Bob, I suspect your comment in re: sanding was directed at my earlier post,
not John's post on the same subject (below).
First, by "sanding" I was suggesting a fine grit which in this context I
meant 600 grit (US terminology) which will definitely not harm the aluminum.
Scuff sanding on the other hand is far more aggressive than I had in mind,
and though I doubt even that would cause trouble over time I would not do it
on these tubes. Early in my engineering career my business card said I was
an extrusion engineer for an aluminum company but in reality I was the
technical support for an aluminum tube manufacturing operation (said tubes
being cold drawn from extruded "bloom" - thick walled extruded tube) so I
have a good technical understanding of things made out of aluminum,
especially tube.
My suggesting mechanical removal of the oxide film was as an alternative to
chemical treatment, not as alternative to degreasing. No amount of
degreasing will help organic coatings stick to aluminum. In order for any
coating to adhere to any aluminum surface, that oxide film must first be
removed. Of course "removed" is a misnomer because it will instantly reform
once the bare aluminum is exposed to oxygen, but chemical or mechanical
treatment will make it less of a problem.
Best regards,
Rob Housman
Europa XS Tri-Gear A070
Airfarame complete
Irvine, CA
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of R.C.Harrison
Subject: RE: Europa-List: Primer for Zn-coated steel
Hi! John.
I believe that sanding is "bad news" with likelihood of inducing fatigue
cracks better degrease and aerosol spray IMHO. Pencil marks and the like
have been known to be an issue also?
Suggest those competants in this field will advice the forum ? Of course
scuff sanding is often called for on embedded components but I guess they
don't get the stresses of flexing in that position?
Regards
Bob Harrison G-PTAG
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of
TELEDYNMCS@aol.com
Subject: Re: Europa-List: Primer for Zn-coated steel
In a message dated 7/1/2003 9:29:03 AM Eastern Daylight Time,
cgalley@qcbc.org writes:
> If the tubes are steel, powder coating is o.k. Aluminum may not as the
> fusing temperature may alter the strength and temper of the aluminum. FAA
> will not approve aluminum to be powder coated for certified aircraft, so
you
> might do some checking before using this process.
Powder coating is also known for hiding cracks, especially in welded areas.
Before I found this out I had my nose gear mount and rudder pedals
powdercoated. I was happy with the finish until I started handling and
installing the
parts. The tubing was zinc coated to start with (shiney, gold finish) and
now the
powder coat is chipping off. I will likely scuff sand and repaint with
Corlar
primer, then a top coat.
Regards,
John Lawton
Dunlap, TN
A-245
|