The Fluorocarbon Company

Samuel Moore and Company

Richard W Farkas

David A Rock

Louis A Miller

James H Anderson

Eric G Hilston

A self-current-limiting device and a method of making self-current-limiting devices. These devices typically comprise melt processable, self-temperature regulating, irradiation cross-linked, electrically semi-conductive polymeric compositions having positive temperature coefficients of electrical resistance. The semi-conductive compositions contain electrically conductive particles, such as carbon black, dispersed throughout the composition in an amount ranging from about 15% to about 20% of the total weight of the composition. Heating cables made in accordance with the invention comprise two or more elongate substantially parallel spaced-apart electrical conductors that are electrically inter-connected by extruded forms of the compositions. The method is characterized by an efficient three step process wherein the semi-conductive composition is extruded over the conductors, radiation cross-linked and annealed. The method of the invention does not require the application of a shape retaining jacket to the cable prior to annealing. Additionally, only one annealing step is utilized.

Self-current-limiting devices and method of making same

A phenomenon sometimes referred to as tracking can occur when the end of an electrical heater, made of two or more metal conductors and a conductive polymer web, comes into contact with water or other electrolytes which allow arcing to take place across the surface of the web. Tracking is stopped by holes in the web which prevent arcing from continuing up the length of the heat tape.

Self-regulating heater having a heat tape that stops tracking

Disclosed are improved melt processable, self-temperature regulating, irradiation cross-linkable, electrically semi-conductive polymeric compositions which in conjunction with annealing at a temperature at or above their melt point temperatures subsequent to their having been radiation cross-linked provide for improved self-temperature regulating electrical heating devices including flexible electrical heating cables. Heating cables made in accordance with the invention comprise two or more elongate substantially parallel spaced-apart electrical conductors that are electrically inter-connected by means of extruded forms of the compositions which have been annealed at a temperature at or above their melt point temperatures prior and subsequent to their having been cross-linked by irradiation. The compositions of the invention have an amount of electrically conductive particles, such as carbon black, dispersed therein, that is controlled within the range of 17% to 25% by weight to the total weight of the compositions. The semi-conductive compositions are characterized by exhibiting a positive temperature coefficient of electrical resistance and by having sufficient crystallinity in their polymeric portion to provide attractive self-temperature heat regulating characteristics in conjunction with a lessening of criticality in their annealing requirements from that heretofore associated with the process of making electrical heating cables utilizing electrically semi-conductive polymeric materials.

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Stow, OH, United States of America

Richard W Farkas