US3401423A - Apparatus for the continuous formation of filaments - Google Patents

Description

R. L. HOUGH Sept. 17, 1968 APPARATUS FOR THE CONTINUOUS FORMATION OF FILAMENTS Filed May 7, 1965 2 Sheets-Sheet 1 FIG-l INVENTOR. RALPH L. HOUGH 44M V ATTORNEY R. 1... HOUGH 3,401,423

2 Sheets-Sheet 2 INVENTOR. RALPH L.HOUGH A ATTORNEY.

Sept. 17, 1968 APPARATUS FOR THE CONTINUOUS FORMATION OF FILAMENTS Filed May 7, 1965 FIG-3 ABSTRACT OF THE DISCLOSURE An apparatus for the formation of continuous pyrolytic refractory filaments utilizing a chamber housing, an ion laden plasma jet mechanism, a rotating disc deposition bed equipped with a pair of electrode gaps containing means for maintaining an arc discharge between said electrode gaps for separating the continuous filament as formed.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to a new and improved apparatus for the formation of continuous filaments such as those of pyrolytic materials and particularly to the formation of such filaments which are composed entirely of such material.

In the rapidly advancing technology of refractory and ablative materials and assemblies, such as are being constantly sought in the fields of aerospace exploration and rocket engines in particular, there is a growing demand for refractory fiber-like materials. Especially is there such a demand for refractory filaments of substantial lengths which are usually referred to as endless or continuous filaments. The materials of which these are most desirably formed comprise a variety of known refractory substances including pyrolytic graphite, borides, carbides, nitrides and the like which have been generally formed by vapor plating which is the deposition of the refractory material from a vapor state upon a gas-phase surface reaction, usually taking place when the vapor comes in contact with a heated substrate within an appropriate vapor-filled deposition chamber.

To obtain continuous filaments in lengths contemplated by the present invention, the prior art has employed a continuous filamentous substrate such as a finely drawn tungsten wire or the like upon which the refractory material is deposited as a coating. The resulting product therefore is made up of the substrate as a core about which the refractory material is deposited with varying degrees of uniformity. While such composite filaments have proven useful, it is obvious that the presence of the nonrefractory substrate has lessened the high temperature performance that might otherwise be expected from filaments of the same size but composed entirely of the refractory material. Moreover, manipulation of the substrate in the deposition process has been diflicult, time consuming and costly and has been responsible for the introduction of many variables into the vapor plating operation, the inability to control many of which has substantially interfered with the uniformity and the quality of the filaments and of their refractory and/or ablative capabilities. The necessary presence of a non- States Patent 0 3,401,423 Patented Sept. 17, 1968 ice refractory core or substrate moreover not only has preempted valuable space that might otherwise have been occupied by a refractory material but also has occasioned discontinuities in the total refractory thickness at which separations were likely to occur to the particular loss of important resistance to gas-shear degradation upon exposure to ablative conditions in high thermal environments.

It is accordingly an object of the present invention to provide an improved apparatus for the formation of continuous filaments of a variety of pyrolytic materials.

Another object of the present invention is to provide such continuous filaments which will be composed entirely of the pyrolytic material and free of any nonrefractory substrates or the like.

To achieve these and other objects and advantages which will be obvious from a reading of the following disclosure, the within invention teaches establishing a concentrated ionic plasma of the vaporized pyrolytic refractory material at a particular portion or zone of a deposition chamber in juxtaposition to a deposition bed which is caused to move through said zone, and, while so moving, is first coated with the pyrolytic material and then, after it has moved from said zone, has the coating stripped from it. Because the ion plasma and the deposition thereof is confined to a specific zone within the chamber, it is possible to allow the deposited coating to pass from the zone and to undergo sufficient cooling and consolidation that, at a point spaced from the zone but still within the chamber, it may be stripped from the bed without breakage or other interruptions in the filament continuity.

One particularly useful deposition bed for such purposes is in the form of a circular disc which is so arranged within the deposition chamber that the plating takes place upon the periphery or edge thereof while it is within the ion zone. As the disc is rotated a coating is continuously built up and then carried from the zone to the point at which means are provided for its removal. The disc itself may be composed of one or more electrically conductive plates which are coaxially aligned and laterally spaced to provide a series of parallel deposition beds upon each of which a separate continuous filament may be deposited while the composite disc is passing through the same concentrated atmosphere of refractory ions. To cause the ion-laden vapor to undergo the necessary gasphase solidifying reaction at the peripheral surface of the disc, at least somewhat in the manner of well-known vapor plating techniques, the disc itself is heated, at least at the point at which it passes through the plasma zone. On the other hand, because of certain teachings of the invention to be hereinafter explained, it is no longer necessary that the deposition bed achieve such high temperatures as to interfere with the economy, efliciency or adaptability of the method and apparatus to a variety of refractory materials and of end products.

