US2230848A - Progressive burning smokeless powder - Google Patents

Description

Patented Feb. '4, 1941 2,23%,848

UNITED STATES PATENT OFFICE PROGRESSIVE BURNING SMOKELESS POWDER Walter P. Regestein, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application October 4, 1939, .Serial No. 297,868

9 Claims. (Cl. 52-22) This invention pertains to progressive burning wise, if a material which is a solvent for the coatsmokeless powder and more particularly to an ing agent be employed, this material almost inimproved method of producing such powders havvariably is also a solvent for the nitroglycerin, ing high potential strength. i so that obvious difiiculties again arise.

" Those engaged in the manufacture of smoke- The object of the present invention is an imless powders realize that variations in the relative p d pr ressive burning nitrogl ri nburning rate at difierent instants during com-bustaining powder. Another object is a novel methtion of the powder are accomplished by variations ed for producing such powder, said hod ein 1 in the ballistic performance of said powder. characterized by enhanced safety and ease of oprelative burning rates at different instants durdding nitrogly erin to smokeless powde grainsing combustion has been effected in order that Other objects will become ap as the inventhe optimum ballistic performance might be attion is described hereinafter.

tained. This regulation has led to the develop- I These objects are attained by tr ng smokement of a class of powders which are commonly less powder of predetermined granulation with a referred to as progressive-burning powders. Coating a ent according to known p e ure a Although progressive burning powders ha then adding nitroglycerin or other explosive liquid been produced by various methods, perhaps the nitric esterffio the ate Po e ai s. said most practicable has been the one whereby the grains being susp i a l q d e um at the surface of the powder grain is modified by coattime the nitroglycerin is brought in contact thereing with a surface moderant such as diethyl diwith. Quite unexpectedly, such procedure does phenyl urea, dimethyl diphenyl urea, dinitronot Cause Substantial Change in the effect of the toluene, dibutyl phthalate, diethyl phthalate, and coating a n hat is to s y, t alli ti p the like. The m d t-, cause th outer layer formances of the powders made in accordance of the powder to burn m slowly, t t with this method are similar to those yielded by sult that the ratio of the pressure development in powders of he same composition produc d y a the later stages f mbu ti t th n; at t process wherein'the surface moderant is applied stages immediately following ignition is material-, t a P e already Containing e explosive q- Whereas vari m th d have beenpdeveleped on the surface of the powder grains increases mawhich are practicable for coating powders free tel'ially the rate at which the powder absorbs the from explosive liquid nitric esters, such as nitroliquid nitric esterglycerin for example none of the methods pres- The process is applicable to granulated smokeently kno n is m et g ti f t when less powder compositions generally. These grains ployed in onjun tion ith powder grams, may or may not contain a substantial amount of {gaining nitroglycerin or it equivalents. The the volatile solvent used for their manufacture. difflculties encountered in the attempt to coat need e r n be ma e in accordance with said nitroglycerin-containing smokeless powder any particular process, but instead may be proalmost invariably must be applied in a liquid or nitrocellulose in the presence of water or solutions molten state. In order to reduce the coating by the addition of suit-able solvents thereto while agent to this condition, it is necessary to employ a t i such mixtures. or e p w ins a solvent forv the coating agent or to supply heat y e for ed by the extrusion of colloided or sufilcient to melt said coating agent, or possibly to partially colloided nitrocellulose from a press, in use a procedure involving both elevated temperathe form of tubes, rods,,,or the like. Thus, the

Consequently, in some cases. regulation of the oration. A further object is a novel method of 1 1y higher than 11-, uld h were th powder not uid nitric ester. Moreover, the presence of modsubjected t thi c mi t t m; erants or coating agents, such as dinitrotoluene,

arise because of the fact that the coating agent duced by a me h involving the colloiding of the tures and a solvent. The use of elevated temparticular process by which the base grain is peratures in conjunction with materials containmade does not constitute a deteimining factor.

