U.S. patent application number 10/698091 was filed with the patent office on 2005-05-05 for propellant extrusion die.
This patent application is currently assigned to Alliant Techsystems Inc.. Invention is credited to Gabrysch, Leslie P., Harris, Marlon D., Worrell, William J. JR., Zeigler, Edward H..
Application Number | 20050092166 10/698091 |
Document ID | / |
Family ID | 32991327 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092166 |
Kind Code |
A1 |
Worrell, William J. JR. ; et
al. |
May 5, 2005 |
Propellant extrusion die
Abstract
An extrusion die for use in producing perforated stick-type
propellant includes a die blank having a central passage
therethrough, the passage having a tapered entry, an open lattice
webbing structure having struts in and spanning the central die
passage, and an array of die pins for imparting perforations in
material forced through the central passage, each pin having a
fixed end attached to the lattice structure and a free end
extending parallel to the passage beyond the lattice structure.
Inventors: |
Worrell, William J. JR.;
(Draper, VA) ; Zeigler, Edward H.; (Radford,
VA) ; Harris, Marlon D.; (Christiansburg, VA)
; Gabrysch, Leslie P.; (Blacksburg, VA) |
Correspondence
Address: |
NIKOLAI & MERSEREAU, P.A.
900 SECOND AVENUE SOUTH
SUITE 820
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Alliant Techsystems Inc.
Edina
MN
|
Family ID: |
32991327 |
Appl. No.: |
10/698091 |
Filed: |
October 31, 2003 |
Current U.S.
Class: |
86/54 |
Current CPC
Class: |
F42B 33/00 20130101;
B29C 48/11 20190201; B29L 2031/777 20130101; B29C 48/05 20190201;
B29C 48/32 20190201; B29L 2031/60 20130101 |
Class at
Publication: |
086/054 |
International
Class: |
F42B 030/02 |
Claims
What is claimed is:
1. An extrusion die for use in producing perforated stick-type
propellant comprising: (a) a die blank having a central passage
therethrough, said passage having an unrestricted tapered entry;
(b) an open lattice webbing structure beyond said tapered entry in
said central passage for passing extruding propellant, said webbing
structure providing struts in and spanning said central die
passage; and (c) an array of die pins carried by said webbing
structure arranged in a pattern for imparting a pattern of
perforations in material forced through said central passage, each
pin having a fixed end attached to said lattice webbing structure
and a free end extending parallel to said passage beyond said
webbing structure.
2. An extrusion die as in claim 1 wherein said die is formed as a
unitary structure.
3. An extrusion die as in claim 1 wherein said central passage is
tapered slightly in the vicinity of said lattice webbing
structure.
4. An extrusion die as in claim 1 wherein said open lattice
structure is machined in said central passage.
5. An extrusion die as in claim 2 wherein said open lattice
structure is machined in said central passage.
6. An extrusion die as in claim 1 wherein at least some of the pins
are formed integrally with said open lattice webbing structure.
7. An extrusion die as in claim 4 wherein at least some of the pins
are formed integrally with said open lattice webbing structure.
8. An extrusion die as in claim 1 wherein one or more of said pins
is separately manufactured and fixed to said lattice webbing
structure.
9. An extrusion die as in claim 8 wherein separately manufactured
pins are press fit into openings provided in said lattice webbing
structure.
10. An extrusion die as in claim 1 wherein one or more of said pins
is of a non-round cross section.
11. An extrusion die as in claim 1 wherein the number of pins
arranged in said pattern is selected from 7, 19 and 37 and wherein
said pattern includes a central pin.
12. An extrusion die as in claim 11 wherein the number of pins is
7.
13. An extrusion die as in claim 4 wherein said machining includes
electron discharge machining.
14. An extrusion die as in claim 5 wherein said machining includes
electron discharge machining.
15. An extrusion die as in claim 1 wherein the area of the open
lattice webbing structure is tapered slightly to enhance reforming
of extruded material into sticks.
16. A method of extruding perforated stick-type propellant
including the step of: extruding propellant through the die blank
of claim 1, said propellant passing through said die blank
maintaining a direction substantially parallel to said pins along
the length thereof.
