Patent Application
20220120513
The present disclosure is directed to a method of making and a method of using a thermal transfer blanket.
Coatings, sealants, and composite structures of laminated material are increasingly being used in industry, particularly in the aircraft industry. From time to time, the coatings, sealants and composite structures will be damaged and need repair in the field rather than replacement of an entire panel or subassembly. Repair typically involves the removal of damaged material and covering the repair site with organic resin or layers of woven material, such as graphite or carbon fiber, which have been impregnated with an organic matrix resin, such as epoxy. The repairs need to be cured, and in some cases pressed and cure at elevated temperatures. When correctly done, such curing involves a controlled heating profile to a predetermined temperature, which is held for a sufficient time to complete the resin's curing reaction followed by a slow cooling profile.
The advantages of designing with composite materials include the ability to tailor the amount of material used to obtain efficient structural components. Many composite designs have been developed that have non-uniform cross-sections (e.g., ply dropoffs, planks, stiffening elements, etc.). The heat sinks from these non-uniform cross-sections require increased thermal control to maintain uniform cures. Curing of resins used in composite materials (including those in repair patches) is an exothermic reaction that requires heat to start the reaction. Without adequate control of the heating or cooling, hot spots or cold spots develop in the repair. Conventional heat blankets and control techniques that seek to reduce cold spots tend to increase problems associated with hot spots or vice versa. Existing portable repair equipment has neither the desired elevated pressures nor the inherent temperature control capabilities of an autoclave. Consequently, repairs to complex structures are often inadequate because of poor temperature control and non-uniform temperatures in the repair zone, thereby reducing the quality or structural capability of the repair.
Controlling the pressure applied and the temperature profile for a repair is desirable as these can affect the strength of a repair. Inadequate temperature control can substantially impact repair strength. Heating too fast can shock and weaken the composite structure. Curing temperatures lower than desired result in poor bonding and temperatures higher than desired can result in burning both the repair patch and the material surrounding the repair. Fluctuating temperatures, especially during the cure, can produce a combination of these effects.
Curing of organic resin repairs is typically done with electronic heater blankets, IR lamps or electrical convection heaters. Electric heater blankets are the most common approach. However, heater blankets can have problems with non-uniform heating, which can be compounded with the underlying repair site having variations of thickness and spar locations. Monitoring the temperature of the repair site and controlling the power supply to the heater in response to follow a profile or maintain relatively constant temperature to cure the resin without local hot and cold spots can be challenging. This can be especially true in cold environments where the electrical blanket controller can continually attempt to maintain temperature and drive heat into the surrounding structure, thereby unintentionally overheating and potentially thermally damaging underlying layers.
Additionally, there is sometimes a need to heat and cure resin coatings for infield repair on composite objects, such as the exterior of aircraft, without a power supply. While an open flame heater may work, open flame heaters are typically not allowed near aircraft, and/or can be dangerous, bulky and provide uneven heating.
The present disclosure is directed to a method of thermally treating a material. The method comprises applying a thermal transfer blanket to a surface of the material. The thermal transfer blanket comprises a thermal energy storage media having a first temperature, the material having a second temperature that is different than the first temperature. Thermal energy is transferred between the thermal transfer blanket and the material, thereby modifying the temperature of the material.
The present disclosure is also directed to a method of making a thermal transfer blanket. The method comprises inserting a thermal energy storage media into a flexible container, the flexible container comprising a thermally insulating material. A thermocouple is attached to the thermal energy storage media so as to be in thermal communication with the thermal energy storage media.
The present disclosure is also directed to a method of repairing an object. The method comprises positioning a thermally curable patch on an exterior surface of an object, such as any of the vehicles or other objects described herein. The thermally curable patch comprises an uncured polymer having a first temperature. The method includes charging a thermal transfer blanket comprising a thermal energy storage media with thermal energy from a heat source, such as any of the heat sources described herein. The thermal transfer blanket is applied to the thermally curable patch. Thermal energy is transferred between the thermal transfer blanket and the thermally curable patch to increase the first temperature of the uncured polymer to a cure temperature for a sufficient amount of time to cure the polymer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrates aspects of the present teachings and together with the description, serve to explain the principles of the present teachings.
