Abstract:
A method of fabricating a wind turbine blade tubular spar, wherein the tubular spar extends along a designated axis, is made of reinforced polymer material having fibers arranged in at least two directions, and a polymer matrix incorporating the fibers, and has two caps and two webs; the method including the steps of: molding and cross-linking at least part of a cap or web in composite material; molding and cross-linking an L-shaped structure, which has two opposite parallel flanges, and at least partly incorporates the previously molded, cross-linked cap or web of composite material; repeating the above steps to mold and cross-link a further L-shaped structure; and joining the two cross-linked, L-shaped structures, with the flanges positioned facing in pairs.

Description:
PRIORITY CLAIM 
       [0001]    This application is a national stage application of PCT/IB2011/054314, filed on Sep. 30, 2011, which claims the benefit of and priority to Italian Patent Application No. MI2010A 001796, filed on Sep. 30, 2010, the entire contents of which are each incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    Certain known wind turbine blades comprise a root connecting the blade to the hub; a supporting frame connected to the root; and a shell defining the blade section and fitted to the frame. 
         [0003]    Wind turbine blades can span considerable lengths, and are subjected to severe stress by the wind, which is transmitted from the shell to the frame, and which the frame is specially designed to withstand. 
         [0004]    As shown in U.S. Published Patent Application No. 2009/0136355 A1 and U.S. Published Patent Application No. 2010/0068065 A1, the supporting frame substantially comprises a tubular, substantially rectangular-section spar comprising two opposite parallel caps connected to the shell, and two opposite parallel webs, and which may vary in cross section from the root to the free end of the blade. The caps are positioned directly contacting the shell, may sometimes even form part of the shell and the blade section, and are subjected to bending stress; whereas the webs are subjected mainly to shear stress. 
         [0005]    The tubular spar and the shell are made of extremely strong, lightweight plastic reinforced with glass fibers (GFRP), carbon fibers (CFRP), or fibers of other suitable material. And known fabricating methods, as described for example in PCT Patent Application No. WO 2009/153341, PCT Patent Application No. WO 2009/153342 and PCT Patent Application No. WO 2009/153343, comprise molding and cross-linking the two caps and webs; and mainly gluing the caps to the webs to form a tubular spar. 
         [0006]    An alternative method is to mold and cross-link two U-shaped members, and glue them together, as described in U.S. Published Patent Application No. 2005/0214122. This solution has the drawback of producing webs with a break along the centreline, and of not allowing use, along the webs, of fibers parallel to the tubular spar axis, thus reducing the structural strength of the webs. 
         [0007]    Another tubular spar fabricating method, described in PCT Patent Application No. WO 2010/037762, comprises molding two non-cross-linked L-shaped members, in which three preformed members, some made of non-cross-linked polymers, are embedded in a fiber-reinforced polymer matrix; and gluing the two non-cross-linked L-shaped members together to form a tubular spar. This method involves using two adjacent molds, and simultaneously cross-linking the non-cross-linked preformed members embedded in the L-shaped members, the L-shaped structures themselves, and the glue between the L-shaped structures. 
         [0008]    Cross-linking in two adjacent molds forming a closed chamber is a complicated job, and, because of the heat liberated, simultaneously cross-linking the polymer matrix and glue calls for complex, high-cost molds, and increases the risk of rejects. The cost of the method is further increased by the preformed non-cross-linked reinforced-plastic members, which are expensive and involve complex handling procedures. 
       SUMMARY 
       [0009]    The present disclosure relates to a wind turbine blade tubular spar fabricating method. 
         [0010]    It is one advantage of the present disclosure to provide a wind turbine blade tubular spar fabricating method configured to eliminate certain of the drawbacks of certain of the known art. 
         [0011]    Another advantage of the present disclosure is to provide a wind turbine blade tubular spar fabricating method configured to produce a tubular spar of highly precise dimensions. 
