Wind turbine blade manufacture

Abstract

A method of making a root end of a wind turbine blade is described. The root end has a root end surface that connects to a wind turbine hub via a pitch bearing when the blade is installed on a wind turbine, and the method comprises providing a plurality of bores in the root end of the blade, each bore extending axially into the blade and having an opening defined at the root end surface; providing a plurality of plugs, each plug having a substantially solid first end portion; inserting the plugs into the respective bores each to a depth whereby the first end portions of the respective plugs extend inside the bores and form a seal against an internal surface of the bore and a sacrificial portion of the first end portion of each plug protrudes from the opening of the respective bore at the root end surface; and machining the root end surface to form a substantially flat root end surface for interfacing with the pitch bearing, wherein the step of machining the root end surface comprises removing the protruding sacrificial portions of the protruding plugs leaving the remaining first end portions of the respective plugs substantially flush with the root end surface.

Claims

1. A method of making a root end of a wind turbine blade, the root end having a root end surface that connects to a wind turbine hub via a pitch bearing when the blade is installed on a wind turbine, and the method comprising: (a) providing a plurality of bores in the root end of the blade, each bore extending axially into the blade and having an opening defined at the root end surface; (b) providing a plurality of plugs, each plug having a substantially solid first end portion; (c) inserting the plugs into the respective bores each to a depth whereby the first end portions of the respective plugs extend inside the bores and form a seal against an internal surface of the bore and a sacrificial portion of the first end portion of each plug protrudes from the opening of the respective bore at the root end surface; and (d) machining the root end surface to form a substantially flat root end surface for interfacing with the pitch bearing, wherein the step of machining the root end surface comprises removing the protruding sacrificial portions of the protruding plugs leaving the remaining first end portions of the respective plugs substantially flush with the root end surface.

2. The method of claim 1, wherein after step (d) the method further comprises attaching a cap to the first end portion of each plug, the cap having a body that substantially covers a peripheral portion of the root end surface surrounding the bore.

3. The method of claim 2, further comprising providing a washer between the body of the cap and the peripheral portion of the root end surface.

4. The method of claim 2, wherein the first end portion of each plug includes a first recess for receiving an insertion portion of the cap, the first recess extending axially into the first end portion, and step (c) of the method comprises inserting the plugs inside the respective bores to a depth whereby the first recess extends above and below the root end surface such that when the sacrificial portions of the respective plugs are removed, the first recess is exposed at the root end surface, and wherein the step of attaching the caps to the plugs comprises inserting the insertion portions of the respective caps inside the first recesses of the respective plugs.

5. The method of claim 4, wherein the method further comprises locking the caps to the respective plugs by means of interlocking features associated respectively with the insertion portions of the caps and the first recesses of the plugs, wherein the interlocking features permit attachment of the cap to the plug and substantially prevent removal of the cap from the plug.

6. The method of claim 1, wherein the bores are threaded and the plugs include a threaded outer surface, and step (c) of the method involves screwing the plugs inside the bores such that the threads on the plugs mate with the threads inside the bores.

7. The method of claim 1, wherein the first end portion of each plug includes a second recess for receiving a tool, the second recess extending axially into the first end portion, and step (c) of the method comprises inserting the plugs inside the respective bores to a depth whereby the second recess extends above and below the root end surface such that when the sacrificial portions of the respective plugs are removed the second recess is exposed at the root end surface.

8. The method of claim 7, wherein step (c) of the method comprises inserting a tool into the second recess and turning the plug with respect to the bore using the tool.

9. The method of claim 7, wherein after step (d) the method further comprises removing the plugs from the bores by inserting a tool into the second recess of the respective plugs and using the tool to turn the plugs inside the bores.

10. The method of claim 7, wherein after step (d) the method further comprises attaching a cap to the first end portion of each plug, the cap having a body that substantially covers a peripheral portion of the root end surface surrounding the bore, and wherein the body of the cap comprises an aperture that overlies the second recess and the step of removing the plugs from the bores comprises inserting the tool through the aperture in the cap and into the second recess defined in the first end of the plug.

