US2261630A - Propellent powder - Google Patents

Description

: Patented Nov. 4, 1941 PROPELLENT POWDER Walter P. Regestein, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing.

Application December '1, 1938,

Serial No. 244,347

6 Claims.

My invention relates to an improvedpropellent powder and in particular to an improved nitrocellulose powder of the cellular type.

It is well known that an important ballistic problem confronting the smokeless powder manufacture is that of producing powders which at- I tain a given velocity with the employment of a weight of charge sufliciently low to provide operable pressures.

Heretofore propellent powders of the cellular type have been commercially unsatisfactory in the above respects. By cellular powders I mean those containing cells wherein the solid has been displaced within the body of .the grain to form minute pockets therein. Such powders are made conventionally by including soluble solids within the structure of the colloid and later dissolving out said solids therefrom to.leave the hollow cells therein.

Such powders of the prior art have been commercially unsatisfactory in that they have been characterized by lack of complete combustion resulting in unusually high residue, exceptionally high weights-of charge for a given velocity, and pressures so high as to be unsatisfactory. This is particularly true of the so-called dense nitrocellulose powders of the cellular type as prepared according to the prior art. The term dense nitrocellulose powder has taken on a fixed meaning in the art and commonly refers to a nitrocellulose powder in which the colloid has been compressed in the process of manufacture, such as by means of a press through dies into ribbons, cords, tubes or the like, or by' means of rolls into sheets, and in general with subsequent subdivision by means of a cutting machineinto grains of suitable size. Naturally, loading companies have avoided the use of cellular powder of this type, due to the aforesaid high weight of charge required for a given velocity and to avoid complaints from excessive pressures, high residue after burning, and the like.

An object of my present invention is a cellular powder of improved ballistic properties. A further object is such a powder characterized by highly efficient burning properties as measured by extremely low residue. Another object is a dense nitrocellulose powder of the cellular type characterized by low weights of charge, low residues and low pressuresat given velocities. A

cellulose, and subsequently removing therefrom, a soluble solid material such as sugar, for ex- 8X Powdered 4X Powdered further object is a process for producing said improved cellular powder.

I have found that the foregoing objects are accomplished and the disadvantages overcome by intimately incorporating in the colloided nitro- The most important application of my invention is in the so-called dense nitrocellulose powders." For the purpose of the present specification and claims, the term "dense nitrocellulose powders shall be taken to refer to that powder in which the colloided nitrocellulose is processed by the application of a compressing force. This powder is usually extruded through dies by means of applying pressure to a colloid contained in a press, or is compressed into thin sheets by passing through rolls. Th dense nitrocellulose powder is thus to be distinguished from the so-called voluminous or bulk nitrocellulose powder which undergoes no such compressing step.

The following is a typical method for the manufacture of a dense nitrocellulose powder according to my invention.

The powder is preferably made from two nitrocelluloses of different nitrogen contents, one soluble in a mixture of two parts of ether to one of ethyl alcohol, and the other of high nitrogen content, practically insoluble in the same solvent mixture. These two nitrocelluloses are thoroughly blended in the pulped condition by stirring under water. The blend may have 1;; nitrogen content varying from 12.90 to 13.30% with a solubility in ether-alcohol from about 50 to 20%, depending on the amount of each type of nitrocellulose used in making up the blend, which in turn is dependent on the particular purpose for which the powder is to be used. The wet blend of nitrocellulose is wrung in a centrifugal wringer to leave about 30% of water in it. The water wet nitrocellulose is then dehydrated in a dehydrating press by means of ethyl alcohol. The blocks of dehydrated nitrocellulose containing the desired amount of alcohol are broken up and placed in a mixing machine. The ether is then added so that the ratio of ether to alcohol is approximately two parts of the former to one of the latter, and the total quantity of ,solvent present is approximately equal to the dry weight of the nitrocellulose. The pulverized sugar is added at this point. Diphenylamine is usually added as a stabilizing agent together with any other special ingredient. The mass of these various ingredients is mixed for about one hour, during which process the ether-alcohol solvent mixture colloids only the soluble nitrocellulose present in the blend, the insoluble nitrocellulose remaining suspended in the colloid in an ungelatinized condition. The sugar, of course, is intimately distributed within the body of the colloid. The colloid,

after mixing, .is formed into blocks by means of a suitable press and these blocks transferred 'to a powder press there, by the use of considerable pressure, the colloid is forced through dies into cords, tubes or ribbons, which are then cut into small grains by means of a cutting machine. These powder grains may be subjected to a solvent recovery treatment to recover the ether and alcohol, and/or a water treatment in which the powder grains are steeped in hot water to leach out the sugar therefrom, leaving a powder having the improved fine cellular texture according to .the present invention. The powder grains may be dried at this point, then glazed and sieved and used as a non-coated powder for a great variety of purposes in rifles, shotguns, pistols and revolvers, in fact in all kinds of small arms.

