Patent Publication Number: US-2012027609-A1

Title: Wind turbine rotor blade with precured fiber rods and method for producing the same

Description:
BACKGROUND OF THE INVENTION 
     The subject matter described herein relates generally to methods and systems for wind turbine rotor blades, and more particularly, to methods and systems for the structural reinforcement of wind turbine rotor blades. 
     At least some known wind turbines include a tower and a nacelle mounted on the tower. A rotor is rotatably mounted to the nacelle and is coupled to a generator by a shaft. A plurality of blades extend from the rotor. The blades are oriented such that wind passing over the blades turns the rotor and rotates the shaft, thereby driving the generator to generate electricity. 
     Typically, the body of a wind turbine rotor blade includes a laminate of a resin and fiber material. Also structural elements like spar caps and the root portions of the rotor blade are fabricated in this manner. Typically, a spar cap is produced by inserting layers of glass fiber in a mold, and by subsequently inserting a resin in order to connect the layers after curing. Also, carbon fiber materials have gained importance in recent years. The spar caps significantly add to the strength and stability of the wind turbine rotor blade. In comparison to other parts of the blade, they are relatively heavy and typically contribute significantly to the weight of the rotor blade. Also the root portion contributes significantly to the overall strength of the blade, as it has to withstand high bending forces during operation. 
     Wind turbines, and consequently also the rotor blades, have grown significantly in size in recent years, requiring increasing stability of structural elements like blade roots and spar caps. 
     In view of the above, it is desired to have a wind turbine rotor blade which delivers improved stability in comparison to conventional designs. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a wind turbine rotor blade is provided. The rotor blade includes a rotor blade body, including a root portion, a leading edge, a trailing edge, and at least one spar cap; a plurality of parallel, elongated elements of a pre-cured composite material, which include fibers and a resin; and a resin connecting the plurality of elements. 
     In another aspect, a wind turbine is provided. The wind turbine includes a tower, a nacelle situated on the tower, and a rotor rotatably attached to the nacelle, having at least one rotor blade. The at least one rotor blade includes a rotor blade body, including a root portion, a leading edge, a trailing edge, and at least one spar cap; and a plurality of parallel, elongated elements of a pre-cured composite material, which include fibers and a resin; and a resin connecting the plurality of elements. 
     In a further aspect, a method for producing a wind turbine rotor blade is provided. The method includes providing an elongated element of a pre-cured composite material; depositing the element in a mold; iterating the depositing so that at least one layer of pre-cured elements is formed; and injecting a resin into the layer formed by the elongated pre-cured elements. 
     Further aspects, advantages and features of the present invention are apparent from the dependent claims, the description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein: 
         FIG. 1  is a perspective view of an exemplary wind turbine. 
         FIG. 2  is an enlarged sectional view of a portion of the wind turbine shown in  FIG. 1 . 
         FIG. 3  is a cross sectional view of a wind turbine rotor blade according to embodiments. 
         FIG. 4  is an enlarged sectional view of a portion of the wind turbine rotor blade of  FIG. 4 . 
         FIG. 5  is an enlarged sectional view of a portion of a wind turbine rotor blade according to further embodiments. 
         FIG. 6  is a cross sectional view of a wind turbine rotor blade according to embodiments. 
         FIG. 7  is a cross sectional side view on a spar cap of a wind turbine rotor blade according to embodiments. 
         FIG. 8  shows five partial cross-sectional views at different positions of a wind turbine rotor blade spar cap according to embodiments. 
         FIG. 9  shows a top view of the manufacturing of a wind turbine rotor blade spar cap according to embodiments. 
         FIG. 10  shows a side view of the manufacturing of a wind turbine rotor blade spar cap according to embodiments. 
         FIG. 11  shows a further side view of the manufacturing of a wind turbine rotor blade spar cap according to embodiments. 
         FIG. 12  shows a top view on a layer of elements of a wind turbine rotor blade spar cap according to embodiments. 
         FIG. 13  shows a side view of the manufacturing of a wind turbine rotor blade spar cap according to embodiments. 
         FIG. 14  shows a further side view of the manufacturing of a wind turbine rotor blade spar cap according to embodiments. 
         FIGS. 15 to 17  show cross-sectional views of a part of a wind turbine rotor blade according to embodiments. 
         FIG. 18  shows a cross-sectional view of a wind turbine rotor blade according to embodiments. 
         FIG. 19  shows a partial cross-sectional view of a wind turbine rotor blade according to embodiments. 
