Casting powder

Virtually all of the HEs and most of the propints for all three Services are manufd in a network of Army Ammo Plants (AAPs) scattered mainly over the eastern and southern portions of the country. They are loaded in other facilities of the same AAPs, in other AAPs which do not themselves manuf chemicals, and in a series of Naval Ammo facilities (NADs). Two Navy facilities manuf some supplementary ingredients, notably NG and casting powder but mostly they load expls obtained from ... 

A layer of this inert powder was placed in an extruded cellulose acetate tube, partly filled with OGK casting powder (NC of 12% 88, 2-nitrodiphenylamine 2,dioctylphthalate 5 and lead stearate 5%) and was then covered over with more OGK powder... 

Fluid Ball . Trademark of Olin Mathieson Chem Corp, Stamford, Conn 06904, for a pro-pint casting powder consisting of fully col-loided NC having an average particle diam of 50 microns or less. Compn can include liq solid modifiers. Used as binder constituent of modified double-base rocket propints Ref CondChemDict(1961), 503-R 504-L ... 

Manufacture of casting powder a product containing all the nitrocellulose and solid ingredients and a portion of the plasticizer is made in the form of a right circular cylinder approximately 1 mm. in diameter and length. 

Propellant Composition. In principle, any solid ingredient which is chemically compatible with nitrate esters can be introduced into the propellant by way of the casting powder. Any liquid ingredient used in the formulation must also be a plasticizer or co-plasticizer for nitrocellulose. In practice, three major families of compositions have been developed, differing in the composition of the casting powder (see Table I for typical compositions) ... 

Single-base casting powder the casting powder consists of nitrocellulose, stabilizer, solid additives for ballistic modification, and a small amount of plasticizer. The normal ratio of casting powder to casting solvent, 2 1 by volume, yields a final composition of approximately 60% nitrocellulose. 

Another substantial increase in delivered energy was obtained by incorporating substantial amounts of solid oxidizer e.g., ammonium perchlorate) and metallic fuel e.g., aluminum) in the casting powder. The resulting family of composite-modified double-base (CMDB) propellants has found widespread use in ballistic missiles and space motors. 

Process Steps. Casting powder manufacture is basically a plastics-forming operation, utilizing a volatile solvent to impart mobility to the polymeric binder. The process is shown schematically in Figure 2 in terms of the major equipment used. For discussion, the process may be divided conveniently into the following operations ... 

Figure 3. Effect of processing solvent on density of casting powder...

An extrusion is comprised of a basket (cylinder) to contain the mix and a hydraulically actuated piston to press the mass through multiple extrusion dies. The baskets are jacketed for temperature control and contain internal screens to retain large agglomerates. Since the casting powder strands are unperforated, the dies are simple cylindrical barrels with conical lead-in sections. Extrusion rates are normally controlled by orifices in the hydraulic supply line however, constant-rate positive displacement devices are also used. As they extrude, the strands are collected separately in suitable containers. 

Double-base and CMDB powders are loaded on shallow trays which are stacked in dry houses and subjected to a stream of hot air (140°F.) for several days. Results of a typical drying run for a double-base casting powder are shown in Figure 5. Initial drying is quite rapid however, extended cycles are required to get consistent values below the specification maximum, in this case 0.50% total volatiles (TV). 

Finishing. After casting powder has been dried, several operations are required to make it suitable for use. The first is glazing, which reduces the electrostatic charge which may accumulate in a moving mass of powder and promotes easy flow. A small amount (typically 0.05%) of... 

Figure 7. Burning rate of casting powder blends...

Finally, the casting powder is screened to remove clusters and foreign material and then packed into containers typically holding 150 lbs. 

Casting Powder Parameters. The steps in the foregoing description of casting powder manufacture are designed to yield certain characteristics in the final product. The properties desired in casting powder and the significance of these properties are described below. 

Figure 10. Effect of casting powder SLD on tensile strength of propellant...

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