Abstract:
The present invention provides a pressure vessel for exerting pressure on a repair to a component made of composite materials to cure the repair in the field. The pressure vessel includes a body having a chamber for receiving the repair to the component; a portal operable to permit a heating element of a heater located inside the chamber to be coupled with a power source located outside the chamber to power the heating element; and a pump operable to pressurize the chamber. By pressurizing the chamber, the pressure vessel may exert pressure on a repair placed inside the chamber that exceeds 14.7 psi, and thus, provide a better cure in the field to produce a stronger repair. Furthermore, the pressure vessel may be more easily transported from one location in the field to another than an autoclave.

Description:
BACKGROUND 
   Many different devices and/or structures, such as an aileron of an airplane wing, a flap on the trailing edge of an airplane wing, and a boat hull, include components manufactured with composite materials. One of the many reasons for this is that the components may be easily contoured into complex curves, like those found in a hull or leading edge of a flap, during the manufacture of the components. Another reason is that the components may be easily repaired in the field, and thus, the time spent completing a repair may be reduced. 
   Repairing a component with composite materials typically involves laying up two or more plies of material such as metal, woven and/or non-woven carbon, fiberglass, and/or Kevlar® fibers with an adhesive and then curing the adhesive to couple the two or more plies together and to couple the plies with the remainder of the component. To provide a strong repair, the adhesive should be properly cured; otherwise the repair and/or component could prematurely fail. Properly curing most conventional adhesives includes three elements: heating the adhesive, exerting pressure on the repair—typically about 200 psi—, and applying a vacuum to the repair. Heating the adhesive changes the adhesive&#39;s molecular structure to solidify and increase the material strength of the adhesive. Exerting pressure on the repair compacts the plies to increase the strength of the interlaminate bonds and increase the distribution of adhesive throughout the repair. And applying a vacuum draws out gas that would otherwise be trapped in the repair once the adhesive solidifies to reduce the number and size of voids in the cured adhesive. Although most conventional adhesives may be cured under a variety of different pressures, in general, as the pressure increases the strength of the repair increases. 
   Unfortunately, properly curing a repair to a component in the field is difficult because the amount of pressure that may be exerted on the repair is typically equal to or less than 14.7 psi. To cure a repair in the field, a heating blanket is typically placed on the repair, and then a bag is placed over the entire repair and sealed to the component. The air between the bag and the repair is then removed to generate a vacuum and the heating blanket is turned on to generate heat. Thus, the only pressure that is typically exerted on the repair is atmospheric pressure that results from the vacuum, which is about 14.7 psi. 
   A possible solution is to design a component that will withstand the stresses and strains encountered in service with a repair that does not contribute to the component&#39;s structural integrity. But this means that the component, when manufactured, will be more robust than is required. Consequently, the cost in material to manufacture the component and the weight of the component will be more than required to meet the expected stresses and strains encountered in service. This increase in cost and especially weight can be significant, for example, in an airplane predominately made of composite materials. 
   Another possible solution is to cure the repair in an autoclave, which is typically used to cure components during their manufacture. But using an autoclave in the field is often impractical because of its size. Most conventional autoclaves are expensive to build, and thus expensive to purchase, because they are designed to perform many complimentary curing functions. For example, most autoclaves are designed to pressurize an internal chamber to about 200 psi, and thus, specifically designed to withstand this pressure. Furthermore, most autoclaves include a pump or compressor to generate this pressure, a heater to heat the atmosphere, a fan to circulate the heated atmosphere, and a system to purge gases from the atmosphere, which may be released into the chamber as the adhesive cures. Consequently, most autoclaves are large to accommodate a wide range of component sizes. 
   The size of most autoclaves makes their use in the field impractical for many reasons. One reason is that large autoclaves are difficult to move from one location in the field to another. Another reason is that large autoclaves are expensive to operate because the volume of air that must be heated and circulated within the autoclave to cure a component and/or repair to a component is large. Consequently, about the same amount of power is required to cure a repair to a small component as a repair to a large component. 