         FIG. 20  shows a cross sectional view and a detailed cross sectional view through the root portion of a rotor blade according to embodiments. 
         FIG. 21  shows a detailed cross sectional view through a root portion of a rotor blade according to embodiments. 
         FIG. 22  shows a schematical view on a process of manufacturing a rotor blade according to embodiments. 
         FIG. 23  shows a further schematical view of a process of producing a rotor blade according to embodiments. 
         FIGS. 24 to 26  show methods of pre-treating elements according to embodiments. 
         FIG. 27  schematically shows a method for producing a wind turbine rotor blade according to embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. It is intended that the present disclosure includes such modifications and variations. 
     The embodiments described herein include a wind turbine system that has at least one rotor blade including pre-cured elements. 
     As used herein, the term “spar cap” is intended to be representative of an elongated structure which increases the strength of a wind turbine rotor blade. As used herein, the terms “injected” and “vacuum infused” are both intended to be representative for a method of inserting a resin into a layer of fibrous material. In technical applications, injection and vacuum infusion describe different methods. However, in the present disclosure, the terms are used interchangeably, as they have the common aim of providing a resin into a layer of fibrous material. Which method is actually chosen for which specific purpose is a matter of choice of the person skilled in the art, on which he will decide on the basis of his standard knowledge. As used herein, the term “blade” is intended to be representative of any device that provides a reactive force when in motion relative to a surrounding fluid. As used herein, the term “wind turbine” is intended to be representative of any device that generates rotational energy from wind energy, and more specifically, converts kinetic energy of wind into mechanical energy. As used herein, the term “wind generator” is intended to be representative of any wind turbine that generates electrical power from rotational energy generated from wind energy, and more specifically, converts mechanical energy converted from kinetic energy of wind to electrical power. 
       FIG. 1  is a perspective view of an exemplary wind turbine  10 . In the exemplary embodiment, wind turbine  10  is a horizontal-axis wind turbine. Alternatively, wind turbine  10  may be a vertical-axis wind turbine. In the exemplary embodiment, wind turbine  10  includes a tower  12  that extends from a support system  14 , a nacelle  16  mounted on tower  12 , and a rotor  18  that is coupled to nacelle  16 . Rotor  18  includes a rotatable hub  20  and at least one rotor blade  22  coupled to and extending outward from hub  20 . In the exemplary embodiment, rotor  18  has three rotor blades  22 . In an alternative embodiment, rotor  18  includes more or less than three rotor blades  22 . In the exemplary embodiment, tower  12  is fabricated from tubular steel to define a cavity (not shown in  FIG. 1 ) between support system  14  and nacelle  16 . In an alternative embodiment, tower  12  is any suitable type of tower having any suitable height. 
     Rotor blades  22  are spaced about hub  20  to facilitate rotating rotor  18  to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. Rotor blades  22  are mated to hub  20  by coupling a blade root portion  24  to hub  20  at a plurality of load transfer regions  26 . Load transfer regions  26  have a hub load transfer region and a blade load transfer region (both not shown in  FIG. 1 ). Loads induced to rotor blades  22  are transferred to hub  20  via load transfer regions  26 . 
     In one embodiment, rotor blades  22  have a length ranging from about 15 meters (m) to about 91 m. Alternatively, rotor blades  22  may have any suitable length that enables wind turbine  10  to function as described herein. For example, other non-limiting examples of blade lengths include 10 m or less, 20 m, 37 m, or a length that is greater than 91 m. As wind strikes rotor blades  22  from a direction  28 , rotor  18  is rotated about an axis of rotation  30 . As rotor blades  22  are rotated and subjected to centrifugal forces as well as to lift and drag forces leading to internal moments, rotor blades  22  are also subjected to various forces and moments. As such, rotor blades  22  may deflect and/or rotate from a neutral, or non-deflected, position to a deflected position. 
     Moreover, a pitch angle or blade pitch of rotor blades  22 , i.e., an angle that determines a perspective of rotor blades  22  with respect to direction  28  of the wind, may be changed by a pitch adjustment system  32  to control the load and power generated by wind turbine  10  by adjusting an angular position of at least one rotor blade  22  relative to wind vectors. Pitch axes  34  for rotor blades  22  are shown. During operation of wind turbine  10 , pitch adjustment system  32  may change a blade pitch of rotor blades  22  such that rotor blades  22  are moved to a feathered position, such that the perspective of at least one rotor blade  22  relative to wind vectors provides a minimal surface area of rotor blade  22  to be oriented towards the wind vectors, which facilitates reducing a rotational speed of rotor  18  and/or facilitates a stall of rotor  18 . 
