US3807026A - Method of manufacturing fine metallic filaments - Google Patents

Abstract

A method of producing a yarn of fine metallic filaments at low cost, which comprises covering a bundle of a plurality of metal wires with an outer tube metal to form a composite wire, drawing said composite wire and then separating the outer tube metal from the core filaments in said composite wire, wherein for ease of said separation treatment, the surfaces of said metal wires are coated with a suitable separator or subjected to a suitable surface treatment before the covering of the outer tube metal, thereby to prevent the metallic bonding of the core filaments to each other in the subsequent drawing or heat-treatment of the composite wire.

Description

United States Patent [191 Takeo et a].

[ METHOD OF MANUFACTURING FINE METALLIC FILAMENTS [75] Inventors: Keinosuke Takeo; I-Iideo Ogita, both of Itami, Japan [73] Assignee: Sumitomo Electric Industries, Ltd.,

Higashi-ku, Osaka, Japan [22] Filed: July 7, 1972 [21] Appl. No.: 269,635

[30] Foreign Application Priority Data [451 Apr. 30, 1974 2,718,049 9/1955 Prache 29/419 3,529,343 9/1970 Gorton 29/419 FOREIGN PATENTS OR APPLICATIONS 633,109 12/1961 Canada 29/470.9 820,033 9/ 1959 Great Britain 29/470.9

Primary ExaminerCharles W. Lanham Assistant Examiner-D. C. Reiley, 111 Attorney, Agent, or Firm-Sughrue, Rothwell, Mion Zinn and Macpeak [57] ABSTRACT A method of producing a yarn of fine metallic filaments at low cost, which comprises covering a bundle of a plurality of metal wires with an outer tube metal to form a composite wire, drawing said composite wire and then separating the outer tube metal from the core filaments in said composite wire, wherein for ease of said separation treatment, the surfaces of said metal wires are coated with a suitable separator or subjected to a suitable surface treatment before the covering of the outer tube metal, thereby to prevent the metallic bonding of the core filaments to each other in the subsequent drawing. or heat-treatment of the composite wire. 5

4 Claims, 6 Drawing Figures ATENTEUAPR 30 I974 FIG. 2

FIG I iafis llilL FIG. 5

FIG. 4

METHOD OF MANUFACTURING FINE METALLIC F ILAMENTS DESCRIPTION OF THE INVENTION This invention relates to a process for producing a yarn of fine metallic filaments, and especially, to a separator for preventing the metallic bonding of core filaments from each other in the bundle drawing method.

In recent years, fine metallic wires with a diameter of 0.3 to 0.005 mm made of such materials as carbon steel, alloy steel or stainless steel have been used for tire cords, metallic fibers for blending purposes, metallic fibers for filters, etc.

Generally, fine metallic filaments having a diameter of not more than 0.25 mm ought to be produced by the repetition of heat-treatment and drawing in accordance with the single wire drawing process by a die, and moreover, the yield per unit time is low, which results in a very high cost of production. Therefore, in an attempt to avoid this defect, the bundle drawing process was devised, and has been utilized to some extent.

The conventional bundle drawing method comprises first coating the surfaces of material wires with a separator, such as metal oxides, graphites or oils, which prevents bonding of wires during drawings and heattreatments, or with a different metal by, for example, plating; inserting a bundle of a plurality of such wires in a tube of a different metal or covering the outer peripheries of a bundle of a plurality of said wires with a metallic tape and then welding the seam portion to form a composite wire; subjecting the composite wire to a diameter reduction treatment by drawing and heattreatment, etc. until the diameter of each wire is reduced to a desired value; and then dissolving the outer tube metal or the outer tube metal and the coated metal by a chemical method thereby to separate the core wires from each other and produce fine metallic wires.

However, according to the conventional method, it is difficult to select a solution which dissolvesthe outer tube metal (A) or the outer tube metal (A) and the coated metal (B) without chemically attacking the fine metallic filaments at all. Furthermore, since the coated metal (B) exists as a very thin layer among the fine metallic filaments, long periods of time are required in order to dissolve this layer progressively from outside by the chemical or electro-chemical method.

With a view to remedying such a defect, we completed an invention of a process which comprises cutting both sides of the outer tube metal of the final composite wire obtained by using material wires coated with a separator with two cutting bites, applying a pushdown force to the cut surfaces upwards and downwards in a direction parallel to the cut surfaces, thereby to continously break the thinnest portions of the cut surfaces along the axial direction of the wires and thus divide the outer metal tube into two portions, and at the same time, separate the yarn of fine metallic filaments therein continuously and mechanically. This invention was applied for a patent under US. Ser. No. 254,124 filed May 17, 1972.

