US2320243A - Smokeless powder composition - Google Patents

Description

May 25, 1943. B. H. MACKEY 72,320,243

SMOKELESS POWDER COMPOSITION Filed Sept. 28, 1940 :BiZZHam g Ma mvEfl 'oR ATTORNEY of its ballistic performance.

.of perforated strands or strings.

2,330,243 smomnss Powmm COMPOSITION Bill Harry Mackey, Wilmington, Del., asslgnor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware Original application March 27,1940, Serial No.

Divided and this application September 28, 1940, Serial No. 358,774

3 Claims.

This invention pertains to a smokeless powder having novel physical characteristics, and more particularly to such smokeless powder in the form of grains having definite dimensions.

This application is a division of my co-pending application Serial No. 326,162, filed March 27, 1940, and contains matter divided out of said co-pending application.

Smokeless powder is usually produced as grains of predetermined size and shape because of the fact that such grains permit some control over the burning of the powder and consequently Often perforations of predetermined size extend through the pow-" der grains, said perforations being designed to afiord an increase in the burning surface as as combustion progresses.

Heretofore, smokeless powders of this type have been produced by forcing a colloid of suitable composition through one or more dies in a press, the colloid issuing therefrom in the form This process has been characterized by the flow of the colloid in a single direction only. Thus, although many dies of widely varying structure have been employed, all of them permit a substantially straight flow of the colloid through the die. After issuing from such dies, the strings of col loid are fed to a cutting machineadjusted to cut segments of the desired length. The green powder grains are then treated in a system which permits recovery of the major part of the solvent, following which they are dried. The resulting conventional powder grains invariably exhibit two outstanding defective characteristics: First, the grain has shrn'rjik much more across the diamcter or web thaii it has in length; second, upon impact the grain shows a cleavage along a line parallel to the longitudinal axis of the grain, rather than across its diameter.

These characteristics are undesirable because the proper ballistic performance of the powder is dependent upon the grains remaining as integral units during the combustion of the charge, rather than breaking into fragments, since fragmentation of said grains exposes a burning surface exceeding that calculated as desirable, with the result that erratic ballistic performance may be'obtained. Various attempts have been made to overcome this undesirable phenomenon, said attempts being directed to a composition better able to withstand the pressures developed, and also to charges of such design-that fragmentation will be less apt to occur. Thus, varying amounts of guncotton and pyro-cellulose have been blended in order to obtain a tougher composition. Likewise. diiferent solvents have been employed and numerous additional ingredients have been incorporated in the composition for this purpose. In addition, experiments have been'made wherein the powder charge was arranged with respect to the ignition charge in order to prevent travel of the charge, as by spacers for example, so that fragmentation would be eliminated or at least diminished appreciably.

The foregoing modifications have in general effected an improvement, but in no case can conventional powder be fired with the assurance that fragmentation and consequent erratic ballistic results will be avoided.

The object of the present invention is a smokeless grain of superior physical strength. Another object is a. smokeless powder granulated to definite dimensions which possesses a greater resistance to impact than that of any such powder grain heretofore known to the art. A further object is a smokeless powder grain which, upon the removal of solvent therefrom, shrinks substantially uniformly in all dimenslouch-Other objects will become apparent as this invention is described more fully hereinafter.

I have found that the foregoing objects are accomplished by means of a smokeless powder grain having a random or improved orientation of the particles of material of which the grain is composed. The method of forming such a grain is disclosed more in-detail in the original application which has been referred to hereinbefore.'

I have found that the two undesirable characteristics mentioned hereinabove, namely the uneven shrinkage and extreme frangibility, can be overcome through the particle orientation achieved if, while forming the grain, I prevent flow of the colloid in one direction only. Thus, if in the formation of the final grain the colloid be moved in a helical or concentric path, the behavior of the finished grain is altered remarkably. The particles then are not aligned in one direction only, but rather point in numerous directions lying at various angles in many differ- Referring in general to the various figures of the drawings, Fig. 1 is a cross-sectional view in elevation of a die mold adapted to form a grain of the type disclosed in the present invention. Fig. 2 is a cross-sectional view in elevation of a die adapted to the continuous formation of a string of colloid which possesses random orientation. Fig. 3 is a plan view of the same. Fig. 4 is a view in cross-section of a string of powder as it is formed when using a die of the type set forth in Figs. 2 and 3.

The following example refers in greater detail to a comparison of the prior art method and the present inventive method of forming smokeless powder grains.

Example A solvent-containing smokeless powder dough is macerated, pressed into a block, and the block extruded through small orifices, thereby forming the material into strings. A portion of these strings was pressed and extruded through the conventional type of die. The colloid was forced by pressure through the openings of the die head D- (over-all diameter, d (diameter of perfora- 1.l05" tions), 0.106" IW (inner web) 0.285" OW (outer web), 0.182"

The length of the powder-grain was 1.90".