     In the exemplary embodiment, a blade pitch of each rotor blade  22  is controlled individually by a control system  36 . Alternatively, the blade pitch for all rotor blades  22  may be controlled simultaneously by control system  36 . Further, in the exemplary embodiment, as direction  28  changes, a yaw direction of nacelle  16  may be controlled about a yaw axis  38  to position rotor blades  22  with respect to direction  28 . 
       FIG. 2  is an enlarged sectional view of a portion of wind turbine  10 . In the exemplary embodiment, wind turbine  10  includes nacelle  16  and hub  20  that is rotatably coupled to nacelle  16 . More specifically, hub  20  is rotatably coupled to an electric generator  42  positioned within nacelle  16  by rotor shaft  44  (sometimes referred to as either a main shaft or a low speed shaft), a gearbox  46 , a high speed shaft  48 , and a coupling  50 . In the exemplary embodiment, rotor shaft  44  is disposed coaxial to longitudinal axis  116 . Rotation of rotor shaft  44  rotatably drives gearbox  46  that subsequently drives high speed shaft  48 . High speed shaft  48  rotatably drives generator  42  with coupling  50  and rotation of high speed shaft  48  facilitates production of electrical power by generator  42 . Gearbox  46  and generator  42  are supported by a support  52  and a support  54 . In the exemplary embodiment, gearbox  46  utilizes a dual path geometry to drive high speed shaft  48 . Alternatively, rotor shaft  44  is coupled directly to generator  42  with coupling  50 . 
     Nacelle  16  also includes a yaw drive mechanism  56  that may be used to rotate nacelle  16  and hub  20  on yaw axis  38  (shown in  FIG. 1 ) to control the perspective of rotor blades  22 , respectively the rotor, with respect to direction  28  of the wind. Nacelle  16  also includes at least one meteorological mast  58  that includes a wind vane and anemometer (neither shown in  FIG. 2 ). Mast  58  provides information to control system  36  that may include wind direction and/or wind speed. In the exemplary embodiment, nacelle  16  also includes a main forward support bearing  60  and a main aft support bearing  62 . 
     Forward support bearing  60  and aft support bearing  62  facilitate radial support and alignment of rotor shaft  44 . Forward support bearing  60  is coupled to rotor shaft  44  near hub  20 . Aft support bearing  62  is positioned on rotor shaft  44  near gearbox  46  and/or generator  42 . Alternatively, nacelle  16  includes any number of support bearings that enable wind turbine  10  to function as disclosed herein. Rotor shaft  44 , generator  42 , gearbox  46 , high speed shaft  48 , coupling  50 , and any associated fastening, support, and/or securing device including, but not limited to, support  52  and/or support  54 , and forward support bearing  60  and aft support bearing  62 , are sometimes referred to as a drive train  64 . 
     In the exemplary embodiment, hub  20  includes a pitch assembly  66 . Pitch assembly  66  includes one or more pitch drive systems  68  and at least one sensor  70 . Each pitch drive system  68  is coupled to a respective rotor blade  22  (shown in  FIG. 1 ) for modulating the blade pitch of associated rotor blade  22  along pitch axis  34 . Only one of three pitch drive systems  68  is shown in  FIG. 2 . 
     In the exemplary embodiment, pitch assembly  66  includes at least one pitch bearing  72  coupled to hub  20  and to respective rotor blade  22  (shown in  FIG. 1 ) for rotating respective rotor blade  22  about pitch axis  34 . Pitch drive system  68  includes a pitch drive motor  74 , pitch drive gearbox  76 , and pitch drive pinion  78 . Pitch drive motor  74  is coupled to pitch drive gearbox  76  such that pitch drive motor  74  imparts mechanical force to pitch drive gearbox  76 . Pitch drive gearbox  76  is coupled to pitch drive pinion  78  such that pitch drive pinion  78  is rotated by pitch drive gearbox  76 . Pitch bearing  72  is coupled to pitch drive pinion  78  such that the rotation of pitch drive pinion  78  causes rotation of pitch bearing  72 . More specifically, in the exemplary embodiment, pitch drive pinion  78  is coupled to pitch bearing  72  such that rotation of pitch drive gearbox  76  rotates pitch bearing  72  and rotor blade  22  about pitch axis  34  to change the blade pitch of blade  22 . 
