Method of making a root end joint of a wind turbine blade and a root segment for such a joint

Abstract

A method of making a root end joint for a wind turbine. A plurality of root segments (10) are formed of a composite material. Each has an arcuate end face (11) which subtends an angle of 90 or less and has a plurality of connection holes (12). The segments are joined together side-by-side to build up the circular profile of the root end. The segments include a proportion of uni-axial to multiaxial fiber which decreases from the arcuate end face towards the opposite end.

Claims

1. A method of making a root end joint of a wind turbine blade, the method comprising: forming a plurality of root segments of a composite material, each root segment being generally the shape of a segment of a hollow cylinder having at least one arcuate end face subtending an angle of 90 or less with a plurality of connection holes, an opposite end, and a pair of side faces extending axially from the arcuate end face to the opposite end; arranging a plurality of the root segments side-by-side into a root tool, wherein the root segments include uniaxial and multi-axial fibers, wherein the relative proportion of uni-axial to multi-axial fiber decreases from the arcuate end face towards the opposite end, and wherein each root segment comprises a fixed length between the arcuate end face and the opposite end; aligning the connection holes of the arranged root segments with through holes of an alignment frame that abuts against the root tool; securing the arranged root segments to the alignment frame via a plurality of bolts positioned through the aligned connection holes and through holes; laying up a plurality of laminate layers atop the fixed lengths of each root segment; and securing the laminate layers and the root segments together so as to form the root end joint.

2. A method according to claim 1, wherein adjacent side faces of adjacent root segments have a complementary keying configuration.

3. A method according to claim 1, wherein a thickness of the fixed lengths of the root segments tapers from the arcuate end face towards the opposite end.

4. A method according to claim 1, wherein the root segments are joined together to form a substantially semi-circular configuration.

5. A method according to claim 1, further comprising drilling the connection holes after the root segments are formed.

6. A method according to claim 1, further comprising forming the connection holes as the root segments are formed.

7. A method according to claim 6, wherein the step of forming the connection holes is achieved by forming the root segments with inserts having female screw threads in situ.

8. A method according to claim 6, comprising the steps of inserting disposable inserts into the root segment during the forming step and removing the disposable inserts to form the connection holes.

9. A method according to claim 3, further comprising laying up the plurality of laminate layers atop the tapering fixed lengths of each root segment until a thickness of the root end joint is uniform.

10. A method according to claim 1, wherein securing the laminate layers and the root segments together so as to form the root end joint further comprises infusing the laminate layers and the root segments together via at least one resin material.

11. A method according to claim 1, wherein securing the laminate layers and the root segments together so as to form the root end joint further comprises curing the laminate layers and the root segments together.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An example of a method and a segment in accordance with the present invention will now be described with reference to the accompanying drawings, in which:

(2) FIGS. 1a) to 1c) are schematic representations of the method of assembly of a conventional wind turbine root end joint;

(3) FIG. 2 is a perspective view of a segment according to the present invention;

(4) FIGS. 3a) to 3c) are schematic representations of the method of assembly according to the present invention; and

(5) FIGS. 4a) to 4c) are cross-sectional views aligned to 4a) to 4c) respectively in FIGS. 3a) to 3c).

DETAILED DESCRIPTION

(6) A number of segments as shown in FIG. 2 are used to construct a root end joint by a wind turbine. Each of the segments 10 has a connection end 11 into which a plurality of holes 12 are formed and an opposite end 13. The segment has the general shape of segment of a hollow cylinder which tapers in thickness from the connection end 11 to the opposite end 13. In general, it is intended that 16 segments (8 in each half) will be connected together to form the complete the root end. In this case, each segment will subtend an angle of 22.5 at the centre of the hub.

(7) However, there may be as few as 4 such segments (2 in each half) subtending an angle of 90, or more than 16 segments for larger blades which will subtend a correspondingly smaller angle.

(8) Each side of the segment, is a key 14, 15 designed to locate and interlock with the corresponding key on an adjacent segment.

(9) Typically, each segment will be 2000 mm long and 500 mm wide. At the connection end, there is a significant amount of uni-directional fiber with a small percentage of bi-axial fiber. The amount of fiber moves towards the opposite end 13 where it ends up being 1 ply layer thick.

(10) Depending on its application (infusion or pre-preg blade root), the root segment is made in one of two ways.

(11) For an infusion blade, it can be made by wet lamination with vacuum, vacuum resin infusion, resin transfer moulding or similar process. The first layers of the fiber are laid into the tool, then metallic inserts or tubular spacers are placed into the tool and held in position with an alignment frame at the end of the tool. The alignment frame allows the accurate positioning of the inserts. The final layers of fiber are then placed into the tool. The whole lay-up is then placed under vacuum and the resin is either infused or injected and then fully cured.

(12) For a pre-preg blade, the process is very similar, except that layers of pre-preg are inserted into the tool instead of the layers of fiber. The pre-preg layup is then placed under vacuum and partially cured such that it becomes a semi-cured pre-form.

(13) Alternatively, the segments can be made without the inserts or spacers 16 and the holes are drilled in a subsequent step in a separate jig.

(14) Once the individual root segments are made, they can undergo a quality assurance process to assess the structural integrity of the segments and also to assess the integrity of the inserts.

(15) The inserts may be conventional metallic inserts that are well known in the art. Alternatively, they may be the inserts disclosed in our earlier WO 2010/041008.

(16) The assembly of the root end joint is shown in FIGS. 3a) to 3c) and 4a) to 4c).

(17) In FIG. 3(a), four segments are shown to make up one half of the root end joint. In practice, there will typically be eight. The segments are placed in a tool having a generally semi-circular configuration prior to any other laminate being placed into the tool. The root end of the insert is connected to an alignment frame 15 as shown in FIGS. 4a) to 4c) and are bolted in place using bolts 16. This ensures that the alignment of the bolt circle is maintained during the manufacturing process. In step b), once the segments are accurately positioned, the rest of the blade laminate is laid up. The laminate effectively forms a very long scarf joint with the tapering laminate in the root segment. Once all of the laminate has been laid up, the blade is placed under vacuum and is infused with resin (if it is an infusion blade) or is simply cured (if it is a pre-preg blade). The blade half is then complete ready for final assembly of the two blade halves as normal.