Date:         Sun, 16 Aug 2009 20:48:35 +1200
Reply-To:     Andrew Grebneff <goose1047@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Andrew Grebneff <goose1047@GMAIL.COM>
Subject:      Re: Electronic Rustproofing?
In-Reply-To:  <0a4701ca1dc7$700cb9a0$3400a8c0@tomrmkj2yanjy9>
Content-Type: text/plain; charset=ISO-8859-1

Rust happens when a ferrous steel comes into contact with both oxygen
(O2) and water (dihydrogen oxide, H2O). It cannot occur without the
presence of either chemical.

> But VW and the other car companies did the
> next best thing. They started building cars in the 80s with steel panels
> coated with a sacrificial anode - it's called zinc plating.

This is NOT galvanizing. Galvanizing is electroplating... what you end
up with is a thin coat of zinc metal (visible as flattened crystals on
the surface) over the base metal. What the carmakers do is to treat
the metal sheet with some chemical, which leaves a residue on the
steel. This is rather ineffective.

Thye purpose of galvanizing has nothing to do with electrolysis. What
it does is merely to keep the steel surface completely away from
water. Nio water, no rust (one form of iron oxide, I think a hydrous
one; as a mineral in nature I think it is limonite).

The only manufacturers who galvanize their car bodies, to my
knowledge, are Porsche and more recently Audi. About time Toyota
started!

Now, I don't know whether these companies galvanize the sheet
components before welding them into a body or they galvanize the
finished body and doors. The former will slow rust down but nor stop
it, as any zinc anywhere near the welds will melt and run away... zinc
melts at a low temperature, MUCH lower than any steel. The treatment
used by most manufacturers will not be as badly affected by heat, but
will still disappear at the welds themselves, and of course seams are
where rustproofing is most needed... exactly where there is none of
it!

> And there are other issues with car bodies. Welding and folding plated steel
> damages the zinc coating. Plus, once seam areas get wet they tend to stay
> wet. This is why corrosion usually starts in seams - the zinc coating was
> damaged during manufacturing and / or was used up there first. The right
> answer is to repair those areas then protect them with a good undercoating
> that won't let oxygen (air) or moisture come in contact with the steel
> surface. Undercoating seams that have started to rust will only slow things
> down because you can't get the moisture out.

Actually, nothing will stop seams rusting in the long term. Car bodies
flex when they go over road irregularities, and this causes the seams
to work... eventually... er... WORKING any sealant and paint loose and
cracking them. Then the water gets in. If the car hits anything or is
hit with decent impact, then seams even at the other end of the car
will be "sprung"... which is why a car will soon start to rust at the
seams after an accident (happened to my diesel Skyline, even the rear
apron seams under the back bumper. No rust anywhere before the
accident). Zinc electroplating is flexible and grips the steel far
more strongly than any applied sealant or paint, and so will not crack
under stresses or impacts.

I know that someone working in the German VW factories (Hanover)
bought the very last T3 body made there. He had it galvanized, then
finished. Wish there were chemical baths in NZ big enough to strip and
galvanize a van body!

--
Regards
Andrew Grebneff
Dunedin, New Zealand
Fossil preparator
Mollusc, Toyota & VW van nut