Adhesive bonding and miscellaneous chemical manufacture – Methods – Making electrical conductors of indefinite length
Patent
1993-10-06
1995-09-19
Ball, Michael W.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Making electrical conductors of indefinite length
156 86, 439730, 428 349, H01R 472
Patent
active
054512786
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the environmental protection of substrates such as cables or pipes, particularly telecommunications cable splices especially by means that does not require a large input of energy for installation.
A cable splice is in general formed by removing insulation from the ends of the cables to be joined, splicing the conductors therein, and forming around the resulting splice bundle a covering called a splice case, in order to protect the otherwise exposed conductors. The splice case may be required to offer protection against water, water vapour, dirt and other contaminants and against animal attack, and should have a life-time comparable to that of the cable insulation, typically at least 25 years. Many cables are internally pressurized to keep out water vapour or to provide a means of detecting leaks, and a splice case for such cables should also be pressure retaining.
One of the most successful and widely used designs of cable splice is that marketed by Raychem under the trade marks XAGA and VASM. There a heat-shrinkable sleeve is installed around the splice to be protected, and heat is applied to cause it to shrink down into engagement with the cables either side of the splice. A propane torch is usually used to apply the heat. In order to provide further mechanical strength and, where desired to provide further resistance to water vapour penetration, an internal liner may be provided around the splice bundle. Such a liner and sleeve are disclosed in GB 1431167 (Raychem). These sleeves may be internally-coated with a hot-melt adhesive.
Whilst this type of splice case is simple to install and has excellent performance, it has the disadvantage in requiring the use of a torch for installation. Where a cable to be spliced runs in, for example, a duct or manhole shared with gas pipes or where the substrate to be protected is itself a gas pipe the use of a torch is undesirable and may be forbidden.
Attempts have been made to overcome this problem by providing an electrical source of heat, although that too may be unacceptable if the voltage required is sufficiently high that a short could cause sparking. Also, large, heavy, power supplies may be needed since access to mains power cannot be relied upon. A large amount of power is required since the sleeve must be heated to cause it to shrink, and any adhesive coating has to be heated to cause it to melt or otherwise to be activated.
One electrical solution is disclosed in DE 2136739 (Siemens AG). There a splice case comprises two semi-cylindrical thermoplastic half-shells hinged together along respective edges, allowing the splice case to be closed like a clam-shell around the splice to be protected.
U.S. Pat. No. 4,085,286 (Raychem) discloses a splice case having preformed shrinkable outlets having self-contained electrical heaters comprising a conductive polymer having a positive temperature coefficient of resistance (PTC). A PTC heater as part of a shrinkable sleeve is disclosed in EP 0117762 (Raychem).
EP 0236056 (Raychem) discloses a non-shrinkable splice case comprising a flexible sealing bag that is seam-sealed by a hot-melt adhesive activated by a self-contained, self-regulating, strip heater.
Heat shrinkage is desirable, of course, since a sleeve or other protective article can easily be installed around a cable etc. since it can be supplied over-size. Close tolerances in manufacture can be avoided, and a single size of article can be used over various sizes of cables. After this preliminary installation the article is heat-shrunk causing it to engage the substrate and causing leak paths between it and the substrate to be eliminated. This is particularly useful where an outlet of an article is to be sealed to a cable etc. that passes through it. A problem arises, however, if the heater that is used to bring about heat-shrinkage is other than a flame, a hot-air gun, or a very high temperature radiative heater; and this problem is due to the changing dimension of the shrinking article. Somehow the
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Ball Michael W.
Burkard Herbert G.
Lorin Francis J.
N.V. Raychem S.A.
Zahrt II William D.
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