         [0012]    Another advantage of the present disclosure is to provide a wind turbine blade tubular spar that is relatively easy to produce. 
         [0013]    According to the present disclosure, there is provided a wind turbine blade tubular spar fabricating method, wherein the tubular spar extends along a designated or given axis, is made of reinforced polymer material comprising fibers arranged in at least two directions, and a polymer matrix incorporating the fibers, and comprises two caps and two webs; the method comprising the steps of:
       molding and cross-linking at least part of a cap or web in composite material;   molding and cross-linking an L-shaped structure, which comprises two opposite flanges parallel to each other and to the cap, and at least partly incorporates the previously molded, cross-linked cap or web of composite material;   repeating the above steps to mold and cross-link a further L-shaped structure; and   joining the two cross-linked, L-shaped structures, with the flanges positioned facing in pairs.       
 
         [0018]    The present disclosure provides for producing molded cross-linked parts with good dimensional tolerances, while at the same time reducing the amount of polymer material for cross-linking in the L-shaped structure, and so cross-linking the L-shaped structure faster. In addition, the dimensional accuracy of the flanges, and the fact that they are parallel to one another and to the cap, make the L-shaped structures relatively easier to connect. 
         [0019]    Tests conducted by the Applicant confirm the method according to the present disclosure also minimizes rejects. 
         [0020]    In one embodiment of the present disclosure, the method comprises molding and cross-linking in a first mold a cap comprising a main body, and an anchor comprising a portion perpendicular to the main body; and incorporating the anchor in the web when molding and cross-linking the L-shaped structure in a second mold. 
         [0021]    The cap and web are thus connected structurally to each other, but formed in two separate steps for greater dimensional precision. 
         [0022]    In another embodiment of the present disclosure, the method comprises placing the cap anchor between at least two layers of web fibers, before incorporating the cap anchor in the web polymer matrix. 
         [0023]    This provides for greatly improving the stress resistance of the structural bond between the cap and web. 
         [0024]    In another embodiment of the present disclosure, the method comprises molding and cross-linking in a first mold a web comprising a main body, and an anchor comprising a portion perpendicular to the main body; and incorporating the anchor in the cap when molding and cross-linking the L-shaped structure in a second mold. 
         [0025]    The method of one embodiment comprises placing the web anchor between at least two layers of cap fibers. 
         [0026]    In this case, it is the web which is incorporated partly in the cap. 
         [0027]    In another embodiment of, the method according to the present disclosure, the step of molding and cross-linking the L-shaped structure comprises placing successively inside the second mold: at least one fiber layer; a preformed cross-linked cap portion on top of the fiber layer; a core positioned substantially perpendicular to the preformed cross-linked cap portion and on top of the fiber layer; and a further fiber layer on top of the preformed cross-linked cap portion and the core; and incorporating the fiber layers, the preformed cross-linked cap portion, and the core in a polymer matrix. 
         [0028]    In this way, cross-linking only involves a thin surface portion of the L-shaped structure. 
         [0029]    In one embodiment, the fiber layer and further fiber layer are laid directly one on top of the other at the flanges. 