In order to perform such a mechanical separation, it

is essential that the core filaments in the final compos ite wire should not adhere intimately to one another,

and be in the readily separable state. The present invention has solved this problem.

An object of this invention is to a method of producing fine metallic filaments, wherein prior to coating an outer tube metal on a bundle of a plurality of the material wires mentioned above, the surfaces of the material wires are coated with a suitable separator or subjected to a suitable surface treatment whereby the metallic bonding of the core filaments to one another is prevented in the subsequent drawing or heat-treatment of the composite wire, and the core filaments are rendered easily separable in the above-mentioned separa-- tion treatment.

Another object of this invention is to provide a method of producing fine metallic filaments, in which a mechanical separation treatment can be performed instead of the conventional chemical treatment in the above-mentioned separation treatment, thereby producing products of good quality free from breakage or deterioration in properties without the corrosion of the fine metallic filaments themselves.

Still another object of this inventionis to provide a method of producing brass-plated fine steelfilaments of good quality, in which prior to coating a bundle of brass-plated steel wires with an outer tube metal, a separator containing zinc powders is coated on the surfaces of said steel wires, thereby to prevent the evaporation of the zinc component of the brass-plated layer during the heat-treatment of the composite wire.

In order to achieve these objects, the surfaces of said materials wires are coated with a suitable separator by a suitable method or subjected to a suitable surface treatment, prior to coating an outer tube metal on a bundle of the material wires.

According to this invention, the fine powders of clay minerals or porous minerals such as diatomaceous earth are kneaded with a binder such as sodium silicate or an organic binder and asuitable liquid as a solvent for the binder; and the resulting kneaded mixture having a suitable viscosity is coated on the surfaces of the material wires and then heated to evaporate moisture and the binder substance. Then, an outer tube metal is covered on a bundle of these material wires, and a composite wire is produced by the bundle drawing method,

after which the above-mentioned mechanical separation is rendered possible.

The above and other objects, features and advantages of this invention will become fully clear as the description proceeds with reference to the accompanying drawings. Some embodiments of the invention will be described with reference to the drawings, but the invention is in no way limited thereto.

FIGS. 1, 2 and 3 aresectional views of wires showing one example of the productional process for the fine metallic filaments in accordance with the present invention, FIG. 1 showing the composite wire before drawing, FIG. 2 showing the composite wire after drawing, and FIG. 3 showing fine metallic filaments obtained as final product.

FIG; 4 is a schematic view of the crystal structure of a pyrophilite type mineral used as the separator in the present invention.

FIG. 5 is a schematic view of the crystal structure of a kaolinite mineral used as the separator.

FIG. 6 is a perspective view showing one example of a coating tank used for the coating of the separator compound.

The inventors of the present invention have found that the following six conditions are necessary for a separator to be used in the bundle drawing process.

a. lt should prevent the bonding of the outer tube metal and the core wires and the bonding of core wires to one another during the drawing of the composite wire.

b. The separator should not be bonded to itself during the drawing process.

The above two conditions are necessary for the separation of fine metallic filaments after drawing of the composite wire.

c. The frictional force between the separator particles and the frictional force between the separator and the metal should be greater than a certain value.

Usually, when a workpiece is drawn by a die, it undergoes a compression stress from the wall of the die and a shearing stress owing to friction between the workpiece and the wall of the die in a direction opposite to the drawing direction, and as a result, is deformed. If the workpiece is an ordinary simple material such as rod or wire, these stress are smoothly transmitted to the inside of the workpiece, and deformation is effected. But when the workpiece is a composite composed of an outer tube metal and several tens to several hundreds fine wires of small sectional areas, the transmission of these deformation stresses depend upon the frictional force acting between the outer tube metal and the wires in contact with the inside surface of the tube metal and also between the contacting wires. When this frictional force is small, the stress coming from the die is not fully transmitted to the core wires, but only the outer tube metal is plastically deformed. In this case, there is little or no compression stress from the die to the wires inside, and therefore, they merely undergo a simple tensile stress. Because of this, tensile fracture occurs as the processing proceeds. In other words, since the outer tube metal can be deformed, but the wires inside undergo tensiled fracture, it is impossible to continue the drawing operation. Furthermore, this phenomenon is not dependent only on the amount of the frictional force between the wires, but has a close relation with the deformation resistance, and the thickness of the outer tube metal and the core wire metal, the ratio of sectional area between these two metals, the die angle and the pass reduction degree, etc.

