US3630864A - Method and apparatus for continuous electrolytic polishing of fine metal wires - Google Patents

Abstract

IN AN APPARATUS FOR EFFECTING THE CONTINUOUS ELECTROLYTIC POLISHING OF FINE METAL WIRES AN ELONGATED ELECTROLYTIC CELL IS DIVIDED INTO A PLURALITY OF ELECTROLYTIC CHAMBERS BY MEANS OF A PLURALITY OF PARTITION WALLS HAVING ALIGNED LIMITED OPENINGS TO PASS A STRAIGHT WIRE. AN ELECTROLYTE HAVING LOWER RESISTANCE THAN THE WIRE IS CIRCULATED THROUGH THE CELL SUCCESSIVELY THROUGH THE LIMITED OPENINGS AND CHAMBERS AND ALTERNATING CURRENT IS PASSED THROUGH THE WIRE WHEREBY IN EACH CHAMBER THE CURRENT FLOWS MAINLY THROUGH THE ELECTROLYTE TO CREATE POLARIZATION. THE APPARATUS IS UTILIZED IN A CONTINUOUS WIRE FINISHING LINE.

Description

Dec. 28, 1971 yos mu ETAL 3,630,864

METHOD AND APPARATUS FOR CONTINUOUS ELECTROLYTIC POLISHING 0E FINE METAL WIRES Filed June 13, 1968 FIG.

FIG. 3

United States Patent 3,630,864 METHOD AND APPARATUS FOR CONTINUOUS gvLEgTROLYTlC POLISHING OF FINE METAL IR S Kiyoshi Nakamura, Chiba-shi, Koji Nabae, Yokohamashi, and Nobuo Ohsawa, Kawasaki-shi, Japan, assignors to Tokyo Shibaura Denlri Kabushilri Kaisha, Kawasakishi, Japan Filed June 13, 1968, Ser. No. 736,700 Claims priority, application Japan, June 19, 1967, 42/38,889; Sept. 13, 1967, 42/77,837 Int. Cl. C2310 3/06; Btlllr 3/00 US. Cl. 204140.5 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for continuous electrolytic polishing of fine metal wires.

Continuous electrolytic polishing has been carried out by passing a fine metal wire through one or a plurality of spaced apart rectangular box shaped electrolytic cells Electric current was passed through the wire by means of a contact means outside the cell consisting of a mercury terminal, metal wool, a metal roller of the like and a counter electrode in the cell, or contact means of the type referred to above provided on the opposite ends of the metal wire outside the cell, or contact means on the opposite ends of the metal wire outside the cell and a counter electrode in the cell or two electrodes immersed in separate electrolytic cells. The fine wire to be treated was passed through an electrolyte by means of guide rollers or passed linearly in the electrolyte through small notches or slots, passed between an outside contact and a contact disposed in the cell along a spiral or a plurality of parallel go and return paths. Further direct current has been exclusively used to perform electrolytic polishing. However, in one type of prior method wherein the wire is caused to run linearly-and current is passed through the wire by means of an outside contact and an electrode disposed in a cell, when treating very fine wires having diameters of less than 0.02 mm., for example, the electrical resistance of the wire itself becomes so high that no additional advantage could be expected by increasing the length of the cell or the length of the wire immersed in the electrolyte. In such a case, satisfactory electrolysis could not be realized unless the running speed of the wire was greatly reduced or unless a number of electrolytic cells were employed. Where a number of cells are arranged in cascade, the number of contacts to be installed outside the cells increase whereby the resistance to the passage of the wire is increased thus making it difiicult to increase the running speed of the wire. Installation of a number of cells also increases the cost of installation.

With the arrangement wherein a plurality of electrolytic cells are arranged in cascade and wherein a voltage is applied to the wire across outside contacts on the opposite ends thereof, all of the electric current supplied between the outside contacts and cells and between different cells flow through the fine metal wire being treated, so that it is impossible to use current of the value exceeding the permissible melting current of the wire. Unfortunately unless the electrolysis current is limited to about 50% of the permissible current for the fine wire being treated, the wire is heated to oxidize its surface during the period when it is running in air outside the electrolyte. For this reason, the running speed of the Wire is limited by the number of cells involved. Generally, in order to perform electrolytic treatment at speeds higher than 30 m./min., it is necessary to use a great many cells.

Furthermore, in the arrangement wherein the wire is repeatedly passed between an external contact and an electrolytic cell, the wire to be treated is liable to be subjected to a high tension, so that unless thick wires having considerably high breaking strength is utilized, it is impossible to increase the running speed of the wires. Treatment of fine wires whose mechanical characteristics tend to vary involves many problems.

