In our quest for ever-perfect propellant processing and performance, we have also been looking into vacuum casting our propellants. To date, no vacuum cast grains have been fired in motors, but we have experimented with several vacuum casting trials. The actual vacuum caster is based off of the NASSA design, which can be found here. Here is a photo of our vacuum caster ready to be used:
The aluminum tube is put under vacuum and the propellant is poured into the funnel. Since the propellant itself is a rubber, it seals well against the funnel. Now, all it takes is for the 14.7 psi pressure difference to force the propellant into the vacuum. This method has produced the following grain:
This 76mm Cloud 9 grain was absolutely flawless. It had no voids or microvoids, meaning that the vacuum casting worked as intended. Further updates regarding pourables and vacuum casting will be posted here in the near future.
Harry.
Harry.