Patent Publication Number: US-6209460-B1

Title: Propelling material formed in strips for use in large caliber guns

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of commonly assigned corresponding application Ser. No. 09/206,085 invented by Brian J. Isle, et al and filed on Dec. 4, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to propellant charges in medium and large caliber cased or caseless gun systems. More specifically the invention is directed to the configuration of the charge that is loaded into the cartridge case assembly. The configuration, in this case, generally the shape, density and placement of the propellant charge is a departure from contemporary configurations. 
     Munitions that use solid propellants carried in the cartridge casing typically relied on spherical or cylindrical grain geometry for ease of processing. Burn rates, the speed that a flame front is propagated through the propellant, were controlled through geometry (i.e. grain perforations) or through chemical (i.e. deterrents) means. Burn rate modification and progressivity tuning are important considerations in designing charge loads. Another technique to provide a propellant in the cartridge is to use what are known as co-layered propellants in a disk or rolled scroll. Co-layered propellants being a descriptive term describing the use of layers of precut propellant elements cut from a sheet of propellant material. It is known to use co-layered propellants in the shape of rings or appertured disks of different propellants stacked in a sandwich configuration. In co-layered propellants so called “fast burn” propellant sheet stock, cut in the appropriate appertured disk or ring shape, is sandwiched between two layers of slower burning propellant sheet stock. The source of co-layered propellant sheets is Alliant Tech Systems who can provide the co-layered propellant in die-cut annular ring shapes or in uncut sheets. 
     Another use of co-layered propellants is in a rolled scroll form. In this configuration the propellant sheet is rolled to form a scroll. The scroll form is aligned longitudially with the boom of the projectile and if ignited from the end of the scroll, the normal technique, the flame propagation will be more difficult to control than the flame propagation of this invention. In the scroll form of propellant it is difficult to control burn propagation and there is a risk that waves of pressure may build to the point of weapon destruction. Therefore the scroll form of propellant is more difficult to specify than is the strip embodiment presented here. 
     One of the disadvantages of co-layered propellants is that the stacked disks provide, having only limited natural ullage, a barrier to gas flow which can lead to detrimental pressure waves in the gun. These detrimental waves are caused in part by the blockage presented by the disks. The invention presented in this specification avoids or minimizes the barrier to the gas flow as the strips of propellant allow sufficient ullage between the strips. 
     Another disadvantage of co-layered propellants in disk form, as is used in the prior designs, is that the manufacture of the rings creates a large amount of scrap propellant. It is known that to cut a circular disc from a rectangular sheet of propellant material will cause significant selvage or waste of material. The sheets of propellant are expensive and anytime you can save on material the cost of a loaded cartridge case will be commensurately lower. 
     SUMMARY OF THE INVENTION 
     One aspect of this invention is the use of strips of material which are placed in a shell casing in a direction that is aligned with the longitudial axis of the shell. The strips of material, the material being a propellant compound that is pressed and formed into sheets, are arranged to be vertical when the shell, for reference purpose, is stood on its end. One advantage of the strip contour, as contrasted to the disk shaped propellant, is that the strips are more economical to produce and produce less waste in the production cycle. In the scroll form of propellant packaging the sheets of propellant are well utilized. However, the burn characteristics of the scroll form are not as predictable as the disk embodiments or of the embodiments presented here. 
     In the development of this invention the inventors have found that the strip type of propellant will produce a better combustion event in a gun chamber. Therefore it is an object of this invention to provide a propellant charge in the form of a strip of propellant material such that a better, more complete and more uniform burn rate of the propellant is realized. The strips of propellant will burn more efficiently than known embodiments of either disk, scroll or solid rod type fuel charges. 
     It is another object of the invention to provide a propellant charge that is cut from a sheet of propellant material in an efficient way to minimize the amount of wasted propellant scrap. 
     It is also an advantage of this invention that the strips used will be self-supporting. The configuration and arrangement of the propellant strips will comprise a self-supporting column. This is beneficial as the column arrangement will not buckle or shift during transport or handling. 
     Another advantage of the arrangement of the strips verses the disk arrangement is that with the embodiment incorporating the strips there will be a channel to accommodate the fins of the projectile. 
     One further advantage of the invention is that the position of the strips in a generally vertical column shape will allow the cartridge case to be slipped over the column of propellant material in the assembly phase. This is advantageous as the assembly of the cartridge and the propellant can be done cleanly and swiftly as there will be less potential interference between the edge of the shell and the column of propellant. 
     It is another object of the invention to provide a propellant charge which provides passageways and has an adequate percentage of ullage in the propellant charge to provide effective axial and radial flame propagation and flame spread paths. 
     One further advantage of the invention over the disks of the known art is that the strips can straddle the fins of the projectile boom whereas in the disk embodiment the disks are limited to being large in interior diameter to accommodate the fins extending radially outwardly from the boom of the projectile. 
