US2028990A - Process of making propellent powder - Google Patents

Description

hinned 28, 1936.

UNITED sTA Es PATENT OFFICE 2,028,990 rnoonss or MAKING mommrownnn Fredrick Olsen, Alton, Ill.

asslgnor to Western Cartridge Company, East Alton, 111., a corporation of Delaware No Drawing. Application December 8,1930.

, Serial No. 500,865

cohol; the gelatinization being completed by the application of pressure either by a hydraulic press or through the action of rolls; sometimes these rolls' are heated in which case gelatinization is at least partially eifected through the agency of heat. The gelatinized grains are then pressed into proper forms and dimensions while themass is still plastic, and after the grains are dried they are surfacetreated. The rate of burning of the powder, other things being equal, is, therefore, a function of the composition of the powder, the dimensions of the grain and the nature and extent of the coating. I

While a dense colloided nitro-cellulose powder surface treated with a deterrent, such as dinitrotoluene, is progressive .burning, the burning rate of the interior of the powder grain, is limited on account of its composition; accordingly, such powder is not sufiiciently fast burning in certain situations where the conditions require that the burning rate be increased beyond that obtainable with such a grain. Such a situation is encountered in a shot gun where the conditions of obturation during the development of the powder gases are not favorable, or, at least, not of the same order as is the case in rifles where the projectile moving along the rifling along the bore forms a highly eflicient seal. In the former situation it is desirable that theinterior of the powder grain have very fast burning characteristics while the progressive burning characteristic is-still maintained. If that is not the case, then the shot charge will not be subjected to the uniform acceleration on account of the inability of the powder to develop its gases w'ith the required rapidity in the greatly expanded volume of the powder.

One of the objects of this invention, therefore, is to provide a propellent powder and a process of' making the same which powder is not only progressive burning,but in which the interior of the grain has very fast burning characteristics.

Another object is to provide an ungelatinized propellent powder grain, more particularly'of is produced preferably of a flake-like the nitro-cellulose type, and having an open fibrous structure which is so surface treated as to secure the desired ballistic and water-proofing properties.

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

Generally stated and inaccordance with this invention, an ungelatinized powder grain is surface treated to secure the desired ballistic properties, as well as other advantageous properties. The powder grain is preferably of nitro-cellulose which is, however, ungelatim'zed; it is moreover preferably of open fibrous structure. The surface treating agent is' preferably a deterrent, such as dinitro-toluene, which is also a gelatinizer for nitro-cellulose, as well as awater-prooflng agent, serving in the case where the grain is of open fibrous structure to modify the porous structure,

partially gelatinize the fibres, cement the fibres together and fill up the spaces between the fibres.

In the process of making this powder, a grain character, whose thickness and area are governed, preferably before nitrating, by the ballistic demands upon the powder. I This grain, which is ungelatinized, is then treated with a surface treating agent, preferably, as stated above, a gelatinizer for nitro-cellulose, at the gelatinizing temperature. The surface treatment is performed in the presence of a substantial amount of moisture, so as to cause the agent to spread over the surface of the grains. For this purpose the grains may be moistened prior to or during the surface treatment, or this moisture maybe that contained within the grain, as by not being completely extracted during the washing operation through which the grain passes after nitration.

An illustrative embodiment of this invention will now be described, although it will be understood that this invention is susceptible of various embodiments.

, Cellulose of a suitable grade is prepared in the form of sheets of paper, the thickness of which is governed by the ballistic demands made upon the powder; for in general the thicker the sheet the slower will be the initial rate of evolution of the gas, since less surface will be ofiered to the flames from the igniting agent when a given weight of considerations of the increased burning surface exposed in the case of finely cut flakes as compared with that of more coarsely cut flakes and also by the various conditions of ignition imposed by changes in the size of the flakes; but mainly because of the desire to secure a free flowing grain which will permit uniform charges in an auto,-

matic loading machine to be secured. Taking for an example a powder for use in a 12 gauge shot gun with ammunition intended for trap shooting, the flake can be made .82 mm. square cut from a sheet of cellulose approately .25 mm. thick.

