Abstract:
A mandrel ( 20, 30 ) defines a void geometry in a layup for a blade shell ( 73 ) via a rigid mandrel core ( 22, 32 ) and a plurality of expandable bladders ( 24 A-F,  34 A-F) attached adjacently to each other in sequence around a periphery of the core, forming an expandable outer cover on the mandrel. The bladders are controllably expandable ( 50, 50 B,  60 ) individually or in proper subsets of all the bladders to adjust pressure distribution and mandrel position within the layup after closing a blade shell mold over the layup. The bladders may be transversely partitioned ( 104 ) at multiple spanwise (S) positions along the mandrel in order to define additional sets of adjustable bladders along the span of the mandrel.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to fabrication of wind turbine blades, and particularly to mandrels for layup of fabric for curing in a blade mold. 
       BACKGROUND OF THE INVENTION 
       [0002]    In prior wind turbine blade fabrication, fiber layers such as glass or carbon fabric are laid in a horizontally oriented suction-side mold. Mandrels representing the internal void geometry of the blade are placed on this suction side layup. The fabric is then wrapped around the leading edge and pressure side of the mandrel to meet itself at the trailing edge. This makes a closed C-shaped layup with one seam at the trailing edge. A pressure side mold cover is then closed over the layup. The fabric is infused with a matrix material such as epoxy or thermosetting polymer before or after the layup steps and closing of the mold. The mandrels may be inflatable or solid, or they may have a rigid core covered with a compressible material such as foam to press the layup against the interior surfaces of the mold, as taught for example in U.S. Pat. No. 8,007,624 B2, incorporated by reference herein. 
         [0003]    However, the mandrel may shift position while the layup is being placed on it or while the mold is closing. This occurs mostly in areas of high curvature, resulting in wrinkles and areas of enriched resin, both of which degrade structural integrity and must be repaired after the blade is removed from the mold. If the mandrel shifts too much, it can become stuck inside the blade. Mandrel shifting is possible, in part, because the air in the inflatable or foam parts can shift peripherally and/or diagonally to other locations of the mandrel cross-section. This allows the mandrel shape to be insufficiently maintained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The invention is explained in the following description in view of the drawings that show: 
           [0005]      FIG. 1  is a transverse sectional view of forward and aft mandrels covered with adjacent inflatable bladders illustrating aspects of an embodiment of the invention. 
           [0006]      FIG. 2  is a transverse sectional view of a wind turbine blade being fabricated in a mold with the mandrels of  FIG. 1 . 
           [0007]      FIG. 3  is an enlarged sectional partial view of a mandrel, showing bridge plates between inflatable bladders. 
           [0008]      FIG. 4  is a schematic diagram of a control system with an individually actuated gas flow valve for each inflatable bladder. 
           [0009]      FIG. 5  schematically shows a gang valve with multiple distribution tubes to provide air to the inflatable bladders. 
           [0010]      FIG. 6  shows a mandrel embodiment with a rigid tubular core covered by individually partitioned resilient foam-filled bladders. 
           [0011]      FIG. 7  schematically shows a system that controls the individual inflation condition of each foam-filled bladder in the mandrel embodiment of  FIG. 6 . 
           [0012]      FIG. 8  is a transverse sectional view of an exemplary blade shell formed by the mandrel embodiments herein. 
           [0013]      FIG. 9  illustrates aspects of a method of the invention. 
           [0014]      FIG. 10  is sectional plan view of a wind turbine blade shell with mandrels. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  is a transverse sectional view of forward  20  and aft  30  mandrels covered with adjacent inflatable bladders  24 A-F and  34 A-F. Each mandrel has a substantially rigid core  22 ,  32 , which may be solid or tubular. The bladders are individually partitioned around a periphery of the core. For example the forward core  22  may have a leading edge bladder  24 A, a forward suction side bladder  24 B, a forward suction side spar cap bladder  24 C, a bladder  24 D for the forward side of the spar webbing, a forward pressure side spar cap bladder  24 E, and a forward pressure side bladder  24 F. Bladders around the aft mandrel  32  may include a bladder  34 A for an aft side of the spar webbing, an aft suction side spar cap bladder  34 B, an aft suction side bladder  34 C, a trailing edge bladder  34 D, an aft pressure side bladder  34 E, and an aft pressure side spar cap bladder  34 F. The bladders may be individually valved such that air cannot shift among them at a given stage, such as during a closing of the mold, thus preventing shifting of the mandrels. The bladders may further be individually pressure controlled to adjust the position of the mandrels and the distribution of normal pressure of the bladders against the interior of the blade shell layups. This maintains the shape and position of the mandrel. 
         [0016]      FIG. 2  shows the mandrels of  FIG. 1  wrapped in a blade shell fabric layup SS, PS and enclosed in a mold  40  with lower and upper parts  40 A,  40 B. The mandrels in this embodiment are spaced from each other chordwise and may be substantially parallel to provide room for blade spar webbing  42  between the suction side SS and pressure side PS of the blade shell. 
