Process of producing a hot dipped wire

Abstract: A process of producing a hot dipped wire. During the wire drawing (S1) by the use of a water soluble lubricant, the base wire (1) is passed over apparatus (10) having a passage surface made of a non-iron material. The drawn wire (1) is heated (S3) in an atmosphere of a reducing gas for effectively removing any organic residue such as the lubricant and/or an oxide such as an iron oxide, inevitably adhered to the surface of the wire (1), and for annealing and for preheating the wire (1) to accelerate a reaction between the wire (1) and a molten hot dipping metal used in a subsequent hot dipping step (54).

Description: The present invention relates to a process of producing a hot dipped wire which is suitable for use as a lead for an electronic component and a conductor of an electronic wiring, and more particularly but not exclusively relates to a process of fabricating a hot dipped tinned, or tin plated wire and a hot dipped solder plated wire. A typical conventional process of producing hot dipped wires is illustrated in FIG. 5, in which a base wire to be plated undergoes wire drawing to produce a wire 1′ of predetermined diameter to be plated usually in a water soluble lubricant or an oil lubricant, using a wire drawing machine (not shown) including shoulder rollers, pulleys, a capstan, etc, all of which have wire passage surfaces made of iron contining materials. The drawn wire 1′ to be plated is wound over a spool 2′. In the next step, the wire 1′ to be plated which is unwound from the spool 2′ is pulled to pass through a steam annealing furnace 3′ for annealing, and is then cleaned while travelling through a cleaning bath 5′ using water 4′. Subsequently, the wire 1′ to be plated is dried by heating in the dryer 6 to remove moisture on it, is passed through an acid flux bath 11 for acid cleaning the surface thereof, and is finally directly introduced with the acid flux adhering to it into a hot dipping metal bath 8, where the wire 1′ to be plated makes contact with the molten metal for plating as well as cleaning the surface thereof. Then, the wire 1′ to be plated passes through a drawing die d to produce a hot dipped wire 1′a. Heretofore, iron materials are commonly used in shoulder rollers, pulleys, a capstan, etc of the wire drawing machine which define the wire drawing passage. For this reason, in the wire drawing step a trace amount of iron powder adheres to the surface of the wire 1′ to be plated, which is then wound around a spool 2′ with the iron powder adhered. Furthermore, an iron spool is used as the spool 2′. Thus, the wire 1′ to be plated is placed into contact with iron materials in the spool for a long period of time during storage as well as during the wire drawing step. Particularly, during storage on the iron spool, the wire 1′ to be plated is brought into contact with the iron materials of the body and the flange of the spool, and hence it is inevitable that iron oxides, such as an iron rust, adhere to the surface of the wire 1′ to be plated. Such iron oxides have very adverse effects on the quality of the plated wire during the following hot dipping step. More specifically, the iron oxides adhering to the surface of the wire 1′ to be plated change to iron hydroxides during traveling in the steam annealing furnace 3′ of a plating pretreatment step. When the wire 1′ to be plated is introduced into the hot dipping bath 8, the iron hydroxides are decomposed to produce water, which is vaporized at once and dissipated from the surface of the wire 1′ to be plated. As a result, nonplated portions are produced at surface portions of the wire 1′ to be plated where the iron hydroxides has been adhered, and exposed surface portions are thus produced in the hot dipped wire. Moreover, since the acid flux bath 11 is used in the plating pretreatment step, the acid is likely to scatter or disperse and the acid flux adhered to the wire 1′ to be plated is vaporized in the hot dipping bath 8 which is kept at a high temperature. These phenomena are liable to cause deterioration or damage to the equipment, and to pollute the working environment. Furthermore, the acid flux produces a metallic salt by reacting with the molten metal of the hot dipping bath, resulting in degradation of the hot dipping bath. Thus, the plating may also be deteriorated in quality. Accordingly, it is an object of the present invention to provide a process of producing a hot dipped wire, which process is capable of producing a hot dipped wire of good quality preferably with a reduction in exposed portions of the core wire. Embodiments of the present invention provide a process of producing a hot dipped