Abstract:
The present invention relates to a pressure application device for curing an adhesive on a component, particularly components of complex geometries. The device comprises a pair of jaws, at least one spring recessed into a cavity defined within the first jaw, and a cap. A first end of a spring partially extends into the cavity and a second end of the spring contacts the cap. When force is applied to the cap, the cap transmits the force through the spring to the first jaw. In order to limit the separation of the cap from the first jaw, a retainer is used.

Description:
STATEMENT OF GOVERNMENT INTEREST 
       [0001]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of N00019-02-C-3003 awarded by the United States Navy. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to devices used to adhesively bond gas turbine components. Gas turbine components can have very intricate geometries that sometimes require composite pieces to be adhered together in order to form the gas turbine component. In order to cure the adhesive, a desired pressure needs to be applied to the composite pieces. Elevated temperatures also may be used in order to cure the adhesive. 
         [0003]    Fixturing devices using mechanical tooling are often used to apply pressure to composite materials in order to cure an adhesive under desired conditions. However, in some applications, this curing process sometimes requires applying a specific, known pressure to the composite materials. Such devices may not be designed to adequately accommodate the temperatures needed to thermally cure the particular adhesive. Additionally, these fixturing devices may be bulky and cumbersome to use, and may be too large to use in certain applications. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    The present invention relates to a pressure application device for curing an adhesive on a component, particularly components of complex geometries. The device comprises a pair of jaws, at least one spring recessed into a cavity defined within the first jaw, and a cap. A first end of a spring partially extends into the cavity and a second end of the spring contacts the cap. When force is applied to the cap, the cap transmits the force through the spring to the first jaw. In order to limit the separation of the cap from the first jaw, a retainer is used. Besides curing the adhesive with pressure, the pressure application device can be placed into an oven to thermally cure the adhesive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is an exploded perspective view of a fan inlet case. 
           [0006]      FIG. 2  is a top view of a pressure application device. 
           [0007]      FIG. 3  is a side view of the pressure application device. 
           [0008]      FIG. 4  is a front view of the pressure application device. 
           [0009]      FIG. 5  is a perspective view of a disassembled portion of the pressure application device. 
           [0010]      FIGS. 6A-6C  are cross-sectional views of alternative spring arrangements for use with the pressure application device. 
           [0011]      FIGS. 7A and 7B  are cross-sectional views of the pressure application device and a workpiece before and after application of force. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    As shown in  FIG. 1 , a fan inlet case  10  has an outer hub  12 , an inner hub  14 , and a plurality of struts  16  extending therebetween. Struts  16  can each be covered with a fairing  18  having an inside surface  22  and an outside surface  24 . Each strut  16  has an outer surface  26 . Inside surface  22  of fairing  18  is attached to outside surface  24  of strut  16  using an adhesive  28 , such as an adhesive of the type described in commonly-assigned U.S. application Ser. No. 11/494,830. Generally, in order for adhesive  28  to cure, it must be subjected to pressure and heat. Furthermore, the strict geometric limitations of fan inlet case  10  make it difficult to apply pressure to fairing  18  in order for adhesive  28  to cure and secure fairing  18  to strut  16 . 
         [0013]    As shown in  FIG. 2 , pressure application device  30  includes clamps  32  and  34 , a first jaw  36 , a second jaw  38 , and a cap  40 . First jaw  36  and second jaw  38  apply pressure to the workpiece, in particular fairing  18 . In order for the first jaw  36  and second jaw  38  to apply pressure to the workpiece, a force applicator applies force to cap  40 . The force applicator can be a mechanical device, such as vices and clamps, or hydraulic or pneumatic devices (e.g., pressure cylinders). In the illustrated embodiment, clamps  32  and  34  are each threadably-adjustable cantilever C-clamps. Clamps  32  and  34  are positioned on cap  40  and second jaw  38  to apply a force to cap  40 . When this force is applied to cap  40 , cap  40  transmits the force through a spring mechanism (shown in  FIG. 5  and described in detail later in this description) located between cap  40  and first jaw  38  to apply a controlled amount of pressure to the workpiece. The force transmitted to first jaw  38  is a function of the distance cap  40  moves toward first jaw  38  and the spring constant of the spring mechanism. 
