Abstract:
A wire capable of operating at high temperatures and a method of making the same is disclosed. The high temperature wire comprises fiberglass, which surrounds the conductor. The fiberglass insulates the conductor and enables it to operative at relatively high temperatures. The fiberglass is heat-treated without any additional, or in lieu of, other chemical treatment and is sufficiently frangible to be easily removable from the conductor. The frangible fiberglass may be easily stripped away from the conductor without leaving strands which need to be individually removed.

Description:
This application is a continuation-in-part application of Ser. No. 09/365,269, HIGH TEMPERATURE WIRE CONSTRUCTION filed Jul. 30, 1999, now U.S. Pat. No. 6,249,961, issued Jun. 26, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of Invention 
     This invention pertains to the art of methods and apparatuses for providing electrical conductors encompassed by a layer of fiberglass to provide high temperature operating capability, and more specifically to methods and apparatuses for providing insulated electrical conductors for which the fiberglass, in close proximity to the conductor, is heat-treated to render the fiberglass sufficiently frangible to enhance the strippability of the fiberglass. 
     B. Description of the Related Art 
     It is well known to use fiberglass in the fabrication of high temperature electrical wires and cables. Fiberglass is used to encase a conductor material, as an electrical insulation, because it can withstand high temperatures. Fiberglass has a softening point above 800° C. Additionally, fiberglass is flexible and comes in the convenient forms of filaments, yarn strands, woven cloths, braided cloths, tapes, and sleeves. 
     It has also been the practice to impregnate fiberglass electrical insulation with high temperature binders, varnishes, and resins of various kinds and types improve electrical insulation properties and resistance to moisture. Characteristically, they tend to stiffen the insulated conductor or cable. 
     In some instances, high temperature resistant electrical insulation combine mica with fiberglass to provide resistance to temperatures of 450° C. or higher. The mica may be bonded to the fiberglass by any means known to be of sound engineering judgment. For example, hard and non-plyable resinous compositions may be used to bond the mica to the fiberglass. U.S. Pat. No. 3,629,024, which is incorporated herein by reference, discloses the foregoing methods to incorporate mica into the fiberglass for high temperature applications. 
     It is thus obvious that numerous methods and apparatuses have been developed to produce electrical conductors that operate at high temperatures. And, as mentioned above, it is generally well known that fiberglass alone, or fiberglass in conjunction with other materials such as mica, has been used to produce insulation for high temperature wire products. However, high temperature electrical conductors utilizing fiberglass have an inherent difficulty in that the fiberglass may be difficult to strip away from the wire. Untreated fiberglass when stripped away, leaves filaments and rough edges. 
     Fiberglass is difficult to strip away from the electrical conductor because of its long, soft, fibrous nature. Additionally, tools used to strip layers of material away from the electrical conductor are typically sized so that they do not contact the conductor itself. This is commonly done so that the conductor itself is not crimped or damaged during the stripping process. Consequently, the fiberglass closest to the electrical conductor is not cut. This results in a time consuming process wherein these remaining fibers must be removed individually. 
     The fact that fiberglass is difficult to strip is a serious problem because frequently the conductor needs to be exposed by removing the protective layers which surround it. This is typically done so that lengths of the conductive wires or cables may be coupled together. Alternatively, the layers covering the electrical conductor may need to be stripped away so that the conductor may be attached to a particular device or power supply. Thus, fiberglass which is difficult to strip away from the electrical conductor creates a time consuming and expensive difficulty. 
     Thus, it would be desirable to have a high temperature electrical conductor encased in fiberglass that can be completely and easily stripped away from the conductor itself. The current invention provides fiberglass that can be used to create high temperature electrical conducting products, but which is sufficiently frangible so that it may be easily removed from the conductor. The current invention also provides a method to make this frangible fiberglass. 
     It should be noted, however, that an insulated conductor comprising an easily shippable fiberglass does exist in the related: art. However, unlike the invention disclosed in the current application, the fiberglass in this known insulated conductor must be chemically treated before it may be easily removed from the conductor. This is disclosed in U.S. Pat. No. 5,468,915 (&#39;915 patent), which is incorporated herein by reference. 
     The &#39;915 patent discloses that the fiberglass is treated with a chemical such as sodium silicate so that the fiberglass may be more easily removed from the conductor. As shown in FIGS. 2 and 4, the chemical reacts with the fiberglass, causing the fiberglass to become sufficiently frangible to break, and thus eliminating stringing when the fiberglass is stripped away from the conductor. Additionally, according to the &#39;915 patent, heat treating the chemically treated fiberglass accelerates the chemical reaction and causes the fiberglass to more quickly become sufficiently frangible. 
