US2543535A - Process for producing smokeless powder - Google Patents

Description

Patented Feb. 27, 1951 UNITED STATES ATENT OFFICE PROCESS FOR PRODUCING SMOKELESS POWDER of Delaware No Drawing. Application January 23, 1948, Serial No. 4,068

'7 Claims. 1

This invention relat s generally to propellent powder and particularly to a process of manufacturing completely gelatinized smokeless powder and controlling the ballistic properties thereof.

The manufacture of smokeless propellent powder in the form of solidified droplets of gelatiniz d smokeless powder base was first tau ht in Patent No. 2,027,114, granted January 7, 1936, to Olsen, Tibbitts, and Kerone. Powders of this type fall into the category of those which are known in the art as dense powders. Their burnin rate is relatively slower than that of powders wherein the nitrocellulose content is substantially ungelatinized, the latter being referred to in the art as bulk powders. In order to alter the ballistic properties of the solidified droplet type of powder, such have been converted by pressure operations to flakes. For example, in Patent No. 2,111,075, granted March 15, 1938, to Olsen and Tibbitts, it is proposed to subject spherical grains of the aforesaid character to a flattening pressure. In practice, the flattening operation on such grains has been carried out both before the spherical grains were hardened (i. e., before the solvent was completely removed therefrom) and after the grains had been hardened. The effect of these flattening operations was to expose more surface of each individual grain for initial burning.

In order to produce a prcpellent powder having a final burning rate substantially in excess of the initial burning rate, the solidifi d droplets of gelatinized smokeless powder base were formed with porous interi rs according to the teachin of Patent No. 2,213,255, granted Septemher 3, 1949, to Olsen, Tibbitts, and Kerone. The latter type of grains, which were gelatinized throughout but had a porous interior and a substantially impervious exterior surface, have also been subjected to the flattening treatments to convert them into flakes and thus expose more surface for initial burning.

In carrying out the flattening operations upon powder grains of the character aforesaid, it has been the practice to pass the grains, while in a water slurry, between pressure rolls, but heretofore the effort has been to maintain such grains as dry as possible after their initial manufacture, which is to that the time period during which they were permitted to remain in the water slurry (utilized during rolling) was as short as possible. This criterion was dictated by the apparent fact that, the longer such grains were allowed to remain in the water slurry, the longer it would take to properly dry them after they were removed from the water slurry.

The object of the present invention, generally stated, is to control the ballistic properties of propellent powder grains so as to adapt a normally slow-burning powder to ammunition rounds requiring a faster burning rate.

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

In accordance with the present invention, propellent powder grains, which have a porous interior but a substantially impervious exterior surface, have their ballistic properties controlled by subjecting the grains to a flattening pressure while the porous interiors thereof contain predetermined quantities of liquid non-solvent, such as water. The invention is predicated upon the discovery that powder grains of the type referred to, which have their interiors partially or wholly filled with water at the time of rolling or flattening, are mechanically burst during the flattening treatment, so that the surfaces thereof are microscopically and macroscopically cracked and crevassed thus exposing for initial combustion a surface having an area far in excess of the apparent surface area of such grains. When such grains, containing substantial amounts of trapped water, are subjected to a flattening treatment, the spaces within which the water is trapped are reduced in volume and the trapped water must escape. In making its escape from a grain which had previously been hardened (that is to say a grain which is practically free of solvent or plasticizer), the escaping water creates and leaves a great multiplicity of ruptures in the exterior surface. The same phenomenon does not occur, however, when the grains contain substantial amounts of solvent, as in the latter case the ruptures, while created, heal themselves.

Powder grains of the character described in Patent No. 2,213,255 contain, at the time of their hardening, substantial amounts of trapped water. It has heretofore been the practice to subject such grains to prolonged drying treatments in 3 order to free them of the trapped water, which makes its escape through the surface of the grains slowly and without rupturing the substantially impervious surface. Such residual water may be utilized in practicing the present invention provided the content thereof is ascertained and either increased or decreased, in accordance with the ballistic properties sought for. Powder grains of the character mentioned, which have been completely dried (i. e., down to the point of containing about 1% of residual moisture), may have their porous interiors refilled, partially or wholly, by prolonged soaking in water. In such cases, the batch being soaked is periodically sampled in order to ascertain when the trapped water content of the grains has reached the desideratum. The rate of reintroduction of Water into the porous interiors of such grains without rupturing the exteriors may be accelerated by subjecting the soaking batch to hydrostatic pressure, care being exercised, however, that the pressure does not exceed the compressive strength of the grains, so as to rupture the substantially impervious exteriors thereof.

