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Old 05-29-2018, 09:56 PM   #6 (permalink)
Join Date: Mar 2017
Location: Houston, Texas
Posts: 898
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RE: Air bubbles - I don't have any peactical experience, but have done quite a bit of casual literature research on the topic. I couldn't find any specific data on polyester, but there is a lot of stuff available on epoxy resins due to use in carbon fiber composites. Unfortunately most of this data is with respect to the strength of the final part and not appearance. Anyway, to make a long story short, vacuum is good for removing bulk gas if the pot life allows, but pressure is necessary to eliminate fine bubbles. Not only does the pressure compress the gas into a smaller volume, it actually causes the gas to dissolve in the resin. When the gas dissolves, it essentially disappears. Obviously, there is a limit to how much gas can be dissolved and how fast it can happen. If the part has a lot of pores that trap gasses, you might want to do a two step, vacuum then pressure. But based on my research I am thinking that at a minimum a pressure pot at about 45psi will be needed to avoid bubbles.
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