<br><font size=2 face="sans-serif">Mike/All</font>
<br>
<br><font size=2 face="sans-serif">You are correct about the evaporation
rate. Warmth always helps. That 9% water in your IPA may be locked in forever.
Most of the commercial epoxy hardeners use a percentage of a chemical called
polyamide. Having a percentage of polyamide in the epoxy hardener blend
allows for mix ratio errors and still get a good cure. The polyamide is
mix ratio forgiving. Polyamide is also so viscous that it will not pour
at room temperature-hence opposite from what we are trying to do here with
our super thin fiberglass on wings. Another use for polyamide is
for coatings because this chemical also allows for application on wet surfaces,
that is, water has little detrimental effect on the polyamide. Polyamide
is what cures the epoxy putty used to plug underwater pool leaks. So that
9% water in the IPA is most likely locked up in the polyamide, and will
not come out without excessive heat.</font>
<br>
<br><font size=2 face="sans-serif">The majority of the epoxy hardeners
is a primary poly- amine. They are slightly soluble with water and once
that happens polyamine will no longer cure epoxy correctly. Getting the
IPA out of the cured epoxy will make the epoxy less rubbery and you will
get back some of the physical properties, and as you mentioned, it will
be strong enough to keep the fiberglass on the wing. Right now I think
this is about removing the dead weight of the solvent.</font>
<br>
<br><font size=2 face="sans-serif">In a thin coating as your wing skins
are and having a 100F temperature for a week (your attic?) should go a
long way to help evaporating the IPA trapped in your epoxy blend. Too
much temperature too fast can cause blistering, so be careful. Try a hair
dryer but NOT a heat gun.</font>
<br>
<br><font size=2 face="sans-serif">I know I just stated a bunch of stuff,
but hopefully this makes sense.</font>
<br><font size=2 face="sans-serif"><br>
<br>
<br>
Gray Fowler<br>
Senior Principal Chemical Engineer<br>
Radomes and Specialty Apertures<br>
Technical Staff Composites Engineering<br>
Raytheon</font>
<br>
<br>
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<td width=40%><font size=1 face="sans-serif"><b>"Dr. Mike Harrison"
<drmikedds@sbcglobal.net></b> </font>
<br><font size=1 face="sans-serif">Sent by: nsrca-discussion-bounces@lists.nsrca.org</font>
<p><font size=1 face="sans-serif">11/26/2007 10:00 AM</font>
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<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">Re: [NSRCA-discussion] epoxy question-I
am back</font></table>
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<br><font size=2 face="Arial">Gray,</font>
<br><font size=2 face="Arial">I am pleased to see your scientific answer.
It is very helpful and I would love to have the epoxy you could make
up. I thought about putting my existing mix full strenght but I know
I could never get all the excess out. Fortunately, having a weakened
epoxy has no real detrimental effects on glassing a wing. With the
info you have given it will lead me to delay primer for a while. I
would think the solvent evaporation rate would be inversely exponential,
meaning most of the evaporation/shrinkage would occur within a couple of
months. Since it is a model and not a bomb, there is room for lax
tolerances. </font>
<br><font size=3> </font>
<br><font size=2 face="Arial">Thanks</font>
<br><font size=2 face="Arial">Mike</font>
<br><font size=3>----- Original Message ----- </font>
<br><font size=3><b>From:</b> </font><a href=mailto:gfowler@raytheon.com><font size=3 color=blue><u>Gray
E Fowler</u></font></a><font size=3> </font>
<br><font size=3><b>To:</b> </font><a href="mailto:nsrca-discussion@lists.nsrca.org"><font size=3 color=blue><u>NSRCA
Mailing List</u></font></a><font size=3> </font>
<br><font size=3><b>Sent:</b> Monday, November 26, 2007 9:23 AM</font>
<br><font size=3><b>Subject:</b> Re: [NSRCA-discussion] epoxy question-I
am back</font>
<br>
<br><font size=2 face="Arial"><br>
1. "Thinning the epoxy saves no weight by evaporation. There
is virtually no evaporation and no weight loss-a big time erroneous assumption
on my part. So if you mix 2 ounces of epoxy and add 2 ounces of thinner
and put it all on the airplane, you have added 4 ounces to the airplane.
"</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
After seeing the real question I expected a weight increase of at least
9% (how much water in the mix). If you put 1oz (by weight) of solvent in
1 oz of epoxy, and apply it as a coating , thin, you will eventually end
up with 1 oz of epoxy. Mike, your solvent got trapped, and now it will
have less adhesion, less tensile, Compression and flexure strength, and
will now shrink slowly as the alcohol exits the cured epoxy, over a year
or so (see Wayne's answer).</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
None of the solvent's listed will react with any epoxy blend. Exotherm
is negligible when applied as a thin coating, but significant in mass.