wire, which process is capable of reducing damage to the equipment, pollution of the working environment, and degradation of the plating. In view of this and other optional features, the present invention is directed to a process of producing a hot dipped wire, comprising the steps of: drawing a wire in a water soluble lubricant, using a wire drawing apparatus having a wire passage surface made of a material not providing iron oxide; pretreating the drawn wire from the wire drawing step, which pretreating consists only in heating the wire in an atmosphere of a reducing gas to remove lubricant and any other contaminant material and at the same time to preheat the wire and hot dipping the pretreated wire in molten metal to obtain a hot dipped wire. The pretreating step includes heating the wire in an atmosphere of a reducing gas to remove contaminants such as an organic residue and/or an oxide, inevitably adhered to the surface of the wire, through carbonization or reduction upon heating, and at the same time to preheat the wire for annealing and accelerating a treatment with a molten metal in a subsequent step. Embodiments of the present invention concern a process wherein the drawn wire is wound around a spool having a wire passage surface not providing iron oxide and subsequently unwound from the spool for pretreating. Also, in some embodiments the hot dipping step is effected immediately after the pretreating step. Conveniently the pretreating step includes use of an apparatus having a wire passage surface made of a material not providing iron oxide, and passing the wire in contact with the wire passage surface. The heating may be effected using a furnace about 1 to about 3m long, and the wire to be heated passes through the furnace, in the heating step, at a speed of about 50 to about 90m/min. The hot dipping step in each process is effected immediately after the pretreating step. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing two processes embodying the invention for producing a hot dipped wire. Fig. 2(a) and Fig. 2(b) are diagrammatic illustrations of a wire drawing step, and plating pretreatment and hot dipping steps in a process embodying the present invention, respectively; FIG. 3 is a diagrammatic illustration of another process embodying the present invention; FIG. 4 is a diagrammatic illustration of a modified form of the hot dipping bath of FIG. 3; and FIG. 5 is a diagrammatic illustration of the conventional process of producing a hot dipped wire. Several modes of this invention will be described hereinafter with reference to the accompanying drawings, but some of the description thereof is simplified or omitted since some steps of present invention are similar to those of the prior art in many respects except both the reducing gas heating in the pretreating step and the use of materials not providing iron oxide, in the wire passages. Conventional techniques relevant to the present invention are disclosed for instance in Japanese Patent Application Laying-Open No. Sho59-129759, Sho59-143057 and the Pamphlet issued by NIEHOFF (German company), a copy of which pamphlet is filed herewith. According to the present invention, as shown by the reference numeral S1 in FIG. 1 and in FIG.2, a base wire A such as a copper wire, is drawn in a commercially available water soluble lubricant (for example, Registered trade mark "LUBLITE 2000" 4.5% conc. NIHON YUZAI KENKYUSHO / Japanese company or trade mark "METALSYN N-321" 6%conc. KYOEISHA YUSHI KAGAKU KOGYO /Japanese company ) into a predetermined diameter, using a wire drawing machine 10 shown in Fig. 2(a) including, for example, shoulder rollers, pulleys and a capstan all of which were coated with a material not providing an iron oxide, such as a ceramic or plastic material, for contact with the base wire. As shown by the reference numeral S2 in FIG. 1 and in FIG. 2(a), the wire 1 thus drawn may be wound around a spool 2 which surfaces are coated with a ceramic or plastic material ( for example, epoxy resin or the like) for contact with the wire 1, and may be then stored with its surface free of any iron powder and any iron oxide adhered to it. Non-iron materials other than the above may be used as or for the shoulder rollers, the pulleys, the capstan and the spool ,for not providing an iron oxide on the wire's surface. After the wire winding step S2, as indicated by the reference numeral S3 in FIG. 1 and in FIG. 2(b), the wire 1 to be plated is pulled at a speed of about 50 to 90 m/min, typically 70 m/min, and is directly introduced into a tunnel furnace 7, say 2 m long, in the atmosphere of a reducing gas at typically about 300 to 500° C (pretreating step). Alternatively, after