[NSRCA-discussion] Micoballons

[Atwood, Mark]

The education and value of this forum (and by definition from its
members) never ceases to amaze me.  

 

-Mark

 

________________________________

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Gray E
Fowler
Sent: Monday, April 17, 2006 2:46 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Micoballons

 


Bob 
You are right on.   
Rule of thumb......for every 12 degrees F increase, epoxy cure time is
cut by 50%. So as the mixture exotherms the balloons insulate the heat. 

Pot life is defined as 100 grams of mixed material in a mass such as a
cup starting at 25degrees C (77F) and the time it is still usable. It is
not unreasnable to realize that the potlife of a neat resin blend is
different than a mixture of fillers or even a solvent such as a coating.




Gray Fowler
Principal Chemical Engineer
Composites Engineering 



Bob Richards <bob at toprudder.com> 
Sent by: nsrca-discussion-bounces at lists.nsrca.org 

04/17/2006 11:46 AM 

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Re: [NSRCA-discussion] Micoballons

 

 

 




I'm not a chemist, so what I am about to say is just an educated guess.
:-) 
  
Epoxy gets warm as it cures, and cures quicker as it gets warm. A thick
mass of epoxy will cure quicker than a thin film since there is less
surface area through which the heat can escape. 
  
Microballons are hollow glass spheres, and probably act as a thermal
insulator. This insulation property is possibly preventing the heat of
the curing process from escaping, and causes the epoxy to cure quicker
in the center since the heat can't escape. 
  
Try using longer curing epoxy. :-) 
  
Bob R. 
  

Glenn Hatfield <randy10926 at comtekmail.com> wrote: 

I recently used micro-ballons in an epoxy for the first time.  I was
really surised how much the cure time changed with just a small ratio of
micro-ballons.   I was able to feel the expoxy warming up in the mixing
cup.  As an experiment I mix a small batch and tried to go for the max
ratio; but ended up with a hot spot in the middle that set before I
could finish the mixing. 
  
This stuff appears to be acting as a catalyst; which really surprised
me.  What is really going on here. 
  
randy 
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