pressure casting or vacuum degassing?

[ScoobiJohn]

i've been doing some work with clear epoxy resins (will also want the system to work with silicone rubbers too) and some what inevitably i'm getting bubbles to varying degrees in my work, so i was wondering what people here thought was the best method for dealing with them? the principle seems similar and seen websites advocating both methods so not sure which way to go. I dont want to spend an absolute fortune either, though living in the uk i am used to being ripped off! but i recognise this is something best bought rather than cobbled together since dealing with significant pressure differentials.

anyway any advice would would be appreciated

 

[clonesix]

Hi John, Welcome to the forum.

Let me start off by saying that these two things are COMPLETELY SEPARATE THINGS.


Vacuum degassing will remove bubbles from a liquid by lowering the ambient pressure, making the bubbles trapped by the liquid expand and float to the top, where they pop. Thus removing trapped bubbles from the liquid.

Pressure casting (more dangerous due to PRESSURE) increases ambient pressure, and does not allow gas bubbles to form in the catalyzed liquid prior to setting.



Now, with these two explanations, I believe you would like to Vacuum Degass the epoxy to clear it of any bubbles. With that purpose in mind, you need a slower cure epoxy. Once the catalyst is added, it begins to cure and there is air trapped in the liquid by the mixing process. So you need to put the catalyzed resin into the vacuum chamber and let the air out. That takes 15-20 minutes, and you can't have it curing while it is in the vacuum chamber. So pick a slow cure epoxy so as to remain liquid long enough to degass.

 

[doppelganger]

I have recently bought a vacuum chamber and I love it. Perfect casts with zero bubbles. It was just a cheapy off the Bay of E but it came quick and works like charm. Didnt come with oil but that was inly £5 next day from Amazon. I'll send you a link if you are interested as we are not allowed to post active ebay auctions in a thread.

 

[ScoobiJohn]

a quick search on ebay and i found the one your using - just wish the pot was a bit wider - i turn bowls too and been trying to incorporate resin into them and like a 12" diameter bowl but few seem that large and cost rather a lot if they are

does a pre-pour degassing help much or does the pour re introduce a lot of air? might have to settle for that for larger items

 

[doppelganger]

Pre pour degassing works very well. Pour the resin into your molds like pouring a pint of beer and you should avoid bubbles.

 

[cavx]

That takes 15-20 minutes, and you can't have it curing while it is in the vacuum chamber. So pick a slow cure epoxy so as to remain liquid long enough to degass.

At a full 30"hg, it should degass quicker than that. Since about 2013, I have been degassing silicone rubbers, rigid and flexible polyurethane, epoxy and polyester resins for far less times than that, with excellent, bubble free results.

What I noticed is that both ambient temperature and atmospheric pressure do have an impact on the time it takes to reach the "boil".

One supplier actually suggested that degassing longer than 2min starts to pull chemical out of the resin.

On average, most stuff I degass is ready at less than 3min after the initial rise and fall.
The surface reaches a very rapidly moving state. Any remaining bubbles are crushed by the repressurisation of the chamber.

Of course, air can be remixed during the pour, so that comes down to technique.


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[ScoobiJohn]

so everyones agreed degassing rather than pressure casting?

 

[cavx]

so everyones agreed degassing rather than pressure casting?

I think unless you are using quick set resin, vacuum degassing will be the way to go. It is also safer than pressure.

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