This invention relates in general to wire-like products and more particularly to a wire-like product having a metallic case and a composite core and to a process for producing the same. The core constitutes a thermo-mechanically bonded, semimetallic, composite and is contained within a malleable and ductile case, thus producing a quasicomposite wire-like product.
Certain manufacturing processes require weld overlays and thermal spray coatings of very specific composition that are applied by melting a feedstock and depositing it on the surface of a substrate. For example, by means of thermal spraying, a steel substrate may be provided with a corrosion-resistant coating of nickel and other constituents, even nonmetal constituents. Indeed, many thermal spraying processes call for coatings having multiple constituents, and those are best obtained from wires or other feedstock that are themselves made of multiple constituents. To this end, tubular wires exist with cores formed from powders of metals or other materials encapsulated in a metallic case, but the powders are loosely compacted and the voids between their particles contain oxygen, which can produce, in the deposit, oxides in quantities greater than desired. Moreover, the powder of the core, being loosely compacted, does not in a heat source, such as a combustion flame or an arc, mix well with the material of the case, thus detracting from the uniformity and integrity of the deposit. Also, a loosely compacted core will not conduct electricity well, if at all, so an arc will attach much more readily to the metal case than to the powder core. This renders the arc less stable and detracts from the quality of the coating.
Apart from that, wires that are formed entirely from alloys have limitations as to their constituent components. For example, a nickel-chromium alloy can contain no more than about 45% chromium by weight. Nickel, and iron as well, will accept no more than about 12% aluminum by weight. Yet greater quantities of chromium or aluminum may be desirable.
Referring to the drawings, a wire-like product 10 (
The process for producing the wire-like product 10 begins with a tubular segment 20 (
One end of the tubular segment 20 is swaged or otherwise closed, leaving the tubular segment 20 with a closed end 22 that is air tight and an open end 24 (
The powder 26 contains constituents, in particle form, that ultimately form the composite core 14 of the wire-like product 10. For most constituents the combined particles of the powder 26 should be in a size range between 300 and 40 microns. Some of the particles should be a metal, and indeed, at least 5% to 8% of the particles by volume should be metal. The remainder may be other metals, carbides, metalloids or ceramics, or a mixture of all or some of the foregoing. Once the tubular segment 20 is filled with the powder 26, its open end 24 is closed, such as by swaging, to provide another closed end 28 (
With the powder 26 encapsulated within the tubular segment 20, the tubular segment 20 is reduced in size to a lesser diameter, with an accompanying extension in length. The reduction preferably occurs between rolls 30 (
The reduced tubular segment 20 and the tightly compacted powder 26 contained within it are then heated to a temperature suitable for sintering the powder 26. That temperature should not exceed melting temperature for the metal of the segment 20, yet should reach the range for annealing the metal of the tubular segment 20. Moreover, the heating should preferably occur in an oxygen-free environment, such as within a sintering furnace that contains hydrogen. Thereupon, the tubular segment 20 is allowed to cool slowly in the oxygen-free atmosphere, or quenched, depending on the metal of the tubular segment 20, to thereby anneal the tubular segment 20 while avoiding oxidation. The powder 26 converts into a partial sinter 32 (
Next, the tubular segment 20 is forced through a die 34 (
Thereupon, the drawn tubular segment 20 of lesser diameter and the compacted, broken partial sinter 32 within it are heated preferably in the absence of oxygen, such as in a sintering furnace, to the sintering temperature for the powder 26, yet below the melting temperature of the tubular segment 20, but nevertheless into the annealing range for the tubular segment 20. The fractured partial sinter 32 reforms as another partial sinter 32, although with different bonds. Then the tubular segment 20 and the new sinter 32 are allowed to cool slowly or quenched to again anneal the tubular segment 20.
The tubular segment 20 is again reduced in diameter by another draw or roll form. The further reduction in diameter fractures the previous partial sinter 32 into particles and further compacts them, so that the particles of the fractured sinter 32 in the tubular segment 20 are even more tightly compacted. Then the tubular segment 20 is again heated in a sintering furnace to the sintering temperature for the powder 26, yet within the annealing range and below the melting temperature for the segment 20. The heating creates another partial sinter 32. A subsequent cooling further anneals the tubular segment 20, so that it remains ductile and malleable.
Further, reduction in diameter of the segment 20 and the resulting fracturing of the partial sinter and the subsequent heating to the sintering temperature for the powder 26, yet below the melting temperature and at the annealing temperature for the segment 20, and subsequent annealing, follow in cycles, so that a total of perhaps three to five reductions and contemporaneous compactions and heating after initial reduction between the rollers 30 occur. After the last cycle, the tubular segment 20 exists in an annealed state as the case 12 of the wire-like product 10, whereas the powder 26, transformed into the partial sinter 32, takes the form of the composite core 14 in which the particles of the last partial sinter 32 are bonded together in a final, yet fractured, partial sinter 32 and along the interior of the tubular segment 20 may be diffused into the tubular segment 20 to effect a bond there as well. In short, the tubular segment 20 and powder 26 and sinters 32, by reason of the several reductions in diameter with accompanying compactions and subsequent heatings, are transformed into the wire-like product 10.
The characteristics of the core 12 depend to a large measure on its constituents. If the constituents are such that at least one is a metal that will melt at the sintering temperature for the powder 26 in the tubular segment 20, the core 14 may include an actual alloy. More likely, however, the powder 26 compacts entirely into a partially sintered mass—one in which the particles are thermo-mechanically joined together, such as by diffusion. Moreover, they may be diffused into the wall of the case 12 along the interior surface of the case 12.
The presence of at least 5% to 8% metal by volume in the core 14 enables the core 14 to conduct electricity as does the metal tubular case 12. Indeed, the high compaction brings the particles of metal in the core 14 close enough together to form an electrical conductor within the core 14. Loosely compacted powder, on the other hand, will not conduct electricity as effectively, if it conducts at all. Since the core 14 serves as a conductor, the wire-like product 10 as it is fed into an arc will have the arc attach to both the metal case 12 and to the core 14, and not just at the case 12. This provides for a more stable arc and a more uniform melting of the wire-like product 10.
In lieu of sealing each end of each wire-like segment 20, multiple wire-like segments 20 may be joined together end to end by welding in an oxygen-free atmosphere, with only the free ends of the endmost segments 20 closed.
The tubular segment 20, instead of being derived from relatively small diameter tubing on the order of 5/16 to ⅜ inches, may derive from a much larger tube, perhaps two inches in diameter, such as a tube formed in a pilger mill. After oxygen is eliminated from the interior of the larger tube, its interior filled with the powder 26, and its ends capped, the larger tube is rolled into smaller and smaller diameters with accompanying extensions in length. In so doing, the powder 26 serves as a mandrel to prevent the tube from collapsing. If necessary, the tube undergoes annealing to relieve work hardening. Eventually it becomes small enough to draw through dies to reduce its diameter even further, with each draw being preceded and followed by annealing that effects a partial sinter of the particles within the tubular segment 20.
In short, the invention resides in a thermo-mechanically bonded, semi-metallic core 14 contained within a malleable and ductile case 12 to provide a quasicomposite wire-like product 10.
This application derives and claims priority from U.S. provisional application 60/871,310, filed 21 Dec. 2006, which is incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/US07/88373 | 12/20/2007 | WO | 00 | 6/17/2009 |
Number | Date | Country | |
---|---|---|---|
60871310 | Dec 2006 | US |