I need some advice on vacuum chamber bubbles

[cunningham]

I am using Crystal Clear 2-part resin from Smooth-On and found that it always had tiny bubbles in it when fully cured without the vacuum chamber. I recently bought a chamber and when I put the mold with the resin in it, it first bubbles up like boiling water, then calms down a little, leaving a frothy layer of bubbles on the surface of the mold, whichdoesn't seem to dissipate. Am I doing something wrong?

 

[8 perf]

Not saying its the problem, but I have never put the resin into a vac chamber. The rubber mold yes, but not the resin. I always used a pressure pot for the casting part. Seems counter intuitive I know, but it works. Smooth-ons own website also shows this resin in a pressure pot as well. Maybe give that a try.

 

[cavx]

I would not be vacuuming the resin in your molds. I did this once and made a mess in my vacuum chamber.

I have found that you can vacuum both polyurethane (1:1) and polyester (that use a catalyst to set off) resins, but it best, from my limited experience, to mix and degas in a wide container first. I use 2 litre ice cream containers for this when mixing between 200 grams and up to 500 grams of product. Remember the resin will increase and raise in depth up to 10x so you need and want high side walls to contain the mix.

Looking at your images, it looks like you did not have the vacuum strong enough. You need -30 inches to actually pull the air out. When you re-pressurize, any small bubbles still left will crush under the re-introduced pressure.

When you pour, you still have to be careful not to trap air and don't drain the container right to the end or you will get small bubbles forming on the top of your part.

If it helps, HERE is a YouTube video I made of degassing clear elastomer.

 

[cunningham]

Thanks Cavx, that video was helpful.

 

[TCSloan]

I always degas the resin before mixing it, it'll get the air bubbles out..though when you mix it you will end up with some ,but not as much as before..then I put the mold into the pressure pot to counter the new bubbles. I think thats whay most people do as well if they have both vacuum and pressure pots