Re: [ATM] Epoxy mirrors (again)

["Wayne Young" <atm@ganimede.demon.co.uk>]

Hi Thomas

Yikes !!

The epoxy I am using is nothing like that reactive. I am only mixing tiny 
amounts ( 15 cc ) and it has a very long pot life - about 2 hours. It takes 
a full 24 hours to cure and I am pouring it into a very thin film ( about 
500 um ), so luckily I don't think I need to worry about setting anything on 
fire.

As for mixing thoroughly - I learned a trick : Mix as well as you can, then 
empty the contents into a clean container and mix again. What tends to 
happen if you just use one pot is that portions of the mixture that are 
either rich in resin or rich in hardener tend to stick to the sides of the 
container and can get transferred to your work when you pour it out. If you 
pour the mixture into another container, you leave some of that stuff behind 
on the inside of the first container and the rest ends up somewhere in the 
middle of the new container. Mixing again in the second container really 
makes sure you have a thoroughly mixed batch.

Wayne

----- Original Message ----- 
From: "Thomas Janstrom" <thomas@moiler.com>
To: "'Dream - Telescopes & Accessories, Inc.'" <shane@dreamscopes.com>; 
"'Wayne Young'" <atm@ganimede.demon.co.uk>
Cc: <atm@atmlist.net>
Sent: Tuesday, January 10, 2006 11:53 PM
Subject: RE: [ATM] Epoxy mirrors (again)


>I have personally seen this happen, it was only 75g, but in a relatively
> tall mixing pot, not really tall, just well bit too tall for this mix...
>
> It was a hot day to start with and well shortly after mixing in the
> hardener, we noticed that the pot was getting hot, we thought no-worries
> this stuff always gets warm when we mix it so we'll get on with the
> lay-up, but before we could get the first layer wet and in position the
> tub was smoking!, we barely got it out of the shop before it burst into
> flames.....
>
> So now we always mix in rather shallow tubs, a bit harder to get a batch
> fully mixed, but we feel the added safety is worth the trouble....
>
> Cheers, Thomas.
>
> -----Original Message-----
> From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
> Of Dream - Telescopes & Accessories, Inc.
> Sent: Wednesday, 11 January 2006 3:29 AM
> To: Wayne Young
> Cc: atm@atmlist.net
> Subject: Re: [ATM] Epoxy mirrors (again)
>
> 100 grams of epoxy sitting in a 2"
> diameter paper cup with no lining can theoretically have such a runaway
> exothermic reaction as to cause the cup to catch on fire.  I've never
> tried
> that...  I can attest to it heating up though.
>
> -- 
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