It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding rather than to maintain strict structural accuracy, detail, and scale.
Reference will now be made in detail to the present teachings, examples of which are illustrated in the accompanying drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific examples of practicing the present teachings. The following description is, therefore, merely exemplary.
The thermal transfer blankets of the present disclosure can provide the ability to repair, for example, coatings, sealants and/or thermal set composites structure, such as for example on the exterior of vehicles (e.g., aircraft or ground-based vehicles) or other objects in very austere environments with few tools and no electrical power. For example, the thermal transfer blankets can heat adhesive, sealant, prepreg or other organic resin-containing repair materials to achieve a reasonable temperature to cure the organic resin at high temperatures, such as, for example, 120° F. or above. The thermal transfer blankets are easily portable and can be used to repair coatings outside and in situations where the resin is initially at low temperatures, such as 20° F. or lower. The thermal transfer blankets of the present disclosure can also function as non-powered hot or cold storage device that can be used to heat or cool various items from, for example, about −65 F to about 1,200 F.
The flexible container 102 can comprise any suitable thermal insulating material 152 described herein. The thermal insulating material maintains thermal energy within the thermal energy storage media 104 so as to reduce unwanted heat loss, as well as to protect users from burns that could occur by touching the thermal energy storage media 104.
The thermal energy storage media 104 comprises a material that acts as a heat sink for storing and releasing thermal energy. Suitable materials can comprise, for example, at least one material chosen from metal oxide or non-oxide ceramics, such as AlN, BeO, BN (either cubic BN or hexagonal BN), diamond, Al2O3, and metals, such as aluminum, copper, silver, brass, iron, gold, steel and combinations thereof, with aluminum, silver and copper having the most suitable combinations of thermal conductivities and specific heat capacities. The metals, such as aluminum, copper, silver, gold and iron, can be pure or alloyed. The term “pure” is defined to mean at least 99% by weight pure. Thus, “pure aluminum” as used herein includes at least 99% by weight aluminum. The thermal conductivities and specific heat capacities of several of these materials are shown in Table 1 below. Materials such as AlN, BN and BeO, which have relatively high thermal conductivities and specific heat capacities will be able to store relatively large amounts of thermal energy per unit mass, while also being capable of transferring the thermal energy quickly, either for purposes of storing or releasing the thermal energy. Examples of suitable thermal conductivities range from about 35 W/m-K to about 500 W/m-K or higher, such as about 100 W/m-K to about 500 W/m-K, such as about 150 W/m-K to about 400 W/m-K, or about
200 W/m-K to about 400 W/m-K (as measured at 25° C.). Examples of suitable specific heat capacities range from about 300 J/kg·K to about 1500 J/kg·K or higher, such as about 500 J/kg·K to about 1000 J/kg·K, or about 700 J/kg·K to about 950 J/kg·K (as measured at 25° C.). It is possible that materials with lower thermal conductivities (e.g., Al2O3) and/or lower specific heat capacities (e.g., gold) can be used, but they will not function as effectively for quickly charging the thermal blanket, quickly delivering heat energy or quickly cooling an object and/or for providing a desired amount of heat energy to the object. In the case where a longer time period for charging of the thermal blanket is not an issue and/or where it is desirable to deliver the heat or cold for long periods of time without too quickly reducing the thermal blanket, a material with a high specific heat and a low thermal conductivity could be desirable. For example, while Al2O3 has a suitable specific heat, its thermal conductivity is only about 35 W/m-K, and so it is not as good a candidate as AlN, BN or BeO for quickly charging and quick heating and/or cooling. However, Al2O3 may be suitable for other applications where longer periods of time for charging, heating and/or cooling are acceptable. Additionally, these and the other ceramics listed are electrical insulators, which is an advantage in situations where electrical conductivity is an issue. Of the metals shown in
The thermal energy storage media 104 employed in the thermal transfer blanket 100 of
The elastomeric polymer 114 can be any polymer that is flexible and can withstand relatively high temperatures of at least 120° F., such as about 300° F. or more, such as about 400° F. to about 650° F. An example of such an elastomeric polymer is silicone. An example of a commercially available silicone is 3145 RTV, available from Dow Corning of Midland, Mich.
