Eric,
It was a pleasure seeing you again at Oshkosh.
>From a common website for steel tempering called Total Materia:
It is necessary, therefore, to warm the steel below the critical range
in order to relieve stresses and to allow the arrested reaction of
cementite precipitation to take place. This is known as tempering.
a.. 150-250=B0C. The object is heated in an oil bath, immediately
after quenching, to prevent related cracking, to relieve internal stress
and to decompose austenite without much softening.
b.. 200-450=B0C. Used to toughen the steel at the expense of hardness.
Brinell hardness is 350-450.
c.. 450-700=B0C. The precipitated cementite coalesces into larger
masses and the steel becomes softer. The structure is known as sorbite,
which at the higher temperatures becomes coarsely spheroidised. It
etches more slowly than troostite and has a Brinell hardness of 220-350.
Sorbite is commonly found in heat-treated constructional steels, such as
axles, shafts and crankshafts subjected to dynamic stresses. A treatment
of quenching and tempering in this temperature range is frequently
referred to as toughening, and it produces an increase in the ratio of
the elastic limit to the ultimate tensile strength.
The guys who make the tapered gear for the RV prefer to limit the powder
coaters to no more than 450F or about 250C back when they were in
Chicago. Different folks now.
Now that temperature range means that the powder coater must keep his
oven running longer to fully flow his paint on a gear leg. They don=92t
like to do that. The RV community is buying the factory powder coated
gear. Only problem is it covers up cracks in the welded spindle end you
will never see. Also corrosion gets underneath the powder coating as
the bolt holes and wear points are not coated and needs a metal
anticorrosion seal like ACP50 or similar to resist this tendency.
Plain old metal primer and a tough paint like an aircraft polyurethane
or even Rustolium primer and top coat lasts quite a while. My concern
in Florida is rust, which is less of a problem for you in =93Lost
Wages=94 (Las Vegas, NV, USA). Just a flexible paint should last
forever out there unless it=92s a cheap enamel.
Just talk to your powder coater. A 3/4 inch piece of steel has no
business in the oven with a bunch of sheet metal. The paint never gets
to its gel point and it fails. So in my case the thick piece, according
to his paint type (TCI Powder Coating), needed a low 250F degrees for
nearly 10 hours where as the sheet metal only needed about 2 hours.
Heck of a thing. I did the oven coated stuff as someone suggested
already on some of my parts and it worked pretty well for an hour in the
the oven. It wasn=92t very shiny but it covered well except where my
prep was not so good. It looks flat in comparison to my aviation paint
and wears fairly well because the paint or powder did not flow out and
stay flowed for long enough... It stunk up the house a bit but only a
wife could smell it. It was a rental house until our current home was
finished so it didn=92t bother me. It just was not worth the criticism
---From the wife. Some of these paints are toxic so read the directions
well.
Nickel plating doesn=92t hold up well to abrasion, but is excellent at
sealing the metal. Not worth the cost and down time to me.
Rustoleum (not the spray can stuff) is cheap and fast. Wears well,
easy to touch up and if properly prepped, lasts as long as anything else
on flexing metal gear. My opinion.
Regards,
Bud Yerly
Custom Flight Creations.
From: Erich Trombley
Sent: Monday, August 15, 2016 12:34 PM
Subject: Europa-List: Re: Powder Coating Tailwheel Spring
Good day,
Thanks to everyone for your responses on powder coating. I also
received a response suggesting nickel plating instead of powder coating.
This would be my preferred choice if flexing of the tailwheel spring
won't cause the plating to flake off. Thoughts?
Erich
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