11. The method of claim 1, wherein the bores are provided respectively in root inserts embedded in the root end of the blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 has already been described above by way of background to the present invention. In order that the present invention may be more readily understood, an embodiment of the invention will now be described, by way of example only, with reference to the following figures, in which:

(2) FIG. 2 is a schematic cross-sectional view of a plug according to an embodiment of the present invention;

(3) FIG. 3 is a plan view of a first end surface of the plug of FIG. 2;

(4) FIG. 4 shows the plug inserted into a bore at a root end of a wind turbine blade with a sacrificial portion of the plug protruding from the root end;

(5) FIG. 5 shows the plug inside the bore after the root end the sacrificial portion of the plug have been milled;

(6) FIG. 6a shows a travel cap to be fitted to the milled end of the plug;

(7) FIG. 6b is a plan view showing a body of the travel cap; and

(8) FIG. 6c shows the travel cap fitted to the plug.

(9) FIG. 6d shows a close-up cross-sectional view of part of the travel cap.

DETAILED DESCRIPTION

(10) FIG. 2 shows a plug 30 according to an embodiment of the present invention. The plug 30 is also referred to as a bung. The plug 30 is elongate and generally circular in cross-section. The plug 30 extends axially between a first end 32 and a second end 34. The first end 32 is closed and is defined by a substantially solid and cylindrical first end portion 36 of the plug 30. The second end 34 is open and is defined by a tubular second end portion 38 of the plug 30. A male thread 40 is provided on an outer surface 42 of the tubular portion 38 of the plug 30. The plug 30 in this example is moulded in one piece from polyamide plastic (Nylon).

(11) The solid first end portion 36 of the plug 30 defines a first end surface 44 of the plug 30, which is substantially flat. The first end surface 44 is shown in plan view in FIG. 3. Referring to FIG. 3, a hexagonal recess 46 having a diameter of approximately 20 mm is defined in the centre of the first end surface 44, and this is surrounded by a narrow annular recess 48. Referring again to the cross-sectional view of FIG. 2, in this example the hexagonal recess 46 extends into the solid end portion 36 to a depth of approximately 12 mm, whilst the annular recess 48 extends to a depth of approximately 15 mm.

(12) Referring now to FIG. 4, this shows the plug 30 inserted into a bore 50 defined in a metal root insert 52 which is embedded in a root end 54 of a wind turbine blade. Prior to machining the root end 54 of the blade, the plug 30 is screwed into the bore 50 such that the male thread 40 on the tubular portion 38 of the plug 30 mates with a female thread provided on an internal surface 56 of the bore 50. The female thread is not shown in these schematic illustrations.

(13) The plug 30 is screwed to a depth whereby the hexagonal and annular recesses 46, 48 in the solid end portion 36 of the plug 30 extend both above and below the annular end surface 58 of the root insert 52. The terms above and below used herein refer to the bore 50 when in the orientation shown in the drawings. Expressed in other terms, the respective recesses 46, 48 extend both into and out of the bore 50. In this way, a so-called sacrificial portion 60 of the solid first end portion 36 of the plug 30 protrudes above the end surface 58 of the root insert 52 (i.e. protrudes out of the bore 50).

(14) Typically the plug 30 is screwed to a depth such that about 2-3 mm of the plug 30 protrudes above the end surface 58 of the insert 52, i.e. such that the sacrificial portion 60 of the plug has a height of about 2-3 mm. However, the exact amount by which the plug 30 protrudes from the end surface 58 is not critical provided that the recesses 46, 48 extend below the end surface 58 of the root insert 52 (i.e. provided that the recesses 46, 48 extend into the bore 50). In this way there is a large tolerance on the depth to which the plugs 30 can be screwed into the bores 50, which conveniently facilitates the process of inserting the plugs 30 into the bores 50. Advantageously a minimum depth marker may be applied for example to the side surface of the solid end portion 36 of the plug 30 to indicate the minimum depth to which the plug 30 must be inserted to ensure that the recesses 46, 48 extend sufficiently into the bore 50.

(15) A similar plug 30 is inserted into each of the bores 50 defined in the respective root inserts 52 at the root end 54 of the blade. Once all of the plugs 30 have been inserted, the root end 54 of the blade is milled (as described by way of background) to form a flat surface 62 to interface with the hub. Referring now to FIG. 5, during the milling process, the sacrificial portion 60 (FIG. 4) of each plug 30 is removed by the milling machine to form a new first end 64 of the plug 30 which lies flush with the milled root end surface 62 of the blade.

(16) The solid end 36 of the plug 30 forms a seal against the side wall 56 of the bore 50 and thus prevents swarf from entering the bore 50 during the milling process. Once the milling process is complete, swarf is removed from the hexagonal and annular recesses 46, 48 in the solid portion 36 of the plug 30. The swarf in these recesses 46, 48 has not come into contact with any grease and so can easily be blown out of the recesses 46, 48. The milled end surfaces 58 of the root inserts 52 are then cleaned.

