Using linen/paper phenolic or other equivalent materials for rocket motor case insulators works really well on small scale motors (4" and below), but on larger motors can be very limiting. In particular, using a tubular phenolic insulator does not guarantee a seal with the case and, in fact, lets hot combustion gases around the insulator and exposes them to the case. We recently had trouble with this on a 6" Q motor firing, where the motor suffered an insulation failure at around 1.9 seconds into the firing. Because of this failure, we are reevaluating our insulation system for large-scale motor firings by incorporating spin casting and case bonding.
For our size of motors, spin casting liquid insulators works well and is easy to do with the right equipment. For larger motors, casting liners into sheets and gluing the sheets in with special adhesive is the primary method for insulator application. Nevertheless, we needed a way to spin the whole motor case and several hundreds of revolutions per minute for an extended period of time (>40 minutes) to let the liner tack into place. Here is what we came up with:
For our size of motors, spin casting liquid insulators works well and is easy to do with the right equipment. For larger motors, casting liners into sheets and gluing the sheets in with special adhesive is the primary method for insulator application. Nevertheless, we needed a way to spin the whole motor case and several hundreds of revolutions per minute for an extended period of time (>40 minutes) to let the liner tack into place. Here is what we came up with:
The motor case rotation is driven by an evaporative cooling motor with a timing belt. Here is a video of it in action:
So that's all well and good. But that begs the question: what formula are you using for the castable insulator? We are currently testing this and will be releasing a formula once adequate data has been collected.