Anyone want something powdercoated?

[jdbubb at verizon.net (Dan Bubb)]

Two thoughts:
1. there is a polyester tape with a silicone adhesive that I use for masking powder coating. It's not that expensive, a 2" wide roll is ~$13. The tape will sometimes shrivel under the baking heat, but it leaves no adhesive residue. Basically you could use anything cause all the masking is doing is preventing the powder from getting on surfaces, so you COULD actually remove the masking before baking, but the chances of messing up the powder are pretty high. The polyester tape works well but is pretty inflexible. There are also silicone plugs available for plugging holes.
Also, relative to tranny cases I'm not sure I'd be all that concerned about masking bearing surfaces as much as masking the entire inside of the case. I'm thinking you don't want to bead blast the interior of the case (why waste the time?) so the powder coat wouldn't stick that well anyway, so better and easier to just mask the whole interior.
2. As far as surface cleanliness my approach (now, after effing it up multiple times) is bead blast, wipe down with a volatile solvent, pre-bake, re-bead blast any areas still needing attention, etch, wipe down again, then powder coat.
This is what I'd do with a transmission case or other part that has spent it's life covered in oil and grit. Simpler, cleaner parts don't get as much prep.
In one case grease had gotten into a small cavity on the outside of the tranny case and despite the bead blast, solvent wash and etch, grease was still in the cavity when I baked it and it expanded out during baking and messed up the finish. Pre-baking would have fixed this.
my <.02
Dan

From: "Daun Yeagley" <vwdaun@yahoo.com>
Sent: Monday, December 04, 2006 9:09 PM
Subject: RE: Anyone want something powdercoated?


> 
> --- Ron Pieper <rapieper@yahoo.com> wrote:
> 
>> Daun, Qs about powdercoating....
>> 
>> - how able are you to tape off areas that you don't want
>> powdercoated?  i.e,. bearing bores,
>> mating faces, threads, etc.?  Sometimes large parts of
>> the piece.  What's the process?
> 
> I've taped off mating surfaces / threads / bearing races
> with good 'ol masking tape.  At these temps though, it does
> get a little gooey so you need to wipe the leftover residue
> with some mineral spirits.  (Incidentally, it's FAR easier
> to peel the masking tape while it's still warm, otherwise
> it's a real b*tch to chisel off.)  I wouldn't  recommend
> masking tape for large areas.  There is a special high-temp
> tape but we've never used it.
> 
>> - how clean would something have to be?  meaning free of
>> oils?
> 
> Yes.  I did the valve cover on my '86 awhile back.  First
> was a trip to the parts washer and a bake dry.  Sandblasted
> the paint and then coated it.  (IIRC)
> 
>> - suppose someone delivered you a few clean but not super
>> sanitary cast aluminum or magnesium
>> parts...meaning that surface dirt would be gone but
>> staining would be there.  Combined, say,
>> they'd be about as big as, oh...an 020 gearbox, for
>> example.  If you didn't have any further
>> cleaning to do, and I taped the areas off, what'd be a
>> ballpark price for that?
> 
> Hard to say - we like to make sure everything is clean,
> etch & alodine for corrosion protection, then coat.  If
> there was a bit of oil residue still left in the metal,
> when heated we've found that it will run and really screw
> up the finish.  Clean it in your parts washer and we can
> blast it here.  (Taping off areas for bearings etc.)
> 
>> - how hot does the oven get?  (wondering if parts were
>> delivered with bearings still installed, if
>> they'd potentially fall out due to the expansion.  This
>> happens in the 400*F range, in my
>> experience, FWIW).
> 
> Remove the bearings.  The temps are in the 350-400 range
> and the grease in the bearings will run / screw up the
> finish.
> 
>> - could one potentially have clean scrap seals installed
>> for the powdercoating, then later remove
>> them so the bores would be pretty and shiny?  Or might
>> the seals melt?  (see above question).
> 
> Again, if they were perfectly oil free, then maybe - but
> can they take that kind of heat?
> 
>> What'd be really cool if if I had all my preload shims
>> installed, and the gearbox otherwise ready
>> to assemble, and gave it to you, then could pretty much
>> proceed with assembly directly afterward. 
>> Thoughts?
> 
> It's best to have things completely disassembled for
> coating, period.  We've done several sets of airplane
> wheels and had the bearings etc removed while coating them.
> 
> Any more questions just fire away...
> 
> 
> Daun Yeagley - Wilmington Ohio
> '80 Scirocco                 '81 Scirocco S 16v to be?
> '86 Scirocco 8v              '88 Scirocco 16v 
> '88 Scirocco Slegato (Gino!) '96 Passat GLX Wagon
> '56 Cessna 172
> The first rule of intelligent tinkering is to save all the parts - Ehrlich's Law.
> 
> 
> 
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