Influence of storage time before casting on viscosities and mechanical properties of AP/HTPB/Al solid composite propellants

Abstract

Solid rocket motors can contain different quantity of solid composite propellant. In the Brazilian Aerospace Program, a considerable difference of the propellant masses used in each rocket motor is observed. However, all Brazilian motors are produced at the same plant, using the same mixer and casting system. To cast large motors, a multibatch process is carried out, in which each batch is prepared consecutively without adding the curing agent. Then, the batches are reserved until all of them are ready and then the curing agent addition is performed. Thus, there is some storage time between the end of the preparation of each batch and the effective casting. The present work evaluated the influence of this storage time and its conditions on the rheological properties of the slurry and the final mechanical properties of the grain. The viscosity during the process was measured and the mechanical properties were determined by tensile and hardness tests. The adoption of the storage with a duration of few days does not affect the use of the stored uncured propellant. The time of homogenization before casting and after the storing time must be optimized. However, a longer storage time, mainly performed at process temperature, can subject the resin to aging. Nevertheless, the observed changes on the mechanical properties are acceptable depending on the mission specifications and the propellant could be used even the adoption of storage time before casting.

Keywords

• Solid composite propellant
• Mechanical property
• Multibatch process
• Propellant viscosity
• Storage time