US2655694A - Manufacture of smokeless powder - Google Patents

Description

Oct. 20, 1953 w PIPER 2,655,694-

MANUFACTURE OF SMOKELESS POWDER Filed July 28, 1945 5HE T 0F COLLO/DED 5MOKELE$5 POWDER COMPOSITION STRIPS cur FROM ABOVE :E'ilj: 4

VACUUM EXTRUS/ON PRESS ROLL FORMED FOR EXTRUDING ROLL FROM ABOVE OF Fla 3 STRIP SOL/D CYL/NDR/CAL. COPE OF .SIVOKELESS POWDER COMPOSITION SIMILAR TO COMPOSITION OF THE ABOVE.

SHEET 4 gvwc/wfo'v Willi-min E. Piper Patented Oct. 20, 1953 res ear m OFFICE MANUFACTURE OF SMOKELESS POWDER Application July 28, 1945, Serial No. 607,666

9 Claims.

This invention relates to a method of preparing smokeless powder grains, and more particularly to an improved method of extruding rolled sheet powder to produce a thick-web, large powder grain with improved characteristics.

Smokeless powder to be used as the propellent charge in jet-actuated devices, such as rockets, jet-assisted take-off devices, and the like, is made into the form of large, thick-web grains. An important reason for this is to obtain a small ratio of burning surface to quantity of material, so that the pressure resulting from burning will not be developed too quickly after ignition. In order to prevent erratic changes in pressure during the burning, it is necessary to avoid fissures in the finished powder grain and/or stresses and other causes which will result in fissuring during the burning of the grain. In order to insure uniform ballistics, each such large grain of powder is carefully inspected by X-rays and the like to detect fissures within the grain. Fissured grains are rejected and reworked.

In general, there are two methods of preparing thick-web, large grains of smokeless powder. In one method, commonly referred to as the solvent method, the powder constituents are colloided with the aid of volatile solvents, pressed into uniform blocks of colloided powder, extruded or otherwise molded to the right dimensions, and then treated for the removal of the volatile solvent. This method has a number of disadvantages, particularly in making large grains, arising from the expense and dificulty of removing and recovering the volatile solvents. In the other method, commonly referred to as the solventless method, the ingredients are uniformly mixed and made into a wet paste, the water is removed by drying, the resulting dry paste is colloided by rolling, the colloided mass is rolled into sheets, the sheet material is made into a carpet roll, the carpet roll is extruded by means of a suitable press into the desired grain shape and then cut into grains of the desired length.

Heretofore, in the manufacture of large grains of smokeless powder for use in jet-propelled devices, by the solventless method, a very high percentage of rejections has resulted on account of fissures in the powder grain. The percentage of grains or sticks having fissures as detected by X-rays, in general, has varied from about 6.9 to 10.2% of all sticks examined; in some instances, fissure frequencies of over 20% have been recorded over relatively short periods of time.

Now, in accordance with the present invention, a method has been discovered for producing an extruded plastic mass, having a relatively large cross-sectional area with a marked reduction in the number of fissures in the extruded product, from a roll made from a sheet of the plastic mass.

Generally described, the improved method in accordance with this invention comprises rolling a sheet of the colloided material onto a solid core of similar colloided material, thus forming a carpet roll with a solid core center, placing the carpet roll in an extrusion press provided with a suitable die, removing the air from the press chamber by evacuation and maintaining the chamber under vacuum, and then extruding the material by the application of pressure thereto.

Described more specifically, the method comprises preparing a rolled sheet of a colloided smokeless powder composition, cutting the sheet into strips of any desired and convenient width, rolling the strips into the form of carpet rolls onto solid cores of a similar colloided smokeless powder composition, placing one or more of said rolls into the press chamber of an extrusion press provided with a reciprocating piston, evacuating the press chamber, and then extruding the powder through a suitable die to give an extruded product with a large cross-sectional area and of any desired cross-sectional configuration.

