Patent Application
20180270909
Heater cables, such as self-regulating heater cables, can provide heat in a great variety of applications. Such cables can be used, for example, to protect against freezing, to maintain viscosity of a fluid in a pipe, or to otherwise help regulate the temperature of conduits and materials. Heater cables offer the benefit of being field-configurable. For example, heater cables may be applied or installed as needed without the requirement that application-specific heating assemblies be custom-designed and manufactured, though heater cables may be designed for application-specific uses in some instances.
In some approaches, a heater cable operates by use of two or more bus wires having a high conductance coefficient (i.e., low resistance). To power a heater cable that uses bus wires, the bus wires are typically connected at one end of the cable to a power supply, with the bus wires terminating at the other end of the cable. The bus wires are coupled to differing voltage supply levels to create a voltage potential between the bus wires. A self-regulating heater cable employs a positive temperature coefficient (PTC) material situated between the bus wires; current is allowed to flow through the PTC material, thereby generating heat by resistive conversion of electrical energy into thermal energy. As the temperature of the PTC material increases, so does its resistance, thereby reducing the current through the PTC material and, consequently, the heat generated via resistive heating. The heater cable is thus self-regulating in that, as temperatures rise, less heat tends to be generated.
Heater cables can exhibit high temperature variations throughout the cable, both lengthwise along the length of the cable and across a cross-section of the cable. These high temperature variations may be caused by small high-active heating volumes within the heater cable that can create localized heating, as opposed to heat spread over a larger surface area or volume. There are two major designs for conventional self-regulating heater cables: monolithic and fiber-wrapped design. In both, there is a small portion of the core/fiber that is active and generates most of the power, resulting in a significant hot spot in that region. Additionally, the power output of conventional cables is normally determined by its core composition, and consequently, once a window of core composition is selected for a heater cable, its power output is not readily adjustable. What is needed is a solution that addresses these and other shortcomings of conventional self-regulating heater cables.
Embodiments of the invention described herein provide for exemplary voltage-leveled self-regulating heater cables comprising one or more cores, each core having a positive temperature coefficient (PTC) material encapsulating a conductor. Electrically conductive material such as conductive foil, conductive wire and/or conductive ink may be applied to cover a portion of the cores. The conductive material may be formed about the cores circumferentially, and the conductive ink portions may be formed over the cores lengthwise. In embodiments with two (or more) separate conductive ink portions and a conductive foil in electrical contact with the cores, the conductive foil may be formed to electrically connect the conductive ink portions.
Such heater cable configurations allow a desired power output to be achieved by adjusting the fraction of the cores covered by conductive material, which may be defined by a wrapping density of the conductive material. In some embodiments, substantially full coverage could provide maximal power output, while zero or near-zero coverage could provide a zero or a small power output. Heater cables having different power outputs can be manufactured from the same extruded cores by varying the wrapping density (“coverage percentile”) conductive materials applied to the surfaces of the cores of each heater cable. In addition to adjustability in heater cable power output by selection of wrapping density, lower core temperature, lower sheath temperature, longer lifetime, reduced core material usage, and less manufacturing waste (resulting from larger manufacturing target windows), can be achieved.
In an embodiment of the present invention, a voltage-leveled self-regulating heater cable may include a conductor, a core that encapsulates the conductor, and a conductive material in contact with only a portion of an outer surface of the core. The core may include positive temperature coefficient material.
In some embodiments, the voltage-leveled self-regulating heater cable may include conductive ink in contact with the outer surface of the core and in contact with at least a portion of the conductive material.
In some embodiments, the voltage-leveled self-regulating heater cable may include an additional conductor and an additional core that encapsulates the additional conductor. The additional core may include positive temperature coefficient material.
In some embodiments, the voltage-leveled self-regulating heater cable may include a first conductive ink portion extending lengthwise along the core and a second conductive ink portion extending lengthwise along the additional core.
In some embodiments, the voltage-leveled self-regulating heater cable may include a web extending between the core and the additional core. The web may be electrically active or electrically inactive.
In some embodiments, the core may physically contact the additional core.
In some embodiments, the conductive material may include an electrically conductive wire that is wrapped around a portion of the core.
