Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02433638 2008-10-03
METHOD OF MANUFACTURE OF POWDER-BASED
FIREP,RM AMbliJNITION PROJECTILE
EMPLOYING ELECTROSTATIC CHARGE
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FIELD OF INVENTION
[0002] This invention relates to methods of making a firearm
ammunition projectile from metal powders. "Powder-based" as used
herein refers to projectiles comprising metal powders as opposed to
shaped solid metal or metal alloys, the latter being excluded as a
part of the present invention.
BACKGROUND OF INVENTION
[0003] "Green" firearm ammunition projectiles generally comprise
projectiles which do not include lead as a component of the
projectile. In recent years lead has been identified as a
"pollutant" and has been banned from much of the firearm ammunition
projectiles. As a substitute for lead projectiles, projectiles
formed from a combination of various metals, particularly, metal
powders, have been developed. Commonly, tungsten metal powder is
mixed with tin, zinc, bismuth, or other metal powder, the mixture is
die-formed into individual cores which are subsequently loaded into
a metal jacket. The leading end of the metal jacket, containing one
or more cores is closed by defining an ogive on such leading end.
[0004] One major problem with powder-based (ie. non-lead
containing) projectiles relates to the non-uniformity of the density
distribution of the powders which go to make up the projectile.
First, it is to be noted that powder-based projectiles desirably
provide at least the same performance when fired to a target as do
lead projectiles, and, in certain instances, produce like recoil
values when the projectile is fired from a weapon. Second, non-
uniformity of density of the projectile, at least about the
longitudinal centerline of the projectile, (a) reduces the accuracy
of delivery of the projectile to a target, (b) reduces the
ballistics coefficient of the projectile, (c) imparts nutation to
the fired projectile thereby limiting its range of travel from a
firearm, among other things. This problem of non-uniformity of
density of the core and/or the resultant projectile, is exacerbated
when using two or more metal powders, of different densities, in a
mixture thereof, for forming a projectile. More specifically, for
example, mixtures of tungsten powder and tin, zinc, bismuth or like
metal powder, for example, tend to separate, by gravity, into layers
of the relative heavy tungsten powder and of the relatively lighter
metal powder, by reason of the difference in their respective
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densities. Such separation may occur in the course of mixing the
metal powders together, in transferring of portions of the mixture
between containers, in transferring of portions (aliquots) of the
mixture into a die, in movement of the mixture from location to
location or even during storage (i.e., any vibration of the mixture)
and/or in the course of die-forming of the portions of the metal
powders into a core which is subsequently encapsulated in a metal,
e.g. copper, jacket.
[0005] Bare, ie. non-jacketed, projectiles containing tungsten
powder are unacceptable for use in small-bore weapons, particularly
those weapons having rifled barrels. The exposed tungsten powder in
the non-jacketed projectile is severely abrasive and quickly erodes
and renders ineffective the barrel of the weapon. Moreover,
individual particles of the tungsten tend to break away from the
projectile and enter the mechanism of the weapon, again rendering
the weapon ineffective, and often completely useless. This latter
factor is particularly a problem with semi-automatic and/or
automatic weapons in that the tungsten particles migrate into the
bolt-actuating mechanism of these weapons to the extent that the
weapon fails to function.
[0006] In the course of loading a die-formed core into a metal
jacket, it is commonly required that the core be pressed into the
jacket to ensure complete filling of the jacket by the core. Also,
it is common to die-form an ogive on the leading end of the jacket
and core container therein. Each of these manufacturing operations
tends to disrupt the powder-based core and further at least
partially destroy whatever uniformity of density the core may have
at the time it is removed from its forming die.
[0007] It is an object, therefore, of the present invention to
provide a method of making a firearm ammunition projectile employing
a mixture of relatively heavy and relatively light metal powders
which are substantially uniformly distributed through the
projectile.
