I've been casting parts, and experimenting for several months. I use fast setting resin for some parts, and slow setting for others. I have a vacuum chamber, and recently added a pressure chamber to the arsenal.
I have degassed slow setting resin prior to pouring, with good results, but have to add a ridiculous amount of microballoons to the mix to get proper buoyancy (fishing lures).
I recently gave my new pressure chamber a try. Using 7 minute, slow set pu. I have my pressure chamber and compressor set up in separate rooms, as a safety measure. I can remotely pressurize, and depressurize my chamber. I use 50 psi as per the pressure chamber manufacturer's suggestion.
My first three casts have huge voids at the top. I've even cut my pour hole Much Bigger to give a larger reservoir of resin, but this doesn't seem to help. The resin is shrinking, and obviously pulling large amounts of air into the mold.
My first question is, how fast/slow should you pressurize your chamber? As fast as you can? Or should you do it more slowly? The resin will of coarse start to set up if you go too slow. Am I filling the chamber to fast/slow?
Do I need more vents? At some point it's gonna get ridiculous, and I'll have a huge cleanup/sanding job to look forward to with too many vents.
Also, I noticed that I have a slight leak. Over the course of 45 minutes (cure time) I have a drop in pressure of about 5 psi. Could this be a big part of my problem?
Keep in mind, my current pour hole and vent hole are situated in a manner that I'm capable of getting air-trap-free castings when I cast without the pressure chamber. I have the pour hole lower than the vent, and the vent is at the high point of my mold. I also squeeze out the air, and slightly vibrate the mold prior to placing in the chamber.
Any suggestions will help, thanks