However, where increased velocity is desired the powder grains are subjected to a surface moderating treatment with dinitrotoluol, dimethyldiphenylurea, or other suitable surface moderating agents, by one of the several wellknown methods, and then finally dried, glazed and sieved. These surface coated powders are also used in all kinds of small arms, the fundamental principle of their use in shot shells being the same as in their use in rifle cartridges.

In order to further illustrate my invention in greater detail, I have summarized in the table given below the results of ballistic tests obtained on three samples of powder in the .22 caliber long rifle, using a high velocity cartridge case with a 40-grain lead bullet. These powders were all made from a blend of nitrocellulose having a nitrogen content of 13.20% with a solubility in ether-alcohol mixture of about 30%. All powders contain 0.6% of diphenylamine calculated on the dry weight of nitrocellulose used. The samples were made up with parts of sugar added at the mixer per 100 parts of nitrocellulose (dry weight) Sample 1 with 4X pulverized sugar, and Sample 2 with granulated sugar as employed in the art. After thorough mixing and colloiding, the three compositions were pressed through dies having diameters of .041 of an inch and cut into grains having a length of A of an inch. The powders from the cutting machine were immediately placed in hot water at a temperature of 55 C. in order to removethe solvent and leach out the sugar. These powders were treated several days in hot water to complete the leaching process. The powders were then removed and surface moderated with dimethyldiphenylurea. These surface moderated powders were then dried, glazed and sieved. The ballistic results were as follows:

Table II t: w m I t M 31 me e erg ns can no Sample g ggi density of velocity presfrom of charge 25 sure 100 powder rounds ioot- LbsJ Per Grains aecemda sq. in. cent 4X pulverized 630 2. l, 298 23, 080 5. 32 Granulatei. 647 2. 60 1, 303 26, 760 10. None 694 2. 70 1, 305 24, 230 10. 45

The pressures given in the above table were recorded with copper crusher cylinders having a diameter of .179 inch and a length of .400 inch, in a pressure gauge having a piston hole located at the mouth of the cartridge case. Lower pressures are recorded by the use of lead crusher cylinders or by making the pressure tests under other conditions."

Sieve tests on the granulated sugar employed in the abovecomparison showed 56.8% coarser than 35-mesh (.0164 inch), 38% between 35 and 65-mesh (.0164 inch-.0082 inch), and substantially all the rest between 65 and -mesh (.0082 inch-.0058 inch).

Comparing the results between Sample 1, 'according to my invention, and Sample 2, made with sugar of the size employed in the prior art, it will be noted that Sample 1, made with the pulverized sugar, burns so much more efliciently than Sample 2, made with the sugar of the size employed in the art, that the residue of the former is less than that of the latter, while a weight of charge of only 2.2 grains is required for the former to produce a given velocity as compared with 2.6 grains for the powder of the art. Furthermore, it will be noted that a much lower, and accordingly much more satisfactory; pressure is obtained with the powder of my invention. The residue is calculated on the basis of 100 rounds fired in the .22 caliber long rifle. This residue represents, chiefly, unburned powder collected from a very large sheet of paper placed in front of the rifle, plus any residue remaining in the gun after firing the 100 rounds. Furthermore, the amount of residue from 100 rounds of Sample 1 was less than the residue from 100 rounds loaded with a surface moderated nitrogylcerin powder fired for comparison. Sample 3 indicates the disadvantages of a non-cellular dense nitrocellulose powder.

I attribute the improvement in ballistic qualities and burning characteristics of Sample 1 over Sample 2 to the presence of an almost infinite number of microscopic cells distributed throughout the powder grains in Sample 1 as contrasted with the relatively large pores present in Sample 2, made with granulated sugar according to the art.

