RU2151436C1 - Ceramic insulator repair technique - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: repair technique includes restoration of chipped edge of ceramic body by placing mold on chipped surface; size of mold interior is equal to that of chipped portion of edge; metered amount of insulating material in viscous fluid state is introduced in mold and allowed to cure on edge; according to invention, prior to fitting mold on chipped portion the latter is coated with sub-layer of solution and mold inner space is filled with main-coat insulating material which is, essentially, compound of following composition, part by mass: dimethyl siloxane rubber SKTN, grade A - 100; silica powder A-175 - 4-7; zinc oxide - 4-6; aluminum hydroxide - 80-100; dibutyl tin dilaurate mixed up with tetraethoxysilane that functions as catalyst in curing main coating - 3-6; used as solution to form sub-layer is 5O% solution of main coating in white alcohol doped with 50% solution of catalyst in white alcohol. Holes may be drilled over perimeter of chipped portion through depth of 3-7 mm to receive glass pins. EFFECT: improved operating reliability of insulator. 3 cl, 2 tbl, 2 ex

Description

 The invention relates to electrical engineering, and in particular to methods of repair of ceramic insulators.

 One of the main disadvantages of ceramic insulators is their fragility. A large number of insulators are damaged during transportation, installation and operation. In addition, the production rate of such insulators is very high, because the bubbles, cracks, scratches and risks are not allowed on their surface (1). GOST 13873-81 "Ceramic insulators. Requirements for surface quality and test methods" imposes very severe restrictions on the acceptable value of surface defects: bubbles, glaze cake, cracks - are not allowed at all, scratches and risks are allowed to a depth of 0.5 mm, and such defects such as lack of glaze, chips with a depth of up to 1 mm are normalized from the total surface area of the insulation and the purpose of the insulator. Electrical equipment with insulation defects exceeding these values is decommissioned. The most dangerous and common types are chips. Despite significant economic losses, such insulators were not repaired.

 To repair the insulator, it is required to restore the chipped rib with a material having high electrical properties (dielectric strength, tracking resistance, arc resistance) and adhesion to ceramics.

 Known methods for restoring missing elements by restoration or obtaining molds according to the model standard (2), according to which a form is made from the undamaged part of the product using low-melting (Wood alloy) or elastic materials (various types of rubbers). Then in this form the missing elements are cast and glued to the original.

 These methods use materials that are unacceptable for repairing insulators (various metals, epoxies, gypsum, wax, etc.).

 The most reliable materials for repairing insulators are organosilicon (silicone) elastomers that retain hydrophobicity even with surface contamination. These materials have high electrical properties and are resistant to solar ultraviolet rays (3).

 The closest in technical essence to the proposed one is a method for producing a ribbed coating on a ceramic body - an insulating rod, by which the coating is obtained in the form into which a metered amount of insulating material is supplied under pressure in the form of a polymer in a viscous-flowing state, it is cured in two stages - to a minimum mechanical strength of the ribs in the injection mold and finally in the additional mold (4).

 In the known method, the polymer compositions used for casting are applied to the glass core inside the insulator and are unsuitable for applying ceramics to the cleaved area, since they will not have adhesion to it.

 The present invention is the creation of a new method of repair of ceramic insulators using a new composition of insulating material having improved adhesion to the repaired surface, increasing the reliability of the insulator after repair.

 The problem is solved when applying the method of repairing ceramic insulators, which consists in restoring a chipped rib of a ceramic body by installing a mold with a cavity with an equal chipped part of the rib in place of a cleavage, applying a metered amount of insulating material in a viscous-flowing state under pressure and curing it on the rib, in which, according to the invention, before installing the mold on the surface of the cleavage, a sublayer is applied from the solution, and insulating material of the main coating, representing a composition consisting of 100 parts by weight dimethylsiloxane rubber SKTN grade A (GOST 13835-73, TU 38403351-80), from 4 to 7 wt. including aerosil A-175 (GOST 14922-77), from 4 to 6 wt. including zinc oxide, from 80 to 100 wt. including aluminum hydroxide, from 3 to 6 wt. including a mixture of tin dibutyl dilaurate with tetraethoxysilane as a catalyst (TU 6-02-805-78) during curing of the base coat, a solution of the formation of a sublayer is used a 50% solution of the main coating in white spirit with the addition of a 50% catalyst solution in white spirit .

 Along the perimeter of the cleavage, holes can be made with a thin drill to a depth of 3-7 mm.

 Glass rods can be inserted into the drilled holes as reinforcing elements, which, after heating, can be given the desired shape.

 In the proposed method, applying a sublayer from a solution to a cleaved surface before installing a mold on it, as well as the composition of the base coat composition and the solution from which the undercoat is applied, increase the adhesion of the main coating supplied to the mold to the cleaved surface.

 The possible implementation of holes along the perimeter of the chip, as well as the insertion of glass rods as reinforcing elements into them, giving them the desired shape, can also increase the adhesion of the main coating to the chip surface.

 This increase in the adhesion of the main coating to the surface of the chip increases the reliability of the ceramic insulator after repair.

 A comparative analysis of the proposed method and the prototype reveals the distinctive features of the proposed method in comparison with the closest analogue, which allows us to conclude that the proposed solution meets the criterion of "novelty."

 The presence of distinctive features makes it possible to obtain a positive effect, expressed in increasing the reliability of the insulator after repair.

 Since when examining the subject of the invention in patent and scientific literature, no solutions were found containing the features of the claimed invention other than the prototype, it should be concluded that the claimed invention meets the criterion of "significant differences".

