US2889216A - Incorporation of water soluble salts in propellent powder - Google Patents

Description

United States Patented June 2, 1959 INCORPORATION OF WATER SOLUBLE SALTS IN PROPELLENT POWDER Godfrey, Ill., and John D. Clark, assignors to Olin Mathieson East Alton, [1]., a corporation Thomas I. Mulqueeny,

Webster Groves, Mo., Chemical Corporation, of Virginia No Drawing. Application ilune 14, 1957 Serial No. 665,665

4 Claims. (CI. 5221) This invention relates generally to propellent powder,

' and particularly to globular powder of the character into the aqueous suspending liquor.

less powder base lacquer rather man be dissolved in the aqueous suspending liquor.

Briefly, the invention involves preparing at least part of the usual lacquer separate and apart from the aqueous suspending liquor, as distinguished from that species of the globular powder process wherein all the lacquer is formed within the suspending liquor. In accordance with the present invention, the lacquer (made externally of the liquor) has the desired amount of water soluble salts incorporated with it before the lacquer is introduced The lacquer into which the salt is incorporated may constitute all or only part of the nitrocellulose (or other smokeless powder base) which is ultimately to be dissolved by the solvent. For example, the lacquer containing the salt may constitute twenty percent or more of the nitrocellulose to be grained in a given batch. The proclivity of the water ders in order to modify their ballistic properties or to reduce or eliminate muzzle flash is well known, but in I view of the propensity of these materials to dissolve in water, it has heretofore been impractical to incorporate the same into powder grains made according to the globular powder process (such as that disclosed in United States Patent No. 2,027,114), wherein droplets of nitrocellulose lacquer are suspended, rounded, and hardened in a liquor composed largely of water. Efforts have heretofore been made to incorporate water soluble salts into globular powder grains but without success except in instances where the suspending liquor was itself saturated with the salt. Otherwise, water soluble salts introducedinto the still, either separately or in mixture with the nitrocellulose or in mixture with the solvent, tended to dissolve in the water phase rather than become occluded in the lacquer phase. The use of such large quantities of water soluble salts as was required to saturate the water phase in such an operation is economically unfeasible, and consequently where it has heretofore been desired to modify the ballistics of globular grains or to render them flashless, the water soluble salts have been applied as a coating to the finished grains. This has been done in the conventional sweetie barrel but there are limitations upon the extent to which such a material may be applied as a coating. No more than 0.5% of a water soluble salt has heretofore been successfully applied by the coating process (the percentage figure is based upon the ratio of the weight of the salt which adheres to the total coated powder weight). Even when a water soluble salt such as potassium nitrate is applied as a coating of a blend with dinitrotoluene and/or diphenylamine no more than about 0.5% of the salt can be applied without so seriously affecting the ballistic properties of the grains as to defeat the purpose. In view of the fact that the coating operation is time-consuming, and the further fact that only small amounts of water soluble salts can be applied in this manner, the coating method is far from satisfactory.

, It is, therefore, the object of the present invention, generally stated, to provide a process for incorporating a water soluble salt as an integral part of a globular powder grain.

Other objects will become apparent to those skilled in the art when the following description is read.

The present invention is predicated upon the discovery that particles of a water soluble salt, when coated with a a lacquer of smokeless powder base, such as nitrocellulose,

have their aflinity for water greatly reduced, and consequently, when given the choice, as in the globular powder process, tend to become occluded in droplets of smokesoluble salt to dissolve in the aqueous suspending liquor (in preference to becoming occluded in globules of lacquer) is quite adequately controlled when each particle of the saltis enveloped by the lacquer; and such enveloped particles become the nuclei of lacquer globules. Where only part of the nitrocellulose is included in the externally made lacquer which contains the salt, the balance of the nitrocellulose may be introduced into and ilissolved in the presence of the aqueous suspending iquor.

The term water soluble salts" is used herein to designate salts having a solubility of at least 1% in water at 20 C.

Numerous water'soluble salts have been incorporated into propellent powder grains to enhance the characteristics of the powder. For example, incorporated potassium nitrate, potassium sulfate, sodium nitrate and the like are effective in reducing or eliminating muzzle flash. In like manner, incorporated barium nitrate, lithium nitrate, potassium sulfate, sodium sulfate and lithium sulfate have been effective in altering the ballistic characteristics of propellent powder grains. Other salts, such as lead acetate and numerous ammonium salts, including ammonium nitrate and ammonium oxalate can be incorporated into propellent powder grains to alter their ballistic characteristics. In fact, the water soluble sulfates and nitrates of the alkali and alkaline earth metals have been found in general to impart advantageous characteristics to powder when incorporated in the grains. While numerous water soluble salts have previously been added to powder grains, future developments will undoubtedly reveal the necessity and desirability of incorporating other water soluble salts into powder grains. The process of the present invention is operable with regard to all such water soluble salts. The advantages of the invention are more readily realized in connection with very soluble salts, but it will be readily appreciated that the invention can be practiced with equal facility on any water soluble salt desired to be incorporated into the powder grain.

The invention and the manner in which the aforementioned and other objects and advantages are accomplished will be more fully understood in view of the following illustrative embodiment, describing the incorporation of Y crystalline potassium nitrate into globular powder grains.

