US-12621908-B2 - Self-regulating heater cable with buffer layer

US12621908B2US 12621908 B2US12621908 B2US 12621908B2US-12621908-B2

Abstract

Embodiments of the invention provide self-regulating heater cables utilizing substantially solid polymeric buffer layers surrounding the heating elements having improved heat transfer efficiency as well as improved reliability and endurance. The assembly includes first and second power supply wires configured to carry electrical power and separated by a solid spacer, a substantially solid electrically-insulating buffer layer in thermal contact with the heating element, and a cable jacket including a polymeric outer surface and an inner metallic sheath surrounding the buffer layer and in thermal contact with the buffer layer. The buffer layer includes a polymeric material having a thermal conductivity greater than air at standard temperature and pressure and surrounds the heating element, power supply wires, and spacer.

Inventors

Jennifer Robison
Wade DePolo
Sirarpi B. Jenkins
Linda D.B. Kiss
Marcus Kleinehanding
Paul Becker

Assignees

CHEMELEX EUROPE GMBH

Dates

Publication Date: 20260505
Application Date: 20200626

Claims (12)

1 . A self-regulating heater cable assembly, the assembly comprising: first and second power supply wires configured to carry electrical power and separated by a solid electrically insulating spacer; a self-regulating heating element in electrical contact with the first and second power supply wires and converting electric current into thermal energy when the first and second power supply wires are energized, the heating element being spirally wound around the first and second supply wires and the spacer, and having a spacing that creates gaps between consecutive windings of the heating element; a conductive ground layer that couples the heater cable to electric ground, the ground layer surrounding and physically separated from the heating element and the first and second supply wires; an outer jacket surrounding the ground layer; and an electrically-insulating buffer layer disposed between the ground layer and the heating element and in thermal contact with the heating element, the buffer layer being extruded over the heating element to result in filling of the gaps between the windings of the heating element, the buffer layer comprising a polymeric material and having a thermal conductivity greater than air at standard temperature and pressure, and the buffer layer being porous and incorporating at least one of voids and pockets containing trapped gasses.
2 . The assembly of claim 1 , wherein the buffer layer further comprises one or more particulate additives disposed within the buffer layer so that the thermal conductivity of the buffer layer is greater than a thermal conductivity of the polymeric material; and wherein at least one particulate additive comprises one of alumina, boron nitride, carbon black, magnesium oxide, sand, silica, and glass.
3 . The assembly of claim 1 , wherein the buffer layer is applied to the assembly by pressure extrusion.
4 . The assembly of claim 3 , wherein the melt point of the polymeric material is below a maximum operating temperature of the heating element, the assembly further comprising an electrically insulating, thermally conductive inner jacket surrounding the heating element, the first and second supply wires, and the spacer, and physically separating the ground layer from the heating element.
5 . The assembly of claim 4 , wherein the inner jacket is applied to the assembly by vacuum extrusion, the inner jacket partially filling the gaps and contacting the heating element, and wherein the buffer layer is applied within the gaps to completely fill the gaps.
6 . The assembly of claim 5 , wherein the inner jacket surrounds the buffer layer.
7 . The assembly of claim 4 , wherein the buffer layer is applied in the gaps and fills the gaps, and wherein the inner jacket is applied over the buffer layer by vacuum extrusion.
8 . The assembly of claim 1 , wherein at least a portion of the buffer layer is applied to the assembly by vacuum extrusion.
9 . The assembly of claim 8 , wherein the buffer layer comprises: a first buffer layer comprising a plurality of fibers disposed in the gaps and filling the gaps and spirally wound around the spacer and the first and second supply wires adjacent the heating element; and a second buffer layer applied by vacuum extrusion over the spacer, the first and second supply wires, the heating element, and the first buffer layer.
10 . The assembly of claim 1 , wherein the buffer layer comprises a plurality of fibers disposed in the gaps and filling the gaps and spirally wound around the spacer and the first and second supply wires adjacent the heating element.
11 . The assembly of claim 10 , further comprising an electrically insulating, thermally conductive inner jacket surrounding the heating element, the first and second supply wires, and the spacer, and physically separating the ground layer from the heating element.
