Abstract:
A method for the continuous production of an elongated continuously extruded and in line polymer coated copper shape that comprises exposing an as extruded elongated copper shape to in line cooling with water covered by an inert gas before it reaches a polymer coating operation. Continuously extruded copper wire having an adherent in line applied polymer coating thereon is also described.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to continuously extruded and polymer clad copper shapes and to methods for their production.  
       BACKGROUND OF THE INVENTION  
       [0002]     U.S. Pat. No. 5,151,147 issued Sep. 29, 1992 describes a method for the production of coated wire or other elongated articles that includes a means to form the wire or other elongated article, preferably a rotary extruder, in tandem with a polymer extruder that extrudes a polymer in tubular form about the periphery of the wire or elongated product using a vacuum to draw the polymer tube down onto the extruded wire. The apparatus described in this patent includes, at the exit of the rotary extruder, a relatively short cooling zone and suggests cooling the wire before applying the tubularly extruded polymeric coating. While this patent suggests that the process described therein is equally applicable to a variety of aluminum alloys and copper, it has been found that in the case of copper, a relatively short cooling zone, or for that matter even an extended cooling zone of the type described in the &#39;147 patent is generally inadequate to provide sufficient cooling of an extruded copper wire or shape prior to polymer application resulting in charring of the polymer (due to the relatively higher extrusion temperatures achieved in the extrusion of copper) and furthermore that adhesion between the copper and an overapplied layer of polymer tends to be weak and unsatisfactory for use in the manufacture of transformers made from the coated wire. These inadequacies, particularly that related to polymer coating adhesion, have been attributed in the past to the formation of oxide on the surface of the copper between the rotary extruder and the polymer coating operation. However, attempts to solve the problem in accordance with the teachings of the &#39;147 patent that uses an air cooling system and even the installation of wire brushes to remove the oxide from the surface of the extruded copper shape have all proven inadequate to sufficiently increase the adhesion of the polymer to the copper. Similarly, lengthening the air cooling zone has proven equally inadequate in reducing the temperature of the as extruded product sufficiently to permit in line polymer coating without charring the coating. In any sort of practically sized manufacturing operation. In fact, in the current commercial production of copper wire and the like the only commonly applied practice is to extrude the copper wire, coil it, let it cool and then apply the polymer in an off-line uncoiling, coating and recoiling operation.  
         [0003]     Accordingly, there exists a need for the development of a process for the in-line coating of continuously extruded copper wire and other elongated copper shapes that, while utilizing the general approach of the &#39;147 patent cools a copper product in a relatively short distance and eliminates any negative adhesion issues relative to the presence of a copper oxide on the surface of the as extruded shape or other adhesion reducing issues.  
       OBJECT OF THE INVENTION  
       [0004]     It is therefore an object of the present invention to provide a method for the continuous production of polymer coated elongated copper wire or other articles using the general method described in the &#39;147 patent that allows for high speed processing of the extruded and coated article without charring of the overapplied polymer coating while yielding a product that exhibits satisfactory to excellent adhesion between the extruded copper shape and the overapplied polymer layer.  
       SUMMARY OF THE INVENTION  
       [0005]     According to the present invention, there is provided a method for the continuous production of an elongated continuously extruded and in line polymer coated copper shape that comprises exposing the as extruded elongated copper shape to an in line cooling mixture of water and an inert gas before it reaches a polymer coating operation. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a schematic side view of a production line for continuously forming and coating an elongated article or wire in accordance with the prior art.  
         [0007]      FIG. 2  is a schematic depiction of a cooling zone that is used between the extruder and the coating station shown in  FIG. 1  in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]     Referring now to  FIG. 1  that depicts the prior art apparatus for the continuous extrusion and coating of an elongated copper wire or the like, a coil of metal feedstock, in the instant case copper, is passed through several successive treating units  11   a  for wire brushing,  11   b  for chemical treatment, and  11   c  for ultrasonic cleaning. A rotary extrusion press  12  receives the incoming treated metal feedstock and extrudes it continuously through a die  14  in the form of a bare metal wire  16 . The orifice of die  14  determines the cross-sectional shape of the wire, that can be circular for some applications, including magnet wire, but may be rectangular in the case of magnet wire required to be wound compactly in an insulated coil connected to an electrical power source.  
         [0009]     As set forth in the &#39;147 patent the wire  16  as extruded is likely too hot for application of the polymer coating until it has been cooled by passing through a cooling unit  18 , where a cooling medium such as air is blown against the wire. After being cooled, the wire passes into a die  20  for extruding plastic coating as shown in  FIGS. 3 and 4  of the incorporated &#39;147 patent. According to the description of the &#39;147 patent, the wire continues through polymer extrusion die  20  which is of annular shape and extends around the wire so that the central axis of the die coincides with the central axis path of the path of wire  16  as it is drawn from extrusion die  14  over a roll  23  and onto a take-up roll  24 . A motor  25  rotates roll  24  with sufficient force controlled by tension maintaining device  26 , as to move wire  16  in a substantially straight and fixed path between die  14  and roll  23 .  
