HEATING BLANKET AND METHOD FOR USE

Abstract

A heating blanket (18), useful for debulking and/or curing composite materials, comprising at least one heating element comprising a carbon nanotube (CNT) structured layer defining an electrically conductive pathway having a first end and a second end and a first electrical terminal (19) electrically coupled to the first end and a second electrical terminal (21) electrically coupled to the second end, and an elastomeric outer covering, encasing the at least one heating element, wherein the at least one heating element is responsive to an electromotive force applied across the first and the second electrical terminals to produce heat.

Claims

1. A heating blanket, useful for debulking and/or curing composite materials, comprising: at least one heating element comprising: a carbon nanotube (CNT) structured layer defining an electrically conductive pathway having a first end and a second end; and, a first electrical terminal electrically coupled to the first end and a second electrical terminal electrically coupled to the second end; and, an elastomeric outer covering, encasing the at least one heating element; wherein the at least one heating element is responsive to an electromotive force applied across the first and the second electrical terminals to produce heat.

2. The heating blanket of claim 1, wherein the elastomeric outer covering is cured so that the heating blanket forms a resilient three-dimensional shape that follows the shape of at least one of a caul tool associated with a part or a part that is to be produced.

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. The heating blanket of claim 3, wherein the thickness of the at least one heating element is between 0.25 millimeters (mm) and 5 mm.

8. (canceled)

9. (canceled)

10. (canceled)

11. (canceled)

12. The heating blanket of claim 1, the structured CNT layer comprises a carbon nanotube (CNT)-polymer film structure including single wall carbon nanotubes (SWCNTs) dispersed in a silicon structure, wherein the mass percentage of the SWCNTs within the CNT-polymer film can be selected from a value between and inclusive of at least about 0.25 to about 5 percent by weight, about 5 to about 10 percent by weight, about 10 to about 15 percent by weight, about 15 to about 20 percent by weight, and about 20 to about 25 percent by weight.

13. The heating blanket of claim 12, wherein the mass of the SWCNTs within the CNT-polymer film can be selected from the group consisting of at least about 0.25 percent by weight of the CNT-polymer film, about 0.5 percent by weight, about l percent by weight, about 2 percent by weight, about 3 percent by weight, about 4 percent by weight, about 5 percent by weight, about 12 percent by weight, about 13 percent by weight, and about 25 percent by weight of the CNT-polymer film.

14. The heating blanket of claim 12, wherein the CNT-polymer film structure comprising a constant uniform dispersion of the CNTs in the polymer comprising silicone is between about 1 mm and about 2 mm in thickness and the CNT weight percentage is about 3 percent to about 10 percent, resulting in a sheet resistance of about 70/ to about 16/, respectively.

15. The heating blanket of claim 12, wherein the thickness of the CNT-polymer film structure is at least about 1 millimeter (mm), and less than about 2 mm.

16. The heating blanket of claim 12, wherein the thickness of the heating blanket is less than about 0.10 inches (2.54 millimeters), or less than about 0.20 inches (5.08 millimeters).

17. The heating blanket of claim 16, wherein the heating blanket can be folded over and/or doubled over on itself, the mean or average radius of the fold approaching the thickness of the heating blanket, without failure of the heating element.

18. The heating blanket of claim 12, wherein the amount of heat produced by the heating blanket can be varied by varying at least one of the thickness of the CNT-polymer film structure, the percentage by weight of CNTs in the CNT-polymer film structure, the length of the CNTs in the CNT-polymer film structure, and the type of CNTs in the CNT-polymer film structure.

19. (canceled)

20. The heating blanket of claim 12, wherein the resistivity of the CNT-polymer film structure comprising SWCNTs in an average bundle length of 100 m is about 5/, about 6/, about 7/, about 14/, about 36/, about 43/, about 46/, about 47/, about 58/, about 288/, about 450/, about 750/, and about 1,620/; the resistivity of the CNT-polymer film structure comprising SWCNTs in an average bundle length of 150 m is about 3/, about 4/, about 5/, about 9/, about 24/, about 28/, about 31/, about 39/, about 192/, about 300/, about 500/, and about 1,080/; and the resistivity of the CNT-polymer film structure comprising SWCNTs in an average bundle length of 175 m is about 3/, about 4/, about 8/, about 21/, about 25/, about 27/, about 31/, about 165/, about 257/, about 429/, and about 926/.

21. The heating blanket of claim 12, wherein the resistivity of the CNT-polymer film structure comprising SWCNTs is at least about 3/, at least about 5/, at least about 10/, at least about 20/, at least about 30/, at least about 40/, at least about 50/, at least about 60/, at least about 70/, at least about 80/, at least about 90/, at least about 100/, at least about 200/, at least about 300/, at least about 400/, at least about 500/, at least about 600/, at least about 700/, at least about 800/, at least about 900/, at least about 1,000/, at least about 1,100/, at least about 1,200/, at least about 1,300/, at least about 1,400/, at least about 1,500/, or at least about 1,600/.

