Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1997-08-27
1999-11-16
Stemmer, Daniel
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
174176, 264135, 264262, H01B 1738
Patent
active
059850876
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electrical insulator having at least one fitting cemented onto an insulating body. Large numbers of insulators and, in particular, high-voltage insulators are used in overhead power transmission lines and outdoor switchgear. Most insulators consist of an insulating body having fittings, in the form of metal caps, fitted forcibly and/or positively on the ends of the insulating body. These fittings are primarily used for force transmission. The external diameter of the insulating body core and, in the case of hollow insulators, also the thickness of the insulating body core are primarily designed in accordance with the mechanical loading of the insulator. According to the magnitude and type of mechanical loading, the core ends and fittings are designed differently. The insulating bodies and the associated fittings are customarily designed essentially with rotational symmetry.
The core ends of long-rod insulators, which are mostly subjected to tensile forces, are usually designed conically. In order to produce the required forcible and/or positive connection between the insulating body and the fitting, the gap between the insulating body core and the fitting is usually filled with a lead alloy.
Post and/or hollow insulators have predominantly cylindrical core ends. Such core ends are frequently covered at the mounting position with round or crushed grit which is sintered in a glazing coat; this improves the forcible and/or positive fitting, as does ribbing, corrugation or rough surfaces in the region of the mounting position. The gap between the fitting and the core end is usually filled with settable or curable cementing material such as, for example, cement mortar. In particular in the case of post and/or hollow insulators, the cylindrical, grit-covered core ends are frequently bonded with a lean Portland cement forcibly and/or with positive fit to a fitting that usually consists of galvanized cast iron or of an aluminum alloy.
It is known to protect the internal sides of the fittings from chemical attack by the Portland cement/mortar by using a bituminous coating. Water situated in the gap between the fitting and the core end can develop a pH value of approximately 12 to 13 by reaction with the cement/mortar, both during setting of the Portland cement/mortar and also when using the high-voltage insulators in a humid climate. In addition, embodiments are known in which a cured epoxy resin coat or a synthetic resin coating with embedded quartz sand grain is chosen instead of the bituminous coating.
The embodiments according to the prior art have, apart from an adhesive layer which is occasionally applied onto the fitting and is intended to improve adhesion of the subsequent coating, only a single layer between the fitting and the cement shell that contains set cementing material. This single layer may consist of a multiplicity of layers of the same material. It has been determined in trials that it is not possible with this single layer between the fitting and the cement shell according to the prior art to produce both high flexural strengths in failure tests and also a low residual fitting displacement after routine tests with flexural and/or internal-pressure loading. Either, as in the case of the bituminous coatings, high residual fitting displacements were achieved in routine tests according to EN 50062, and high flexural strengths in failure tests, or the residual fitting displacements were small, as in the case of epoxy resin or sand-containing synthetic resin coatings, with an increased susceptibility to flaking and a low flexural strength simultaneously resulting. Flaking means exfoliation of the insulating body at its ends, essentially perpendicularly to the longitudinal axis.
The residual fitting displacement is the displacement between the lower side of the fitting and the end face of the insulating body core that is still present one day after the routine testing and due to the previously applied routine test loading according to EN 50062, DIN VDE 0674, part 3, Novembe
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patent: 4316054 (1982-02-01), Willem
patent: 4435615 (1984-03-01), Kaczerginski
Karl Thomas
Kuhl Martin
CeramTec AG Innovative Ceramic Engineering
Stemmer Daniel
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