The thermal transfer blanket 100 can comprise any desired number of layers 110 of the thermal energy storage media 104. For example, thermal transfer blanket 100 can comprise about 1 to about 10 of the layers 110, such as about 2 to about 6 of the layers 110. The number of layers will depend on a desired amount of thermal energy storage capacity for the thermal transfer blanket 100 and the thickness of the layers 110. The thickness of each layer 110 can be any suitable thickness, such as about 0.1 inch to about 1 inch, or about 0.15 inch to about 0.25 inch, or about 0.0157 inch. The thicker the layers 110 are, the fewer that may be used to achieve a desired thermal energy storage capacity. However, using larger numbers of thin layers can provide for a more flexible thermal transfer blanket than using fewer numbers of thicker layers to achieve the same thermal energy storage capacity.
The layers 110 can be attached to the thermal transfer blanket in any suitable manner. For example, the layers 110 can be attached to the flexible container 102 using an adhesive, such as silicone, at an end of each of the layers 110. In an example, the two or more layers 110 of tiles 112 are not attached directly to each other, thereby providing increased flexibility for the thermal transfer blanket 100.
In an alternative example, the layers 110 can be allowed to float freely within the flexible container 102. In this example, thermally transparent layer 118 can act to enclose and retain the layers 110 within the flexible container 102. The thermally transparent layer 118 can be in direct thermal communication with the thermal energy storage media 104. Thermally transparent layer 118 is made of a material that can allow the thermal energy stored in the thermal energy storage media 104 to be released through the thermally transparent layer 118. For example, the thermally transparent layer 118 can be sufficiently thin (e.g., 0.001 inch to 0.01 inch thick, such as about 0.005 inch thick) so as to allow ready transfer of heat therethrough. If desired, the thermally transparent layer 118 can also be non-stick. A commercial example of such a non-stick material is ARMALON®, which is a non-porous polytetrafluoroethylene (e.g., TEFLON) coated fiberglass fabric that is known for use in composite fabrication.
In an example, the thermal transfer blankets described herein include at least one thermocouple. For instance, thermocouples 106, 108 can be arranged as shown in
The thermal transfer blanket 100 of
The thermal transfer blanket 100 of
The thermal transfer blanket 100 of
The one or more plates 120 and pellets 122 can comprise any of the materials described herein for thermal energy storage 104. For example, the one or more plate 120 and pellets 122 can comprise at least one material chosen from AlN, BeO, BN, diamond, Al2O3, and metals, such as aluminum, copper, silver, brass, iron, steel and gold, and combinations thereof. In an example, both the one or more plates 120 and pellets 122 comprise aluminum, such as pure aluminum. The pellets 122 can be coated or uncoated. In an example, the pellets 122 are coated with a chromate conversion coating for reducing corrosion and/or hardening the pellet surface. One example of a commercially available chromate conversion coating is BONDERITE® (formerly known as ALODINE®), available from Henkel Adhesives of Düsseldorf, Germany.
The pellets 122 can have a uniform size. Alternatively, the pellets 122 can comprise a plurality of sizes so as to improve packing density, and therefore increase the amount of thermal energy that can be stored per unit volume of the pellets, which can be desirable for making thermal blankets that are less bulky while still storing sufficient thermal energy for curing. For example, referring to
The elastomeric polymer for matrix material 124 can comprise the same materials as those described above for the elastomeric polymer 114, such as silicone that is capable of withstanding temperatures of at least 120° F., such as about 300° F. to about 650° F. or more, have high elongation and be tear resistant. An example of a commercially available silicone is 3145 RTV, available from Dow Corning of Midland, Mich.
Pellets 122 are incorporated in the matrix material 124 and additional pellets 122 are disposed so as to float freely in a space enclosed on one side by the combination of the thermally transparent layer 118 and the matrix material 124 so as to be sealed within the flexible container 102. The matrix material 124 can thus form a layer proximate the thermally transparent layer 118 and may help to provide a relatively smooth support surface for the pellets 122 disposed above the matrix material 124. Such a smooth surface may be beneficial when curing polymers for providing a smooth cured polymer surface. The combination of pellets and matrix material 124 provide good flexibility for the thermal transfer blanket 100, while the optional plates 120 can increase the thermal energy storage capacity of the blanket.
