Process of producing a hot dipped wire

Abstract: A process of producing a hot dipped wire (1a). During the wire drawing (S1), the base wire (1) is passed over apparatus (10) having a passage surface made of a non-iron material. After steam heating (53), cleaning (S4) and drying steps (S5), the wire (1) is heated in an atmosphere of a reducing gas (S6) for effectively removing any oxide layer on the surface of the wire (1) and for prehating the wire to accelerate a reaction between the wire (1) and a molten hot dipping metal used in the subsequent hot dipping step (S7).

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 in electronic wiring, It 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 containing 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 for 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 comes 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 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 passage through 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 had 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 quality of plating deteriorates. 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, one aspect of the present invention is directed to a process of producing a hot dipped wire which process comprises at least a drawing step during which the wire is drawn in a water soluble lubricant and comes into contact with drawing apparatus, a pretreatment step during which the wire is at least cleaned and a hot dipping step in which the wire is dipped in molten metal characterised in that (a) during at least the drawing step contact of the wire with a surface capable of providing contaminant iron oxide is avoided, and (b) the said pretreatment step comprises at least cleaning and drying the wire and immediately prior to the hot dipping step, heating the dried wire in a reducing gas atmosphere at a temperature of from 300°C to 500°C so as to remove any oxide from the wire surface and to promote reaction between the wire and molten hot dipping metal. According to an embodiment of the present invention, there is provided 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 generating iron oxide; pretreating the drawn wire which pretreatment step comprises steam heating the wire for facilitating separation of the lubricant from the wire and for annealing, cleaning lubricant from the wire, drying the cleaned wire, and heating the dried wire in a reducing gas atmosphere at a temperature of from 300°C to 500°C; and hot dipping the pretreated wire in the molten hot dipping metal, directly after heating in a reducing gas atmosphere. In some embodiments the drawn wire is wound around a spool having a wire passage surface not generating iron oxide and subsequently unwound from the spool for the pretreatment step. Suitably the pretreatment step includes use of apparatus having a wire passage surface made of a material not generating iron oxide, and passing the wire in contact with the wire passage surface. In embodiments of the present invention in the reducing gas heating step, the wire passes through a furnace about 1 to about 3m long at a speed of about 50 to about 90m/min. In some embodiments at least one said wire passage surface comprises a ceramics material or a plastics material. Conveniently the drawn wire is cleaned using an ultrasonic cleaning bath. Preferably the reducing gas atmosphere includes one or more of carbon monoxide, nitrogen and hydrogen. 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 of steps of present invention are similar to those of the prior art in many respects with the exceptions of both the reducing gas heating step and the use of materials not generating 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 a Pamphlet issued by Griller & Co, of the NIEHOFF GRUPPE, Germany, 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 water soluble lubricant (®"LUBLITE #2000" 4.5%conc. NIHON YUZAI KENKYUSHO / Japanese company or ™"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 ceramic 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 plastic ( for example, epoxy resin ) 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. 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 3, say 2 m long, in the atmosphere of a steam at about 650°C, for example. 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 3 on the same conditions. In the furnace 3, the wire 1 to be plated is cleaned with steam so that the water soluble lubricant can be easily separated from the surface of the wire 1. The steam enters the furnace 3 from a source of boiling water by itself without applying any additional pressure, that is, at a pressure slightly higher than the atmospheric pressure. Simultaneously, the wire 1 was annealed in the furnace 3. Thereafter, as indicated by the reference numeral S4 in FIG. 1 and in FIG. 2(b), without exposing to the atmosphere the wire 1 is introduced into a cleaning bath, for example, an ultrasonic cleaning bath 5, containing pure water 4, in which the wire 1 was completely cleaned off to remove the water soluble lubricant and other adhering impurities from its surface. Subsequently, as indicated by the reference numeral S5 in FIG. 1 and in FIG. 2(b), moisture was removed of the wire 1 by a dryer, such as an air wiper 6a into which compressed air k was introduced, so that the wire 1 is dried. Then, as indicated by the reference numeral S6 in FIG. 1 and in FIG. 2(b), the wire 1 is introduced into a gas reducing furnace 7, about 1 to 3 m long, typically 2 m long, in an atmosphere of a reducing gas, such as a carbon monoxide gas and nitrogen gas, at a set temperature of from 300 to 500°C, so that the oxidized layer on the surface of the wire 1 may be reduced. Simultaneously, the wire 1 is preheated in the gas reducing furnace 7. In such a state, as indicated by the reference numeral S7 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 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 S7 may be protected by a material not generating 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 with little impurities adhered and little oxidized layer, 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 coated with 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 3 in the atmosphere of a steam at 650°C. In the furnace 3, the copper wire 1 to be plated was cleaned with steam so that a trace amount of the water soluble lubricant could be easily separated from the surface of the wire 1. Simultaneously, the wire 1 was annealed. Thereafter, without exposing to the atmosphere the wire 1 was introduced into an ultrasonic cleaning bath 5, containing pure water 4, in which the wire 1 was completely cleaned off to remove the water soluble lubricant and other adhering impurities from its surface. Subsequently, moisture was removed of the wire 1 by an air wiper 6a into which compressed air k was introduced, so that the wire 1 was dried. Then, the wire 1 was introduced into a gas reducing furnace 2 m long with a carbon monoxide atmosphere at a highest temperature of 500°C, so that the oxidized layer on the surface of the wire 1 was reduced, and was thereby removed as CO₂ gas. The temperature of the furnace 7 was 300°C at each of the inlet and outlet thereof. Simultaneously, the wire 1 was preheated. In such a state, the wire 1 was introduced into a hot dipping tinning bath 8, 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 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 hot 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 to S6 and hot dipping step S7 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 3 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 to S6 and hot dipping step S7 were conducted in a continuous line as in Example 2 although no drawing die d was used in the hot dipping step S7. 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 the furnace 3, the ultrasonic cleaning bath 5 and the air wiper 6a in the same conditions as in Example 1. Then, the OFHC wire 1 was pulled to pass 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 oxygen layer on the wire 1 is removed by reduction with the wire 1 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 disposed 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 S7 were coated with a non-iron material such as a ceramic and a plastic as in Example 1. The hot dipped wire 1a was excellent in appearance without any exposed core wire and with a uniform plating.