     As shown in FIG. 4 of the &#39;915 patent, the strands are passed through a pool of the sodium silicate prior to being disposed upon the conductor. Subsequently, further layers of fiberglass are wound onto these treated strands of fiberglass. The treated strands of fiberglass operate to transfer some of the sodium silicate solution to these outer layers. Finally, according to the &#39;915 patent, heating the insulated conductor at a temperature of about 600° F. for about 1.5 minutes produces the most desirable results. 
     Consequently, after the chemically treated fiberglass of the insulated conductor, of the &#39;915 patent, is heat-treated, all of the layers of fiberglass may be easily stripped away from the conductor. With the foregoing combined chemical and heat treatments, the fiberglass is rendered sufficiently frangible so that it may be removed from the conductor without having the tendency to leave strands of fiberglass that need to be individually removed. 
     The current invention improves upon the &#39;915 patent in that it does not require the fiberglass to be chemically treated. Rather, the current invention produces frangible fiberglass that is easily removable from a conductor simply by heat treating the fiberglass layers. 
     Difficulties inherent in the related art are therefore overcome in a way that is simple and efficient while providing better and more advantageous results. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the current invention, the electrical conductor is wrapped with fiberglass and then heated to the devitrification temperature of the fiberglass. 
     In accordance with another aspect of the present invention, the fiberglass wrapped electrical conductor is not chemically treated to aid in the devitrification process. 
     Yet another aspect of the current invention includes a method of producing heat-treated fiberglass wrapped electrical conductor. 
     In accordance with still another aspect of the present invention, a method of producing an electrical conductor includes the steps of removing the electrical conductor from a conductor source, wrapping at least one layer of fiberglass onto the conductor, coating the conduct with a mixture of silicone and acetone, wrapping the electrical conductor around a figure eight speed regulating capstan of a second pulley and a third pulley in order to maintain a constant speed of the electrical conductor, heating the conductor to the devitrification temperature of the fiberglass, using a natural gas burner, thereby devitrifying the fiberglass and enhancing the strippability of the at least one layer of fiberglass, cooling the conductor, coating the conductor with mica, wrapping at least one more layer of fiberglass on the conductor, drying the conductor over heat, wrapping the electrical conductor around the figure eight capstan, and winding the conductor around a finished product spool. 
     In accordance with another aspect of the present invention, a method of producing an electrical conductor including the steps of wrapping at least one layer of fiberglass onto the conductor, applying silicone to the at least one layer of fiberglass, and heating the conductor to the devitrification temperature of the fiberglass. 
     One advantage of the present invention is that it is easy to manufacture and can be made economically. 
     Another advantage of the present invention is that an electrical conductor, capable of operating at high temperatures, is produced wherein the layers on the conductor may be easily removed therefrom. 
     Yet another advantage of the current invention is that frangible fiberglass can be produced with fewer materials and using fewer procedures. 
     Another advantage of the current invention is the frangible fiberglass layer heat set around the conductor allowing for immediate application of insulation enhancing coatings and or binding agents. 
     An unexpected advantage that wire made with a heat set glass layer exhibits is is dramatically reduced glass fly and dust that normally results during the insulation removal process necessary to terminate wire. 
     Another unexpected advantage of the current invention is a 100% to 150% increase in insulation strength as measured by insulation resistance testing at 900° F. over wire manufactured by the process in the &#39;915 patent. 
     Another advantage of the current invention is a 200% to 300% improvement in current leakage performance at 90% relative humidity as compared to wire manufactured by the process in the &#39;915 patent. 
     Still another advantage of the current invention is that after exposure at 460° C. for 10 days, the mica wire will still not fracture when wrapped around a round mandrel that is two times the diameter of the wire. Normally, a mica wire will fracture after seven days when wrapped around a round mandrel that is two times the diameter of the wire. 
     Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: 
     FIG. 1 is a diagram of the inventive process used for producing the heat-treated fiberglass wrapped electrical conductor; 
     FIG. 2 is an exploded view of section I of FIG. 1, showing the conductor source, the untreated conductor, and the first pulley; 
     FIG. 3 is an exploded view of section II of FIG. 1, showing the fiberglass wrapping mechanism, the fiberglass-wrapped conductor, and the figure-eight capstan pulleys; 
     FIG. 4 is an exploded view of a section III showing the burner and the IR sensor; 
     FIG. 5 is an exploded view of section IV of FIG. 1, showing the fifth pulley and the cooler; 
     FIG. 6 is an exploded view of section V of FIG. 1, showing the mica/binder solution, the second fiberglass wrapping mechanism, and sixth, seventh, and eighth pulleys; 
     FIG. 7 is an exploded perspective view of the figure-eight capstan pulleys; 
     FIG. 8 is a top view of the burner showing the burner port; and, 
     FIG. 9 is a cut away perspective view of the finished wire subassembly showing the conductor under the treated frangible fiberglass layers. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, which are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting the same FIG. 9 shows an electrical conductor  66  (i.e. finished product) capable of operating at high temperatures. The finished subassembly  64  comprises essentially a conductor  42 , a small amount of silicone and mica, and a layer of fiberglass  88 . The conductor  42  is made of a material having highly conductive electrical properties. For example, conductor  42  may be made out of copper or carbon as well as any other materials known to those skilled in the art of electrical wire construction. In the preferred embodiment, the conductor  42  is made of a 27% Nickel-coated copper. It is to be understood that the percentage of Nickel coating is simply a preferred embodiment and any percentage of Nickel coating can be used as long as chosen using sound engineering judgment. 
