I cast small windows in a PVC molded device, think 1mm thick X 2mm dia. Have been doing this for years. Now I am getting almost 100% failure in that the clear resin turns milky white in the pressure pot. The left over resin in the mixing tray is clear with bubbles.
I have tried pressures from 40 PSI to 120 PSI, temperatures from room temp to 150 F.
Altered mix ratio from 40/60 to 60/40.
Is it possible to have 2 bad batches of resin? :-[
Tried 4 more castings today. Heated resin before mixing and during mixing. Leftovers on mixing tray are nice and clear, but with some bubbles. All 4 cast parts from the pressure chamber are milky white.
Can anyone shed some light on why the parts turn white when cured under pressure?
Do you have any water in your air lines? Do you have a water separator on your compressor to remove water from your air? If not drain your air compressor down to get any moisture out of the tank. Blow some air on a paper towel do you get moisture? Another cause can be warm air on your pressure pot and cold air going in causing condensation.
Compressor is a small handheld 110v unit, the type used to pump up a tire. Room air being pumped in. No observable moisture in pressure pot, which is 2" stainless pipe about 12" long. What I really do not understand is that this technique has worked for years, just the last 6 months it is consistently failing. The last batch, heated resin separately, heated mixing tray, heated while mixing, pre-warmed pressure pot, even heated the toothpick used to stir the resin. Result in the castings looked like skim milk. Leftover on tray was crystal clear with some small bubbles and numerous bubbles around the toothpick.
this really sounds like moisture creep. pressure pots really expose it due to the pressure. I have to run a dehumidifier in my room and get the humidity waaay down before i run the compressor. but i have a tank on my compressor so i can run it in a small room that has been de humidified then i can take it out of the room and run it into the chamber. and even then if the chamber has moisture in it it could cause this. if your excess in the cup is clear then i think its not from the mix. it doesnt take much moisture and i dont think you would notice it. it wont leave droplets in the chamber.