US 3223756 A
Description (OCR text may contain errors)
Dem 1955 E. s. GOODYEAR ETAL 3,223,756
SMOKELES S POWDER MANUFACTURE Filed Dec. 20, 1957 2 Sheets-Sheet 1 CUTTING MACHINE LEACHING ELLSWORTH S. GOODYEAR CHARLES E. THOMAS INVENTORS AGENT Dec. 14, 1965 GQQDYEAR ETAL 3,223,756
SMOKELESS POWDER MANUFACTURE Filed Dec. 20, 1957 2 Sheets-Sheet 2 ELLSWORTH S. GOODYEAR CHARLES E. THOMAS INVENTORS BY W PM AGENT United States Patent 3,223,756 SMQK-ELESS POWDER MANUFACTURE Ellsworth'S. Goodyear and Charles E. Thomas, Kenvrl,
N.J., assignors to Hercules Powder Company, Wilmington, Del.,-a corporation ofDelaware Filed Dec. 20, 1957, Ser. No. 704,205 Claims. (Cl. 2643) This invention relates to perforated smokeless powders and to their manufacture employing a shock gel-type process. In still another aspect, this invention relates to a method for making perforated smokeless powders wherein a solution of nitrocellulose is extruded into a body of water while maintaining a perforation in the resulting strand and wherein water is simultaneously injected into contact with the walls of the perforation, so that shock gelation of both the inner and outer strand surfaces takes place to form a rigid perforated strand which can be further processed for cutting into grains. In still another aspect, this invention relates to apparatus for the manufacture of perforated smokeless powders by the shock gel method.
In the copending application of Ralph F. Preckel, Serial Number 477,585, filed December 24, 1954, now Patent No. 3,037,247, is disclosed and claimed a shock-type g'el process for the manufacture of smokeless powders which eliminates disadvantages associated with well-known methods of the prior art. In carrying out the shock gel method of the said copending application, nitrocellulose in solution with a water-miscible alkoxy alcohol is introduced into a water bath under conditions which provide for precipitation of the outer layers of the solution (gelation) at the instant of contact to form an envelope of nitrocellulose composition about the exterior of the body which is of sufiicient toughness that the body retains its shape. The shock gel particle is then retained in the Water bath or otherwise contacted with water to leach the alcohol solvent and replace it with water to complete the gelation.
'As set forth in the said copending application, the nitrocellulose containing solution can be introduced into the water body in accordance with several different techniques. In accordance with one such technique the solution is extruded through an orifice into the water body as a cord or strand and is shock gelled and initially leached in that form. The resulting strand is then cut into the desired grain size in accordance with conventional solvent technique, leaching is completed and the grain is dried to form finished product.
Prior methods for the manufacture of smokeless powder include the well-known solvent, solventless, and casting methods. As is well-known, in the solvent method nitrocellulose is dissolved in a volatile solvent such as acetone, ether-alcohol, acetone-alcohol, or the like so as to form a resulting viscous mass, which mass is then granulated and the volatile solvent removed. This process is quite time consuming relative to the time required for removal of the solvent from the green grain and is also hazardous from the standpoint of the handling of volatile solvents that is required. Further, the solvent is never completely removed so that residual solvent migration from the grain results in a change in the ballistics of the powder.
In the solventless extrusion process, the desired powder ingredients are mixed in a water slurry which is then dried to the desired moisture content and the resulting mass rolled on hot rolls to obtain a colloidal sheet, which sheet is then extruded to the desired granulation. This process inherently constitutes a fire hazard and can even encounter detonation during colloiding of the composition in the rolling step.
Casting techniques have been developed in which small grains made, for example, by the solvent process are introduced into a mold together with other required components such as a plasticizer, and the grain of the desired size is cast through the solvation of the granules by the plasticizer. However, in order to produce the cast grain in this manner, it is necessary to accept the disadvantages of either the solvent or solventless extrusion processes in production of the base grain to be used in the casting operation.
The shock gel method as described in the copending application above referred to has provided a technique which eliminates disadvantages associated with the wellknown methods above discussed. Thus it has, in particular, eliminated safety hazards connected with the use of volatile solvents and with hot rolling colloiding steps, and has provided for marked decrease in processing'time.
