[NSRCA-discussion] epoxy question-I am back

[Jay Marshall]

West's 105/205 system seems to be a low viscosity epoxy. It is a slow cure
(8 hrs) so if you add solvent it should have plenty of time to evaporate. I
have only used it for sheeting, not glassing - yet.

 

Jay Marshall 

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Gray E Fowler
Sent: Monday, November 26, 2007 10:23 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] epoxy question-I am back

 


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.  " 

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). 

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. 

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. 

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. 

1. Operator cannot operate a scale. 
2. Operator has a crappy scale. 
3. Operator added solvent anyway because thats how he has always done
it...since 1976 
4. Operators basement is 100% realative humidity..condensation on the wing. 
5. Operator added "more" hardener to make it cure faster. 
6. Operator......(enter F/U here). 

As you can see there is one common theme to all of these possible problems,
Operator, i.e. customer. 

So if you are STILL interested please respond and Lance and I will take it
under advisement. 

  



Gray Fowler
Senior Principal Chemical Engineer
Radomes and Specialty Apertures
Technical Staff Composites Engineering
Raytheon 




"Dr. Mike Harrison" <drmikedds at sbcglobal.net> 
Sent by: nsrca-discussion-bounces at lists.nsrca.org 

11/23/2007 01:57 PM 


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[NSRCA-discussion] epoxy question

 


 

 




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. 
  
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.   
2.  The properties of the epoxy are changed-it becomes rubbery. 
3.  Changing the properties is not an issue regarding finishing the
airplane(painting) 
4.  Using thinned epoxy is fine for applying glass cloth. 
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.   
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.   
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.   
8.  A second thinned coat of epoxy on the glassed wing is .75 ounces each
wing panel-1.5 oz total. 
  
  
Pick your poison. 
  
Later, 
Mike 
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