BRIEF DESCRIPTION OF THE FIGURES
Figure 1 is a schematic diagram depicting the steps of one
embodiment of the method of the present invention;
Figure 2 is a schematic representation of one embodiment of
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apparatus employed in the mixing of metal powders in accordance with
one aspect of the method of the present invention;
Figure 3 is a schematic representation of one embodiment of
apparatus employed for die-forming a core in accordance with one
aspect of the present invention
Figure 4 is a further schematic representation of the
apparatus depicted in Figure 3 and showing a cold-pressed core
following its removal from a forming die; and
Figure 5 is a representation, partly in section, of one
embodiment of a firearm ammunition projectile produced by the method
of the present invention.
SUMMARY OF INVENTION
[0008] In accordance with one embodiment of the method of the
present invention, a first metal powder having a density greater
than the density of lead is mixed with a second metal powder having
a density not greater than the density of lead to provide a mixture
of these powders. In accordance with one aspect of the present
invention, there is simultaneously mixed with these metal powders a
matrix micronized polymeric powder which is itself a poor
electrical conductor but very susceptible to accumulation of
an electrostatic charge during handling and/or transportation
thereof. The mixing of these metal powders and the micronized
polymeric powder is performed under conditions which maintain,
promote or enhance the electrostatic environment within a
blender, for example, with the result that the mixed metal and
non-metal powders become substantially uniformly distributed
throughout the mixture, and retain their uniform distribution
after removal from the blender. In accordance with a further
aspect of the present invention, this uniformity of
distribution of the powder particles within the mixture
carries forward into and throughout subsequent conversion of
the mixture into ammunition projectiles without the heavy and
light metal powder particulates separating, according to their
respective densities, into semi-layers or strata, even when vibrated
in the course of transfer of the mixed powders from the blender to a
storage container, during the storage of the mixture, and/or during
subsequent manufacturing steps involving the mixture.
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[0009] In one embodiment of the present invention, the metal
powders are admixed in a laboratory "V"-blender having a shell
formed of a polymeric material, e.g., an acrylic polymer in a
preferred embodiment. In one embodiment of the present invention,
the micronized polymeric powder itself possesses an electrostatic
charge at the time it is admitted to the blender. Normally, the
metal powders do not exhibit an electrostatic charge at the time
these powders are admitted to the blender. Through observation the
inventor has discovered that when the metal powder particles are
mixed with the micronized polymeric powder in the blender having a
polymeric, preferably acrylic, shell, an electrostatic charge exists
within the blender. It appears that in some manner this
electrostatic charge within the blender effects uniform distribution
of the heavy and light metal powder particles irrespective of their
relative densities in the course of the mixing process. Moreover,
this mixing process has been observed to enhance any electrostatic
charge initially carried by the micronized polymeric powder,
presumably the movement of the polymeric powder particles relative
to one another and/or relative to the polymeric shell of the
blender. operation imparted to at least the metal powder
particulates.
DETAILED DESCRIPTION OF INVENTION
[0010] Referring initially to Figure 1, one embodiment of the
method of the present invention comprises the steps of (a) selecting
a quantity of a metal powder (A) having a density greater than the
density of lead, (b) selecting a quantity of a metal powder (B)
having a density not greater than the density of lead, (c) selecting
a non-metal, electrically conductive, matrix micronized polymeric
powder (C), and, (d) mixing the selected quantities of the two metal
powders and the micronized polymeric powder in a blender preferably
having a polymeric shell. As also depicted in Figure 1, the
incorporation of the mixture into a firearm ammunition projectile
may include the further steps of (e) forming individual quantities
of the mixed powders into individual cores suitable for the receipt
thereof in respective elongated cup-shaped metal jackets, (f)
loading, preferably with pressing, a core into the jacket, (g)
closing the open end of the jacket, preferably employing a die
having a cavity which is suitable for the forming of an ogive at the
open (leading) end of the jacket, thereby forming a firearm
ammunition projectile of a density which is at least uniformly
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distributed radially about the longitudinal axis of the completed
projectile, and (h) recovery of the finished projectile.
