US 3700486 A
Description (OCR text may contain errors)
Oct. 24, 1972 R, D..v|-:LTR| ETAL l 3,700,486
METHOD FOR COATING FILAMENTS Filed Dec. 31, 1970 United States Patent O Ace U.S. Cl. 117-71 R 4 Claims ABSTRACT F THE DISCLOSURE A method for continuously coating high modulus, high strength filaments having a boron or silicon carbide surface with a complete and uniform ductile metal matrix overcoat of aluminum or magnesium comprising passing the filament through a pair of axially aligned tubular conduits having matable end portions immersed in a molten bath of the metal matrix material, the end portions being initially conjoined to prevent contact of the filament with the molten metal, and separating the conduit end portions a distance sufficient to expose the moving filament to the molten metal and cause uniform coating thereof.
BACKGROUND OF THE INVENTION It is known to coat high modulus, high strength filaments of, for example, boron, silicon carbide or silicon carbide-coated boron, with a matrix coat of a ductile metal of the desired composition by drawing the same through a molten bath thereof. One such technique is shown in copending application Ser. No. 618,514 to Basche et al. filed Feb. 24, 1967, now Pat. No. 3,556,836 and assigned to the same assignee as the present invention. Another technique is shown in U.S. Pat. 3,410,715, issued to Hough on Nov. 12, 1968. A process for using such matrix overcoated filaments is disclosed in U.S. Pat. 3,443,301 issued to Basche et al. on May 13, 1969.
One of the paramount problems in coating filaments and utilizing them in such processes resides in the difliculty of obtaining a complete and uniform coating on the lamentary substrate. In order to simplify and expedite article fabrication, uniformly coated filaments are necessary to consistently establish the desired filament-matrix volume ratio. Further, complete and uniform coating is necessary in order to advantageously distribute localized mechanical stresses and thermal effects. Although dipping a substrate in a molten bath is a known method for coating, the application of conventional molten bath technology to small diameter filaments has been disappointing in its ability to produce complete and uniform coatings.
SUMMARY OF THE INVENTION The present invention relates to a process for continuously producing a complete and uniform coating of a ductile matrix metal on high modulus, high strength filaments. It contemplates providing an overcoat of the lightweight metals including aluminum, magnesium and alloys thereof onto such filaments as boron, silicon carbide and silicon carbide-coated boron by passing the filaments through a molten bath of the matrix material.
More particularly, the invention relates to a lfilament coating technique wherein a 3-5 mil filament is initially passed through a molten metal bath via a generally horizontal immersed two-piece conduit which is initiaily conjoined to prevent contact of said filament with said molten metal and which is subsequently axially separated a distance sufficient to expose the filament and cause uniform coating thereof. The present invention provides an exceptional technique wherein ingress and egress of the filament are made beneath the molten bath surface to 3,700,486 Patented Oct. 24, 1972 prevent slag pickup as Well as to preheat the substrate. Further, the ability to controllably space the aligned conduits in an open or closed position not only greatly facilitates rethreading but also permits increased fiexibility with regard to variance of bath residence time.
BRIIEF DESCRIPTION OF THE DRAWING The invention will be better understood by reference to the detailed description and accompanying drawing wherein the figure is a side elevation view, taken in cross section, of apparatus capable of performing the process of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Various experiments were conducted to establish the efiiciency of the inventive technique. Silicon carbidecoated boron filaments commercially available from the Hamilton Standard Division of United Aircraft Corporation, as well as filaments of boron were at various times provided with an overcoat of aluminum. `In general, the filaments utilized had a diameter of 3'5 mils with coatings provided thereover of 0.10 and 0.26 mil.
The boron filaments are produced by chemical deposition on a heated '1A mil tungsten Wire from a mixture of gases including boron trichloride and hydrogen, producing filaments in general having a diameter of 3-5 mils. A coating of stoichiometric silicon carbide is effected by chemical deposition on the heated boron filament from a gas mixture including methyldichlorosilane, hydrogen and methane.