In the manufacture of fine wires of tungsten or molybdenum which are utilized to manufacture incandescent lamps or electronic tubes, the drawn wires must be finished through a number of steps including a curl removing step in which the curl of wires caused by residual strain which was imparted to the wires when they are reduced through wire drawing dies, a step of electrolytic polishing in which oxides or lubricant such as fine particles of graphite utilized in the wire drawing dies is removed, a step of washing wires after electrolytic polishing, and a step of continuously measuring the diameter of wires.

It is of course desirable to perform these steps in one continuous processing line at a high speed. Among these various steps, the step of electrolytic polishing is most important because the running speed of the wire through the processing line is essentially determined by the speed at which the Wire can pass through the electrolytic polishing device without the accompanying troubles mentioned above.

SUMMARY OF THE INVENTION Accordingly it is an object of this invention to provide a new and improved method and apparatus for electrolytically polishing metal wires and which is capable of polishing or cleaning fine metal wires at high speeds.

Another object of this invention is to provide an improved continuous finishing apparatus for fine metal wires.

Briefly stated, according to this invention, an elongated electrolytic cell is divided into a plurality of electrolytic chambers by means of a plurality of spaced apart partition walls which are provided with aligned limited openings to linearly pass therethrough a wire and an electrolyte. The electrolyte has a resistance lower than that of the wire and is circulated through the electrolytic cell successively through limited openings and electrolytic chambers.

A pair of electrodes are provided in the electrolytic chambers at the opposite ends of the cell to pass alternating current through the wire. As the electrolyte in each chamber has a much lower resistance than the wire, most of the current fiows through the electrolyte in each electrolytic chamber whereby a polarization phenomenon is created to electrolytically polish the surface of the wire. The invention is especially suitable for treating fine wires of tungsten or molybdenum having diameters ranging from 0.005 to 0.1 mm.

For these applications, the electrolyte advantageously consists of 1 to 30% solution of caustic soda.

As the novel electrolytic polishing apparatus permits high speed running of the wire being treated without any appreciable friction, it is suitable for use in a continuous metal wire finishing line including means to eliminate curl, an electrolytic polishing apparatus, a washing device and means to continuously measure the diameter of the wire which are arranged in the order mentioned.

BRIEF DESCRIPTION OF THE DRAWING tially all the current flows through the wire while it is passing through the notch. However, in each electrolytic chamber, current flows through the electrolyte in parallel with the wire as indicated by arrows in FIGS. 2A and 2B. FIG. 2A shows the flow of current during a positive half This invention can be more fully understood fr m th cycle while FIG. 2B shows that during a negative half following description taken in connection with the accycle. companying drawing in which: Taking a tungsten wire as an example, the resistivity FIG. 1. shows a perspective view of an electrolytic cell of tungsten is about 5.5 micro ohm-cm. and the resistance utilized to carr out this invention; 10 of a tungsten wire of 13 micron diameter and 10 cm. FIGS. 2A and 2B are plan views of the electrolytic cell length is about 42 ohms. On the other hand the resistivity shown in FIG. 1 useful to explain the operation of th s of caustic soda solution is about 5 ohm-cm. but since invention, and the cross-section of the electrolyte in each electrolytic FIG. 3 is a diagrammatic repres ntation of a C tiH chamber is much larger than that of tungsten wire, the ous wire finishing line employing the novel electrolytic 15 resistance of the electrolyte is very small. Accordingly, in cell. the electrolytic chamber most of the current flows through DESCRIPTION OF THE PREFERRED the electrolyte. During the positive half cycle, current EMBODIMENT flows as shown in FIG. 2A. At portions a near one end Referring now to the accompanying drawing, the elec of the chamber where current flows into the electrolyte trolytic apparatus 1 shown in FIG. 1 comprises an elon- 29 F the tungsten, W1re ar l oxldlzl ng rfaacnon correspond gated electrolytic cell or tank 2 of a suitable electric inmg to the electric quantlly ,fiowmg Into Electrolyte sulating material such as hard vinyl resin, a pay-out reel convert .tungsten Into tungsten Oxide (W93) 3 and a take-up reel 4 on the opposite sides of the cell. As 15 then dlsolved m the olyte 9 forfflfotasslum shown, the cell is divided into a plurality of chambers or tungstate dlssolvable therem' At Pomons near the compartments 7a, 7 71) by means of a plurality of 2; other end of the chamber where current returns to the equally spaced parallel partition walls 6 having axially tungsten hydrogel, F h the metal aligned small notches or slots 5 at the upper center theresurfac? exposed at Pomons a by dlssolvmg the Surface of. Both side edges and the bottom edge of each partition layer further Chang] the eYolved hydrogen Dumlg wall 5 are liquid-tightly or fluid-tightly secured to side 9 neganve half cycles simllar reactlons prfmeed as shown In Walls and a bottom wall respectively, of the Cell to define .10 FIG. 2B. These reactions are repeated in successive eleca plurality of independent electrolytic Chambers 7 a troyltlc chambers to pollsh and clean the fine metal wire. 71) 711 which are electrically isolated from each other h dlameter of the Wire Increases the resls tance of the except through the narrow passages comprising the wire tself decreases so that current flows mainly through notches 5. A pair of electrodes 8a and 812 made of stainless h wlre thus reducmg the pollshmg effect by the Polanza' sheet, for example, are disposed in the endmost electrotion phenomena lytic chambers 70 and 7/1 on both ends of the cell 2. The t hls manner accordmg to thls electFolytlc electrodes are electrically connected to a source of alterfine metal W1res can R B ovlded Wlth an nating current 10 via an adjustable resistor According electrolytic cell of a speclal construct1on 1n the same manto this invention, it is important to use an electrolyte hav- 40 as If a number of Spaced apart Cells were arranged ing an electric resistance lower than that of the fine wire Cascade- 11 being treated. Thus for example, when it is desired to Following Table 1 shows various parameters utilized treat a tungsten or molybdenum wire having a diameter of in three examples.