In addition to determining the marked improvement in ballistic qualities obtained with the use of the pulverized sugar, I have also determined that by varying the fineness of subdivision of 'the pulverized sugar employed, and by varying the amounts of said sugar employed, I may produce powders adequate for a largevariety of cartridges for use in all kinds of small arms where any given velocity is desired with a minimum of pressure and a minimum of unburned powder. The following table shows the ballistics obtained on various samples of uncoated powders in which the pulverized size has been varied over a considerable range. The powders were tested under the same conditions as the samples of -mesh screen.

Table II, previously mentioned, but at a lower velocity as indicated.

.22 caliber long rifle components, the bullet weighing 40 grains. Pressures were recordedwith Winchester 146L400 coppers. Each test repre- In general, the effect of increasing the fineness of the pulverized surgar employed appears I to be a lowering in the weight of the charge while maintaining the ballistics fairly constant, This effect is most noticeable in the coated powders which are shot at higher velocity. The small differences in pressure can be accounted for by the non-uniformity in components. In Table V a similar situation is shown with respect to both coated and uncoated powders with various types of sugar obtained by blending standard grades so that the given "percentage through-200-mesh is known.

Table V Sam S Weight 5523 Mean Coat- I ple g of charge Over 50 pressure ing Liza/sq. l1 Grains in. Parts l 50% thru 20041113511- 1. 61 l, 154 22, 370 None ll 75% thru mil-mesh. l. 60 l, 154 20, 370 None I 12 6X sugar l. 56 1, 151 None 13 50% thru ZOO-mesh. 2. 2| 1, 300, 26, 150 3 l4. 75% thru 200-mesh. 2. 18 1, 303 24, 000 3 15.- 6X sugar 2. 12 1, 299 25, 590 3 16".. 50%thru 200-mesh... 2.28 1,300 23,630 3% 17.. 75% thru mil-mesh 2. 23 l, 299 22, 820 3% 18. 6X sugar 2. 18 1, 300 21, 800 3% Coating was .dimethyldiphenylurea.

In the preparation of the above samples, the composition of the powder was 100 parts of nitrocellulose, parts of sugar, and "0.6% diphenylamine. The various mixtures of sugar employed were obtained by blending standard 6X sugar with a, slightly coarser sugar in such proportions that 50 or 75% of the sugar would pass a 200- The powderwas granulated at .041 x 1/150. Tests of both coated and uncoated I powder werermade in theRemington Hi-Speed Table III sents a 10 shot series, The uncoated powders G 5 show a slight. but distinct lowering of "the weight ravi- Sam s meme Weight Inst: Mean of charge as the size of the sugar particles deple 128 of sugar used delzsflty chgige prw creases. In the case of the coated powders thispowder Sure effect is more pronounced. Further variations in properties of the powders v 10 were obtained by varying the percentage of sugar. /115 mesh 567 f g incorporated therein, as shown in the following mesh 570 1.52 1,152 221470 table: 7 e Thru mesh 550 1.51 1,151 22,460 Table The sugar size is given in terms of the mesh 15 43mg 7 through which all of the material passes along Sample sugar metric Weight X. Mean with the mesh on which all is held. For instance, oi fit tii er wilds mm 100/115 indicates that substantially all passed through a 100-mesh and substantially all is held Per may, on a 115- mesh, It will be noted from the fore- 20 cm! Grains 4 going table that the weight of charge can be $3 3 lowered appreciably by varying the type of pul- 15 1:160 verized sugar employed. The same situation is 2 {:22 i1 f8 313 shown in Table IV with respect to powders coated I 485 39 1-158 291870 with three parts of dimethyldiphenylurea. 58 $33 113,8 ,1; it? 25123 Table IV These results show an increase in emciency' as the Sam (ivy I ht Inst M perezergage of sugar ifs inerl easedhsnce tehef p311- size orsu mused me 1'10 '91 v loci't can VB! e sugar 1S pre era y 83.0 e 011 0 e P g f gg fig charge 2513 pressure 30 powder by steeping with hot water, it is customary to refer to the amount used as so many G Few flirts based on 101? parts of nitrocellulose rather ra ns sec s in. an on a percen age basis of composition. Be- Zjiji: "iiiiiifi 233211: 1 .32 3:53 1:333 it?" tween 5 and 25% of sugar, the ballistics are Thru 180 mesh-U. 5 -06 1,304 7,7 35 practically the same, while the weight of charge drops progressively from 1.75 grains to 1.44

powders satisfactory with respect to pressures, I

with very low weights of charge, adequate velocity, and extremely low residues. It will be appreciated that the size of the cells .in the finished powder will be measured by the size of the sugar displaced therefrom, with allowance for small changes which the powder goes through in the leaching and drying stages.

