US2112256A - Method of manufacture of smokeless powder - Google Patents

Description

Patented Mar. 29, 193$ UNM'ED ,iast

METHOD OF MANUFACTURE 10F SMOKE- LESS POWDER No Drawing. Application April 3, 1936, Serial No. 72,563

8 Claims. (01. 52-20) This invention relates to an improved method of manufacture of smokeless powder, and more specifically to an improved method of manufacture of colloided smokeless powder.

Colloided smokeless powder, also called dense smokeless powder, is usually made from nitrocellulose colloided by a volatile or non-volatile solvent therefor, or by a mixture of volatile and non-volatile solvents. The colloided mixture of nitrocellulose and solvent or solvents is pressed into strands, which are cut into short sections known as grains. The grains are treated for removal of solvent and moisture, dried, glazed, etc. Such colloided or dense smokeless powders may,

' or may not, contain nitroglycerin.

powder may be subjected for solvent removal and drying, the apparatus required, and the percentage of solvent recovered, are important factors in the ultimate cost of the powder.

Heretofore, various methods have been used for removing the solvent from the grains of dense smokeless powder. In one process, known as water drying, the powder grains are soaked in hot water, into which the solvent diffuses. The powder grains are removed from the water and dried in acurrent of hot air, to remove the adhering moisture. This process is most frequently used in the case of large grains of smokeless powder for large caliber guns.

The process most frequently used for drying relatively small grains of powder for small caliber guns is known as air drying. The cut grains, containing solvent, are exposed on shallow trays in large dry houses to a current of warm air for a long period of time. The warm air slowly removes the solvent as vapor in such a dilute form that economical recovery of the solvent is impossible.

Solvent recovery, without the complete drying of the grains of smokeless powder, has heretofore been accomplished by placing the cut grains of powder containing solvent in a closed container. Warm air is circulated through the powder and passes through a condenser, kept cold bysuitable refrigeration exterior to the powder container. The air current carries the solvent vapor to the condenser, where the solvent is condensed to a liquid form and is collected and removed for re-use. The air detrained from solvent vapor is heated up to a point at which it is capable of reabsorbing more solvent and is again passed through the powder grains. This cycle may be repeated indefinitely. In such a process, solvent is recovered, but the powder grains must subsequently be removed from the container for final drying.

Processes for solvent removal and drying of smokeless powder have heretofore required from three to five days and large dry house installations. Large quantities of powder are exposed to the risk of fire in the dry houses. The passage of, warm air through smokeless powder grains generates static electricity, the discharge of which may ignite the powder dust attendant to such operations. The equipment of dry houses usually consists of wooden trays for holding the powder grains during the drying process. Metal trays are undesirable, because of the possibility of friction. Wooden trays are unsatisfactory, due to the possible contamination of the powder from wood splinters. Splinters are difiicult to screen from the powder, and cause trouble in the machines used for loading the smokeless powder into shells. The usual dry houses are more or less hazardous to the workmen, as it is necessary to enter them from time to time to re-arrange the trays or to fill or empty the trays. Attempts to speed up the rate of drying in such dry houses by raising the temperature or increasing the air velocity have not been successful. Such changes result in caking the grains together, in distortion of the individual grains, and in surface hardening of the grains, which closes the pores and materially retards the removal of the solvent or contained moisture.

To my surprise, I have found that the passage of a mixture of steam and a fixed gas, preferably an inert gas, such as nitrogen or carbon dioxide, althoughair may be used, through the body of smokeless powder grains containing solvent, results in the very rapid removal of the solvent from the powder grains without the attendant disadvantages of distortion of the grains, surface hardening thereof or caking together of the grains. The solvent can be removed from the grains so treated, and the powder dried completely by the use of air for this final operation, within a period of time of from one to three hours, approximately, as compared to approximately five days heretofore required, and without the disadvantages recited above, attendant to theolder methods.