Description
BACKGROUND OF THE INVENTION
[0001] I. Field of the Invention
[0002] The present invention relates generally to the field of
propellant charges, particularly propellant charges suited to be
used in large or medium caliber projectile ammunition which are
made up of extruded perforated stick-type propellant grains. More
particularly, the present invention relates to a propellant
extrusion die design that incorporates an array of
perforation-forming pins but that eliminates the need for a pin
plate and enables straight through propellant extrusion thereby
substantially eliminating flexing of the die pins. This further
enhances uniformity in perforation patterns associated with
extruded perforated stick-type propellant shapes extruded through
the die and the enhanced uniformity reduces the amount of unburned
propellant slivers resulting at burnout. In addition, in accordance
with the present invention, dies can be manufactured with pins of
any desired cross sectional configuration and thus they can produce
any desired perforation shapes in the propellant stick grains.
Certain shapes have been found to significantly reduce propellant
slivers associated with multi-perf propellant burns.
[0003] II. Related Art
[0004] The success of all ammunition rounds depends greatly upon
the performance and reproducibility of the performance of the
associated propellant system. In this regard, those skilled in the
art have long sought to control the mass rate of gas generation
with predictable progressive burns. 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.
[0005] 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 even 37 or more perforations (perfs) to
enhance progressivity. Controlled progressivity is vital to the
performance required by modern gun systems.
[0006] Stick propellant is extruded through extrusion tools in the
form of extrusion dies which 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 the 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 hexagonal
pattern of 6 perforations surrounding the central perforation.
Other patterns including 19 perforations (a pattern of 1, 6, 12
perfs) and even 37 (a pattern of 1, 6, 12, 18 perfs) or more
perforations are used in certain propellant designs.
[0007] Particular limitations regarding the production of
stick-type propellant grains have resulted from limitations
associated with the extruding dies themselves. FIGS. 1(a) and 1(b)
depict top and cross sectional views of a typical 2-piece prior art
extrusion die, generally at 10, which includes a die body 12 which
may be heat treated tool or stainless steel and a pin plate 14 of
the same material which nests in the die body at the entrance to
the die when it is assembled in place. An orienting pin for the pin
plate and matching recess in the die body are shown at 15. The pin
plate is provided with an array of inlet passages 16 through which
propellant must be forced at high pressure (usually >5000 psi)
to be admitted to the die from a supply of propellant to be
extruded upstream of the die. An array of 7 pins is shown at 18
forming a regular hexagon surrounding a central pin. The pins
themselves designated as 20 are fixed to the pin plate as by being
press fit into the plate in openings at 22, the remainder of the
pin 20 being free and extending the length of the die body 12. The
die body 12 is rather wide at the top or entrance to accommodate
the pin plate and must be provided with a transitional zone as at
24 which tapers down to the size of the actual extrusion or agate
area 26 which defines the cross sectional size of the stick.
[0008] Propellant entering the transitional zone 24 through the
openings or passages 16, as can be seen from the drawings, is
forced at high pressure to approach and converge on the pin array
18 and thus the die pins 20 from the outside at an angle that
approaches perpendicular to the die pins 20. In the transitional
zone 24, the propellant flows nearly perpendicular to the die pins
20 and this causes flexing of the die pins. Prior die designs which
processed a specific propellant formulation and web size could make
some allowances for the predicted pin flexure. However, process
variation such as propellant solvent content (rheology),
temperature, extrusion rate, etc. cause unpredictable variations in
forces impinging the pins and, thus, changes in the pin
flexure.
[0009] Variation in propellant die pin flexure has been ultimately
manifested in variation of key physical dimensions such as web size
and web difference (difference between inner and outer web
thicknesses which are designed to be equal) in the perforated stick
grains. While modifications have been made to the dies in an effort
to reduce pin stress such as rounding the transition zone and
utilizing fewer, larger openings in the pin plate, they have only
met with partial successes and there remains a long-felt need to
improve perforated stick grain propellant extrusion dies.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, there is provided
a new extrusion die design that solves many problems enumerated
above by allowing for secure placement of the die pins without a
pin plate. The result is a straight-through die design that
eliminates the disadvantages of using a pin plate and reduces
inconsistencies in extruded propellant caused by pin flexure.
