US2577298A - Flashless powder sheet - Google Patents

Description

Patented Dec. 4, 1951 in, f w imingeet, 113a ternity, b y. g'nfiiiits, to-"th e United States of America-as represented by th secretary'of War NkiDi'afwirTg l plicat on May 3 fg4e, Serial No. 667,128

-' mm -invention i erates to s'friokelss tamer *an'qflniore "mammary, to "a solventleS's-"tyne smokeless powder sheet suitable'for-use in trench inortars.

Smokeless"powdersysuitahle for usees prepei- "the"" ne-i'ghborhood" of 12 500 'poun'ds per square Considerations infiuencirig thl'e's'e requirements *arethe length and thickness bf thembrtarhar- *relandthespace available forth'e propellent. "It

- Will b'eappreciated, in view of the lin'lite'oi space is that they be of a nature such that they lend i' themselves to manufacture intosheets by a rolling operationas customarily practiced inthe pro- .duction of mortar-typepowders. Althoughnot requirement, ;-it is also-highly desirable and somewhat; essential 'that such powders "be substantially fiashless when fired The shortness of the mortar barrel together-with the ballistic;requirements make this very difficult of attainii t the present "time these requirements are inlet in part by a mortar-type powder sheet havinga thickness in the neighpprhood of 0.025 inch, "a calorificvalue of about 1250 calories per-grain, ancljacomposition comprisingnitrocellulose and nitroglycerin in combination with other suitable a dld rab e ma l th er ic .cqm- T on of this type-is nitrocellulose'abo'ut 52%, l nitro cerinjabout 43%, diphenylamine about 0.0% ;dieth"yl phthalate about 3%, andpotassiumnitrate about 1.25 --Although such powder f-sheets. give the desired ballisticproperties they are subject to the disadvantage thatwhen fired ."irom a mortar and particularly the 4.2-inch {chemical mortar they produce a flash which fbefs'een'atnightfrom along distance. Such I" ishi s readily p'iekedupby aln alert enemy and usuall'fisults inne'niy fire which may beefic- (CL IOZ DS) =2 itive nougm destroyene or 'nrore r'nortars ahd kill *or *woundthe'-'o'peratiiig "persdri'ri'el. Previous atth'ipts to eliihiriatethe muzzre ria sh of mortar-type powders, as by varying th coniposition-of -the' powdrfaddingfiash depressants, etc, have been genera11y unsatisfactOTY, The *utilization 6f 'powd'e'rs -'having lower "calorific "values h'a's not been considered feasible, siri'ce "skilled worliers in the art have' -s uppos'e thata powder of high calorificvalue w s necessary in "order'to o'btain required muzzle' velocit'ies within fixed pressure limits. Furthermorefkrfown powder compositions of lower calorific value are not suitable for use as 'mortar-type powders, since theirna'ture is such that they are not susceptible 'of-finanufacture in accordance with th' {and additionally --do mot-give the I lis'ticpropertiessuchas, for quisite -m-uzzlevelocity1 ll be obtained -by a-relati'v-ely large increase F in the weight-of the 'powder charge. However, when this is attemptedexcessive pressures are likely to be encountered and it frequently becomes 'necessary, in iewer the li'rnited propellant charge space available in most mortars, to redesign the :mortar toaccornmodate the increased icharge. This always results ina lowering ofpro di1cti6'n which is particularlycriticalintime 'of war. I

The'above disadvantaes' weaver-come b'y 'this invention by p'rovid'ing a"niortar-ty1iie smokeless powder sheet having athickriess substantially less than that hithertdused, a "calorific' value I or from 900-1-1'00calori'es' perlg'ram, which produces substantially no flash when fired in a 42-inch chemical mo'rtar; and which fulfills all ballistic requirements of this type of powder without re quiring any modificatidn of existing mortar cons't'ruc'tion. t

In accordand'with the'bresent' inventidnthe mortar-type smokeless 'riowder sheets may ccm- -prise frofn about to about 58% nitrocellulose (12.2% to 13.4% nitrogen content), about'-'-1"2'% 'to{ about 44% nitroglycerin, "about 2% 'toabout 10% of a COOIiIlgp1asticizer,-fro'm'abo'ut 0% to 'about35% of diethanol nitrami'ne dinitrate, a small amount of stabilizer such as diphenyla'mine "or ethyl centralite, a small amountof inorganic salt to facilitate ignition and regulate burning, and in some cases asmall amount of a desensitizer. Theproportion of the cooling plasticiaer Examples I and II. The powder sheets may be manufactured in accordance with a process which will generally include the steps of mixing, drying, rolling into sheets, and sewing, slitting, and punching the sheets into packs, bundles, etc., as required.