The method is illustrated, partly diagrammatically, in the accompanying drawings, wherein Fig. 1 represents a plan view of a sheet of colloided smokeless powder composition; Fig. 2, plan views of five strips cut from the sheet illustrated in Fig. 1; Fig. 3, a carpet roll formed by rolling strips of the kind illustrated in Fig. 2 onto a solid cylindrical core of a colloided smokeless powder composition similar to the composition of the sheet of Fig. 1; Fig. 4, an extrusion press of the type indicated above; and Fig. 5, a powder grain of cruciform cross-section resulting from the operation of the extrusion press of Fig. 4 upon the roll of Fig. 3.

Having now indicated in a general way the nature and purpose of the invention, there follows a more detailed description of a preferred em bodiment thereof in the following example:

Fifty-one parts of nitrocellulose (13.25% nitrogen) of lint base, about 43 parts of nitroglycerin, about 3 parts of diethyl phthalate, about 1 part of ethyl centralite, all parts by weight, and a small amount of carbon black and candelilla wax, were made into a wet paste by known methods. The wet paste was air-dried to about 12-14% moisture content and then blended and uniformly mixed with about one part by weight (same basis as for above constituents) of finely- 3 subdivided potassium sulfate to give a final dry paste.

The dry paste, in 6-pound charges, was rolled on one or more differential roll assemblies at a temperature of about 210 F. until homogeneous, colloided sheets were obtained. The colloided sheets were stripped from the rolls, cooled, and then several-such sheets, together With rolled sheets of reworked material, werestacked together and made into a single sheet by passing through an even speed roll assembly.

The sheet from the even speed.rolls..was -cut into strips about inches wide and"severalfeet long. The strips were thenwrolledv onto solid rods (about 1 /2 inches in idiameter) :of sazsimilar colloided powder composition .totiormsso-called carpet rolls. The carpet rolls..,thus. formed were about 5 inches long and aboutIO inches indiameter and had solid longitudinal centersicores.

Two of the thus prepared carpet rolls were placed end .to end in thepress .chamber .of...an ,oildraulic horizontal extrusionpress. .The,.press chamber was evacuated andithe chargcwonsisting of about 50 pounds, was.extr.u'ded. into. asingle continuous long. grain of .cruciformscrosssec- .tion which was ,cut intojfivesticksor grains, .each

.fmeasuring about T217 1 inches Jdiametr-ically -across the arms .and about $34 inches longitudinally. The. arms .of I the cruciform were about 3.110 inch thick, .the :controlling webithitzkness of ..this..ty.pe .gl'alin.

" The-,grains .were anneaIe'dLby being. exposedato air .at? 140.1'Fffor- .45 hours. IiThey werathengiven an inspection fondimensional.to1erances:and.surface characteristics, followed 'Izby -an ;X-.ray exanimation for internalifiaws; particiilarlylissures.

The results/of thelinspectionofsticks i grains) .of. powderrma'de in-accordance .with this; example. are. given in .tabular;for1rLbelow,.tQgether with ..comparable .dataforsticks ofithesameitypeoand 40 -..,composition preparedinan identicalmanner ex- .cept .for .omissioneof.the.solid.core,:,provided.=or

.the .carpet ,rolls. L'Thetabulated ldataareier to inspections .made von .several .thousandlsing le grains ..(sticks) -in .the course ..of approximately one .weeks plant. operation1bylhighlysskilledioperatorsin-eachcase.

The:foregoingresultsiiemonstrate conclusively the improvement-insulting .fromrthezmethod accordanceavith-- this invention wherein theecar- ..pet .roll' was? provided with: a-,,-solid .center'. instead of the-usual hollow center z-which-always results from simply rollinga sheet (strip) zofwthe :fairly :stiff colloided, powdeniormulatiom. although ;the

sheet. is warmed to soften. it .prior.,.to.;rol1ing.

