Process and apparatus for the coating of an electrically conductive fibrous strand

Abstract

An apparatus and process for coating and treatment of an electrically conductive fiber strand made of a multiplicity of individual filaments of a quasi indefinite length, said process comprising electrically connecting the fiber strand to a voltage source to act as a cathode, passing the strand through an anode-equipped whirl chamber, and opening up the strand by subjecting the strand to a continuously or discontinuously supplied jet of fluid electrolyte to thereby uniformly treat the filaments throughout the strand to said electrolyte. The jet of electrolyte is arranged with a sinusoidal line in the axial direction of the strand and annularly to the strand in a direction counter to the direction of the twist in the strand.

Description

This invention relates to a process and an apparatus for electrocoating of an electrically conductive fibrous strand made up of thin filaments.

The continuous electroplating of electrically conductive fiber strands and/or bundles having a large number of thin individual filaments (approximately 10,000) causes difficulties, as is known, since the outer filaments of the bundle electrically shield the filaments disposed in the core, i.e. center of the bundle--in accordance with the effect of a Faraday cage. In order to electroplate these fiber bundles, attempts have been made heretofore to untwist the fiber groups or bundles so that the individual filaments or threads are disposed approximately side-by-side in the electrolytic bath (R. V. Sara: "Fabrication and Properties of Graphite-Fiber, Nickel-Matrix Composites," 14th National Symposium, November 1968, Union Carbide Corp., Carbon Products Division). Various deficiencies were encountered in this process, such as, for example, mechanical damage to the individual filaments, a local depletion of discharge-capable ions of the electrolyte, as well as a nonuniform metallic deposition on the periphery of the individual filaments.

It is an object of this invention to provide a process, as well as an apparatus for conducting the process, for the coating and/or treatment of a thin, electrically conductive fibrous strand or bundle of a quasi infinite length, (i.e. a continuous or endless strand) wherein the above-described disadvantages are substantially avoided. Advantageously, metal from the electrolyte is deposited in a maximally dense and uniform manner on all individual filaments (e.g. carbon filaments) in the fiber bundle, without necessitating a mechanical treatment (untwisting) and a damaging of the individual filaments. The process furthermore is suitable for being conducted in one operating step in a maximally simple apparatus to thereby ensure a substantial automation.

According to the invention, the desired objective is attained by electrically connecting the fiber strand as a cathode and pulling the strand through an anode-equipped whirl chamber in such a manner that it is fanned out by at least one continuously or discontinuously supplied jet of fluid electrolyte that impinges on the periphery of the strand. Furthermore, according to the invention, the fiber strand electroplated in the whirl chamber is conveyed so that it comes subsequently into contact with a roll also electrically connected as the cathode.

The fiber strand serving as a cathode thus travels through the whirl chamber into which an electrolytic fluid, especially liquid, is sprayed. This liquid is sprayed radially inwardly into the fiber strand so that the strand is fanned out approximately across the length of the whirl chamber. Since the liquid electrolyte jet, due to its passage past the anode, is simultaneously a current-conductive element or means, a deposition of metal takes place at the points in the strand reached by the jet. The electrolyte advantageously also reaches the filaments in the core of the fiber strand, without any interspersed shielding due to external filaments. The fanning out of the fibrous strand by the turbulence of at least one liquid electrolyte jet ensures a statistically uniform, optimum deposition of metal or other conductive material on the strand. The feeding of fresh electrolyte furthermore prevents any local depletion of discharge-capable ions. A special advantage of the process of this invention is, moreover, seen in that any desired electrolyte fluid can be employed (for example an alkaline or acidic Cu electrolyte; nickel sulfamate, etc.). Exemplary of the metal-containing electrolytes suitable for the purposes of this invention are alkaline tin electrolyte and silver-cyanide electrolyte.

In accordance with the invention, the apparatus for conducting the process of this invention resides essentially in that the whirl chamber, consisting of an electrically nonconductive material e.g. polyvinyl chloride (PVC), exhibits an annular space defined on the inside by a bushing or inner wall means; this space accommodates an annular anode, and the liquid electrolyte feed inlet terminates in this space.

In order to achieve a satisfactory turbulence of the jet (i.e. stream spray or the like) of fluid electrolyte, it is suggested according to a further feature of this invention, to dispose in the jacket of the bushing radially oriented nozzles or orifices extending essentially in the longitudinal direction so that they are uniformly distributed along the periphery or the fiber strand.

