Patent Application
20050193915
I. Field of the Invention
The present invention relates generally to the field of propellant charges, particularly propellant charges suited for use in large or medium caliber projectile ammunition made up of extruded stick-type propellant grains and to the solution of a shortcoming associated with burning characteristics of extruded stick-type propellant shapes having multiple perforations. Specifically, the use of certain non-round longitudinal perforation shapes in propellant stick grains offers a technique to significantly reduce propellant slivers associated with multi-perf propellant at burnout.
II. Related Art
The success of all ammunition projectiles depends greatly upon the performance and the reproducibility of the performance of the associated propellant system. In this regard, the use of multi-perforated stick propellant shapes have long been utilized to enhance the progressivity of the mass rate of gas generation to enhance ballistic performance of many propellant systems. Control of the burn has been enhanced for certain types of munitions by the use of perforated extruded stick propellant shapes packed into the munition cartridge to be fired.
Almost all extruded gun propellants have perforations parallel to the lengthwise dimension of the extruded stick grains to provide ballistic progressivity as the propellant burns. Depending on size and application, stick propellants are normally processed with 1, 7, 19 or up to 37 perforations to enhance progressivity. Proper progressivity is necessary to achieve the needed performance in modern gun systems. Extrusion tools, which are commonly referred to as extrusion dies, are designed to produce an extrudate having the desired shape including the internal voids associated with the perforations. The physical shape, of course, is determined by the requirements of the gun ammunition system. Extrusion dies of the class described are provided with die pins that are used to impart perforations in the finished propellant grains. Typically, 7-perf gun propellant grains, for example, are provided with one central perforation and a single row radial pattern of six perforations surrounding the central perforation. Other patterns include 19 perforations (2 row pattern) and even 37 (3 row pattern) or more perforations in certain propellant designs. Traditionally, the pins and, consequently, the perforations have been round, owing at least in part to limitations in die manufacturing techniques.
FIGS. 1(a)-1(l) illustrate in cross section progressivity of a burn in a prior art 7-perf propellant grain utilizing round perforations and assuming that the perforations are perfectly round and uniformly distributed within the grain such that, based on the web dimensions illustrated in
The need to reduce slivering associated with burning perforated stick propellant grains has remained a longstanding problem in the art and there remains a need for improving the performance of gun propellants by reducing propellant slivers associated with conventional multi-perf propellant geometries.
The present invention provides an extruded stick-type perforated propellant grain that maintains the ballistic progressivity of earlier grains as the propellant burns yet greatly reduces residual slivers associated with prior stick-type perforated propellant grains. The propellant grain of the invention utilizes perforations having a geometric cross-section of a non-round shape that enhances uniformity in the unburned web thickness during a normal burn. The more uniform reduction of web thicknesses throughout the grain greatly reduces the size of any unburned propellant slivers. One shape that has been found to work successfully in round stick propellant grains has a geometric cross-section resembling a trapezoid radially deployed with the longer base directed toward the outside of the propellant grain. The bases, and particularly the longer base, of the trapezoid is preferably also curved in accordance with the outer shape of the propellant grain itself.
While a trapezoidal shape in the radially spaced array of grain perforations is shown in the detailed embodiment, it will be appreciated that perforations of other geometric shapes may also be used so long as they achieve the desired reduced slivering in progressive propellant grain burns. In accordance with the invention, a central perforation may also be round or another shape such as in the form of a six-pointed star shape in accordance with improved performance during the burn.
Perforations of a generally trapezoidal shape have been found to be optimal with respect to a 7-perf round stick propellant grain such as that illustrated in the detailed embodiment and should also provide improved performance with respect to 19 and even 37-perf grains. The optimal shape of pins for other applications may differ and these may be determined by propellant grain testing.
In the drawings wherein like reference characters are utilized to denote like parts throughout the same.
FIGS. 1(a)-1(l) represent a series of enlarged cross-sectional view through a prior art 7-perf stick-type propellant grain illustrating burn progressivity and sliver formation;
FIGS. 2(a)-2(j) depict cross-sectional views of a 7-perf stick propellant grain provided with generally trapezoidal perforations and illustrating a burn progression;
The process of using certain non-round shaped pins for producing perforations parallel to the length of stick-type propellant grains facilitates the production of stick propellant grains having a progressive burn characterized by a dramatic reduction in the size of propellant slivers resulting at burnout.
In FIGS. 2(a)-2(j) there is shown a series of cross-sectional views of a 7-perf propellant stick 20 having a round central perforation 22 surrounded by six substantially equidistant radially distributed perforations having a generally trapezoidal shape. The trapezoidal shapes have radially directed inner shorter bases 24 and outer longer bases 26. The bases 24 and 26 may preferably be of arcuate shapes generally matching a connecting circle as depicted by broken lines at 28 and 30, respectively (FIGS. 2(c)).
As can be seen in the progressive burn figure representations, the unburned web 32 is consumed in a manner that produces an unburned web residue of a generally uniform thickness that greatly reduces slivering as the progressive burn is completed. This not only reduces problems associated with unburned slivers, but it also enhances propellant performance efficiency by increasing timely consumption.
This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct new such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different devices and that the various modifications, both as to the equivalent details and operating procedures can be accomplished without departing from the scope of the invention itself.
