Self-regulating electric heating element for heaters shaped as cartridges or test tubes
First Claim
1. An electric resistance heating element for heaters shaped as cartridges or test tubes, comprising a plurality of resistive conductors (2,8) connected to an electric supply by a system of electrodes (11, 12, 16, 17) and at least a core (3), said core being made of electric insulating material, said resistive conductors (2, 8) being applied to said core, said resistive conductors (2, 8) being formed of a mixture of a polymeric binder, an electric conductive filler, constituted by a conductive powder in the form of micrometric particles, said powder being carbon black, graphite or silver, said mixture having an electrical resistance with high positive temperature coefficient (PTC) at the operation temperatures, wherein said resistive conductors (2, 8) are formed as strips applied onto said core (3), wherein said electrodes (11, 12, 16, 17) are made of metallic materials in the form of foils, plates, wires, cables, said metallic materials including conductive coating layers consisting of inks or paints, said electrodes being disposed on said core (3), and wherein said core (3) is provided with at least a longitudinal internal hole (4) for the passage of a supply cable or electric conductors, and a longitudinal slot (5) for the entire length thereof, whereby said core (3) is caused to be expanded for being introduced into a test tube or cartridge, and wherein said resistive conductors (2, 8) are disposed on said core (3) with such an arrangement as to permit the electric current to flow axially, circumferentially or helically with respect to the core extent.
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Abstract
An electric resistance heating element preferably of cylindrical or prismatic shape to be inserted into a test tube, a cartridge or in another cavity has one or more conductors connected to the supply system by the use of one or more electrodes. The conductors are made of a conductive composite material of a polymeric matrix with resistive function which are formulated at such ratio and materials as to achieve an electric resistance with high positive temperature coefficient (PTC) at the operation temperatures. The electrodes may be made of metallic materials. At least a core is made of insulating material, onto which the conductors with resistive function (PTC) and the electrodes are applied.
18 Citations
7 Claims
- 1. An electric resistance heating element for heaters shaped as cartridges or test tubes, comprising a plurality of resistive conductors (2,8) connected to an electric supply by a system of electrodes (11, 12, 16, 17) and at least a core (3), said core being made of electric insulating material, said resistive conductors (2, 8) being applied to said core, said resistive conductors (2, 8) being formed of a mixture of a polymeric binder, an electric conductive filler, constituted by a conductive powder in the form of micrometric particles, said powder being carbon black, graphite or silver, said mixture having an electrical resistance with high positive temperature coefficient (PTC) at the operation temperatures, wherein said resistive conductors (2, 8) are formed as strips applied onto said core (3), wherein said electrodes (11, 12, 16, 17) are made of metallic materials in the form of foils, plates, wires, cables, said metallic materials including conductive coating layers consisting of inks or paints, said electrodes being disposed on said core (3), and wherein said core (3) is provided with at least a longitudinal internal hole (4) for the passage of a supply cable or electric conductors, and a longitudinal slot (5) for the entire length thereof, whereby said core (3) is caused to be expanded for being introduced into a test tube or cartridge, and wherein said resistive conductors (2, 8) are disposed on said core (3) with such an arrangement as to permit the electric current to flow axially, circumferentially or helically with respect to the core extent.
- 5. An electric resistance heating element for heaters shaped as cartridges or test tubes, comprising a plurality of resistive conductors (2, 8) connected to an electric supply by a system of electrodes (11, 12, 16, 17) and at least a core (3), said core being made of electric insulating material, said resistive conductors (2, 8) being applied to said core, said resistive conductors (2, 8) being formed of a mixture of a polymeric binder, an electric conductive filler, constituted by a conductive powder in the form of micrometric particles, said powder being carbon black, graphite or silver, said mixture having an electrical resistance with high positive temperature coefficient (PTC) at the operation temperatures, wherein said electrodes (11, 12, 16, 17) are made of metallic materials in the form of foils, plates, wires, cables, said metallic materials including conductive coating layers consisting of inks or paints, said electrodes being disposed on said core (3) wherein said core (3) is made of an elastomer material and is provided with peripheral and radially protruded ribs (21), the height of said ribs being almost equal to the thickness of said resistive conductors (2, 8), said ribs (21) being squashed inwardly by said resistive conductors (2, 8) during the assembling of said resistive conductors (2, 8) on said core (3).
Specification