[0011] Figures 3 and 4 schematically depict one embodiment of a
die 12 for cold-pressing an aliquot 14 of the powder mixture into a
self-supporting core 16 (see Figure 4). The depicted die 12
includes a die body 18 defining a die cavity 20 adapted to receive
therein an aliquot of the powder mixture. The bottom end 22 of the
die cavity is closed by a first punch 24. A second punch 26 is
provided for insertion into the die cavity to compact the aliquot of
powder into a core. After formation of the core, the second punch
is withdrawn (see Figure 4) and the second punch is activated to
push the pressed core out of the die.
[0012] Figure 2 depicts one suitable blender for use in the
mixing the powders in accordance with the present invention.
Preferably, the blender 40 employed in the present invention
comprises a "V" shaped blender having a shell 42 of a polymeric,
e.g. acrylic resin, material for a time sufficient to uniformly mix
the metal powders and the polymeric powder into a mixture of
substantially uniformly distributed metal and non-metal powder
particles. The depicted blender comprises a frame 44 which
rotatably supports the "V" shaped shell 42 therein. Rotation of the
shell is effected by a motor (not shown) contained within a housing
48 also supported by the frame, as is well known in the art.
Notably, the frame is electrically isolated as by insulative feet 50
(typical), such as rubber cushions.
[0013] Whereas the mechanism or mechanisms by which the
uniformity of distribution of the two or more metal powders having
different densities is initially developed and subsequently
maintained during manufacturing operations is unknown with
certainty, it has been found that in the absence of an electrostatic
charge within the blender, when the mixture of removed from the
blender, the heavy and light metal powders will deleteriously
separate, by gravity according to their respective densities, into
at least semi-layers strata of heavy metal powder and light metal
powder. The magnitude of the electrostatic charge is known to be
relatively small in that no physical "electrical shock or sparking"
can be detected upon grounding of a quantity of the mixed powders.
On the other hand, the powder mixture of the present invention
exhibits clear indications of electrostatic interaction and/or a
combination of electrostatic interaction and mechanical interaction
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between the particulates of the metal powders and the particulates
of the micronized polymeric powder in that the powders remain
physically associated with neighboring particulates of the mixture
and the metal powders do not separate in accordance to their
respective densities in the course of ordinary handling of the
mixture, such as when transferring the mixture from the blender to a
storage vessel, storage of the mixture, and/or aliquoting of the
mixture into forming dies. The presence of an electrostatic charge
associated with the powders within the blender may be seen by merely
inserting one's hand and/or forearm into the blender containing the
mixed powders. When an electrostatic charge is present, the hairs
on the hand and/or forearm will extend as is common in the presence
of an electrostatic field.
[0014] Even though the precise mechanism or mechanisms by which
the observed results are produced in accordance with the present
invention, the present inventor has determined that the presence of
an electrostatic environment with the blender is a prerequisite to
the success of the present invention. For example, mixing only the
two metal powders, and excluding the micronized polymeric powder,
produces a mixture of the metal powders which will separate, by
gravity, into at least semi-layers or strata of heavy metal powder
particles and light metal powder particles, irrespective of the
material of construction of the blender.