To cite an example, a composite wire is produced by inserting 90 aluminum wires 0.5 mm in diameter coated with a vegetable oil as the separator in a copper tube having an outer diameter of 12.5 mm and a thickness of 2.25 mm. The vegetable oil acts as a lubricant; and the frictional forces between the outer tube metal and the aluminum wires, and between the aluminum wires are very small. But both the copper and aluminum have a small resistance to deformation, and the deformation resistance of aluminum is especially small. Thus, it is possible to draw this composite wire by a die until the diameter is reduced to 0.4 mm.

On the other hand, when the same outer tube metal and vegetable oil as used above are employed, and carbon steel wires of the same diameter are inserted, the composite wire can be processed to an outer diameter of the composite wire of 7.3 to 7.1 mm at which point all the wires geometrically come into contact, and the inner surface of the outer tube metal also comes into contact with the wires. However, attempts to draw the composite wire to a smaller outer diameter for which plastic deformation of core wires is necessary result in the tensile fracture of the core wires or breakage of the outer tube metal, thus making it impossible to continue the drawing process. This is due to a small frictional force. Accordingly, having a close relation with the construction of the material, etc., the separator should impart a suitable frictional force between the wires.

d. The particles of the separator should become smaller in size with the processing of the composite wire, thereby reducing the thickness of the separator layer.

When a composite wire consisting of an outer tube metal and wires coated with a separator is drawn by a die, its sectional area becomes smalller and its length becomes larger. The surface area of each core wire increases in inverse proportion to the diameter of the composite wire. At this time, the separator layer should be progressively decreased in thickness without break. For this purpose, the separator particles need to be divided to smaller particles as the drawing process proceeds. The reduction in thickness can also be effected by the plastic deformation of the particles. However, the plastic deformation is liable to cause bonding of the particles with one another, and therefore, is not desirable as being contradictory to the requirements (a) and (b) mentioned above.

Accordingly, in order for a given separator compound to be divided into small particles, it is desirable that the compound should be soft and have cleavability. Or the separator should be soft and porous particles, and be divided into fine particles by a compression stress, a shearing stress, etc.

This requirement is partly inconsistent with the requirement (c). Graphite or molybdenum disulfide has a very strong cleavability, and because of this, is used as a solid lubricant. But because of its excessively good lubricating properties, such a compound cannot give frictional force to a metal having high deformation resistance such as steel.

Therefore, as mentioned in (0) above, the separator should be chosen so that it meets both of the requirements (0) and (b) having regard to the construction of the material to be used (such as the deformation resistance of the workpiece).

(e) When heat-treatment is required during the drawing of the composite wire, the separator should not be thermally degraded or should not change the properties mentioned in requirements (a) to (d) upon reaction with the metal surface of the outer tube metal or the core wires. Furthermore, a gas ascribable to the thermal decomposition of water of crystallization, adsorbed water, or the like contained in the separator should not be evolved.

When a gas is evolved during the heat-treatment, especially in the case of the thermal decomposition of a solid such as water of crystallization, an abrupt expansion of volume accompanies, and causes an increase in the pressure inside the composite wire. If this pressure exceeds the strength of the outer tube metal, the tube is broken, or locally expands even if breakage does not occur. Such a phenomenon causes a trouble in the subsequent drawing process, and becomes the cause of the breakage of the wires or the separation of the outer tube metal during the processing operation.

We have taken these requirements (a) to (e) into consideration, and found that readily available and inexpensive substances to be described are effective as separators, especially for use with metals of high strength such as steel.

a. Powders of minerals having a pyrophilite-type crystal structure.

The crystal structure of a pyrophilite-type is shown in FIG. 4. Such a substance having a three-layered structure has cleavability, and the particles of its powder are in the form of scale-like fragments. This is a relatively soft substance, and does not possess lubricating properties due to cleaving so high as in the case of molybdenum disulfide. This substance therefore well meets the requirements of the separator mentioned above.

b. Powders of montmorillonite minerals.

