At 07:51 AM 7/23/2006, Mark Beckwith wrote:
> > Last week I had some hot-dip galvanizing done and
> > wanted to share my experience with all of you.
> > I was really intrigued by the entire process. [snip]
>
>Thanks Mike, I found your post very interesting. We have a hot-dip
>galvanizing place here that I may have to take stuff to someday. They price
>by the "hundredwight".
And that's the weight of the thing being galvanized, not the mass of the
zinc added.
>I always thought this would make a novel finish for just the right restored
>car or truck :) I imagine they could get a premium if Hummers were
>available in "galvanized." I can hear helicopters and artillery in the
>distance now.
Interestingly, most car bodies ARE galvanized before being painted.. at
some point in the process the shell takes a dip in the tank...
>When you asked about galvanizing your crank-up tower, did they caution you
>about sufficient vent passages to the inner walls? The place here won't
>take anything that has only a hole drilled to the inside of a chamber, or
>even a pipe with one end closed - they require pipe to be open at both ends,
>i.e. a tower's okay. Something about pressure and explosions.
This is somewhat of a judgement call on the part of the galvanizer. Imagine
a long tube, sealed at one end. Drop the open end in the zinc, so it's
below the molten zinc surface. Now, drop the rest.. the air inside heats
up, and "blurps" out the end, spattering zinc everywhere.
>A friend took some old straight-but-rusty 25G in for re-galvanizing, and he
>concluded it was only barely worth it because of the amount of hand work to
>be done afterwards to get the leg joint clearances back down to something
>that fits from section to section (i.e. maybe they left it in the zinc too
>long).
More likely, it wasn't in long enough... Drop a cold piece of metal into
molten zinc, and a lot of zinc freezes onto it.
Again, this is a matter of the roughness of the metal (surface tension for
the molten zinc), the relative temperatures of both, etc. In general, the
hotter it gets or the longer it stays in, the less zinc winds up, because
it melts off. Too hot, though, and the zinc comes off. Even trickier is
when the thing has some zinc on it already.
This is very much an arts and craft sort of thing. It may look like a
simple industrial process, but the skill and experience of the crew makes a
huge difference, especially if they are galvanizing random things (as
opposed to something like car bodies, where they have time to "dial in" the
process). Even such things as the day of the week have an effect,
especially if they shut down over the weekend.
It is very much worth it to find a shop that is used to doing latticey
kinds of things with tubing(like wrought iron fences, and the like), as
opposed to, say, structural steel I-beams.
>I could see it being more "worth-it", however, on things like how thick the
>zinc coating is, whether it's 25G or something bigger and more expensive to
>buy new, and one's personal money to time ratio. It's nice to know the
>re-galv option exists, though. Thanks again for the report on your field
>trip!
>
>Do you know if the galv plant had the ability to strip old paint?
Around here (Los Angeles), some do, some don't. Kind of depends on the
market segment they are dealing with. There are galvanizing shops that
specialize, for instance, in galvanizing large structural steel components
for use in building, and they're very different from the places doing small
job lots for local sheet metal fabricators. Some have extensive pre-galv
prep capability, others don't.
Jim, W6RMK
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