US2008888A - Propellant powder - Google Patents

Description

Patented July 23, 1935 UNITE s'rArs A f I i O FF i PROPELLANT POWDER No Drawing.

Application December 8, 1930,

Serial No. 500,874

1 Claim. (CI. 5220) This invention relates to propellant powders,

and more particularly those employing nitrocellulose as a base.

Nitro-cellulose powders are of two general types,

.5. namely, gelatinized and ungelatinized. In the manufacture of gelatinized or dense colloided nitro-cellulose powders, the nitro-cellulose is treated with a solvent to effect gelatinization and the grains are then formed by either extrusion into strings or rolling into sheets followed by cutting the strings or sheets into grains.

It has been known that the addition of a nonsolvent for nitro-cellulose will often increase the activity of a solvent; thus ethyl acetate containing a small percentage of ethyl alcohol is a more active solvent for nitro-cellulose than pure ethyl acetate. While this fact has been taken advantage of in the preparation of lacquers, in order to secure the desired low viscosity, it has found no application in the manufacture of smokeless powders. In the gelatinization of nitro-cellulose in the manufacture of smokeless powder, the proportion of nitro-cellulose to the solvent must be high; for here it is not desirable to obtain a solution of low viscosity, but on the contrary, to maintain the nitro-cellulose in a gelatinized state of as tough and dense consistency as can be extruded into strings or rolled into sheets and subsequently cut up into grains. Moreover, the proportion of nitro-cellulose to the solvent should be kept as high as practicable, in order to reduce shrinkage of the powder grains when the solvent is subsequently driven off. In the manufacture of gelatinized smokeless powder, any dilution of a solvent with a non-solvent should, therefore, be avoided; in fact, the use of a'combination, of what may be termed non-solvents, is employed simply for the reason that when combined, the solvent action of the combination is enhanced.

The effect which non-solvents, particularly for nitro-cellulose, have on the action of solvents, or vice versa, as the case may be, is taken advantage of in the preparation and treatment of smokeless powder in accordance with this invention. In accordance with this invention, combinations .of solvents and non-solvents can be used in which the percentage of non-solvent to solvent is much One of the objects of this invention is to provide a process or treatment of propellant powder grains, and particularly ungelatinized nitro-cellulose powder grains, whereby the burning rate can be eilectively controlled. 7 Another object is to provide a propellant powder grain of ungelatinized nitro-cellulose which is so surface treated with a deterrent as to secure the desired ballistic properties.

Further objects will appear from the detail description, in which will be described a number of embodiments of this invention; it is to be understood, however, that this invention is susceptible of various other embodiments without departing from the spirit of this invention.

Generally stated, in accordance with this invention, a powder grain, and preferably a preformed ungelatinized nitro-cellulose powder grain, is treated with a solvent for nitro-cellulose in the presence of a non-rsolvent for nitro-cellulose, which latter is preferably more volatile than the solvent and provides a vehicle therefor. The

treatment is carried on sufficiently to effect a.

penetration suflicient to secure the desired burning rate. This is accomplished in accordance with one embodiment of this invention by the employment of a proportion of solvent to non-solvent and by extending the period of treatment, both of which are controlled, in order to secure such desired burning rate. After penetration of the grain to the desired extent, the non-solvent is removed; this can be conveniently accomplished where a volatile non-solvent is employed by evaporating this non-solvent.

The solvent employed is preferably one to secure a deterrent action; a deterrent which is particularly applicable for the surface treatment of preformed ungelatinized nitro-cellulose powder grains is diamyl phthalate; and where the latter is employed, a suitable non-solvent vehicle such as benzol secures the desired impregnation or surface treatment of the grain. There is thus produced an ungelatinized nitro-cellulose powder grain whose ballistic properties are controlled by being surface treated with a deterrent;

The powder grains to be treated are immersed in a solution of solvent and non-solvent of relative proportions and for a length of time required to give the desired penetration in order to secure the desired burning rate. The thinner the solution and the longer the immersion, all'other factors remaining the same, the less will be the progressive rate of the burning of the resultant powder and also the less volatile the solvent used, the

more will be retained by the finished product :and

, manner.

as the amount of solvent retained has an effect on the burning rate, it is important to choose the solvent best suited for the ballistic properties desired, as well as the non-solvent, the time and temperature of the treatment.