The improved powder grains produced in accordance with this invention exhibited fissuring to a markedly smaller extent than sticks produced without the solid center core. Although the improved results were associated with what might be termed the central longitudinal section of the powder sticks, it Was evident that -fissuring.-.occurre.d toeazsmallera-extent even in the arm's-sections of the'cruciform'stick, i. e., in sections which did not contain any of the powder zmaterial of the solid center core.

-Erom..examination of successive cross sections of the extrude'd'grains from rolled sheet powder awithoutrsolidt-corezcenters, it would appear that :thescentemholenwas responsible for most of the fissuring. Further, it would appear that a major -portion of,-,this,fissuring cause was eliminated in the first portion extruded. Thus, the following results.=-show that the largest percentage of bad sticks due to fissures is to be found in the first ..portion of the extruded, powder.

TABLE "2 .Dz'stributz'on :0) fissures in "total of :104 :fissured sticks Percent Stl'ckNo. 35: 2:35

sticks i 1 (first part of extrusion) .L

Thus-sover two-fifths of the ""fissu-redsticks are in the'first-z'one-fifthof the extruded' pow'der.

'From =the comparative results obtained with "and without 'a sol-id center-core; it appears that 1 the causeof-thefissuresyavhen a solid center core is not=-used,=is that some of the airin the-hollow center is not removed even when the presschamzber *is 1 evacuated. Furthermore,- even vv-ith *substantial removal of the air from 'the hollow cen- 1 ter,- 'this wou1d be expected to cause collapseof circumsciibed layers of the "sheet powder -=with "resultant buckling of *the 'layers' and-entrapment I of air :at -other places throughout the 'powder. "These phenomena would be eliminated by preventing the possibility'o'f "coll-apse'ofthematerial --upon =evacuation *such as by 'providing '-the roll :with a solidacenter core. 'Although this appears to be =a'reasonable'explanatiomfor*:the* improvement resulting from application of this invention, it "is not intended that the invention-shall 'be' l-imited to any-particular"theory of operation. In theforegoing example the colloidedpowder (sheet was preparediwithout the aid ofvolatile solvents, such sas @alcoholp ether, acetone, and i the 1 like,; .as well 5 as mixtures rthereof. .However, sexztrusions from ;-:solvent-type, .ccolloided powder .:sheetcmay:.bez mafdezaccording :to the methodzof this invention with s-similarximprovement. .The qpowder 1 constituents: may.-,be-..co1loided tbysiknown -methods and :withthe 21156.10f- V019r13118L0l311i0 :solvents, .thecolloidedimass @i-nade :intmsheets, -..the volatile solvent 1or.=solvents .removed Joy-known imethods the sheetsmade into -a carpet.- roll pro- .-v-ided .with a ,so1id..center..core, andsextruded.

The solid reenter -core'may .be .of any suitable dimensions, which..of .course, will; beJdetermined .by,.the dimensions, particularly .crossesectional, of. 'the graimto -be prepare'dby extrusion. Of course, vi.the -cross .section .will Lbe limited .to a uninimumbrosssection which .willlbe dependentupon the particular physical characteristics of the sheet. Thus, a formulation which gives a very stiff sheet will require a larger core than one which can be bent and folded over easily to form a roll with a small hollow center. The maximum diameter of the core will be limited only by the maximum allowable core-type material in the finished grain, on account of any possible differences in ballistics and other characteristics. The solid rod to be used as the solid center core was prepared from a roll of colloided sheet powder, similar to that to be extruded, by extrusion under pressure using a circular die of the appropriate size. Solid rods free of fissures are selected for use.