     The layer of fiberglass  88  surrounding the conductor  42  may be applied in any manner chosen using sound engineering judgment. Preferably, the layer of fiberglass  88  comprises strands of fiberglass wrapped around the conductor  42 . 
     In this embodiment, the finished product  66  has at least two layers of fiberglass wrap  88 , and has not been chemically treated to aid the devitrification process. The finished product  66  has simply been heat-treated to the devitrification temperature of the fiberglass. Devitrification is the process by which glass, or fiberglass, loses its glassy state and becomes crystalline. The devitrification temperature of fiberglass is typically about 1200° F. The finished product  66  will be completed into a final wire construction by adding additional layers that might include in an additional mica layer, additional fiberglass wrap or wraps, overall fiberglass braid, or coatings or extrusions of PTFE, ETFE, FEP, silicon rubber or other materials chosen using sound engineering judgment. 
     With reference now to FIG. 1, the diagram shows the inventive process and assembly broken down into five sections, labeled as I, II, III, IV, and V. The diagram shown in FIG. 1 is merely a preferred embodiment of this invention, and is not intended to limit the invention in any way. The inventive process of heat-treating a fiberglass-wrapped conductor  44  can be carried out by any process using sound engineering judgment. 
     FIG. 2 shows an exploded view of section I, which is the starting point of the inventive process. FIG. 2 shows the conductor source  10  (preferably a reel as shown), with a conductor coil  50 , having a conductor  42  wrapped thereon. The conductor  42 , preferably a 27% Ni-coated copper, is drawn from the conductor coil  50  onto a first pulley channel  52  of first pulley  12 . The untreated conductor  42  then travels across a conductor guide frame  14 . The conductor  42  then travels into a first fiberglass wrapping device  16 , which is shown in FIG.  3 . 
     FIG. 3 shows an exploded view of section II, which consists of the fiberglass wrapping device  16 , for wrapping the fiberglass  88  around the conductor  42 , a fiberglass wrapped conductor  44 , silicone solution  46 , and eleventh pulley  41 , eleventh pulley channel  83 , a figure-eight speed regulating capstan  18  consisting of a second pulley  20  and a third pulley  22 , and a fourth pulley  24 . The conductor  42  receives a wrap of fiberglass  88 , as shown in FIG. 9, and then comes out as a fiberglass wrapped conductor  44 . After the conductor  44  passes through the wrapping device  16 , the conductor  44  passes through the eleventh pulley channel  83  in eleventh pulley  41 , thereby being coated by the silicone/acetone solution  46 . In this embodiment, the solution  46  is eight parts acetone to one part of an equal mix of Dow  3037  (a silicone resin) and Dow  200  (a silicone fluid. It is to understood however, that the solution can range from approximately 4:1 to 10:1. It is also to be understood that the Dow  200  can be removed from the solution  46  all together. Any silicone resin and/or silicone fluid can be mixed with the acetone. It is also to be understood that this invention is not limited to the use of acetone; any volatile solvent can be used, as long as chosen using sound engineering judgment. It is also a part of this invention to wrap the fiberglass  88  onto the conductor  42  in any manner chosen using sound engineering judgment. 
     The fiberglass wrapped conductor  44 , shown in FIG. 3, then travels onto the figure-eight speed regulating capstan  18 , by traveling approximately half way around second pulley channel  54  of the second pulley  20  and therefrom onto third pulley channel  56  on the third pulley  22 . The figure-eight speed regulating capstan  18  helps maintain a consistent speed of the fiberglass wrapped conductor  44  by maintaining a consistent tension on the fiberglass wrapped conductor  44 . The fiberglass wrapped conductor  44  then travels from the third pulley channel  56  to a fourth pulley channel  58  in the fourth pulley  24 . From the fourth pulley channel  58  on FIG. 3, the fiberglass wrapped conductor  44  then proceeds to the burner  26  as shown in FIG. 4, which shows an exploded view of section III. 
