US3037891A - Smokeless powder - Google Patents

Description

lawm United States Patent 3,037,891 SMOKELESS POWDER Raymond H. Maag, Florissant, Mo., assignor to Olin Mathieson Chemical Corporation, East Alton, BL, a corporation of Virginia No Drawing. Filed Home 8, 1959, Ser. No. 818,535 5 Claims. (Cl. 149-97) This invention relates to smokeless powder and more particularly to an improved method of making double base smokeless powder.

Commercially available smokeless powders are formed predominantly of nitrocellulose or of a mixture of nitro cellulose with a liquid explosive nitric ester such as nitro glycerin. Such powders have been traditionally prepared by processes involving extrusion of a thick dough-like mixture of the base material with a volatile solvent. More recently, propellent powder grains have been manufac tured by solidifying suspended droplets of a smokeless powder base lacquer in accordance with the teachings of US. Patent 2,027,114 to Olsen. Although single base, or nitrocellulose powders, can readily be prepared by such manufacturing methods, the preparation of double base, or nitrocellulose-nitroglycerin powders, has always presented formidable problems. The extrusion processes involving mechanical working, such as blocking, extruding and cutting of a mixture containing nitroglycerin in the presence of a volatile solvent has been recognized as an exceedingly hazardous operation. Thus, even when this process is employed, only relatively small batches are processed in order to reduce the dangers to a reasonable minimum.

Although double base powders can be prepared from mixtures of their components in accordance with the process of US. Patent 2,027,114, the subsequent treatment of the spherical grains after being formed necessarily results in the loss of appreciable amounts of nitroglycerin. Such losses are encountered primarily in the wet screening of the grains which is required to obtain fractions of substantially equal dimensions. The treatment of double base powder with large amounts of water in this process, particularly when the powder contains appreciable amounts of nitroglycerin, results in the loss of a considerable amount of nitroglycerin. Thus, the preparation of double base propellent powder directly from a mixture of its components in the extruded type process is dangerous and in the spherical process is wasteful and uneconomical.

Because of such operational difliculties, double base powder formed predominantly of nitrocellulose and nitroglycerin is normally prepared by adding nitroglycerin to an aqueous suspension of single base nitrocellulose smokeless powder grains. These conventional procedures are generally satisfactory when the amount of nitroglyc erin to be incorporated into the powder is nominal; that is, up to about 20%. However, in the production of double base powders containing larger amounts of nitroglycerin between about 30% and 45% the previously used impregnation methods have been unsatisfactory. These procedures are quite slow and considerable time is required to insure the absorption of large proportions of nitroglycerin by the nitrocellulose in the powder grains. Even when the grains are subjected to nitroglycerin solutions for an extended period of time in the preparation of high nitroglycerin content powder, a major portion of the nitroglycerin is concentrated near the surface of the grains. This renders them excessively tacky and makes subsequent handling and processing exceedingly difficult.

Such tacky grains obtained by the previously known impregnation methods are not free flowing and thus not adaptable to standard loading machines employed in ammunition manufacture. Also, it has been found that high Patented June 5, 1962 ice I this invention is to provide an improved process for the preparation of powder containing more than 20% nitroglycerin.

ln accordance with this invention, these and other objects are achieved, generally speaking, by impregnating solvent-laden nitrocellulose propellent powder grains with a solution of nitroglycerin and subsequently removing the solvent from the grains. More specifically, this invention contemplates impregnating solvent-laden nitrocellulose powder grains with from about 30% to about 45% dissolved nitroglycerin followed by removal of the solent. The process is most conveniently carried out in an aqueous suspending medium. Thus, the single base nitrocellulose grains forming the base material of the present process are suspended in an aqueous medium. A substantially water immiscible nitrocellulose solvent is added to the suspension which is maintained until there is a solvent equilibrium between the suspending medium and the nitrocellulose. When this equilibrium is reached, the nitroglycerin solution is then added to the suspension. The nitroglycerin is preferably dissolved in -a solvent which is also a solvent for the nitrocellulose. In any event, the nitroglycerin solvent is compatible with nitrocellulose and also with the solvent previously added to the nitrocellulose. In most instances, it has been found convenient to use the same solvent in these two steps of the process. The nitroglycerin solvent, like the nitrocellulose solvent, must also be substantially immiscible in water.

