Patent Abstract:
Disclosed is a method for manufacturing a composite high voltage insulator in which a plurality of skirts are manufactured and joined to a rod, and more particularly to a method for manufacturing a composite high voltage insulator in which an expanding pipe is inserted into a plurality of skirts arranged in a line by a skirt holder to expand the inner diameters of the skirts, so that the skirts are mounted on precise positions of the rod, and an adhesive agent is easily applied, so that an interface between different materials is not formed in order to improve reliability of insulator products.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a composite high voltage insulator in which a plurality of skirts are manufactured and joined to a rod, and more particularly to a method for manufacturing a composite high voltage insulator in which an expanding pipe is inserted into a plurality of skirts arranged in a line by a skirt holder to expand the inner diameters of the skirts, so that the skirts reach precise positions of the rod, and an adhesive agent is easily applied, so that an interface between different materials is not formed in order to improve reliability of insulator products. 
     2. Description of the Related Art 
     Generally, insulators are used to simultaneously insulate and mechanically maintain or support power transmission lines or naked wires of electric equipment, and include a plurality of bellows to achieve sufficient dielectric strength in order to increase the distance thereof per surface area. These bellows prevent the deterioration of the dielectric strength of the insulator, when the surface of the insulator is wet, particularly when salt content or dust is attached to the surface of the insulator. 
     The above insulators are divided according to application into suspension insulators used in power transmission lines, long-rod insulators, fog-type insulators used to withstand typhoon-force winds, pin insulators used in distribution lines, knob insulators used in interior wirings, insulating tubes, cleat insulators, and support insulators used in circuit breakers or arresters. 
       FIG. 1  is a sectional view of a conventional composite insulator. 
     The conventional composite insulator  20  comprises a sheath portion  22  formed on the outer surface of a core rod  10  made of FRP by covering the core rod  10  with a material having a high resistance to environments, such as air pollution or ultraviolet rays, for providing mechanical stress, and skirt portions  24  including sheds formed integrally with the sheath portion  22 . 
       FIG. 2  is an exploded sectional view of the conventional composite insulator illustrating a modular-type method for manufacturing the conventional composite insulator. 
     The length of composite insulators used in superhigh-voltage lines increases in direction proportion to increase in service voltage. The increased length of the composite insulator generates various problems in a process for manufacturing the composite insulator. 
     A method for manufacturing the composite high voltage insulator by injection molding once does not form an interface between different materials, thus producing the most reliable product. However, since the composite high voltage insulator has a length of 3˜7 m, it is difficult to solve the warpage of the rod  30 , and since a mold corresponding to the length of the composite insulator and a large-volume catapult are essentially required, initial costs are increased. 
     In order to solve the above problems, a modular method, in which a sheath  34  and skirts  40  are separately molded and are then assembled and attached, has been proposed. In the above modular method for manufacturing a composite high voltage insulator, the sheath  34  and the skirts  40  are separately molded, the sheath  34  is inserted into holes formed through the skirts  40 , and an adhesive agent is applied to an interface between the sheath  34  and the skirts  40  to attach the sheath  34  and the skirts  40 . 
     The above conventional method for manufacturing a composite high voltage insulator is divided into two approaches. The first approach is where an adhesive agent is applied to the outer surface of the rod  30  covered with the sheath  34  and the rod  30  is inserted into the holes of the skirts  40  such that the skirts  40  slide towards the inside of the rod  30  using the lubricating function of the adhesive agent In this approach, when the inner diameters of the skirts  40  are excessively small, the adhesive agent applied to the rod  30  covered with the sheath  34  is peeled off by inserting the rod  30  into the holes of the skirts  20 . Accordingly, it is difficult to uniformly apply the adhesive agent to the overall surface of the rod  30 . 
     Further, when the inner diameters of the skirts  40  are excessively large, it is easy to insert the rod  30  into the holes of the skirts  40 . However, in this case, adhesive characteristics caused due to the compressive force of the skirts  40  are not obtained, and an air layer may be formed in the interface between the skirts  40  and the sheath  34  after the manufacture of the insulator is completed. The above approach is disadvantageous in that the exposed adhesive agent generates an interface between difference materials, the above interface is a weak point of the composite insulator requiring the reliability, and the adhesive agent must have improved resistance to tracking and weather so that the composite insulator is proper to be used outdoors. 