 The use of the claimed invention in electrical engineering ensures that it meets the criterion of "industrial applicability".

 The method is as follows.

 The casting mold of the future casting is preliminarily made from fusible material. To do this, on the undamaged part of the insulator, formwork is made of any material (for example, tin), where the fusible material is poured (Wood's alloy). After solidification, the mold is removed and holes are made in it for filling the material.

 Coarse cleavage of the insulator is done with a cord brush and then with a sandpaper. In the event that a paint was applied to the chip to waterproof it, the paint is annealed with a hairdryer. Then the surface is degreased with gasoline (the best is BR-2 gasoline), after which it is dehydrated with acetone to remove adsorbed water. Dry the surface with a hairdryer. For better adhesion of ceramics and the applied coating along the perimeter of the chip, holes with a depth of 3-7 mm are made with a thin drill. With large chips, reinforcement is made. For this, glass rods are inserted into the drilled hole, heated and given the desired shape.

 In parallel, the main repair coating and the coating from the solution (sublayer) are prepared.

 The main repair coating is a composition consisting of 100 wt. including dimethylsiloxane rubber SKTN brand A, from 4 to 7 wt. including aerosil brand A-175, from 4 to 6 wt. including zinc oxide, from 80 to 100 wt. including aluminum hydroxide. As the curing system, a standard catalyst is used - a mixture of tin dibutyl dilaurate + tetraethoxysilane, added in an amount of from 3 to 6 wt. hours. The amount of catalyst determines the pot life of the composition. With this amount, it is optimal: from 20 to 30 minutes.

 The sublayer is a 50% solution of the main coating in white spirit with the addition of a 50% solution of the catalyst in white spirit. In relation to the mass of rubber, the catalyst solution contains 3 wt. including catalyst and 10 wt. including white spirit.

 The surface of the cleavage is treated with a sublayer with an introduced catalyst.

 After the sublayer has cured, a mold is placed in place of the cleavage, pressed against the surface of the insulator with elastic screeds, car chambers are installed on the lateral ends of the mold and inflated (There are other options for sealing joints).

Through the hole in the mold using a syringe (it is better to use a syringe with a worm gear), the mold cavity is filled with the main component. The mold may be heated and unheated. For a closer contact between the sublayer and the main repair coating, the mold is not heated for the first two hours, then to accelerate the curing process, it should be maintained at a temperature of 60-80 ^o C.

 The mold is removed, cleaned of excess material, sanded, coated with a composition used as a sublayer. Curing is carried out in the cold for 1-2 hours.

 Example 1

To repair the cleaved rib, dehydration and degreasing of the cleaved surface with white spirit and acetone are carried out, followed by exposure at a temperature of 120 ^o C (using an industrial hair dryer) for 8-10 minutes. After that, a sublayer is applied to the surface to be protected. After the solvent has evaporated (5-10 minutes), the sublayer is heated at a temperature of 60-80 ^o C for 30 minutes and the main sealing composition with a catalyst is applied to the prepared surface with a sublayer. The composition cures naturally, depending on the ambient temperature, from 2 hours (50 ^° C) to 48 hours (-50 ^° C).

 According to the described technology, we make the composition of the following composition (table. 1).

 After curing, the compositions were tested in a number of ways. The results are shown in table 2.

 As can be seen from the data presented, a decrease in the content of components below the established limits significantly reduces the physical, mechanical and operational performance. An increase in the content of components above the established limit does not lead to a significant increase in the indices, while elongation to rupture and dielectric strength drop.

 Example 2

 Checked the adhesion of the composition to the ceramic insulator.

 It was found that when the content of the components at the limit is lower than in composition 1, a separation of the material from the ceramic insulator was observed. For the limits indicated in formulations 2 and 3, the adhesive strength was higher than the tensile strength that passed through the repair material.

 Example 3

 Varying the amount of catalyst, the pot life of the composition was determined. Pot life was determined by yield loss when filling out the form.

Sources of information
1. GOST 13873-81.

 2. The book "Art casting of precious metals", edited by L.A. Gutova., L .: Engineering, 1988, Ch. 4, s.p. 154-158.

 3. E. A. Cherny. IEE Electrical Insulation Magazine, May / June, 1996, y. 12, N 3, p. 7-15.

 4. Copyright certificate of the USSR N 1379810, cl. H 01 B 19/00, publ. 03/07/88 (prototype).

Claims (3)

 1. A method of repairing ceramic insulators, which consists in restoring a chipped rib of a ceramic body by installing a mold with a cavity equal to a chipped part of the rib on a cleaved surface, applying a metered amount of insulating material in a viscous-flowing state under pressure and curing it on the rib, characterized in that that before installing the mold, a sublayer from the solution is applied to the cleavage surface, and the insulating material of the main coating, which is a composition consisting of and 100 parts dimethylsiloxane rubber SKTN brand A, from 4 to 7 parts by weight Aerosil A-145, from 4 to 6 parts by weight zinc oxide, from 80 to 100 parts by weight aluminum hydroxide, from 3 to 6 parts by weight mixtures of tin dibutyl dilaurate with tetraethoxysilane as a catalyst during curing of the basic coating, a 50% solution of the main coating in white spirit with the addition of a 50% catalyst solution in white spirit is used as a sublayer solution.  2. The method according to claim 1, in which along the perimeter of the chip perform a thin drill hole to a depth of 3 to 7 mm  3. The method according to claim 2, in which glass rods are inserted into the drilled holes as reinforcing elements, heat them and give them the desired shape.

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