22. The heating blanket of claim 1, wherein the response to an applied electromotive force results in a power density of 1-10 watts per square inch (0.2-1.6 watts per square centimeter).

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. The heating blanket of claim 1, wherein the first and the second electrical terminals comprise an expanded metal foil.

29. The heating blanket of claim 1, wherein the CNT structured layer and the electromotive force are selected to produce a debulking temperature in the range of 100-200 F. with a tolerance of +/10 F. (38-93 C. with a tolerance of +/6 C.).

30. (canceled)

31. (canceled)

32. (canceled)

33. (canceled)

34. (canceled)

35. (canceled)

36. A method of debulking and/or curing, comprising the steps of: placing a plurality of a composite materials that are pre-impregnated with a resin, the resin including a curing agent, onto a mold tool; placing a heating blanket having a CNT structured layer over the plurality of composite materials; placing a flexible, air impermeable sheet over the plurality of composite materials on the mold tool; sealing the flexible, air impermeable sheet to the mold tool around the periphery of the plurality of composite materials; withdrawing air from between the flexible, air impermeable sheet and the mold tool; and, applying an electromotive force to the heating blanket.

37. The method according to claim 36, further comprising increasing the electromotive force to cure the resin.

38. (canceled)

39. (canceled)

40. (canceled)

41. (canceled)

42. The method of claim 36, further comprising heating the composite materials to a debulking temperature in the range of 100-200 F. with a tolerance of +/10 F. (38-93 C. with a tolerance of +/6 C.).

43. (canceled)

44. A method of composite processing, comprising the steps of: placing a heating blanket having a CNT structured layer over composite materials that at least one of contain a resin and are wetted with a resin; and, applying an electromotive force to the heating blanket to debulk the composite materials.

45. The method of claim 44, wherein debulking is performed without moving the composite materials into an autoclave.

46. The method of claim 44, further comprising increasing the electromotive force to cure the resin without moving the composite materials into an autoclave.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Various embodiments of a heating blanket are understood with regards to the following description, appended claims and accompanying drawings wherein:

[0063] FIG. 1 is an exploded perspective view of an in situ debulking layup including a heating blanket of the present invention.

[0064] FIG. 2 is a cross sectional illustration of the heating blanket shown in FIG. 1, taken along line 2-2, the heating blanket flattened out.

[0065] FIG. 3 is a cross sectional illustration of an alternative embodiment of a heating blanket shown in FIG. 1, taken along line 2-2, the heating blanket flattened out.

[0066] FIG. 4 is a graph showing the sheet resistances as a function of the weight percentage of single wall carbon nanotubes (SWCNTs) within a carbon nanotube (CNT)-polymer.

[0067] FIG. 5 is a schematic diagram of a heating blanket having a plurality of heating elements.

[0068] FIG. 6 is a diagram illustrating a CNT structured layer defining an electrically conductive pathway having a serpentine configuration with rounded corners.

[0069] FIG. 7 is a diagram illustrating a CNT structured layer defining an electrically conductive pathway having a serpentine configuration with square corners.

DETAILED DESCRIPTION

[0070] FIG. 1 illustrates an in-place or in situ debulking layup 10 including a heating blanket 18 in accordance with principles of the present invention. As used herein, in situ refers to debulking conducted in the location where a part or subpart is laid up, for example in a clean environment or in a cleanroom, free from foreign matter, and on the tool on which the laminate/part is laid up. When constructing component parts that require a high degree of structural integrity, such as aerospace parts, clean environments are typically used to ensure that foreign object debris, also referred to as FOD, is excluded from the laminate layup, which otherwise might compromise the structural integrity and/or strength of the parts being produced.

[0071] Conventionally, and without the benefit of the present invention, laminate prepregs of a subpart are typically laid up on a tool or mold, in a clean environment, and moved, along with the associated mold or tool, into an autoclave for debulking. In circumstances where parts have complex shapes and/or include many prepreg/laminate layers, the process of taking the tool and the laid-up prepreg laminates of the part to and from the autoclave must be repeated over and over again, each iteration having an associated duration of time and accompanying cost.

[0072] In the debulking layup 10 shown in FIG. 1, the blanket 18 provides heat to composite materials 26 laid up on the tool, for debulking the laminate in-place in the clean environment or in a cleanroom, i.e., in situ, without needing to move the composite materials 26 laid upon the mold tool 32 from the clean environment or location, to an autoclave. The heated debulking is conducted or occurs in place or in situ, on the tool 32, from the heat provided the heating blanket 18. Debulking, in accordance with the present invention, is more efficient in terms of both part-making time, scrap-rate, rework, and general economy (cost), and without the associated risks of introducing foreign objects into the laminate/composite material 26, or damaging the tool, when moving the subpart to and from an autoclave.