     Pitch drive system  68  is coupled to control system  36  for adjusting the blade pitch of rotor blade  22  upon receipt of one or more signals from control system  36 . In the exemplary embodiment, pitch drive motor  74  is any suitable motor driven by electrical power and/or a hydraulic system that enables pitch assembly  66  to function as described herein. Alternatively, pitch assembly  66  may include any suitable structure, configuration, arrangement, and/or components such as, but not limited to, hydraulic cylinders, springs, and/or servo-mechanisms. Moreover, pitch assembly  66  may be driven by any suitable means such as, but not limited to, hydraulic fluid, and/or mechanical power, such as, but not limited to, induced spring forces and/or electromagnetic forces. In certain embodiments, pitch drive motor  74  is driven by energy extracted from a rotational inertia of hub  20  and/or a stored energy source (not shown) that supplies energy to components of wind turbine  10 . 
       FIG. 3  schematically shows a cross-sectional view of a wind turbine rotor blade  22  according to embodiments. Two spar caps  230  each include a plurality of parallel, elongated elements  240 . The elements include a pre-cured composite material including fibers and a resin, wherein the elements are bond together by a resin. The spar caps  230  protrude from a root portion of the blade in a direction of the longitudinal axis of the blade to a tip portion of the blade. They are typically connected by a shear web  280  (only schematically shown). 
       FIG. 4  shows a more detailed cross-sectional view of a spar cap  230  with elongated elements  240  according to embodiments. The elements  240  are connected via a resin  250 , which fills gaps between the elements. The elements  240  themselves may have a rectangular cross section as shown in  FIG. 3  and  FIG. 4 , or may have a circular cross section as shown in  FIG. 5 . In embodiments, also other cross sections are possible, for instance, a polygon, a rectangle, or an ellipse. 
       FIG. 6  shows a top view of the wind turbine rotor blade  22  according to the embodiments of  FIGS. 3 to 5 , with a cross-sectional view on the outline of a spar cap  230 . The spar cap  230  includes various layers  290  and protrudes from a root section  260  of the rotor blade  22  to a tip portion  270 . 
       FIG. 7  shows a side view of a spar cap  230  as of  FIG. 6 . Therein, the proportions are not depicted on scale for illustrational purposes. The spar cap includes a plurality of layers  290 . Each layer  290  includes a number of parallel elongated elements  240 . The elements  240  within a layer are bond together by a resin (not shown). The layers  290  are bond to their respective neighboring layers by a resin. The different layers  290  typically have different lengths in a direction of the longitudinal axis of the rotor blade  22 . Accordingly, spar cap  230  has different thickness values along its length, resulting from the varying number of layers contributing thereto. This accounts, amongst other factors, for varying bending and torsional moments acting on the rotor blade  22  at different positions along its length. It is noted that the different layers  290  shown in  FIG. 7  are visible in  FIG. 6 , where the edges of layers  290  are visible. Further, the elements  240  of the layers  290 , as shown in  FIG. 8 , are not depicted in  FIG. 6  for illustrational purposes. 
       FIG. 8  shows a number of cross-sectional views of the spar cap  230  at different positions along its length, which are depicted by letters A to E in  FIG. 7 . In the exemplary embodiment, at position A in the tip portion  270 , the spar cap  230  includes one layer  290 , which includes six parallel elements  240  having a rectangular cross section each. At position B, the spar cap has two layers, at position C three layers, at position D it has the maximum of seven layers  290  with six elements  240  each. At position D, the spar cap has its maximum thickness. As depicted in  FIG. 8 , the thickness of the spar cap decreases from there in a direction to the root portion  260  of the blade. At the root portion  260  (see  FIG. 6 ), the spar cap exhibits a thickness corresponding to one layer  290 , such as in the tip portion  270 . The number of consecutive layers at different positions of the rotor blade, as well as the thickness of the layers itself, of course strongly depend on the strength and stiffness of the rotor blade as well as on the thickness and stiffness of the procured elements. Hence, these parameters may vary significantly from those in the exemplary embodiment as shown in  FIG. 8 . 