The thickness of the finished powder sheets will vary with the size of the mortar and will be coordinated with the diameter of the bore and the length of the barrel so that the requisite ballistics are obtained without a substantial increase ;in the weight of the charge over that necessary in powders of higher calorific value now used for this purpose. Where quick burning is required, as in the case of a mortar with a relatively short barrel, the sheets should be relatively thin. Where longer burning is suitable, as in the case of a comparatively long barrel, the sheets may be thicker. Thus, for the 4.2-inch chemical mortar, the thickness of the sheets may vary from about 0.012 inch to about 0.020 inch but is preferably about 0.016 inch. For the 60 mm. trench mortar the sheet thickness may be as little as 0.003 inch.

' In all cases the thickness of the sheets will be substantially less than and of the order of about one-half the thickness of those utilized heretofore for this purpose. This is made possible by the low calorific value of the improved powder composition of this invention.

The following is an example of a preferred powder made according to this invention.

Example I Percentage Material: by weight Nitrocellulose (13.25% N) 55.00 Nitroglycerin 33.65 Diphenylamine 0.60 Diethyl phthalate 9.50 Potassium nitrate 1.25 Methyl cellulose (added) 0.20

The ingredients were mixed, dried, rolled into sheets 0.016 inch thick, and the sheets cut, sewed, slit, and punched into packs, bundles, and half bundles for the 4.2-inch chemical mortar. This powder had a calorific value of 1007 calories per gram;jand produced substantially no flash when fired-at night in the 4.2-inch mortar. A charge weight of 3284 grains of this powder, when utilizedto fire a projectile from a 4.2-inch mortar, produced a mean muzzle velocity of 812 feet per second and a mean pressure of 10,300 pounds per square inch. 2958 grains of a standard powder having a calorific value of 1250 calories per gram' produced a mean muzzle velocity of 817 feet per second and a mean pressure of 11,600 pounds per square inch under similar conditions.

Another preferred embodiment of this invention is given by the following example.

Example II 3 Percentage Material: by weight Nitrocellulose (12.60% N) 51.00 Nitroglycerin 15.00 Ethyl centralite 1.50 Diethyl phthalate 3.25 Potassium. nitrate 1.25 Diethanol nitramine dinitrate 1 28.00

This powder was mixed by the slurry method rather than the standard Schrader method. The

nitrocellulose was suspended in ten times its weight of water heated to 85 C. and the nitroglycerin added while stirring. The centralite and g diethyl phthalate were added and the whole stirred for 15 minutes. The diethanol nitramine dinitrate was added, while stirring, and the mixture cooled to 57 C. and held there for fifteen minutes. Then the whole was cooled to below C. and filtered. The material was then dried, and rolled into sheets 0.016 inch thick in accordance with the usual procedure for manufacturing trench mortar powder.

This powder had a calorific value of 1036 calories per gram and produced substantially no flash when fired at night in the 4.2-inch mortar. A charge of 3200 grains produced a mean muzzle velocity of 807 feet per second and a mean pressure of 9925 pounds per square inch when fired in the 4.2-inch mortar. This compares favorably with a mean velocity of 817 feet per second and a mean pressure of 9200 pounds per square inch obtained with 2956 grains of a standard powder under similar circumstances.

From the above examples it will be seen that there has been provided a mortar-type powder of low calorific value which is substantially flashless when fired in a mortar at night, and which meets all ballistic requirements of a powder of this type.

In practicing this invention the nitrocellulose content of the powder should be held within the range of from about to about 58%. Utilization of percentages above and below this range is not satisfactory, since the resultant powder is not suitable for rolling into sheetsasfrequired in the manufacture of mortar-type powder. The nitrogen content of the nitrocellulose used may vary from about 12.2% to about 13.4% but is preferably within the range from about 12.6% to about 13.3%.

The nitroglycerin and cooling plasticizer are incorporated in proportions to obtain a calorific value of 900 to 1100 calories per gram with the amount of nitrocellulose used. Thus, when the percentage of nitrocellulose is increased with respect to the percentage of nitroglycerin, the percentage of cooling plasticizer may be decreased. The nitroglycerin will be present in amounts ranging from about 12% to about 44% and the cooling plasticizer in amounts ranging from about 2% to about 10%. cooling plasticizer is diethyl phthalate.' Other suitable cooling plasticizers, such as dimethyl phthalate, dibutyl phthalate, triacetin, trinitrotoluene, dinitrotoluene, anda partial substitution of any of these with ethyl centralite may be used alone or in suitable combinations'to produe the desired low calorific value.

From about 0% to about 35% of diethanol nitramine dinitrate may desirably be incorporated in the mixture to replace a portion of the nitroglycerin. In such cases the percentage of nitroglycerin may be reduced to but notbelow about 12% and the cooling plasticizer to about 2% to give the desired calorific value.

