Electric heating – Heating devices – With heater-unit housing – casing – or support means
Patent
1994-09-29
1996-10-01
Walberg, Teresa J.
Electric heating
Heating devices
With heater-unit housing, casing, or support means
219541, H05B 358
Patent
active
055608477
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to environmental protection and/or mechanical joining of pipes or cables, particularly thermally-insulated pipes such as district-heating pipes.
SUMMARY OF THE INVENTION
The present invention in one embodiment provides the use of a conductive polymer backing sheet in the environmental protection of a thermally-insulated pipe to enclose the pipe and to act as a source of heat to seal overlapping longitudinal edges of the sheet.
In another embodiment the invention provides a method of sealing an elongate object which comprises: wrapping a sheet comprising a conductive polymer backing sheet and a bonding layer around the object so that longitudinal edges thereof overlap over a longitudinal region; pressing two electrodes into contact with the sheet so that they extend substantially parallel to each other along opposite edge portions of the sheet; and powering the electrodes to cause electrical current to flow across the region to fuse the bonding layer.
DETAILED DESCRIPTION OF THE INVENTION
The product consists of a heat-shrink backing, shrink ratio preferably from 10-50%, for example about 20%. The backing may be electrically conductive with a resistivity around 1-10 ohm-cm, especially from 2-6 ohm-cm. Preferably the material comprises a conductive polymeric material. A conductive polymeric material is a composition comprising a conductive filler, typically carbon black, distributed in a polymer, tyrpically an organic polymer. The filler is preferably provided in an amount of 20-60 parts by weight. The polymer may be for example polyethylene or EVA. A preferred material is 100-500%, particularly 300%, expanded, 0.75-2.5, particularly 1.5, mm thick sheet made in polyethylene or EVA 30-50%, particularly 39%, carbon filled.
The product is wraparound and can be supplied on the roll or cut to length in the field or elsewheter. The product can replace oversized casings used in district heating joints.
The product can be installed over a cut back between two joined district heating pipes. A support plate or profile can be installed in the cut back area. This plate can support a longitudinal seal formed during installation of the new sheet.
The sheet can be wrapped around the cut back and closed with a cotton Tessa or other suitable tape.
Two metal bars, e.g. aluminium bars, may be used as electrodes. These are typically spaced at 25-45, particularly about 35, mm with electrical isolators. The electrodes are positioned over an overlap of ends of the sheet and optionally over a metal or other support. They may be kept in position by, for example two straps or clamps, etc. These clamps are preferably positioned over the pipe section, rather than over the cut back area. Another possibility is to provide the electrodes fixed on a backing sheet, so that this provides a separate integral powering device that can be strapped to the sheet to power and heat the overlap region, and then optionally removed. Instead of aluminium bars the electrodes may comprise, for example, electrically conductive braids, or other strips.
The product can be installed with a constant wattage or other power supply, preferably at a power density of 1.5-3, especially about 2.4, Watt/cm.sup.2.
Application of power causes electrical current to flow circumferentially, primarily across the overlap region.
No extra pressure need be applied during installation. A surface type thermocouple may be used to regulate the temperature (preferably about 155.degree. C.) during installation for a certain dwell time (preferably about 60 secs). Circumferential seals can be installed after cool down of the longitudinal seal.
Any excess amount of material can be cut away next to the electrode of the longitudinal seal together with the closing Tessa tape, and, as mentioned above, the electrode optionally removed. A piece of electrical insulation tape may be glued on the overlap to prevent re-heating of the longitudinal seal during separate installation of circumferential seals of the sleeve to the pipe jacket
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Patent Abstracts of Japan, Aug. 19, 1987, abstract of Japanese Patent Publication No. 62733/1987 (Somar Corp.).
Patent Abstracts of Japan, vol. 8, No. 146 (M-307) (1583), Jul. 7, 1984, abstract of Japanese Patent Pubication No. 42920/1984 (Kiyoo raku K.K.).
Burkard Herbert G.
Gerstner Marguerite E.
NV Raychem SA
Paik Sam
Walberg Teresa J.
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