Patent Application
20200084841
The present disclosure generally relates to heating blankets and, more particularly, to heating blankets and methods for heating a structure to a substantially uniform temperature across the structure.
Heating blankets are used in industrial applications to manufacture and repair structures. In some applications, the structure has a complex, contoured surface, in which case it is advantageous for the heating blanket to be highly formable to conform to the structure surface. Additionally, some structures may be formed of materials that require a high temperature, such as in excess of 500° F., to manufacture or repair. Accordingly, it is highly desirable to provide a heating blanket and method that can conform to complex contours and heat to higher temperatures.
In accordance with one aspect of the present disclosure, a heating blanket includes an interlaced heating layer having a fabric thread and a heat-generating thread interlaced with the fabric thread to form the interlaced heating layer. The heat-generating thread includes a conductor wire configured to generate a magnetic field in response to an electrical current applied to the conductor wire, and a susceptor wire formed of a susceptor material configured to inductively generate heat in response to the magnetic field of the conductor wire when a temperature of the susceptor wire is below a Curie point of the susceptor wire.
In accordance with another aspect of the present disclosure, a method is provided of forming an interlaced heating layer of a heating blanket. The method includes providing a heat-generating thread having a conductor wire formed of a plurality of conductor wire strands in a Litz wire configuration, the conductor wire configured to generate a magnetic field in response to an electrical current applied to the conductor wire, and a susceptor wire formed of a susceptor material configured to inductively generate heat in response to the magnetic field of the conductor wire when a temperature of the susceptor wire is below a Curie point of the susceptor wire. The heat-generating thread is interlaced with a fabric thread to form the interlaced heating layer.
In accordance with a further aspect of the present disclosure, a method of heating a contoured surface is provided. The method includes placing on the contoured surface a heating blanket, the heating blanket having an interlaced heating layer. The interlaced heating layer includes a fabric thread formed of a high temperature fabric material, and a heat-generating thread interlaced with the fabric thread to form the interlaced heating layer. The heat-generating thread includes a conductor wire configured to generate a magnetic field in response to an electrical current applied to the conductor wire, and a susceptor wire formed of a susceptor material configured to inductively generate heat in response to the magnetic field of the conductor wire when a temperature of the susceptor wire is below a Curie point of the susceptor wire, the Curie point being at least 500° F. The method further includes providing electrical current to the conductor wire to inductively heat the susceptor wire to the Curie point of the susceptor wire.
In another aspect of the disclosure that may be combined with any of these aspects, the conductor wire comprises a plurality of conductor wire strands bundled in a Litz wire configuration, and the susceptor wire is wrapped, around the conductor wire in a spiral configuration.
In another aspect of the disclosure that may be combined with any of these aspects, each conductor wire strand comprises a conductor wire metal core and a ceramic coating surrounding the conductor wire metal core.
In another aspect of the disclosure that may be combined with any of these aspects, the conductor wire metal core comprises pure nickel.
In another aspect of the disclosure that may be combined with any of these aspects, the conductor wire metal core comprises nickel clad copper.
In another aspect of the disclosure that may be combined with any of these aspects, the heating blanket further includes a sheath surrounding the plurality of conductor wire strands.
In another aspect of the disclosure that may be combined with any of these aspects, the sheath comprises a ceramic filament.
In another aspect of the disclosure that may be combined with any of these aspects, the sheath comprises a thermoplastic film.
In another aspect of the disclosure that may be combined with any of these aspects, the susceptor material comprises a high temperature susceptor material selected from the group consisting of an iron alloy, a cobalt alloy, and a nickel alloy.
In another aspect of the disclosure that may be combined with any of these aspects, the fabric thread is formed of a high temperature fabric material selected from the group consisting of fiberglass, vermiculite fiberglass, and ceramic fiber.
In another aspect of the disclosure that may be combined with any of these aspects, the heating blanket further includes a pair of outer layers sandwiching opposite sides of the interlaced heating layer, each outer layer being formed of an outer layer fabric material.
In another aspect of the disclosure that may be combined with any of these aspects, the Curie point of the susceptor material is at least 500° F.
In another aspect of the disclosure that may be combined with any of these aspects, the Curie point of the susceptor material is approximately 2000° F.
In another aspect of the disclosure that may be combined with any of these aspects, the conductor wire comprises a plurality of conductor wire circuits connected in parallel.
In another aspect of the disclosure that may be combined with any of these aspects, the conductor wire is arranged in a double-back configuration, so that the conductor wire includes a first segment, configured to carry current in a first direction, and a second segment positioned adjacent the first segment and configured to carry current in a second direction opposite the first direction.