For example, the present invention may be practiced by the utilization of grains manufactured in accordance with the teaching of Patent No. 2,213,255, but which have been hardened but have not been subjected to drying. In one complete typical case, powder grains thus manufactured were found, at the completion of the hardening process (at which time they were fully saturated with water), to contain approximately 32% water. With this content of water, the grains may be passed between rollers and flattened, with consequent reduction of the volume of the voids within the grains and violent expulsion of the trapped water therefrom creating, as above described, many ruptures in the previously impervious outer surface. Such a powder has a greatly increased initial burning rate and a greatly increased potential over the same owder, rolled in the same way, but without substantial amounts of water being trapped inside the grains. For example, such spherical grains, flattened while containing 5% water, when loaded as the propellant in a 12-gauge shot shell at a charge of 26.0 grains, was found to impart to a 1 ounce projectile charge a velocity of 1267 feet per second. The same powder, flattened to the same thickness while containing water, had such increased potential and burning rate, however, that a charge of only 18 grains, loaded in a 12-gauge shot shell, imparted to a 1 ounce projectile charge a velocity of 1117 feet per second. Thus a reduction in the propellent charge of approximately resulted in a reduction in velocity of less than 12%. Calculating the energy content per unit of weight in accordance with the formula:

Energy= (Mass) (Velocity) /32.2,

it is found that the powder containing 5% trapped water at the time of rolling imparted approximately 67 foot-pounds of energy per grain to the shot charge, while the same powder, rolled in the same way, with a 25% content of trapped water, imparted approximately foot-pounds of energy per grain to the shot charge, all other elements being the same.

The potential (energy imparted to the projectile) and burning rate of the powder manufactured in accordance with the present invention vary directly with the amount of trapped water (or other liquid non-solvent) present at the time of rolling. This is illustrated by the following table, the data for which were obtained by loading and firing 12-gauge shot shells each containing a one-ounce shot load:

M & V at Charge in Press X Velocity, T Sample Web Grains p. s. i. ftJsec.

Per cent Inches 1 32. 0 0. 005 18. 0 1, 225 25. 7 0. 005 18. 0 123 1, 220 3 20. 9 0, 005 18. 0 119 1,196 16. O 0. 005 18. 0 98 l, 153 8. 6 0. 005 18. 0 74 1, 028 4. 9 0. 005 18. 0 73 l, 021 1. 8 0. 005 18. 0 69 l, 004

The base powder for the several samples was of identical composition. The original granulation (before rolling) was the same in each case and all samples were rolled to the same web thickness. The only difierence among the several samples was the trapped water content at the time of rolling, as indicated by the column entitled M&V at time of Rolling. It is significant that, where the moisture and volatile content of the powder is below about 8%, the voids within the individual powder grains are insufficiently filled with trapped water to produce the violent surface ruptures exhibited where the trapped water content is greater. Consequently, the foregoing data indicate that substantial amounts of trapped water must be present in the voids in order to achieve substantial variations in the energy content of the powder per unit of weight.

In practicing the present invention, the desired ballistic characteristics of a given powder are readily achieved as follows:

The given powder rolled either dry (containing up to about 1% water) or saturated with water, is subjected to ballistic tests. If, upon suc tests, the dry rolled powder is too slow for the purpose and the wet rolled powder is too fast, a sample containing an intermediate percentage of water at the time of rolling may be prepared and subjected to ballistic tests. By such a succession of cut-and-try ballistic tests upon a series of powders, each having diilerent trapped water content at the time of rolling (but being otherwise identical), 2. powder having the desired ballistic characteristics may be readily arrived at. It is to be noted in this connection that the ballistic testing by the cut-and-try method, just referred to, is the conventional practice followed in the art for fitting a propellent to a load, the present invention being characterized by the feature that variation in the content of trapped water at the time of fiattening effects a proportional variation in the ballistic properties of the powder. Consequently, in practicing the present invention, it is essential to predetermine the moisture content of powder grains which have a porous interior but an impervious exterior, as without such moisture predetermination, proper adjustment ofsucceeding test samples cannot be made.

From the foregoing description and the ballistic results herein stated, those skilled in the art will realize that the present invention accomplishes its objects and provides for the control of the ballistic properties of a given propellent powder by a novel mechanism.

