<br><font size=2 face="sans-serif">Bob</font>
<br><font size=2 face="sans-serif">You are right on. </font>
<br><font size=2 face="sans-serif">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.</font>
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<br><font size=2 face="sans-serif">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.</font>
<br><font size=2 face="sans-serif"><br>
<br>
<br>
Gray Fowler<br>
Principal Chemical Engineer<br>
Composites Engineering</font>
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<td width=40%><font size=1 face="sans-serif"><b>Bob Richards <bob@toprudder.com></b>
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<br><font size=1 face="sans-serif">Sent by: nsrca-discussion-bounces@lists.nsrca.org</font>
<p><font size=1 face="sans-serif">04/17/2006 11:46 AM</font>
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<div align=center><font size=1 face="sans-serif">Please respond to<br>
NSRCA Mailing List <nsrca-discussion@lists.nsrca.org></font></div></table>
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<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">randy10926@comtekmail.com, NSRCA Mailing
List <nsrca-discussion@lists.nsrca.org></font>
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<div align=right><font size=1 face="sans-serif">cc</font></div>
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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] Micoballons</font></table>
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<br><font size=3>I'm not a chemist, so what I am about to say is just an
educated guess. :-)</font>
<br><font size=3> </font>
<br><font size=3>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.</font>
<br><font size=3> </font>
<br><font size=3>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.</font>
<br><font size=3> </font>
<br><font size=3>Try using longer curing epoxy. :-)</font>
<br><font size=3> </font>
<br><font size=3>Bob R.</font>
<br><font size=3> </font>
<br><font size=3><b><i><br>
Glenn Hatfield <randy10926@comtekmail.com></i></b> wrote:</font>
<br><font size=3 face="Arial"><br>
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.</font>
<br><font size=3 face="Arial"> </font>
<br><font size=3 face="Arial">This stuff appears to be acting as a catalyst;
which really surprised me. What is really going on here.</font>
<br><font size=3 face="Arial"> </font>
<br><font size=3 face="Arial">randy</font>
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