         [0030]    Additional features and advantages are described in, and will be apparent from the following Detailed Description and the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    A number of non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying drawings, in which: 
           [0032]      FIG. 1  shows a cross section, with parts removed for clarity, of a tubular spar produced in accordance with a second embodiment of the present disclosure; 
           [0033]      FIG. 2  shows a larger-scale section, with parts removed for clarity, of a step in the fabrication of a web of the  FIG. 1  tubular spar; 
           [0034]      FIG. 3  shows a larger-scale section, with parts removed for clarity, of a step in the fabrication of a structure of the  FIG. 1  tubular spar; 
           [0035]      FIG. 4  shows a larger-scale section, with parts removed for clarity, of a detail of  FIG. 3 ; 
           [0036]      FIG. 5  shows a cross section, with parts removed for clarity, of a tubular spar produced in accordance with a third embodiment of the present disclosure; 
           [0037]      FIG. 6  shows a larger-scale section, with parts removed for clarity, of a step in the fabrication of a cap of the  FIG. 5  tubular spar; 
           [0038]      FIG. 7  shows a larger-scale section, with parts removed for clarity, of a structure of the  FIG. 5  tubular spar; 
           [0039]      FIG. 8  shows a larger-scale section, with parts removed for clarity, of a detail of  FIG. 7 ; 
           [0040]      FIG. 9  shows a cross section, with parts removed for clarity, of a tubular spar produced in accordance with a fourth embodiment of the present disclosure; 
           [0041]      FIG. 10  shows a larger-scale section, with parts removed for clarity, of a step in the fabrication of a cap of the  FIG. 9  tubular spar; 
           [0042]      FIG. 11  shows a larger-scale section, with parts removed for clarity, of a structure of the  FIG. 9  tubular spar; and 
           [0043]      FIG. 12  shows a larger-scale section, with parts removed for clarity, of a detail of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0044]    Referring now to the example embodiments of the present disclosure illustrated in  FIGS. 1 to 12 , number  22  in  FIG. 1  indicates as a whole a tubular spar configured to support a hollow blade (not shown) of a wind turbine (not shown). In the example shown, tubular spar  22  extends along an axis A, and comprises two opposite caps  23  configured to withstand bending stress, and two opposite webs  24  configured to withstand shear stress. Caps  23  and webs  24  are made of polymer material reinforced with carbon or glass or other suitable fibers, which are normally preassembled in layers with a designated or given orientation. The number or quantity of fiber layers and orientation of the fibers depend on the application, and on the type and degree of stress to which caps  23  and webs  24  are subjected in use. Each cap  23  is joined to a respective web  24  to form an L-shaped structure  25 , which is, connected to another L-shaped structure  25  by layers of glue GL to form tubular spar  22 . 
         [0045]    The method of producing each L-shaped structure  25  comprises the steps of forming and cross-linking web  24 ; and then molding cap  23 , and simultaneously anchoring web  24  in the liquid polymer matrix of cap  23 , before cross-linking the polymer matrix of cap  23 . 
         [0046]    More specifically, as shown in  FIG. 2 , web  24  is formed in a mold  26  by:
       laying at least one fiber layer FL on the bottom of mold  26 ;   placing a core  27  inside mold  26 , on top of fiber layer FL;   laying at least one further fiber layer FL in mold  26 , at least partly over core  27 ;   closing mold  26  to form a closed chamber  28  about fiber layers FL and core  27 ;   forming a vacuum in closed chamber  28 ;   feeding the liquid polymer matrix into the closed vacuum chamber  28  to incorporate the fiber layers FL and core  27  in the polymer matrix; and   cross-linking the polymer matrix in mold  26  by heating mold  26 ; wherein one embodiment includes heat-setting polymers for this type of application.       
 
         [0054]    Web  24  comprises a main body  29 ; a flange  30  substantially perpendicular to main body  29 ; a curved connecting portion  31  of flange  30 ; and a curved anchor  32  located on the opposite side to flange  30  and having an end portion substantially perpendicular to main body  29 . 
         [0055]    As shown in  FIG. 3 , cap  23  and L-shaped structure  25  are formed by:
       laying at least one fiber layer FL in a mold  33 ;   positioning web  24  inside mold  33 , with the shoulder formed by flange  30  and connecting portion  31  in a designated or given position with respect to a reference point  34  on mold  33 , and with anchor  32  resting on fiber layer FL;   laying at least one further fiber layer FL in mold  33 , partly on top of anchor  32 ;   closing mold  33  to form a closed chamber  35  about fiber layers FL and web  24 ;   forming a vacuum in closed chamber  35 ;   feeding the liquid polymer matrix into the closed vacuum chamber  35  to incorporate the fiber layers FL and anchor  32  in the polymer matrix, as shown more clearly in  FIG. 4 ; and   cross-linking the polymer matrix in mold  33  by heating mold  33 ; wherein one embodiment includes heat-setting polymers for this type of application.       