In an embodiment of the present invention, a voltage-leveled self-regulating heater cable may include a first conductor, a first core that encapsulates the first conductor, a second conductor, a second core that encapsulates the second conductor, and conductive material in contact with outer surfaces of the first core and the second core. The first core may include positive temperature coefficient material. The second core may include positive temperature coefficient material. The conductive material may electrically couple the first core to the second core. The conductive material may be metal or conductive ink.
In some embodiments, the voltage-leveled self-regulating heater cable may include first conductive ink printed on a first portion of the first core and second conductive ink printed on a second portion of the second core. The conductive material may be in physical contact with the first conductive ink and the second conductive ink.
In some embodiments, the conductive material may include electrically conductive metal foil that encircles the first and second cores.
In some embodiments, the voltage-leveled self-regulating heater cable may include a web interposed between the first core and the second core. The web may connect the first core to the second core. The web may be electrically active or electrically inactive.
In an embodiment of the present invention, a method of manufacturing voltage-leveled self-regulating heater cables may include applying conductive material to a first pair of extruded cores at a first wrapping density with manufacturing equipment to produce a first voltage-leveled self-regulating heater cable. The first pair of extruded cores may include positive temperature coefficient material. The first pair of extruded cores may each encapsulate a respective conductor. A coverage percentile of the applied conductive material may be less than 100 percent.
In some embodiments, the method may further include automatically determining, with a resistivity measurement device, a resistivity of the first pair of extruded cores, and determining, with a processor of a computer system, the first wrapping density based on at least the determined resistivity of the first pair of extruded cores.
In some embodiments, the first wrapping density may be selected based on a predefined power output for the first voltage-leveled self-regulating heater cable.
In some embodiments, the method may include automatically determining, with a resistivity measurement device of the manufacturing equipment, a first resistivity of the first pair of extruded cores, determining, based on the first resistivity, that the conductive material applied to the first pair of extruded cores at the first wrapping density produces the first voltage-leveled self-regulating heater cable with the predefined power output, automatically determining, with the resistivity measurement device, a second resistivity of a second pair of extruded cores comprising the positive temperature coefficient material encapsulating a third conductor and a fourth conductor, the second resistivity being different from the first resistivity, determining, based on the second resistivity, that the conductive material applied to the second pair of extruded cores at a second wrapping density produces a second voltage-leveled self-regulating heater cable with the predefined power output, and applying, with the resistivity measurement device to the second pair of extruded cores, the conductive material at the second wrapping density to produce the second voltage-leveled self-regulating heater cable.
In some embodiments, applying the conductive material to the extruded cores may include wrapping electrically conductive wire around the first pair of extruded cores at the first wrapping density.
The foregoing and other advantages of the disclosed apparatuses and methods will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration exemplary embodiments of the invention. Such embodiments do not necessarily represent the full scope of the contemplated apparatuses and methods, however, and reference is made therefore to the claims in subsequent applications claiming priority to this application for interpreting the scope of the invention.
Before the present invention is described in further detail, it is to be understood that the invention is not limited to the particular aspects described. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting. The scope of the present invention will be limited only by the claims. As used herein, the singular forms “a”, “an”, and “the” include plural aspects unless the context clearly dictates otherwise.
It should be apparent to those skilled in the art that many additional modifications beside those already described are possible without departing from the inventive concepts. In interpreting this disclosure, all terms should be interpreted in the broadest possible manner consistent with the context. Variations of the term “comprising”, “including”, or “having” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, so the referenced elements, components, or steps may be combined with other elements, components, or steps that are not expressly referenced. Aspects referenced as “comprising”, “including”, or “having” certain elements are also contemplated as “consisting essentially of” and “consisting of” those elements, unless the context clearly dictates otherwise. It should be appreciated that aspects of the disclosure that are described with respect to a system are applicable to the methods, and vice versa, unless the context explicitly dictates otherwise.
Numeric ranges disclosed herein are inclusive of their endpoints. For example, a numeric range of between 1 and 10 includes the values 1 and 10. When a series of numeric ranges are disclosed for a given value, the present disclosure expressly contemplates ranges including all combinations of the upper and lower bounds of those ranges. For example, a numeric range of between 1 and 10 or between 2 and 9 is intended to include the numeric ranges of between 1 and 9 and between 2 and 10.