Referring to the drawing, a low density, ductile metal 10, of aluminum or magnesium, is melted in a steel trough 12 which is disposed in a suitable furnace enclosure shown schematically by the numeral 14. A pair of generally horizontal axially aligned, hollow tubular conduits 16 and 18, preferably made of aluminum oxide, extend inwardly through the side walls of the trough under the surface of the molten metal bath 10. The conduits are, of course, in appropriate sealing engagement with the walls with at least one of the conduits being axially movable by suitable means (not shown). As shown, the immersed inner ends are conical in a malefemale relation for mating contiguity when moved to the closed or conjoined position. The outer ends of the conduits, which are without the Walls of the trough, are provided with inlets 20, 22 for communicating inert gas such as argon with the axially aligned passageways 24 and 26 in order to prevent the occurence of contamination and oxidation. As will be appreciated, a filament 28, having a surface of boron or silicon carbide, is adapted to pass through the passageways 24 and 26 by means of the guide rolls 30 and 32 and the takeup spool 34. The passageways 24 and 26 are of a sufficiently small dimension, with regard to the surface tension forces and capillary action, to prevent ingress of any molten metal therein.
The filament 28 is initially threaded through the conduits 16 and 18 while they are in the closed or mated position. When the desired temperature conditions and filament speed are reached, the conduits are axially separated a predetermined distance to expose the filament to the molten metal and begin the coating operation. By controlling the residence time by the rate of filament travel and the spacing of the immersed conduit ends, as well -as the temperature of the bath, various thicknesses and qualities of the coating can be provided. It should be noted that the sequence wherein the filament is first exposed to the molten bath and then allowed to solidify while still within an argon filled aluminum oxide tube prevents oxidation and other contaminates from affecting the overcoat, and lalso provides a gradual heating and cooling effect, respectively before and after the coating operation. Of course, further preheating or cooling may be included as necessary.
EXAMPLE I In one experiment, utilizing apparatus as described hereinabove, including two aluminum oxide tubes 16 and 18 have an outside diameter of 1A inch and inside diameter of 1764 inch, a uniform and complete coating of 0.26 mil of commercially pure aluminum was provided on a four mil silicon carbide coated boron filament when the bath temperature was maintained at 750i5 C., the conduit end spacing at 1/2 inchilg inch and the rate of filament travel at 1500i ft./hr.
EXAMPLE II In another experiment, using the same apparatus as in Example I, a uniform and complete coating of 0.10 mil of 2024 aluminum was yprovided on the same substrate as described above when the bath temperature was maintained at 880i10 C., the conduit spacing at 1A inch i/gg inch and the rate of `filament travel at 2400 ft./hr.
EXAM-PLE III Using the same apparatus and conditions as in Example I, a uniform and complete coating of 0.26 mil of commercial pure aluminum was provided on a four mil boron filament.
In all cases, While measurement was difficult, the coatings effected covered the entire substrate boron or silicon carbide surfaces, with the coating thickness varying at generally less than 10.05 mil.
What has been set forth above is intended primarily as exemplary to enable those skilled in the art in the practice of the invention and it should therefore be understood that, within the scope of the appended claims, the invention may be practiced in ways other than as specifically described.
What is claimed is:
1. A method for continuously coating high modulus, high strength filaments selected from the group consisting of approximately 3-5 mil diameter boron, silicon carbide and silicon carbide-coated boron with a uniform layer of a ductile metal matrix material selected from the group consisting of aluminum, magnesium and alloys thereof comprising:
5 passing said filaments through a pair of generally horizontal axially aligned tubular conduits having matable end portions immersed in a molten bath of said metal matrix material, said end portion of each tube having an opening which is sufficiently large to allow free passage of the filament therethrough but which is sufficiently small to prevent ingress of molten metal therein;
said end portions of the tubes being initially conjoined to prevent contact of said filament with said molten metal, and
separating said end potrions a distance sufficient to expose said moving filament to said molten metal and uniformly coat the yfilament therewith.
2. The method of claim 1 including the step of flush- 20 ing said conduits with an inert gas.
3. The method of claim 1 wherein said filament is boron or silicon-carbide coated boron.
4. The method of claim 3 wherein said metal is aluminum or an alloy thereof.
References Cited UNITED STATES PATENTS 3,556,836 1/1971 Basche et al 117-128 X 3,468,695 9/1969 Federman 117-114 C X 867,659 10/1907 Hoopes et al. 118-405 UX 2,111,853 3/1938 Fourness et al. 118-405 X 2,123,894 7/ 1938 Hazelett 118-405 UX 2,231,142 2/1941 Schultz 118-405 X 3,170,968 2/1965 Rokunohe et al. 118-125 X 3,410,715 11/1968 Hough 117-114 C X RALPH S. KENDALL, Primary Examiner J. R. BATTEN, JR., Assistant Examiner U.S. Cl. X.R.
117-71 M, 114 R, 114 C, 119, 128; 118-405