AN OPEN-WIRE INSULATOR AND A METHOD FOR THE PRODUCTION THEREOF

Abstract: An open-wire insulator and a method for the production thereof. For the avoidance of the problems resulting from the connection between the annular flanges and a bar of reinforced plastic forming the core in previously known structures, the insulator according to the invention comprises an open-wire insulator comprising a core (3) of cast resin and an outer covering formed by plate-like flanges (1) piled one upon another and distance sleeves (2), said covering surrounding the core portion (3) formed of a cast resin capable of reacting with the covering essentially on all sides except the end faces and in which insulator the core is reinforced with fiber glass.

Description: An open-wire insulator and a method for the production thereof This invention relates to an open-wire insulator and a method for the production thereof, which open- wire insulator comprises a core of cast resin reinforced with fiber glass and one or more platelike flanges attached to said core, in which method said flanges are preformed of cast resin optionally reinforced with glass fiber into annular flanges. Conventional open-wire insulators of the type described above comprise a core which has been cut off a bar of reinforced plastic and on the surface of which a necessary number of plate-like flanges is attached by glueing. This structure provides an extremely high tensile strength owing to the use of a core portion reinforced with fiber glass. When the necessary number of annular flanges is provided, it is not, either, difficult to obtain the required dielectric strength. However, it has more recently been found out in practice that it is fairly difficult to join a core of reinforced plastic and flanges made of a synthetic EPD-rubber, for instance, with a glueing which with¬ stands stresses resulting from the environmental conditions acting on the insulators. Obviously due to the different coefficients of thermal expansion of the core portion and the flanges and the effects of frost and moist, hair cracks or the like fairly often occur in the glueing between the core portion and the flanges in conventional insulators of the above described type, which considerably decreases the dielectric strength of - . the insulator. So the object of the present invention is to eliminate the above problem. This is achieved in the method for the production of an open-wire insulator according to the invention by piling up pre-cast annular flanges one upon another to form an integral structure defining an outer covering of the insulator, a bunch of fiber glass filaments being passed through a central opening thereof, and by casting the core portion of the insulator of a cast resin capable of reacting with the material of the flanges using said structure as a mould. In order to obtain a desired axial spacing between the annular flanges, they can be provided with cylindrical sleeves forming an integral part thereof or such sleeves can be fitted between the flanges as separate bodies during the piling step. In an insulator manufactured by the method according to the invention, the outer covering forms an integral structure so that the problem of electric breakdown, which occured with previously known insulators of the similar type, cannot arise here. Because the number of flanges to be piled up can be varied according to the requirement and because also the length of the glass fiber filaments fitted in the core can be chosen almost arbitrarily, the method according to the invention can be used also in the production of insulators for extremely high voltages. As already appeared from the afore-said, the insulator according to the invention is, for the elimination of the problem of electric breakdown occuring with the previous insulators, characterized in that the insulator is provided with an outer covering of cast resin, said covering surrounding a core portion reinforced with fiber glass and made of a resin capable of reacting with the outer covering essentially on all sides except the end faces. Because the materials of the outer covering and the core portion are chosen so as to be capable of reacting with each other, chemical bonds are formed therebetween during the casting step, whereby a highly efficient connection is provided between the outer covering and the core portion which can be said to form an integral body. This applies particularly when the outer covering and the core portion are made of the same material. The open-wire insulator according to the invention and the method for the production thereof are described more closely in the following with reference to the attached drawings, wherein Figure 1 illustrates a bar insulator manufactured by the method according to the invention, Figure 2 illustrates a massive pin insulator manufactured by the method according to the invention. Figure 3 more closely illustrates one detail of the insulator according to the invention, and Figure 4 is a partial view of an alternative structure of the insulator according to the invention. Figures 1 and 2 illustrate types of insulators suitable to be produced by the method according to the invention. Figure 1 shows a bar insulator provided with several annular flanges 1 and distance sleeves 2 providing the axial spacing between the flanges, which sleeves can, in an insulator manufactured in accordance with the invention, be either integral with said annular flanges 1 or manufactured separately therefrom. The ends of the insulator of Figure 1 are further provided with conventional means 4 for the attachment of the insulator to open-wire structures to form a part thereof. The structure shown in Figure 1 is extremely suitable to be manufactured by the method according to the invention, because the annular flanges 1 and the distance sleeves 2 comprised therein are all identical so that one mould only is needed for them. The massive pin insulator shown in Figure 2 is also suitable to be manufactured by the method according to the invention even if the distance sleeves 2 therein are unequal in size. However, such, variation in the size or shape of the distance sleeves or the annular flanges 1 considerably increases the manufacturing costs. Figure 3 more closely illustrates one detail of the insulator of the type shown e.g. in Figure 1. This insulator comprises annular flanges 1 and distance sleeves 2 integral therewith. In the manufacture of the insulator according to the invention, these parts forming the outer covering of the insulator are preformed e.g. through extrusion or injection moulding of a cast resin optionally reinforced with fibers. One end face of the annular flange is thereby preferably provided with a ridge 5 and the other end face with a corresponding recess 6. So the annular flanges can be simply piled up on an other, thus obtaining a reliable positioning of the flanges with respect to each other. After a desired number of annular flanges has been piled up one on the other, they are locked in a suitable frame, whereafter a desired number of glass fiber bunches 7 is introduced in a tubular space formed within the flanges. These bunches are distributed in said tubular space in a desired manner by means known per se. Thereafter the outer insulator covering formed by the annular flanges is used as a mould and a cast resin capable of reacting with the material of the annular flanges is poured into said tubular space in order to form the core portion of the insulator. Because the fiber glass filaments 7 fitted in the core portion are continuous, the core portion is provided with an extremely high tensile strength. Because the material of the core portion is chosen so as to be identical with or capable or reacting with the material of the annular flanges, chemical bonds are formed between the annular flanges and the core so that they form a practically integral body after the casting step. Even though the finished insulator possibly comprises joint faces between the annular flanges, these extend transversely with respect to the longitudinal axis of the insulator so that they do not essentially affect the dielectric strength of the insulator. Furthermore, the separate annular flanges 1 can be cast so that the joint of the mould will be positioned on the outer perimeter of the flanges 1 , which ensures that there does not occur any decrease in the dielectric strength as a result of contamination of the axial joint places as in the case of conventional massive pin insulators. Figure4 shows an alternative structure for the structure of Figure 3, the reference numerals used in Figure 4 corresponding to those shown in Figure 3. The only difference between the structures of Figure 3 and 4 is that the cylindrical distance sleeves 2 providing the axial spacing of the annular flanges 1 are now manufactured as separate bodies so that they are not integral with the annular flanges as in the embodiment of Figure 3. The end faces of the distance sleeves 2, too, are provided with ridges 5 and recesses 6 respectively so as to make it easier to pile up the annular flanges 1 and the distance sleeves 2 one upon another. The embodiment of Figure 4 simplifies the manufacture of such insulator structures as shown e.g. in Figure 2 because therein the annular flanges 1 can be identical while the diameter of the distance sleeves must increase. The invention has been described above only by means of some structural examples and it is to be understood that nearly all conventional known insulator structures are suitable to be manufactured by the method according to the invention. So such dimensional matters as the shapes, diameters or lengths of the flanges as well as the distance sleeves are irrelevant to the invention. The flanges or the distance sleeves do not, either, need to be identical with each other, although it is naturally of advantage in view of the manufacturing costs to use the least possible number of parts that differ from each other.