In an example, the one or more plates 120 comprise materials with higher specific heat than the material used for the pellets 122 to increase thermal energy storage. In an example for cooling applications, the plates 120 can be dry ice or paraffin in the form of blocks, ice packs or other cold packs. While paraffin wax has a low melting point, it has a heat capacity of 3260 J/kg·K, and thus could store relatively large amounts of thermal energy at colder temperatures compared with, for example, aluminum. For low temperature or high temperature cooling or heating applications, the one or more plates 120 can comprise blocks of organic resins, ceramics or metals that have higher specific heat than the material used for the pellets. As an example, the one or more plates 120 can comprise phenolic resin, which is able to withstand temperatures of 600-700° F. and has a heat capacity of about 1250-1650 J/kg·K.
The thermal transfer blanket 100 of
The thermocouples 106 and 108 can be attached to the fabric of containers 128 (including thermally transparent layer 118) using any suitable technique. One exemplary technique for attached thermocouples 106 is to bond them to the thermally transparent layer 118 using a high temperature adhesive, such as silicone (e.g., 3145 RTV available from Dow Corning of Midland, Mich.). In cases where thermally transparent layer 118 includes a non-stick coating, such as PTFE (e.g., TEFLON®), the non-stick coating can first be removed from the location where the one or more thermocouples 106 are to be bonded using any suitable technique, such as, for example, a tetra etch, as is generally well known in the art. The one or more thermocouples 106 are then attached to the thermally transparent layer 118. The one or more thermocouples 108 can be attached to, for example, a place holder 130 that is attached to the container 128. The place holder can be, for example, a piece of fabric or other material attached to the container 128 by stitching, so that the thermocouple 108 is maintained in a desired position in the pellets 122 that are free floating in container 128.
The thermal transfer blanket 100 of
The thermal transfer blanket 100 of
The thermal resistive pad 150 can be employed as a stand-alone pad that is separate from the thermal transfer blankets described herein. Alternatively, at least one thermal resistive pad 150 can be attached to the thermal transfer blanket 100. For example, one or more of the thermal resistive pads 150 can be attached to the flexible container 102 of any of the thermal transfer blankets 100, either in place of, or in addition to, the heat storage flap 119. In an example, the heat storage flap 119 comprises at least one thermal resistive pad 150, such as 2 to 4 of any of the thermal resistive pads 150 of
The thermal resistive pads 150 can be made of any number of flexible insulating materials and can be stacked between the thermal transfer blankets and a repair patch to reduce the thermal transfer rate. When the thermal storage device is fully charged it may too hot (or cold) and a particular thermal energy transfer rate maybe desired. A thermal resistive pad or pads can be placed between the thermal transfer blanket and the repair patch to reducing thermal energy transfer rate. During heating or cooling, thermal resistive pads can be added or removed to maintain the heating rate as the thermal transfer blanket is depleted, or to speed up the heating rate or limit the repair to a maximum temperature. Thermal couples on the thermal resistive pads and the thermal transfer blanket can be monitored and/or data recorded with a battery operated handheld device to facilitate proper cure repair.
The present disclosure is also directed to a method of making a thermal transfer blanket, such as any of the thermal transfer blankets described herein. As shown at 160 of
In the case where the thermal energy storage media comprises one or more layers 110 of tiles 112 bonded by an elastomeric polymer 114, such as in
In an example, the elastomeric polymer 114 is a silicone that can withstand high temperatures, such as a cross-linked silicone. In an example, the elastomeric polymer can withstand temperatures of 300° F. or higher, such as 400° F. to 650° F., or 550° F. to 610° F. The tiles 112 can be treated with a primer, such as DOWSIL™ PR-1200 silicone primer, commercially available from Dow Chemical, prior to applying the silicone so that the silicone will adhere to the tiles. In an example, the silicone is cross-linked, as cross-linked silicones are generally capable of withstanding higher processing temperatures without degradation than are silicones that are not cross-linked.