The crystal structure of this mineral is based on the pyrophilite type in which a part of the Si atom is re-' placed by Al and a part of the Al atom is replaced by Mg, and Na comes into among the lattices. These minerals also have properties of a separator as in (a) above.

c. Powders of kaolinite mineralsv has the property of being collapsed to small particles on application of force. It is chemically inert, and is suitable as a separator.

The properties of typical minerals which come within the minerals given in (a) to ((1) above are shown in Table 1. These substances are converted to far finer particles by their cleavability or by pressure due to their porosity and form a thin layer. They further exhibit a suitable frictional force, and meet the other requirements of a separator.

When these substances are used as a separator, they are converted to powders having a size of 300 to 200 mesh (mainly of a particle diameter of about 1 to 5 microns), and coated on the surfaces of the material wires by a suitable method to be described. When the composite wire obtained by inserting these core wires in an outer tube metal is heat-treated, the temperature should be below the decomposition temperature of the water of crystallization shown in Table 1. Since a montmorillonite mineral and diatomaceous earth contain adsorbed water, it should be heated and dried at a temperature above the temperature (100 to 200C.) at

which adsorbed water is released.

Decomposition temperature Hardof water of Specific ness cyrstallization Type Name of mineral Chemical formula gravity (Morse) C.)

. Mg (Si4O1o)(OH)2 2.83 1 901,000 Pymphlhte mmemls Tale --i l s i rcgm or r% z 2. 82 1-1.5 600-700 Bentonite.... g 2( i, 4 1D 2 1. 2. 5-2. 6 850-900 Montmonuomte ""{Acid claya part of AL and Si is substitu d by ullfifs earth Mg and Al). 1 2 61 2 2 5 520 57 a0 nite O K3011 numerals {Nacrite Al2(Si O )(OI-I)4 2.58 2. 5-3 550-100 Dickite 2. 59 2. 5-3 600-700 Porous minerals- Diatomaceous earth... SiOz 2.1-2.5

1 No water of crystallization; heat-treatment up to 950 C. possible.

Diatomaceous earth is composed of the siliceous skeletons of dead unicellular aquatic plants called diatoms. Diatomaceousearth consisting essentially of hydrous amorphous silica has an innumerable number of pores with a diameter of about one micron or less, and

The method of coating the separator on the material wires will be described.

The separator should be coated in a uniform thickness on the surfaces of material wires prior to coating an outer tube metal on a bundle of the material wires. Powders of the separator compound cannot be directly coated on the surfaces of the material wires. The powders of the separator should be kneaded with a adhesive substance (binder) and a liquid or a adhesive liquid in order to impart adhesiveness against the material wires. We have found that the use of (1) an organic compound such a methyl cellulose, glycerine, polyvinyl alcohol or carboxymethyl cellulose and (2) water glass as the binder is very effective.

The properties required of the binder, of course, include one wherein a kneaded mixture of powders of a separator, the binder and the liquid should be readily coated on material wires. Also, the binder should not damage the processability of composite wire during drawing, nor impair the effect of the separator by degenerating it, nor injure or degenerate the surfaces of the core wires, nor cause gas decomposition at the heat-treating of the composite wire. However, most of the substances having adhesiveness or cohesion at room temperature are decomposed and gasified at high temperatures. Inorganic water glass exceptionally does not undergo decomposition. When such thermal decomposition occurs in the composite wire during heattreatment, the pressure inside the wire becomes high owing to the gas generated, and may lead to the rupture of the outer tube metal, which in turn results in the failure f the subsequent processing.

The organic binder used in the present invention also undergoes this thermal decomposition. Accordingly, if a bundle of material wires coated with the abovedescribed kneaded mixture of the separator and the binder is directly inserted in the outer tube metal, it cannot beheat-treated in the subsequent step. To avoid this, after coating the kneaded mixture on the material wires, they are heated to a temperature above the thermal decomposition temperature or combustion temperature of the organic binder to gasify the binder almost completely and release it. At this time, liquid such as water or alcohol is also evaporated. After this heattreatment, only the separator remains. For example, a

separator comprising the powders of clay mineral has hydrating properties, and when it is coated on material wires together with water and a binder, it is in the state of being lightly sintered even after the dissipation of water and the binder by heating. Thus, the separator remains on the surfaces of the material wires while having some strength, and the object of coating the material wires with the separator can be achieved.

Thus, in accordance with this invention, the separator is kneaded with an organic binder and a liquid to render it readily adhesive to the surfaces of material wires. The kneaded mixture is coated by a suitable method, and before insertion of the coated wires'in an outer tube, the liquid and the binder are removed by evaporation, decomposition, gasification or burning, leaving only the separator on the surfaces of the material wires.