[0073] As shown in FIG. 1, debulking is accomplished through a combination of heat and pressure. Therefore, the present invention is configured or adapted for those debulking situations where just heat is used or where both heat and pressure are used. Again, the heating blanket 18 provides the heat necessary for heated debulking of the composite materials 26, while the atmosphere applies pressure to the composite materials 26 for pressurized debulking, as will now be described.

[0074] As illustrated in FIG. 1, a mold tool 32 is provided having the shape or the contour of a part that is to be made using composite materials 26. Typically, with aerospace parts, a mold tool follows the outer contour or windswept or windward side of the part, though this need not necessarily be the case. With other parts or in other embodiments, a mold tool can be made to follow an inner contour of a part should a particular circumstance dictate or need arise. Mold tools come in many shapes and sizes associated with the wide variety of parts made using composite or laminated materials. As shown, the mold tool 32 generally provides for a part that has a longitudinally convex shape. However, those of ordinary skill in the art will appreciate that the present invention is not limited to any particular part or mold tool shape, but rather applies universally to all in situ debulking layups.

[0075] Around the periphery of the mold tool 32, a vacuum sealant tape 30 has been secured. The vacuum sealant tape 30 is generally sealably affixed to the mold tool 32 and is configured to seal to a flexible, air impermeable film or sheet 14 that is placed over the mold tool 32. In use, a vacuum is created between the film 14 and the mold tool 32, as facilitated or provided by the seal of the vacuum sealant tape 30, by withdrawing air from between the film 14 and the mold tool 32, through a vacuum valve 12. The vacuum that is created between the film 14 and the mold tool 32 eliminated substantially all air within the vacuum space, which allows ambient air pressure or atmospheric pressure to press upon the composite materials 26, pressing the composite materials 26 against the mold tool 32, debulking the composite materials 26 using pressure.

[0076] As shown in FIG. 1, a number or plurality of uncured fiber reinforced composite materials 26, often referred to as prepregs, are placed or laid up on the mold tool 32. For example, prepreg is the term commonly applied to a carbon fiber fabric that has been pre-impregnated with a resin, typically epoxy, that already includes a suitable curing agent, and is ready to be laid into a mold. The layup 10 is typically done in accordance with a build sheet or a part program, designating the type, kind, orientation, and/or quantity of layers or composite sheets that are to be used to construct a part. For example, in the layup 10 shown, a number or plurality of prepreg carbon fiber sheets are used, some of which can be woven fabric and others of which can be non-woven fabric, typically vapor permeable. One of ordinary skill in the art will appreciate that any type of composite materials may be used, as desired, with the heating blanket 18, and that the present invention is not limited to any particular type or construction of composite materials. It should also be appreciated that this process can be applied to hand layup of dry fiber material, whereas the resin is applied (also by hand) during the laminate stack-up process.

[0077] Prior to placing the composite materials 26 on the mold tool 32, a release agent 28 is applied or sprayed onto a contoured surface of the mold tool 32 that is to receive the composite materials 26, as indicated a reference numeral 28. The release agent 28 is typically a clear substance (film or solution), although that need not necessarily be the case. The release agent 28 allows for the easy removal of the composite materials 26 after debulking and/or curing is complete.

[0078] In another embodiment, a porous film 24, typically referred as a peel ply, and a non-porous film 22, typically referred to as a release film, can be overlapped, respectively, over the laid-up composite materials 26, on the mold tool 32. The porous film 24 allows air or gas to percolate or pass from between and through the layers of the composite materials 26 during debulking, while the non-porous film 22 prevents resin, contained in the prepregs, from contacting the heating blanket 18 during debulking, thereby allowing for the release, for reuse, of the heating blanket 18 once debulking is complete. Once the non-porous film 22 is in place, the heating blanket 18 is placed over non-porous film 22, proximate the composite materials 26, so as to allow heat produced by the heating blanket 18 to warm the composite materials 26 during debulking. A breather fabric 16 is placed over the heating blanket 18 and allows uniform distribution and/or passage of air over the heating blanket 18 as air is extracted from between the bagging film 14 and the mold tool 32, i.e., a vacuum is applied to the debunking layup 10.

[0079] The heating blanket 18 includes at least two electrical terminals 19, 21 for use in electrically connecting or coupling the heating element(s) to an electromotive force. When electrically-coupled to an electromotive force, the heating blanket 18 produces electrothermal heat that warms or heats the composite materials 26. For example, in one embodiment, and when configured for use with carbon fiber prepreg materials, the heating blanket 18 heats the composite materials 26 to a debulking temperature of 100-200 F. with a tolerance of +/10 F. (38-93 C. with a tolerance of +/6 C.). One of ordinary skill in the art will appreciate that different composite materials having different resins, typically epoxies, can require different temperatures, and that the heating blanket 18 can be configured, as needed, to provide a debulking temperature associated with those thermoplastic or thermoset resins in accordance with principles of the present invention.