         [0014]    First jaw  36  has a front side  46  and a back side  48 , and second jaw  38  has a front side  52  and a back side  54 . First jaw  36  and second jaw  38  are configured so that pressure application device  30  can fit within the tight geometrical restrictions of mounting locations of a component, such as fan inlet case  10 , when the adjacent struts are occupied by clamps. In order to meet these geometrical restrictions, the overall width of first jaw  36  (measured between front side  46  and back side  48 ) can be between about 0.64 cm (0.25 inch) and 2.54 cm (1 inches). Portions of first jaw  36  and second jaw  38  can be tapered as shown in the illustrated embodiment to reduce widths in selected areas, in order to further accommodate placement of device  30  in geometrically restricted areas (e.g., between struts  16  near inner hub  14  of inlet case  10 ). First jaw  36  can be made from stainless steel, titanium, aluminum or other metallic materials. In the present embodiment, first jaw  36  and second jaw  38  are substantially rectangular members, although depending on the desired pressure profile they can have various other shapes. 
         [0015]    Front sides  46 ,  52  of jaws  36 ,  38  each form a clamping surface. Front sides  46 ,  52  can include a layer of material, such as an elastomer, silicone or other polymer, to create a soft face in order to not damage fairing  18  or other workpieces when pressure is applied. 
         [0016]    In the illustrated embodiment, first jaw  36  is connected to second jaw  38  by support pieces  56 ,  58  and shoulder bolts  62 ,  64 ,  66 ,  68 . Support pieces  56 ,  58  each have holes  72 ,  74 ,  76 ,  78  where shoulder bolts  62 ,  64 ,  66 ,  68  are inserted. Holes  72 ,  74 ,  76 ,  78  are elongated slots so that the spacing between first jaw  36  and second jaw  38  can be regulated. Support pieces  56 ,  58  can have notches  82 ,  84  to allow the workpiece to be inserted between first jaw  36  and second jaw  38  with enough clearance. 
         [0017]    Cap  40  surrounds first jaw  36 . In the illustrated embodiment, cap  40  is positioned between support piece  56  and support piece  58 . As shown in  FIG. 3 , cap  40  is a C-shaped or U-shaped cap that covers back side  48  of first jaw  36 . A first end  86  of clamp  32  is adjacent cap  40  and a second end  88  of clamp  32  is adjacent the back side  54  of second jaw  38 . First jaw  36  is connected to second jaw  38  by support pieces  56 ,  58  and shoulder bolts  62 ,  64 ,  66 ,  68 . When pressure is to be applied to the workpiece, clamps  32 ,  34  apply a force to cap  40  and to back side  54  of second jaw  38 . When this force is applied to cap  40 , cap  40  transmits the force through a spring mechanism (shown in  FIG. 5  and described in detail later in this description) located between cap  40  and first jaw  38  to apply a controlled amount of pressure to the workpiece. As this force is applied to cap  40 , first jaw  36  moves relative to second jaw  38 . The movement of first jaw  36  relative to second jaw  38  is controlled by support pieces  56 ,  58 . 
         [0018]    As shown in  FIG. 4 , pressure device  30  also has retainers  90 ,  91  that are comprised of alignment rods  92 ,  94  and disc members  96 ,  98 . Each disc member  96 ,  98  is positioned onto an end of each alignment rod  92 ,  94 . Disc members  96 ,  98  and alignment rods  92 ,  94  could be a single piece, such as a bolt or other fasteners. However, disc members  96 ,  98  can also be adjustable along alignment rods  92 ,  94 . For example, disc members  96 ,  98  can be threaded rings (e.g., nuts) and alignment rods can be threaded rods (e.g., bolts). Retainers  90 ,  91  limit separation of cap  40  from first jaw  36 . Furthermore, when no force is applied to cap  40 , cap  40  abuts disc members  96 ,  98  of retainers  90 ,  91 . 
         [0019]    As shown in  FIG. 5 , each pressure transferring assembly is comprised of clamp  34 , first jaw  36 , cap  40 , alignment rod  94 , disc member  98 , and spring  102 . Spring  102  can comprise a plurality of springs that can be arranged in series, in parallel or in combinations thereof to achieve various pressure profiles. Springs  102  can be disc springs, coil springs, leaf springs, or other types of springs. In the illustrated embodiment, springs  102  are disc springs, which have a relatively low profile that helps reduce the overall thickness of the device  30 . First jaw  36  has cavity  104 , and springs  102  are inserted into cavity  104 . By recessing springs  102  inside cavity  104 , the overall thickness of pressure device  30  is significantly reduced. Cap  40  has a hole  106 , and alignment rod  94  is inserted through hole  106  and into cavity  104 . When inserted into cavity  104 , alignment rod  94  is surrounded by spring  102 . First jaw  36  also has a hole  108  wherein the shoulder bolt  68  can be inserted through the hole  78  in the support piece  58  and secured in first jaw  36 . 