[0015] It is known that a micronized polyethylene powder
commonly develops an electrostatic charge during handling and
transportation. This electrostatic charge is retained by the powder
for a relatively long time, e.g. weeks or months unless electrically
grounded. The magnitude of such charge, however, may vary very
widely. Moreover, such micronized polymeric powder may take on a
lessor or greater electrostatic charge as a function of the
humidity, temperature, and/or other atmospheric conditions and/or
mechanical movement to which the powder is exposed. In the present
invention the metal powders and micronized polymeric powder are
stored prior to mixing, and are mixed, at convention room
temperature, e.g., about 70 F at a relative humidity of between
about 50% and 70%. It has been found by the present inventor that
under certain atmospheric conditions, e.g., relative high humidity
at room temperature, one an employ a blender having a metallic
shell, as opposed to a polymeric shell, in combination with the
described non-metal micronized polymeric powder, and obtain a
mixture of the metal powders (and the polymeric powder) which
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exhibits an electrostatic field after mixing. It is believed,
therefore, that one can impart to, or enhance the strength of, an
electrostatic field to the polymeric powder prior to introduction of
the powder into the blender. Alternatively, it is believed that an
electrostatic charge may be imposed on the powders of the mixture in
the course of the mixing operation, such as through the use of a
Tesla coil or the like that is electrically connected with the
mixture within the blender, whether the shell be of a metal or
polymeric material. Notably, the presence of the non-metal matrix
micronized polymer powder affords advantages other than those
advantages associated with the presence of an electrostatic charge
on the polymer powder particulates. For example, it has been found
that the polymeric matrix powder enhances the pourability of the
mixture, particularly with respect to the introduction of the powder
mixture into a die cavity. Further, the presence of the polymeric
matrix powder in the mixture has been found useful in reducing the
pressure required to die press the powder mixture, at room
temperature, into a self-supporting core. Accordingly, the
polymeric matrix powder serves multiple functions in the course of
the manufacture of a powder-based core. Still further, the presence
of the polymeric matrix powder has been found to enhance the
frangibility of the projectile formed from the mixture, when fired
into a solid or semi-solid target. Other advantages arising by
reason of the presence of the polymeric matrix powder in the mixture
have been noted. Accordingly, in a preferred embodiment, the
micronized polymer powder is retained with the mixture and carried
over into the completed projectile. Thus, no sintering of the powder
mixture either during or after die-pressing of the mixture into a
self-supporting compact is required and is to be avoided.
[0016] In one example employing the method of the present
invention, eight lbs. of tungsten metal powder having a particle
size of about 325 mesh and two lbs. of tin metal powder having a
particle size of about 325 mesh and about one-hundredth of one
percent (0.01%) of the total weight of the tungsten and tin powders,
of a micronized oxidized polyethylene powder having an average
particle size of about 12 microns, were introduced into a ten pound
capacity P-K Blend Master Lab Blender, manufactured by Patterson-
Kelley of East Stroudsburg, PA, and having a polymeric shell. The
density of the micronized polyethylene powder was about 0.99 g/cc so
that it will be recognized that the percentage by weight of the
micronized polyethylene powder was minuscule compared to the
percentage by weight of the tungsten and/or tin powder and would be
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expected to have no material effect on the density distribution of
the mixture of metal powders. Nonetheless, it has been found that
the presence of this very small amount of the micronized
polyethylene powder, in combination with the mixing of the three
powders in a blender having inner walls of a polymeric, e.g. acrylic
resin, material, imparted to the mixture the ability of resisting
separation of the two metal powders into semi-layers or strata
according to their respective densities. As presently known, this
phenomenon occurs consistently when the mixing of the powders is
carried out in a blender which is electrically insulated from
electrical ground, as by means of rubber feet or the like, and which
has a shell which is either fabricated preferably of a polymeric
material, such as an acrylic material, or which has its inner walls
formed of such a polymeric material.
[0017] In accordance with a further aspect of the present
invention, it has been found that the quantity of micronized
polymeric powder provided in the mixture of metal powders and non-
metal powder preferably is between about 0.01% and 1.5%, by weight,
of the total weight of the metal powders within the mixture. Lessor
amounts of the micronized polymeric powder fail to produce and/or
maintain the desired uniformity of distribution of the metal powders
within the mixture. Amounts of micronized polymeric powder greater
than about 1.5%, by weight, produce mixtures which are unsuitable
for being die-pressed into self-supporting compacts at room
temperature. As employed herein, "micronized" refers to the average
particle size of the individual powder particles a powdered
material. A suitable micronized polymeric powder for use in the
present invention comprises polymeric powder particles having an
average particle size of between about 5 and about 18 microns. A
suitable polymeric powder for use in the present invention comprises
a micronized oxidized polyolefin, and preferably polyethylene.