As stated above, the power output of a conventional self-regulating (SR) heater cable is generally determined by the core composition of the heater cable, which is set during the fabrication of the core(s) and may be subject to unintentional variations as a result of manufacturing non-idealities. When the core composition properties (e.g., resistivity) of an extruded core fall outside of an acceptable window (e.g., defined in part by the desired power output of the heating cable(s) being manufactured using the extruded core(s)), the extruded core(s) would conventionally be scrapped, resulting in wasted time, energy, and materials.
In contrast, embodiments of the present invention allow for the power output of an SR heating cable to be selected during manufacturing of the SR heating cable by applying conductive material (e.g., electrically conductive material) to one or more surfaces of the core(s), the conductive material being applied with a selected (in some embodiments, automatically selected) wrapping density corresponding to a coverage percentile, subsequent to fabricating the core(s). This “coverage percentile,” as used herein, refers to a percentage of the outer surface of the core(s) that is covered by the conductive material. For example, the coverage percentile and corresponding wrapping density needed to be applied to the core(s) in order to meet a particular set of power output requirements may be determined automatically based on a measured resistivity of the core(s). A 100% coverage percentile may provide maximum cable power output, while a 0% coverage percentile may result in zero or only a small power output, depending on the configuration of the heater cable. In some embodiments, heater cables with different power outputs can be made from the same extruded core(s), and the desired power output of the heater cable can be achieved in a later process step by selecting the coverage percentile of the conductive material (e.g., foil, wire and/or conductive ink) over the core(s) of the heater cable. Some embodiments of the heater cables described herein may be next-generation, monolithic (solid core) SR heater cables, able to achieve thermal balancing (e.g., with no hot spots) as well as a desired power output that is set by selecting the coverage percentile of the conductive material over the core(s).
A conductive material 6, which may have a high electrical conductivity (e.g., the electrical resistivity of the conductive material 6 may be below 500 ohm·cm) may be formed or applied to physically and electrically contact a portion of the outer surfaces of cores 3 and 4 in order to enhance voltage leveling on the cores 3 and 4. The conductive material 6 may, for example, be a conductive wire (e.g., copper wire, nickel coated copper wire, or any other applicable conductive wire), conductive foil (e.g., aluminum foil or any other applicable conductive, metal foil), or patterned conductive ink (e.g., which may be film-forming). For embodiments in which the conductive material 6 is patterned conductive ink, the conductive ink may be applied directly onto the cores 3 and 4 or, alternatively, may be applied onto an interior surface of a polymer jacket 9 situated around the cores 3 and 4. The width (i.e., longitudinal span along the cores 3 and 4) of the conductive material 6 per unit of heater cable length corresponds with the coverage percentile of the conductive material 6, and is positively correlated with a power output of the cable. The conductive material 6 may be configured, for example, as a thin band that is placed around the cores 3 and 4 with a desired pitch and may electrically couple the cores 3 and 4 together. The thin band may, for example, be round, flat, elliptical, tri-lobal, or any other applicable shape. Alternatively, the conductive material 6 may be a continuous strip that is wrapped about a desired length of the cores 3 and 4 with a desired wrapping density. The wrapping density of the conductive material 6, in combination with the width of the conductive material 6, may determine the coverage percentile that defines the percentage of the outer surfaces of the cores 3 and 4 that are covered by the conductive material 6.
As shown in
In alternative embodiments conductive ink may be applied to the core(s) a SR heater cable to enhance conductive contact with the surface of the core(s) of the heater cable.
In yet other embodiments, web 5 may be absent, allowing for cores 3 and 4 to be in direct contact with one another (e.g., in a straight arrangement, or in a twisted arrangement).