As is well-known in the art, perforation of smokeless powders provides for regulation of burning rates of the grain by controlling the amount of available powder surface during the entire combustion. Perforation has generally been carried out during extrusion by employing a conventional die containing. a pin rnerriber around which the powder is extruded and the perforationforr'ned. In such instances the powder has been at sufficiently low fluidity that the perforation initially formed has retained its form during subsequent recovery treatment to provide the desired perforated powder. However, in the shock gel method above described, although the outer layer of the powder strand precipitates (or g'els') almost instantly without change in shape and the gelation spreads rapidly throughout the mass, the gelation is not sufficiently rapid as to cause the interior strand portions to set up and prevent flow of the strand material into the perforate area. Accordingly, the interior strand portion in its relatively high state of fluidity flows into the initially formed perforation to close it and form a solid or nonperforated strand.
This invention is concerned with a method for utilizing shock gelation in the manufacture of perforated smokeless powders which powders heretofore have been made only with the disadvantages and hazards of solvent, solventless and casting methods of the prior art and which heretofore have not been possible by shock gelation.
An object of this invention is to provide for the manufacture of perforated smokeless powders. Another object is to provide for the utilization of the shock gel method for the manufacture of perforated smokeless powders. tAnother object is to provide for the extrusion and perforation of a strand of nitrocellulose from a solution and for simultaneously shock gelling the extruded nitrocellulose to form a perforated smokeless powder. Another object is to provide apparatus for the production of perforated smokeless powders by shock gelation. Other objects and aspects will be apparent in light of the accompanying disclosure and the appended claims.
In accordance with this invention, a method is provided for the manufacture of perforated smokeless powders by shock gelation, which comprises extruding a solution of nitrocellulose in a water-miscible solvent into a body of water in form of a perforated strand, and injecting water into the resulting perforation in direct contact with the strand portions forming same, whereby gelation of both the outer surface of the strand and the inner surface thereof forming said perforation takes place to maintain said strand in its perforated form.
In the practice of a now-preferred embodiment, a solution of nitrocellulose in a water-miscible alkoxy alcohol is extruded through an elongated passageway and around an obstructing member therein, which extends to the point of discharge of said solution from the passageway, to form a perforated strand of said solution; and the resulting strand is immediately passed into a body of water while at the same time water from Within the said obstructing member is injected into the perforation to provide for gelation of both the outer surface of the strand and the inner strand surface forming the perforation. In this manner the strand walls forming the perforation are immediately gelled to a degree sufficient to prevent the strand from flowing into the perforation to close it, and the strand retains its perforated form throughout the remaining processing.
Further in accordance with the invention, .apparatus is provided for carrying out the above-described process which comprises a first conduit, open at one end; a tube member, open at one end and coaxially extending through at least a portion of said first conduit, with its open end disposed in close proximity to the open end of said first conduit; means for flowing fluid through said tube toward its open end; and means for flowing fluid through said first conduit, around the said tube therein, in a direction toward the said conduit open end.
The invention is further illustrated with reference to the drawings of which FIGURE 1 is a. front elevation illustrative of an embodiment of apparatus comprising a pair of chambers with associated conduit structure for delivering the separate fluid streams to the extrusion tube assembly; and FIGURE 2 is a front elevation of an embodiment of apparatus for delivering the said fluid stream to the extrusion assembly, but containing only a single chamber.
With reference to FIGURE 1 extruder 9 comprises housing 10 containing a nipple 11 extending into an upper portion thereof to form chamber 11a. Nipple 11 abuts cylinder block element 12, containing gasket 8, in housing 10 which is disposed coaxially with nipple 11 and contains circumferentially disposed annulus 13 closed by the interior wall portion 15 of the housing 10 but which is in direct closed communication with the interior of conduit 14 extending into housing 10 from an external point. A plurality of openings 16 are formed in cylinder 12 in direct communication with annulus 13. All of conduits 16 are in direct communication with longitudinally disposed conduit 17 in cylinder 12.
A secondary reservoir 11b, generally considerably smaller than reservoir 11a is disposed in housing 10 below cylinder 12 out of communication with reservoir 11:: except via conduits 19. Conduit 21 extends from outside housing 10 through the bottom 22 of housing 10 into direct closed communication with reservoir 11b. Perforate pin, or tube, 23 extends longitudinally within conduit 21 from the external end 24 into closed communication of its interior with conduit 17 thus being disposed to accept delivery of fluid from conduit 17 and to deliver same toward the end 24 of conduit 21. The annulus 26 formed by tube member 23 within conduit 21 provides for flow, or extrusion, of liquid from reservoir 11b through conduit 21 to an external point, i.e. extrusion of fluid from reservoir 11b takes place via annulus 26 and around pin 23.
