancerIF it Catches...Let it Burn
Reply:So I gather it's a pretty toxic process? I guess then the dirty guys who book in the jobs are better off than they guys who do the work or work with the completed jobs? I might tell them that next time to cheer them up.Thanks for the link, Sandy. Given the nature of the process...Galvanizing forms a metallurgical bond between the zinc and the underlying steel or iron, creating a barrier that is part of the metal itself.
Reply:Scott, there are some cold-galv sprays that are very good. Mil-spec good. CalTrans good.
Reply:I'll see if I can find some spray on ones down here. Spray would be handy.
Reply:Originally Posted by TEKScott, there are some cold-galv sprays that are very good. Mil-spec good. CalTrans good.
Reply:Thanks Sandy.Yes, given that it is a dirty, hot, nasty job, it surprises me that it isn't more expensive to get things galvanised.
Reply:Originally Posted by scott brunsdonThanks Sandy.Yes, given that it is a dirty, hot, nasty job, it surprises me that it isn't more expensive to get things galvanised.
Reply:We regularly send material out for galvanizing.  In fact I am making up some parts for a trash grate on a creek somewhere.The steel is dipped in acid to remove all scale and rust then neutralized and let dry.  It is then dipped into a molten bath of zinc.  The tank can be up to fifty feet long depending on the size of the operation.  The zinc coats all the surfaces and the part is lifted out to drain and cool.  Galvanizing is good for up to 100 years and fifty in areas close to the ocean.  Locally the cost of a good epoxy coating is more.  If you are intending to galvanizing grind off all sharp edges to a small radius.  This reduces the possibility of too thin a layer of zinc at the corner.  Remove all spatter because if it falls off years later it will leave a bare spot.  All cracks/joints must be sealed with weld.  The zinc will not run between two pieces of steel held together.  Eventually water will get between and rust will bleed out of the crack.  If you are getting any hollow sections coated you must locate drain holes all the ends.  The holes should be as large as possible.  If a pipe handrail is immersed in the zinc bath and it has no drain holes the pressure will build up inside the pipe.  The pipe will burst throwing molten zinc into the air and on the people around.  If you supply these guys will a closed pipe or a pipe with holes too small they will cut extra holes with a cutting torch and they are not particular about the shape and location.   Make sure your drain holes are situated so that the zinc can completely drain out as it is lifted out.  If not done properly you can end up with fifty pounds of solid zinc caught inside.     Any bolt holes should be made an extra sixteenth larger than normal clearance.   It is a great way to make something permanent.
Reply:Something I forgot:  galvanizing if it is scratched will protect the steel that is exposed at the bottom of the scratch unlike other metal coatings.
Reply:gee thanks lotech  I really never knew much about galvanizing     great infoIF it Catches...Let it Burn
Reply:If anybody has ever wondered about how metal is composed of "grains", you can often see the outlined shape of very large flat grains of zinc on the surface of galvanized steel.  You may also have seen the pattern of large grains on a brass hand rail that has been polished and etched by years of use.  The grains in most steels and alloys are too small to see without about 30X magnification and a polished and acid etched surface.
Reply:Thanks Iotechman. That's great, practical information.Wish I'd known some of it before I took the job out there. Oh well, I'll know for next time.Scott
Reply:So Pulser, would softer metal have larger grains?
Reply:Several months ago I was at a AWS meeting and let a galvanizer tell me what the fabricators did to make his life miserable.  I got an earfull :'))  I didn't know this but they hold the zinc temperature a bit on the low side because if they have it too high it will completely soften the weldments and often result in excessive twisting and distortion when it is removed.  This is not a concern if one is galvanizing small plates but is of concern when dipping larger structural components like light standards or beams and columns.   There are some good websites around.  One I believe is put up by the galvanizers association???
Reply:There's a Galvaniser's Association? Bet their meetings are fun.
Reply:Originally Posted by pulserIf anybody has ever wondered about how metal is composed of "grains", you can often see the outlined shape of very large flat grains of zinc on the surface of galvanized steel.  You may also have seen the pattern of large grains on a brass hand rail that has been polished and etched by years of use.  The grains in most steels and alloys are too small to see without about 30X magnification and a polished and acid etched surface.
Reply:................IF it Catches...Let it Burn
Reply:.................IF it Catches...Let it Burn
Reply:You can order galvy "shaken" and that gets rid of most of the klingons.
Reply:Howdy Howdy!  What are the costs of this process? How do they charge for a weekend warrior project?  Say a 50 lb welding cart?  Just as a curiosity.  Brian Lee  Sparkeee27
Reply:I'd like to throw in one trick of the trade if I may, My old boss would heat sections of pipe railing with the torch at the joints after we welded them together and then paint them with a can of cold galvanizing spray when they were red hot. That way we could make the whole railing hot dip galvanized no matter how long it was.
Reply:Brian,My costs won't really be relevant to you, but it cost me $120 (AUD) to have some welded flat bar galvanised. That's their minimun charge - if I'd known I would have taken more stuff along. The weight would have been 25 kilograms.