In order to place the fiber strand to be electroplated in the whirl chamber under current, a roll is provided which is connected with the cathode of an electrical current source over which roll the electroplated fiber strand is passed.

The nozzles, through which the electrolytic fluid exits from the annular space to the fiber strand, can be of a circular or slot-like shape; however, their configuration must ensure that an appropriate amount of turbulence required for fanning out the fiber strand is positively provided. An additional advantage can be obtained, if required, by moving the nozzles, as well as feeding the electrolyte in a pulsating manner.

The use of the apparatus of this invention is not limited merely to the electroplating of fiber strands; rather, it is also possible to utilize the apparatus for electrolytic etching or scouring of fiber strands or otherwise treating the strands with a fluid electrolyte.

The process and apparatus of the invention will be further understood from the following detailed description and the accompanying drawing wherein:

FIG. 1 shows the apparatus of the invention in an elevational view; and

FIG. 2 shows a whirl chamber of the invention.

The fiber strand 2, consisting of about 10,000 individual carbon filaments, passes from a take-off reel 1 approximately in the axial direction through the passage provided in whirl chamber 3 and over a guide roll 4 to a windup reel 5. In the annular space 6 of the whirl chamber 3, described in greater detail in FIG. 2, a ring-shaped anode 7 is arranged which is connected with an electrical current source 9 via an electrical line 8 provided with an ammeter A; the voltage of this current source is measured by a voltmeter V. Furthermore, a feed line 10 leads into the annular space 6, by means of which the liquid electrolyte E (e.g. nickel sulfamate solution) is conveyed by a pump 11 from a storage tank 12 through the nozzles 13 against the fiber strand 2. The excess electrolytic liquid dripping off from the fiber strand drips into the storage tank. After the fiber strand 2 has been coated in the whirl chamber 3, it is conducted via the roll 4, connected to the cathode of the current source 9 by way of an electrical line 14. By the contact of the fiber strand with this roll, the objective is achieved that the fiber strand becomes effective to serve as a cathode. The electroplated fiber strand is finally, after a drying step (by drier means not shown), wound up on the windup reel 5 in the direction of the arrow.

The whirl chamber 3 (FIG. 2) comprises essentially two circular housing sections 15 and 16, connected with each other and made of an electrically nonconductive material, e.g. PVC, teflon (PTFE), or glass; these sections form the annular space 6. The housing section 15 has a disk portion and a bushing portion 15a defining a wall extending from the bore of the disk portion disposed along the axis A'. The wall of this bushing has six nozzles 13 uniformly distributed along the circumference; each of these nozzles extends approximately in accordance with a sinusoidal line in an axial parallel manner (axis A'). The length of these nozzles, projected onto the axis A', corresponds approximately to the height of the anode 7. However, the nozzles can be of any desired configuration; for example, it is possible to arrange bores or slots of any desired shape, but the nozzles must ensure that the fiber strand moving in the axis A' is uniformly exposed along its entire periphery to the turbulent jets of electrolyte and is thereby fanned out.

The annular anode 7, as well as the wall portion of the second housing section 16 are seated on the disk portion of the housing section 15. The contact surfaces of the two housing sections 15 and 16 are provided with gaskets 17 and 18 which thus seal the annular space 6 appropriately. Furthermore, bores 10' and 19 are provided in the housing section 16 for the feed line 10 of the liquid electrolyte as well as for the anode line 8. The bores 20 are intended for the screws that are used to assemble the housing.

Within the scope of this invention, still further embodiments of the whirl chamber, especially the nozzles, are possible, by means of which the effect of a fanning out of the fiber strand with the aid of the electrolyte jet or jets is attained. Thus, it would be possible, for example, to make the nozzles movable, their cross section variable, or to make the annular anode adjustable with regard to the periphery of the strand during operation.

The process of this invention will be further understood from the following examples.

EXAMPLE 1

In an apparatus as illustrated in FIGS. 1 and 2 a strand of carbon filaments (10,000) having a denier of 1 gram per meter and of a twist of 6 turns per meter under a tension of 2 pounds is passed at a speed of 1/4 feet per minute through a whirl chamber having six nozzles through which nickel sulfamate is supplied as an electrolyte. The electrolyte is injected via the nozzles (each having a discharge opening with a length of 1 inch and a width of .02 inch) at a rate of 5 liters per minute and under a pressure of 1000 mm water column. The high velocity jets of electrolyte impinging on the strand cause the strand to open or fan out so that the center filaments are uniformly coated with the electrolyte. A voltage of 5 volts and a current of 2 amperes are used to effect the required electroplating of the nickel metal.

