From: RWolf99@aol.com
Message-ID: <9b.a180485.26ea7b6b@aol.com>
Date: Fri, 8 Sep 2000 13:27:07 EDT
Subject: Alodine vs anodize vs powder coating
To: lancair.list@olsusa.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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Alodine coatings are nice because you can do them at home in just a few 
minutes.  Professional painters have told me that the single most important 
thing to promote paint adhesion on aluminum is to alodine it first.  I use 
Alumprep 33 and Alodine 1201, but there are other products out there.  
(Metalprep doesn't seem to work that well.)  The problem with alodine is that 
is scratches very easily.  Way more easily than anodize.  Given a choice, I'd 
anodize.  However, you probably have to pay $50 for a minimum anodize order 
so unless you can wait for a bunch of parts, it's kinda expensive.  If I'm 
going to make a bracket and flox it in place right away, I use alodine.  If 
it's a removable piece, I send it out with the next anodize batch.

To alodine, you first etch the surface with the Alumiprep to remove the oxide 
coating.  Yes, the surface you see is aluminum oxide, not aluminum.  In fact, 
I'm told that aluminum oxidizes so quickly that you will never see bare 
aluminum unless you machine it in a nitrogen atmosphere or -- sorry, I can't 
resist this one -- in one of those other noble (oops, I mean inert!) gasses.  
Fortunately, aluminum oxide is a good protective layer -- that's why bare 
aluminum lasts so long -- and we can usually ignore this effect.  

Back to business.  You remove the oxide coating with the phosphoric acid etch 
(Alumiprep).  Rather than sandpaper, I like to use Scotchbrite.  Rub it 
gently while soaking in the alumiprep.  (Under no circumstances use steel 
wool.)  Rinse it off but don't let it dry or you'll get the oxide coating 
back.  Then dump it in the Alodine solution.  The soaking times are on the 
bottle but it's fairly short, about a minute or so.  Then air dry.  If you 
rub it dry you'll rub the coating off, but it seems to be more hardy when 
it's dry.  All you need for protection is rubber gloves.  I have found that 
using tap water can give you funky color streaks, so I go to the grocery 
store and get a couple of bottles of distilled water.  Don't get "drinking 
water" that has the minerals put back in or you defeat the purpose.

Actually, you get better results with professional alodining.  They have 
heated tanks (I think) and frankly, do a better job.  Send all your pushrod 
raw stock out to be alodined all in one big batch.  This way the inside of 
the tubes get a good coating, too.  They'll also be wrapped in paper when you 
get them back for scratch protection.  When you cut them to length, only the 
cut ends are unprotected, and who cares about those?  Then you can paint or 
powder coat.

I send my completed pushrods out for powder coating.  Normally they want to 
sand blast before powder coating but I tell them not to and I haven't had a 
coating failure yet in my shop.  This is a similar price to anodizing.  By 
the way, tape the ends or they'll powder coat those, too.  They'll probably 
replace your masking tape with a high temperature tape that won't burn when 
they bake it, but at least they'll know where to mask it off.  FYI, a flap 
pushrod (about 2 feet long, 3/4 inch diameter) weighs only 2 grams more after 
powder coating.

I had my control crossover weldment powder coated, too.  You have to mask off 
the areas that the stick slides into, and where the weldment slides over the 
phenolic, because the powder coat does add a little thickness.  I actually 
had a small patch of light surface rust forming on my weldment so I let them 
sandblast that piece prior to coating.

- Rob Wolf
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