EP1178496B1 - Method for making a pin insulator - Google Patents

Description

The invention relates to a method of manufacturing a rigid electrical rod insulator for supporting an electrical conductor and comprising a rigid electrically insulating core integrally molded and having an upper end, a lower end with a bore for receiving said rod and which extends in an axial direction between said upper and lower ends, and an outer surface covered by a molded dielectric envelope having a profiled outer surface defining at least one groove for supporting said electrical conductor and annular fins coaxial with the bore.

Such an insulator is generally intended to be installed on a high-voltage or medium-voltage tower to support, for example, an electrical conductor such as a cable of an insulated or uninsulated electrical transmission line, while keeping it electrically insulated from the pylon.

Thus, such an insulator is generally made to undergo high mechanical stresses due in particular to the weight of the cable that it supports, while ensuring significant electrical insulation. Classically, such an insulator was made of glass or porcelain, and the recent development of materials leads to the realization of this type of insulator for example composite material, which allows a significant weight gain compared to glass and a gain in cost of manufacture, but presents difficulties related to the molding of these composite materials.

Such an insulator made of composite material is known from patent US-5945636. In this known insulator, the core which is covered with a thin skin intended to protect the core from environmental aggressions, is massive and has varying thicknesses which makes it difficult to obtain by molding without internal defects.

In general, obtaining a solid piece by molding results in shrinkage or residual stresses that are due in particular to the removal of the material during cooling. Thus, when it comes to molding a massive piece, one of the difficulties is to implement a molding technique adapted to avoid such irregularities.

To mold a solid piece, one can for example add vents and weights to facilitate the flow of material into the mold and to ensure that the pressure is homogeneous in the molded part to avoid the occurrence of mechanical irregularities like holes or sinkholes. The lack of these solutions is to complicate the shape of the mold, to increase the manufacturing cycle times and to require an empirical development which represent an additional manufacturing cost.

The object of the invention is to overcome these disadvantages.

To this end, the subject of the invention is a method of manufacturing a rigid electric rod insulator for supporting an electrical conductor and comprising a rigid electrically insulating core coming from molding and having an upper end, a lower end with a bore. for receiving said rod and extending in an axial direction between said upper and lower ends, and an outer surface covered by a molded dielectric envelope having a profiled outer surface defining at least one groove for supporting said electrical conductor and annular fins coaxial with the bore, characterized in that said core is molded such that its outer surface defines radial ribs which extend in the axial direction from the upper end of the core, said ribs being spaced apart from each other a substantially constant and sensitive distance equal to the thickness of the core.

Such a method simplifies the manufacture by molding of a rod insulator of composite material by overcoming the problems related to molding thicknesses without altering the mechanical and electrical properties of the insulator and without increasing the manufacturing cost of the insulator .

According to a particular embodiment of the method according to the invention in which the core and the dielectric envelope are molded with the same material, the envelope being overmolded on said core, optimal cohesion is obtained between the core and the core. envelope.

According to another particular mode of implementation of the method according to the invention in which the core and said dielectric envelope are molded with different materials, the envelope being fitted on said core, one can choose the best materials to optimize the cost of the insulator according to desired mechanical and electrical performance.

According to yet another particular embodiment of the process according to the invention in which the core is made of epoxy, and / or silicone, and / or thermoplastic material, and / or polyester, and / or composite material, a cheap insulator is obtained.

According to yet another particular embodiment of the method according to the invention, wherein the core is formed of several molded parts and each having a substantially constant thickness, it is possible to obtain a massive insulator of large size.

The method according to the invention will now be described in more detail, and with reference to the accompanying drawings which illustrate one embodiment thereof by way of non-limiting example.

Figure 1 is a sectional view showing the core of an insulator made with the method according to the invention.

Figure 2 is a top view of the core of an insulator made with the method according to the invention.

Figure 3 is a perspective view of the core of an insulator made with the method according to the invention.

Figure 4 is a sectional view of a second insulator made with the method according to the invention.

In FIG. 1 appears an electrical insulator with a rod I made with the method according to the invention which is seen according to a section plane comprising the longitudinal axis A. In this figure, it can be seen that this insulator consists mainly of two pieces which are an envelope E shown in broken lines and whose profiled outer surface defines annular fins A1, A2 which extend coaxially substantially along the axis A, and a core N whose outer surface is covered by the The outer surface of the envelope E also defines at the top of the insulator and the core N a groove C in the form of a half-cylinder which is intended to support an electric cable disposed along an axis normal to the plane. of the figure. In the lower part of the insulator and the core N, a bore T having a thread F made in the core N, coaxial with the main axis A is intended to receive the support rod of the insulator which can be fixed here by screwing.