     FIG. 4 shows the burner  26 , ninth pulley  38 , ninth pulley channel  80 , and infrared sensor  48 . The sensor  48  is used to monitor the temperature of the heated fiberglass wrapped conductor  44 , so that the burner  26  can be adjusted to achieve proper fracture of the fiberglass. In the preferred embodiment, the burner  26  can be any type of ribbon burner, such as the one produced by Ensign Ribbon Burners Inc. In the most preferred embodiment, the burner  26  is a high intensity, over air gas burner using natural gas and air from the factory (not shown) and a zero pressure regulator (not shown). The operation of the burner  26 , and infrared sensor  48  are well known in the art, and, for the sake of brevity, will not be described herein. The fiberglass wrapped conductor  44  travels through the burner  26  at a specific rate of velocity, and the fiberglass wrap  88  is heated to approximately 1200° F. In the preferred embodiment, the fiberglass wrapped conductor  44  is treated in the burner  26  for approximately 4 seconds. In the burner  26 , during the heating process, the fiberglass wrap  88  undergoes the process of devitrification, which in the past was something to be avoided. The devitrification process involves the fiberglass  88  losing its glassy state and becoming crystalline and heat-set around the conductor, thereby increasing the strippability of the fiberglass  88 . The process of devitrification is well known in the art, and the process will not be described in detail. In the most preferred embodiment, the burner  26  uses a relatively short length high intensity natural gas flame, which heats primarily the fiberglass wrap  88 , and does not significantly effect the conductor  42 . The burner  26  described above is only a preferred embodiment of the invention and is not intended to limit the invention in any way. Any burner  26  may be used to heat the fiberglass  88 , as long as chosen using sound engineering judgment. Once the finished subassembly  64  emerges from the burner  26 , the finished subassembly  64  proceeds to a fifth pulley  28 , as shown in FIG.  5 . 
     FIG. 5 shows an exploded view of section IV, which consists of the fifth pulley  28 , a water cooler  30 , a sixth pulley  32 , a seventh pulley  34 , and an eighth pulley  36 . The finished subassembly  64  travels over a fifth pulley channel  70  and onto the cooler  30 , which cools the finished subassembly  64 . The finished subassembly  64  then travels onto a sixth pulley channel  72  on the sixth pulley  32 , and then down into a mica/binder solution  62 . In this embodiment, the mica solution  62  is divided muscovite mica mixed with a 9:1 non-silicon glue/water solution. The mica and glue/water solution are mixed at a 1:1 by volume for approximately 10 to 20 seconds in a #2 Zahn Viscosity cup. The inventive process could also use phologopite mica, fine ceramic, or other non-carbon containing materials, as long as chosen using sound engineering judgment. In this embodiment the glue is a polyvinyl acetate, but any glue can be used as long as chosen using sound engineering judgment, with a preference for water-based glues. The mica/binder solution  62  prevents the recently applied fiberglass wrap  88  from peeling off of the conductor  42 , improves the electrical insulation properties, and allows the finished subassembly  64  to be processed in succeeding manufacturing steps. As shown in FIG. 6, the finished subassembly  64  wraps around the seventh pulley channel  74  on the seventh pulley  34 . The seventh pulley  34  is immersed in the mica/binder solution  62 , so when the finished subassembly  64  travels around seventh pulley  34 , the product  64  is coated with the solution  62 . From the seventh pulley channel  74 , the finished subassembly  64  then travels up a second wrapping device  60 . The second wrapping device  60 , wraps a second layer for fiberglass  88  around the finished subassembly  64 . The product  64  then travels to an eighth pulley channel  76  on an eighth pulley  36 . The product  64  travels around the pulley  36  to ninth pulley  38 , as shown in FIG.  1 . The product  64  then travels above the burner  26 , so that the product  64  dries after the application of the mica/binder solution  62 . After the product  64  has been dried, it is now finished product  66 . The finished product  66  then travels to the tenth pulley  40 , and around the figure-eight  18  and onto a finished product spool (not shown). 
     The process described herein is merely a description of the preferred embodiment and is not intended to limit the invention in any way. The conductor  42  can be wrapped with fiberglass  88  and heated to its devitrification temperature by any means chosen using sound engineering judgment. 
     Additionally, the elimination of the sodium silicate solution allows the introduction of an impregnation, which improves electrical performance and aids in the control of glass dust that results from the removal of the fiberglass insulation. 
     The invention has been described with reference to preferred embodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alternations in so far as they come within the scope of the appended claims or the equivalents thereof. 
     Having thus described the invention, it is now claimed: