The funny thing is, the way they do the coating is to put the powder and graphite together and TUMBLE THEM.
Not always, P
UNITED STATES PATENTS 20 Claims, No Drawings 1,393,623 1 0 1 921 Henning 149/9 PROCESS OF MAKING DETERRENT-COATED AND GRAPHITE-GLAZED SMOKELESS POWDER This invention relates to a process for manufacture of smokeless powder in which each of the processing steps of nitrocellulose densification, deterrent coating, and graphite glazing can be performed in an aqueous slurry. More particularly this invention relates to an aqueous slurry process for rapidly deterrent coating and graphite glazing of granulated nitrocellulose particles. In still another aspect, this invention relates to an aqueous slurry process for manufacture of deterrent-coated and graphite-glazed double-base smokeless powder from a single-base type of granulated nitrocellulose in which all of the processing steps are conducted in an aqueous slurry.
The conventional process for manufacture of smokeless powder involves as a first step the granulation of nitrocellulose. In this process water-wet nitrocellulose is dehydrated with denatured alcohol in a blocking press. The resulting dehydrated nitrocellulose is broken up in the blocking press and subsequently masticated in a large mixer by the addition of solvents such as denatured ethyl alcohol and acetone to form a homogeneous stiff dough. Energetic plasticizers such as nitroglycerin are admixed with the dough if a double-base composition comprised of nitroglycerin and nitrocellulose is to be made. The stiff dough is blocked in large hydraulic presses and subsequently extruded at high pressure into strands of powder. The strands of powder are cut into a desired length. These particles are then dried for several days to remove processing solvents and water. The particles of powder produced are referred to herein as smokeless powder. Some of these dried particles can be coated with various buming rate deterrents if desired in order to obtain progressive burning smokeless powder. The coated smokeless powder particles or granules are dried and then glazed with graphite to prevent the build up of a static charge on the granules and to increase ease of handling.
The foregoing process is tedious, requires considerable amounts of massive and expensive equipment and requires much skilled labor in order to produce a quality product. Over the years numerous attempts have been made to develop processes to obviate one or more of the processing difficulties encountered in this process for manufacture of smokeless powder. Many of these processes, sometimes referred to as nitrocellulose densification processes, are directed to alternative methods for granulation of nitrocellulose which eliminate long mixing times, extrusion of doughs, and cutting of strands of powder. One such process is the Ball Powder Process and is disclosed in U.S. Pat. No. 2,027,114. A modification of this process is disclosed in U.S. Pat. No. 2,885,736.
Other processes have been developed for granulation of nitrocellulose in which water wet nitrocellulose is agitated in a slurry to which solvents for the nitrocellulose are added to partially gelatinize the nitrocellulose without dissolution thereof. The solvent is then removed from the slurry producing smooth, hardened, densified nitrocellulose particles. Such processes are described in U.S. Pat. Nos. 2,946,673 and 2,948,601. A recent patent disclosing both a granulation method for fibrous nitrocellulose by a nitrocellulose densification process and a process for manufacture of double base smokeless powder therefrom is U.S. Pat. No. 3,346,675 to J. Sapiego. With the exception of the conventional process all of the foregoing processes have one basic step in common, i.e., that nitrocellulose is granulated through the action on nitrocellulose of one or more solvents for nitrocellulose dispersed in the presence of a nonsolvent for nitrocellulose, such as water.
The product produced from the foregoing granulation processes which are intended to represent the basic prior art process is particles of granulated nitrocellulose. These particles can be deterrent coated, graphite glazed, and converted from single-base particles to double-base particles, (where applicable) with each step performed in an aqueous slurry in accordance with the process of this invention. The process of this invention is particularly suitable for manufacture of smokeless powder from granulated nitrocellulose prepared by a process such as is described in U.S. Pat. No. 3,346,675, so that each step of the process including granulation is performed in an aqueous slurry. However, granulated nitrocellulose in particle form manufactured by the conventional solvent process can be employed. The process of this invention provides a highly safe method for deterrent coating, graphite glazing, and nitroglycerin absorption of granulated nitrocellulose particles since the granulated nitrocellulose is processed in an aqueous slurry in each step.
Broadly, the process of this invention comprises (a) forming a slurry of granulated nitrocellulose particles and water, (b) admixing in the slurry of step (a) a burning rate deterrent or finely divided graphite to form a slurry comprising a continuous phase of water and a dispersed phase of burning rate deterrent or finely divided graphite, (c) heating the slurry to a temperature at which the burning rate deterrent, when present, melts but to at least 150 F. until substantially all of the burning rate deterrent or finely divided graphite adheres to the granulated nitrocellulose particles, and (d) separating smokeless powder from the slurry.
In the deterrent-coating and graphite-glazing steps heretofore described, it has been found that if energetic plasticizers are employed in manufacture of the granulated nitrocellulose particles some of these plasticizers are extracted out of the particles into the water phase of the slurry causing a change in the composition of the resulting coated and glazed smokeless powder. In the process of this invention temperatures of at least 150 F. are required in order to achieve rapid and suitable deterrent coating and glazing. At these temperatures plasticizer extraction rates increase. While powder can be manufactured with an amount of excess plasticizer equivalent to that which would be extracted under a particular set of processing conditions for aqueous slurry deterrent coating and graphite glazing, it is in general undesirable from an economic and process standpoint to do so. To eliminate loss of explosive plasticizer from a powder composition where composition is critical as is often times required, it is necessary to employ in the water in the aqueous slurry an equilibrium concentration of plasticizer. This equilibrium concentration of plasticizer is dependent upon the slurry composition, and the slurry temperature; the equilibrium concentration of nitroglycerin as an energetic plasticizer being preferably from about 0.1 to about 0.3 percent by weight based on the weight of the water in the aqueous slurry. The term equilibrium concentration" is used herein with reference to energetic plasticizer is defined as a concentration of energetic plasticizer in the aqueous slurry at which there is substantially no tendency for the plasticizer to be either absorbed into or extracted from the granulated nitrocellulose particles during the processing cycle. If the granulated nitrocellulose contains no plasticizers, then no extraction problem exists.