the wire drawing step S1, the wire 1 is, as shown in FIG. 3, unwound from the spool 2, and is fed to the tunnel furnace 7 on the same conditions. Specific examples of the reducing gas include a carbon monooxide gas, a hydrogen gas and the mixture thereof. The reducing gas may be used as admixed with a suitable inert gas not causing oxidation during the pretreating step. Examples of the inert gas includes a nitrogen gas and an argon gas. In the furnace 7, the wire 1 to be plated is treated with the reducing gas under such a high temperature. During the treatment, an organic residue such as a water soluble lubricant or the like, which may inevitably be brought into the furnace with the wire as adhering to the surface thereof, will convert to caibonaceous materials mainly by heating to be easily removed from the wire through the furnace. Further, an oxide such as an iron oxide or copper oxide, which may also be formed on or adhered to the surface of the wire, will be reduced and/or converted to a volatile product to be removed from the wire in the furnace. As a result, the wire 1 is completely cleaned to remove any undesirable contaminants or layer from the surface. Moreover, in the pretreating step, the wire 1 is suitably preheated as annealing itself as well as for accelerating the subsequent hot dipping treatment. Thereafter, as indicated by the reference numeral S4 in FIG. 1 and in FIG. 2(b), the wire 1 is introduced into a hot dipping bath 8, such as a tinning bath and/or a soldering bath, where a molten metal is adhered to the wire 1, which is then passed through a drawing die d , provided just above the hot dipping bath 8 for drawing the molten metal adhering to the wire 1 so as to provide a molten metallic plating with a predetermined thickness over the wire 1. Then, the wire 1 is introduced into the atmosphere to cool and solidify the plating layer, so that a hot dipped wire 1a is fabricated. The surfaces, on which the wire passes, of the wire passage from the wire drawing step S1 to the hot dipping step S4 may be protected by a material not providing iron oxide, for example a conventional non-iron material such as a ceramic and a plastic. As a result, the copper wire 1 is hot dipped substantially with no contaminants adhered and no oxidized layer or materials, and thus a hot dipped tinned wire 1a excellent in quality may be fabricated without any exposed core surface. Example 1 A copper base wire A with a diameter 2.6 mm, as illustrated in FIG. 2(a), was drawn in a water soluble lubricant into a 0.3 mm diameter copper 1 wire to be plated, using a wire drawing machine 10 including shoulder rollers, pulleys and a capstan all of which were made of a ceramic for contact with the base wire. The copper wire 1 thus drawn was wound around a spool 2 which surfaces was coated with a plastic for contact with the wire, and was thus stored with its circumferential surface free of any iron powder and any iron oxide adhered to it. Then, as shown in FIG. 2(b), the copper wire 1 to be plated was unwound from the spool 2 at a speed of 70 m /min, and was pulled to travel through a 2 m long tunnel furnace 7 in the atmosphere of a carbon monoxide gas (reducing gas) at 500° C. The temperature of the furnace was 300° C at each of the inlet and outlet thereof. In the furnace 7, the copper wire 1 to be plated was cleaned with the reducing gas and the heating so that a trace amount of the water soluble lubricant or other organic substances and an oxide layer could be easily removed, through carbonization and reduction producing C02 gas, from the surface of the wire 1. Simultaneously, the wire 1 was annealed and heated at a suitable temperature for effectively conducting the subsequent hot dipping step. In such a state, the wire 1 was introduced into a hot dipping tinning bath 8 which had been heated at 260° C, where a molten tin was adhered to the wire 1, which was then passed through a drawing die d , provided just above the hot dipping bath 8 for drawing the molten tin adhering to the wire 1 so as provide an about 5 µm thick molten tin plating over the wire 1. Then, the wire 1 was introduced into the outer atmosphere to cool and solidify the plating layer, so that a hot dipped tinned wire 1a was fabricated. The surfaces, on which the wire passed, of the passage from the wire drawing step to the hop dipping step were coated with a non-iron material such as a ceramic and a plastic. As a result, the copper wire 1 was hot dipped with little impurities adhered and little oxidized layer, and thus a hot dipped tinned wire 1a excellent in quality was fabricated without any exposed core surface. Example 2 As illustrated in FIG. 3, wire drawing step S1, plating