Recently, we have found out about high performance pourables. Now, I'm not talking about disgusting 68% solids pourables in which the solids settle to the bottom within a matter of minutes, but rather high solids (~82%). So, why do pourables rather than pack? Well, when packing, many microvoids are introduced into the grains. These microvoids, if small enough, often don't affect density too much, but they affect the burn-rate drastically. They cause propellants to run away at much lower Kns than if they didn't have these microvoids. For example, NASSA Red sims to about 1000 psi at Kn 450 in BurnSim, but in real life it starts getting hot at Kn 400. I personally have run a NASSA Red motor at Kn 400 and reached around 1100-1200 psi. If these microvoids weren't present, this likely would not happen. Pourables remove these microvoids because, after pouring, the propellant can be vibrated, and the bubbles are allowed to rise to the top of the grain and escape.
In the last couple days, we have conducted a couple pourable propellant test batches. One such batch was our new Cloud 9 propellant. This is a high aluminum, dense, and moderately fast propellant that is intended to be used in extremely high performance motors. Test burns should be conducted in the near future.
Here are some pictures of the pourables:
In the last couple days, we have conducted a couple pourable propellant test batches. One such batch was our new Cloud 9 propellant. This is a high aluminum, dense, and moderately fast propellant that is intended to be used in extremely high performance motors. Test burns should be conducted in the near future.
Here are some pictures of the pourables:
And, much more helpful than pictures, here is a video of a pourable in action:
We found that the two most important factors to making a propellant pour are heat and bimodal, rounded AP. Surfactants and high plasticizer ratios help a lot, too, but the two predominant factors were the two listed above. Without bimodal AP, the propellant was not able to flow, even with high temperatures.