         [0017]      FIG. 3  is an enlarge sectional partial view of mandrel  20 , showing a rigid bridge plate  44 A between inflatable bladders  24 D and  24 E, and a bridge plate  44 B between inflatable bladders  24 E and  24 F. These bridge plates are shaped to provide smooth transitions between the bladders to avoid imprinting ridges in the layup and to accurately define respective portions of the interior surface of the shell. The bridge plates may be attached to the inflatable bladders directly or to a flexible sheet that is attached to the outer surface of the bladders. The outer surfaces of the bladders, bridge plates, and sheet may be coated with adhesion resistant material such as polytetrafluoroethylene. 
         [0018]      FIG. 4  is a schematic diagram of a control system  50  with an individually actuated gas flow valve  52 A-F for each respective inflatable bladder  24 A-F. The valves are controlled by a controller  54  to expand the bladders with compressed air  55  or other gas or to contract the bladders with a vacuum  56 . The valves may be operated both in unison and individually to adjust inflation rates and pressures in the bladders  24 A-F. This provides fine control of the mandrel shape, position, and outward pressure. 
         [0019]      FIG. 5  schematically shows an alternative control system embodied as a gang valve  60  with an air inlet/outlet  62 , multiple air distribution tubes  63 - 68 , and a valve cylinder  61 , which may be rotated manually or automatically by a lever  70 . This arrangement provides equal air pressure to all of the inflatable bladders. Optionally, each distribution inlet  72  or outlet  74  may be individually metered to provide substantially equal fill rates for inflatable bladders of different volumes. When the cylinder  61  is rotated 90 degrees, all distribution tubes  63 - 68  are closed. This prevents shifting of air from one bladder to another. For air removal, the valve  60  may be opened, and a vacuum pump may operate on the inlet/outlet  62 . 
         [0020]      FIG. 6  shows a mandrel embodiment  20 B with a rigid tubular core  22 B covered by multiple individually partitioned foam-filled bladders  71 D-F containing a resilient foam such as open-cell polyurethane or polyester foam. An air distribution tube  63 - 68  ( FIG. 5 ) may be provided to each bladder for individual pressure control, but such tubes are not needed in this embodiment. Instead, each bladder may be simply provided with a controllable air valve  52 D,  52 E to the interior  75  of the mandrel. The foam may provide sufficient inflation force so that only an air inlet  79  is needed instead of compressed air. The bladders may be deflated by providing a vacuum in the interior  75  of the mandrel tube  22 B. The foam provides a self-limiting inflated shape of the bladders, and expanded by opening an air inlet valve.  FIG. 7  schematically shows a control system embodiment  50 B that controls the expansion of each foam-filled bladder individually in the mandrel embodiment  20 B of  FIG. 6 . 
         [0021]      FIG. 8  is a transverse sectional view of a an exemplary blade shell  73  formed by the mandrel embodiments herein, the shell having a leading edge LE, trailing edge TE, suction side SS, pressure side PS, and chord CL. A web  42  between the suction side and the pressure side forms an I-beam spar. Flanges or end caps  77  for the spar may be formed of additional layers or thickness on the pressure and suction sides and filleted with the web  42 . 
         [0022]      FIG. 9  illustrates aspects of a method  80  of the invention, comprising the steps: 
         [0023]      81 —Open the mold; 
         [0024]      82 —Layup the suction side of the blade shell in the bottom half of the mold; 
         [0025]      83 —Place the mandrels on the suction side layup and position a vertical layup for the spar webbing between the mandrels; 
         [0026]      84 —Expand a first proper subset of the bladders, such as the lower and middle champers  24 A-D and  34 A-D; 
         [0027]      85 —Layup the pressure side of the blade shell on the mandrels; 
         [0028]      86 —close the blade mold; 
         [0029]      87 —Expand the remaining bladders, such as the upper bladders  24 E-F and  34 E-F, and adjust the distribution of pressures; 
         [0030]      88 —Cure the blade shell; 
         [0031]      89 —Contract the bladders; 
         [0032]      90 —Open the mold; and 
         [0033]      91 —Remove the mandrels from the blade shell. 
         [0034]    The fabric layup may be pre-impregnated with a matrix material, or impregnated after closing the mold. One example of the latter method is described in U.S. Pat. No. 8,007,624. 
         [0035]      FIG. 10  is sectional plan view of a wind turbine blade shell with a leading edge LE, trailing edge TE, root  100 , tip  102 , span S, and spar web  42 . Forward and aft mandrel cores  22 ,  32  are positioned on opposite sides of the web  42 . The inflatable bladders may be partitioned  104  transversely at multiple positions along the span S of the blade shell in addition to the previously shown partitioning around the perimeter of the core as seen in a transverse section. Each transverse partition  104  may bound and define another set of bladders such as  24 A-F and  34 A-F of  FIG. 1  around the periphery of the core with further valves thereof for additional control of pressure distribution and mandrel position. Optionally an additional mandrel core  106  may be provided in the shoulder of the blade. The rigid cores of the mandrels may be sized to fit through the root  100  for extraction after deflation or contraction of the bladders. 
         [0036]    The expansion and contraction of the bladders herein may be controllable individually or in selectable proper subsets to adjust the position of the mandrel and the distribution of pressure on the blade shell layup. 
         [0037]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. The figures are exemplary and should not be interpreted as limiting. For example, the present invention is not limited to the blade designs having one reinforcing web, but may also be applied to blade shells having any number (or no) reinforcing webs, I-beams, box beams, etc., with the appropriate number of mandrels being used for each such design. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.