The ion-laden plasma may be formed or otherwise obtained according to a wide variety of procedures; but, as will be apparent from the following description, certain methods are particularly adaptable to the teachings hereof and participate in a unique manner in the new and unobvious improvements provided hereby. One of the important features of the invention is the confinement within the larger chamber of the refractory plasma to a particular zone or zones at pre-selected locations; and

one preferred method for such confinement is the introduction of the plasma into the chamber through a rcstrictive nozzle capable of establishing a high-density jet stream. The plasma itself may have been formed in the first instance by conventional techniques such as by electrical excitation or heating of the precursory refractory substance, particulariy in a vacuum. In certain instances, the ion-laden plasma thus formed may be sutficicntly confined by nothing more than the mechanical effects of the fluid dynamics of the nozzle, properly positioned and directed.

In a more refined embodiment however, the ions, once received within the chamber or there formed in situ, are electrically influenced somewhat in the manner of a glow discharge tube and are concentrated at a desired point near the deposition bed by the manipulation of a nonuniform electrical field. The non-uniformity may be cre ated by the selection of electrodes of particular geometrical configurations and by the positioning thereof within the overall chamber so that deposition will take place at one point therein while removal of the plated and partially cooled material may take place at another point in the chamber. The influence of a jet stream established by a nozzle and the concentrating efiects of electrode focusing may be combined by applying an electromotive force to a jet nozzle formed of an electrically conductive material and to some other electrically conductive area of surface dimensions larger than those of the nozzle within the chamber. Where the disc providing the deposition bed is an electrical conductor, it may be the electrically energized component of larger area to cooperate with the nozzle in focusing the ion plasma at the gap between the jet nozzle and the periphery of the disc at which the deposition is to take place. Where the disc is not an electrical conductor, the entire interior of the chamber may be made of dielectric materials except for the nozzle and for some other area spaced from the nozzle to accomplish the same glow discharge plating at the gap between the nozzle and the bed.

In further modifications of the invention, a plurality of nozzles may be circumferentially spaced about the disc so that successive multiple applications of the plated material may be applied to build up a thicker coating. So also, where three-phase current is employed, the disc may be segmentally insulated by two or more radially extending insulating strips to provide separate heating segments circumferentially of the disc each of which, under the influence of the passage of electrical energy therethrough, may be heated to a different temperature to offer a variety of plating and solidifying conditions for the ions during and immediately after their deposition upon the peripheral deposition bed.

The invention thus generally described may be more clearly understood by reference to the following detailed description of certain preferred embodiments thereof in connection with which reference may be had to the appended drawings.

In the drawings:

FIGURE 1 is an elevational end view in cross section of a preferred deposition chamber according to this invention.

FIGURE 2 is a front elevational view of the deposition chamber shown in FIGURE 1.

FIGURE 3 is an elevational view in cross section of a modification of the deposition chamber according to the present invention.

FIGURE 4 is an enlarged fragmentary view in cross section of a composite disc to be employed in the apparatus of this invention.

FIGURE 5 is a fragmentary elevational view of a modified apparatus according to the invention employing a plurality of circumferentially spaced, radially directed plasma injecting nozzles.

Referring now to FIGURES 1 and 2, the deposition chamber housing It) comprises sidewall members 11 and 12 and edgewall members 13, I4 and 15 which, together with a comparable edgewall member (not shown), generally define an enclosure which, in the case of this invention, is the deposition chamber 16. Rotatably mounted by the journaled shaft 17 is the disc assembly designated generally by the number 18 which, in the preferred embodiment illustrated, comprises a pair of metal clamping plates 19 and 20, the axially extending externally threaded lug 21 of the former of which is acted upon by the nut 22 hearing against the latter to force them together and to hold between them the support discs 23 and 24 which are on opposite sides of and give lateral support to the deposition bed disc 25. It is to be noted that the peripheral portion 26 of the disc projects radially outwardly from the supporting plates 23 and 24 and is the portion of the entire disc assembly 18 which is the closest to the edgewalls such as 13, 14- and 15 of the chamber.

Associated with the chamber housing 10 at least at one point circumferentially of the disc 25 is an electrode-jet assembly 27 which is shown to comprise the copper blocks 28 and 29 having the protuberances 30 and 31 which, when the blocks are brought into substantial contact, cooperate to form the apex 32, opening at which is the fluid passage 33. This passage may be formed by mated semicircular grooves in each of the abutting faces of the blocks 28 and 29 or by suitably placed shims. In any event the passage will act as a nozzle through which a gas and particularly an ion-laden plasma according to this invention may be passed by virtue of suitable connections via the conduit member 34 for example with a source of the plasma (not shown). In certain modifications it will be desired to provide the electrode blocks with labyrinth passages 35 and 36 through which a coolant such as water may be circulated to maintain a reasonably low temperature of the electrodes when the device is in operation.