factory because of the hazard involved, but, in process particularly attractive when used in conaddition, such use causes loss of some of the nijunction with a cellular type grain which is protroglycerinby volatilization with the result that duced in accordance with my copending applicait is difficult to produce various lots of powder tion Serial No. 244,347, filed December 7, 1938, be-

ing nitroglycerin not only is generally unsatis- However, it may be stated that I find the present having the same ballistic performance. Likecause of the high absorptive capacity of this type I of grain. Likewise, the composition of the powder or base grain, as I prefer to call it, may be varied widely without causing deleterious effects. Thus, the nitrocellulose present in the base grain may be of the soluble type or may -be a mixture of soluble and insoluble nitrocellulose.

The base grains are surface treated with a well-known moderant for smokeless powder. Such moderants include dinitrotoluene, either liquid or solid, diethyl diphenyl urea, dimethyl diphe'nyl urea, dibutal phthalate, diethyl phthalate, and the like. Although both liquids and solids are included in the foregoing examples, all have the power of gelatinizing or plasticizing nitrocellulose to some extent.

As stated hereinbefore, the coating of the base grain may be effected according to known procedures. Following the coating operation, the surface treated grains are agitated in the presence of water, and the required amount of nitroglycerine is added to the powder-water slurry at the maximum permissible rate. If the rate of addition of the nitroglycerin is materially greater than the rate at which the nitroglycerin is absorbed by the nitrocellulose, agglomeration or caking of the grains of the finished powder will occur. Said maximum rate, of course, is not a constant, but rather must be established for each type of base grain employed. In general, however, said rate decreases as the density of the base grain increases.

The following examples illustrate my novel method in greater detail.) They-serve merely as specific embodiments and are not intended to limit the invention:

Example 1 Twenty-five pounds of a shotgun type powder having a nitrogen content of 12.60% and sieved through a 14-mesh standard screen and caught on a 38-mesh standard screen were coated with five parts of dinitrotoluene by intermingling the powder and coating agent at a temperature of about 75 C. in the presence of water. After coating, the powder, together with 75 lbs. of water, was charged into 'a vessel provided with means for agitating vigorously the powder-water mixture, the temperature of said mixture was raised to 35 C., and then 10.73 lbs. of nitroglycerin were added to the agitated slurry. Two hours were required for the addition of this quantity of nitroglycerin; the rate of addition decreasing progressively during this time interval. After the addition of the nitroglycerin had been completed, agitation of the mixture was continued for a period of one hour, the temperature being maintained at 40 C. throughout the entire three-hour period. The impregnated powder was se arated from the water and then dried. Analysis of the finished powder showed that it contained 30 parts by weight of nitroglycerin. Inspection of the grains failed to reveal the presence of any free nitroglycerin on the surface thereof, nor was there in evidence any undesirable aggregation or clusters of said grains.

Example 2 An additional 25 lbs. of the identical base grain described in the foregoingexample were treated in the present example. In this instance, however, the base grain was not coated, but instead was charged into the apparatus employed for the addition of nitroglycerin to the powder grains. The method of introducing the nitroglycerin into the powder grain, the ratio of the various in gredients, the temperature, etc., were identical with those prevailing in Example 1, so that the resultant powder not only had the same amount of nitroglycerine present, but also had been made in the same manner as the powder described in said example. Inspection of the powder in this case, however, showed that there was a definite tendency for the grains to cling to each other and thus cause the formation'of clusters or aggregates,.which could not be broken down very readily. Said formation of aggregates indicates that the nitroglycerin was absorbed slowly and thus permitted sufiicient nitroglycerin to remain near or on the surface of the powder grain to render said surface soft and sticky. Hence, when two or more grains having such surfaces, came into contact with one another during the course of the operation, they united and became cemented together when the powder was dried.