Table 1 Cone. of Diameter of Diameter of caustic AC untreated finished soda, Speed Example Material wire, mm. wire,mm. percent Volt. Amp m/min 1 Tungsten 0. 014 0.011 2 15 1.5 100 2 -do 0. 032 0. 027 2 13 2. 0 3 Molybdenum 0.104 0. 004 5 12 10.0 30

from 0.005 to 0.100 mm., 1 to 30% solution of caustic After electrolytic treatment, the surface of each wire soda is preferred. The electrolyte is serially circulated was extremely clean, smooth and brilliant. through successive electrolytic chambers from a tank 12 A described above, in fine wire of tungsten and connected to the bottom of electrolytic chambers 7a and molybdenum ar d wn throu h di at high temperatures, 712 at the opposite ends via a pump 13. Alternatively, the their surfaces are covered by layers of graphite which was electrolyte can be supplied to chamber 7a from above. utilized as the lubricant or oxides. However, these layers In operation, the fine metal wire 11 is caused to travel can be effectively removed by hydrogen gas evolved at from reel 3 to reel 4 through the small slots or notches 5 portions [1 acting as cathodes. This cathodic cleaning of respective partition walls 6 and through the electrolyte action further improves the efliciency of the anodic eleccontained in the cell 2. trolytic polishing action ettected at portions a.

Concurrently therewith, a suitable AC voltage is ap- While the novel method is particularly effective for plied across electrodes 8a and 8b to cause electrolytic fine wires of the diameter of from 0.005 to 0.100 mm., polishing. FIGS. 2A and 2B diagrammatically illustrate the result of experimentation showed that the invention the polarization phenomena occurring at this time. Where can be applicable to wires having larger diameters. By the resistance of the electrolyte is considerably higher the selection of a suitable electrolyte, nearly all metals than that of the wire being treated, substantially all curcan be treated according to this invention. rent fiows through the wire thus causing no electrolytic Since alternating current is utilized to carry out the action. However, where the resistance of the electrolyte novel method of continuous electrolytic polishing of fine is lower than that of the wire (e.g. where the diameter metal wires, the polishing efficiency can be improved, with of the wire is smaller than 0.15 mm.), a substantial porlarge reduction in diameter or large quantity of removal tion of the current flows through the electrolyte contained by electrolytic polishing. Further, the fioor space can be in each chamber as shown in FIG. 2. More particularly, saved because a number of. spaced apart cells are not since the cross section of the notch 5 is small, substanused as in the prior arrangement.

In addition, as the wire being treated is always kept immersed in the electrolyte, it is etfectively cooled by the electrolyte with the result that more current can be passed therethrough, thus increasing the current density. The surface condition or flatness of the treated wire is excellent and the surface is brilliant. Very fine wires of less than 0.020 mm. diameter can be passed through the electrolytic cell at a very high speed of the order of 100 m./ min. Linear running of the Wire does not alter the mechanical characteristics thereof before and after treatment. Use of alternating current eliminates the need of a rectifier device, thus reducing the cost of installation.

FIG. 3 illustrates a continuous finishing line including the novel electrolytic polishing apparatus 20.