EXAMPLE 2

Additional strands of the following electroconductive filaments are treated with various electrolytes by following the procedure set forth in Example 1.

______________________________________ Number of Type of Strand Filaments Kind of Electrolyte ______________________________________ Maraging Steel Wires 2,000 Silver Cyanide Maraging Steel Wires 2,000 Cobaltous Cyanide ______________________________________

In each case the filaments within the center are observed to have the same degree of treatment as the filaments on the outer periphery.

From the above examples it is apparent that the process of this invention is suitable for electrotreating a wide variety of conductive strands with electrolytes.

It will be understood that the process of this invention as applicable to coating various conductive strands including those of carbon fibers, and metallic wires such as maraging steel wires. These fiber strands are usually in a twisted condition.

Furthermore, it will also be appreciated that many different metal-containing electrolytes may be used for treating the fiber strand. Among the suitable electrolytes are nickel sulfamate, silver cyanide and like electrolytes which contain metal ions of cobalt, chromium, zinc, cadmium, tin, lead, gold, platinum, iron, indium, antimony, arsenic, manganese, rhenium, selenium, tellurium, and bismuth.

While the novel principles of the invention have been described, it will be understood that various omissions, modifications and changes in these principles may be made by one skilled in the art without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A process for the coating and treatment of an electrically conductive fiber strand made of a multiplicity of individual filaments of a quasi infinite length, said filaments in said fiber strand being twisted together, which comprises the steps of:

electrically connecting the fiiber strand to a voltage source to act as a cathode,

passing the strand through an anode-equipped whirl chamber,

supplying fluid electrolyte to said whirl chamber from a storage tank containing a reservoir of said fluid electrolyte, said whirl chamber being separated from said storage tank such that said whirl chamber is substantially free of the fluid electrolyte reservoir, and

subjecting the strand to at least one jet of said fluid electrolyte to open up the strand such that the filaments throughout the strand are uniformly treated exclusively with said electrolyte jet, said at least one jet of fluid electrolyte being suppliled annularly to the strand, wherein each jet of electrolyte is arranged with a sinusoidal line in the axial direction of the strand and annularly to the strand in a direction counter to the direction of the twist in said strand.

2. The process according to claim 1, in which the fiber strand is electroplated in the whirl chamber by conveying the strand over and into contact with a roll connected as the cathode of said voltage source.

3. The process according to claim 1, in which the jet of electrolyte is directed perpendicular to the axis of said strand.

4. The process according to claim 1 in which a plurality of jets of a liquid electrolyte are directed against said strand.

5. The process according to claim 1 in which the fiber strand is made of carbon and the electrolyte contains metal ions in solution.

6. An apparatus for treating a continuous fiber strand of a multiplicity of electrically conductive filaments, said apparatus comprising

a storage tank for storing a reservoir of fluid electrolyte,

a whirl chamber of an electrically nonconductive material, said chamber having a passage and an annular space defined by an outer and an inner wall means, an anode within said space, a fluid electrolyte feed means terminating in said space, said chamber being separated from said storage tank such that said passage is substantially free of the fluid electrolyte reservoir in said storage tank,

means for passing an electrically conductive strand through said passage,

means for supplying said fluid electrolyte from said storage tank to said fluid electrolyte feed means, and

nozzle means for directing at least one jet of electrolyte onto said strand, said nozzle means being arranged so that the strand is opened up by the electrolyte to allow exclusive treatment of the filaments within said strand by said jet of electrolyte, wherein said nozzle means includes a plurality of individual nozzles, each of said individual nozzles extending in a sinusoidal line in the longitudinal direction and annularly with respect to the strand.

7. The apparatus according to claim 6, in which the nozzle means are radially oriented slots extending through said inner wall means, each of said slots being disposed to extend essentially in the longitudinal direction and being uniformly distributed along the periphery of said strand.

8. The apparatus of claim 6, in which a roll is provided which is connected with the cathode of the current source for placing the fiber strand to be electroplated in the whirl chamber.

9. The apparatus of claim 6 in which said plurality of nozzle means are radially positioned around said passage.

10. The apparatus of claim 9 in which the nozzles are spaced equidistant from each other and are substantially identical to each other.

11. The apparatus of claim 6 in which the nozzles are spaced equidistant from each other.