12 . The assembly of claim 11 , wherein the inner jacket is applied to the assembly by vacuum extrusion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a nonprovisional claiming the benefit of priority from U.S. Prov. Pat. App. Ser. No. 62/866,973, filed under the same title on Jun. 26, 2019, and incorporated in its entirety herein by reference. BACKGROUND OF THE INVENTION Conventional heating devices such as heater tapes and heater cables rely on resistive heating of a dissipative element such as a resistive wire. Certain conventional heating tapes and cables are self-regulating, namely, they are configured to maintain a surface (e.g., of a pipe or walkway) to which they are applied at a roughly constant temperature regardless of changes in ambient conditions while also protecting against excess heat generation in the case of unintended flows of excess currents due to short-circuits, etc. Such self-regulating heating devices frequently employ conductive polymeric materials which expand when heated, increasing their electrical resistance and thereby reducing their heat output in response to overheating. Similarly, such materials contract when cooled, decreasing their electrical resistance and thereby increasing their heat output in response to undereating. Conventional self-regulating heater cables have disadvantages. For example, as will be made clear from the figures and accompanying description, the electrical contacts between the self-regulating heating elements and the metal wires used to supply power to them may be fragile. Over time, due to mechanical stresses and other factors, the electrical contacts may weaken, causing the heater cable to perform poorly or fail. The self-regulating heating elements may also be subject to degradation due to oxidation and/or the metal wires may be exposed. Certain conventional self-regulating cables use strands of polymeric material wound about a core comprising electrical supply wires and a spacer as the self-regulating heating element to save weight and manufacturing costs compared to monolithic cables. Such conventional self-regulating cables may have various gaps within them caused by the variation in height between windings of the strands over the supply wires. These gaps impede optimal heat transfer from the heating elements within the cable to the outside of the cable in contact with a workpiece to be heated. This sub-optimal heat transfer reduces efficiency and also causes components of the cable to operate at elevated temperatures, which may shorten the lifespan of those components. BRIEF SUMMARY In one embodiment, a self-regulating heater cable assembly comprises first and second power supply wires configured to carry electrical power and separated by a solid spacer; a self-regulating heating element in electrical contact with the first and second power supply wires; a substantially solid electrically-insulating buffer layer in thermal contact with the heating element; and a cable jacket including a polymeric outer surface and an inner metallic sheath surrounding the buffer layer and in thermal contact with the buffer layer; The power supply wires and the heating element are arranged so that, when a voltage differential is established between the first and second power supply wires, an electrical current flows through the heating element and between the first and second power supply wires; the buffer layer surrounds the heating element, the power supply wires, and the spacer; and the buffer layer comprises a polymeric material that has a thermal conductivity greater than air at standard temperature and pressure. In some embodiments, the buffer layer may further comprise one or more particulate additives disposed within the buffer layer so that the thermal conductivity of the buffer layer is different from a thermal conductivity of the polymeric material. At least one particulate additive may comprise one of the following: alumina, boron nitride, carbon black, magnesium oxide, sand, silica, and glass. In one embodiment, the buffer layer may be a porous material incorporating either voids or pockets containing trapped gasses. In another embodiment, a method of manufacturing a self-regulating heater cable assembly comprises providing substantially parallel lengths of first and second power supply wires separated by a solid spacer; forming a first subassembly by fixedly coupling a self-regulating heating element in electrical contact with the first and second power supply wires; and surrounding the first subassembly with a substantially solid electrically-insulating polymeric buffer layer in thermal contact with the heating element to form a second subassembly; and surrounding the second subassembly with a cable jacket including a polymeric outer surface and an inner metallic sheath surrounding the buffer layer and in thermal contact with the buffer layer to form said heater cable assembly. The power supply wires and the heating element are arranged such that the first and second power supply wires are coupled electrically to each other through the h