DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

[0015] Referring now to the drawing, as shown in FIG. 3, there is shown a simplified process of the invention where a volume of free-flowing sinterable powder made of pre-agglomerated particles of at least two metals is selected 1 and then press-molded 2 into a compact preform 3 having the desired net shape of the shaped charge liner for use in oil well perforation. The pressing is done under a pressure of a range of approximately 1350 to 3400 atmospheres (20,000 to 50,000 lbs/in²).

[0016] Alternately, the free-flowing powder can be suspended in a volatile carrier such as an organic binder such as wax, polyester resin, polyethylene or polypropylene to form a feedstock for an injection molding step. Free-flowing powder refers those powders so having a flowability defined by the Metal Powder Industry Federation (MPIF).

[0017] The preform 3 is then partially sintered 4 at ambient pressure and at a temperature just above the melting point of the metal having a lower melting point to form a partially sintered body 5. If the lower melting point metal is copper, then that temperature will range between 1090° C. and 1230° C.

[0018] The partially sintered body is strong enough to withstand the rigors of further individual automated manipulation and processing. Partial sintering also prevents unwanted overflow of the melted lower temperature metal to the surface of the body. The melted metal is partially constrained by adjacent unmelted particles.

[0019] The partially sintered body is then maintained at a temperature of between 200° C. and 800° C. and then hot-coined or forged 6 in a hydraulic press under a pressure within a range of approximately 1350 to 6800 atmospheres (20,000 to 100,000 lbs/in²) to form the final shape liner 7. The coining or forging step allows for the inexpensive automated creation of liners within acceptable tolerance without significant additional machining. However, the liner may be machined 8 if necessary to further desired tolerances. Final machining can also include various other finalization steps such as annealing, grinding, lapping, stripping, cleaning or other known processing.

[0020] In general, the term “coining” means pressing an existing body or plug so as to reshape it without removing a large portion of material. The term “forging” in this specification generally means coining while the material has been heated.

[0021] Now will be described the preferred free-flowing powder for use in the above described process. The preferred powder is made of clusters of agglomerated particles of at least two metals having different densities and melting points. A first type of particle is made of a metal or alloy having a melting point of less than 1500° C. such as copper and alloys thereof. A second type of particle is made from a metal or alloy having a melting point of more than 1500° C. and a density of at least 10 g/cm³. Tungsten and molybdenum are preferred choices that can be used singly or together. These metals exhibit a higher density than those of the first type, and a higher melting point. They also have lesser coefficients of thermal expansion.

[0022] By adjusting the weight ratio of the first type to the second type of metals within a range of between approximately 5 and 30 percent, one can create a sintered liner of adequate strength, homogeneity and desired density.

[0023] Various different types of clusters of pre-agglomerated may be used to form the preferred powder.

[0024] In a first embodiment, as shown in FIG. 4, each cluster of pre-agglomerated particles is formed by particles of the first type of metal 10 and particles of the second type of metal 11 bonded together by a volatile adhesive 12. The bond between the two metals is weak enough to be breakable during the press-molding step. This allows the preform to attain a density which both maintains shape under its own weight before the partial sintering step and brings the particles into close enough proximity to prevent undue flow of melted metal during partial sintering.

[0025] As disclosed in Polese et al. U.S. Pat. No. 5,413,751, incorporated herein by this reference, the pre-agglomerated clusters may be formed by mixing together separate powders of the different density metals and adding a volatile liquid adhesive to the mixture to form a slurry. The slurry is then atomized into droplets through a process whereby the slurry is subjected to blasts of a gas, typically air, heated to a temperature above the melting point of the volatile liquid adhesive. After drying, the droplets combining all types of particles are continuously collected to form the pre-agglomerated powder.

[0026] In another embodiment, as shown in FIG. 5, free-flowing powder is made of pre-clustered nodules, where each nodule comprises a grouping of subnodules wherein each subnodule 20 includes a core 21 made of the denser metal surrounded by a blanket of smaller particles 22 of the agglutinating metal.

[0027] In another embodiment, referring now to FIG. 6, free-flowing powder is made of pre-clustered nodules, where each nodule 30 comprises a grouping of subnodules 31 wherein each subnodule includes at least one particle 32 of the first type of metal and at least one particle 33 of the second type of metal. The nodules are breakably agglutinated by a binder. Within each subnodule, the particles are paired by surface alloying occurring during the fabrication process.

[0028] The desired proportion of the first metal to the second is determined by the relative size or weight of the particles of each subnodule. When this type of powder is compacted into a body, and the body sintered at a temperature slightly above the melting point of the agglutinating metal, the lower melting point agglutinating metal is partially constrained by surrounding particles of non-melted metal, and thereby, prevented from flowing further.

[0029] The powder of clustered pre-agglomerated particles shown in FIG. 6 is formed according to a proprietary process developed by OSRAM-SYLVANIA of Towanda, Pa. as disclosed in part in U.S. Pat. No. 5,439,638 Houck et al., which is incorporated herein by this reference. The powders of FIGS. 5 and 6 are commercially available from that company. More specifically, the powders are respectively designated as Type I and Type III powder electronic grade. The diameters of the nodule range between about 40 and 350 microns. The diameter of the particles range between about 0.5 and 7 microns.

EXAMPLE

[0030] A copper and tungsten powder available from Sylvania of Towanda, Pa. sold under the designation TUNGSTAR-Type III was selected that contained approximately 15% copper and 85% tungsten by weight (27.7% and 72.3% per volume). The powder mixture consisted of particles of metal averaging 0.6 to 2.5 microns in diameter.

[0031] The powder was then press-molded at room temperature under 2050 atmospheres (30,000 lbs/in²) into the net shape of the desired liner component. The resulting preform compact was placed in a sintering furnace and subjected to temperatures of approximately 1100° C. for about 100 minutes under ambient atmospheric pressure to form a partially sintered body. The body was allowed to cool to a temperature of approximately 300° C. whereupon it was placed in a hot stamping press and forged under a pressure of about 3400 atmospheres (50,000 lbs/in²) to form a forged liner.

[0032] After cooling, the liner was then machined to tolerances of about ±0.07 millimeter for the final shaped charge liner.

[0033] The final article exhibited a specific gravity of about 96% of theoretical gravity of a perfectly solid composite, and a high homogeneity. No surface bleeding of the copper could be observed on the surface of the liner. The liner exhibited a coefficient of thermal expansion of about 8.0×10⁻⁶/° C.

[0034] Other liners were made with powder having a ratio of copper to tungsten varying between 5 and 30 weight percent copper according to the same process.

[0035] While the preferred embodiments of the invention have been described, modifications can be made and other embodiments may be devised without departing from the spirit of the invention and the scope of the appended claims.