         [0010]     As shown in  FIG. 1 , bare wire  16  enters die  20 , where it receives a polymer coating and becomes coated wire  16 . The freshly coated wire preferably passes through a baking unit  32  to cure the polymer. It may then pass through an air-cooling zone  34  before passing through a cooling trough  36  where the wire is submerged in a cooling medium such as overflowing water by entering and leaving through weirs at the ends of the trough. The coated wire then passes through an insulation testing unit  38 , and thence through the tension maintaining unit  26  onto roll  24 . Various other elements of the apparatus of the &#39;147 patent shown in  FIG. 1  including motor  60 , vacuum drawing unit  56  computer control means  62 ,  64  and  66  and polymer pellets  46  and pan  48  that are not of particular relevance to the instant invention are not further described herein, but reference can be readily made to the &#39;147 patent for their detailed description.  
         [0011]     It is in region  100  of  FIG. 1  that the apparatus and method of the present invention find use as it is in this region that treatment of wire  16  in accordance with the present invention makes possible the fabrication of polymer coated copper wire or other elongated shapes that could not be practically fabricated using the apparatus and practices described in the &#39;147 patent.  
         [0012]     Referring now to  FIG. 2 , the area designated  100  in  FIG. 1 , that is the area between and including metal extrusion die  14  and polymer extrusion die  20 , is the area of concentration for the application of the method of the present invention. It is in this area where controlled cooling of the extruded copper product coming out of the extrusion die  14  must be appropriately cooled, prior to entry into polymer extrusion die  20 .  
         [0013]     To accomplish this appropriate cooling, a trough  102  suitable for the containment of water and having a closeable and openable top  104 , inert gas inlet valves  106  and water inlet valves  108  as well as water outlet drains  110  equipped with conventional traps  112  is provided. Regular tap water is fed through water inlet valves  108  from a normal commercial water tap is allowed to flow into trough  102  at a rate that provides for the maintenance of a water level above the level of extruded wire  16 A that passes therethrough so that extruded wire  16 A is immersed in the water  115  and an inert gas such as nitrogen, argon or the like is fed through gas inlet valves  106  at a pressure to insure displacement of any air in trough  102  and is allowed to escape through any openings or gaps in trough  102 , for example around the edges of top  104 . The pressure of the gas provided through gas inlet valves  106  as currently applied cannot be detected on a conventional gas pressure gauge  112  mounted in the wall of trough  102  and accordingly is apparently just slightly above ambient air pressure, although, as will be apparent to the skilled artisan, a higher gas pressure could be used without detriment to the instant process.  
         [0014]     Simultaneously with the application of the above described inert gas/water trough treatment of wire  16 A, inert gas is also used to shroud wire  16 A as it is formed/extruded within die  14 , but most importantly that it is shrouded as it exits die  14 . Inert gas accesses the interior of die  14  through a valved aperture  114  in die  14 . A peripheral groove about the interior of die  14  can be used to insure that the entire periphery of the extruded material is shrouded as it exits the die. Such a practice is known in the extrusion of certain aluminum alloys, and accordingly, the design of such an apparatus is well known in the art. Again, the pressure of the introduced inert gas is quite low being only adequate to provide shrouding of wire  16  as it is formed/extruded within die  14  and exits die  14 .  
         [0015]     According to a preferred practice of the present invention, copper rod  10  about one half inch in diameter is subjected to a hot water rinsing prior to its entry into die  14 . Other pretreatments such as wire brushing, caustic wash etc. as described in the &#39;147 patent have not been found necessary in our preferred practice. The preferred input rod for the method is a commercially available so-called “oxygen free” rod. The rod  10  is then extruded in the conventional fashion with the previously described inert gas shrouding and exits die  14  a temperature above about 1000° F. and preferably between about 1100° F. and 1200° F. As extruded wire/elongated shape  16  passes through the water/inert bath as described above, it is cooled to reach a temperature of between about 450° F. and 700° F. when it reaches the polymer extrusion die. Polymer is applied in the fashion described in the &#39;147 patent.  
         [0016]     Although a wide variety of polymeric materials can be applied to the wire/elongated shape, according to the preferred practice of the present invention for the manufacture of magnet wire useful particularly in the fabrication of high temperature transformers (180° C.+) the following polymers are preferred: Radel® R; Acudel®; and Hyfalon® the first two of which are polyphenylsulfones (of 180° C. and 220° C. capability respectively) and the third is a tetrafluoroethylene copolymer. All of these materials are commercially available from Solvay Advanced Polymers, LLC, 3702 Clanton Rd., Augusta, GA 30906.  
         [0017]     The degree of adhesion of the polymer coating to the extruded copper material is to some extent a function of the temperature at which the polymer is coated on the copper. Coating temperatures of between about 450° F. and about 700° F. have been found satisfactory for the production of useful product.  
         [0018]     There has thus been described a method for the continuous extrusion and coating of copper magnet wire or other elongated product that exhibits the ability to control the level of adhesion of the polymer coating to the copper product.  
         [0019]     As the invention has been described, it will be apparent to those skilled in the art that the same may be varied in many ways without departing from the intended spirit and scope of the invention, and any and all such modifications are intended to be included within the scope of the appended claims.