In particular, the powders of my invention are characterized by relatively high gravimetric densities. It is true, for example, that in spite of the cellular structure obtained, my dense nitrocellulose powders have gravimetric densities much higher than the so-called vo1uminous" or bulk powders. My powders are particularly useful in a large variety of cartridges for usein all kinds of small arms where the highest velocity is desired with a minimum of pressure and a minimum of iinburned powder.

I do not limit myself to any particular amount of moderating agent used in the manufacture of my powder. I have found that the amount of dimethyldiphenylurea, for example, can be in- I creased or decreased in accordance with the purpose for which the powder is intended. In place Furthermore, I do not limit myself to the values of nitrogen content or solubility of the nitrocellulose given above, it being understood that the compositions given are for the purpose of illustration only. While I. prefer to use a mixture of two types of nitrocellulose, one soluble in and the other insoluble in an ether-alcohol mixture, it should be understood that my invention relates to improvements in dense nitrocellulose powders whether they be made from one type of nitrocellulose obtained in a single nitration or a blend of two or more types of nitrocellulose obtained in two separate nitrations under difi'erent nitrating cqnd My invention is also applicable to dense nitrocellulose powders in which the colloid containing the pulverized sugar may be, after drying, subdivided by grinding and sieving instead of being subdivided while soft by means of cutting machines: Furthermore, my invention is not limited in principle to the dense nitrocellulos powder but is applicable generally to nitrocellulose powders as a whole. Indeed, it may be applied to powders containing nitroglycerine as well as nitrocellulose. However, it should be remembered that by far the most beneficial effects are obtained when applying the same to the dense nitrocellulose powder.

Although I have described my invention in the foregoing with particular reference to the use of sugar as the soluble solid material which is displaced from the powder, it should be clearly understood that this is merely the preferred form of the invention, and that the invention is not limited to sugar alone but includes soluble solids in general, such as, for example, soluble salts of the type of potassium nitrate or the like.

I particularly do not limit the use of powders made in accordance with my invention to rifle cartridges. I have found that the powders are very suitable for use in all types of small arms, shotguns, pistols and revolvers, in addition to sporting and military rifles. For example, the following table demonstrates the suitability of my improved cellular powder for use as a shotgun load.

Both of these powders give ballistic results which compare favorably with standardiconventional shotgun powders, but have the additional advantage of being much cleaner burning.

Accordingly, I intend to be limited only in accordance with the following patent claims:

I claim:

l. The process of producing a dense nitrocellulose powder of improved burning characteristics which comprises forming the colloid, incorporating in the colloid pulverized sugar of such a state of subdivision that substantially all the particles thereof pass through a standard loo-mesh screen having openings of .0058 of an inch in width, subjecting said colloid to a compressing force, forming said compressed colloid into grains, and leaching out said sugar from said grains.

2. The process of producing a dense nitrocellulose powder of improved burning characteristics which comprises forming the colloid, incorporating in the colloid pulverized sugar of such a state of subdivision that the greater part thereof passes through a ZOO-mesh screen having openings of .0029 of an inch in width, subjecting said colloid to a compressing .force, forming said compressed colloid into grains, and leaching out said sugar from said grains.

3. The process of producing a dense nitrocellulose powder.of improved burning characteristics which comprises forming the colloid, incorporating in the colloid from 5 to 25% of pulverized sugar based on the weight of nitrocellulose, said sugar being in a state of subdivision such that substantially all the particles thereof pass through a standard IOU-mesh screen having openings of .0058 of an inch in width, subjecting said colloid to a compressing force, forming said pressed colloid into grains, and leaching out said sugar from said grains before drying them.

4. A dense nitrocellulose powder of improved burning characteristics comprising colloided ni- 5. A dense nitrocellulose powder of improvedburning characteristics comprising colloided nitrocellulose having a fine cellular texture resulting from the removal therefrom of pulverized sugar of such a state of subdivision that the greater part thereof passes through a 200-mesh screen having openings of .0029 of an inch in