Table 2 shows typical organic binders identified by chemical formulae and also the amounts of the binders necessary for incorporation in a ca. 3:7 mixture of talc powders as the separator and water as the liquid.

TABLE 2 Chemical fromulae (nNa O'mSiO or nK O'mSiO is also suitable as the Now, the description will be directed to the case of producing a composite wire continuously while coating the surfaces of material wires with a separator using such an organic or inorganic binder. A separator mixture having high viscosity is placed in a coating tank as shown in FIG. 6. Front and back walls 15 and 16 ofthis tank have a plurality of holes 17 same in number as the material wires to be inserted. The diameter of each of these holes determines the thickness of the separator to be coated, and should suitably be about (the diameter 7 of the material wire) (the required coat thickness multiplied by 2) 0.05.

Since the thickness tends to become larger with higher viscosity of the separator mixture, the viscosity, hole diameter, and the coat thickness should be determined optionally. The material wires are passed through the holes 17 of the walls 15 and 16. During this operation, the material wires pass through the separator mixture having high viscosity and are thus coated with the separator mixture at their surfaces. By passage through the outlet holes, the thickness of the. coat is adjusted to a certain desired value. By inserting in tandem a bundle of the coated material wires in metal pipe, a composite wire can be obtained. It is however necessary to heat and dry them before insertion. The reason istwofold.

l. The separator mixture solidifies upon heating, and firmly adheres to the surfaces of the material wires.

2. When heat-treatment is desired after drawing the composite wire, water in water glass, or water incorporated as a solvent for the binder, and adsorbed water of the fine mineral powders are released in advance from the surfaces of the material wires and the organic binder is also released by decomposition. This prevents the evolution of gas inside the composite wire during heat-treatment.

This heating and drying can be carried out using a tubular furnace provided at the rear of the coating tank shown in FIG. 6, through which the composite wire is passed for one minute to 30 seconds at 300 to 600C.

The material wires which have been coated with the separator and dried are finished into fine metallic filaments through the steps shown in FIGS. 1 to 3.

As is shown in FIG. 1, an outer tube metal 3 is coated on the outer peripheries of a bundle of a plurality of material wires 1 coated with separator 2 on the surfaces, to form a composite wire. The composite wire is then, as shown in FIG. 2, subjected to a diameter reduction treatment by drawing or heat-treatment, etc., until the diameter of each core wire reaches a desired value. Then, the outer tube metal 4 of the final composite wire shown in FIG. 2 is separated and removed by the above-mentioned mechanical method or a chemical or electrochemical method. The core filaments l are readily separated from one another by the separator 2, and fine metallic filaments 1 such as shown i FIG. 3 can be obtained.

The production of brass-plated fine steel filaments in accordance with the above-described method will now be described.

The most important thing in obtaining a bundle of fine filaments by heat-treatment and drawing a composite wire consisting of a bundle of brass-plated steel wires inserted in an outer tube is that during the heattreatment, the zinc component in the brass-plated layer is evaporated, and after the heat-treatment, only the copper remains or brass contains a very small amount of zinc component. This phenomenon occurs because the vapor pressure of zinc is as high as 0.313 atmosphere at 800C. It has long been thought that the control of atmosphere is not effective for the heattreatment of a brass article, and there is no way but to perform the heat-treatment in a slightly oxidizing atmosphere at a temperature not higher than 450C, while forming a thin layer of oxides of zinc and copper on the surface of the article.

According to the present invention, a mixture of a separator with 1 by weight of'zinc powders is coated on the surfaces of brass-plated steel wires and inserted in an outer tube. After the repetition of heattreatment and drawing operations, the outer tube is mechanically or chemically removed, to form a bundle of brass-plated fine steel filaments.