Instead of immersing the powder grains in a solution of solvent and non-solvent and draining off the excess solution, the solution may be poured or sprayed onto a quantity of the powder grains to be treated, as in a rotating barrel or the like, to secure a uniform distribution of the solution through the powder. In any case, the volatile non-solvent is driven off in any suitable The quantity of solution to be used with a given quantity of powder may be varied to give the desired penetration and the desired proportion of deterrent.

Whatever method employed, the result in general is the same; for as the more volatile nonsolvent evaporates, the solution becomes more and more active in gelatinizing the nitro-cellulose, until in the final stage practically pure solvent remains which actively attacks the nitrocellulose fibres to gelatinize them. By choosing the proper proportions of solvent to non-solvent and by controlling the other factors, the process can be controlled so that as the non-solvent evaporates there is not enough active solvent left on the exterior fibres of the nitro-cellulose grains to soften them sufficiently to cause them to stick together. This preventing of sticking is advantageous; for where powder grains are simply immersed in a solvent in the absence of a non-solvent, particularly in the absence of a preponderant proportion of the non-solvent, the grain will become gummy, resulting in a balling up of the powder grains so treated, This is not only prevented by the employment of a non-solvent but by controlling the proportion of the non-solvent to solvent, and particularly by using a substantially large proportion of non-solvent, there is at no time during the treatment suflicient active solvent on the surface of the grains to cause them to'stick together.

As a practical embodiment of this invention, ungelatinized preformed nitro-cellulose' powder 7 grains of open fibre structure are immersed for 3 minutes in an 8% solution of diamyl phthalate in benzol, the grains being 1.5 mm. in diameter and 0.3 mm. thick. The temperature during this treatment is maintained at about 20 C. After the desired period of immersion has elapsed, the powder grains are removed, drained of the solution and dried in any suitable apparatus, preferably provided with a solvent recovery means, at a temperature of 50 C. until the more volatile non-solvent has been evaporated to the desired extent. The grains may then, if desired, be further surface treated with a solution of nitro-cellulose in ethyl acetate to which is added suflicient of a non-solvent, such as benzol, to bring the composition of the solution to nearly the precipitation point of the nitro-cellulose, as described in my application Serial No. 359,708, filed May connection with a suitable non-solvent which is preferably volatile. The invention .is best carried out by the use of non-solvents and solvents,

one of which, at least, is insoluble in water. In-

stead, however, of using a strictly non-solvent volatile carrier, a very mild volatile solvent, such as methyl or ethyl alcohol or a mixture of a volatile solvent and a volatile non-solvent, may be used, which will act as a very mild solvent for the nitro-cellulose, as for instance, 8 parts ethyl acetate to 92 parts of benzol. The non-solvent may contain a small portion of a non-volatile non-solvent substance which will remain in the powder after the volatile portion is driven oil and by its presence help to control either the burning rate or the hygroscopicity of the powder. The solutions as heretofore employed in the gelatinization of nitro-cellulose have always been of an inflammable nature with the attendant hazards in the recovery system, but by this process the hazard can be obviated by choosing a nonsolvent which composes the bulk of the solution, a non-inflammable substance, such as carbon tetra chloride, ethylene dichloride, or even water can be used with solvents, such as diacetone alcohol, which are miscible with water.

If the grains treated by this process aregelatinized by a solvent of low vapor pressure which remains in the powder after it has been dried, the grains may' not have I the desired hardness in which case a further coating of a solution of nitro-cellulose in a solvent and non-solvent is given them, as described in application Serial No. 359,708.

This invention provides a process by which the burning rate of even the highest nitrations of cellulose, such as gun cotton, can be controlled so as to become serviceable for shot gun and small arm loads and also makes unnecessary the preliminary stage in which nitro-cellulose exists as discrete fibres by permitting the grain structure to be maintained throughout the process.

While in the specific embodiment described, an example of a treatment of ungelatinired preformed nitro-cellulose powder grains has been given, it will be understood that as to some of its features, this invention is applicable to the treatment of other nitro-cellulose powder grains generally, and even for the treatment of other powder grains more particularly of the smokeless tym. It will be furthermore understood that various features, combinations and subcombinations are of utility andmay be employed with reference to other features and combinations;

that is contemplated and is,within the scope of this invention is not to be limited to the specific details described.

Having thus described the invention, what is claimed is: v

A preformed propellant powder grain of un gelatinized nitro-cellulose surface-treated with O6 diamyl-phthalate to an extent sumcient to retard the initial combustion rate and render the grain progressive burning.

WILLIAM E. WAGNER.