The one or more layers 110 of tiles 112 can be attached to the flexible container 102 using any suitable attachment technique. An example of a suitable attachment technique comprises sewing the adhesive to the flexible container 102 using, for example, a glass or other suitable thread. Another example of a suitable attachment technique comprises employing an adhesive, such as silicone, to attach the layers 110. For example, any of the silicones taught herein can be employed as the adhesive. In an example, the layers 110 can be attached to the flexible container 102 only at an end of each of the layers 110, which can provide for flexibility of the thermal transfer blanket 100.
The present disclosure is also directed to a method of thermally treating a material. As shown at 170 of
In an example, the thermally treating at 170 in the method of
The thermal storage blanket can be charged using any suitable heat source. For example, the method can comprise positioning the thermal energy storage media in thermal communication with any heat source having a suitably high temperature, such as a temperature ranging from about 120° F. to about 1700° F., about 120° F. to about 1200° F. or about 120° F. to about 600° F. The thermal energy storage media is then charged as thermal energy is transferred from the heat source to the thermal energy storage media until the thermal energy storage media reaches a desired temperature. For example, the thermal energy storage media can be heated during the charging to a temperature ranging from about 120° F. to about 1700° F., about 120° F. to about 1200° F. or about 120° F. to about 600° F. Any suitable heat source can be used. For example, the heat source can be an engine (e.g., aircraft engine, automobile engine or boat engine), an oven, a furnace, a radiator, a heating blanket, a chemical reaction heating pad or an open flame.
The amount of energy stored in the thermal transfer blanket will be a function of the specific heat capacity of the thermal energy storage media, as well as the mass and the temperature of the thermal energy storage media after charging is complete. Examples of specific heat capacity for the thermal energy storage media can range from about 120 J/KgK to about 1500 J/KgK, such as about 700 J/KgK to about 1200 J/KgK. The larger the specific heat capacity, the greater the amount of thermal energy that can be stored for a given mass of thermal storage media. The actual amount of thermal energy stored can vary widely. The larger the thermal conductivity of the thermal energy storage media, the faster the rate at which thermal energy can be transferred to and from the thermal transfer blanket. As an example, the thermal conductivity can be 30 W/M·K or more, such as about 150 W/M·K to about 400 W/M·K.
In an example, the method further comprises applying a thermal resistive pad 150 to the surface of the material prior to applying the thermal transfer blanket to the material. The thermal transfer blanket can then be positioned onto the thermal resistive pad. A detailed example of such a method is set forth below with respect to
In yet another example, the method of thermally treating of
For either heating or cooling it may be desirable to determine one or more of: a temperature at or proximate to a surface of the material being heated or cooled, the temperature of the thermal energy storage media, and a difference between the temperature of the thermal energy storage media and the temperature of the material being heated or cooled. The temperature data can be determined using thermocouples 106 and/or 108, as illustrated herein in
The thermal transfer blankets of the present application can be used for various heating or cooling applications. Examples of such applications include: curing any kind of organic resin or cements, even in cold environments; accelerating the cure of organic composites for repairs for objects 210, such as vehicles including aircraft, cars, boats or other watercraft, motorcycles and bicycles, as well as other objects such as sporting goods; and keeping items hot or cold for storage or shipping without melting or release of any liquid, such as water from ice.
A plate of aluminum about ½″ thick was put in an oven at 350° F. to absorb the heat. The hot plate was placed on top of a piece of frozen prepreg (which specified a cure temperature greater than about 250° F. for at least about 90 min. for curing). A layer of ARMALON and woven glass fabric (acting as a thermal resistive pad) was positioned between the prepreg and the heated aluminum. The heat from the aluminum cured the prepreg.
While the present teachings have been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the present teachings may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function.
Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” Further, in the discussion and claims herein, the term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the intended purpose described herein. Finally, “exemplary” indicates the description is used as an example, rather than implying that it is an ideal.
It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompasses by the following claims.
This patent application claims the benefit of U.S. Provisional Application No. 63/094,332, filed Oct. 20, 2020, the disclosure of which is incorporated herein by reference it its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63094332 | Oct 2020 | US |