Usually, a separator not containing zinc powders is coated on the surfaces of brass-plated steel wires, and the coated wires are inserted in an outer tube to form a composite wire. The composite wire is drawn, and when it is subjected to a patenting heat-treatment during the drawing process, it is performed at 800 to 850C. By this heating, zinc present in the brass-plated layer is gasified into spaces among the particles of the separator, and zinc is eliminated from the brass. In order to prevent this, a small amount of zinc powders is mixed with the separator in advance. By this, zinc is gasified at the time of heat-treatment of the composite wire to increase the partial pressure of zinc. If the pressure is above the equilibrium vapor pressure of zinc, zinc present in the brass-plated layer is not gasified. This is a theory by which the climination of zinc from the brass-plated layer is prevented in the present invention. 7

If the amount of zinc powders to be mixed with the separator is below 1% by weight, the above-mentioned elimination of zinc cannot be fully prevented. If, on the other hand, the amount of zinc powders is above 10%, the effect of preventing zinc elimination does not appreciably increase, but rather impairs the function of the separator. It is sometimes not necessary to use the separator or binder described above. When a very compact layer of an oxide of iron is formed on the surfaces of steel wires, such steel wires, made into a composite wire, can be fully drawn, and the bonding of the core filaments to one another in the composite wire can be prevented.

In some way or other, this differs somewhat from the conditions necessary for the separator as described above. An iron oxide as the separator is firmly bonded to the surfaces of the material wires. Generally, it is considered that wires not having some oxide on their surfaces cannot be produced, but in' the present invention, this phenomenon is positively utilized. The iron oxide cannot be expected to have cleavability or plasticity as mentioned in (e) above, but since the oxide is firmly bonded to the surface, the oxide on the surface is broken as the wire is being drawn. Thus, the oxide is made into fine particles and present among the individual core wires, thus covering the surfaces of the wires uniformly. If the iron oxide forms too thick a layer in the form of scales, the frictional force between the wires is reduced, and the force is not transmitted at the time of the drawing of the composite wire. However, a compact oxide coating of a thickness about 0.0005 to 0.002 mm is effective. In the case of a soft metal such as copper or aluminum, a coating of its oxide cannot be expected to have the effect of a separator if the degree of surface reduction of the composite wire increases. When material wires obtained by coating the surfaces of brass-plated steel wires with the oxides of zinc and copper in a thickness of about 0.0005 mm are made into a composite wire and the composite wire is subjected to a surface reduction treatment without heattreatment, the core filaments are not bonded to one another. This is effective when the plated layer is very thin, for Example, not more than 0.005 mm in a material wire. If this layer becomes thicker, the oxide coating is broken, and the plated layers are bonded to one another. Furthermore, heat-treatment promotes this bonding further. Thus, only under the specific limited conditions, a compact oxide layer on the surface of wire acts as a separator.

Now, the invention will be illustrated by the following Examples.

EXAMPLE 1 A well kneaded mixture of fine talc powder, water, and carboxymethyl cellulose in a ratio of 30:65:5 was placed in a coating tank 14 having 61 holes 17 with a diamter of 0.7 mm on both walls 15 on the inlet side and 16 on the outlet side as shown in FIG. 6. Sixty-one annealed 0.80% carbon steel wires having a diameter of 0.6 mm were passed through the tank via the holes. The kneaded mixture on the material wires were squeezed by the holes 17 on the outlet side of the coating tank, and coated uniformly on the surfaces of the material wires. Then, the material wires were passed continuously through a heated furnace kept at 500 to 600C. Water was evaporated there, and carboxymethyl cellulose was decomposed and gasified. The white dried and solidified talc was uniformly adhered to the surfaces of the material wires in a thickness of 0.05 to 0.1 mm. These 61 wires were charged into a fabricating apparatus for fabricating a mild steel tape into a pipe form and a seam welding apparatus provided in tandem, and a composite wire in which the core wires were enclosed with an outer tube of iron (outer diameter 6.5 mm, pipe thickness 0.6 mm) was continuously obtained. The composite wire was cold drawn until the outer diameter reached 4.5 mm, heated at 850C for 5 minutes, cooled for 1 minute in lead at 450C., and air cooled (the so-called continuous patenting treatment). Further, the drawn composite wire was cold drawn until the outer diameter reached 0.5 mm. The outer tube metal of this thin composite wire was removed by the mechanical method described above. Each of the core filaments in the tube had an outer diameter of about 0.045 mm. Since the core filaments were separated from one another by talc used as a separator, there could be obtained a yarn of 65 fine steel filaments with an outer diameter of 0.045 mm.

EXAMPLE 2 A kneaded mixture of fine bentonite powders, water and glycerin in a ratio of 50:40:10 was coated on material wires in the same way as in Example 1. The coated wires were then passed through a heating furnace at 400 to 450C. to evaporate water and decompose and burn glycerin. Then the same operation as in Example 3 was performed to give a yarn of 61 fine steel filaments with an outer diameter of 0.045 mm.