     Another advantage of this invention is that the propellant strips can be contoured to follow the ramp angle of the boom allowing the use of more propellant in the cartridge or the same amount of propellant in a better distribution when compared to a conventional disk style embodiment. 
     One further advantage of the invention is that it lends itself well to the use in a modular charge. That is, the strips are easily contoured to a shape appropriate to a large number of possible uses, for instance in different gun systems. 
     Basically the invention set forth herein has as its object the improvement in the burn propagation of a flame in a large munition. This is to be accomplished while at the same time making the cost to produce the propellant charge less expensive through the elimination of waste in the production of usable propellant inserts. 
     These and other objects and advantages of the invention will be apparent to a person of skill in the munitions field as the following specification is comprehended and the accompanying drawing figures are studied. 
     The preferred embodiments of the invention presented here are described below in the drawing figures and Detailed Description of the Drawings. Unless specifically noted, it is intended that the words and phrases in the specification and the claims are given the ordinary and accustomed meaning to those of ordinary skill in the applicable arts. If any other special meaning is intended for any word or phrase, the specification will clearly state and define the special meaning. 
     Likewise, the use of the words “function” or “means” in the Detailed Description of the Drawings is not intended to indicate a desire to invoke the special provisions of 35 U.S.C. 112, Paragraph 6, to define the invention. To the contrary, if the provisions of 35 U.S.C. 112, Paragraph 6 are sought to be invoked to define the inventions, the claims will specifically state the phrases “means for” or “step for” and a function, without also reciting in such phrases any structure, material or act in support of the function. Even when the claims recite a “means for” or “step for” performing a function, if they also recite any structure, material or acts in support of that means or step, then the intention is not to invoke the provisions of 35 U.S.C. 112, Paragraph 6. Moreover, even if the provisions of 35 U.S.C. 112, Paragraph 6 are invoked to define the inventions, it is intended that the inventions not be limited only to the specific structure, material or acts that are described in the preferred embodiments, but in addition, include any and all structures, materials or acts that perform the claimed function, along with any and all known or later-developed equivalent structures, material or acts for performing the claimed function. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be understandable by a reading of the specification in combination with the drawing figures wherein: 
     FIG. 1 is a perspective view of a large caliber gun cartridge with a portion broken away to reveal the interior of the cartridge; 
     FIG. 2 is a cross-sectional view through  2 — 2  (without regard to the broken away portion of FIG. 1) of a large caliber gun cartridge illustrated in FIG. 1; 
     FIGS. 3 a ,  3   b  and  3   c  are plan of sheets of propellant with the outline of the shape of strips that will be cut from the sheets drawn on the sheets; 
     FIG. 4 is a cross-sectional view of another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     A large caliber gun cartridge  10 , FIG. 1, comprises a cartridge case assembly  11  and a projectile  12 . (In this specification, and in some claims, the term “shell casing” is sometimes used rather than the term “cartridge.” These terms are intended to be descriptive and describe the container in which a charge portion of a munition is contained. No unusual or limiting definition is intended by this word choice.) A portion of the cartridge case  11  has been broken away to reveal the contents of the cartridge case. The cartridge case assembly  11  comprises a cartridge wall  13 , a stub case  14 , an igniter  15 , and a propellant charge  16 . The cartridge may include a chambrage region  17 . In this preferred embodiment, the propellant charge  16 , comprises four sets of propellant strips. Each set of propellant strips has a different contour which are most discernable when comparing the widths of each set of propellant strips. It is contemplated to use more or less than four sets of propellant strips but for this preferred embodiment four sets will be described. 
     The stub case  14  is located at a first end  23  of the cartridge case assembly  11 . The projectile  12  of the round is located outboard of the chambrage  17  of the cartridge case assembly  11 . 
     The cartridge  10  has a central axis C—C running the length of the cartridge  10 . 
     FIG. 2 is a cross-sectional view through plane  2 — 2  without regard to the broken away portion of the cartridge case assembly  11  of the cartridge illustrated in FIG. 1. A specific arrangement of propellant strips are set forth in this view. Other arrangements and configurations are also possible. FIGS. 3 a ,  3   b  and  3   c  illustrate an assortment of sheets of propellants  18 . Strips of propellant material are cut out of these sheets of processed propellant. 
     The strips of the first set of radial strips  19  each have a length, the length of the strip being identified as  28  and the width of the strip being identified as  29 . The thickness, identified as  30 , of a strip of the first set of radial strips  19  is shown in FIG.  2 . The length  28  of a strip is greater than the width  29  of a strip. The thickness of all the strips in this embodiment is less than the length or the width of the strips. The thickness of the strips will be on the order of between 0.100 inches and 0.200 inches. Strip thicknesses which are thicker or thinner, or otherwise outside the stated range, are also possible. The necessities of the design will dictate the actual optimum width however it is believed that a width in this range will be acceptable to the functionality of the design. 