Instead of steam, I may use the vapors of a light petroleum hydrocarbon, such as gasoline, or the vapors of carbon tetrachloride, or the vapors of other volatile liquids which have no solvent action upon the powder grains. I have found that the vapors of coal tar hydrocarbons, such as benzene, toluene or xylene, are unsuitable, for the reason that such vapors in themselves or in combination with the solvents in the smokeless powder, exert a solvent action on the powder grains and cause softening and caking of the grains. However, I prefer to use steam and air for the sake of economy and for simplicity in the subsequent recovery of the solvent or solvents.

A further advantage of my improved process lies in the increased stability of powders so dried, for the reason that I subject powders in my process to a relatively moderate temperature for only a short period, and it is well known that the longer a. smokeless powder is subjected to an elevated temperature the greater its degree of decomposition and the lower its stability test.

A further advantage of my process is that, due to the greater uniformity of the shape of the grains of smokeless powder produced by my improved method of drying, because of the more uniform removal of solvent therefrom and less distortion I obtain with a given charge of powder in a given gun a lower breech pressure than has heretofore been possible .by methods of solvent removal and drying used heretofore.

In my improved process I pass a mixture of steam and air or other flxed gas inert to the powder through the grains of solvent-containing smokeless powder in such a manner as to raise the temperature of the powder rapidly to a point near 100 C. in a few minutes, and then pass air or other fixed gas inert to the powder, through the same powder for a relatively longer time while again raising the temperature gradually to about 30-95"' C.

In a typical example of the carrying out of my process, using 107.5 lbs. of a. 22 caliber double-base smokeless powder containing solvent, I pass steam and air through the powder as follows:

Inlet Outlet lbs. per sq. Time a 0 p inch above min.

atmospheric or a total time of steam-air treatment under the above temperature conditions of 19 minutes.

I then give the same powder an air drying treatment to remove the moisture left in. the powder by the steam, as follows:

Inlet Outlet n per Time 1 6 5 3 inch above min.

atmospheric or a total time of drying treatment under the above conditions of 75 minutes, so that, in the above example, the combined time of total treatment is 94 minutes. Such treatment reduced the total volatile content of the powder grains to 0.22%.

While, in the above example, a pressure of 2 to 4% lbs. is shown in the treatment, this is in no way limiting, and I may use any suitable tem perature and pressure adapted to the grain size of the powder being treated. I may use atmospheric pressure, although it is preferable, for convenience, to use pressures slightly above atmospheric in the closed powder container, in order to carry out the vapors.

In the above example, my finished, dried smokeless powder had the following composition and characteristics:

Nitrocellulose percent 83.29

A smokeless powder made from the same mix, but dried in the prior art way, hada com- In addition to the much shorter time of treatment, already mentioned as an advantage of my improved process, it will be noted by comparison of the above tables that a further improve-- ment resides in the lower moisture content (0.30 vs. 0.66%), a higher Tallani test (208 hours vs. 189 hours) and an improved surveillance test (53 days vs. 45 days).

In the above example, there was recovery of 7.17 lbs. of alcohol and 2.08 lbs. of acetone, all of .which would have been lost in the prior art, hot air dry-house method.

In a further example of the carrying out of my improved process of drying smokeless powa sample of .22 caliber powder, was steamair dried as in the foregoing example, then coated with 3% of di-ethyl phthalate to make a progressive-burning powder. This, with a charge of 2.26 grains, gave a pressure of 18,000 lbs., and a velocity of 1301 foot/seconds, as compared to prior art powder having a charge of 2.56 grains and giving a pressure of 18,400 lbs.,.and a velocity of 1309 foot/seconds. Thus my improved powder required a lower weight of charge and a lower pressure to give essentially, within experimental error, the same velocity.