In the operation of the apparatus of FIGURE 1 to form a perforated smokeless powder, a solution of nitrocellu lose in any suitable concentration that can be uniformly consolidated, say from about 1-40 weight percent or higher, in a water-miscible alkoxy alcohol, ethylene glycol being now preferred, is introduced into reservoir 11a and passed via conduits 19 into reservoir 11b. Simultaneously, water is introduced via conduit 14 annulus 13 and conduits 16 into and through perforated pin, or tube, 23 to a point in close proximity to tube end 24-. Pressure is applied to reservoir 11a in an amount suflicient to flow the solution to reservoir 11b and through annulus 26 in conduit 21, the said annulus being so dimensioned as to provide a strand 28 of predetermined web thickness. The rate of flow of water into tube 23 is sufficiently high that water is continuously supplied therefrom to the strand perforation.
Solution emerges from annulus 26 at the end 24 of conduit 21 directly into water body 27 under suitable conditions for effecting shock gelation of the solution to form strand 28. The solution in annulus 26 is fluid so that ordinarily the perforation formed in conduit 21 by tube 23 will be closed by flow of solution into it to produce a solid strand. However, by injection of water via tube 23 into the resulting perforation of strand 23 the inner surface of the strand forming the said perforation is shock gelled so as to become sufficiently nonfluid to retain strand 23 in perforated form.
Water upon immediate contact with strand 28 exerts an initial leaching action to replace the solvent and form the gel. Thus, both the outer surface of the strand and the inner surface thereof forming the perforation, immediately undergo gelation without change in shape to form or firm up the perforated strand 28.
Although sufficient leaching takes place to immediately cause the gelation, additional leaching is generally required for completely replacing the solvent with water to provide the finished gel product. Accordingly, the initial perforated strand product is conveyed from water body 27 by roller assembly 30 and to conventional cut ting machine 31 for cutting the strand into grains for example, from about 11 to grains per inch. The resulting grains are passed into a leaching system 33 via line 32 to complete solvent removal by leaching action of water and then via line 34 to a conventional drier assembly 36 from which they are withdrawn via line 37 as product of the process.
With reference to FIGURE 2, housing 10 contains a single chamber 11a connected with conduit 46, through closed top 20 of housing 10', as a fluid inlet to chamber 11a. Conduit 21' extends from outside chamber 11a into direct communication with chamber 11a. Tube member 23 extends longitudinally through conduit 21 through chamber 11a and the top 20 of housing 10. Conduit 14' is connected with tube 23 as a fluid inlet therefor for delivery of fluid through tube 23 in a direction toward outside end 24 of conduit 21'.
In the operation of apparatus of FIGURE 2 a glycolnitrocellulose solution described with reference to FIG- URE l is introduced into reservoir 11a via conduit 46' and passed under the desired extrusion pressure through annulus 26 formed around'tube 23 within conduit 21. Annulus 26 is so dimensioned as to provide for a strand of predetermined web thickness. Simultaneously, water is introduced via conduit 14 into and through tube 23'.
Solution from annulus 26' at the end 24- of conduit 21' is passed directly into water body 27 under conditions for effecting shock gelation of the solution to form strand 28, while at the same time water injected into the perforation of the strand 28 causes shock gelation of the perforation surfaces so that, as illustrated with reference to FIGURE 1, the strand is sufficiently firm to retain its perforated form.
Strand 23' is removed from water bath 27 for cutting, final leaching, and drying, all as illustrated with reference to FIGURE 1.
The conventional additives to nitrocellulose and smokeless powder compositions may be added at various points in the process without detracting from the method as hereinabove set forth. For example, plasticizers and other additives such as stabilizers and ballistic modifiers for the nitrocellulose may be incorporated in the original solution, thus giving a finished particle in which the plasticizers and additives are uniformly incorporated. Alternatively, the plasticizers may be introduced into the grain subsequent to leaching for example by contacting the waterlogged particles with an equeous solution, suspension or emulsion of the plasticizer or additive for a period necessary to obtain the desired degree of absorption.
In general, it is preferred to introduce only substantially water-insoluble plasticizers and additives into the original solution prior to the gelation step. In most instances, it is not desirable to incorporate such plasticizers as liquid explosive nitric esters, pentaerythritol trinitrate or dimethylphthalate in the original solution, since even their limited water solubility causes a leaching of an undesirable amount of the plasticizers from the gelled particles along with the alkoxy alcohol solvent. For such materials, it is preferred to employ the alternate method of incorporation. For example, the water-logged grains may be contacted with an emulsion of nitroglycerin and water preferably with agitation, until the desired amount of nitroglycerin is absorbed by the nitrocellulose. Then, when subjected to the drying operation, the residiual water is removed and a colloided double base propellant body is obtained. As will be subsequently discussed, nonplasticizers for nitrocellulose may also be introduced into the nitrocellulose structure to produce compositions having novel and desirable properties.