Having thus described the invention, what we claim and desire to secure by Letters Patent is:

1. In the art of making propellent pewder of determined ballistic properties, the process comprising, providing a quantity of smokeless powder in the form of hardened gelatinized grains having a porous interior and a substantially impervious exterior and having their interiors laden with predetermined substantial quantities of liquid non-solvent, subjecting some of the grains to a flattening pressure, determining the ballistic properties of the flattened grains, and then adjusting the internally trapped liquid content of other grains to regulate their ballistic properties in accordance with the rule that the burning rate of the powder varies as the content of internally trapped water.

2. In the manufacture of propellent powder, the process comprising, providing gelatinized powder grains having hard substantially impervious exterior surfaces and porous interiors, said interiors containing trapped water in a substantial amount, predetermining the amount of water trapped on the interior of said grains, regulating the amount of trapped water to vary the ballistic properties of the powder according to the rule that the greater the content of trapped water the faster the burning rate of the powder, and subjecting the grains to a flattening pressure while containing the regulated amount of trapped water.

3. In the manufacture of propellent powder, the process comprising, providing solidified droplets of gelatinized propellent powder base having porous interiors and substantially impervious exteriors, said interiors containing a substantial amount of trapped non-solvent liquid, determining the content of trapped liquid, flattening some of the grains, ballistically testing the flattened grains, adjusting the content of trapped water in the unflattened grains by increasing the trapped water content to increase the burning rate of the powder and by decreasing the trapped water content to reduce the burning rate of the powder, and flattening the grains having adjusted trapped liquid content.

4. In the art of manufacturing ammunition wherein the several ammunition components are assembled and tested with different propellants until the desired ballistic results are achieved, the method comprising providing a quantity of propellant the grains of which have substantially impervious exterior surfaces and porous interiors, said interiors containing a substantial amount of trapped water, determining the water content of the grains, flattening some of the grains, and testing a charge of the flattened grains; then adjusting the trapped water content of other grains to change the burning rate thereof according to the rule that increasing the trapped water content increases the burning rate of the grain and decreasing the trapped water content decreases the burning rate of the grain, flattening the grains of adjusted trapped water content, and testing a charge of the latter.

5. In the manufacture of propellent powder, the process comprising, providing solidified droplets of gelatinized propellent powder base having porous interiors and substantially impervious exteriors, said interiors containing trapped nonsolvent liquid in an amount constituting at least 8% by Weight of the powder droplets, determining the content of trapped liquid, flattening some of the grains, 'ballistically testing the flattened grains, adjusting the content of trapped water in the unflattened grains by increasing the trapped water content to increase the burning rate of the powder and by decreasing the trapped water content to reduce the burning rate of the powder, and flattening the grains having adjusted trapped liquid content.

6. The process of claim 2' wherein the grains are flattened while containing between 8 and 32 per cent trapped water.

'7. The method of increasing the burning rate of propellant powder grains which are solidified droplets of gelatinized smokeless powder base, which grains have porous interiors and substantially impervious exteriors, and which interiors contain trapped non-solvent liquid, comprising increasing the content of trapped liquid to a value preselected according to the rule that the burning rate increases directly as the content of trapped water increases, and then, while the grains contain the preselected trapped water content, flattening the grains to a thinness such that the volume of the porous interiors is reduced below the volume of trapped liquid, whereby the surfaces of the grains are ruptured.

EMERALD P. REICHARDT. BYRON C. BALDRJDGE.

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

UNITED STATES PATENTS Number Name Date 438,816 Lundholm et a1 Oct. 21, 1390 2,213,255 Olsen et a1 Sept. 3, 1940

Claims (1)

1. IN THE ART OF MAKING PROPELLENT POWDER OF DETERMINED BALLISTICS PROPERTIES, THE PROCESS COMPRISING, PROVIDING A QUANTITY OF SMOKELESS POWDER IN THE FORM OF HARDENED GELATINIZED GRAINS HAVING A POROUS INTERIOR AND A SUBSTANTIALLY IMPERVIOUS EXTERIOR AND HAVING THEIR INTERIORS LADEN WITH PREDETERMINED SUBSTANTIAL QUANTITIES OF LIQUID NON-SOLVENT, SUBJECTING SOME OF THE GRAINS TO A FLATTENING PRESSURE, DETERMINING THE BALLISTIC PROPERTIES OF THE FLATTENED GRAINS, AND THEN ADJUSTING THE INTERNALLY TRAPPED LIQUID CONTENT OF OTHER GRAINS TO REGULATE THEIR BALLISTIC PROPERTIES IN ACCORDANCE WITH THE RULE THAT THE BURNING RATE OF THE POWDER VARIES AS THE CONTENT OF INTERNALLY TRAPPED WATER.