The body of the core N is represented by a hatched area and comprises radial ribs R, extending along planes comprising the longitudinal axis A from the upper end of the core.

In this figure, it can be seen that the insulator has a relatively large thickness, especially if it is measured along an axis contained in the plane of the figure and perpendicular to the axis A, crossing the core. On the other hand, the thickness of the insulator is very low at the level of, for example, annular fins. Figure 1 also shows that the thickness of the envelope E alone, and that of the nucleus N alone, are lower, and above all relatively constant.

The method according to the invention consists in producing the core N with a relatively constant thickness during a first molding operation, then, after cooling and stabilization of the core N, casting the envelope E by overmoulding on this core N which has been placed in another mold, so that this second molding operation allows both to make the second piece E with a relatively constant thickness and equal to that of the core N. Thus, the method according to the invention allows to achieve an insulator having both large and very variable thicknesses, without having to face problems of molding thicknesses.

FIG. 2, which is a plan view of core N alone, shows sixteen radial ribs R regularly spaced apart on the periphery of the core N. More particularly, each fin is arranged in a plane normal to the plane of the figure, and comprising the axis A which is here normal to the plane of the figure. The distance between two consecutive ribs is constant and substantially equal to the thickness of the core and the thickness of a rib.

FIG. 3 shows in perspective the core with its radial ribs R uniformly distributed around the axis A. These radial ribs R contribute in addition to obtaining a mechanical interface between the core N and the envelope E of good quality by increasing the contact area.

In FIG. 4 appears an insulator I made with the method according to the invention which is seen according to a sectional plane comprising the longitudinal axis A. In this figure, it can be seen that this insulator further comprises an envelope E represented in solid lines. with annular fins A3, A4, A5, A6 which extend coaxially substantially perpendicularly to the axis A, and a core N shown in dashed line, which is embedded inside the envelope E. This insulator comprises in its upper part a groove C in the form of a half-cylinder which is intended to support an electric cable disposed along an axis normal to the plane of the figure and in its part lower, a bore T having a thread F made in the core N, coaxial with the main axis A is intended to receive a rod, fixed by screwing.

The outer profile of this insulator is different from that of Figure 1 but its core N is identical to that of Figure 1.

The core and the envelope of the insulator according to the invention can be made by molding an epoxy resin, a silicone, a polyester, or any other thermoplastic and / or composite material. The core N and the envelope E may be made of the same material or with different materials so as to adapt the mechanical, electrical, and manufacturing cost of the insulator by choosing the most suitable material or materials available existing on the market.

If one uses the same electrically insulating material to make the core and the envelope, the envelope can be directly overmolded on the core so that there will be no interface between these two parts. If different materials are used to make the envelope and the core, the envelope can be nested on the core and fixed thereto by gluing or by any other assembly method with or without prior treatment (corona treatment, plasma cold ....) to improve the envelope / core interface.

To produce an insulator of great size and of great thickness, it will be possible to mold the core N in several steps to form at each molding step a workpiece having a substantially constant thickness as indicated above.

Finally, the shell, core or core parts may be molded by injection molding, and / or compression, and / or transfer to further reduce the cost of manufacture or to use a molding technique. specific to a particular type of material.

Of course, the manufacturing method according to the invention applies to a skirt-shaped insulator envelope E like that of FIG. 1 but also to an envelope E with annular fins A1, A2 which extend completely radially. with respect to axis A.

Claims (6)

1. A method for manufacturing a rigid electrical pin insulator (I) for supporting an electrical conductor and comprising a molded electrically insulating rigid core (N), said core having a top end, a bottom end with a bore (T) for receiving said pin and extending in an axial direction (A) between said top and bottom ends, and an outer surface covered with a molded dielectric covering (E) and having a shaped outside surface defining at least one groove (C) for supporting said electrical conductor and annular fins (A1,A2), said annular fins being coaxial to the bore, characterized in that said core is molded in such a manner that its outer surface is provided with radial ribs (R) which extend in the axial direction (A) from the top end of the core, this ribs being spaced apart by a constant distance and relatively equal to the material thickness of the core (N).
2. The method of claim 1, in which the core (N) and said dielectric covering (E) are molded with the same material, the covering (E) being overmolded onto said core (N).
3. The method of claim 1, in which the core (N) and said dielectric covering (E) are molded out of different materials, the covering being engaged on said core.
4. The method of claim 2 or 3, in which the core (N) is made of epoxy, and/or silicone, and/or thermoplastic material, and/or polyester, and/or composite material.
5. The method according to claim 2, 3 or 4, in which the core is made of several molded pieces having each a relatively constant thickness.
6. The method of claim 3, in which the covering is stuck onto said core.

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