     The second approach is that an adhesive agent is applied only to the inner walls of the holes of the skirts  40  or is applied to the surface of the rod  30  covered with the sheath  34  to be inserted into the holes of the skirts  40  so that the skirts  40  are attached to the rod  30  using the adhesive agent by inserting the rod  30  into the holes of the skirts  40  under the condition that the holes of the skirts  40  are expanded and then by releasing the expanded state of the holes of the skirts  40 . However, this approach is disadvantageous in that it is difficult to expand the holes of the skirts  40  due to the general shapes of the skirts  40  and characteristics of materials of the skirts  40 . 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for manufacturing a composite high voltage insulator in which a plurality of skirts are arranged in a line in a skirt holder and an expanding pipe is then inserted into the skirts under the condition that the expanding pipe is rotated to easily expand the inner diameters of the skirts so that an adhesive agent is uniformly applied to the outer surface of a rod by preventing the agent from being peeled off when the rod is inserted into the skirts, and the adhesive agent is not applied to the portion of the rod exposed to the outside to prevent the formation of an interface between different materials. 
     In accordance with the present invention, the above and other objects can be accomplished by the provision of a method for manufacturing a composite high voltage insulator comprising: manufacturing a plurality of skirts, and manufacturing a rod by covering an outer surface of an FRP rod with a sheath so that the skirts are continuously disposed along the cylindrical surface of the rod; arranging the skirts in a skirt holder such that the skirts are connected in a line; expanding inner diameters of the skirts by applying an adhesive agent to the outer surface of an expanding pipe and inserting the expanding pipe into the holes of the skirts under the condition that the expanding pipe is rotated at a designated speed; inserting the rod into the expanding pipe; positioning the inner surfaces of the holes of the skirts to contact the outer surface of the rod by separating the expanding pipe from the holes of the skirts; and hardening the adhesive agent by heating the skirts and the rod to a designated temperature for a designated time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a sectional view of a conventional composite insulator, 
         FIG. 2  is an exploded sectional view of the conventional composite insulator, 
         FIG. 3  is a sectional view illustrating the expansion of inner diameters of skirts in a method for manufacturing a composite high voltage insulator in accordance with the present invention; 
         FIG. 4  is a sectional view illustrating the insertion of a rod into an expanding pipe in the method of the present invention; 
         FIG. 5  is a sectional view illustrating the state of a skirt holder after the insertion of the rod into the expanding pipe in the method of the present invention is completed; 
         FIG. 6  is a sectional view illustrating the separation of the expanding pipe from the skirts in the method of the present invention; and 
         FIG. 7  is a sectional view illustrating the composite insulator manufactured by the method of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, a preferred embodiment of the present invention will be described in detail with reference to the annexed drawings. 
       FIG. 3  is a sectional view illustrating the expansion of inner diameters of skirts in a method for manufacturing a composite high voltage insulator in accordance with the present invention.  FIG. 4  is a sectional view illustrating the insertion of a rod into an expanding pipe in the method of the present invention.  FIGS. 5 and 6  are sectional views illustrating the state of a skirt holder after the insertion of the rod into the expanding pipe in the method of the present invention is completed. 
     The method for manufacturing a composite high voltage insulator in accordance with the present invention comprises manufacturing a plurality of skirts  40 , and manufacturing a rod  30  by covering the outer surface of an FRP rod  32  with a sheath  34  so that the skirts  40  are continuously disposed along the cylindrical surface of the rod  30 , arranging the skirts  40  in a skirt holder  50  such that the skirts  40  are connected in a line, expanding the inner diameters of the skirts  40  by applying an adhesive agent to the outer surface of an expanding pipe  60  and inserting the expanding pipe  60  into holes of the skirts  40  under the condition that the expanding pipe  60  is rotated at a designated speed, inserting the rod  30  into the expanding pipe  60 , Positioning inner surfaces of the holes of the skirts  40  to contact the outer surface of the rod  30  by separating the expanding pipe  60  from the holes of the skirts  40 , and hardening the adhesive agent by heating the skirts  40  and the rod  30  to a designated temperature for a designated time. 
     In the manufacture of the skirts  40  and the rod  30 , the manufacture of the skirts  40  is achieved by general molding, and as shown in  FIG. 2 , a plurality of the skirts  40  are manufactured such that the skirts  40  are separated from each other. 