[0011] The present invention provides an extrusion die for use in
producing perforated stick-type propellant which includes a die
body having a central passage extending through the body, the
passage having an open tapered entry cavity and an open lattice
webbing structure within the body of the die spanning the central
die passage. The strut members of the open lattice webbing
structure extend parallel to the central die passage and divide but
provide very little obstruction to the passage of material being
extruded. An array of die pins for imparting perforations in
material forced through the central passage includes pins each
having a fixed end fixed to the lattice structure and a free end
extending parallel to the passage beyond the lattice structure such
that the material being extruded flows parallel to and around the
pins.
[0012] The die of the invention may be formed as unitary structures
from a die blank utilizing both conventional machining and electron
discharge machining (EDM) techniques. Thus, after the outside of
the blank is machined and holes are drilled in the blank
corresponding to openings in the lattice structure, EDM may be used
to cut out the lattice web, together with the desired array of pins
with great accuracy. The pins may be formed at the time the open
lattice web is machined, or they may be separately fabricated and
attached as by press fitting into recesses provided in the open
lattice webbing itself. If separate pins are to be inserted, a
slightly thicker webbing is used.
[0013] The preferred material of construction for the extrusion die
of the invention is precipitation hardened stainless steel,
possibly 15-5 PH or 17-4 PH stainless steel. Separately
manufactured pins may be constructed of hardened tool steel. The
die passage surrounding the vicinity of the pins preferably may be
slightly tapered in accordance with reforming the propellant stick
after it becomes segmented when it encompasses the open lattice web
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the drawings, wherein like reference characters depict
like parts throughout the same:
[0015] FIG. 1(a) is a top view of a prior art propellant extrusion
die showing the top of the die pin and indicating the central pin
pattern;
[0016] FIG. 1(b) is an elevational view partially in section of the
extrusion die of FIG. 1(a);
[0017] FIG. 2 is a top view of an extrusion die fabricated in
accordance with the present invention;
[0018] FIG. 3 is an elevational view partially in section of the
extrusion die of FIG. 2, taken along lines 3-3 of FIG. 2;
[0019] FIG. 4 is an elevational sectional view taken substantially
along lines 4-4 of FIG. 2;
[0020] FIG. 5 is a greatly enlarged view showing one pin detail of
an extrusion die fabricated in accordance with the invention;
[0021] FIG. 6 is a greatly enlarged top perspective view of the die
constructed in accordance with the invention; and
[0022] FIG. 7 is a greatly enlarged bottom perspective view of the
die of FIG. 6 showing the area of pins as integral with lattice
webbing struts in the area of free length of the pins.
DETAILED DESCRIPTION
[0023] The extrusion die of the present invention will now be
described with respect to a specific embodiment, however, the
descriptions contained herein are intended to present examples of
embodiments of the invention and examples of methods of making the
embodiments of the invention and are not meant to be limiting with
regard to the scope of the invention in any manner. In this regard,
an important aspect of the invention involves the provision of a
straight-through extrusion arrangement which eliminates the need
for propellant to encounter the perforation pins from the side. By
enabling extrusion directly into the web, all propellant motion is
substantially parallel to the pins which is beneficial both to
product quality and pin life.
[0024] FIGS. 2-4 depict one embodiment of the extrusion die of the
invention which is depicted generally by the reference character
40. The die may be of a single piece unitary construction and
includes an upstream or die body entry opening 44 which is
generally tapered at an acute angle narrowing down to the entry of
the main body or agate section of the die 46 which contains the
open lattice webbing which includes a center 48 and a series of
relatively thin radial struts connecting the center with the inner
wall of the die as at 50 which form the open lattice webbing
structure through which the extruded propellant passes during the
extrusion process. Each of the webbing struts 50 includes an
enlarged, raised shaped area as at 52 (see also FIGS. 6 and 7) that
is in the shape of and at the radial location of a perforation pin
54. The pins 54 preferentially end a short distance before the end
of the die to prevent pin damage. A minor recess may be machined
into the bottom of the die as at 56, if desired.
