Chemically Collapsible Mandrel for Solid Rocket Motor Processing

Abstract

Composite propellant mainly consists of two parts, binder matrix (prepolymer, plasticizer, cross linker, antioxidant and curative etc.) and solid ingredients (oxidizer, metal fuel, burn rate modifier, combustion stabilizer etc.). Its processing involves several stages like ingredient preparation (grinding, 1.1 Hazard Division – 1.1 HD), mixing (1.1 HD), casting (1.1 HD), curing (1.3 HD) and extraction (1.3 HD). Each and every process is very hazardous. Removal of any of the mentioned step will be a great achievement for solid rocket motor processing. Mandrel is used to give proper grain geometry. But for metal mandrel, its extraction process (1.3 HD) is very dangerous. Proper safety precaution should be taken to perform the said operation. Also, for a metal mandrel, it is very difficult to develop intricate grain geometry due to extraction problem. This paper mainly deals with casting techniques of propellants (case bonded or cartridge loaded) with a chemically collapsible mandrel. This mandrel is collapsed in presence of suitable chemicals, hence extraction step (1.3 HD) becomes simpler. As the extraction process is very easy, intricate grain geometry can be developed in solid rocket motor. The mandrel is cheap, recycleable and relatively lightweight compared to the metal mandrel, thus handling becomes very easy. The mandrel material and the dissolution solvent have no effect on the propellant, which will be confirmed by evaluation of physicochemical as well as ballistic properties measurement.