The term water immiscible solvent as used in the present specification designates that the solvent is capable of forming a two-phase system with water. In general, it is preferred that the water miscibility of the solvent be between about 3% and about 25% by weight at approximately C. to C. Since the solvent must be removed from the powder grains after they have been subjected to the process of this invention, it must be more volatile than water. Suitable volatile solvents having the requisite water immiscibility include ethyl acetate, methyl ethyl ketone, isopropyl acetate, methyl isopropyl ketone, nitromethane, and the like. Also, mixtures of such solvents can be used with equal facility.

The amount of Water used in making the powder slurry or suspension is not particularly critical but the weight of the water should generally be at least 5 times as great as the weight of the powder so as to insure equal distribution of the powder grains and of the nitroglycerin solution. in most instances, it is preferred to maintain the water-to-powder ratio between about 8:1 and about 12:1. Although larger amounts of water can be employed, they offer no advantages and render the process somewhat cumbersome.

The weight ratio of the solvent to the nitrocellulose powder grains must be carefully controlled to avoid deformation of the grains and also to insure uniform distribution of the nitroglycerin throughout the grain. Thus, the weight ratio of the solvent to the powder must be maintained between about 0.7 :1 and about 2:1 prior to the addition of the nitroglycerin. When smaller amounts of solvent are used, there is an undesirable nitroglycerin gradient throughout the cross section of the grain. On the other hand, larger amounts of solvent result in liquefication and deformation of the nitrocellulose grains. When a nitrocellulose solvent is used in making up the nitroglycerin solution, the over-all solvent-to-powder ratio can be increased somewhat with the introduction of nitroglycerin into the system but it cannot exceed about 2.25:1.

After the nitroglycerin has been impregnated into the nitrocellulose grains in accordance with the present invention, the solvent is removed from the grains and the suspending medium by any convenient means. While ordinary distillation is preferred, the solvent can also be removed from the system by vacuum distillation, air stripping, or other standard means. With the solvent thus removed, the grains are subsequently separated from the suspending medium by decantation, filtration, centrifugation, or any other suitable method.

The process is also readily amenable to the incorporation of various operational steps to improve the physical and chemical properties of the final product. For example, the solvent-laden powder containing nitroglycerin can be dewatered to prepare substantially non-porous powder by the addition of a solute to the suspending medium in accordance with the teachings of US Patent 2,160,- 626 granted to Schaefer. Also, the powder obtained in accordance with this invention'can be surface modified by treatment with deterrents such as diphenyl phthalate, dinitrotoluene, or the like, or with a variety of finely divided solid materials such as metallic salts and graphite.

The manner in which the advantages of the present invention are obtained will be more readily understood by reference to the following specific example illustrating a preferred embodiment of the invention. In this embodiment and throughout the specification, all parts and proportions are expressed in parts by weight unless otherwise indicated.

About 50 parts of a substantially non-porous nitrocellulose base powder prepared in accordance with the process described in U.S. Patent 2,375,175 granted to Silk, were mixed with about 450 parts of water containing approximately 4 parts of animal glue as a protective colloid in a still at ambient temperature, approximately 20 C. The powder grains were substantially spherical having diameters between about 0.025 inch and 0.034 inch. The water was agitated to keep the powder grains in suspen sion and the agitation was maintained throughout the operation. The suspension was heated to about 50 C. and approximately 50 parts of ethyl acetate were gradually added thereto over a half-hour period. Since the ethyl acetate has a greater afiinity for nitrocellulose than for water, it was rapidly absorbed by the suspended nitrocellulose powder grains, leaving only a small amount dissolved in the water.

