Abstract: A heat recoverable sleeve has a high recovery ratio of at least 60%. It uses a specific arrangement of recoverable fibers in one direction woven in a twill configuration with both heat stable fibers and heat recoverable fibers extending in another direction.

Abstract: A elongate electrode of an impressed current protection system comprises a polymeric jacket sleeve (10) that contains a particulate carbonrich filler (12) around a central elongate conductive core (4,6). The invention provides a method of repairing such an electrode that has a damaged jacket section (14), and involves securing the jacket (14) to the core (4,6) on each side of the damaged section (14), which can then be removed together with the associated filler (12). A wraparound repair sleeve (18, 20, FIG. 3) is secured to the jacket (10) on each side of the damaged section (14) and filled with a carbon-rich particulate filler (12) effect the repair.

Abstract: An arrangement for protecting an electrical circuit such as a telephone circuit from a voltage transient comprises a voltage clamp or foldback device (3) arranged to be connected between a current-carrying line (1) and ground (1'), a capacitor (2) in series with it, and an inductance (4) series connected in the line. During normal operation the arrangement acts as an LC filter whose high frequency break-point is determined by the capacitance of the voltage clamp or foldback device (3) and the value of the inductance (4) which are chosen to give a break point of 1 kHz to 10 MHz. However, when the arrangement is subjected to a voltage transient, the voltage clamp or foldback device (3) fires causing the break-point to fall to a value determined by the values of the capacitor (2) and inductance (4). The arrangement may be used, for example, to protect the circuit against a rapid voltage drop caused by the firing of another circuit protection device such as a gas discharge tube 5.

Abstract: An impressed current corrosion protection system comprises a distributed anode in the form of a conductive core (4) covered with a conductive polymeric coating (6) and surrounded by packed coke (8) contained within a polymeric jacket (18). This outer jacket is typically a fabric having a specified resistance to acid conditions and chlorine conditions.

Abstract: A method of covering a joint between pipelines comprises installing a heat recoverable polymer sheet coated on its inner surface with a hot-melt adhesive comprising a mixture of 25 to 40 parts by weight of a polyethylene alkyl acrylate terpolymer containing maleic anhydride and having a melt flow index as determined according to ASTM D1238-70 of at least 40, and 25 to 70 parts by weight of a polyethylene alkyl acrylate copolymer having a melt flow index as determined according to ASTM D1238-70 of at least 40.

Abstract: A substrate (12,14) is enclosed with a heat recoverable backing with a layer of a thermosetting adhesive composition (20) comprising an amorphous thermoplastic resin and a thermosetting resin positioned between the heat recoverable article (10, 26) and the substrate (12,14). The adhesive composition can be in the form of a self supporting sheet or tape or it can be on a surface of the heat recoverable article (10). In some embodiments, a polymeric insert (32) is also used to ensure adequate sealing between the substrate and the thermosetting adhesive.

Abstract: A conductive polymer composition which has a resistivity of less than 10 ohm-cm and which exhibits PTC behavior comprises a polymeric component and a particulate conductive filler. The polymeric component comprises a first crystalline fluorinated polymer having a first melting point T.sub.m1 and a second crystalline fluorinated polymer having a second melting point T.sub.m2 which is from (T.sub.m1 +25).degree. C. to (T.sub.m1 +100).degree. C. The composition exhibits one of a number of characteristics, including a relatively high PTC anomaly. The composition is useful in circuit protection devices to be used at high ambient conditions.

Abstract: An electrical device in which a conductive terminal is physically and electrically attached directly or indirectly to a face of a laminar PTC resistive element. The terminal comprises a laminar portion and a non-laminar shaped portion which lies within a projection of the periphery of the PTC resistive element. The shaped portion serves to improve thermal transfer between the PTC element and the atmosphere surrounding the device. Devices of the invention are useful as circuit protection devices.

Abstract: An arrangement for protecting an electrical circuit such as a telephone circuit from a voltage transient comprises a voltage clamp or foldback device (3) arraigned to be connected between a current-carrying line (1) and ground (1'), a capacitor (2) in series with it, and an inductance (4) series connected in the line. During normal operation the arrangement acts as an LC filter whose high frequency break-point is determined by the capacitance of the voltage clamp or foldback device (3) and the value of the inductance (4) which are chosen to give a break point of 1 kHz to 10 MHz. However, when the arrangement is subjected to a voltage transient, the voltage clamp or foldback device (3) fires causing the break-point to fall to a value determined by the values of the capacitor (2) and inductance (4). The arrangement may be used, for example, to protect the circuit against a rapid voltage drop caused by the firing of another circuit protection device such as a gas discharge tube 5.

Abstract: A conductive polymeric tape has elongate electrodes, (6) extending along its long edges, and comprises a central longitudinal strip (8) of different resistance to the remainder of the tape. The strip (8) extends part way only along the tape. The tape may also, or instead, contain discontinuities (20) preferably extending across the tape. The purpose of the strip (8) and the discontinuities (20) is to control the passage of electrical current and also the heat output of different parts of the tape.