       FIGS. 9 to 11  depict phases of an exemplary production process of a spar cap  230  according to embodiments.  FIG. 9  shows a spool  215 , on which the pre-cured material forming elements  240  is provided. The material includes fibers and a cured resin and is typically previously produced in a pultrusion process. Suitable fiber materials include carbon fiber, glass fiber, combinations thereof, or any other high strength fibrous material, which also pertains to any other embodiments described herein. After being rolled on spool  215 , it is transported to the production facility of rotor blade  22 . Starting from one end of the spar cap  230  to be formed, a line of the pre-cured material is unrolled from the spool and laid into a mold having the shape of the spar cap  230  to be formed. After the length needed for the first element  240  is unrolled, the pre-cured material is cut, and the process is repeated with a subsequent line of pre-cured material which is laid parallel to the first element  240 . In  FIG. 9 , this process has been repeated three times, and the fourth element  240  is about to be completed. The numbers of elements used herein are merely by way of non-limiting examples and may differ in practical use. When a layer  290  of elongated elements  240  is completed, that is, when all parallel elements  240  of a layer  290  are positioned, the production of a further layer  295  on top of the first layer  290  is started. This is depicted in  FIG. 10 .  FIG. 11  shows how an element  240  of a third layer  300  is positioned on layer  295 . 
       FIG. 12  shows an end portion of a layer  290  according to embodiments. Therein, the end portions  330  of the single elongated elements  240  are tapered. This feature provides for a smooth force progression along the spar cap  230  including a plurality of layers  230 . If the end portions of the elements  240  would exhibit a sharp edge, the force progression of a force on spar cap  230 , which is due to a bending moment, would exhibit a rapid incline respectively decline at the position where a layer ends. The end portions of the elements  330  may be milled to obtain the tapered end, just before positioning the element in the mold, respectively on the previous layer. The milling process is schematically shown in  FIG. 13 , with a milling tool  310  and a tool plate  320 , through which end portion  330  is supported. 
       FIG. 14  schematically shows an end portion of a spar cap  230  according to a further embodiment. Therein, the end portion  330  of element  240  is squeezed between rollers  340 ,  350  in order to partially destroy the structure of the pre-cured fiber-resin material of the element  240 . An element  295  which has been treated accordingly and exhibits an end portion  330  with a broken structure is schematically shown. The broken structure of the end portion of the fiber-resin-compound, respectively of all ends of the elements of a layer, lowers the ability of this portion of the element to transmit force between the end of the layer and the adjacent layer, in  FIG. 14  layer  290 , which serves the same purpose as the tapering of the end portions in the embodiment of  FIG. 13 . 
     The end portions  330  of the elongated elements  240  shown in  FIGS. 13 and 14  exhibit a cross sectional shape different from that of other portions of the element, due to the described treatments. 
       FIG. 15  shows a cross-sectional view of an embodiment, wherein two spar caps  230  are connected by a shear web  280 . Therein, it is shown how a tapered spar cap is formed by layers  290  of elements  240 , wherein the layers include different numbers of elements each. In the embodiment, the outermost layers  290  of spar caps  230  includes 13 elements  240 , the second layer  295  includes 11 elements, and the innermost layer includes 9 elements. 
       FIG. 16  shows a further embodiment, wherein the spar caps  230  are formed to exhibit a kind of channel for taking up the shear web  280 , which provides for improved stability. 
       FIG. 17  shows a further embodiment, wherein the spar caps exhibit both a tapered shape as in  FIG. 15  and a channel as in the embodiment of  FIG. 16 . 
     The embodiments shown in  FIGS. 15 to 17  may be produced by a method as described hereinbefore. 
       FIG. 18  shows a cross section of a rotor blade, wherein possible positions of pre-cured elongated elements  240  are shown according to embodiments. Therein, elements are provided in a spar cap  230  as described before, and as a reinforcement to the trailing edge  370  and the leading edge  380 . 
       FIG. 19  shows a partial cross-sectional view of a rotor blade  22 , in which pre-cured elements  240  are provided in a root portion  24  according to embodiments. 
     The circular root portion  24  of rotor blades may be formed from pre-produced halves, which are fabricated separately from the rest of the rotor blade body. These parts are typically produced by placing layers of fibrous material in a mold and injecting or vacuum infusing them with a resin. As shown in  FIG. 20 , the circular root portion  24 , according to embodiments, includes layers  410 ,  420  of fibrous material injected with a resin  250  (not shown in detail), and at least one layer  415  of pre-cured elongated elements  240  injected with a resin  250 . Typically, all layers are first placed in the mold and subsequently, the whole stack of layers  410 ,  420 ,  430  is injected or vacuum infused with resin  250 . In order to further improve the stability of the root portion  24  and to ease flow of the resin through the stack, the surface of the pre-cured elements  240  may be pre-treated. This may include roughing their surface, for instance by sand-blasting, or by mechanically producing grooves in the surface, or by producing small bumps respectively protrusions on the surface, for instance by applying a plurality of droplets of resin or other materials on the surface of the elements prior to placing them in the mold. 
