Overview

By casting a liner in place the amount of propellant in a given case size can be increased while furthermore decreasing the cost of the motor by not requiring a commercially wound liner. This technology will open up a multitude of non-standard case diameters.

Material Trade

The first set of choices that need made is a material selection. This will drive infrastructure design, thermal design, and chemical acquisition. Commonly used in industry and the hobby, EPDM rubber provides a pliable, strain relieving, insulating layer. The other alternative is a HTPB based cocktail of various additives.

EPDM has a large body of prior art. A suggested EPDM rubber formulation is 93% EPDM rubber and 7% kevlar fiber.

HTPB has also been used before. Literature suggests that it is more suited for high-G flights where case adhesion is paramount. HTPB used as a liner should be around 50% solids for strength, with carbon being the primary additive, with TiO2, fiber, zinc borate, and other additives potentially useful. A plasticizer is also strongly suggested for HTPB based liners to improve casting performance.

Literature

http://dtic.mil/dtic/tr/fulltext/u2/a242297.pdf

http://www.iom3.org/sites/default/files/event-documents/Torry.pdf

http://www.rocketryforum.com/showthread.php?144434-Home-Brew-case-bond&p=1760873#post1760873