The concentration of nitrocellulose in the water-miscible alkoxy alcohol solution is generally about 1 to 40 weight percent, the nitrogen content of the nitrocellulose being from about 11.3 to 13.9 weight percent, generally above about 12 percent. However, any concentration of nitrocellulose up to that which does not render the solution unduly viscous can be employed, such concentration varying with the solvent employed and the supplemental ingredients present as well as the pressure of extrusion. Thus, up to about 8 percent (12.6% N) nitrocellulose in ethylene glycol can be satisfactorily employed at an extrusion pressure varying from the hydrostatic head of the solution to about 300 p.s.i. while higher concentrations can be utilized at higher extrusion pressure such as up to 3000 p.s.i. and higher.
The water body into which the strand is extruded accumulates polyhydroxy alcohol solvent which must not be present in a concentration exceeding about 90 percent. Thus, in continuous operation a stream of fresh water can be continuously added to the water body 27 via line 38 at a point in close proximity to the point of withdrawal of strand 28, and a stream of solvent-containing water can be withdrawn at about the same rate, at a point in close proximity to the point of introduction of the strand into the water body, via line 39, to maintain the desired ratio of water to solvent. Alternatively the grains can be progressively contacted with water bodies of successively lower alcohol solvent concentration for recovery substantially free from the said alcohol.
Any suitable temperature can be utilized for water body 27 and for leaching step 33, as for example from 10 to 90 F. Exemplary nitrocellulose solution temperatures are in the order of from about 50 to 125 F.
Exemplary of alkoxy alcohols employed in the practice of this invention are diethylene glycol, glycerol-a-allyl ether, glyceroLa-methyI ether, diethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, methoxyethanol, diethylene glycol methylether, diethylene glycol methylether/diethylene glycol, and glycerol-c:- allylether/diethylene glycol methylether.
In view of the fact that the solubility characteristics of nitrocellulose depend upon the percent nitrogen of the nitrocellulose, all nitrocellulose cannot be dissolved in every one of the alkoxy alcohols to the same concentration and in most instances nitrocellulose is not soluble in one particular solvent throughout the entire nitration range. However, the solubility of a particular grade of nitrocellulose in a particular solvent is a strictly physical phenomenon and the selection of the preferred solvent or solvent mixtures to be employed in the present invention is a routine matter. In Table 1, data are presented which are illustrative of alkoy alcohols or mixtures in which the indicated nitrocellulose can be dissolved and the resulting solutions gelled to produce, after leaching and drying, excellent perforated smokeless powder strands. The table does not represent limits of solubility but instead preferred alkoxy alcohols for nitrocellulose of specific percent N.
6 Table 1 Percent N Solvent Glycerol-a-allyl ether. GlyCBlOl-uJnBtllyl ether. Diethylene glycol Polyethylene glycol Dipropylene glycol Polypropylene glycol Methoxyethanol Diethylene glycol methylether Diethylene glycol methylether/diethylone glycol Glycerol-a-allylether/ diethylene glycol methylether Of all the alkoxy alcohols, diethylene glycol is preferred, especially when employed with nitrocellulose having a percent N or" between 12 and 13.
Although the tube 23, or 23', advantageously terminates at the end 24 of the conduit 21 or 21', as shown in the drawings, it can extend through the end 24 or terminate short of the end 24 it being important, in any event, that the water injection can be accomplished immediately as the strand passes from the end of said tube, i.e. tube 23 or 23'.
Any suitable apparatus arrangement for eflecting gelation and initial leaching can be utilized: Generally, the water body 27 is of sufficient length that the strand can be passed through it on a continuous flow basis to the cutting machine.
Drying is advantageously done by supporting the grains in a current of dry air at about -140 F., although any suitable drying arrangement can be employed.