In another aspect of the disclosure that may be combined with any of these aspects, the plurality of conductor wire strands is coated with a low temperature binder, the method further comprising melting off the low temperature binder.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings.
It should be understood that the drawings are not necessarily drawn to scale and that the disclosed embodiments are sometimes illustrated schematically. It is to be further appreciated that the following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses thereof. Hence, although the present disclosure is, for convenience of explanation, depicted and described as certain illustrative embodiments, it will be appreciated that it can be implemented in various other types of embodiments and in various other systems and environments.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Referring now to
The fabric thread 28 is formed of a high-temperature fabric material capable of withstanding elevated temperatures. As used herein, the term “elevated temperatures” includes temperatures of at least 500° F. In some embodiments, the elevated temperature may be at least 1000° F. In other embodiments, the elevated temperature may be at least 2000° F. Suitable high temperature fabric materials include fiberglass, vermiculite fiberglass, or continuous ceramic oxide wire such as that sold by 3M® under the trademark Nextel™.
The heat-generating thread 30 includes multiple components that interact to inductively generate heat in response to an applied electrical current. As best shown in
In the illustrated embodiment, the conductor wire 32 is formed of a plurality of conductor wire strands 32a that are bundled together to form a Litz wire, as best shown in
A sheath 42 may be provided that surrounds and holds the plurality of conductor wire strands 32a in the bundled, Litz wire configuration. The sheath 42 may be a permanent component, in which case it is formed of a high-temperature material such as ceramic filament. Alternatively, the sheath 42 may be a sacrificial component that is subsequently removed. Exemplary sacrificial sheath materials include a low-melting point wax or thermoplastic film, which may be subsequently melted or burned off during fabrication of the interlaced heating layer 26.
The conductor wire 32 is operatively connected to a portable or fixed power supply 44, either directly or via wiring 45. The power supply 44 may provide alternating current electrical power to the conductor wire 32 and may be connected to a conventional electrical outlet. In addition, the power supply 44 may operate at higher frequencies. For example, the minimum practical frequency may be approximately 50 kilohertz, and the maximum practical frequency may be approximately 500 hundred kilohertz. Other frequencies, however, may be used. Furthermore, the power supply 44 may be connected to a controller 46 and a voltage sensor 48 or other sensing device configured to indicate a voltage level provided by the power supply 44. Based on the indicated voltage level from the voltage sensor 48, the controller 46 may adjust the alternating current of the power supply 44 over a predetermined range in order to facilitate application of the heating blanket 20 to various heating requirements. Furthermore, each conductor wire strand 32a may have a diameter sized for the electrical frequency to be carried. For example, the diameter of each conductor wire strand 32a may be 18-38 American Wire Gauge (AWG).
The susceptor wire 34 is configured to inductively generate heat in response to the magnetic field generated by the conductor wire 32. Accordingly, the susceptor wire 34 is formed of a metallic material that absorbs electromagnetic energy from the conductor wire 32 and converts that energy into heat. Thus, the susceptor wire 34 acts as a heat source to deliver heat via a combination of conductive and radiant heat transfer, depending on the distance between the susceptor wire 34 and a workpiece to be heated.
The susceptor wire 34 is formed of a material selected to have a Curie point that approximates a desired maximum heating temperature of the heating blanket 20. The Curie point is the temperature at which a material loses its permanent magnetic properties. When used in an inductive heating arrangement as described herein, where the susceptor wire 34 generates heat only as long as it is responsive to the magnetic field generated by the conductor wire 32, the amount of heat generated by the susceptor wire 34 will decrease as the Curie point is approached. For example, if the Curie point of the magnetic material for the susceptor wire 34 is 500° F., the susceptor wire 34 may generate two Watts per square inch at 450° F., may decrease heat generation to one Watt per square inch at 475° F., and may further decrease heat generation to 0.5 Watts per square inch at 490° F. As such, portions of the heating blanket 20 that are cooler due to larger heat sinks generate more heat and portions of the heating blanket 20 that are warmer due to smaller heat sinks generate less heat, thereby resulting in all portions of the heating blanket 20 arriving at approximately a same equilibrium temperature and reliably providing uniform temperature over the entire heating blanket 20. Thus, the interlaced heating layer 26 may provide uniform application of heat to an area to which the heating blanket 20 is applied, compensating for heat sinks that draw heat away from portions of the area that is being heated by the blanket 20. For example, the interlaced heating layer 26 will continue to heat portions of the area that have not reached the Curie point, while at the same time, ceasing to provide heat to portions of the area that have reached the Curie point. In so doing, the temperature-dependent magnetic properties, such as the Curie point of the magnetic material used in the susceptor wire 34, may prevent over-heating or under-heating of areas to which the heating blanket 20 is applied.