   SUMMARY 
   The present invention provides a pressure vessel for exerting pressure on a repair to a component made of composite materials to cure the repair in the field. In one aspect of the invention, the pressure vessel includes a body having a chamber for receiving the repair to the component; a portal operable to permit a heating element located inside the chamber to be coupled with a power source located outside the chamber that provides power to the heating element; and a pump operable to pressurize the chamber. By pressurizing the chamber, the pressure vessel may exert pressure on a repair placed inside the chamber that exceeds 14.7 psi, and thus provide a better cure to produce a stronger repair. The portal allows one to cure a repair with a conventional heating element, such as a heating blanket, typically found in the field. By eliminating the other components and subsystems typically found in an autoclave, such as a heater to heat the atmosphere in the autoclave and a fan to circulate the atmosphere, the manufacturing cost and the size of the vessel may be reduced. Thus, the vessel may be more easily moved from one location to another. 
   In another aspect of the invention, the portal may include an interface that may releasably couple a heating element located inside the chamber of the vessel with the power source located outside the chamber. Furthermore, the interface may be removable from the portal and replaceable with a different interface. With the interface, the vessel may be used with many different types of heaters to cure a repair in the field. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is a perspective view of a system for curing, in the field, a repair to a component made of composite material, according to an embodiment of the invention. 
       FIG. 2  is a perspective view of a pressure vessel included in the system of  FIG. 1 , according to an embodiment of the invention. 
       FIG. 3  is a cross-sectional view of a portal included in the pressure vessel of  FIG. 2 , according to an embodiment of the invention. 
       FIG. 4  is a cross-sectional view an additional portal included in the pressure vessel of  FIG. 2 , according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   The following discussion is presented to enable one skilled in the art to make and use the invention. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention as defined by the appended claims. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     FIG. 1  is a perspective view of a system  10  for curing, in the field, a repair  12  to a component  14  made of composite materials, according to an embodiment of the invention. The system  10  may also be used to cure a component (not shown) that is manufactured in the field. The system  10  includes a heater  16  to heat the repair  12  to a cure temperature—typically between about 250° F. and about 400° F. depending on the type of adhesive used in the repair at—which the adhesive (not shown) in the repair  12  will cure, and a pressure vessel  18  to exert pressure on the repair  12  as the repair  12  cures. With the pressure vessel  18 , the system  10  may cure the repair  12  with a pressure greater than 14.7 psi, for example 60 psi, to increase the strength of the repair  12  compared to the strength typically obtained when only using a vacuum bag (not shown) to exert pressure on the repair  12 . 
   The heater  16  of the system  10  includes a heating element  20 , which may be coupled with the repair  12 , to generate heat, and a power source  22  to power the heating element  20 . The pressure vessel  18  of the system  10  includes a chamber  24  to receive the repair  12  or all of the component  14  that requires the repair  12 , and a pump  26  coupled with the chamber  24  to pressurize the chamber  24  as desired. The pressure vessel  18  also includes a portal  28  to permit the power source  22  of the heater  16  to be located outside the chamber  24  while the heating element  20  heats the repair  12  inside the chamber  24 . Thus, the vessel  18  may be used with many different types of heaters  16  having different heating capacities that are or may be found in the field. Furthermore, the vessel  18  may be smaller in size than a conventional autoclave to facilitate easy transportation of the vessel  18  from one location in the field to another. 
