EP0066262A1 - Method of making a metal end fitting for an electrical insulator - Google Patents

Abstract

The invention concerns an end fitting having a dummy anchorage cavity which must have a good surface finish. According to the invention two complementary half-parts (10) constituting this end fitting are made separately by moulding or forming. They are then consolidated and optionally equipped with a ring (11). <IMAGE>

Description

The present invention relates to a method for manufacturing an electrical insulator fitting and relates to fittings intended, in particular but not exclusively, to equip the ends of composite insulators.

Such a fitting schematically has a cavity open on one side to receive the end of a rod made of agglomerated glass fibers which is immobilized by sealing or shrinking. It is generally made of cast iron, steel, aluminum alloy or copper alloy and is produced by casting.

FIG. 1 schematically illustrates in section a fitting 1 of this kind and its cavity 2. In order to facilitate the anchoring of a rod in this fitting, a side wall 4 is generally provided, forming an internal narrowing 5 of diameter d.

It will be appreciated that the molding of such a fitting is all the more delicate the lower the ratio of the diameter d to the height of the cavity. In addition, such a geometry makes it almost impossible to control the surface condition of the cavity 2.

For some insulators this ratio can reach 1/5. It is then practically impossible to use a core in several removable parts to produce the cavity 2.

The only usable process is casting on a core of sand. This process has many drawbacks. First, the sand cores leave a rough surface state; in addition they are slightly porous and the degassing which appears at high temperature, and which cannot be released since the cavity is blind, further deteriorates the surface condition. However, this surface condition must have a quality which allows relative sliding of the anchoring material on the interior surface of the cavity of the fitting in order to obtain a "self-locking" action by a wedging effect. A high specific resistance is thus obtained from the anchoring of the rod thus produced.

The object of the present invention is to propose a method of manufacturing a fitting making it possible to obtain a satisfactory internal surface condition.

The present invention relates to a method of manufacturing an end fitting of a composite electrical insulator, fitting having an internal cavity with a predetermined surface state to receive the sealed end of an insulating rod; for this, two complementary parts are produced separately having said surface condition by a process chosen from casting on a metal core, or stamping, stamping, stamping of a sheet metal; then said complementary parts are joined to one another by an assembly process of the welding, crimping, riveting type, the joining connector being sufficiently fine so as not to alter said surface condition and to leave the possibility of sliding for " self-locking "explained above.

The complementary parts can therefore be made of any flowable material, for example cast iron, steel, aluminum alloy or copper.

They can be obtained from sheet metal, steel, aluminum, bronze or equivalent.

Any means such as induction welding and pressure welding, welding by "ultra-pressure" or the like can be used for welding.

The complementary parts can be identical, and their contact zone is then located in a plane of symmetry of the fitting. However, the contact faces may have more or less crenellated or wavy zones favoring their joining or mutual interlocking.

It is particularly advantageous to further provide a metal hoop at least around the portion of the fitting capable of undergoing the most mechanical stresses.
This hoop is put in place by a process known per se. It can be welded to the fitting. Its material is chosen so as to have a coefficient of expansion compatible with that of the complementary parts of the fitting.

Means may also be provided for consolidating the assembled zones, external to the complementary parts. The latter may include anchoring grooves for safety keys.

• - la figure 2 montre en élévation une partie complémentaire d'une ferrure selon l'invention,
• - la figure 3 est une vue en coupe selon la ligne III-III de la figure 2,
• - la figure 4 montre en élévation une variante de réalisation de la ferrure de la figure 2,
• - la figure 5 est une vue en coupe selon la ligne V-V de la figure 4,
• - la figure 6 est une vue en perspective d'une autre variante de réalisation.

Other characteristics and advantages of the invention will appear during the description which will be made using ( ^{1 ..} appended drawing given by way of illustration but in no way limitative and in which:

• FIG. 2 shows in elevation a complementary part of a fitting according to the invention,
• FIG. 3 is a sectional view along line III-III of FIG. 2,
• FIG. 4 shows in elevation an alternative embodiment of the fitting of FIG. 2,
• FIG. 5 is a sectional view along the line VV in FIG. 4,
• - Figure 6 is a perspective view of another alternative embodiment.

FIGS. 2 and 3 show a half-fitting 10 according to the invention. This half-fitting was molded and its surface condition could be perfectly checked. After welding the facing faces 14 of the two half-fittings, the part of the fitting between its upper part and the throttle 15 is surrounded by a one-piece cylindrical hoop 11. The hooped part is capable of withstanding significant mechanical stresses.

The hoop is put in place by a process known per se on ribs 12 molded with the wall of the half-fitting 10. These ribs each have a shoulder 16 which serves as a stop for the hoop 11. The latter can be welded locally at the wall of the fitting. We see in Figure 3 the polygonal shape taken by the hoop 11 after its shrinking.

Figures 4 and 5 show another variant of half-fitting 20 according to the invention, which is not molded but made from a sheet of a deformable metal. The end 22 of the half-fitting 20 is pierced or cut at 21 after the latter has been formed.

To reinforce the assembly formed by the welded half-fittings, a hoop 23 is made around the most mechanically stressed zone 23 by casting in a mold of which a half-shell 24 can be seen in FIG. 4. The material of the hoop 23 is chosen from an appropriate alloy which causes pre-stress on the half-fittings when it cools, by shrinking.

FIG. 5 shows a section of the two half-fittings 20 and 30 welded together and provided with their hoop 23.

The weld zone has been identified and it will be noted that the half-fittings 20 and 30 are thicker at this zone.

FIG. 6 illustrates another embodiment without using a hoop. The two half-fittings 41 and 42 are welded according to a surface, the outer line 40 of which can be seen; in the vicinity of the weld, the conical walls of the half-fittings have angled edges 43 and 44 defining two housings for the edges 45 and 46 of a key 51. A second key 52 is provided to reinforce the opposite weld surface. The upper part of the keys can be optionally closed.

Of course, the invention is not limited to the embodiments which have just been described. Instead of welding the contacting faces of the two half-fittings, they can be crimped or riveted, or use any other equivalent assembly method without departing from the scope of the invention.

Claims (6)

1 / Method for manufacturing an end fitting of a composite electrical insulator, fitting comprising an internal cavity with a predetermined surface state to receive the sealed end of an insulating rod, characterized in that one realizes separately two complementary parts (10) presenting said surface condition, by a process chosen from casting on a metal core and stamping, stamping, stamping of a sheet metal and which one is secured to the other said complementary parts by an assembly process of the welding, crimping, riveting type, the connection fitting being sufficiently fine so as not to alter said surface condition. 2 / A method according to claim 1, characterized in that two identical complementary parts are produced. 3 / A method according to claim 1, characterized in that the walls in contact with said complementary parts have complementary nesting zones. 4 / Method according to one of the preceding claims, characterized in that there is surrounded by a metal hoop (11) said complementary welded parts, along at least part of their height. 5 / A method according to claim 4, characterized in that said hoop is welded to said complementary parts. 6 / A method according to claim 4, characterized in that the material of said hoop and the material of said complementary parts are chosen so as to have neighboring expansion coefficients. 7 / A method according to one of claims 1 to 3, characterized in that said complementary parts (41, 42) have in the vicinity of the weld zone (40) anchoring grooves for added keys (51, 52 ).

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