(17) Referring to FIG. 6a, in order to protect the flat end surfaces 58 of the root inserts 52 during storage and transportation of the blade, a travel cap 66 is inserted into the solid end 36 of the plug 30. Referring also to FIG. 6b, which is a plan view of the travel cap 66, the travel cap 66 is generally top-hat shaped, and comprises a body 68 and an insertion portion 70. The body 68 comprises an annular disc 72 defining a central circular aperture 73, and the insertion portion 70 comprises a tubular wall 74 that extends from an inner periphery 76 of the disc 72 in a direction perpendicular to the plane of the disc 72. A series of teeth 78 or barbs are provided on the tubular wall 74. The barbs 78 are annular projections which are substantially triangular in cross section. The travel cap 66 is moulded as a single piece from polyamide plastic (Nylon).

(18) Referring to FIG. 6c, an annular washer 80 is placed on the milled end surface 58 of the root insert 52 surrounding the bore 50, and the tubular wall 74 of the travel cap 66 is inserted into the annular recess 48 defined in the solid first end portion 36 of the plug 30. The annular disc 72 of the travel cap 66 seals against the washer 80 and thereby serves to protect the milled end face 58 of the root insert 52 during transportation and storage of the blade.

(19) Referring to FIG. 6d, which is a close-up cross-sectional view of part of the tubular wall 74 of the travel cap 66 inserted into the annular recess 48, here it can be seen that a pair of opposed ribs 82 protrude from the side wall 84 of the annular recess 48. The barbs 78 provided on the tubular wall 74 of the travel cap 66 ride over the ribs 82 when the travel cap 66 is inserted into the plug 30. The travel cap 66 is pushed firmly against the end surface 58 of the root insert 52, which causes several of the barbs 78 to ride over the ribs 82. Once pushed firmly into the plug 30, a flat back surface 86 of one of the barbs 78 locks against the ribs 82 and prevents the travel cap 66 from being removed from the plug 30. The barbs 78 and ribs 82 together form a snap fit and keep the travel cap 66 pressed firmly against the root insert 52 and prevent it from being removed or dislodged.

(20) The plug 30 and travel cap 66 assembly remains in place until such time as the blade is installed on a wind turbine hub. Immediately prior to installation of the blade, the plug and cap assembly is removed using a suitable tool such as a hex key or Allen key. The hex key is inserted through the circular aperture 73 defined in the centre of the travel cap 66 (see FIG. 6b), and into the hexagonal recess 46 defined in the centre of the solid portion 36 of the plug 30. The hex key is then turned anticlockwise to turn the plug 30 inside the bore 50, thus allowing the plug 30 to be removed.

(21) Once the plugs 30 have been removed, stud bolts are used to connect the blade to the hub, with the bolts being received in the bores 50 of the root inserts 52. As the bores 50 were firmly plugged during the machining process, there is no possibility of swarf being present inside the bores 50 at the time of installation. Furthermore, as the plugs 30 remain inside the bores 50 until the blade is ready for installation, the plugs 30 prevent any debris from entering the bores 50 after the manufacturing process, i.e. during storage and transportation of the blade. Installation of the blades is therefore facilitated by virtue of the perfectly clean bores 50. The blade manufacturing process is also simplified as it is no longer necessary to clean the bores 50 after the machining process, which was a time consuming task.

(22) The present invention may be employed in the manufacture of a wind turbine blade in which the root end of the blade is formed integrally with the remainder of the blade. Equally, the present invention may be employed in the manufacture of modular blades in which the root end of the blade is manufactured separately to other sections of the blade and later joined together to form a complete blade.

(23) Many modifications may be made to the example described above without departing from the scope of the present invention as defined in the accompanying claims. For example, whilst part of the plug described above is tubular, in other embodiments the entire plug may be solid. A tubular second end portion is advantageous however as it reduces the material cost of the plug. The specific dimensions provided above are by way of example only and are not intended to limit the scope of the invention. In other examples the recesses may have different depths for example. Whilst a series of teeth are provided on the travel cap in the above example, in other embodiments the teeth may be provided inside the annular recess, for example, or other interlocking formations may be employed. Whilst the bores described above are defined in root inserts, it will be appreciated that the plug and travel cap of the present invention may be suitably sized for insertion into other bores to prevent debris from accumulating in those bores.