Referring to
Referring to
The power output of exemplary heater cable configurations may depend on, for example, the composition of the cores 3 and 4, the voltage applied, the substrate temperature, whether the web 5 is electrically active or inactive, and the coverage percentile of the conductive foil 6 and (optionally) the conductive ink portions 16 over the core(s). As an example, for a given core composition, when the SR heater cable 20 is powered at 240 V and placed on a substrate at 10 degrees Celsius, an exemplary heater cable outputs (with no conductive ink portion 16, as shown in
20 W/ft for heater cable configurations with active or inactive webs 5 when the coverage percentile of the conductive material 6 is 100%;
9 W/ft for heater cable configurations with active webs 5 when the coverage percentile of the conductive material 6 is 7%;
4 W/ft for heater cable configurations with inactive webs 5 when the coverage percentile of the conductive material 6 is 7%;
7 W/ft for heater cable configurations with, active webs 5 when the coverage percentile of the conductive material 6 is 0% (e.g., the conductive material 6 is omitted); and
0 W/ft for heater cable configurations with inactive webs 5 when the coverage percentile of the conductive foil is 0% (e.g., the conductive material 6 is omitted).
Therefore, a desired power output of the SR heater cable 20 for given cable configurations can be achieved by selecting the coverage percentile of the conductive material 6 over the cores 3 and 4 (e.g., by selecting a winding density of the conductive material 6 around the cores 3 and 4) during manufacture of the SR heater cable 20. In this way, manufacturing tolerances for the resistivity of the cores 3 and 4 may be made less stringent as, by altering the coverage percentile of the conductive material 6, the power output of the SR heating cable 20 may be adjusted subsequent to the fabrication of the cores 3 and 4. In contrast, the power output of conventional heater cables may be determined primarily by the resistivity of the core of the heater cable. Thus, it may result in material waste when fabricated cores of conventional heater cables have resistivities that are outside of acceptable manufacturing tolerance levels (e.g., which would result in a heater cable that would not meet power output requirements). Thus, when manufacturing SR heating cables according to embodiments of the present invention, material waste may be reduced compared to that of conventional methods.
An illustrative “wire wrapped” SR heater cable 50 is shown in
At step 102, method 100 may begin. For example, preceding the execution of method 100, one or more extruded cores may be fabricated. The extruded core(s) may encapsulate one or more conductors, which may, for example, be bus wires.
At step 104, the resistivity of the extruded core(s) is determined using a resistivity measurement device. In some embodiments, this resistivity measurement may be performed automatically (e.g., without the need for human intervention in measuring the resistivity of the extruded core(s)).
At step 106, a processor (e.g., a processor of a computer system controlling one or more pieces of manufacturing equipment) automatically determines a wrapping density (e.g., for wrapping electrically conductive material such as wire or foil around the extruded core(s)) based on the determined resistivity of the extruded cores. This determination of the wrapping density may further be determined based on a predefined power output value for the SR heating cable being manufactured. For example, the predefined power output value may be defined (e.g., in memory hardware of the computer system in which the processor is included) according to the desired power output to be exhibited by the SR heater cable being manufactured.
At step 108, manufacturing equipment (e.g., controlled by the processor used to perform step 106) applies electrically conductive material (e.g., electrically conductive wire or foil) around the extruded core(s) at the determined wrapping density. For example, the electrically conductive material may be applied by wrapping electrically conductive wire around the extruded core(s). Alternatively, the electrically conductive material may be applied by adhering electrically conductive foil to the extruded core(s). Alternatively, the electrically conductive material may be applied by printing electrically conductive ink onto the extruded cores (e.g., according to a predefined pattern corresponding to the determined wrapping density). The applied electrically conductive material may be tested and evaluated in order to ensure that the electrically conductive material maintains good electrical contact with the extruded core(s) directly after application and subsequent to heating operations.
At step 110, the method 100 ends once the extruded core(s) have been wrapped with the electrically conductive material at the determined wrapping density. Additional process steps may be subsequently performed on the wrapped extruded cores, such as applying polymer jackets (e.g., polymer jackets 9 and 11 of
The present invention has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, additions, and modifications, aside from those expressly stated, and apart from combining the different features of the foregoing versions in varying ways, can be made and are within the scope of the invention.
It is also noted that, although reference numerals are reused for like components of different embodiments in the figures, the components need not have the same configurations, and the components may have differences from each other in different embodiments.
This application claims priority from U.S. Provisional Application No. 62/471,202 filed Mar. 14, 2017, which is hereby incorporated by reference as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 62471202 | Mar 2017 | US |