pretreatment S3 and hot dipping step S4 were conducted in a continuous line. According to the same conditions as in the wire drawing step of Example 1, a 2.6 mm diameter copper base wire A to be plated was drawn by the same wire drawing machine as in Example 1 into a 0.3 mm diameter copper wire 1, which was continuously introduced into the tunnel furnace 7 used in Example 1 without having been wound around a spool. The subsequent steps were conducted in the same conditions as in Example 1, and thereby a hot dipped tinned wire 1a was produced. Also in this example, the wire 1 was pulled at a speed of 70 m/min. The surfaces, on which the wire passed, of the passage from the wire drawing step to the hop dipping step were also coated with a non-iron material such as a ceramic and a plastic. The hot dipped tinned wire 1a fabricated in Example 2 was also excellent in appearance without any exposed core wire surface. Example 3 As shown in FIG. 3 and FIG. 4, wire drawing step S1, plating pretreatment S3 and hot dipping step S4 were conducted in a continuous line as in Example 2 although no drawing die d was used in the hot dipping step S4. As a base wire A to be plated a 2.6 mm diameter oxygen free copper (OFHC) wire was used, and was drawn into a 0.46 mm diameter OFHC wire 1 according to the same conditions as in the wire drawing step using the same wire drawing machine 10 of Example 1. Then, without having been wound on a spool, the OFHC wire 1 was continuously passed through a 2 m long gas reducing furnace 7 in the atmosphere of a nitrogen gas containing 10 volume % of hydrogen gas at a set temperature of 500° C, so that the organic residue and the oxide layer on the wire 1 is removed by carbonization and reduction with the wire 1 annealed and preheated. The OFHC wire preheated was, as shown in FIG. 4, introduced into a hot dipping bath 8 at a set temperature 260° C. After dipped in the molten tin, the OFHC wire 1 was drawn out vertically upwardly, so that the OFHC wire 1 was tinned without using any drawing die. In this event, the OFHC wire 1 vertically passed through a CO containing non-oxidizing atmosphere chamber 9 which was spatially placed to contact the level of the molten tin. This uniformly controlled the thickness of the plating adhered to the OFHC 1, and then the wire 1 was introduced into the atmosphere to cool and solidify the plating layer. The hot dipped tinned wire 1a thus produced had a 12 µm thick plating. In this example, the wire 1 was pulled at a speed of 30 m/min. Also, in this example, the surfaces, on which the wire 1 passed, of the passage from the wire drawing step S1 to the hot dipping step S4 were coated with a non-iron material such as a ceramic and a plastic as in Example 1. The hot dipped wire 1a obtained was excellent in appearance without any exposed core wire and with a uniform plating. The present invention thus allows contact of the drawn wire wits steam to be avoided. The process also enables removal of contaminant material, such as lubricant, to be effected directly by the step of heating the wire in a reducing gas so that any preliminary cleaning step may be avoided.

Claims: A process of producing a hot dipped wire, comprising the steps of: drawing a wire in a water soluble lubricant, using a wire drawing apparatus having a wire passage surface made of a material not providing iron oxide; pretreating the drawn wire from the wire drawing step, which pretreating consists only in heating the wire in an atmosphere of a reducing gas to remove lubricant and any other contaminant material and at the same time to preheat the wire and hot dipping the pretreated wire in molten metal to obtain a hot dipped wire. A process according to Claim 1 wherein the drawn wire is wound around a spool having a wire passage surface not providing iron oxide and subsequently unwound from the spool for pretreating. A process according to Claim 1 or 2 wherein the hot dipping step is effected immediately after the pretreating step. A process according to any preceding claim, wherein the pretreating step includes use of an apparatus having a wire passage surface made of a material not providing iron oxide, and passing the wire in contact with the wire passage surface. A process according to any preceding claim wherein the heating step is effected using a furnace about 1 to about 3m long, and the wire to be heated passes through the furnace, in the heating step, at a speed of about 50 to about 90m/min.

Inventors: HANAI YOSHITADA, KUBOTA MISAO, OTANI KOUICHI, HANAI, YOSHITADA, KUBOTA, MISAO, OTANI, KOUICHI
Applicants: TOTOKU ELECTRIC, TOTOKU ELECTRIC CO., LTD.
Application year: 1991
Main classification: C23C2
IPC codes: C23C2