Getting rid of bubbles in mold (repost)

Getting rid of bubbles in mold (repost)

Post by Elda » Thu, 13 Jun 2002 04:25:39



I'm in the process of creating several molds that have to be
transparent. Having decided on a *** compound from Smooth-On that
meets the necessary criteria there is one other hurdle to overcome --
tiny air bubbles that seem to form while the mold material is curing.
These bubbles effectively render portions of the mold opaque after
curing. Posts seem to suggest that most of these bubbles are created
during the mixing process but this doesn't seem to be the case here
unless they were microscopic after pouring and merely got larger
during curing. A Smooth-On rep suggested that it may have been too
much release agent, too much moisture in the master etc., etc., etc..
Whatever, I am investigating taking the vacuum chamber approach in
getting rid of these bubbles since it would seem that the possible
sources are many. Would placing the poured setup in a vacuum chamber
(20 - 25") for the duration of the material's  pot life (30 minutes)
be worth a try? I don't see any advantage in placing the mixed
material in a vacuum chamber before pouring if the entire poured setup
can fit in the chamber. Perhaps I'm missing something here.
 
 
 

Getting rid of bubbles in mold (repost)

Post by Wanne » Thu, 13 Jun 2002 08:09:41


Quote:
> 11-06-2002 21:25  - Eldata :
> Whatever, I am investigating taking the vacuum chamber approach in
> getting rid of these bubbles since it would seem that the possible
> sources are many. Would placing the poured setup in a vacuum chamber
> (20 - 25") for the duration of the material's  pot life (30 minutes)
> be worth a try? I don't see any advantage in placing the mixed
> material in a vacuum chamber before pouring if the entire poured setup
> can fit in the chamber. Perhaps I'm missing something here.

A vacuum chamber does help to get the air out.
Same for having everything on a vibrating table while the poured mold
material or resin sets.
Or a combination.
--
mail: wannes at mac.com

 
 
 

Getting rid of bubbles in mold (repost)

Post by EmilA19 » Thu, 13 Jun 2002 10:32:54


Quote:
>I'm in the process of creating several molds that have to be
>transparent. Having decided on a *** compound from Smooth-On that
>meets the necessary criteria there is one other hurdle to overcome --
>tiny air bubbles that seem to form while the mold material is curing.
>These bubbles effectively render portions of the mold opaque after
>curing. Posts seem to suggest that most of these bubbles are created
>during the mixing process but this doesn't seem to be the case here
>unless they were microscopic after pouring and merely got larger
>during curing. A Smooth-On rep suggested that it may have been too
>much release agent, too much moisture in the master etc., etc., etc..
>Whatever, I am investigating taking the vacuum chamber approach in
>getting rid of these bubbles since it would seem that the possible
>sources are many. Would placing the poured setup in a vacuum chamber
>(20 - 25") for the duration of the material's  pot life (30 minutes)
>be worth a try? I don't see any advantage in placing the mixed
>material in a vacuum chamber before pouring if the entire poured setup
>can fit in the chamber. Perhaps I'm missing something here.

Easy solution:  Degass the *** before pouring.  If you have a true vacuum
pump (one that will pull a vacuum equal to 29" of mercury) and a sealed vacuum
chamber, this shouldn't take more than about 5 minutes or so to do.

Degassing the *** pulls out all the air bubbles mixed in when stirring the
catalyst into the ***.  For this, you will need a vessel equal to at least
twice the volume of the *** to be degassed.

Afterwards, simply pour the *** carefully around the sides of the master,
between master and the mold box, to avoid trapping air against the master.

AA

 
 
 

Getting rid of bubbles in mold (repost)

Post by Derek Hawkin » Fri, 14 Jun 2002 10:40:49


Thanks. Why is 29" hg such a magical number? Nothing under $300.00 seems
capable of achieving that.


Quote:
> Easy solution:  Degass the *** before pouring.  If you have a true
vacuum
> pump (one that will pull a vacuum equal to 29" of mercury) and a sealed
vacuum
> chamber, this shouldn't take more than about 5 minutes or so to do.

> Degassing the *** pulls out all the air bubbles mixed in when stirring
the
> catalyst into the ***.  For this, you will need a vessel equal to at
least
> twice the volume of the *** to be degassed.

> Afterwards, simply pour the *** carefully around the sides of the
master,
> between master and the mold box, to avoid trapping air against the master.

> AA
> >I'm in the process of creating several molds that have to be
> >transparent. Having decided on a *** compound from Smooth-On that
> >meets the necessary criteria there is one other hurdle to overcome --
> >tiny air bubbles that seem to form while the mold material is curing.
> >These bubbles effectively render portions of the mold opaque after
> >curing. Posts seem to suggest that most of these bubbles are created
> >during the mixing process but this doesn't seem to be the case here
> >unless they were microscopic after pouring and merely got larger
> >during curing. A Smooth-On rep suggested that it may have been too
> >much release agent, too much moisture in the master etc., etc., etc..
> >Whatever, I am investigating taking the vacuum chamber approach in
> >getting rid of these bubbles since it would seem that the possible
> >sources are many. Would placing the poured setup in a vacuum chamber
> >(20 - 25") for the duration of the material's  pot life (30 minutes)
> >be worth a try? I don't see any advantage in placing the mixed
> >material in a vacuum chamber before pouring if the entire poured setup
> >can fit in the chamber. Perhaps I'm missing something here.