(707b) Effects of High Shear Processing On Single Base Propellant

Effects of High Shear Processing on Single
Base Propellant

J. K. Wyckoff, D.
Park, M. Fair, D. Thompson

                The
performance of solid gun propellant is historically a function of the initial
temperature of the propellant.  At hot
temperatures, the maximum pressure reached in the gun and the resulting muzzle
velocity is greater.  If the propellant
is cold, the opposite is true.  Therefore
propellant charges must be designed around the maximum pressure at hot so the
gun barrel will not be damaged and the subsequent drop in performance in cold
must be accounted for.  This change in
performance over temperature is broadly referred to as the temperature
coefficient or temperature profile.  The
greater the coefficient is, the greater the difference between hot and cold
performance.  Much research has been
performed to produce flat temperature coefficients.  While some new techniques have been developed
that lessen the impact, temperature effects are still noticeable.  Some initial results suggest that mixing
propellant with high shear can improve a propellant performance over
temperature by decreasing the variations in burn rate or improving mechanical
properties.  For this study a single base
propellant was chosen.  Single base
propellants, in which the bulk of the material is nitrocellulose, are often
made with a Beken style mixer that imparts a moderate
amount of shear into the material.  Results
will be presented in which different processing techniques using varying
degrees of shear are used to produce single base propellant.  Our investigation included a low-shear, sigma
blade mixer and a relatively high-shear, twin screw extruder.  A design of experiments approach was adopted
to examine the effects of various processing parameters on the final properties
of the propellant.  Factors such as blade
speed, residence time, and solvent ratio were varied.  Closed bomb and mechanical properties tests
were performed and compared to baseline propellant manufactured on a Beken style mixer.