[0080] Referring to FIGS. 2 and 3, the heating blanket 18, 118, respectively, includes a heating element 34, 134, respectively, encased within an elastomeric outer covering 40. The heating element 34, 134, respectively, comprises a CNT structured layer 38, 138, respectively, defining an electrically conductive pathway having a first end 50 and a second end 52, and a first electrical terminal 19 electrically coupled to the first end 50 and second electrical terminal 21 electrically coupled to the second end 52. As shown in FIG. 3 and in a first process, the CNT structured layer 38 can be made in accordance with International PCT Publication WO 2016/019143 published on Feb. 4, 2016 and US Patent Publication US 2017/0210627 A1 published on Jul. 27, 2017 or U.S. Pat. No. 9,107,292 B2 granted on Aug. 11, 2015, said publications and patent incorporated herein by reference. In another embodiment, the CNT structured layer 38 can further comprise graphene.

[0081] In the first process for manufacturing the CNT structured layer 38 a continuous conveying belt is moved along a path that traverses a pooling region and a vacuum box, and a continuous porous carrier material is applied to an upper side of the continuous conveying belt. An aqueous suspension of CNTs dispersed in a liquid is applied on the porous carrier material. In an embodiment, the dispersed CNTs have a median length of at least 0.05 mm and an aspect ratio of at least 2,500:1, the aspect ratio referring to the length of the CNTs versus the width or diameter of the CNTs, e.g., length to diameter. A continuous pool of the aqueous suspension of the CNTs is formed over and across the width of the continuous porous carrier material in the pooling region, to a uniform thickness sufficient to prevent puddling upon the continuous porous carrier material. As the porous carrier material and the continuous pool of the aqueous suspension of the CNTs are advanced over the vacuum box, the liquid of the aqueous suspension of the CNTs is drawn by vacuum through the porous carrier material, thereby filtering a uniform dispersion of filtered CNTs over the porous carrier material to form a filtered CNT structure. Optionally any residual liquid from the filtered CNT structure can be dried to form a CNT sheet over the porous carrier material. Optionally the CNT sheet can be removed from the porous carrier material. In another embodiment of a process for manufacturing the CNT structured layer 38, carbon nanostructures that are branched, crosslinked, and that share common walls with one another are dispersed in a solvent until the carbon nanostructure are non-agglomerated. The solution is then passed through a support layer including a plurality of fibers, whereby the carbon nanostructures conform to the fibers and bridge across apertures or gaps between the fibers to form a continuous carbon nanostructure layer. In yet another embodiment of a process for manufacturing the CNT structured layer 38, a solution containing carbon nanostructures, that are branched, crosslinked and that shared common walls with one another, and chopped fibers are filtered to collect the carbon nanostructures on and between the fibers in a structured layer.

[0082] In one embodiment of the present invention, described hereinafter, the maximum quantity of heat, in terms of power per unit area, e.g., watts per square inch (centimeter), produced by the heating blanket 18 can be adjusted by varying the thickness 48 and therefore the electrical resistance of the structured CNT layer 38. In yet another embodiment of the present invention, the maximum quantity of heat produced by the heating blanket 18 can be adjusted by changing the CNT structure in the structured CNT layer 38, for example by using single wall carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs).

[0083] The heating element 34 further comprises a thermoplastic film 36 disposed against the upper and lower surface of the CNT structured layer 38. The thermoplastic film 36 adds durability and/or functions to protect the structured CNT layer. A carrier material, e.g., carbon fiber, fiberglass, thermoplastic veils, can also increase the durability and/or function to protect the structured CNT layer. The thermoplastic film 36 can also function to prevent the ingress of the molten or floury elastomer that forms the elastomeric outer covering 40, into the CNT structured layer 38 during application, thereby preventing the elastomeric outer covering 40 from raising the resistivity of the structured CNT layer 38. Although the ingress of the molten or floury elastomer into the CNT structured layer 38 raises the resistivity of the structured CNT layer 38, once the outer covering 40 cures, the heating blanket is still responsive to an electromotive force 42 and able to produce heat, albeit with higher resistivity.

[0084] Referring to FIG. 3 and in a second process, the CNT structured layer 138 can be made in accordance with International PCT Application PCT/US2017/045422 filed on Aug. 4, 2017, which claims the benefit of U.S. Provisional Application 62/370,712 filed on Aug. 4, 2016, both of which are incorporated herein by reference.