After all of the ethyl acetate had been added to the .suspension, about 67 parts of a 50% solution of nitroglycerin in ethyl acetate was slowly added to the suspension over a period of about 30 minutes. The temperature of the suspension was then gradually increased from 50 C. to about 68 C. This heating was extended over a four-hour period and insured complete impregnation of the nitrocellulose powder grains with the nitroglycerin solution. At the end of this period, about 9 parts of sodium sulfate were added to the suspension which was then heated to a temperature of about 99 C. to recover the solvent. The distillation at 99 C. was conducted at atmospheric pressure and over a 6 hour interval. At the end of this period, substantially all of the solvent had been recovered. The agitation was stopped and the powder removed from the aqueous suspending medium by decantation and filtration. The powder was subsequently washed with water to remove any colloid or sodium sulfate adhering to its surface and was then rolled to a web of approximately 0.018 inch. This rolled powder was then coated with about 1% potassium sulfate by tumbling in a sweetie barrel.

The rolled, coated powder thus obtained is particularly well adapted for use as a propellent charge in 8 gauge kiln gun cartridges. In order to illustrate the advantaglycerin.

geous characteristics of this powder, it was charged into 3% inch 8 gauge shells having a 3 ounce lead slug, and test fired to determine the pressure generated and the velocity imparted to the slug. For purposes of comparison, similar cartridges were charged with a commercially available 8 gauge powder. This extruded powder had a diameter of about 0.060 inch, a web of about 0.015 inch, and a nitroglycerin content of about 35% in comparison with the 40% nitroglycerin-content of the powder prepared in accordance with the above embodiment. The nitroglycerin was incorporated into the commercial powder by conventional means rather than by the present impregnation method. Samples of 8 gauge shells loaded with both of these powders were fired at ambient temperatures (70 F.) and also at 140 F. The results obtained are set forth in the following table in which AP represents pressure variations and AV velocity variation.

Prior Art; Present Powder Powder Charge (grnins) 101.0 101. 0 110.0 110. 0 Temperature, 11. 70 140 70 140 Pressure .s.i./l00) 214 238 228 230 A P (p.s.i.i 24 2 Percent A P 11. 0. Velocity (it/sec.) 1,736 1,786 1, 739 1 758 A V 50 10 Percent A V 2. 9 1.1

The commercial specifications for the 8 gauge kiln gun require that the load shall have a velocity level of 1730 feet per second with a maximum pressure below 25,000 psi By reference to the above table, it will be noted that the pressure generated by the present powder varied only slightly when the firing temperature was increased from 70 F. to F. Also, the velocity of the present powder increased only slightly over 1% as the temperature was increased, whereas the velocity of the prior art powder showed a variation in velocity of almost 3%. The functioning of 8 gauge powder at elevated temperatures is particularly important because the temperatures occurring at the point of gun use are normally above 100 F. Thus, the powders of the present invention which demonstrate only small increases in pressure and velocity at elevated temperatures otfer a great margin of safety to kiln gun operations.

Another batch of the single base powder used in the previous example was impregnated with about 40% nitroglycerin in the same manner as described above. After the nitrocellulose powder had been completely impregnated with the nitroglycerin solution, however, the solvent was removed from the system without adding a solute such as sodium sulfate. The resultant powder was more porous, having a gravimetric density of about 0.912 gram per cc. The powder was separated from the suspension in the same manner as described in the foregoing embodiment and was then rolled to a web of about 0.010 inch forming a flaky product. This flaky powder was dry tumbled with graphite so as to provide it with a 1% graphite glaze. Because of its increased porosity, this powder had a very fast burning rate. Also, upon combustion, it provided a sustained force because of the uniform and relatively high nitroglycerin content. The powder made in accordance with this modification is particularly well adapted as a propellent for use in conjunction with powder actuated tools of the type described, for

example, in US. Patent 2,869,127 granted to Jesse E. Williams.