     The manufacture of the rod  30  is achieved by extrusion molding in which the outer surface of the FRP rod  32  is covered with the sheath  34 . Here, the sheath  34  is formed on the RFP rod  32  separated from the skirts  40  by the extrusion molding, thereby allowing the rod  30  having a length of approximately 3 m to have a designated shape without partial disposition. 
     In the arrangement of the skirts  40 , a plurality of the skirts  40  are continuously arranged in the skirt holder  50  such that the skirts  40  are spaced from each other by a designated interval. Here, the skirt holder  50  restrains the skirts  40 , thereby allowing the expanding pipe  60  to be inserted into the holes of the plural skirts  40  by a single process. The skirt holder  50  may have various structures so long as the skirt holder  50  can support the plural skirts  40  without movement. 
     In the expansion of the inner diameters of the skirts  40 , the expanding pipe  60 , which is installed on a transfer system  70  such that the expanding pipe  60  is rotated at a designated speed and rectilinearly moves in a horizontal direction, is moved by the transfer system  70  and enters into the skirt holder  50 , thereby being instead into the holes of the skirts  40 . 
     Here, the inner diameter of the expanding pipe  60  is larger than the outer diameter of the rod  30  by approximately 1˜5 mm so that the rod  30  can be inserted into the expanding pipe  60 . Preferably, the expanding pipe  60  is made of an aluminum pipe having a thickness of approximately 1.5˜5 mm. 
     A designated pattern is formed on the outer surface of the expanding pipe  60  so that the roughness of the outer surface of the expanding pipe  60  is increased, thereby allowing the adhesive agent to be maximally uniformly applied to the outer surface of the expanding pipe  60 . Further, a front end  62  of the expanding pipe  60  has a conical shape so that the expanding pipe  60  can be more easily inserted into the holes of the skirts  40 . 
     Hereinafter, the method for manufacturing the above composite insulator of the present invention will be described. 
     First, the skirts  40 , which were manufactured in advance by molding, are installed in the skirt holder  50 , and the adhesive agent is applied to the outer surface of the expanding pipe  60 . Then, the expanding pipe  60  is inserted into the holes of the skirts  40  under the condition that the expanding pipe  60  is rotated, thereby expanding the inner diameters of the skirts  40 . 
     The rotational speed of the expanding pipe  60  is varied according to the number of the skirts  40 , into which the expanding pipe  60  is inserted. Most preferably, the rotational speed of the expanding pipe  60  is 30˜300 rpm. The expansion of the inner diameters of the continuously arranged skirts  40  is more easily achieved by the lubricating function of the adhesive agent applied to the outer surface of the expanding pipe  60 . 
     The skirts  40  are mounted on the outer surface of the rod  30  by inserting the rod  30  into the expanding pipe  60  and then separating the expanding pipe  60  from the skirts  40  as described above. 
     Thereafter, the skirt holder  50  provided with the skirts  40  and the rod  30  is hardened in a space maintained at a high temperature of 100˜200° C. for at least 1 minute. Thereby, a composite high voltage insulator having a structure in which the adhesive agent is not exposed to the outside is manufactured. 
     [An Embodiment] 
     In accordance with an embodiment of the present invention, rods are manufactured by respectively covering FRP rods having diameters of 22 mm and 26 mm with sheathes made of silicon rubber having a thickness of 5 mm by extrusion molding. Then, the sheathes of the rods have thicknesses of 32 mm and 36 mm by vulcanization at a temperature of 270° C. for 10 minutes. 
     Skirts are manufactured such that the inner diameters of the skirts are smaller than the outer diameters of the rods by 1˜5 mm, and expanding pipes are manufactured such that the inner diameters of the expanding pipes are larger than the outer diameters of the rods by 1˜5 mm. 
     As apparent from the above description, the present invention provides a method for manufacturing a composite high voltage insulator, in which an expanding pipe to which an adhesive agent has been applied is simultaneously rotated and inserted into a plurality of skirts so that a rod is inserted into the expanding pipe under the condition that holes of the skirts are expanded, and the expanding pipe is then separated from the skirts, thereby mounting the skirts on precise positions of the outer surface of the rod so that the adhesive agent is uniformly applied between the skirts and a sheath and preventing the adhesive agent from being exposed to the outside of the insulator so that reliability of the composite high voltage insulator product is improved. Further, the method of the present invention is easily performed, thus reducing the time and costs taken to manufacture the composite high voltage insulator. 
     Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Technology Classification (CPC): 8