bubbles in details of clear cast

kenno3 · Post by **kenno3** » Fri Dec 23, 2011 11:49 am

Hello im casting a part using "Castin'Craft Easycast Clear Casting Epoxy" and "Oomoo 30" silicone rubber mold. I am getting some tiny bubbles inside the walls of the part which is tolerable.

But my big problem is I'm getting bubbles at the edges of fine details, meaning the Epoxy isn't filling inside the gap or point of the fine detail, thus air stays in and the part is never produced by the epoxy.
I heated the mold and the epoxy, used a heater, and tapped the mold, all which didnt work. I also tilted the mold with some epoxy inside it, but gravity is not strong enough to pull the epoxy into the fine detail.
What else can I do? I don't have a vacuum or pressure chamber. I used search for "bubbles" but didnt find specific help for my problem.

The picture below shows an example of the part, with details as small as 2.4 mm. I am casting the part upside down, so that the bottom of it is flat.

I can use a toothpick to pull out the bubble at the "shallow" detail, but I cant see to the "deep" detail, to know if I got the bubble out with a toothpick.
Thank you.

http://img.photobucket.com/albums/v187/ ... /mold1.png

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Moderator edited to change pic to link as per Forum Rules.

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Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Fri Dec 23, 2011 1:25 pm

You'll have to "slide" a layer of resin down the side of the mold, then
work the bottom with your toothpick to remove the deep air bubbles.
Once that is done you can then fill the mold.
Filling the mold can be down with a small syringe to put the resin in deep and
force material up from the bottom pushing any air bubbles to the top.
(I use a vacuum chamber myself...

)

kenno3 · Post by **kenno3** » Wed Dec 28, 2011 9:28 pm

Thanks for the reply.
I had a successful casting of the model by picking out the air bubbles with a plastic toothpick. Even tho I couldnt see in, I just picked at each hole and it worked.
But when I cast a 2nd time, it didnt work. Would using a pressure pot at 35-40 psi work at pushing the resin/epoxy into the small details so there's no voids?

Antenociti · Post by **Antenociti** » Fri Dec 30, 2011 8:20 am

kenno3 wrote: Would using a pressure pot at 35-40 psi work at pushing the resin/epoxy into the small details so there's no voids?

yes, just make sure that the pressure stays on until full-cure.

Personally I pressure clear-cast resin to 80psi because the pot i use for it (the heated one) can keep 80psi for a very long time and "just because I can to make sure".

But 40psi is usually enough to get rid of small bubbles and fill gaps between resin and mould surface.

kenno3 · Post by **kenno3** » Fri Dec 30, 2011 11:24 am

Thanks for your reply.
Im using the "Clear Casting Epoxy" and I notice even after 24 hours, the part is still soft. And the full cure time is listed at 72 hours.

Today im investing $80 in the Harbor Freight Pressure Paint Tank and converting it for pressure casting.
http://www.harborfreight.com/2-1-2-half ... 66839.html

Its rated at 30-60 PSI. Since my part is still soft after 24 hours, should I keep it in the pressure pot longer - so that the bubbles inside wont expand and push out (deform) part walls? Or by then, are the air bubbles already pushed out of the resin and released into the air in the pot?
And would casting at a higher PSI such as 55 help it cure faster?

I already heat my resin and have a heater blowing on the molds before and after I pour it. But if I put the mold in the pot, im not sure if applying heat to the pot might expand pipe joints and cause a leak or explosion.

You mentioned yours heats, which pot do you use?