The cellulose employed may be made from wheat straw produced in accordance with de- Vains process, in which the flake will be of the open fibrous structure; however, other sources of cellulose may be employed. Such powder flakes may be nitrated in any suitable manner until the desired nitrogen content has been achieved. The acid may then be removed and the nitrated grains subjected to, a series of boiling and washing operations, employing for this purpose hard water or water which is slightly alkaline followed by steeping in diluted solutions of urea and of dlphenyle- After final centrifuging, the powder grains need not be completely dried, but may contain from 30 to 40% of moisture or water.

While various surface treating agents may be employed, such as dinitro-toluene, trinitrotoluene, diamyl-phthalate, dibutylphthalate and the substituted ureas (centralites), dinltrotoluene is particularly suitable in the treatment of an ungelatinized nitro-cellulose powder grain, particularly of open fibrous structure, because it does not have such a strong deterrent efiect as some of the other agents mentioned; due probably to the fact that D. N. T. is a nitrated product and semi-explosive in its properties. e, therefore, the other surface treating agents may be employed to advantage, a particular example will be given of the treatment of powder flakes, as heretofore described, with D. N. I.

As an illustrative embodiment of this invention, 20 to 25 parts of D. N. T. are added to a charge of so to parts of the powder flakes containing from 30 to 4.0% or more of water. This water may, as described above, be that left in the grain after washing and centrifuging and even drying, or it may be added to the grains before or during the surface treating. The D. N. T. is added to the powder in the form of a dry powder and thoroughly mixed therewith in an ordinary tumbllng'barrel. Heat is then applied, as by immersing the barrel in hot water, until the powder and the D. N. T. are brought to a point somewhat above the melting point of the latter; a suitable gelatinizing temperature being 75 to C. Tumbling is continued at this temperature to secure impregnation of the surface layers of the flakes with the D. N. T. As the D. N. T. melts, it is caused to spread over the surface of the grain, perhaps, through the aid of the water in the grain. The powder is then removed from the barrel dried at a temperature of 50 C. until the moisture content has been reduced below 1%. After drying, the flakes are tumbled in a sweetie barrel with about 5% graphite until a suitable smoothness has been imparted to the grain to permit the powder to flow freely in the loading machine. Any excess graphite is removed by screening.

The depth of the penetration of the flakes by D, N. T. is governed partly by the amount of D. N. T., partly by the temperature, by the time scopicity.

of tumbling and by other factors, and this degree of penetration may be influenced by the ac! tlon of warm water either during a part of the tumbling process or at a subsequent time. In addition to providing a means for controlling the initial stages of the burning of the flakes, the surface treating process also aflords a method of considerably improving the degree of non-hygroscopicity of the powder. The porous structure of the grain is modified, the D. N. '1. not only partially gelatinlzing the individual fibers, but also cementing these fibers on the surface together and filling up the spaces between the fibers. The structural changes in the flake produced thereby causes the resultant powder grains to difier material y from those obtained by the surface treatment of a gelatinized or dense collolded nitro-cellulose 1 grain; for not only is water-proofing oi the open fibrous structure secured, but the interior of the grain is fast burning, while the initial combustion rate will be retarded.

Since the ungelatinized nitrated flake is char-' acterized by the undesirable high degree of hygroscopicity, even though the degree of nitration be high, it will be seen that the use of a surface treating agent must have special reference to securing both a water-proofing effect, as well as securing the progressive burning characteristic, while still leaving the interior of the grain sumciently fast burning. The employment of an agent such as D. N. T. which can be used in large proportions without adversely afiecting the potential of the powder with reference to ballistic properties, anords a means for improving the hygroscopic character of the powder to almost any desired extent. on the other hand, it has been found that more strongly deterrent materials, when added in amounts which give the desired burning characteristics to the flake, can be employed only in such small proportions as to not efiect the desired reduction in hygro- The powder after being surface treated is subjected to a drying operation in a dry house and this treatment may also serve as a sort of seasoning process to permit the D. N. T. to achieve a more stable condition in the powder grain. A certain degree of control of ballistic properties is also efiected in the graphiting process, since the gravimetric density of the grain is modified by mechanical tumbling. It is believed, therefore,

to efiect a change in the density and, therefore, in ballistic properties, to a control of such processing steps as the treatment in the surface treating barrel and in the sweetie barrel.