   Still referring to  FIG. 1 , in one embodiment, the heater  16  may include a control unit  30 , for example an HCS9200B Single Zone manufactured by Heatcon® Composite Systems, to modify the amount and duration of the heat generated by the heating element  20 , and temperature sensors  32  to sense the temperature of a region of the repair  12 . The control unit  30  may be located outside the chamber  24  to protect its components from the hot, pressurized atmosphere inside the chamber  24  and may be coupled with the heating element  20  and power source  22  via the cord  34  and with the temperature sensors  32  via the wires  36 . The heating element  20  may be any desired heating element, such as a conventional heating blanket for curing composites. To permit the temperature sensors  32  to be coupled with the control unit  30  located outside the chamber  24 , the vessel  18  may include additional portals  38 . As the system  10  cures the repair  12 , the control unit  30  may monitor the temperature of the sensors  32  and may modify the power it provides the heating element  20  accordingly. 
   Still referring to  FIG. 1 , in one embodiment, the pressure vessel  18  may include a pump  26  located outside the chamber  24  and a line  40  to operatively couple the pump  26  with the chamber  24 . The pump  26  may be any desired pump, such as a conventional pump capable of moving air or any other type of gas and/or liquid into the chamber  24  to pressurize the chamber  24 . Locating the pump outside the chamber may be desirable to protect the components of the pump  26  from the hot, pressurized atmosphere inside the chamber  24 . The pump  26  may also be releasably coupled with the chamber  24  to allow the vessel to be used with many different pumps having different capacities. 
   Other embodiments of the system  10  are contemplated. For example, the control unit  30  may be coupled with the pump  26  to modify the pressure generated in the chamber  24  and may be coupled to a pressure sensor located in the chamber  24  to monitor the pressure inside the chamber  24 . In addition, the system  10  may include a vacuum source coupled with a vacuum bag that may be mounted on the repair  12  and/or the component  14  to draw out gas that would otherwise be trapped in the repair  12  once the adhesive solidifies. This may be desirable to reduce the number and size of voids in the cured adhesive. The vacuum source and bag may also exert pressure on the repair to permit a lower pressure inside the chamber  24  of the vessel  18  during a cure of the repair  12 . Furthermore, the control unit  30  may be coupled with the vacuum bag and vacuum source to monitor and accordingly modify the vacuum generated between the bag and the repair  12  and/or component  14 . In addition, the heater  16  may include more than or less than two temperature sensors  32 , and the vessel  18  may include more than one portal  28  and more than or less than two portals  38 . Also, the system  10  may include a purge sub-system to purge excessive nitrogen molecules or other molecules from the chamber  24  that may be released during a cure. Furthermore, the control unit  30  may be coupled with the purge sub-system to monitor the chamber&#39;s atmosphere and modify the operation of the purge sub-system accordingly. 
     FIG. 2  is a perspective view of the pressure vessel  18  (pump  26  omitted for clarity) included in the system  10  of  FIG. 1 , according to an embodiment of the invention. Because the vessel  18  does not include most of the components and sub-systems that most autoclaves include, the vessel  18  is significantly less expensive to build than most autoclaves. Thus, the vessel  18  may be sized and shaped as desired to facilitate its re-location in the field and reduce the amount of power required to cure a repair to a component with pressure exceeding 14.7 psi. 
   In one embodiment, the vessel  18  may include a body  42  shaped like a cylinder and having the chamber  24  sized to accommodate long and narrow parts, such as a trailing edge flap for an airplane. For example, the body  42  may include a chamber  24  having a chamber diameter substantially equal to 20 inches and a chamber length substantially equal to 60 inches. In addition, the body  42  may be made of any desirable material capable of withstanding the desired pressures and heat in the chamber  24 . For example, the body  42  may be made of a conventional metal for durability or a conventional plastic to minimize weight for mobility between different locations in the field. 
   Other embodiments of the vessel  18  are contemplated. For example, the body  42  may be shaped like a sphere to efficiently cure a small component and/or a repair to a small component and to facilitate relocation in the field. Because the vessel  18  is less expensive than most autoclaves, one may have a small vessel  18  shaped like a sphere to use when curing repair to a small component, and a large vessel  18  shaped like a cylinder to use when curing a repair to a large component. Thus, a repair to a small component may be cured with less expense than a repair to a large component. 