     The strips, such as strips  50  and  51 , of the first set of strips  19  are the widest strips. These strips are generally as shown in FIG. 3 a  with a multi-angle blunt nose and an extended tail portion as shown to the right side of the drawing. The length and width of the strips would be dependent on the cartridge into which the strips are to be packaged or loaded. 
     The strips, such as  52  and  53 , of the second set of strips  20  are the second widest strips. They are just slightly more narrow than the width of the first set of wide strips. These strips,  52  and  53  for instance, have generally parallel edges and a semi-blunt nose portion. The tail portion, such as  58 , has a cutback zone, that being the upper contour in FIG. 3 b . The cutback portion  59  is the same contour shape as the tail contour shape of the first, second and third strip sets. The tail portion of all except the fourth set of strips is actually the leading or upper end of the packed cartridge when the cartridge is stood on its first end. 
     The strips, such as  54  and  55 , as shown in FIG. 3 c  of the third set of radial strips  21  are the third widest strips. These strips have a nose portion that is less blunt then the wider strips. The tail contour on the cutback zone is the same as the cutback zone tail contours of the wider strips. 
     The strips, such as  56  and  57 , of the fourth set of radial strips  22  are the narrowest strips. These strips have what appears to be a totally different contour but there are similarities to the other sets of strips. These similarities include the ramp portion  60  of the cutback contour  59 . They also include a relief cutout  61  at the nose of the strip. This relief cutout  61  is also formed in each of the other three strip contours as can be seen in FIG. 3 a.    
     The position of the relief cutout, such as  61 , can be seen generally as the zone  61  in FIG.  1 . The blunt nose portions of the strips can be generally seen in the zone  62  of FIG.  1 . 
     The strips discussed above would normally have a flat surface on each side of the strip. This would be one surface option when the strips are calendared in the production process. Alternatively, the strips can be embossed or provided with a textured or patterned surface that can enhance the ignition characteristics, flame propagation, or structural characteristics of the strips. In the disk embodiment of propellant sheets the disks are often pressed or calendared to have an embossed surface. Similar techniques can be used in the production of propellant sheets destined to be cut into strips as discussed above. 
     In the cross section shown in FIG. 2, the boom or boatel  25  of the projectile is placed along a central axis C-C of the cartridge case assembly  11 . Fins  26  extend radially from the boom  25 . The length of the cartridge extends along the central axis C—C of the cartridge  11  from the first end to the second end. In this FIG. 2 the relationship between the fins  26  and the surrounding strips can be seen. The fins  26  are interstitially positioned between adjacent widest strips such as  50  and  51 . Outboard of the ends of the fins are positioned a selection of strips which are not as wide as the strips adjacent the fins in FIG.  2 . 
     In the manufacture of an a large caliber gun cartridge  10  using the preferred embodiment described above, the cartridge  11 , without the stub case  14 , is placed on the end of the projectile  12  around the boom  25  and fins  26 . In a typical production environment fifteen sheets of propellant  18  will be used to provide thirty strips of the first set of strips  19 . These are the widest strips of the assembly. Thirteen sheets of propellant  18  are needed to supply the forty-two strips of the second set of strips  20 . Six strips can be cut from a little more than one standard sheet of propellant to provide what is needed the third set of radial strips  21 . Obviously these numbers relate only to one given production embodiment and would be different with other size sheets and other strip contours. 
     As stated above the strips of the sets of first, second, third, and fourth strips are tapered, as shown in FIGS. 3 a ,  3   b  and  3   c  to allow the strips to conform to the geometry of the host cartridge. Because the sheets of propellant  18  all have the same thickness in this embodiment, the strips of the sets of first, second, third, and fourth strips end up being the same thickness. There is no reason why various strips can&#39;t be cut from different thicknesses of base stock of propelling sheets. Embodiments of this invention having a combination of different thickness strips is contemplated. 
     The configuration of the strips, as contrasted to the punched out annular or disk shapes, cut from the sheets of propellant  18  allows the minimization of wasted square inches of propellant. 
     Returning to the assembly of the package, it should be noted that the cartridge is assembled from the first end  23 . The cartridge case  11  is open at the first end  23  during loading. After loading the strips of propelling material the stub case  14  is fitted to the end of the cartridge case. The second end  24  of the cartridge case contains the projectile to which may be attached the extended boom and fin section. Envision this assembly being upright in a holding fixture waiting for the propellant strips to be placed around the boom and fin section. 
     The radial strips will be arranged around the boom and fins with the tail portions  58  of the strips projecting into the second end of the cartridge case. The strips can be closely contoured to fit adjacent the boom. This is in contrast to the disk embodiments of the contemporary embodiments which have to have fin clearance and therefore can&#39;t be contoured close to the boom. 