[0085] In the second process for manufacturing the CNT structured layer 138, a multiplicity of carbon nanotubes (CNTs), a polymer, and a solvent are mixed using sonication and, in some embodiments, shear mixing to form a CNT-polymer suspension of CNTs in a uniform dispersion within the polymer and solvent liquid. In some embodiments, the polymer comprises fluoroelastomers (FKM), silicones, fluorosilicones, perfluoroelastomers, ethylene propylene diene rubber (EPDM), and thermoplastic elastomers, such as, for example, thermoplastic polyurethanes (TPU). The CNT-polymer suspension is then applied onto a flexible carrier using a solvent cast coating process, a dip coating process, or a spray coating process. Heat is then directed to the applied CNT-polymer suspension and flexible carrier to heat the suspension and evaporate most, substantially all, or all of the solvent from the suspension, leaving the CNTs and polymer film to form a CNT/polymer film structure comprising a dispersion of the CNTs in the polymer structure upon the flexible carrier. The CNT-polymer film structure can then be removed from the flexible carrier, cut to size, and used as shown in FIG. 3 for the CNT structured layer 138.

[0086] A person of ordinary skill in the art will appreciate that the purpose of mixing the CNT-polymer suspension is to evenly distribute the CNTs within the suspension so that when the solvent is driven off and the suspension is dried, the resulting CNT-polymer film structure has substantially uniform resistivity throughout the entire film structure in the plane.

[0087] In some embodiments, the thickness of the CNT-polymer film structure is at least about 1 millimeter (mm), less than about 2 mm, or between about 1 mm and about 2 mm to facilitate an automated manufacturing continuous solvent cast coating process and to aid in or facilitate timely drying therein. The thicker the CNT-polymer film structure, the more drying time is required.

[0088] In a non-limiting example, the CNTs can be SWCNTs, the polymer can be a silicone, the solvent can be toluene, and the flexible carrier can be a polyether ether ketone (PEEK) film. Using the forgoing, a number of CNT-polymer film structures where made using a manual solvent cast coating process in a thickness of 100 micrometers (m). For the CNT-polymer film structures made, FIG. 4 shows the sheet resistances (/) as a function of the weight percentage (%) of SWCNTs within a CNT-polymer comprising silicone using three different batches of CNTs having three different CNT lengths, i.e., 100, 150, and 175 micrometers (m) or microns, average bundle size. A person of ordinary skill in the art will appreciate that CNTs can be produced/purchased targeting a desired length, e.g., 100, 150, or 175 m, but pragmatically, the actual length of each CNT will vary from one CNT to another, i.e., some CNTs being somewhat shorter and some CNTs being somewhat longer, a bundle of produced/purchased CNTs having an average length or an average bundle size. For example, SWCNTs in average bundle sizes of 100, 150, and 175 m in length are available from OCSiAl headquartered in Grand-Duch de Luxemburg, and also in Columbus, Ohio. As used herein the term silicone refers to polysiloxanes, the terms used interchangeably. Polysiloxanes are polymers that include any inert, synthetic compound made up of repeating units of siloxane, which is a chain of alternating silicon atoms and oxygen atoms, combined with carbon, hydrogen, and sometimes other elements. As shown, the sheet resistance can be increased by using shorter length CNTs, other factors being equal, e.g., thickness, weight, etc. Conversely, the sheet resistance can also be decreased by using longer CNTs, again, other factors being equal, e.g., thickness, weight, etc.

[0089] The sheet resistance can be at least about 3/, at least about 5/, at least about 10/, at least about 20/, at least about 30/, at least about 40/, at least about 50/, at least about 60/, at least about 70/, at least about 80/, at least about 90/, at least about 100/, at least about 200/, at least about 300/, at least about 400/, at least about 500/, at least about 600/, at least about 700/, at least about 800/, at least about 900/, at least about 1,000/, at least about 1,100/, at least about 1,200/, at least about 1,300/, at least about 1,400/, at least about 1,500/, or at least about 1,600/. A useful sheet resistance can be selected from any value between and inclusive of about 3 to about 1,600/. Non-limiting examples of sheet resistances using SWCNTs in an average bundle length of 100 m can include about 5/, about 6/, about 7/, about 14/, about 36/, about 43/, about 46/, about 47/, about 58/, about 288/, about 450/, about 750/, and about 1,620/. Non-limiting examples of sheet resistances using SWCNTs in an average bundle length of 150 m can include about 3/, about 4/, about 5/, about 9/, about 24/, about 28/, about 31/, about 39/, about 192/, about 300/, about 500/, and about 1,080/. Non-limiting examples of sheet resistances using SWCNTs in an average bundle length of 175 m can include about 3/, about 4/, about 8/, about 21/, about 25/, about 27/, about 31/, about 165/, about 257/, about 429/, and about 926/. The useful weight percentage of SWCNTs by weight of the CNT-polymer film structure can be selected from any value between and inclusive of about 0.25 to about 25 percent. For example, in a CNT structured layer including SWCNTs and a silicone, the mass percentage of the SWCNTs within the layer can be selected from any value between and inclusive of at about 0.25 to about 5 percent by weight, about 5 to about 10 percent by weight, about 10 to about 15 percent by weight, 15 to about 20 percent by weight, and about 20 to about 25 percent by weight. Non-limiting examples of percentages include about 0.25, about 0.5, about 1, about 2, about 3, about 4, about 5, about 12, about 13, and about 25.

