Subject: How to recover a weld on zinc-plated steel ?

From: C++ Freak <[email-masked]>
Date: 18 Sep 1996 10:52:43 GMT

Welding zinc-plated steel (usually immersed in a zinc bath) is harder
as (noxious) zinc vapors disturb the welding process, but it does work.
But after welding the zinc is gone, so it is susceptible to corrosion.
Is there any paint or whatsoever to recoat this weld ?
I know about a metallic gray paint with 'zinc dust' (?) available
in hardware or paint shops but is that effective ?

Klaas

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From: "Steven O. Smith" <[email-masked]>
Date: Wed, 18 Sep 1996 15:11:22 GMT

> in hardware or paint shops but is that effective ?

The spray galvanizing stuff is supposed to be pretty effective. I have
no experience to back that up.

MSC has the stuff for about $5 a can; I've seen it in specialty catalogs
for $20 a can!

-- 
Steven O. Smith
[email-masked]

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From: [email-masked] (Tim Carter)
Date: Thu, 19 Sep 1996 08:23:09 Local

In article <[email-masked]> C++ Freak <[email-masked]> writes:
>From: C++ Freak <[email-masked]>
>Subject: How to recover a weld on zinc-plated steel ?
>Date: 18 Sep 1996 10:52:43 GMT

>Klaas

You're quite right, the area around the weld will corrode easily, because the 
heat of welding has vapourised the protecting zinc. The fumes you get with 
welding over galvanising are the zing floating away.

Zinc-rich paint works well, not as good as the original hot-dipped zinc, but a 
lot easier to apply. It doesn't last as long as the HD zinc either.

regards

tim

"My opinions are my own, and other usual disclaimers."

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From: Ted Mooney <[email-masked]>
Date: Thu, 19 Sep 1996 12:48:33 -0400

> "My opinions are my own, and other usual disclaimers."

For critical applications it is possible to brush electoplate zinc onto 
the area, making it the equal of the original galvanized surface. But I 
certainly agree that this is much harder to do than just using zinc-rich 
paint. It would be rarely justified.

-- Ted Mooney
------------
Visit 'the home page of the finishing industry'
http://www.finishing.com
------------

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From: "Steven O. Smith" <[email-masked]>
Date: Thu, 19 Sep 1996 19:12:07 GMT

> paint. It would be rarely justified.

What I'm familiar with is spray galvanizing. Comes in a spray can,
basically zinc dust with an epoxy binder. What is zinc rich paint? Is
this what makes up Rustoleum? Where do I get zinc rich paint (esp. in
colors)?

-- 
Steven O. Smith
[email-masked]

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From: Steve Herrick <[email-masked]>
Date: Thu, 19 Sep 1996 15:26:25 -0700

There is a process called hot galvanizing. You use a bar of zinc, and heat
the surface of the steel to the melt temperature (about 600 deg F.) of the
sinc. By lightly applying the zinc bar, and vigoruous wire brushing, a
fully galvanized surface can be achieved. Caution is required hough as the
fumes from the zinc bar are hazardous. Use great ventilation AND a
respirator. The zinc bar should be available through a welding supply
store.

Hrolthgar -   [email-masked]
           Steve Herrick

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From: "Antti S. Korhonen" <[email-masked]>
Date: 20 Sep 1996 03:37:32 GMT

>in hardware or paint shops but is that effective ?
Industry uses laser welding for welding of zinc coated plates. The seam 
is so narrow that the corrosion resistance is not lost. I think that one 
of the first applications were the bottom plates of Audi which were first 
welded together and then formed.This technique of tailored blanks is now 
used commonly and also some other welding techniques in addition to laser 
have been used.

-- 
Antti S. Korhonen
Helsinki University of Technology
e-mail: [email-masked]
http://www.hut.fi/HUT/Treatment/alku.html
arro

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From: [email-masked] (Bart Smaalders)
Date: 19 Sep 1996 18:10:38 GMT

> in hardware or paint shops but is that effective ?

I've used the "cold galvinizing" paint after welding; it's like any other
paint in that surface prep is critical.  If you grind the weld bead smooth
you'll get much better results than you will by just covering over the bead.
Since the original finish is damaged over a wider area, you'll want to remove
that damaged area as well.

When I weld (or braze) galv. material, I always end up setting the zinc on
fire, which makes for more of a mess.  Any ideas on how to prevent that
>from  happening (particularly on the inside of galv. pipe)?

- Bart

---
Bart Smaalders			Solaris Clustering	SunSoft
[email-masked]		(415) 786-5335		MS UMPK17-301
http://playground.sun.com/~barts			2550 Garcia Ave
							Mt View, CA 94043-1100

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From: Tom Shaffer <[email-masked]>
Date: 22 Sep 1996 15:38:57 GMT

> MSC has the stuff for about $5 a can; I've seen it in specialty catalogs

There are several ways to repair weld damage to zinc coatings; the application of 
proprietary zinc-rich paints, sometimes called "cold galvanizing" is one of them.  
Others include zinc spraying (metallizing) and application of a special low-melting 
zinc solder stick.  The choice of method to use depends on the thickness of the steel, 
thickness of coating, type of weld, etc.

Suggest you contact the International Lead Zinc Research Organization 
(http://www.ilzro.org) or the American Galvanizers Association (http://usalink.net/aga/) 
or the International Zinc Association (http://www.iza.com)

Tom Shaffer

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From: [email-masked] (Greg Naylor)
Date: Mon, 23 Sep 1996 12:17:22 GMT

>Is there any paint or whatsoever to recoat this weld ?

The welded area can be thermally sprayed with zinc which will melt
into the existing hot dipped galvanizing.

Check our Web page at http://intmetl.com or http://intmetl.com/pacific

Regards, Greg Naylor
International Metalizing Corporation

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From: [email-masked] (James M. Scherer)
Date: 24 Sep 1996 13:58:09 GMT

Steven O. Smith ([email-masked]) wrote:
: C++ Freak wrote:
: > 
: > Welding zinc-plated steel (usually immersed in a zinc bath) is harder
: > as (noxious) zinc vapors disturb the welding process, but it does work.
: > But after welding the zinc is gone, so it is susceptible to corrosion.
: > Is there any paint or whatsoever to recoat this weld ?
: > I know about a metallic gray paint with 'zinc dust' (?) available
: > in hardware or paint shops but is that effective ?
: > 
: > Klaas
: 
: The spray galvanizing stuff is supposed to be pretty effective. I have
: no experience to back that up.
: 
Another method is to spot galvanize using a torch.  This is similar to
tinning or soldering except that zinc is applied to the hot area.  I
understand that this is superior to zinc based paint.

Repair of damaged galvanized coatings is described in ASTM standard
A 780-80.

If you have trouble locating materials or information on the subject,
you might ask the American Galvanizers Association for help.

1-800-HOT-SPEC
Mitch