In the preferred embodiment illustrated, provision is shown for establishing a non-uniform electrical field by applying an electromotive force or potential difference across or between the electrode assembly and the disc assembly from an electrical source such as a generator 37. The generator wire 38, together with the conductor 39 leading from the electrode assembly, is connected to the ground 40 while the wire 41 in combination with the terminal member 42 is in electrical contact with the shaft 17 of the disc assembly which is itself an electrical conductor and transmits the electrical energy to the disc 25.

At a point on the edgewall of the housing spaced from the electrode assembly and, in the preferred embodiment illustrated, diametrically opposed thereto is mounted the filament stripping unit comprising the caliper type electrodes 43 and 44 one end of each of which is connected to a high voltage electrical power source such as the generator and isolation transformer assembly 45 and the other ends of which are closely spaced on opposite sides of the peripheral portion 26 of the disc 25 to provide the gaps 46 and 47 between the electrodes and the disc across which an electrical arc may be caused to jump. \Vhere either the disc 25 or the filament deposited thereon is an electrical conductor, it is preferred that the power source for energizing the electrodes includes the isolation transformer in order that the arc Will not interfere with the electrical field participating in the glow discharge at the opposite side of the chamber. In certain instances it will also be desired that the electrodes be hollow tubular members as shown in FIGURE 1 so that an inert gas may be forced through them and into the gaps 46 and 47 to prevent the deposition at this particular heated area of such of the plating gases as might drift from the plating zone within the chamber.

In operation, a gaseous suspension of ionized particles of a precursor such as a methane series gas for the ultimate deposition of pyrolytic graphite or a borohydride for the production of borides is introduced into the deposition chamber 16 through the conduit 34 and the nozzle assembly represented by the protuberances 30 and 31, the apex 32 and the channel 33 opening thereon. The jet stream of the plasma issuing forth from the nozzle is concentrated at the nozzle opening and where, as shown in the drawing, the deposition bed represented by the edge 48 of the disc 25 is closely spaced to the nozzle opening and where other deposition conditions are favorable, a plating out of the precursory material will take place on the edge of the disc. According to this invention, the establishment of favorable deposition conditions involves the heating as by electrical resistance of the disc 25 to the point at which its edges achieve a temperature at which a gas phase surface plating reaction occurs and/or the energizing of the incoming ions and concentrating them at the deposition surface as by establishing a nonuniform electrical field to the extent that glow discharge plating will occur.

In one specific embodiment of the apparatus illustrated in FIGURE 1, the disc 25 is composed of an electrically conductive material such as Inconel. The disc is twelve inches in diameter and .050 inch wide, and the area of the electrically energized copper blocks of the electrode assembly exposed to the interior of the chamber is approximately a tenth of a square inch. The distance between the nozzle opening and the nearest point on the edge of the disc is .050 inch. Where a mixture of titanium tetrachloride, nitrogen and hydrogen is passed through the jet nozzle 33 while the pressure within the chamber is maintained at approximately eight millimeters of mercury and where an electromotive force on the order of from 500 to 1,000 volts is applied to the electrode and disc assembly by the power source 37, a uniform deposit of titanium nitride will build up upon the periphery of the disc and may be removed therefrom as a continuous filament. Where the energization and geometry of the electrically charged components exposed to the interior of the deposition chamber is such that a non-uniform electric field results in a high electrical energization and concentration of the ions at or near the deposition bed, it has been found that sufiicient plating or deposition from the concentrated ion plasma will occur at relatively low and easily achievable temperatures in the range of from 300 to 600 degrees Fahrenheit. In many instances the same electrical energy applied to the disc to establish the non-uniform field will be sufiicient to heat the disc to the required temperature. In other cases, a separate electrical current for heating purposes may have to be applied to the disc.

As the disc 25 rotates, a continuous build-up of the deposited material 48 will form on the disc edge; and, after the coating has passed for some distance from the concentrated plasma zone where the deposition has taken place, it may be removed from the edge of the disc in a continuous fashion so that a continuous filament may be withdrawn from the chamber and taken up on a supply roll. In the case of the embodiment illustrated in FIG- URES 1 and 2, one means for thus removing the deposited coating from the edge of the disc comprises the caliper electrode arc assembly which, upon the energization of the electrodes as by the application of a 500 volt, 5 to 25 watt current, will cause the electricity to arc between the electrodes and the disc and rapidly to increase the temperature of the peripheral portion of the disc as a result of which it will thermally expand and break away from the deposited coating 48a allowing it to be easily removed in the form of the filament 49 from a suitable opening in the chamber and stored upon the take-up roll 50.