[0090] In some embodiments, for a CNT-polymer film structure between about 1 mm and about 2 mm in thickness comprising a constant uniform dispersion of the CNTs in the polymer comprising silicone, a CNT weight percentage of less than about 15 percent proved workable without crumbling with handling, while a CNT weight percentage of about 20 percent, or more, was unusable, crumbling with handling, in some other embodiments, a CNT weight percentage of about 3 percent to about 10 percent resulted in a sheet resistance of about 70/ to about 16/, respectively.

[0091] Referring to FIGS. 2 and 3, and some embodiments, the elastomeric outer covering 40 is selected for use in a cleanroom, the heating blanket 18, 118, respectively, configured for use in situ. In other embodiments of the present invention, the elastomer covering 40 can be formed from fluoroelastomers (FKM), silicones, fluorosilicones, perfluoroelastomers, ethylene propylene diene rubber (EPDM), and thermoplastic elastomers, such as, for example, thermoplastic polyurethanes (TPU). One of ordinary skill in the art will appreciate that the elastomeric outer covering 40 can be selected from a variety of materials, natural and synthetic, as desired, depending on the use environment of the heating blanket 18, 118, respectively, without departing from the spirit of the present invention.

[0092] Still referring to FIGS. 2 and 3, and in some other embodiments, the elastomeric outer covering 40 is as silicon-based material that offers high reversion resistance and strength, and that can be used in composite laminating and bonding systems using vacuum, e.g., bagging or hydraulic pressure during curing or bonding. One silicon-based material is Airtech 4140 silicon rubber available from Airtech International, Inc. of Huntington Beach, Calif. Another silicon-based material is Airtech 5553 silicon rubber also available from Airtech International, Inc. It was found that in some applications, a heating blanket constructed using Airtech 4140 would undesirably wear over time and in repeated use during testing, the outer cover stretching or deforming. The fiberglass reinforcement found in Airtech 5553 combats this problem. Both these silicon-based materials are available in thicknesses of 0.030 and 0.060 inches (0.762 and 1.524 millimeters (mm)), the selection of which thickness depends on how flexible the blanket need be, and as will be discussed in further detail hereinafter. Those of ordinary skill in the art can select an appropriate covering material and thickness for a particular application with the benefit of the teachings contained herein.

[0093] The elastomeric outer covering 40 can be cured and/or formed so that the heating blanket forms a resilient three-dimensional shape that follows or mimics the shape of a caul tool associated with a part. The elastomeric outer covering 40 can also be cured and/or formed so that the heating blanket forms a resilient three-dimensional shape that follows or mimics the shape of part, be it an inner or outer contoured surface of a part. A heating blanket with a predisposed shape or contoured shape rather than a shape that is substantially planar in nature makes the heating blanket easier to work with and particularly suited for placing the heating blanket into tight radiuses or narrow crevices in a part or for more closely following, i.e., staying in contact with, transitions between concave and convex portions of a part. For example, a heating blanket can be formed to follow the shape of a caul tool, placed over the caul tool, and then the caul tool with the heating blanket disposed there over, can be placed or inserted into a tight radius area or narrow crevice in a part that is being laid-up to debulk and/or cure the composite materials forming the part. Further, and as another example, a heating blanket with a predisposed shape or contoured shape makes the heating blanket able to follow transitions between the outer surface of an aircraft, e.g., a wing, and an opening therein, e.g., an air intake or outlet. One of ordinary skill in the art will appreciate that the elastomeric outer covering 40 can be cured in a multitude of ways, as desired, to make the heating blanket easier to work with and use without departing from the spirit of the present invention.

[0094] Electrically coupled to the CNT structured layer 38, 138, respectively, are at least two electrical terminals 19, 21, each representing different electrical nodes 50, 52. In one embodiment of the present invention, the electrical terminals 19, 21 are electrically coupled to the CNT structured layer 38, 138, respectively, by crimping the terminals 19, 21 over an end or edge of the CNT structured layer. In some other embodiments, the electrical terminals 19, 21 comprise a metal foil or expanded metal foil, the expanded metal foil preferred for enhanced flexibility of the blanket. In other embodiments of the present invention, the electric terminals 19, 21 can be electrically coupled by alternative means without departing from the spirit of the present invention such as electrically conductive adhesives or pastes, or simply with pressure fittings, fasteners, or clamps that provide enough force against the CNT structured layer 38, 138, respectively, to maintain acceptably low contact resistance.