         [0020]      FIGS. 6A-6C  are cross-sectional views of alternative spring arrangements for use with the pressure application device  30 . As shown in  FIG. 6A , a first disc spring  102   a  provides a maximum spring travel x and a maximum spring force y. Value of the maximum spring travel x and maximum spring force y are a function of mechanical properties of the spring  102   a , and a suitable commercially-available disc springs can be selected to match the values desired for a particular application. If a first disc spring  102   a  is put in series with a second disc spring  102   b  both having identical spring properties, as shown in  FIG. 6B , the maximum spring travel x will remain essentially constant while the maximum spring force will be 2y. However, if first disc spring  102   a  is put in parallel with second disc spring  102   b , as shown in  FIG. 6C , the maximum spring travel will be 2x, while the maximum spring force will remain y. Therefore, depending on how springs  102  are arranged inside cavity  104 , different amounts of force can be applied to first jaw  36  and thus different amounts of pressure can be applied to fairing  18  in order to cure adhesive  28 . Additional disc springs  102  can be utilized together in serial and/or parallel in order to achieve desired travel and force parameters. The use of springs allows a regulation of applied force, as explained further below. 
         [0021]      FIGS. 7A and 7B  are cross-sectional views of the pressure application device  30  and a portion of the inlet case  10  before and after application of force, respectively. As shown in  FIG. 7A , when pressure assemblies of the pressure application device  30  are at rest and no force is applied to cap  40 , cap  40  rests against disc member  98 . When force is applied to cap  40 , as shown in  FIG. 7B , gap  110  is created. Gap  110  is measurable and can be calibrated to the force applied to front side  46  of first jaw  36 . Thus, a specific, known amount of force can be transferred to fairing  18  in order to cure adhesive  28  and adhere fairing  18  to strut  16 . If disc member  98  is fixed on alignment rod  94 , gap  110  may be adjusted by using a new disc member  98  and a new alignment rod  94  or if threaded, by adjusting the length of the alignment rod  94 . If disc member  98  is adjustable on alignment rod  94 , gap  110  may be calibrated by adjusting disc member  98  relative to the cap  40  when it is at rest. Besides calibrating gap  110 , the force applied to the front side  46  of first jaw  36  can also be adjusted by changing the arrangement of springs  102  depending on the desired pressure profile as discussed previously. By combining springs  102  in various combinations of series and parallel arrangements, a desired maximum force can be applied and a known spring travel can be used to determine a desired size of gap  110 . 
         [0022]    Pressure application device  30  can have more than two pressure transferring assemblies located along first jaw  36 . As mentioned earlier, a pressure transferring assembly comprises clamp  34 , first jaw  36 , cap  40 , retainer  90 , and spring  102 . Pressure application device  30  can also have multiple caps  40  along first jaw  36 , each cap  40  having at least two pressure transferring assemblies. 
         [0023]    In one embodiment, pressure application device  30  is configured to apply a maximum pressure between about 0 N/mm 2  (0 psi) and 6.90 N/mm 2  (1000 psi) to a surface (e.g., to the fairing  18 ), preferably between about 0.345 N/mm 2  (50 psi) and 1.38 N/mm 2  (200 psi). Pressure application device  30  also can operate during the thermal cure cycle of the adhesive  28  at temperatures between about −17.8° C. (0° F.) and 232° C. (450° F.), preferably between room temperature (about 22° C. (72° F.)) and about 148° C. (350° F.), but could operate at temperatures greater than about 232° C. (450° F.) with a limited life. 
         [0024]    It is possible to place pressure application device  30  into an oven (not shown) or other high temperature environment along with components being adhered (e.g., fan inlet case  10 ) in order to simultaneously apply pressure and heat to cure adhesive  28 . Simple mechanical clamps alone, like prior art C-clamps, would generally not provide precise, controllable levels of force when placed in a high temperature environment, but rather would tend to vary the applied force due to thermal expansion of the clamps and/or workpiece. Moreover, the use of force sensing equipment in a high temperature environment like an oven would be difficult, and sensing equipment that could survive the high temperature environment tends to be cost-prohibitive. Pressure application device  30  utilizes springs  102  to regulate applied force while still allowing consistent performance in high temperature environments and a relatively compact overall size. 
         [0025]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the particular type and arrangement of springs used to regulate applied force can vary as desired for particular applications.