Ernest Christley wrote:
clare at snyder.on.ca wrote:
On Thu, 22 Mar 2007 23:29:15 -0400, "Phil" wrote:

Hello
Was watching American Chopper this evening , I see things on that
show that make me cringe but I do enjoy the antics of that family,
they always refer to Pipe if they are building a frame out of Tubing
etc. , this evening they were working on a dragster bike for NAPA and
when it came time to paint the machine they said that powder coat
couldn't be used because of the heat involved would ruin the 4130
tubing , seems like a lot of engine mounts and other A/C parts will
have to be junked , would like to hear some thoughts on this concept
, as an A/C welder it is of interest to me.
Thanks
Phil Lohiser
EAA 12873
Powder coating won't hurt 4130, but is NOT RECOMMENDED for aircraft
use because it can hide developing cracks.At least that's what I've
been told.


Bwhahaha!!

Powder coating is done at what, 275 degree F? I gotten my airframe
hotter than that by cussing at it when members wouldn't meet up
properly. 4130 will see it as a pleasantly warm temperature, suitable
for shorts and maybe a light sweater.

Some people don't recommend powder coating because it may hide
developing cracks. Others swear by it because it give better protection
to keep cracks from ever forming. Truth is, if the only thing you have
to identify developing cracks is a visual inspection, you're not going
to have much luck. Use white powder coat, and linseed oil inside the
tube. A hairline crack will seep the oil and make and ugly black mark.

But if the hairline crack doesn't break the paint film the oil will
still be contained. Besides the oil, weld a boss on a longeron tube end
and install a tire valve and pressurize to 100 or so psi pressure during
the annual. The pressure should be enough to make the paint film fail
and cause leakdown. Find the leak by listening or water/soap.

Llama helicopters charge the truss permanently with dry nitrogen and
have a pressure gauge that is in view behind the cabin and can be
checked on a DI.

John