 
         [0063]    As shown in  FIG. 3 , the cap  23  so formed is connected rigidly to web  24 , and comprises a main body  36 ; a lateral flange  37  on the opposite side to web  24  and substantially parallel to main body  36 ; and a partly curved connecting portion  38  between main body  36  and flange  37 . 
         [0064]    Each L-shaped structure  25  comprises two parallel, outwardly-projecting flanges  30 ,  37 , and is formed when molding cap  23 , with no need to glue cap  23  to web  24 ; and two L-shaped structures  25 , formed as described above, are connected by two layers of glue GL to form tubular spar  22  in  FIG. 1 . 
         [0065]    Number  39  in  FIG. 5  indicates a tubular spar comprising two opposite, parallel caps  40  configured to withstand bending stress, and two opposite, parallel webs  41  configured to withstand shear stress. Each cap  40  is C-shaped and connected to a respective web  41  to form an L-shaped structure  42 , which is connected to another L-shaped structure  42  by layers of glue  21  to form tubular spar  39 . 
         [0066]    The method of producing the tubular spar  39  comprises the steps of forming and cross-linking cap  40 ; and then molding web  41 , and simultaneously incorporating cap  40  in the liquid polymer matrix of web  41 , before cross-linking the polymer matrix of web  41 . 
         [0067]    More specifically, as shown in  FIG. 6 , cap  40  is formed in a mold  43  by:
       laying at least one fiber layer FL on the bottom of mold  43 ;   closing mold  43  to form a closed chamber  44  about fiber layer FL;   forming a vacuum in closed chamber  44 ;   feeding the liquid polymer matrix into the closed vacuum chamber  44  to incorporate the fiber layer FL in the polymer matrix; and   cross-linking the polymer matrix in mold  43  by heating mold  43 ; wherein one embodiment includes heat-setting polymers for this type of application.       
 
         [0073]    Cap  40  comprises a main body  45 ; a lateral flange  46  substantially parallel to main body  45 ; a connecting portion  47  between main body  45  and lateral flange  46 ; and an anchor  48  located on the opposite side to lateral flange  46  and having an end portion substantially perpendicular to main body  45 . 
         [0074]    As shown in  FIG. 7 , web  41  and structure  42  are formed by:
       laying at least one fiber layer FL inside a mold  49 ;   positioning cap  40  inside mold  49 , with the shoulder formed by lateral flange  46  and connecting portion  47  in a designated or given position with respect to a reference point  50  on mold  49 , and with anchor  48  resting on fiber layer FL;   placing a core  51  on fiber layer FL;   laying at least one further fiber layer FL in mold  49 , partly on top of anchor  48  and partly on top of core  51 ;   closing mold  49  to form a closed chamber  52  about fiber layers FL, core  5 , and anchor  48 ;   forming a vacuum in closed chamber  52 ;   feeding the liquid polymer matrix into the closed vacuum chamber  52  to incorporate the fiber layers FL, core  41 , and anchor  48  in the polymer matrix, as shown more clearly in  FIG. 8 ; and   cross-linking the polymer matrix in mold  49  by heating mold  49 ; wherein one embodiment includes heat-setting polymers for this type of application.       
 
         [0083]    Web  41  so formed is connected to cap  40 , and comprises a main body  53 ; a lateral flange  54  located on the opposite side to cap  40  and substantially perpendicular to main body  53 ; and a connecting portion  55  between main body  36  and flange  37 . 
         [0084]    In this embodiment, L-shaped structure  42  is formed when pouring web  41 , with no need to glue cap  40  to web  41 ; and two L-shaped structures  42 , formed and cross-linked as described above, are connected by two layers of glue GL to form tubular spar  39  in  FIG. 5 . 