This invention is of utility in the manufacture of thick-web, large grains of smokeless powder adapted for use in jet-propelled devices. As indicated hereinbefore, powder grains for such use are advantageously prepared by rolling a sheet of the colloided powder into the form of a carpet roll and then extruding it axially of the roll through a suitable die, such as of a cruciform shape. Heretofore, such practice has resulted in the preparation of a large number of rejects or unsatisfactory powder sticks on ac count of fissures present in the powder stick. The proportion of such unsatisfactory sticks is advantageously reduced when practicing the method of this invention. This increases materially the capacity of a given unit of plant facilities, decreases the total number of inspections required for a given net quantity of satisfactory sticks, decreases the hazards involved in reworking unsatisfactory sticks, etc. All such advantages are gained without any disadvantageous effects, such as alteration in ballistic properties, and the like, contrary to what was expected and as indicated in earlier specifications for rocket powder grains. The demonstration of advantages without corresponding disadvantages is substantiated by the alteration of earlier Government specification so as to specify now the use of a solid center core in extruding sheet powder for thick-web, large grains of smokeless powder for rocket use.

Where in the specification and appended claims the term thick-web, large grain is used, it is meant to designate a powder grain having a minimum burning web of about 0.25 inch and to have a length greater than the web thickness.

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

1. In the art of forming thick-web, large grain smokeless powder by extruding longitudinally a roll prepared from a sheet of colloided smokeless powder, the improvement which comprises preparing said roll by rolling a sheet of said powder onto a solid core of colloided smokeless powder.

In the art of forming thick-web, large grain smokeless powder by extruding longitudinally a roll prepared from a sheet of colloided smokeless powder, the improvement which comprises preparing said roll by rolling a sheet of colloided smokeless powder about a solid core of colloided smokeless powder.

3. The method of forming thick-web, large grain smokeless powder from a colloided sheet of said powder which comprises forming the sheet of colloided powder into a roll provided with a solid core of colloided smokeless powder, and extruding said powder axially into a thickweb, large grain.

4. The method of forming thick-web, large grain smokeless powder from a colloided sheet of said powder which comprises rolling the sheet of colloided powder into a carpet roll provided with a solid core of colloided smokeless powder, and extruding said powder axially into a thickweb, large grain.

5. The method of forming thick-web, large grain smokeless powder from a colloided sheet of said powder which comprises rolling the sheet of colloided powder about a solid core of colloided smokeless powder, and extruding said powder axially into a thick-web, large grain.

6. The method of forming thick-web, large grain smokeless powder from a colloided sheet of said powder which comprises forming the sheet of colloided powder into a roll provided with a solid core of colloided smokeless powder, and extruding said powder axially into a thickweb, large grain having a solid center core.

7. The method of forming thick-web, large grain smokeless powder from a colloided sheet of said powder which comprises rolling the sheet of colloided powder about a solid core of colloided smokeless powder, and extruding said powder axially into a thick-web, large grain having a solid center core.

8. The method of preparing a thick-web, large grain smokeless powder which comprises preparing a sheet of colloided smokeless powder, rolling the sheet of powder about a solid core of colloided smokeless powder, and extruding said powder into a thick-web, large grain.

9. The method of preparing a thick-web, large grain smokeless powder which comprises preparing a sheet of colloided smokeless powder in the absence of volatile solvents therefor, rolling the sheet of powder about a solid core of colloided smokeless powder, and extruding said powder into a thick-web, large grain.

WILLIAM E. PIPER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 620,775 Hoifmann Mar. 7, 1899 1,477,094 Wilson Dec. 11, 1923 1,994,164 Bailey Mar. 12, 1935 2,165,827 Zuckert July 11, 1939 2,229,131 Root Jan. 21, 1941

Claims (1)

1. IN THE ART OF FORMING THICK-WEB, LARGE GRAIN SMOKELESS POWDER BY EXTRUDING LONGITUDINALLY A ROLL PREPARED FROM A SHEET OF COLLOIDED SMOKELESS POWDER, THE IMPROVEMENT WHICH COMPRISES PREPARING SAID ROLL BY ROLLING A SHEET OF SAID POWDER ONTO A SOLID CORE OF COLLOIDED SMOKELESS POWDER.

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