Abstract:
A method of manufacturing a composite tower, includes at least partially filling a form with a curable resin; at least partially curing the resin in the form; raising the form partly over the at least partially cured resin; and at least partially filling the raised form with more curable resin applied against the cured resin.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The subject matter disclosed here is generally related to commonly-owned, copending U.S. patent application Ser. No. 12/109,463 (Attorney Docket No. 229348) for “A Composite Wind Turbine Tower and a Method for Fabricating Same” filed on Apr. 25, 2008 and U.S. patent application Ser. No. 12/038,471 (Attorney Docket No. 227235) for “Composite Wind Turbine Tower” filed on Feb. 27, 2008, each of which is incorporated by reference here. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The subject matter described here generally relates to wind turbine tower structures and methods of forming composite wind turbine tower structures. 
         [0004]    2. Related Art 
         [0005]    A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by the machinery, such as to pump water or to grind wheat, then the wind turbine may be referred to as a windmill. Similarly, if the mechanical energy is converted to electricity, then the machine may also be referred to as a wind generator or wind power plant. 
         [0006]    Wind turbines are typically categorized according to the vertical or horizontal axis about which the blades rotate. One so-called horizontal-axis wind generator is schematically illustrated in  FIG. 1  and available from General Electric Company. This particular configuration for a wind turbine  2  includes a tower  4  supporting a nacelle  6  enclosing a drive train  8 . The blades  10  are arranged on a hub  9  to form a “rotor” at one end of the drive train  8  outside of the nacelle  6 . The rotating blades  10  drive a gearbox  12  connected to an electrical generator  14  at the other end of the drive train  8  arranged inside the nacelle  6  along with a control system  16  that receives input from an anemometer  18 . 
         [0007]    As the size of blades  10  has increased, so has size of the towers  4 . Current wind turbine towers  4  are typically fabricated from steel sheets that are manufactured at a remote location and then assembled at the site of the turbine  2 . However, these materials are often difficult and expensive to manufacture, transport, and assemble. While using composite material can reduce the weight and transportation costs for the components of the tower  4 , conventional techniques often still require transportation of multiple pieces that must then be joined together at an outdoor construction site. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    These and other drawbacks associated with such conventional approaches are addressed here in by providing, in various embodiments, a method of manufacturing a composite tower including at least partially filling a form with a curable resin; at least partially curing the resin in the form; raising the form partly over the at least partially cured resin; and at least partially filling the raised form with more curable resin applied against the cured resin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various aspects of this technology will now be described with reference to the following figures (“FIGs.”) which are not necessarily drawn to scale, but use the same reference numerals to designate corresponding parts throughout each of the several views. 
           [0010]      FIG. 1  is a schematic side view of a conventional wind generator. 
           [0011]      FIG. 2  is a schematic cross-sectional view of a system for vertical manufacturing of the wind turbine tower shown in  FIG. 1 . 
           [0012]      FIG. 3  is a schematic diagram of a reinforcing system for the system shown in  FIG. 2 . 
           [0013]      FIG. 4  is a schematic view of a reinforcing arrangement for the system shown in  FIG. 2 . 
           [0014]      FIG. 5  is a schematic view of another reinforcing arrangement for the system shown in  FIG. 2 . 
           [0015]      FIG. 6  is a schematic view of yet another reinforcing arrangement for the system shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 2  is a schematic cross-sectional view of one embodiment of a system  20  for vertical manufacturing of the wind turbine tower  4  shown in  FIG. 1 , or any other tower. Although the illustrated tower  4  has a substantial circular cross-section with decreasing diameter in the vertical direction, other tow cross-sections may also be used including elliptical and/or polygonal. 
         [0017]    The vertical manufacturing system  20  includes a form or collar  22  that is raised as lower portions of the tower  4  are formed. The form  22  may be annular extending fully or partially around the tower  4 . In the example shown here, the form  22  is connected to a chain or cable  24  by a releasable fastener  26  such as a hook or clasp. The cable  24  extends over one or more pulleys  28  and/or other tackle on support structures  29  to a winch  30  where the cable is wound in order to raise the form  22 . The system  20  may therefore be referred to as “self-jack-up collar.” However, various other techniques may also be used to raise and/or lower the form  22 . Each new layer of resin may be about one-half to one foot tall. An optional cover  23  may be provided to protect the interior of the tower  4  from the environment during fabrication, and allow interior placement of production materials. 