EXAMPLE 3 A separator kneaded mixture consisting of fine talc powder and water glass in a ratio of 2:l was placed in a coating tank of the type shown in FIG. 6 in which the diameter of each holes on the outlet side was adjusted to 0.7 mm. Ninety-one annealed 0.8% carbon steel wires with a diameter of 0.6 mm were passed through the coating tank, and then continuously heated in a tubular furnace kept at 500C for a heating time of 30 seconds. The treated wires were inserted in a mild steel tube having an outer diameter of 10.0 mm and a thickness of 0.5 mm in the same way as in Example 3. At this time, a 0.04 mm thick coating of the separator was adhered to the surfaces of the material wires.

The composite wire obtained was cold drawn until the outer diameter reached 3.9 mm, and then subjected to a patenting treatment at an austenitization temperature of 800C and a lead bath temperature of 500C. The treated composite wire was further drawn to an outer diameter of 2.0 mm, and subjected again to the patenting treatment under the same conditions. The composite wire so treated was cold drawn until the outer diameter reached 0.6 mm. By the same method as in Example l, the outer tube metal was removed, and there was obtained a yarn of 91 separated fine carbon steel filaments with a diameter of about 0.055 mm.

EXAMPLE 4 The procedure of Example 3 was repeated except that bentonite was used instead of talc. There was obtained a yarn of 91 fine steel filaments having a diameter of about 0.055 mm.

EXAMPLE 5 A kneaded separator mixture consisting of fine kaolinite powders, water glass and water in a weight ratio of 3:l:0.5 was placed in a coating tank of the type shown in FIG. 6 in which the diameter of each holes on the outlet side was adjusted to 0.60 mm. Ninety ne an: nealed A151 304 Type stainless steel wires with a diameter of 0.5 mm were passed through the coating tank via the holes, and then continuously heated and dried in a tubular furnace held at 300C for a heating time of 30 seconds.- The treated wires were continuously inserted in a mild steel pipe having an outer diameter of 9.5 mm and a thickness of 0.7 mm to form a composite wire. At this time, a ca. 0.03 mm thick coating of the separator was adhered to the surfaces of the material wires. Without heat-treatment, this composite wire was cold drawn until the outer diameter of the tube reached 1.55 mm.

The composite wire was then subjected to the same mechanical separation as in Example 1 to form a yarn of fine stainless steel filaments with a diameter of about jected to diameter reduction treatment by a die until EXAMPLE 6 An adhesive kneaded mixture of fine talc powders, water methyl cellulose and zinc powders in a weight ratio of 2025512223 was coated on the surfaces of heattreated 61 brass-plated (Cu:Zn=7:3; amount of plated brass 2L0 g/kg) 0.8% carbon steel wires in a thickness of 0.004 to 0.05 mm, using the same apparatus as used in Example 1. The coated wires were continuously passed through a tubular furnace held at 500 to 600C for a heating time of about 30 seconds, thereby to evaporate water and burn methyl cellulose. The material wires were continuously inserted in a mild steel tube with a diameter of 12 mm and a thickness of 0.6 mm to form a composite wire. The composite wire was subthe diameter reached 6.5 mm. All of the abovd steps were performed in tandem. The composite wire was cold drawn until its outer diameter reached 3.0 mm, and was heated at 800C for 4 minutes, and then immersedin lead at 450C for 1 minute (patenting treatment). The treated composite wire was cold drawn until the outer diameter reached 0.55 mm. By the same method as in Example 1, the outer tube metal was mechanically removed. There was obtained continuously a yarn of fine brass-plated steel filaments containing a uniform and smooth plated layer and having the following properties.

61 62.3 microns l.2 microns 282.5 l'Cg/mm Number of core filaments per yarn: Diameter of the core filament: Tensile strength:

Elongation: 1.4% Brass ingredients: Cu 14.7 g/Kg Zn 6.3 g/Kg Total 2l.0 g/Kg (Cu:Zn=z30) COMPARATIVE EXAMPLE EXAMPLE 7 As material wires there were used 0.70% carbon steel wires having a diameter of 0.6 mm which had been austenitized at 850C for one minute in a non-oxidizing atmosphere, and then immediately, immersed in a lead bath at 500C for 30 seconds. Since these material wires were exposed to a slightly oxidizing atmosphere for about 0.5 second between the heating furnace and the lead furnace, a compact iron oxide layer of a thickness 0.00050.00l mm was formed on the surface. Sixty-one such steel wires were inserted in a mild steel tube having a thicness of 0.6 mm and a diameter of 7.5 mm to form a composite wire. The composite wire was subjected to the same surface reduction treatment and heat-treatment as in Example 1, and the outer tube metal was removed in the same way as set forth in Example I. There was obtained a yam of 61 fine steel filametns with a diameter of 0.045 mm.