As a stabilizing agent it is desirable to use either diphenylamineor ethyl centralite. The

7 diphenylamine should be present in amounts from about 0.5% to about 1% and preferably about 0.60%. From about 0.5% to about 1.50% of the ethyl centralite is normally adequate to insure satisfactory storage life of the powder, but an additional amount may be used on account of its plasticizing properties and also on account of its cooling effect as indicated by its negative partial calorific value. Thus, when incorporated for these additional purposes, a total of up to about 8% may be used with a consequent The preferred reduction in the amount of cooling plasticizer required. In most cases, however, it is preferable not to use more than about Other stabilizers which may be used are carbazole, beta-nerolin, or similar compounds capable of reacting with oxides of nitrogen.

It is preferred to incorporate in the powder minor amounts of a potassium salt such as, for example, from about 0.75% to about 1.50% and preferably about 1.25% of potassium nitrate. This salt facilitates ignition of the powder and helps to regulate burning. Although potassium nitrate is a preferred salt for this purpose, other salts, and preferably potassium salts, such as potassium sulfate, are satisfactory. Salts of biand poly-valent cations are also satisfactory. In general. salts of the univalent type are the least satisfactory since they appear to adversely effect the stability of the powders at elevated temperatures, while salts of other valence types are inactive in so far as any effect on the stability of the powders is concerned and, therefore, are preferred from these considerations.

In some cases, as in the mixture of Example I, it is desirable to add a very minor amount in the order of about 0.20% of a desensitizing material such as methyl cellulose.

The smokeless powder of this invention is useful as a propellent in trench mortars and particularly the 4.2-inch chemical mortar. By virtue of its lower calorific value of 900-1100 calories per gram and its reduced sheet thickness properly coordinated with the bore and length of the mortar barrel, it is possible to obtain a fiashless discharge without substantial increase in charge weight while at the same time meeting all ballistic requirements. The advantages of this invention may, therefore, be realized without modification of the structure of the mortar.

Where in the specification and appended claims the term calorific value is used, it is meant the heat of explosion in calories per gram obtained when a sample of the substance is burned in a bomb calorimeter, for example, of the Parr oxygen bomb type, in an inert atmosphere so as to duplicate as closely as possible the state of oxidation prevailing in the weapon.

What I claim and desire to protect by Letters Patent is:

1. A fiashless mortar-type smokeless powder sheet havin a thickness of between about 0.003 inch and about 0.020 inch and comprising nitrocellulose in an amount from about 50% to about 58%, nitroglycerine from about 12% to about 44% and from about 2% to about of a cooling plasticizer having a negative calorific value chosen from the group consisting of diethyl phthalate, dimethyl phthalate, dibutyl phthalate, triacetin, trinitrotoluene and mixtures thereof, the nitroglycerine and cooling plasticizer being in such proportions that the powder sheet has a calorific value between about 900 to 1100 calories per gram.

2. The flashless powder sheet of claim 1 containin in addition diethanol nitramine dinitrate in an amount up to 35% of the total weight of said sheet.

3. The powder sheet of claim 1 containing in addition as an auxiliary cooling plasticizer ethyl centralite, the total amount of said cooling plasticizer not exceeding 10%.

4. The flashless mortar-type smokeless powder sheet of claim 1 containing in addition between about 0.05% and 1.5 of a stabilizing agent.

5. The powder sheet of claim 4 in which the stabilizing agent is chosen from the group consistin of diphenylamine, ethyl centralite, carbazole, and beta-nerolin.

6. A fiashless mortar-type smokeless powder sheet having a thickness between about 0.003 inch and about 0.020 inch and comprising by weight about 55% nitrocellulose (13.25% N), about 33.65% nitroglycerin, about 9.50% diethyl phthalate, and a stabilizer, the ingredients being proportioned to give a powder sheet having a calorific value between about 900 and 1100 calories per gram.

7. A fiashless mortar-type smokeless powder sheet having a thickness between about 0.003 inch and about 0.020 inch and comprising by weight about 51% nitrocellulose (12.60% N), about 15% nitroglycerin, about 3.25% diethyl phthalate, about 28% diethanol nitramine dinitrate and a stabilizer, the ingredients being proportioned to give a powder sheet having a calorific value between about 900 and 1100 calories per gram.

ALPHEUS M. BALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,757,584 Olin May 6, 1930 1,788,438 Norton Jan. 13, 1931 1,838,345 Woodbridge Dec. 29, 1931 2,003,914 Whitworth June 4, 1935 2,008,889 Wagner July 23, 1935 2,120,324 Dickerman June 14, 1938 2,440,267 Hale Apr. 27, 1948 2,440,327 Crawford Apr. 27, 1948 FOREIGN PATENTS Number Country Date 122,509 Great Britain Jan. 30, 1919 621,685 Great Britain Apr. 14, 1949 OTHER REFERENCES Meyer, Science of Explosive, (1943), pages 26 and 104, Crowell Publishing Company, New York. (Copy in Scientific Library.)

Elements of Ammunition by Maj. Theodore C. Ohart, copyright 1946 by John Wiley and Sons, New York, New York. Published March 21, 1946. (Copy in Division 70.) Page 27.