Fan Shroud(housing) - original finish?(gold) (Type 4)

[XXX/Rx/RnR]

You'll be dead before it will rust out.
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78' westy, 2.4 195hp ecotec, audi turbo a/t, a\c, 2 1/2" lift spindles, index rear, 930 cv's & axles, 225x65x17 BFGs ## 77' hardtop 2.0 T-4 duel 44 weber's, 225x50x17s ## 74' baha bug

[SGKent]

[Bleyseng]

I went from this:

To silver powder coating:

not too worried about Rust on the fan shroud....
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70 Ghia Black convert-9/69 build date-stock w/133k 1600 SP-barn find now with a rebuilt tranny and engine
77 Westy 2.0L w/Ljet, Camper Special engine-95hp and with LSD!(sold)
76 Porsche 914 2.1L L20c, 120hp Djet (sold)
87 Syncro Westy Titan Red 2.1L 2 knob 100k miles

[SGKent]

[skills@eurocarsplus]

[SGKent]

[jtauxe]

[SGKent]

[skills@eurocarsplus]

[SGKent]

[skills@eurocarsplus]

it's me and my staff, all 3 of us. me, myself and I. trust me, I watch every penny (pass through my hands to the tax guy, the insurance guy, the...)
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[SGKent]

[ivwshane]

I powder coated my fan so I guess we’ll see how it goes. I didn’t dissemble the fan assembly but I did media blast it. I did silver for the fan and black for the pulley.
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77 westy 2.0 FI
69 ghia coup 1600dp
70 single cab

[SGKent]

[ivwshane]

[raygreenwood]

I am actually just about to do some small scale magnesium "Alodine" work in about 2-3 weeks (brake master cylinder pistons to start with). Some of this is also prep for doing the two shrouds I have on hand.

So since somewhere in the middle of this thread...back in 2011 the last time I had any input....I have been working with more and more plating and coating clients. Its a big part of several segments of my industry.

So working on two different chromate conversion type coatings....doing lots of research and a little testing. Would like to clarify a couple of things some of which busdaddy already has in the past .

1. No....this is not ONLY a proprietary Dow process. Dow is one of many (at one time) manufacturers who made a version....or sveral versions of this coating system.

2. Dow #1....as busdaddy noted.....is the original "chrome pickel" treatment. It used sodium dichromate, nitric acid and potassium fluoride.....that last one being damn nasty. It has almost exclusively used as an underbase for paint in aircraft.

Scroll down here and you can find the process.
https://www.finishing.com/faqs/magnesium.shtml

Its pretty much defunct now.....and only used as the Dow #19 process....which is an interim process in plating. It is useful but not exactly the same as what the factory used in large scale.
Its listed as a spot process. Its used to temporarily coat magnesium parts that must sit for a while before their next or final stages of coating. In that process chain.... its almost always stripped off again using a weak nitric or phosphoric acid dip, then back into something like sodium hydroxide....then into a final coating whether its electroplating, powder coating etc.

It IS a chromate.....but chrome 6 is only used in aerospace legacy projects (weapons, rockets, aircraft.....that cannot requalify a newer process). Chrome 3 and various other mixtures are used. Its most dichromte or trichromate. Still not healthy.....but nothing like chrome 6.
This is not quite a classic conversion coating. It is a variation of what is also used in modern zinc plating....on place of chrome or cadmium. But.....unlike classic conversion coating....these must be top sealed....immediately after application to have the same or better anti-corrosion lifespan as classic chrome 6 or cadmium conversion coatings.

Since Alodine as a company is long gone.....and was bought by Henkel.....when you research the Alodine product line.....they are all made by Henkel now.

Yes.....in aerospace....."Alodine" is thought of as an aluminum process....but factually they do make an Alodine chromate conversion system for magnesium. Different part # and chemistry and hideously expensive. Its mainly used as a spot coating for repair of original coatings on small scale.

2. Dow # 17....may have been used but I doubt it. It is an anodizing product. Thats an electrochemical coating. Conversion coatings use no electricity other than the electrolytic action of the chemistry and metal reaction.

Most chromate or dichromate dips that use a Dow process are listed as Dow #7.


So the gist is that these tan to pinkish to iridescent green coatings coatings we see on parts like the shroud are technically used as a "passivation". When a process like electroplating is done on a metal.....say...like zinc.....it forms a sacdifical anode layer that prevents corrosion.

The anodic/sacrificial coating does this by corroding itself... to prevent the base metal from corroding. This process starts virtually immediatly after emerging from the plating bath when it hits oxygen.
It can take years or decades for that anodic coating to corrode away into powder.....and at that point the base metal will start corroding. So to delay the start that process....they dip it in a chromate conversion coating......which is like a sacrifical anode ...for the sacrificial anode.

The outer conversion coating needs to corrode away first before oxygen and moisture can get to the zinc or whatever anode they plated onto it. It effectively doubles the life of the plating in many cases.

With the magnesium like our shrouds.....since its not plated.....these conversion coatings are reacting with a surface layer of the base metal.....to form a light anodic layer a few microns thick (if that much....more like angstroms). It slows down oxygen from reaching the metal surface....and starting the corrosion process.

But...eventually oxygen gets in here or there (years down the line if done properly).....and the metal starts corroding. It forms a corrosion layer that spreads laterally along the metal surface under the chromate coating...causing the coating fo flake off and peel like snake skin.

The kind of modern version available these days from companies like Henkel, MacDermid and few others.....is basically a single part tri-chromate dip used after a soak in sodium hydroxide to totally degrease.....then a very quick dip in a light acid/water mixture just to neutralize the caustic.....and then into the chromate dip for a minute or two. The longer it goes the darker it gets.

These are very similar to modern zinc top chromate dips......and the key is since they are not the heavy chromates like those used years ago......they must be top sealed to get equivalent lifespan.
Thats really just any of dozens of clear gloss or satin paints you spray on to keep oxygen from starting oxidization of the chromate. Since chromates are some of the best adhesion primers in the world.....if you do this cleanly.....the sealer you spray on should keep it corrosion free and looking good for years.

So yes....you can do this fairly simply at home. Cheaply......yeah....kind of.....if you do say....three shrouds. Expect about $250 in chemicals. And no with these modern products there is not much to dispose of.

This post is too long already but if you want a product list let me know and I will post it.

Yeah.....its probably simpler for most to just paint or powdercoat and redo it every 8-10 years. Ray

[SGKent]

Thanks Ray. This thread is a great place for that info. I know that here in California you can order Alodine but you can't find anyone who will take it when you are done with it because it can contain small traces of Chromium 6 as an oxidization byproduct. Dumping it is a fate worse than death if one gets caught. The disaster super fund at Hinkley was the reason the state changed a lot of rules on it.

My current thinking is to powder coat the shroud, and paint the fan - with the black portion being powder coated too.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

[SGKent]

Ray - we have a fellow in SoCal who does the process. He runs an ad here. His work is excellent - he did my 091 case for me. example: https://www.thesamba.com/vw/classifieds/detail.php?id=2357259
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]