Powder metallurgy processes – Forming articles by uniting randomly associated metal particles – Consolidation of powders
Reexamination Certificate
1998-03-20
2001-01-16
Mai, Ngoclan (Department: 1742)
Powder metallurgy processes
Forming articles by uniting randomly associated metal particles
Consolidation of powders
C419S064000, C419S065000, C102S517000
Reexamination Certificate
active
06174494
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to powder metallurgy, and more specifically, to projectiles or other objects made from consolidated powdered materials. The materials are chosen to emulate or improve upon the mechanical properties and mass of lead.
DESCRIPTION OF THE RELATED ART
Bullets are a type of projectile which have relied on the density of lead to generate a desirable force, commonly measured in foot pounds of energy, when propelled at a desired velocity.
One type of bullet includes a lead core jacketed with copper. This type of construction and combination of materials has been used successfully because the density of lead produces desirable ballistic performance. Moreover, the ductility and malleability of lead makes it easily worked into projectile shapes, and produces desirable impact deformation.
Lead-containing bullets present both environmental and safety problems, when fired at practice ranges. Health issues arise from breathing airborne lead contaminants generated from firing the projectiles and their impact on the backstop. Environmentally, lead from the projectiles fired at an outdoor range accumulates in the ground and can leach into surface water and ground water. In terms of safety, projectiles fired indoors or outdoors can ricochet and thereby cause unintended collateral damage.
The safety, health and environmental issues with regards to the firing of projectiles at ranges and other training facilities (or in general, any training exercise where projectiles are fired into the environment) have prompted the development and evaluation of alternative ammunition that eliminates the undesirable health, safety and environmental aspects of lead.
It has not been a simple matter to replace lead as a material for making projectiles. Alternative projectiles considered in the past have not been able to maintain the mechanical and physical properties of lead so as to achieve comparable performance. For example, the ability of the projectile to retain its velocity and energy is measured by its sectional density is proportional to the projectile mass divided by the square of the caliber. Thus, it is seen that a projectile of low mass or density will not retain its velocity and energy as well as a projectile of higher mass and energy.
Recent efforts to replace lead in bullets have focused on powdered metals with polymer binders, plastic or rubber projectiles, and bismuth metal., However, these replacements have yet to meet all desired specifications and performance goals.
At the end of World War II, projectiles used in 50 caliber weapons for training, and to replace lead, were fabricated from tungsten, iron, and bakelite. These were used for some time in training exercises and for special applications. However, attempts to reproduce these materials in the early 1970's were unsuccessful. In addition, bakelite, which is fabricated from phenolic-formaldehyde mixtures, has experienced declining usage as newer, less expensive polymer materials have been developed.
Frangible projectiles are also employed as training ammunition in place of kinetic energy penetrators. The simulated projectiles must exhibit similar flight characteristics to the actual penetrators, but ideally self-destruct in flight or on impact for safety reasons (for example, to reduce ricochet). A partially densified iron powder component encased in a low-strength, thermally-degradable plastic container has been used. These replacement projectiles fail on light impact or after heating in flight, thus meeting range safety requirements.
Commercially available non-lead, frangible munitions for training and certification of personnel are presently being fabricated using bullets formed from tungsten and copper powders in a nylon matrix. The projectiles are a direct spin-off from technologies first explored for replacing lead weights used by commercial fishermen in Europe. The projectiles are formed employing injection molding techniques and various lots have been delivered to various organizations for testing.
While the aforementioned ammunition is functional, the density of the bullet material is only approximately half that of the lead-containing components (5.8 versus 11.4 g/cm
3
). The low weight of the projectile causes problems in weapon functionality and accuracy, especially at extended ranges.
Another solution being explored is the replacement of lead with other metals such as bismuth. Bismuth metal possesses properties similar to those of lead. Shotgun ammunition that utilizes bismuth shot is also commercially available, but the density of this metal is only 86% of that of lead (9.8 versus 11.4 g/cm
3
), and again this creates concerns with regards to ballistic performance.
In pelletized projectiles, such as shotgun shot, lead has been used for many years in hunting waterfowl and other game birds. Where lead shot has been banned, steel shot has been required. However, due to the high hardness and strength, and low density (7.5 versus 11.4 g/cm
3
), steels are less desirable choices for use as projectile materials.
Steel shot has also caused intense controversy for it is believed that due to its reduced ballistic properties (primarily to the lower density), many birds are being wounded and maimed, dying gruesome deaths. The manufacturers recommend using a steel shot at least two sizes larger in diameter than lead for the same target and similar distances. This further diminishes effectiveness by decreasing pattern density (the number of pellets in the shot change).
Although ammunition manufacturers are developing new and improved components for use with steel shot, the ammunition appears to cause excessive wear and undue damage to many shotgun barrels.
Several United States patents have described lead-less or lead-reduced projectiles. For example, U.S. Pat. No. 5,264,022 to Haygarth et al. describes a lead-free shotshell pellet made of an alloy of iron and tungsten. The pellets may be coated with a polymeric coating, resin or lubricant.
U.S. Pat. No. 4,881,465 to Hooper et al. discloses a non-lead shotgun pellet in which particles made of a first alloy are suspended in a matrix of a second alloy. The first alloy is primarily ferrotungsten, and the second alloy is primarily lead. The second alloy is poured over crushed particles of the first alloy to form the pellets.
U.S. Pat. No. 4,498,395 to Kock et al. discloses a powder made of tungsten particles coated with either nickel, copper, silver, iron, cobalt, molybdenum or rhenium, wherein the particle diameters are in the range of 10 to 50 &mgr;m. The particles are sintered to form projectiles.
U.S. Pat. No. 4,428,295 to Venkataramaraj discloses a high density shot made of a cold-compacted mixture of at least two metal powders. A representative mixture includes 50% lead and 50% tungsten, which is cold pressed in shot molds at 20,000 psi.
It is clear from the above that several attempts have been made in the past to obviate or diminish the use of lead as a primary material for making projectiles. Yet, no one heretofore has achieved satisfactory performance from non-lead materials.
Explosive charges are typically packaged in metallic or polymer-metal containers. These containers protect the explosive charge from the environment and from damage by handling, and also contain the expanding gases for a short period of time (microseconds) during detonation. Moreover, for shaped charges, the container assists in the shaping of the discharge gas jet or penetrator. In particular military applications, the container provides collateral damage through fragmentation.
The ductility of the container material and the reactive mass of the container both assist in the initial containment of the expanding gases during detonation. This initial containment influences the efficiency of the explosive charge. As noted, the fragmentation effects of the container may be desirable in certain military applications; however, there are situations where explosive charges are utilized where no fragmentation effects are desired or where the fragmentation e
Dooley Joseph B.
Lowden Richard A.
McCoig Thomas M.
Smith Cyrus M.
Jones & Askew LLP
Lockheed Martin Energy Systems, Inc.
Mai Ngoclan
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