Metal working – Method of mechanical manufacture – Shaping fiber or fibered material
Reexamination Certificate
2000-09-05
2002-12-24
Bryant, David P. (Department: 3726)
Metal working
Method of mechanical manufacture
Shaping fiber or fibered material
C029S423000, C029S424000
Reexamination Certificate
active
06497029
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to metallic fibers and more particularly to an improved method of making fine and ultra fine metallic fibers through a new cladding and drawing process.
2. Background of the Invention
In recent years, the need for high quality, small diameter metallic fibers has grown as new applications for such fibers are developed by the art. High quality, small diameter metallic fibers have been used in diverse applications such as filtration media as well as being dispersed within a polymeric material to provide electrostatic shielding for electronic equipment and the like. This need for high quality, small diameter metallic fibers has produced various new ways and processes for making these high quality metallic fibers for the various uses in the art.
Typically, high quality metallic fibers may be characterized as small diameter metallic fibers having a diameter of less than 50 micrometers with a substantially uniform diameter along the longitudinal length thereof. Typically, the fibers are produced in a fiber tow and severed to have a longitudinal length at least 1,000 times the diameter of the metallic fiber.
The metallic fibers as set forth herein are typically manufactured by cladding a metallic wire with a cladding material to provide a first cladding. The first cladding is drawn and annealed for reducing the diameter of the first cladding. A plurality of the first claddings are clad to provide a second cladding. The second cladding is subjected to a multiple drawing and annealing process for reducing the diameter of the second cladding and the corresponding diameter of the first claddings contained therein. Depending upon the desired end diameter of the first cladding, the plurality of second claddings may be clad to provide a third cladding. Multiple drawings of the third cladding reduces the diameter of the first and second claddings to provide metallic fibers within the first claddings of the desired diameter. After the desired diameter of the metallic fibers within the first cladding is achieved, the cladding materials are removed by either an electrolysis or a chemical process thereby providing metallic fibers of the desired final diameter.
Ideally, the metallic fibers are made of a stainless steel and are produced by a drawing process. The drawing process comprises cladding a stainless steel wire with a cold roll steel clad material to produce a first cladding. The first cladding is subjected to a series of drawing and annealing processes for reducing the diameter thereof. Thereafter, a plurality of the first claddings are encased within a second cladding material such as cold roll steel for producing a second cladding. The second cladding is subjected to a series of drawing and annealing processes for further reducing the diameter of the second cladding. After the second drawing process, the original wires of the first cladding are reduced to a diameter of 10 to 50 microns that is suitable for some applications. For applications requiring finer metallic fibers, a plurality of second claddings are clad with a third cladding material to provide a third cladding. Third cladding is subjected to a series of drawing and annealing for further reducing the diameter of the original metallic wires. A triple cladding process can produce final wires having a diameter of as low as 6 microns in diameter.
The cladding material is removed by subjecting the finally drawn cladding to an acid leaching process whereby the acid dissolves the cladding material leaving the metallic fibers. The metallic fibers may be severed to produce metallic sliver or cut metallic fibers or may be used as metallic fiber tow.
Although the foregoing process of making fine metallic fibers has been found satisfactory in the prior art, the process has certain disadvantages for some applications. The first disadvantage is the requirement of incorporating a three cladding process in order to produce metallic fibers in the range of 6 microns in diameter. Another limitation is the initial diameter of the metallic wire must be of a sufficient size in order to clad carbon steel thereto. Another disadvantage of the aforementioned process includes the incomplete removal of the cladding material from the metallic fibers during the leaching process.
Another disadvantage of this prior art process is the diffusion of impurities of the carbon steel into the metallic fibers during the drawing process. A substantial amount of heat and pressure are produced during the drawing process causing a fusion of undesirable materials from the carbon steel upon the surface of the metallic fibers. These undesirable materials such as carbon, hydrocarbon materials such as oils and the like remain on the surface of the metallic fibers through the leaching process and reside thereon in the end product. In certain applications, these undesired impurities are detrimental to the application and the use of the metallic fibers. For example, these undesirable impurities may be detrimental when the metallic fibers are used in a filtration process or the like.
Some of the prior art have attempted to use copper as a cladding material for producing fine metallic fibers. U.S. Pat. No. 2,050,298 to Everett discloses a method for producing filaments from a rod, which comprises the steps of bundling the rods side by side in a matrix, drawing the bundle, removing the matrix, and separating the wires. The matrix serves to separate the elements, limiting distortion during drawing and preventing adjacent elements from becoming attached to each other. Two embodiments of matrix material given are metal powder and individual metal sheaths, or a combination of the two. The sheath may be dissolved off with acid. An example given consisted of stainless steel fibers having a copper matrix and a tubular casing of high carbon steel, the removal of which was effected by a hot acid bath. An alternative method for stainless steel fibers consisted of encasing the fibers in separate copper tubes and then packing a number of these in a copper tube.
U.S. Pat. No. 2,077,682 discloses a process for the production of fine wires, strips, thin sheets or the like by reduction from elements of larger cross-section which comprises assembling inside a tubular casing a plurality of metal elements composed of alloy steel comprising 0.05% to 0.20% carbon, 6% to 14% nickel and 10% to 20% chromium, and subjecting the encased elements as a unit to reducing operations to reduce the cross-section area of all the elements, simultaneously, and then removing the casing.
U.S. Pat. No. 3,066,384 discloses a method of making from 80″ wide to 160″ wide thin sheets of a metal which is difficult to roll selected from the group consisting of stainless steel, ferrous alloys, titanium, zirconium and their alloys, which consists in assembling a pack of plates of the metal with weld-preventing material therebetween, placing the pack within a box welded up from steel top and bottom plates and steel side and end bars with the top and bottom plates overlapping the side and end bars, providing vent holes in all of the bars, hot rolling the resulting pack-in-a-box first by cross rolling and then by rolling longitudinally, thereby reducing the first-mentioned plates to sheets, then subjecting the sheets while still confined within the box to heating and cooling stages in predetermined order thereby developing desired physical properties in the sheets, roller leveling the hot-rolled pack while still in the box, and then opening the box and removing and separating the sheets.
U.S. Pat. No. 3,204,326 discloses a method of making a fused energy-conducting structure having a multiplicity of juxtaposed long and thin energy-conducting guides extending from one end toward the other end thereof utilizing a rolling mill, the method comprising the steps of placing a multiplicity of energy-conducting fibers each clad with a glass having a relatively low softening temperature and coefficient of expansion in side-by-side bundled relationship
Liberman Michael
McNeice Raymond R.
Quick Nathaniel R.
Sobolevsky Alexander
Bryant David P.
Knobbe Martens Olson & Bear LLP
Pall Filtration and Separations Group Inc.
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