The invention is more specifically illustrated with reference to the following example:
Four parts (weight basis) of nitrocellulose (12.6% N) was dissolved in 96 parts of diethylene glycol. The nitrocellulose was stabilized with 1 part of 2-nitrodiphenylamine per 45.4 parts of nitrocellulose. The solution was extruded through a water-injection assembly of FIGURE 1 of the drawings. The extrusion pressure was 21 p.s.i. The temperature of the ethylene glycol solution was 20 C. Water, at .20 C. was passed through the pin 23, shock gelling the perforation in the strand. The completely shock gelled strand was cut, afterinitial leaching, to 0.2 inch lengths. After granulation the sample was leached with water over a 48 hours period to remove all of the diethylene glycol. The resulting water-logged grains were then held in a hot air drying chamber for 2 days at 55 C. The extrusion die was 0.096 inch inside diameter and the tube 23 was 0.032 inch outside diameter. Fully colloided dried grains of perforated smokeless powder were obtained. The grain dimensions were as follows:
inch Length 0.0645 Diameter 0.0377 Perforation dia 0.0169 Web 0.0104
Extrusion pressure was provided by pumping nitrocellulose solution into reservoir 11a under predetermined pressure head, on a continuous flow basis, as shown with reference to pump assembly 41 comprising solution storage tank 42, reciprocating pump 43 and pump inlet and discharge lines 44 and 46, the latter discharging into reservoir 11a.
Although the invention is described herein with reference to the use of water-miscible alkoxy alcohol solvents in formation of the nitrocellulose solution to be extruded, it is within the scope of the invention to utilize any suitable water-miscible solvent.
As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.
What we claim and desire to protect by Letters Patent 1. A method for the manufacture of perforated smokeless .powder, which comprises extruding a water-miscible alkoxy alcohol solution of nitrocellulose of from 11.3 to 13.9 weight percent N content around an elongated obstruction member in form of a perforated strand into a body of water containing at the point of initial contact not more than 90 volume percent of said alcohol, and passing water through the said elongated obstruction member toward and into the resulting perforation in direct contact with the strand portions forming same, whereby gelation of both the outer surface of the strand and the inner surface forming said perforation takes place to maintain said strand in its perforated form.
2. A method for the manufacture of perforated smokeless powders, which comprises extruding a water-miscible alkoxy alcohol solution of nitrocellulose of from 11.3 to 13.9 weight percent N content, through an elongated passageway and around an elongated obstructing member therein into a body of Water containing at the point of initial contact not more than 90 volume percent of said alcohol, to form a perforated strand; said elongated member extending in said passageway to the point of discharge of said solution from said passageway; passing water through said elongated member toward and into the resulting perforation in direct contact with the strand portions forming same, as said strand emerges from said passageway, whereby gelation of both the outer surface of the strand and the inner surface forming said perforation takes place to maintain said strand in its perforated form.
3. In the extrusion of a water-miscible alkoxy alcohol solution of nitrocellulose of from 11.3 to 13.9 weight percent N content into a water body containing at the point of initial contact not more than 90 volume percent of said alcohol to shock gel the resulting strand, the improvement comprising extruding said solution around a tube member to form a strand containing a perforation, and immediately passing water from said tube toward and into said perforation to cause gelation of the strand surface forming said perforation.
4. A method for the manufacture of perforated smokeless powder, which comprises extruding a solution of nitrocellulose of from 11.3 to 13.9 weight percent N content in a water-miscible alkoxy alcohol around a tube member in form of a perforated strand into a body of water containing at the point of initial contact not more than volume percent of said alcohol, and passing water through the said tube toward and into the resulting perforation in direct contact with the strand .portions forming same, whereby gelation of both the outer surface of the strand and the inner surface forming said perforation takes place to maintain said strand in its perforated form, cutting resulting strand product into grains, substantially completely water leaching residual alcohol from grains so produced, drying resulting water-logged grains, and recovering dry grain as product of the Process.
5. A method of claim 1 wherein said solvent is diethylene glycol.
6. A method of claim 5 wherein the concentration of nitrocellulose in said solvent is within the range of from 1 to 8 weight percent, the pressure of said extrusion is up to 300 p.s.i., the temperature of said water body and of said water passed into said perforation is in the range of from 10 to 90 F. and the temperature of the said solution is in the range of 50 to F.
'7. A method of claim 1 wherein the concentration of nitrocellulose in said solution is up to 40 weight percent and the extrusion pressure is up to 3000 psi.
8. A method of claim 4 wherein said water-logged grains are contacted with an aqueous emulsion of nitroglycerin .prior to said drying to incorporate nitroglycerin into each of the said grains.
9. A method of claim 4 wherein the concentration of water in said water body is maintained by introducing fresh water into said water body at a point in close proximity to the point of withdrawal of said strand therefrom and by withdrawing solvent-containing water from said body at a point in close proximity to the point of introduction of said strand into said body.
10. A method of claim 5 wherein the N content of said nitrocellulose is from 12 to 13 weight percent.
ROGER L. CAMPBELL, WILLIAM MCEWEN,