[0095] The electrical terminals 19, 21 of the heating element 34, 134, respectively, are electrically connected or coupled to an electromotive force 42, through wires 44, forming an electrical circuit 46. The heating element 34, 134, respectively, is responsive to the electromotive force 42, thereby generating heat. Further, by varying, adjusting, setting, or selecting, i.e., raising or lowering, the voltage potential provided by the electromotive force, the quantity of heat, in terms of power per unit area, e.g., watts per square inch (centimeter), produced by the heating blanket 18, 118, respectively, can be raised or lowered. In one embodiment of the present invention, the CNT structured layer 38, 138, respectively, and the electromotive force 42 are selected to produce heat to raise the temperature of the laminate to a debulking temperature, for example, to a temperature in the range of 100-200 F. with a tolerance of +/10 F. (38-93 C. with a tolerance of +/6 C.). In another embodiment, the electromotive force 42 provides a power density of approximately 1-10 watts per square inch (0.2-1.6 watts per square centimeter), see FIG. 1 at reference numeral 60, for example, such a selection being made to achieve a debulking temperature that softens, and debulks prepregged carbon fiber composite materials 26, without curing the resin contained therein. If more power is applied, the heating blankets described herein can heat the composite materials 26 enough to fully cure the resin, This affords use of the heating blanket 18, 138, respectively, for composite repair and out-of-autoclave curing. Moreover, by using a CNT structured layer 38, 138, respectively, of the present invention, the temperature and power density remains relatively constant and uniform across the length and width of the CNT structured layer 38, 138, respectively, designated at reference numerals 62 and 64, respectively, and shown in FIG. 1.

[0096] Still referring to FIGS. 2 and 3 and in accordance with one aspect of the present invention, the heating blanket 18, 118, respectively, comprised of a heating element 34, 134, respectively, comprised of a structured CNT layer 38, 138, respectively, is significantly thinner, and more flexible and drape-able, than a conventional metallic filament-based heat blanket. For example, using the first process for making the CNT structured layer 38, a thickness 54 of the heating element 34 can be less than 0.04 inches (1 millimeter) and, in one embodiment, the thickness 54 of the heating element 34 can be approximately 0.01 inches (0.25 millimeters), see FIG. 2. Further, a corresponding thickness 56 of the heating blanket 18, including the elastomeric outer covering 40, can be less than 0.045 inches (1.5 millimeters) and, in one embodiment, the thickness 56 of the heating blanket can be approximately 0.015 inches (0.38 millimeters). Using the second process for making the CNT structured layer 138, a thickness 57 of the heat blanket 118 is less than about 0.10 inches (2.54 millimeters) or less than about 0.20 inches (5.08 millimeters), see FIG. 3, the thickness of less than about 0.10 inches (2.54 millimeters) being based on a CNT polymer structure thickness, i.e., thickness 48, of about 1 mm (0.040 inches) and two layers of 0.030 inch (0.762 mm) elastomeric material that are cured together to form the elastomeric covering 40, and a CNT polymer structure thickness of about 2 mm (0.080 inches) and two layers of 0.060 inch (1.524 mm) elastomeric material that are cured together to form the elastomeric covering 40, respectively.

[0097] In other embodiments, a thickness of the heating blanket according to the present invention is at least 0.01 inch (0.25 millimeters), and up to about 0.40 inch (10.2 millimeters), which can include a thickness of at least 0.05 inch (1.3 millimeters), at least 0.10 inch (2.5 millimeters), or at least 0.15 inch (3.8 millimeters), or at least 0.20 inch (5.1 millimeters), or at least 0.25 inch (6.4 millimeters), and up to about 0.35 inch (8.9 millimeters), or up to about 0.30 inch (7.6 millimeters), or up to about 0.25 inch (6.4 millimeters). The heat blanket can be thinner, or thicker, than the indicated thickness.

[0098] The heating blanket 18, 118 is also quite flexible in nature. For example, in one embodiment, the heating blanket 18 can be folded over and/or doubled over on itself without failure, wherein the mean or average radius of the fold approaching or less than the thickness 56 of the heating blanket 18, e.g., 0.045 inches (1.5 millimeters) or less. In another embodiment, the heating blanket 118 can be folded over and/or doubled over on itself without failure, the mean or average radius of the fold approaching or less than the thickness 57 of the heating blanket 118, e.g., 0.10 inches (2.54 millimeters) or less, or 0.20 inches (5.08 millimeters) or less.