EXAMPLE 8 Steel wires which had been subjected to the same patenting treatment as in Example 7 were pre-treated to remove oxide film, copper-plated and zinc-plated in tandem. The wires were then electrically heated at 400 to 450C for l to 2 seconds to diffuse copper and zinc and 7/3 brass-plated steel wires were obtained. Since this diffusion treatment was performed in air, very thin layers (less than 0.0001 mm) of copper and zinc oxides were formed on the surfaces of the wires.

A composite wire was produced from 61 such steel wires in the same way as set forth in Example 7, and then drawn by a die without heat-treatment until the outer diameter reached 1.3 mm. The outer tube metal was mechanically removed in the same way as set forth in Example 1. There was obtained a yarn of fine brassplated steel filaments with a diameter of 0. 127 mm having the same brass-plating components as in the material wires.

What is claimed is:

l. A method of producing fine metallic filaments which comprises coating the fine powder of a mineral selected from the group consisting of a mineral having a pyrophilite-type crystal structure, a montmorillonite mineral, a kaolinite mineral, and a diatomaceous earth, as a separator, on the surfaces of material wires, covering a bundle of a plurality of said wires with, an outer tube metal, drawing the composite wire obtained and if desired, heat-treating the composite wire, and thereafter, separating the outer tube metal from the core filaments of the composite wire, said separator preventing the metallic bonding of the core filaments to each other during the drawing or heat treatment operation,

wherein the step of coating said separator on the surfaces of the mineral wires comprises coating the surfaces of the mineral wires with a kneaded mixture having a moderate viscosity consisting of the fine powders of a mineral, an organic binder, and water, and then passing the coated material wires continuously through a heating furnace, to thereby remove said organic binder in said water by gasification.

2. The method of claim 1, wherein the step of coating the separator on the surfaces of the material wires comprises coating the surfaces of the material wires with a kneaded mixture having moderate viscosity consisting of the fine powders of a porous mineral, a binder and a liquid or a tacky liquid, and then passing the coated material wires continuously through a heating furnace thereby to remove said liquid, tacky liquid, and binder by gasification.

3. The method of claim '1, wherein said organic binder is a member selected from the group consisting of carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol and glycerine.

4. The method of claim 1 wherein the fine metallic filaments are fine brass-plated steel filaments and the separator contains one to ten percent by weight of zinc powders, the coating of the separator preventing the evaporation of the zinc component of the brass-plated layer during the heat treatment.

Claims (4)

1. A method of producing fine metallic filaments which comprises coating the fine powder of a mineral selected from the group consisting of a mineral having a pyrophilite-type crystal structure, a montmorillonite mineral, a kaolinite mineral, and a diatomaceous earth, as a separator, on the surfaces of material wires, covering a bundle of a plurality of said wires with, an outer tube metal, drawing the composite wire obtained and if desired, heat-treating the composite wire, and thereafter, separating the outer tube metal from the core filaments of the composite wire, said separator preventing the metallic bonding of the core filaments to each other during the drawing or heat treatment operation, wherein the step of coating said separator on the surfaces of the mineral wires comprises coating the surfaces of the mineral wires with a kneaded mixture having a moderate viscosity consisting of the fine powders of a mineral, an organic binder, and water, and then passing the coated material wires continuously through a heating furnace, to thereby remove said organic binder in said water by gasification.

2. The method of claim 1, wherein the step of coating the separator on the surfaces of the material wires comprises coating the surfaces of the material wires with a kneaded mixture having moderate viscosity consisting of the fine powders of a porous mineral, a binder and a liquid or a tacky liquid, and then passing the coated material wires continuously through a heating furnace thereby to remove said liquid, tacky liquid, and binder by gasification.

3. The method of claim 1, wherein said organic binder is a member selected from the group consisting of carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol and glycerine.

4. The method of claim 1 wherein the fine metallic filaments are fine brass-plated steel filaments and the separator contains one to ten percent by weight of zinc powders, the coating of the separator preventing the evaporation of the zinc component of the brass-plated layer during the heat treatment.

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