Claims: Claims: 1. Method for the production of an open-wire insulator comprising a core (3) of cast resin and one or more plate-like flanges (1) attached thereto, in which method said flanges (1) are preformed of a cast resin optionally reinforced with fibers into annular flanges (1) which are piled up one upon another into an integral structure defining an outer covering (1, 2) of the insulator, said structure being used as a mould when the core portion (3) of the insulator is cast of a cast resin capable of reacting with the material of the flanges, c h a r a c t e r i z e d in that a bunch of glass fiber filaments (7) is passed through a central opening of said structure before the casting step. 2. Method according to Claim 1, c h a r a c ¬ t e r i z e d in that when the annular flanges (1) are piled up one upon another, cylindrical distance sleeves (2) are positioned therebetween in order to provide a desired axial spacing between said flanges. 3. An open-wire insulator comprising a core (3) of cast resin and an outer covering formed by plate¬ like flanges (1) piled one upon another and distance sleeves (2) , said covering surrounding the core portion (3) formed of a cast resin capable of reacting with the covering essentially on all sides except the end faces, c h a r a c t e r i z e d in that said core portion (3) is reinforced with fiber glass.

Inventors: KARO JORMA H, KARO, JORMA, H.
Applicants: KAROLON OY
Application year: 1986
Main classification: H01B17
IPC codes: H01B17