[0099] Additionally, the heating blanket is also quite durable. For example, the flexural strength of a material can be defined as the ability of the material to resist deformation under load. For materials that deform significantly but do not break, for example, the thermoplastic film 36, the load at yield, typically measured at 5 percent deformation divided by the strain of the outer surface, is reported as the flexural strength or flexural yield strength. The American Society for Testing Materials (ASTM) D790 standard provides a test geometry for the forgoing measurement. The analogous test to measure flexural strength in the International Organization for Standardization (ISO) system is ISO 178. Typical average flexural strengths and flexural moduli ranges for polymers, of which a thermoplastic film 36 is one, are from 40 to 270 Megapascals (MPa) and 0.7 to 7.5 Gigapascals (GPa), respectively. For example, in the embodiment shown in FIG. 2, the flexural strength of the CNT structured layer 38 is equal to or greater than the flexural strength of the thermoplastic film 36. These thicknesses, flexibility, and durability makes the heating blanket 18 generally suited to follow or conform to the surfaces and shapes found in aerospace component parts and, more particularly suited to, in situ debulking, as shown in FIG. 1. For in the embodiment shown in FIG. 3, the flexural strength of the CNT structured layer 138 is even greater still, not being limited by a thermoplastic film.

[0100] Referring now to FIG. 5, the scalability of a heating blanket 68 will be discussed. One of ordinary skill in the art will appreciate that composite parts can be so large that it is impractical or impossible to move them laid up on their accompanying mold into a suitably-sized autoclave for debulking; for example, the wing of a large passenger airplane. However, the scalability of the present invention provides for the debulking of such large parts as will be described below.

[0101] In accordance with another aspect of the present invention and as shown in FIG. 5, a plurality of heating elements 66.sub.X,Y can be electrically and thermally combined to realize a heating blanket 68 that is physically larger than that typically afforded by a single heating element 66. As shown, a plurality of heating elements 66.sub.X,Y are arranged in close physical proximity with one another, side-by-side, end-to-end, etc., in a planar arrangement. More specifically, physically adjacent, i.e., not overlapped, side-by-side, end-to-end, heating elements 66 can be electrically connected together to increase the physical, planar size of the heating blanket 68. For example, heating elements 66.sub.1,1 and 66.sub.1,2, are electrically connected in series, the CNT structured layers of each heating element electrically coupled together through a terminal 80.

[0102] Similarly, heating elements 66.sub.1,1 and 66.sub.2,1, are electrically connected in parallel, the CNT structured layers of each heating element likewise electrically coupled together through a terminal 78. It has been found that there is minimal temperature variation across the terminals 78, 80, and that a heating blanket 68 that is physically larger than that afforded by any of the heating elements alone, e.g., 66.sub.1,1, 66.sub.1,2 or 66.sub.2,1, can be realized.

[0103] Those of ordinary skill in the art will appreciate that although the heating elements 66.sub.X,Y in FIG. 5 are shown as a matrix, the heating elements 66.sub.X,Y are, in fact, electrically connected in a series-parallel circuit arrangement, the series heating elements designed by the variable Y as referenced by numeral 74 and the parallel heating elements designed by the variable X as referenced by numeral 72, the placement of each respective heating element designated as 66.sub.X,Y. In some embodiments of the present invention, the series-parallel arrangement can be used to create zones in the heating blanket 68, each having different power densities and producing different amounts of heat to be applied to the laminate, as can be required by the complex shape of a mold tool, the mold tool acting as a heatsink with a varying heat profile.

[0104] Those of ordinary skill in the art will also appreciate that the electrical load, in terms of voltage and current, of the heating blanket 68 can be varied, as desired, in accordance with the electrical circuit arrangement, i.e., series-parallel combinations, of the plurality of heating elements 66.sub.X,Y. The plurality of heating elements 66.sub.X,Y, encased within the elastomer outer covering 76, are electrically connected or coupled to an electromotive force 70 via electrical terminals 78, such as through wires 82, forming an electrical circuit 84. The plurality of heating elements 66.sub.X,Y, electrically connected in series, parallel, and/or a series-parallel combination, are responsive to the electromotive force 70, producing heat in response thereto. Further, by varying, adjusting, or setting, i.e., selecting, the voltage potential provided by the electromotive force 70, the heat produced by the heating blanket 68 can be varied proportionally.

[0105] With reference to FIGS. 2, 3, 6, and 7, the CNT structured layer 38 can also be designed, manufactured, and/or constructed such that the electrical pathway defined by the CNT structured layer 38 is in a serpentine configuration 86. The serpentine configuration 86 allows for the first and the second terminals 19, 21 to be co-located, i.e., located in close proximity to one another or next to each other, to promote easy electrical connections thereto with good cable management. For example, the CNT structured layer 38 can be cut with a punch, a laser cutter, or by other means to form the serpentine configuration 86. FIGS. 6 and 7 show examples of serpentine configurations 86 with round corners 88 and square corners 90, respectively.

[0106] While various embodiments of a heating blanket have been illustrated by the foregoing description and have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will become readily apparent to those skilled in the art.