       FIG. 21  shows a partial cross sectional view similar to that of  FIG. 20 , wherein the root portion  24  includes a plurality of fibrous layers  410 ,  420 ,  430 , which are stacked with layers  415 ,  425  of pre-cured elements  240 . The fibrous layers may be applied in a unidirectional and biaxial orientation, wherein the greater part of the fibers is typically provided in biaxial orientation. The biaxial orientation provides for greater stability in various directions than is achieved by unidirectional layers. Further, biaxial orientation may ease the resin flow during subsequent infusion/injection. 
       FIG. 22  shows how the pre-cured elongated elements  240  are placed into mold  440  in order to form a layer of pre-cured elements. In order to stabilize the elements in the half-circular mold prior to the injection of resin, the elements may be held by one or more auxiliary stabilization elements  450  (only schematically shown). In  FIG. 22 , element  450  only covers a part of the circumferential span of the mold for illustrational purposes. The pre-cured elongated elements  240  in this embodiment typically have ends which are similar shaped as the end portions  330  in  FIG. 12 . 
       FIG. 23  shows how a plurality of layers of fibrous material  410 ,  420 ,  430  are stacked (indicated by the arrow) intermittently with double layers  415 ,  425  of pre-cured elements  240  onto mold  440 . The surfaces of elements  240  are pre-treated to have an elevated roughness as described before. After the stacking, resin  250  is vacuum-infused (not shown) into the stack of layers. 
       FIGS. 24 to 26  show the pre-treating of a pre-cured element  240  according to embodiments.  FIG. 24  shows how the surface roughness of surface  241  of element  240  is increased or elevated by sandblasting with a sandblasting device  500 . 
       FIG. 25  shows how at least one groove is cut into the surface  241  of element  240  by a cutting device  520 . Element  240  may be turned during the process, achieving at least one spirally wound groove. Alternatively, cutting device  520  may be moved in a spiral or circular movement around the element  240 , which is indicated by the arrow above device  520   
       FIG. 26  show how droplets  540  of a resin are applied to the surface  241  of element  240  by a device  530 . The density of droplets is strongly dependent on the individual case. In embodiments, the droplet density may be 0.1 to 20 per cm 2 , more typically 1 to 10 per cm 2 . After curing, the droplets form small protrusions or bumps on the surface  241 , elevating the effective surface roughness. 
     The elements  240  shown in  FIGS. 24 ,  25 , and  26  exhibit a round shape. However, they may have any cross sectional shape as described before. 
       FIG. 27  shows a flow chart of a method for producing a wind turbine rotor blade according to embodiments. The method includes providing an elongated element of a pre-cured composite material in block  1100 ; depositing the element in a mold in block  1200 ; iterating block  1200  so that at least one layer of pre-cured elements is formed in block  1300 ; and injecting a resin into the layer formed by the elongated pre-cured elements in block  1400 . 
     Pre-treating methods for pre-cured elongated elements as used in the production of wind turbine rotor blades are described. In various embodiments described herein, the elements exhibit a rectangular or square shape. When these elements are positioned parallel to each other when forming a layer, the side faces of parallel elements may be in tight contact with each other. Moreover, typically all layers of a spar cap are formed by positioning their respective elements, before starting to insert resin into the so formed layer in order to connect the various elements. Hence, there is a stack of elements which tightly fit together, before it is started to inject the resin in order to connect the elements. Consequently, if the elements are not treated to increase flow of resin into the stack, parts of the contact faces between elements may not be reached by resin, or it may take a long time before all faces are sufficiently covered with resin to allow for a stable bonding. 
     In order to ease this process, some or all faces of the elements may be pre-treated before being positioned in the spar cap mold to form a layer, or the stack of layers, respectively. 
     In another embodiment, small droplets of a quick-binding resin are applied to the surface of the elements before positioning them in the mold. This resin cures before the element is positioned in the mold, and the droplets thus form kind of spacers between the elements, providing enough space for the resin to flow through the stack. 
     The above-described systems and methods facilitate the production of wind turbine rotor blades with improved characteristics. More specifically, they facilitate the production of rotor blades having improved mechanical stability. 
     Exemplary embodiments of systems and methods for the production of wind turbine rotor blades are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may be applied to other rotor blades, and are not limited to practice with only the wind turbine systems as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other rotor blade applications. 
     Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. While various specific embodiments have been disclosed in the foregoing, those skilled in the art will recognize that the spirit and scope of the claims allows for equally effective modifications. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.