         [0018]    A resin supply  22  provides resin and any optional reinforcing material to the trough  34  formed between the inner and out walls of the form  22 . For example, the resin may be pumped through a hose from the ground. Suitable resin matrix materials may include, but are not limited to, polyester, polyvinyl, epoxy or any other matrix suitable for formation of composite material. 
         [0019]    In an initial position, the bottom of the form  22  will be resting on a foundation as it is filled with resin. Various sealing techniques may be used to prevent the resin from leaking from the form  22  if necessary. For example, the bottom of the form  22  may be provided with a permanent or disposable rubber skirt that secures tightly against lower portions of the tower  4 . Alternatively, or in addition, the walls of the form  22  may provide a surface against which a wet or dray lay-up process is used to form the tower  4 . 
         [0020]    The resin is allowed to cure, or partially cure before the form  22  is raised to a new position. For example, an energy source  36  such as an infrared red or ultra violet radiation may be provided to promote the curing process. Once the resin is cured, or partially cured, and the formed  22  is raised to a new position, then the process is repeated. In this way, the tower  4  is gradually built up in a series of relatively thin layers resting upon previous layers. 
         [0021]    Various techniques may be used to provide reinforcement to the tower  4  in order to enhance bending strength and/or stiffness of the resin matrix. As illustrated in  FIG. 3 , one or more rib rings  38  may be arranged in the trough  34 . For example, a ring  38  may be secured to the form  22  while the resin cures or partially cures. Two or more of the rings  38  may also be connected or otherwise joined with axial supports, such as axial windings  40 . Although only two axial windings  40  are shown in  FIG. 3 , any number of windings may also be provided and they may extend around the rings  38 . One of the joined rings  38  may be submerged into the resin-filled trough  34  with the other ring arranged above the trough  34  for receiving axial windings  40  for the next ring when the form  22  is moved upward. 
         [0022]    As illustrated in  FIG. 4 , vertical protrusions  42  may extend from the wall of the tower  4  into the trough  34  to provide axial reinforcement. As illustrated in  FIG. 5 , the protrusions  42  may act as a mandrel  44  around which reinforcing fibers  44  may be wound. Alternatively, or in addition, the inner wall of the trough  34  may provide a suitable mandrel for winding the fibers  44 . In this regard, the form  22  may also be provided with various rotational capabilities in order to facilitate winding of the fibers  44 . Alternatively, or in addition, a short mandrel (not shown) may be provided in the trough  34  in against which the fibers  44  may be wound. The form  22  may be also provided with multiple walls that act as both the mandrel for the fiber winding process and resin solidification mold. A fiber pre-form may also be used in the trough  44 . 
         [0023]    As discussed in commonly-owned, copending U.S. patent application Ser. No. 12/038,471 (Attorney Docket No. 227235) for “Composite Wind Turbine Tower” filed on Feb. 27, 2008, the fibers  44  may include longitudinal fibers and hoop-wise fibers. Alternatively, or in addition, a tape  46  may be wound around the tower  4  as illustrated in  FIG. 6 . The axial windings  40 , vertical protrusions  42 , fibers  44 , and/or tape  46  may be natural or man-made fibers, such as glass fibers, carbon fibers, metal fibers or any other fibers suitable for forming a composite material. The tape  46  may be fabric tape with a high axial orientation. The number of windings  40 , protrusions  42 , and fibers  44  is not limited and may include any number and any density suitable for providing a suitable strong composite material. 
         [0024]    The technology describe above offers a various advantages over conventional approaches. For example, the vertical manufacturing system  20  allows the tower  4  to be formed as a contiguous body, rather than in multiple sections. One-piece construction substantially reduces the cost of the tower by eliminating the need for intra-section flanges and the attended bolt torque maintenance. The system  20  provides for the use of composite materials while avoiding the costly logistics associated with transporting tower sections from factory locations and providing significant on-site manufacturing facilities 
         [0025]    It should be emphasized that the embodiments described above, and particularly any “preferred” embodiments, are merely examples of various implementations that have been set forth here to provide a clear understanding of various aspects of this technology. One of ordinary skill will be able to alter many of these embodiments without substantially departing from scope of protection defined solely by the proper construction of the following claims.