     The strips of the sets of first, second, third, and fourth strips are placed in the cartridge  11  around the boom  25 . The length of each strip of the sets of first, second, third, and fourth strips is substantially parallel to the central axis C—C. The width of each strip of the sets of first, second, third, and fourth strips is substantially perpendicular to the central axis C—C and radial central axis, as show in FIGS. 1 and 2. Gaps between the strips creates passageways  31 . These gaps and voids are sometimes called “ullage.” The passageways  31  extend radially from near the boom  25  of the projectile  12  to near the cartridge wall  13 . The passageways  31  also extend axially along the length of the cartridge  11 . This ullage is beneficial in the flame propagation and the promotion of the controlled burn and combustion of the propellant strips. 
     The stub case  14  is placed in the end of the cartridge  11  after the cartridge  13  has been slid over the propellant strips that have been arranged around the boom and fins. Sliding the cartridge case over the propellant strips is a smooth operation as it is easier to keep the strip elements aligned properly. In disk embodiments the disks present what equates to a series of steps that have to be carefully navigated as the cartridge is placed in position. The stub case  14  covers the strips of the sets of first, second, third, and fourth strips. An igniter device  15  is installed in the stub case  14 . The igniter  15  resides inboard of the nose ends of the collection of strips, that is between the nose portions of strips of the sets of first, second, third, and fourth strips. 
     In operation, the cartridge  10  is placed in a gun system. A signal to the igniter  15  causes the igniter  15  to ignite the propellant charge  16  adjacent to the igniter  15 . The passageways  31  allow the ignition of the propellant to quickly travel radially from the igniter  15  to the cartridge wall  13 , and to quickly travel axially from the first end  23  of the cartridge case assembly  11  adjacent to the igniter  15  to the second end  24  of the cartridge case assembly  11  adjacent to the projectile  12 . The passageways  31  also allow the first ignited propellant adjacent to the igniter  15  to expand and pass with little or no hindrance through the passageways  31  to the projectile  12 . This will provide pressure on the projectile while minimizing detrimental axial pressure waves. The ignited propellant puts a force on the projectile  12 , causing the projectile to accelerate and be shot out of the gun barrel. The cartridge case assembly  11  is removed from the gun and replaced by an unfired, fresh cartridge. 
     FIG. 4 is a cross-sectional view of another embodiment of the invention. A boom  40  of a projectile with fins  41  is placed along a central axis of a cartridge  43 . A first set of strips  45  are placed so that the widths of the first set of strips  45  extend from the wall of the cartridge  43  to the fins  41  of the tail  40  as shown. A second set of strips  46  are placed so the widths of the second set of strips extend from the cartridge  43  to the tail  40  adjacent to the fins  41 . A third set of strips  47  of various widths are placed so that the widths of the third set of strips  47  fill-in a portion of the remaining gaps as shown. Some ullage remains and this is beneficial for flame propagation. The strips of the second set of strips  46  have the widest widths. All of the first, second, and third sets of strips  45 ,  46 , and  47  are shown having the same thickness  50  in this embodiment. The lengths of the strips of the first, second and third set of strips is not apparent from this view but they will project generally from a stub case to the second end of the cartridge case as in the first embodiment. As in the previous embodiment, passageways are formed between strips that pass from the cartridge wall to the boom, and from the back end of the cartridge to the front end of the cartridge. 
     In its most basic embodiment the invention comprises a first strip of propellant material having a length and a width. The length of the propellant material is greater than the width of the propellant material and the first strip comprising a flat plane when viewed in a planar view. Of course in most instances it will be necessary to use a plurality of strips together and in that usual case at least one additional strip of propellant material each comprising a flat plane will be combined with the first strip of propellant material to form a set of strips of propellant materials. It has been found that flat strips are very effective in most embodiments however the strips of propellant material can have embossed surfaces. In another embodiment the strips will be of a non-rectangular shape. This being the usual rather than the exceptional situation. In this embodiment the first strip of propellant material has a first edge, as viewed in a planer view, defining the length of the first strip and a second edge non-parallel to the first edge. At least one of these edges, the planer view not a “side on” or elevation view, will define different radii relative to each other. 
     While preferred embodiments of the present invention have been shown and described herein, it will be appreciated that various changes and modifications may be made without departing from the spirit of the invention as defined by the scope of the appended claims. For instance, it is certainly possible to change the contour of the strips, they could even be as simple as rectangular strips with no curves at all. The idea is that the contour is determined by the interior space available in a cartridge and the amount of ullage needed for good burn propagation. Another example is an embodiment wherein the strip propellant is packaged in preconfigured, unified, “ready to use” packages for use in large caliber guns.