A further advantage of my improved drying process is, that such allows the use of an excess of deterrent solvent on the powder in the coating operation, with subsequent recovery of the solvent, instead of economizing in deterrent solposition and characteristics as follows: Nitrocellulose pe'rcent 83.39

\ Nltroglycerin do 14.79

Diphenylamine 'do.. .63 Potassium nitrate do .41 Unaccounted for do .12 Moisture do .66 Taliani test hours 189 Surveillance test 775 C. ..days 45 vent by using only suillcient of the deterrent by the use of an excess of deterrent solvent, to 100 lbs. of .22 caliber smokeless powder I added 4 lbs. of di-ethyl phthalate in solution in 20.5

. cient to merely wet the powder grains, (a solu- "der grains), and leaves deterrent solution collected at the base of the vessel, the entire mass of smokeless powder and deterrent solution is placed in my drier, and a mixture of steam and air at a temperature of 60 C. at the inlet, 56 C. at the outlet thereof, under a pressure of 3 lbs., passed through for a time of 10 minutes. Then a mixture of steam and air at a temperature of 79 C. at the inlet, and 75 C. at the outlet, is passed in at a pressure of 3 lbs. for a period of 5 minutes. Then air at a.temperature of 60 C., and an outlet temperature of 55 C. under a pressure of 4 lbs., is passed through the smokeless powder for a period of 180 minutes. The vapors escaping from the outlet of my treatment'chamher are passed to a condenser, and all alcohol possible recovered therefrom by condensation.

- After the above treatment the smokeless powder contained about 30% moisture. To show the ballistics of smokeless powders treated by the above process, and by the coating process heretofore used, I give below a table:

A substantial advantage resulting from my above treatment. of smokeless powder with the deterrent in excess of'dilute alcohol solution, is

' that there is no sticking together and clustering of the smokeless powder grains, a disadvantage encountered heretofore in old processes when the deterrent was carried by 95% alcohol.

I do not limit my process to the treatment of any particular variety of smokeless powder, and I may use my process in the solvent removal and drying of single or double-base powders of any size or shape of granulation. The time taken by my solvent removal and drying treatment will naturally vary with size or shape of the powder grain, since the larger grains will require a longer time for removal of solvent than will the finer grains. I do not limit my temperatures to those shown in the examples, since I may wish to subject certain powders to a longer time of treatment at somewhat lower temperatures, and other ppwders to a' shorter treatment at somewhat higher temperatures. I may treat by my improved process the so-called deterred or progressive-burning powders, 'i. e., those coated with a deterrent, for example dinitrotoluol, di-ethyi phthalate, and the like.

My improved solvent removal and drying proccss may be carried out in any suitable form or apparatus in which undried powder grains are subjected to a'current of air and water vapor or steam. Such apparatus may consist of a column containing the powder, a tank, a box, or any container through which can be passed the steam/air current which accomplishes the solvent removal and drying.

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

1. In a method of removing solvent from smokeless powder, the step comprising subjecting smokeless powder to the action of a rapid current of a fixed gas and a vapor of a volatile liquid having no solvent action upon smokeless powder.

2. In a method of removing solvent from smokeless powder, the step comprising subjecting smokeless powder to the action of a rapid current of a fixed gas and a vapor of a volatile liquid having no solvent action on smokeless powder at an elevated temperature.

3. In a method of removing solvent from,

smokeless powder, the step comprising subjecting smokeless powder to the action of a rapid current of air and a vapor of a volatile liquid having no solvent action on smokeless powder.

4. In a method of removing solvent from smokeless powderIthe step comprising subjecting smokeless powder to the action of a current of nitrogen and a vapor o'f a volatile liquid having no solvent action on smokeless powder.

5. In a method of removing solvent from smokeless powder, the step comprising subjecting smokeless powder to the action of a current of carbon dioxide and a vapor of a volatile liquid having no solvent action on smokeless powder.

6. In a method of removing solvent from smokeless powder, the step comprising subjecting smokeless powder to the action of a rapid current of a fixed gas and water vapor.

7. In a method of removing solvent from smokeless powder, the step comprising subject- BERNHART TROXLER.