Claims: A process for producing a hot dipped wire, which process comprises at least a drawing step during which the wire is drawn in a water soluble lubricant and comes into contact with drawing apparatus, a pretreatment step during which the wire is at least cleaned and a hot dipping step in which the wire is dipped in molten metal characterised in that (a) during at least the drawing step contact of the wire with a surface capable of providing contaminant iron oxide is avoided, and (b) the said pretreatment step comprises at least cleaning and drying the wire and immediately prior to the hot dipping step, heating the dried wire in a reducing gas atmosphere at a temperature of from 300°C to 500°C so as to remove any oxide from the wire surface and to promote reaction between the wire and molten hot dipping metal. A process according to Claim 1 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 generating iron oxide; pretreating the drawn wire which pretreatment step comprises steam heating the wire for facilitating separation of the lubricant from the wire and for annealing, cleaning lubricant from the wire, drying the cleaned wire, and heating the dried wire in a reducing gas atmosphere at a temperature of from 300°C to 500°C; and hot dipping the pretreated wire in the molten hot dipping metal, directly after heating in a reducing gas atmosphere. A process according to claim 1 or 2, wherein the drawn wire is wound around a spool having a wire passage surface not generating iron oxide and subsequently unwound from the spool for the pretreatment step. A process according to Claim 1, 2 or 3 wherein the pretreatment step includes use of apparatus having a wire passage surface made of a material not generating iron oxide, and passing the wire in contact with the wire passage surface. A process according to any preceding claim, wherein in the reducing gas heating step, the wire passes through a furnace about 1 to about 3m long at a speed of about 50 to about 90m/min. A process according to any one of claims 1 to 5 wherein at least one said wire passage surface comprises a ceramics material or a plastics material. A process according to any one of claims 1 to 6 wherein the drawn wire is cleaned using an ultrasonic cleaning bath. A process according to any preceding claim, wherein the reducing gas atmosphere includes one or more of carbon monoxide, nitrogen and hydrogen.

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