         [0085]    Number  56  in  FIG. 9  indicates a tubular spar comprising two opposite, parallel caps  57  configured to withstand bending stress, and two opposite, parallel webs  58  configured to withstand shear stress. Each cap  57  is connected to a respective web  58  to form an L-shaped structure  59 , which is connected to another L-shaped structure  59  by layers of glue GL to form tubular spar  56 . 
         [0086]    Cap  57  comprises a part—in the example shown, a core  60 —made of cross-linked, fiber-reinforced polymer material, and web  58  comprises a core  61  made of polymer foam or balsa or other relatively lightweight material. 
         [0087]    The method of producing each L-shaped structure  59  comprises the steps of partly forming cap  57 ; and then molding web  58  and simultaneously incorporating the preformed part of cap  57  in the liquid polymer matrix of web  58 , before cross-linking the polymer matrix of web  58 . 
         [0088]    More specifically, as shown in  FIG. 10 , the preformed cross-linked part of cap  57  (i.e., core  60 ) is formed in a mold  62  by:
       laying at least one fiber layer FL on the bottom of mold  62 ;   closing mold  62  to form a closed chamber  63  about fiber layer FL;   forming a vacuum in closed chamber  63 ;   feeding the liquid polymer matrix into the closed vacuum chamber  63  to incorporate fiber layer FL in the polymer matrix; and   cross-linking the polymer matrix in mold  62  by heating mold  62 ; wherein one embodiment includes heat-setting polymers for this type of application.       
 
         [0094]    As shown in  FIG. 11 , web  58  and structure  59  are formed simultaneously by:
       laying at least one fiber layer FL on the horizontal and vertical walls of a mold  64 ;   placing core  60  on top of fiber layer FL in mold  64 ;   placing core  61  on top of fiber layer FL in mold  64 , in a position substantially perpendicular to core  60 ;   laying at least one further fiber layer FL in mold  64 , partly on top of cores  60  and  61 ;   closing mold  64  to form a closed chamber  65  about fiber layers FL and cores  60  and  61 ;   forming a vacuum in closed chamber  65 ;   feeding the liquid polymer matrix into the closed vacuum chamber  65  to incorporate fiber layers FL and cores  60  and  61  in the polymer matrix, as shown more clearly in  FIG. 12 ; and   cross-linking the polymer matrix in mold  64  by heating mold  64 ; wherein one embodiment includes heat-setting polymers for this type of application.       
 
         [0103]    Arrow F 1  indicates where and the direction in which air is extracted to form the vacuum in closed chamber  65 ; and arrow F 2  indicates where and the direction in which the liquid polymer matrix is fed in. 
         [0104]    As shown in  FIG. 10 , cap  57 , core  58 , and L-shaped structure  59  are completed simultaneously inside mold  64 . 
         [0105]    More specifically, cap  57  comprises a main body  66 ; a lateral flange  67  located on the opposite side to web  58  and substantially parallel to main body  66 ; and a connecting portion  68  between main body  66  and flange  67 . 
         [0106]    Web  58  comprises a main body  69 ; a lateral flange  70  substantially perpendicular to main body  69 ; and a connecting portion  71  between main body  69  and lateral flange  70 . And L-shaped structure  59  comprises a connecting portion  72  configured to connect cap  57  and web  58 , and which is formed integrally with web  58  and part of cap  57 . 
         [0107]    The present disclosure has major advantages. In particular, it provides for producing tubular spars of extremely accurate dimensions. 
         [0108]    The thickness of the layer of glue enables adjustment to the height of the tubular spar (i.e., the distance between the two opposite caps). 
         [0109]    And the connections and joints are made in low-stress areas of the tubular spar. 
         [0110]    Clearly, changes may be made to the method as described herein without, however, departing from the scope of the accompanying Claims. It should thus be understood that various changes and modifications to the presently disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.