The susceptor wire 34 may be formed of a susceptor material suitable for high temperature applications. Exemplary high temperature susceptor materials include iron alloys, cobalt alloys, nickel alloys, or combinations thereof. The exact composition of the susceptor material may be selected based on a desired Curie point. For example, pure nickel has a Curie point of 669° F., pure iron has a Curie point of 1418° F., and pure cobalt has a Curie point of 2060° F. Accordingly, the amount of nickel, iron, and cobalt (as well as other trace elements, such as molybdenum) used in an alloy may be adjusted to achieve a desired Curie point. An alloy having a higher concentration of cobalt, for example, may be selected to provide a susceptor material having a Curie point of approximately 2000° F. Alternatively, an alloy having a higher concentration of iron and other materials having a lower Curie point may be selected to provide a susceptor material having a Curie point of approximately 500° F. Regardless of the exact composition of the susceptor material, the resulting Curie point of that susceptor material will approximate a maximum heating temperature of the heating blanket 20, as noted above.
The susceptor wire 34 may be sized to balance heating capacity with the smart response of the wire as it reaches the Curie point of the susceptor wire material. On the one hand, a larger diameter susceptor wire 34 provides more mass available to provide heat at temperatures below the Curie point. On the other hand, an increased diameter for the susceptor wire 34 will delay the smart effect achieved when the susceptor wire reaches the Curie point. Although susceptor wire diameter may impact the watts per square inch generated by the heating blanket 20, the Curie point of the susceptor wire 32 will still approximate the maximum temperature of the heating blanket 20.
The conductor wire 32 and susceptor wire 34 may be assembled together to form the heat-generating thread 30 suitable for interlacing with the fabric thread 28. For example, in the embodiment illustrated in
The fabric thread 28 and the heat-generating thread 30 are interlaced to provide flexibility to the interlaced heating layer 26, thereby allowing the interlaced heating layer 26 to conform to the contoured surface 23. The heat-generating thread 30 may be advantageously distributed evenly throughout the entire interlaced heating layer 26 to provide more uniform heating across the heating blanket 20. Furthermore, the particular type of interlacing may be sufficiently tight to physically support the heat-generating thread 30. Various types of patterns and processes may be used to form the interlaced heating layer 26. For example, the fabric thread 28 may form one or more weft yarns and the heat-generating thread 30 may form a warp yarn, in which case the fabric thread 28 and the heat-generating thread 30 may be woven together in a plain weave 60, as best shown in
An alternative embodiment of an interlaced heating layer 70 is illustrated at
In another alternative embodiment illustrated at
In a further embodiment illustrated at
In general, the foregoing disclosure provides numerous technical effects and benefits in various applications relating to high temperature heating blankets. For example, the disclosed heating blanket can be used to cure coatings, process and repair ceramic material, perform pipeline weldment repair, preheat welds, relieve stresses after welding, and other industrial, manufacturing, and repair applications requiring heating to at least 500° F. The disclosed heating blanket provides uniform, controlled heating of surface areas. More specifically, the Curie point of the susceptor wire in the interlaced heating layer is used to control temperature uniformity in the area to which the heating blanket is applied. All portions of the area being heated may achieve the same temperature, such as the Curie point of the susceptor wire, thereby helping to prevent over-heating or under-heating of certain portions of the area being heated. Additionally, the materials used for the fabric thread, conductor wire 32, and susceptor wire 34 are all selected to permit use of the heating blanket in high temperature applications.
Referring now to
Referring now to
It is to be understood that the flowcharts in
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended to illuminate the disclosed subject matter and does not pose a limitation on the scope of the claims. Any statement herein as to the nature or benefits of the exemplary embodiments is not intended to be limiting, and the appended claims should not be deemed to be limited by such statements. More generally, no language in the specification should be construed as indicating any non-claimed element as being essential to the practice of the claimed subject matter. The scope of the claims includes all modifications and equivalents of the subject matter recited therein as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the claims unless otherwise indicated herein or otherwise clearly contradicted by context. Additionally, aspects of the different embodiments can be combined with or substituted for one another. Finally, the description herein of any reference or patent, even if identified as “prior,” is not intended to constitute a concession that such reference or patent is available as prior art against the present disclosure.