Referring now to FIGURE 3, the disc 51 upon the edge of which the pyrolytic material is to be deposited may, for the purposes of desirable rigidity, heat control or the like be composed of a non-electrically conductive material such as glass in which case the electrical energization and concentration of the ion-laden plasma may still be achieved by establsihing a non-uniform electrical field. Where the disc is not capable of being an electrode, the entire interior of the chamber 52 is insulated by suitable lining with a dielectric material 53 except for portions such as 54 and 54a which are not so insulated and will in fact be composed of an electrically conductive material exposed to the chamber interior as is the nozzle 55 through which the concentrated spray of the ionized plasma is introduced to provide a cloud 56 of the concentrated ions at the gap between the nozzle opening and the disc. In this case, the non-uniform electrical field is provided by applying an electromotive force from a generator 57 through the conductors 58 and 58a to the areas 54 and 54a respectively and through the grounded wire 59 to the nozzle 55. The non-uniform field results from the fact that the areas 54 and 54a are substantially larger than the nozzle area at which the vapor is gathered.

Where the deposition conditions resulting from the non-uniform electric field and/ or the heating of the deposition bed and from the quantity of plasma being introduced are such that there is a greater deposition potential or capacity than would be necessary for the formation of only one pyrolytic strand, a multiple-leaved disc assembly as illustrated in FIGURE 4 may be employed. In the assembly of FIGURE 4, three concentrically aligned laterally spaced circular metal plates 60, 61 and 62 are shown to be separated by suitable spacing and supporting wheels '63 and 64 which are of a lesser diameter than the plating discs allowing the latter to extend beyond the general assembly to receive the full effect of the non-uniform electrical field. In this case, the edges 65, 66 and 67 of each of the discs 60, 61 and 62 respectively will accommodate the building up of a separate filament as the total disc assembly rotates through a single ion-laden deposition zone, thereby increasing the output capacity of a given plating chamber.

Further efficiencies and more precise control of the nature of the deposited material may be achieved in an apparatus similar to that illustrated in FIGURE 5 wherein the periphery of a disc 68 similar to the disc 25 of FIG- URE 1 is under the influence of or acted upon by a plurality of circumferentially spaced plasma-injecting nozzleelectrode assemblies such as 69, 70, and 71. The electrical energy from the power source 72 may, by manipulation of the variable resistors 73, 74 and 75, be adjusted to distinct potential differences as to each of the electrodenozzle assemblies thereby to alter the characteristics of the electrical field and of the deposition rate and characteristics at each of the nozzle openings. In such an apparatus, not only may a coating of pyrolytic material be built up faster or to a greater thickness within a given time but the built-up coating and the filament ultimately resulting therefrom may be composed of different materials, depending upon the passage of different gases through certain of the circumferentially spaced nozzles. Where different gases or different concentrations of the same gas are applied through successive nozzles, appro priately spaced walls may be inserted around the disc to shield the gas emitted by one nozzle from the gases being admitted by the nozzles on either or both sides of it.

While the foregoing invention has been described in considerable detail in connection with certain specific embodiments thereof, it is to be understood that the foregoing particularization has been for the purpose of illustration only and does not limit the invention as defined in the *subjoined claim.

I claim:

1. An apparatus for the formation of continuous filaments comprising an enclosed deposition chamber housing, conduit means for supplying an ion laden plasma to the housing, a jet nozzle receiving its input from the conduit means and delivering a cloud of vaporous pyrolytic refractory ion laden plasma to a deposition zone within said housing, a rotating disc deposition bed peripheral edge moving through the deposition zone within the housing and adjacent the delivery end of said jet nozzle,

7 7 8 heating means maintaining the deposition zone between References Cited the discharge end of the jet nozzle and the rotating disc UNITED STATES PATENTS peripheral edge at a predetermined temperature, a pair of electrode gaps diametrically remote from the deposition 21158'415 5/1939 Formhals' zone Within the housing and between which the pyrolytic 5 3,239,368 3/1966 Goodman 117-106 refractory deposit along the peripheral edge of the rotat- 32941880 12/1966 Turkat 26481 3,315,208 4/1957 Gerstenberg 117106 ing disc passes, and means maintaining an arc discharge between the electrode gaps for separating as a continuous filament the pyrolytic refractory deposit from along the JULIUS FROME P'lmary Exammer' peripheral edge of the rotating disc. 10 I. R. THURLOW, Assistant Examiner.

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