Pressure vs. Vacuum

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kenlholley

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Apr 15, 2013
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I am thinking about making a pressure pot for casting. What is the difference between using vacuum or pressure? Is one better than the other? The pot would be used for hopefully bubble free casting.
Thanks for any input.
 
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jcjc

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You have to use pressure to reliably eliminate bubbles. Degassing/ vacuuming works well to get rid of most of the bubbles but it may not be feasible to do this effectively with short pot life resins. I don't bother with vacuum degassing anymore even though my resin has a 40 working time, I strictly use pressure now.
 

chartle

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Its also my understanding that resins like Alumilite create gas as they cure and the pressure keeps the gas in solution.
 

leehljp

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FYI, while some may caution you about using the HF Pots, I use the HF pot for both pressure and vacuum. They are not too difficult to configure to use both ways on a single pot.

The cautions on HF pressure pots is that they (some) do not to handle higher pressures past 50 PSI 100% reliably, and there are always the folks that think that they are the best judges of what is acceptable and end up destroying something or maiming themselves and blaming others. I have been using HF pressure pots for about 12 years now and have not had a problem. I do not exceed the limits recommended.
 

jcjc

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Its also my understanding that resins like Alumilite create gas as they cure and the pressure keeps the gas in solution.
not saying this isn’t true but I’ve never used or heard of a resin that creates gas as it cures. that to me is a serious design flaw for several reasons.
 

TattooedTurner

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I never had any luck at all degassing resin with vacuum. In fact, I got far more bubbles with polyresin than I did without degassing. Like Hank, I too use a HF pressure pot without any worries. I put dry teflon lube on the gasket and it’s held 50psi for 3 days straight. I once forgot to turn the pressure down on my compressor after inflating my bike tires. The safety relief valve I put on mine goes off at 70psi and worked like a charm! No damage at all to the pot itself, but I highly recommend not going past 50psi just to be safe.
 
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