[0018] Employing the P-K Blend Master blender, fitted with a
acrylic shell and having a capacity of about ten pounds, the present
inventor blended a mixture of tungsten metal powder (about 80% by
wt.), tin metal powder (about 20% by wt.), and a micronized
oxidized polyethylene matrix powder (about 0.1% by wt.) for about
thirty minutes at room temperature and a relative humidity of
between about 30% and 40%. The blender was rotated at a speed of
about 25 rpm (nominal).
[0019] The mixture of powders of this example was transferred
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from the blender into a storage vessel where it remained pending its
use. In due course, the mixture was aliquoted into one or more die
cavities and cold-pressed into a self-supporting core at room
temperature. Preferably the pressed core has a crush strength of at
least 2 Mpa and not greater than about 35 Mpa. Following removal of
the core from the die, it was inserted into the open end of a cup-
shaped copper metal jacket. The core was pressed into the jacket
employing a punch entering the open end of the jacket. Thereafter
the punch was withdrawn and the open end of the core-containing
jacket was inserted into a die cavity having a geometry suitable for
the formation of an ogive at the leading (open) end of the jacket
and pressed into the die cavity thereby forming an ogive and at
least substantially closing the open end of the jacket.
[0020] Multiple ones of the projectiles formed by the method of
the present invention were loaded into ammunition cartridges which
were subsequently fired from a firearm. The observed accuracy of
delivery of the projectile to the target, its ballistics
coefficient, and its effective range were noted to be appreciably
enhanced over projectiles fired under essentially identical
conditions, but which did not include the non-metal micronized
polymeric powder.
[0021] In accordance with another aspect of the present
invention, it has been also found that the presence of the
electrostatic charge exhibited by the powder mixture at the time it
exited the blender has the further effect of enhancing the
frangibility.of the projectile into powder particulates upon impact
with a target.
[0022] One embodiment of a projectile 60 manufactured in
accordance with the present invention is depicted in Figure 5 and
comprises a cup-shaped jacket 62 having a longitudinal centerline
63, a closed end 65 and a leading end 64 which is substantially
closed and defines an ogive 66. A core 68 made in accordance with
the method of the present invention is encapsulated in the jacket
and pressed into intimate engagement with the inner wall 70 of the
jacket adjacent the closed end thereof. Thereafter, the open
(leading) end of the core-containing jacket is placed in a die and
die-formed to define the ogive at the leading end of the projectile
as is known in the art.
[0023] In one embodiment, the closed end of the jacket, with the
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core disposed therein, may be initially die-formed to define an
ogive and thereafter the open end of the jacket may ne partly or
fully closed to capture the core within the jacket. Commonly the
jacket is formed of copper metal which also serves a lubricative
function between the rifle barrel and the projectile.
[0024] Cores for projectiles of various caliber firearms may be
made employing the method of the present invention, particularly 50
caliber and smaller firearms. The cores may be formed from various
combinations of metal powders and various weight percentages of each
of the metal powders. For example, in the method of the present
invention, tungsten powder may be employed in weight percentages of
between about 10% to about 99%. Other heavy metal powders such as
uranium, tantalum, or combinations of such metal powders or their
carbides may be employed. Similarly, tin, zinc, bismuth, aluminum,
copper and/or combinations of these lighter metal powders, in
amounts from 90% to about 3%, by wt., may be employed. In all
instances, between about 0.01% and about 1.5%, by wt. of a
micronized polyethylene non-metal powder, such as Acumist 12
available from Allied Signal Advanced Materials of Morristown, NJ,
or like non-metal micronized polymeric powder, need be included in
the mixture.
[0025] Whereas the present invention has been described in
considerable detail for purposes of teaching one skilled in the art
how to carry out the invention, it will be recognized by such person
skilled in the art that the concepts of the present invention may be
carried out employing not significantly different apparatus and/or
operational parameters. Optionally, the method may include
additional steps, depending upon the desired characteristics of the
resultant projectile, such as the incorporation of additional
components, such as a cap at the leading end, and internally of, the
jacket. Further, multiple cores may be included within a single
jacket. Other modifications and alternatives will be recognized by
one skilled in the art.
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