As stated hereinbefore, explosive liquid nitric esters other than nitroglycerin may be employed quite satisfactorily. Among these may be mentioned tetranitrodiglycerin, ethylene glycol dinitrate, trim'ethylene glycol dinitrate, propylene glycoldinitrate, and the like. When one of these explosive liquid nitric esters is used instead of nitroglycerin, slight modifications in the mode of procedure are made in order to compensate. for the difi'erences in the physical properties of the various materials. Thus, for example, if the par ticular material employed possesses a high solubility in water or a high vapor pressure as compared to nitroglycerin, these factors must be considered in order to produce a finished powder of given composition. The principle of operation, however, remains unchanged.

The desirability of smokeless powders made in accordance with my novel process is indicated by reference to the following example which sets forth the median ballistic performance of various powders adapted for use as .22 calibre long rifle ammunition, said performance representing the results obtained after the firing of many rounds:

Example 3 Weight of Mean Pressure Powder charge, velocity, I grains bs./s.1.|n.

A 2.25 1,295 21,860 X 2.05 l, 312 22, 710

In' the foregoing example, A represents a coated nitrocellulose-nitroglycerin powder made by a process whereby the nitroglycerin is incori it is necessary to use 0.2 gr. or 10% more powder than when X powder is used, so that'the advantages of this latter composition are appreciable.

It will be understood that I do not contend that powders made in accordance with the present invention yield ballistic results heretofore unknown. Such is not the casefb'ut all other known methods of producing a powder capable of similar performance entail the disadvantages set forth hereinbefore.

It will be apparent to those skilled in the art that the description herein permits of many variations without departing from the spirit and scope of the invention. Thus, the liquid constituting the medium in which the powder is suspended while the liquid nitric ester is added thereto, may be composed of flash inhibiting salts in aqueous solution. Likewise, the powder at the time of the nitric ester addition may contain varying quantities of solvents, both of the volatile and non-volatile type. Indeed, experiments have shown that in the case of a densely colioided powder, the presence of a quantity of volatile solvent exceeding that usually deemed permissible in a finished powder, is a material aid to the absorption of the liquid nitric ester. I intend therefore to be limited only by the following claims.

I claim: I

' 1. A method of producing a progressive burning smokeless powder of high potential energy, which comprises forming a nitrocellulose base grain, coating said base grain with a moderant and then adding an explosive liquid nitric ester to the coated grain while maintaining said coated grain in a water-suspension.

. grains with a plasticizer for nitrocellulose, suspending said coated grains in an aqueous liquid, adding an explosive liquid nitric ester to said suspension, separating the resultant powder grains from-the liquid and drying said powder.

ing smokeless powder, which comprises coating 4. A method-of producing a progressive burnnitrocellulose base grains with a plasticizer for nitrocellulose, agitating said coated grains in the presence of at least an equal quantity of an aqueous liquid, adding nitroglycerin at a rate not exceeding that at which the nitroglycerin is ab- :orbed, separating the resultant powder and dryng it.

5. The method of claim 4, wherein the plasticizer for nitrocellulose is dinitrotoluene.

' 6. The method of claim 4, wherein the plasticizer for nitrocellulose is diethyl-diphenyl-urea.

7. The method of claim 4,'wherein the plasticizer for nitrocellulose is dibutyl phthalate.

8. A method of producing a progressive burning smokeless powder, which comprises forming base grains of nitrocellulose structure, coating the surface of said base grains with dinitrotoluene, producing a powder-water suspension by agitating said coated base grains in .the presence of about three times their weight of water, adding from 5 to 40 parts by weight of nitroglycerin at a rate substantially equal'to that at which the powder absorbs the nitroglycerin, continuing the agitation after all the nitroglycerin has been added, and separating the resultant powder and drying the same. 9. A method of producing a progressive burning smokeless powder of high potential energy, which comprises adding a finely-divided watersoluble solid to the nitrocellulose-containing colloid, extruding said colloid through dies, and cutting it into grains, leaching the grains in water in order to remove the water-soluble solid therefrom, coating the resultant grains with a moderant, suspending said coated grains in an aqueous liquid, and adding an explosive liquid nitric ester to the coated grains while maintaining said coated grains in a water suspension.

- WALTER P. REGES'I'EIN.