Abstract: A wraparound heat shrinkable sheet for covering pipes or cables is positioned therearound so its longitudinal edges overlap. A first patch is then positioned over the lapped edges, and a second patch, which is wider than the first patch, positioned over the first patch and secured to the underlying wrapped sheet. Heat is then applied, preferably by hot mastic. The heat acts to shrink the sheet which tensions the second patch, thereby directing a radial force downward onto the first patch.

Abstract: A conductive polymer composition in which a particulate conductive filler is dispsered in a polymeric component which is a mixture of an essentially amorphous thermoplastic resin and a thermosetting resin. In preferred compositions, the amorphous thermoplastic resin and the thermosetting resin are substantially mutually soluble. In order to improve the thermal stability of the composition on exposure to successive thermal cycles, it is preferred that the composition be cured by heating the uncured mixture of amorphous thermoplastic resin, thermosetting resin, and particulate conductive filler at a rate of at least 15.degree. C./minute to the cure temperature.

Abstract: A conductive polymer composition which has low resistivity and good electrical stability. In one aspect the composition comprises a nonconductive filler which is a dehydrated metal oxide. In another aspect the composition comprises a conductive filler which is metal particles in which the bulk density is less than 0.15 times the true density. Compositions of the invention are particularly useful for circuit protection devices.

Abstract: A heat recoverable wraparound fabric sleeve comprises 7-13 heat recoverable fibers in one direction and 4-8 fibers some of which are heat recoverable and some of which are heat stable in a perpendicular direction. This sleeve has particularly useful recovery behavior where recovery ratios are less than 40% and where an auxiliary patch is used to bond overlapping edges of the wraparound sleeve to each other.

Abstract: A number of arrangements for protecting an electrical circuit from an electrical overcurrent are disclosed. In the arrangements the base or gate of a switching transistor (4, 101, 161, 222, 401) is held in a voltage divider, one arm of which comprises a control transistor (6, 102, 162, 222, 404) whose base or gate is itself held in a voltage divider. When an overcurrent is experienced the control transistor switches on causing the switching transistor to turn off. The arrangement may include a shunt switching circuit to shunt the overcurrent across the load. It may include a resetting circuit that will attempt to reset the switching circuit after the overcurrent has been experienced. In one embodiment the arrangement includes means such as a battery, dc--dc voltage converter or Seebeck device in order to reduce or eliminate any initial voltage drop across the switching circuit.

Abstract: A composition which contains 35 to 85% by weight of a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), 10 to 60% by weight of a copolymer of tetrafluoroethylene and perfluoropropylvinyl ether (PFA), and 5 to 60% by weight of melt-processable polytetrafluoroethylene (PTFE). The composition is particularly suitable for use as an insulating material on a substrate such as a resistive element in a conductive polymer heating cable. The composition has good physical properties, low creep, and low secondary crystallization, and exhibits little stress-cracking when exposed to elevated temperatures.

Abstract: A circuit protection device in which a PTC element made from a PTC composition includes or has at a boundary thereof a mechanical stress riser. The device will be tripped by, and provide reversible protection against, a first set of fault conditions, and will also provide protection at least one time against a second, more severe, set of fault conditions which cause physical disruption of the device and which cause the device to have a substantially infinite resistance. Devices of the invention are useful in protecting against relatively high voltages.

Abstract: A polymer composition comprises a solid fusible particulate polymer material and a quantity of metal particles that have been blended with the particles of polymer material to render the composition electrically conductive. The composition may be consolidated by subjecting the particulate blend to heat and/or pressure. The electrically conductive polymer composition may be used to connect the electrically conductive screen (7) of a dimensionally recoverable article (6) to the electrically conductive shield (4) of a cable (1).

Abstract: Conductive polymer compositions which exhibit PTC behavior comprising a first polymeric component which may be crystalline, a second component, and a particulate conductive filler. The second component may comprise either a polymer which exhibits side chain crystallization or a crystalline material which has a sharp melting point and has poor physical properties at room temperature and/or exhibits no melt strength at elevated temperatures. The compositions are particularly useful in electrical devices which exhibit "square" resistance vs. temperature characteristics.

Abstract: A conductive polymer composition in which a particulate conductive filler is dispersed in a polymeric component which is a mixture of an essentially amorphous thermoplastic resin and a thermosetting resin. In preferred compositions, the amorphous thermoplastic resin and the thermosetting resin are substantially mutually soluble. In order to improve the thermal stability of the composition on exposure to successive thermal cycles, it is preferred that the composition be cured by heating the uncured mixture of amorphous thermoplastic resin, thermosetting resin, and particulate conductive filler at a rate of at least 15.degree. C./minute to the cure temperature.