As shown, a fine wire 21 to be treated is payed out from a pay-out reel 22 connected to a split phase start type motor 23 which functions to apply a predetermined back tension to the wire. After passing through a guide roller 24, the wire enters into a curl eliminating device 26 including an electric heater 28 which is energized by a regulating transformer 27 to maintain the temperature of the wire in a range of from 500 to 700 C., for example, which is required to remove curl. Where the wire is in the as-drawn state, curl removal may be effected in the open air but in some cases it is advantageous to perform this operation in a reducing or inert atmosphere.

The straightened wire is then passed through the electrolytic polishing device 20 embodying this invention and comprising an electrolitic cell 29 divided into a plurality of chambers 31 by partition walls 30 including slots (not shown) similar to slots shown in FIG. 1. Electrodes 25a and 25b immersed in end chambers are energized by a source of alternating current 10. The wire is then washed by a washing device 32 to remove remaining alkaline electrolyte and then passed through a hot air drier 33. The wire 21 is then passed through a continuous diameter measuring device 34 and is finally wrapped around a takeup reel 40.

Diameter measuring device 34 includes a pair of mercury cups 35 containing mercury to pass current through the wire to continuously measure the electrical resistance thereof. The measured resistance is indicated by an indicator (not shown) in terms of the diameter. Between diameter measuring apparatus 34 and the take-up reel 40 are provided a length measuring device 36 with a suitable length meter and a guide roller 37. The take-up reel may comprise an auxiliary reel upon which the wire is to be wrapped during the starting or accelerating period and a main reel upon which the wire is to be wrapped after it has been accelerated to a predetermined constant speed.

Table 2 shows comparison of running speed of the novel device and a conventional finishing device.

Increase in the running speed by about three times is due mainly to linear movement of the wire and substantially no contact resistance at the contacts for supplying current thereto. It is evident that such a continuous finishing line greatly saves the labor and time when compared with the prior arrangement wherein various process steps are carried out independently and non-continuously.

While the invention has been described in terms of preferred embodiments it will be clear that various changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of continuously electrolytically polishing metallic wire comprising: providing a metallic wire to be polished; provided a plurality of serially spaced-apart compartments each containing therein an electrolytic solution having an electrical resistance within each compartment less than the electrical resistance of the metallic wire and wherein only each endmost compartment contains therein an electrode; serially circulating said electrolytic solution through said compartments; longitudinally advancing said metallic wire successively through said compartments in the direction of circulation of said electrolytic solution; and applying an alternating electric current to said electrodes effective to create alternating electrical polarization zones within the electrolytic solution contained in each said compartment except said endmost compartments during the longitudinal advancement of said metallic wire to effect electrolytic polishing of the metallic wire.

2. A method according to claim 1; wherein said metallic wire has a diameter of from 0.005 mm. to 0.1 mm. and wherein said electrolytic solution comprises a 1 to 30% solution of caustic soda.

3. Apparatus for continuously electrolytically cleaning metallic strands comprising: means defining a plurality of. fluidtight compartments successfully spaced-apart along a longitudinal axis receptive during use of the apparatus of an electrolytic solution, each compartment having means therein defining strand openings all of which are positioned in alignment along said longitudinal axis; advancing means for longitudinally advancing a metallic strand to be cleaned through said strand openings; circulating means including said strand openings for circulating the electrolytic solution serially through said compartments; and alternating current means comprising a pair of electrodes each disposed within an end one of said plurality of compartments as viewed along said longitudinal axis, the intermediate compartments being free of electrodes, and an alternating electric current source connected to said pair of electrodes coacting with said electrolytic solution and the metallic strand for establishing in each of said compartments except said end ones-an alternating current flow accompanied by the creation of correspondingly alternating polarization zones to effect electrolytic cleaning of the metallic strand; and wherein each said compartment has opposed side wall portions disposed in spaced-apart relationship along said longitu dinal axis, wherein said strand openings comprise means defining a slot in the upper portion of each side wall portion dimensioned to concurrently receive therethrough both the metallic strand and the circulating electrolytic solution, and wherein the cross-sectional area of said slots is dimensioned sufficiently smaller than the cross-sectional area of said compartments to ensure that the current flow within each compartment occurs primarily within said electrolytic solution while the current flow between each said compartment within the region of said slots occurs primarily within the metallic strand.

References Cited UNITED STATES PATENTS 3,287,238 11/1966 Latawiec et al 204-140.5 3,338,809 8/1967 Stricker 204- JOHN H. MACK, Primary Examiner N. A. KAPLAN, Assistant Examiner US. Cl. XrR.

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