The process embodying this invention is such as to enhance the safety in the course of manwfacture. The tendency to generate static electricity which is characteristic where powder grains are prepared by the aid of solvents is greatiy reduced, since the flakes are wet up to and including the surface treating process; as soon as the moisture content has been reduced to a suitable low point, (an operation which may be carried out expeditiously due to the non-gelatinized general structure of the flake) the powder manufacture is completed, except for glazing and screening. Not only is the time of manufacture greatly reduced in this process, but the period during which the powder is a source of hazard is very greatly reduced, existing only at the final stages of the drying. The short period of manufacture also tends to a much safer plant operation, since a factory of any given capacity will have a much smaller amount of material in 75 the saving in capital invested connected with the.

' these coated process. In addition economieswill be eil ected by the elimination of the use of solvents due to erection-of buildings and equipment for solvent recovery, solvent rectification, manufacture, etc. Economies willalso be effected in the avoidance of the customary losses of solvents.

It will be apparent that the manner in which powders burn will depend, other things beingv equal, upon the manner in which the coating agent is distributed throughout the surface layers of the grains. 1! the coating is concentrated at the surface, initial burning will be very slow, but once this shallow layer of coating has been burned through, the rate of burning of the remainder the flake is much deeper; and the concentration of the coating forms a gradient where the richest portions are on the surface and weaker portions toward the center of the grain, it will be obvious that many variations in these burning characteristics can be secured by changing the sharpness of this-gradient.

A convenient method of achieving a desired gradient in the penetration of the coating, D. N. T. for example, consists in first wetting the grains with a material which does not gelatinize the nitro-cellulose but which is a solvent for the D. N. T. Ordinary ethyl alcohol is a suitable material for this purpose. It the flakes are steeped in a bath of ethyl alcohol and the excess alcohol removed by wringing, an alcohol content of 40% or more can be readily obtained.

. D. N. T. into the When these flakes are introduced into a tumbling or other device with an appropriate charge of D. N. T. in the form of a crystalline powder, the D. N. T. will tend to dissolve in the alcohol and thus penetrate the outer layers of the grain, the solution tension existing between the D. N. T. and the alcohol being responsible for drawingthe flake. It, on the other hand,

of the flake will be very high. It, on the other hand, the impregnation of a concentrated solution of D. N. T. in alcohol is applied, this will ailorda means of establishing this gradient in D. N. T. concentration through the diflusion of the D. N. T. from the concentrated solution into the alcohol contained in the grain. The depth or penetration in either case can be regulated by the time interval allowed for the penetration. Other vehicles than ethyl alcohol can, of course, be employed, and advantage may be taken oi. the partial gelatinizing tendency oi such material as methanol, or mixtures otracetone and alcohol, or methanol and alcohol, to produce a swelling of the nitro-cellulose and perhaps a more intimate association oi these swollen fibers with the coating agent.

,It will be understood that various features, combinations and sub-combinations are of utility and may be employed without reference to other features and combinations; that is contemplated by and is' within the scope of the appended claims. It will furthermore be understood that various changes .may be made in details, within the scope or the appended claims.

without departing from the spirit of this invention. It is, therefore, to be understood that this invention is not to be limited to the specific details described.

Having thus descri d the invention what is claimed is:

1. In the art of making propellent powders, the process comprising, treating anungelatinized nitro-cellulose powder'grain with a geiatinizer tor nitro-cellulose while the grain contains a solvent for the gelatinizer.

2. In the art of making propellent powders,

the process comprising, treating an ungelatinized nitro-cellulose powder grain with a gelatiniker for nitro-cellulose while the grain contains a solvent for the gelatinizer which is a non-gelatinizer i'or nitro-cellulose.

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