[0025] FIG. 5 shows a greatly enlarged alternate pin detail in
which a circular hexagonal array of substantially trapezoidal
shaped pins 70 are machined as integral extensions of the lattice
webbing struts 50 and the center pin 72 is a round press fit,
separately manufactured pin. Note that the inner and outer bases of
the trapezoidal pin are indicated by and are co-incident with
concentric circles 74 and 76, at least the outer, longer base of
each trapezoid being of an arcuate shape to coincide with the round
outer dimension of propellant extruded through the subject die.
[0026] The trapezoid is one non-round shape that has been used to
greatly enhance burn progressivity (by elimination of slivers) in
certain propellant sticks. The use of non-round shaped extrusion
pins and propellant stick grains made with them is described in
greater detail in co-pending application Ser. No. 10/______, filed
of even date and assigned to the same assignee as the present
invention, entitled "PROPELLANT EXTRUSION USING SHAPED PERFORATION
PINS". That application is hereby incorporated by reference herein
in its entirety for any purpose.
[0027] FIGS. 6 and 7 show greatly enlarged top and bottom
perspective views of an embodiment of the invention which utilizes
7 round pins to create a 7-perf extruded stick. FIG. 7,
particularly, depicts the free ends of the pins extending beyond
the open lattice webbing struts 50. As can be seen from the
figures, and particularly, FIG. 4, the area of the open lattice
webbing between its beginning at 58 and ending at 60 is tapered.
The taper is normally between about 9.degree. and 11.degree., but
may be varied as desired. The taper slightly constricts the
propellant that has been segmented in moving past the struts 50 of
the open lattice webbing of the die so that it more readily
re-forms a single stick in the lower or exit die area 62. The area
62, of course, is in the area of the free length of the pins 54. It
should be noted that very little movement of the propellant is
required in the direction perpendicular to the pins during the
extrusion process.
[0028] The dies 40 can be made from a single piece of stainless
steel first machined using conventional machining techniques where
possible to achieve the desired outer surface and inner entry
taper, and if desired, an outlet recess. In the case of a 7-perf
system, 6 holes are then drilled in the blank corresponding to the
void areas between the webbing struts and an EDM device using a
wire cutout system is utilized to make the web and, if desired, the
pins so that the entire device is integral with the original blank.
This technique allows highly accurate web and pin structures to be
produced. As indicated before, the material of the die blank is
preferably heat treated stainless steel as it must be a material
which is corrosive resistant when exposed to various propellant
compositions, caustic cleanout material and other materials
associated with processing the propellant. Such techniques are
known and can create webs or pins of any desired shape or
thickness.
[0029] While this technique has been found quite successful, the
applicants contemplate that other hybrid techniques might also be
employed. For example, the center pin is typically manufactured
separately and press fit into a central tapered opening as shown at
64 in FIG. 4. In addition, the radially distributed pins of any
desired shape may be fabricated separately and added to the web
after other machining is completed. This requires slightly enlarged
shaped areas for receiving pins as at 52 to be created on the
struts of the web and press fit or other techniques employed to
implant the pins such as that described for the center pin.
[0030] The straight-through extrusion die enables great
improvements to be achieved in geometric stability of the pin
pattern. Using the techniques of the present invention, pin flexure
associated with the extrusion process has been reduced by 75-80%
from conventional dies. Variations in the web thickness of
propellant extruded through the dies have been greatly improved
(reduced), i.e., from about 7.0%, which has been commonly
encountered with prior dies, to 4% or less utilizing the dies of
the present invention. The dies of the present invention may
achieve a web uniformity variance as little as 2-3% in some cases.
In addition, in recent extrusion tests, dies in accordance with the
present invention have experienced a first pass yield of 90% or
greater of usable material versus no more than 80% with prior
conventional dies.
[0031] 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.
* * * * *