While the description of the present invention has been directed primarily to impregnation methods utilizing nitroglycerin, it will be readily appreciated that other liquid explosive nitric esters can also be used. Thus, the liquid nitroglycols, ethylene glycol dinitrate, diethylene glycol dinitrate, triethylene glycol dinitrate, pentaerythritol trinitrate, and the like, can be employed instead of nitro- In addition, it is to be distinctly understood that the process can be utilized with any single base powder regardless of its shape since the shape of the powder being treated remains substantially unchanged throughout the operation. Therefore, cylindrical, disc, and other shapes of powder, as well as spherical powder can be treated with equal facility.

Also, the manner in which the solvent and nitroglyc erin solution are added to the aqueous powder suspension can be modified in any convenient manner. Although the above examples employ gradual additions, the material can also be added incrementally or it can be emulsified with water prior to addition so as to facilitate distribution throughout the aqueous medium.

The invention has been described in considerable detail in the foregoing but it is to be understood that many variations may be made by those skilled in the art without departing from the scope of the invention except insofar as it is limited by the appended claims.

What is claimed is:

l. A process of impregnating nitrocellulose propellent powder grains with a liquid explosive nitric ester selected from the group consisting of nitroglycerin, liquid nitroglycols, ethylene glycol dinitrate, diethylene glycol dinitrate, triethylene glycol dinitrate, and pentaerythritol trinitrate, which comprises agitating the grains in water to form an aqueous suspension, adding to the suspension a substantially water immiscible solvent for nitrocellulose and for the liquid explosive nitric ester to form a two-phase liquid system, maintaining the suspension until sufiicient solvent is absorbed by the grains so as to return the suspending medium to a single phase liquid system, adding to the suspension a solution of a liquid explosive nitric ester in a substantially water immiscible 6 solvent for the ester and for nitrocellulose, maintaining the suspension until substantially all of the liquid explosive nitric ester is absorbed by the grains, the total amount of solvent employed being insufficient to dissolve the nitrocellulose, and subsequently removing the solvent from the grains.

2. A process for the manufacture of double base propellent powder grains from single base propellent powder grains which comprises suspending the single base grains in water to form an aqueous suspension thereof, adding a substantially water immiscible solvent for nitrocellulose to the suspension in amounts insufficient to dissolve the grains, adding to the suspension a solution of a. liquid explosive nitric ester selected from the group consisting of nitroglycerin, liquid nitroglycols, ethylene glycol dinitrate, diethylene glycol dinitrate, triethylene glycol dinitrate, and pentaerythritol trinitrate, in a substantially Water immiscible solvent, maintaining the suspension until the grains are impregnated with the liquid explosive nitric References Cited in the file of this patent UNITED STATES PATENTS 2,417,090 Silk et al Mar. 11, 1947

Claims (1)

1. 2. A PROCESS FOR THE MANUFACTURE OF DOUBLE BASE PROPELLENT POWDER GRAINS FROM SINGLE BASE PROPELLENT POWDER GRAINS WHICH COMPRISES SUSPENDING THE SINGLE BASE GRAINS IN WATER TO FORM AN AQUEOUS SUSPENSION THEREOF, ADDING A SUBSTANTIALLY WATER IMMISCIBLE SOLVENT FOR NITROCELLULOSE TO THE SUSPENSION IN AMOUNS INSUFFICIENT TO DISSOLVE THE GRAINS, ADDING TO THE SUSPENSION A SOLUTION OF A LIQUID EXPLOSIVE NITRIC ESTER SELECTED FROM THE GROUP CONSISTING OF NITROGLYCERIN, LIQUID NITROGLYCOLS, ETHYLENE GLYCOL DINITRATE, DIETHYLENE GLYCOL DINITRATE, TRIETHYLENE GLYCOL DINITRATE, AND PENTAERYTHRITOL TRINITRATE, IN A SUBSTANTIALLY WATER IMMISCIBLE SOLVENT, MAINTAINING THE SUSPENSION UNTIL THE GRAINS ARE IMPREGNATED WITH THE LIQUID EXPLOSIVE NITRIC ESTER, AND REMOVING ALL SOLVENT FROM THE GRAINS AND SUSPENDING MEDIUM.