Thanks for the excellent information, Rob! Just great.
That's pretty much what I figured. The baking process for powder coat is just
long enough to raise the temp of the surface to the required flow/polymerization
point of the the powder. It's fairly short for light parts, longer for heavier
parts, of course. I'll find out a bit more before the parts go through the
paint line. Basically, the time the parts are going to be at full oven temp
is pretty short, so it shouldn't affect the properties of the parts. I'll do
a little more research on my end, calling a few local heat treaters.
Chris
<RobH@hyperion-ef.com> wrote:
>
> Source: Aluminum Vol. III, Fabrication and Finishing, Kent R. Van Horn,
> Editor, American Society for Metals, Metals Park, OH, page 333, Table 7.
> This is a book I purchased (a long time ago) when my business card displayed
> the title "aluminum metallurgist."
>
> The recommended solution heat treatment for .125 inch to .250 inch (3.175 mm
> to 6.35 mm) thick extruded 6061-T6 is 980 deg F (527 deg C) for 55 to 65
> minutes followed by rapid quench in room temperature water. Precipitation
> heat treatment (artificial ageing) is subsequently done at 350 deg F (177
> deg C) for 8 hours soak time. There is another higher temperature solution
> treatment cycle at 1025 deg F (552 deg C) which has a longer ageing time of
> 12 hours at the same 350 deg F soak. Sheet and plate use the lower solution
> treatment temperature and a 18 hour soak at 320 deg F (160 deg C) for
> artificial ageing. To get from T6 to T651 the metal is stretched at least
> 1% (permanent set) for stress relief. The Europa hardware is probably cut
> from sheet or plate (if I remember correctly plate is sheet that is thicker
> than .125 inch).
>
> The precipitation hardening cycle, if extended for a much longer time, can
> result in the "over aged" condition, but powder coating soak time should not
> be long enough to "over age" the aluminum parts.
>
> For reference, the annealing cycle (to get the metal dead soft) is to soak
> at 775 deg F (413 deg C) for 2 to 3 hours; a partial anneal that will only
> partially remove the effects of solution heat treatment and ageing is done
> at 650 deg F (343 deg C). (This is on page 327, Table 4, Ibid)
>
> So, although the powder coating temperature is indeed in the range of the
> precipitation heat treatment soak temperature, the soak time should be much
> less than what it would take to do any harm (I'm guessing here because I
> don't know how long the powder coat soak time is).
>
> If you are still concerned, have the powder coater process a sample (not
> coated) through the soak cycle, e. g., a small square of comparable
> thickness 6061 sheet. Check the Rockwell hardness before and after the
> powder coat thermal cycle and compare the values. The real test for over
> ageing is to measure the conductivity but you may have more difficulty
> finding a lab to perform that test.
>
>
> Best regards,
>
> Rob Housman
> A070
>
>
> -----Original Message-----
> From: owner-europa@post.aviators.net
> Subject: Powder coating aluminum - help!
>
> I believe we went over this previously here, but I want to be doubly sure.
> I just sent out all the wing/flap hardware to be powder coated gloss white
> (W19, W20, OR3, etc.)
>
> My wife, who works for Midwest Express Airlines, says two of the guys on the
> maintenance floor said that the powder coating process would screw up the
> heat treat of the aluminum. Now, I remember looking up the age hardening
> time and temps for aluminum, and from what I remember, it was quite a bit
> hotter than what the powder coating oven runs at(which is about 375 to 400
> deg. F).
>
> Before I go and wreck a bunch of parts, I want to be doubly sure that I'll
> be OK. Powder coat is far superior to paint in both protection and
> durability, so I'd like to be able to use it.
>
> Thanks for the info, gang.
>
> Chris and Sue
> A159
> http://webmail.netscape.com/
>
>
|