The ability to have the solvent evaporate out of the epoxy coating is directly
related to the mixed viscosity of the neat epoxy blend and the cure rate
of the epoxy. Those of you who ran experiments with 5 minute epoxy reported
bad results because of high viscosity and fast cure rate.The high viscosity
(even Mike's blend is apparently too high) will cause a skin effect where
the solvent evaporates from the surface first, creating a high viscosity
skin, then the epoxy starts to cure increasing viscosity even more, thus
trapping the solvent. Using fiberglass makes this even worse. MIKE- in
one year from now your wings will weigh less.</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
So it sounds like the the Pattern Dudes of the world need a solution. What
AeroSlave can do is provide a super low viscosity epoxy for sale. This
will be 100% solids (which means NO solvents). Chances are, as a mixed
epoxy, the viscosity will be lower than even blends with some solvent in
them. This can be used to apply fiberglass to wings or as a general laminating
resin.</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
How much interest would there be for such a a product? It would probably
cost about $50/ quart, $25/ pint. It would absolutely require an accurate
scale (+/- 1 gram) to WEIGH the epoxy and hardener into the appropriate
mix ratio. AND I offer no warranty, simply because you guys are the biggest
bunch of experimenters in the world, and I cannot control, nor anticipate
how this could get screwed up.</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
1. Operator cannot operate a scale.</font><font size=3> </font><font size=2 face="Arial"><br>
2. Operator has a crappy scale.</font><font size=3> </font><font size=2 face="Arial"><br>
3. Operator added solvent anyway because thats how he has always done it...since
1976</font><font size=3> </font><font size=2 face="Arial"><br>
4. Operators basement is 100% realative humidity..condensation on the wing.</font><font size=3>
</font><font size=2 face="Arial"><br>
5. Operator added "more" hardener to make it cure faster.</font><font size=3>
</font><font size=2 face="Arial"><br>
6. Operator......(enter F/U here).</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
As you can see there is one common theme to all of these possible problems,
Operator, i.e. customer.</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
So if you are STILL interested please respond and Lance and I will take
it under advisement.</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
</font><font size=3> </font><font size=2 face="sans-serif"><br>
<br>
<br>
<br>
Gray Fowler<br>
Senior Principal Chemical Engineer<br>
Radomes and Specialty Apertures<br>
Technical Staff Composites Engineering<br>
Raytheon</font><font size=3> <br>
<br>
</font>
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<td width=46%><font size=1 face="sans-serif"><b>"Dr. Mike Harrison"
<drmikedds@sbcglobal.net></b> <br>
Sent by: nsrca-discussion-bounces@lists.nsrca.org</font><font size=3> </font>
<p><font size=1 face="sans-serif">11/23/2007 01:57 PM</font><font size=3>
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<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">[NSRCA-discussion] epoxy question</font></table>
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</font><font size=2 face="Arial"><br>
I have read with interest all the comments and some of you have educated
me on this issue. If I may, I will share what I have learned.</font><font size=3>
<br>
</font><font size=2 face="Arial"><br>
1. Thinning the epoxy saves no weight by evaporation. There
is virtually no evaporation and no weight loss-a big time erroneous assumption
on my part. So if you mix 2 ounces of epoxy and add 2 ounces of thinner
and put it all on the airplane, you have added 4 ounces to the airplane.
</font><font size=3> </font><font size=2 face="Arial"><br>
2. The properties of the epoxy are changed-it becomes rubbery.</font><font size=3>
</font><font size=2 face="Arial"><br>
3. Changing the properties is not an issue regarding finishing the
airplane(painting)</font><font size=3> </font><font size=2 face="Arial"><br>
4. Using thinned epoxy is fine for applying glass cloth.</font><font size=3>
</font><font size=2 face="Arial"><br>
5. I have tried MEK(epoxy thinner), denatured alcohol, 91%alcohol,
acetone. My preference is denatured alcohol because it is the safest
and most economical, I think. I thought MEK would be the answer.
It is the worst of the bunch. </font><font size=3> </font><font size=2 face="Arial"><br>
6. The best way to glass surfaces is to thin the epoxy and apply
as sparingly as possible. A way to do that is to apply and wipe off
excess with paper towels. </font><font size=3> </font><font size=2 face="Arial"><br>
7. It is almost exactly 2 ounces to glass a wing panel complete,
so 4 ounces for a whole wing. About 2 ounces for a stab. Properly
done wings and stab glassed and painted is 2-2.5 times the weight of monokote.
</font><font size=3> </font><font size=2 face="Arial"><br>
8. A second thinned coat of epoxy on the glassed wing is .75 ounces
each wing panel-1.5 oz total.</font><font size=3> <br>
<br>
</font><font size=2 face="Arial"><br>
Pick your poison.</font><font size=3> <br>
</font><font size=2 face="Arial"><br>
Later,</font><font size=3> </font><font size=2 face="Arial"><br>
Mike</font><font size=3> <br>
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