   Still referring to  FIG. 2 , the vessel  18  includes a portal  28  to permit the power source  22  ( FIG. 1 ) of the heater  16  ( FIG. 1 ) to be located outside the chamber  24  while the heating element  20  ( FIG. 1 ) heats the repair  12  ( FIG. 1 ) inside the chamber  24 . The portal  28  may be located anywhere on the body  42  as desired. In one embodiment, the portal  28  may be located close to an end of the body  42  and may include an interface  44  to couple, releasably or not, the heating element  20  with the power source  22 . The interface  44  may include a mount  46  to mount the interface  44  to a receiver  48  of the body  42 , and a coupler  50  (discussed in greater detail in conjunction with  FIG. 3 ) to couple the power source  22  with the heating element  20 . The mount  46  may be removable from the receiver  48 , as desired, to allow one to remove the interface  44  and replace it with a different interface. This may be desirable to allow different heating elements to be coupled with different power sources. 
   Other embodiments are contemplated. For example, the interface  44  may include a coupler to also couple additional devices located inside the chamber  24  with other devices located outside the chamber  24 , such as the temperature sensors  32  ( FIG. 1 ) with the control unit  30  ( FIG. 1 ). 
   Still referring to  FIG. 2 , the vessel  18  may also include additional portals  38  to permit communication between a device located inside the chamber  24  and another device located outside the chamber  24 . In one embodiment, the vessel  18  may include a first portal  28 , and second and third portals  38  to permit temperature sensors  32  located inside the chamber  24  to be coupled with the control unit  22  located outside the chamber  24 . The second and third portals  38  may be located anywhere on the body  42  as desired and may include a second and third interface  43 , respectively, (discussed in greater detail in conjunction with  FIG. 4 ) to couple the sensors  32  with the control unit  22 . 
   Still referring to  FIG. 2 , the vessel  18  also includes an entry  52  to permit the insertion of the repair  12  to the component  14  into the chamber  24  to be cured. In one embodiment, the entry  52  may include a door  54  hingedly coupled with the body  42  to close the entry  52 , and thus maintain the desired pressure in the chamber  24 , while the repair  12  cures. 
     FIG. 3  is a cross-sectional view of the portal  28  included in the pressure vessel  18  of  FIG. 2 , according to an embodiment of the invention. To allow the vessel  18  to be used with many different combinations of heating elements and power sources as desired, the interface  44  of the portal  28  is removable and replaceable with another interface having a different coupler. 
   In one embodiment, the interface  44  may include the mount  46 , which may be releasably mounted to the receiver  48  of the body  42  ( FIG. 2 ) using any desired fastening technique. For example, nuts  56  may be threadingly coupled with bolts  58  to couple the mount  46  with the receiver  48 . The interface  44  may also include the coupler  50  having a three-pronged plug  60  to couple the heating element  20  ( FIG. 1 ) with a single phase, standard voltage power source that includes an electrical ground. If a different heating element  20  and/or different power source  22  is desired then one removes the interface  44  from the body  42  and mounts a different interface  44  having a different coupler  50 . For example, the only available power source may provide high voltage, three-phase power. To be able to use power from this power source, a different heating element may be required which may require a different coupler. 
   Other embodiments are contemplated. For example, the coupler  50  may be removable from the interface  44  and replaceable with a different coupler  50 . 
     FIG. 4  is a cross-sectional view an additional portal  38  included in the pressure vessel of  FIG. 2 , according to an embodiment of the invention. To allow the vessel  18  to be used with any desired additional devices and/or sub-systems for curing a repair to a component, the additional portal  38  includes a coupler  62  that may be removable from the body  42  and replaceable with another, different coupler  62 . In one embodiment, the coupler  62  includes a double-pronged plug  64  to couple, releasably or not, the temperature sensor  32  ( FIG. 1 ) with the control unit  22  ( FIG. 1 ), and external threads  66  sized to correspond with internal threads  68  to removably fasten the coupler  62  with the body  42 .