Parts Water 3009 Sodium sulfate 300 Ninety-five parts of fibrous nitrocellulose is charged into this suspending liquor either before or afterrthe lacquer, now to be described, is introduced into the suspending liquor.

Externally of the suspending liquor, just described, a

lacquer of smokeless powder base, solvent and potassium Such a lacquer is sufficiently thin to facilitate uniform distribution therein of the particles of potassium nitrate. This lacquer may be prepared at room tempcrature.

The suspending liquor is introduced into an appropriate still provided with an agitator and elevated to a temperature of about 55 C. at which time the externally prepared lacquer is introduced into the still and maintained under agitation. Thereafter 95 parts of fibrous nitrocellulose are charged into the mixture.

After the fibrous nitrocellulose has been charged into the still, the temperature thereof is increased to about 70 C. over a period of about two hours during which time the fibrous nitrocellulose will have dissolved in the lacquer. During this time, the mixture is agitated at a relatively slow rate until the fibrous nitrocellulose is completely dissolved by the lacquer.

After the fibrous nitrocellulose is completely dissolved, the lacquer is disintegrated into particles of the desired size and such particles suspended in accordance with the usual practice-of making globular powder as taught in liquor. Where 100% of the nitrocellulose is included in the externally prepared lacquer, however, it is more diflicult to obtain uniform distribution of the salt and care should be exercised to carry out the distillation of the solvent from the suspended droplets at the lowest possible temperature. Indeed, it is desirable in such cases to distill under vacuum so as to keep the temperature below about 90 C. as otherwise there is a greater loss of salt from the lacquer to the liquor.

While the invention has been illustrated with reference to potassium nitrate, nitrocellulose, and ethyl acetate, it will be apparent to those skilled in the art that other water soluble salts, other smokeless powder bases, other U.S. Patent No. 2,027,114. When the desired degree of disintegration has been achieved, the rate of agitation is reduced in accordance with the usual practice to an extent just sufficient to maintain the lacquer droplets in suspension while they round, i.e., approach spherical shape.

When the droplets are sulficiently rounded, the temperature of the still is gradually increased to distill off the solvent from the suspended droplets and harden them. The distillation temperature preferably does not exceed 99 C.

When the suspended droplets are hardened, they are recovered in the usual manner.

As a result of the procedure above described, 176 parts of globular powder grains are produced, having a potassium nitrate content of 31.1%. Despite the fact that only 36.5% of the potassium nitrate utilized was recovered in the finished product, the procedure is economically feasible and enables the incorporation of 1 many times as much potassium nitrate or any other water soluble salt as can be applied to the grains by coating.

Although it is preferred that half or less of the nitrocellulose to be granted in a given operation be included in the externally prepared lacquer (containing the water 5 water immiscible solvents, other amounts and conditions can be used in the place and stead of those mentioned. Accordingly, it is to be understood that the invention is not limited to the details of the illustrative example hereinbefore described.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In the manufacture of propellent powder grains by the process wherein globules of a lacquer of smokeless powder base and water immiscible solvent are hardened while suspended in an aqueous liquor, the method of incorporating in the grains water soluble salts selected from the group consisting of lead acetate, ammonium nitrate, ammonium oxalate, and the-water soluble nitrates and sulfates of the alkali and alkaline earth metals, which comprises, coating particles of the water soluble salt with iaid lacquer and thereafter introducing the same into said iquor.

2. The method of claim 1 wherein the particles of water soluble salt are incorporated with the lacquer and intro duced into the liquor simultaneously with the lacquer.

3. The method of claim 2 wherein after the salt containing lacquer is introduced into the liquor, additional smokeless powder base is dissolved in the lacquer.

4. In the manufacture of globular powder grains containing a water soluble salt selected from the group consisting of lead acetate, ammonium nitrate, ammonium oxalate, and the water soluble nitrates and sulfates of the alkali and alkaline earth metals, the process comprising; preparing a lacquer composed of nitrocellulose, solvent and water soluble salt; preparing a suspension liquor composed essentially of water; introducing the lacquer into the liquor, subdividing the lacquer into droplets, and suspending the droplets in the liquor; and then removing the solvent from the lacquer droplets while suspended in the liquor. V

, References Cited in the file of this patent UNITED STATES PATENTS ONeil May 10, '1927

Claims (1)

1. IN THE MANUFACTURE OF PROPELLENT POWDER GRAINS BY THE PROCESS WHEREIN GLOBULES OF A LACQUER OF SMOKELESS POWDER BASE AND WATER IMMISCIBLE SOLVENT ARE HARDENED WHILE SUSPENDED IN AN AQUEOUS LIQUOR, THE METHOD OF INCORPORATING IN THE GRAINS WATER SOLUBLE SALTS SELECTED FROM THE GROUP CONSISTING OF LEAD ACETATE, AMMONIUM NITRATE, AMMONIUM OXALATE, AND THE WATER SOLUBLE NITRATES AND SULFATES OF THE ALKALI AND ALKALINE EARTH METALS, WHICH COMPRISES, COATING PARTICLES OF THE WATER SOLUBLE SALT WITH SAID LACQUER AND THEREAFTER INTRODUCING THE SAME INTO SAID LIQUOR.