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Old 11-13-2017, 02:37 AM   #1 (permalink)
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Default Casting in a Vacuum

Has anybody tried casting in a vacuum?

I have recently been given some mini pine cones and banksia integrifolia pods to try casting. I have had varying degrees of success using a slow curing resin and a 60psi paint pot. But due to the structure of the organic materials and viscosity of the resin, I find that I still end up with little holes close to the core of the material. (I use PVC pipe as a mold)

One of the solutions that I have thought of making a vacuum chamber with a vacuum port and a nozzle with a ball valve and reservoir. I would place my chamber over my mold with the nozzle pointing down into it, ball valve closed and resin in my reservoir before creating my vacuum. The next step would be to open the ball valve and filling the mold with resin. In theory, as the material is under a vacuum, the resin should penetrate into every hole, leaving no voids.

Things that I wonder about is:

1.) Would the cohesion of the resin and gravity should be sufficient to allow the resin to flow into the mold without it 'exploding' in the chamber.
2.) The rate that the vacuum will suck the resin into the chamber. It might be to fast for me to be able to stop the flow once the mold has been filled.

Any thoughts?
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Old 11-13-2017, 09:38 AM   #2 (permalink)
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Old 11-13-2017, 10:27 AM   #3 (permalink)
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I have a friend who works at the local Woodcraft who casts pine cones, acorn caps, magnolia seed pods, using Liquid Diamond epoxy resin with a pressure pot. It seems to work extremely well for him because of the long cure time. You have 45 minutes before it starts to gel and it is very thing so it gets into all of the nooks and crannies.
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Old 11-13-2017, 11:11 AM   #4 (permalink)
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that's an interesting idea. i use artresin epoxy which has all the attributes of liquid diamonds but is more resistant to yellowing. anyway, i've cast some very porous wood with it that i later bandsawed into cross sections and there were no voids. maybe first try to warm the resin to lower the viscosity.
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Old 11-13-2017, 11:18 AM   #5 (permalink)
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I use PR under pressure not vacuum. Tried vacuum once and had a heck of a mess, PR expanded into a bubble filled mess.
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Old 11-13-2017, 03:03 PM   #6 (permalink)
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after reading tom's post, it seems bubbles would be a huge issue.
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Old 11-14-2017, 02:00 AM   #7 (permalink)
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Default Thanks for the feedback

Thanks to everybody for the feedback. But just to clarify, the major problem I have with this specific organic material is not with the viscosity of my resin or the gel time (40mins), but air bubbles trapped in the holes. If there is no clear path for the bubble to escape, placing it under vacuum will not remove the bubbles (and there is no way to orientate it so all the holes face upward unless I am able to turn it in the resin - messy and very time consuming). I stabilize the material before casting so it is not porous any more. Placing it under pressure will only reduce the bubble size not remove it. Some of the holes are fairly large and at 60psi you basically reduce the bubble to a sixth of its original size. That is why I have been thinking of removing the air before I cast the resin.

I will try my solution out and give feedback.
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Old 11-14-2017, 12:52 PM   #8 (permalink)
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You could try and vibrate the mould to shake loose the bubbles. An orbital sander touching the side can work as can a blade-less jigsaw or reciprocating saw.
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Old 11-15-2017, 08:04 AM   #9 (permalink)
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Some times it helps if you stabilize the material first then cast. You don't have to all the time but I think it makes a nicer blank with a lot less issues.
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Old 11-15-2017, 07:25 PM   #10 (permalink)
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Sounds like it may help. You should just give it a try and let us know =)
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