Heat shrinkable article

Details Heat shrinkable article Heat shrinkable article

1995-12-14

1998-04-07

Dye, Rena

Stock material or miscellaneous articles

Hollow or container type article

Shrinkable or shrunk

428 351, 428913, 156 85, 174189, 174209, 174DIG8, 29887, H01B 1738

Patent

active

057362084

DESCRIPTION:

BRIEF SUMMARY
SUMMARY OF THE INVENTION

This invention relates to a tubular, shrinkable, and particularly though not exclusively heat shrinkable, article that in use is shrunk on to a substrate in sealing engagement therewith.
Shrinkable, and particularly heat shrinkable, articles have been known for many years, for example being shrunk into position on a substrate to provide environmental, chemical and/or electrical protection therefor. Often the articles are internally coated with an adhesive, for example a hot melt adhesive, or sealant, such as a mastic, layer to enhance or ensure good sealing thereto, for example with the exclusion of voids. For convenience, such a material will hereinafter generically be referred to as an adhesive. In one range of application, for example, heat shrinkable sheds are applied to the termination of an outdoor medium or high voltage cable (ie. above 1 kV, and usually above 15 kV or 24 kV). A shed is a generally tubular article for providing surface contact with an outer electrically-insulating and environmental-protecting layer, usually of an electrically non-tracking polymer, of the cable termination, and has a flange or skirt extending radially from one end thereof so as in use to shed, or divert, any water or other liquid contaminant off the termination, thereby to avoid the formation of an electrically-conductive path between parts of the termination that in use are at appreciably different voltage (eg. 24 kV and earth voltage). Such sheds also increase the creepage current path length over the outer surface of the termination. To enhance or to ensure the latter function, it is usually necessary to provide an adhesive at the interface between the shed and substrate so as to fill any voids therebetween and thus to prevent flow of current or any contaminant along that interface. Typically, a heat-shrinkable shed would therefore be coated on its inner, substrate-contacting surface with a hot-melt adhesive. An article of the above kind having a plurality of flanges on its outer surface is disclosed in U.S. Pat. No. 4,045,604 (Raychem, Clabburn), the entire contents of which are herein incorporated by this reference. In general, however, the term shed also applies to an article having a tubular part and only a single skirt.
For convenience and by way of example only, reference hereinafter to a tubular article will specifically be made to a shed, although it is to be understood that any tubular article may advantageously employ the present invention.
It has been found that under certain conditions, the shed may still not be securely mounted on the substrate (cable, insulator, surge arrestor for example), and can slide a short distance therealong. Contributing factors to such relative movement are: size and weight of the shed, orientation of the substrate (vertical being the most severe), ambient temperature (higher temperatures tend to weaken the interfacial bonding), and operating conditions of the substrate. In the latter two instances, thermal cycling, as between day
ight or power on/off can lead to a pumping effect on the adhesive, causing or allowing the shed to move. The adhesive, especially a hot-melt adhesive, can act to an extent, as a lubricant in such circumstances. Although a more solid adhesive, for example a high melting point adhesive, would be better than a soft mastic for solving this problem, a softer, and thus more mobile, material is itself advantageous in ensuring that all voids and potential leak paths at the interface are filled, and in ensuring that the sealing between the article and the substrate is maintained during thermal expansion and contraction.
Movement of the shed in such conditions usually takes place in a manner that results in a portion of the adhesive on the substrate being exposed beyond and adjacent an end of the shed. Electrical and/or environmental activity, such as electrical discharges or contamination, can then preferentially lead to local degradation of the substrate surface, or the end of the shed, and/or of the interface between the shed an

REFERENCES:
patent: 4016356 (1977-04-01), McLoughlin
patent: 4045604 (1977-08-01), Clabburn
patent: 4804733 (1989-02-01), Bataille
patent: 4816309 (1989-03-01), Hutt et al.
patent: 5451278 (1995-09-01), Nolf

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