The second portion of the colloid was divided into predetermined quantities and charged into die molds of the type shown in Fig. 1, wherein Ill represents a die head having the die pins l I, said die head fitting snugly within the walls l2. Pressure was applied by appropriate means via the piston IS. The particular die molds employed were designed to yield a green smokeless powder grain having dimensions identical with those produced above. Thus, grains having identical size and shape were produced, the sole difference being in the actual formation of the final grain. Both types of grains were dried under identical conditions to the same content of volatile material, and were then measured todetermine the shrinkage of the various dimensions. The amount of shrinkage determined by measurement of numerous grains is as follows:

Grains Shrinkage 13 Molded grains A Grains formed in usual manner..

The foregoing data reveal that the A type grains shrank over 5 times as much in diameter shown (Fig. 4) it is clear that more can be added asses la as they did in length, whereas the molded grains (type B) showed that the shrinkage in diameter was approximately equal to that in length.

Grains of the present invention exhibited a strikingly large increase over the ordinary powder grains with respect to resistance to impact. This was shown by a test wherein the dried A and B grains were placed on a smooth metal surface, and fiat metal weights were .permitted -to fall on the grains in that position. In order to eliminate possible irregularities in the grains, /2" sections were taken from each grain, and these sections subjected to the test. The results were as follows:

Wt. of falling Distance required to crack metal Grains grams Pounds No breakage-69" max. ht.

1 Some grains failed to break when the weight was dropped from the maximumheight of 69 inches.

In conducting the foregoing impact tests, it was noted that the A grains almost invariably cracked along the longitudinal plane regardless of the position in which the grains were placed. Whether they were placed with the cross-section uppermost or to one side made no difference.

- the longitudinal dimension of the pins. The

if desired. Referring to Fig. 4, it may be seen that the particles of the smokeless powder colloid, due to the direction in which they are forced in the die, take a path which is helical or concentric, so that the string of powder is composed of particles which have been aligned in one direction only, since in moving through the die they are forced in a tortuous path, which is indicated by the fine lines representing the smokeless powder colloid.

The fact that prevention of streamlined flow of the colloid during formation of the powder grain should cause the properties of the finished powder grain to be different is very surprising, in view of the fact that the usual manufacture of smokeless powder entails working of the colloid to a considerable extent prior to final formation of the grain. Thus, the solvent-laden colloid is thoroughly mixed, macerated, pressed in a blocking press, and then extruded through small orifices prior to its extrusion in final form. Due to this rather extreme treatment, it was commonly believed that the fibrous structure of the nitro-cellulose had been substantially destroyed and that the colloid was essentially homogeneous. Therefore, it was natural, in the absence of explanation, to consider the non-uniform shrink- The colloid is forced esc ees tudinel axis of the promos inherent oherecter istics of smokeless powder; That this is not true is demonstrated by the feet that powder ermine mode in accordance with the present invention, difierlng-irom the usual powder grains in that they are composed of particles having random orientation, also exhibit very different physical characteristics. These cherecteristics include uniform shrinkage of the powder grain'in all dimensions upon removel or the solvent therefrom, increased resistance to impact, end an irreeulsr cleaveee pattern. I

By producing: e powder having an impact re sistunce for superior to'thet oi powders of similar shape and composition, it is possible to deoreese, and in many cases-to elimineterthe iratementotion of smokeless powder charges which gio occurs upon initiation. Moreover, the grains oi e the present invention, although they do exhibit very difierent physical characteristics from the smokeless powder grains known heretofore heiore ignition, show no substantial change with rerpect to burning. it follows, therefore, that the erratic lmllistic performance due to the frogmentotion of the powder grains may be proportionately reduced or eliminated. Likewise, theadoption oi grains of this type obviates the necessity oi enercisincsome of thepreceutions heretoiore taken to keep fragmentation to the limit. um possible degree, such es spacing of the chcree ior example.

, it will he evident to those skilled in the smokeless powder art that the foregoing description permits oi variations without departing from the spirit or scope oi the invention. I intend, therefore, to'be limited only in accordance with the following patent claims;

I claim:

1. In e, smokeless powder charge adapted to resist fragmentation upon initiation, a grain of definite dimensions which'possess a random orientation or the particles thereof.

2. In a, smokeless powder charge adapted to resist fragmentation upon initiation, a grain pressed to definite dimensions, seid grain possessinc a. random orientation of the particles f thereof and having at resistance to impact meterielly greater than grains of similar composition which have been extrudedthrough a die importing streemlme flow.

3. A powder grain of definite dimensions, having random orientation of the particles of which it is composed, said grain having been shrunk

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