Method for repairing a root of a rotor blade of a wind turbine

Provided is a method for repairing a root of a rotor blade of a wind turbine, the root including several bores for receiving a bolt and extending form the root front surface into the blade, wherein at least a part of the front surface blade material surrounding the bore is removed using a removing tool and that at least one shim plate is attached to the processed front surface surrounding the bore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Application No. 19158010.9, having a filing date of Feb. 19, 2019 and European Application No. 18197714.1, having a filing date of Sep. 28, 2018, the entire contents both of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a method for repairing a root of a rotor blade of a wind turbine, the root comprising several bores for receiving a bolt and extending from the root front face into the blade.

BACKGROUND

Rotor blades are attached to a hub usually by means of blade bolts. If the rotor blade can be pitched the blade is attached to a bearing respectively one of the bearing rings, with the bearing being also attached to the hub with the other bearing ring. The bolts used for mounting the blade are inserted into respective bores provided in the root front surface, which bores extend parallel to each other into the blade. Each bolt is screwed into a threaded bore or a holding bolt which is fixed to the blade and which extends transvers to the bore. With these bolts the blade can be firmly fixed to the hub respectively the bearing.

The blade bolts are subjected to wear, which is quite frequently a symptom of wear of the blade root itself. Wear may occur by leaking grease or lubricant from the sealing of the bearing, which leakage ingresses in the mounting area, thus the root front surface and the bolts. The wear of the bolts may finally result in a breakage.

As depicted above, due to the direct attachment of the blade respectively the root front surface to the bearing the ingress of leaking material negatively influences at first the blade root material. Wear was seen from 0.3-1.0 mm leading to increased stress on the blade bolts in this area. Even if a bearing reinforcement blade protects the blade root, wear may occur in this area visually as a collar around the bolt bore in the root, where the bearing reinforcement blade protects the blade root.

SUMMARY

An aspect relates to a method for repairing a root in case of wear.

For solving the problem embodiments of the invention proposes a method for repairing a root of a rotor blade of wind turbine, the root comprising several bores for receiving a bolt and extending from the root front surface into the blade, which method is characterized in that at least a part of the front surface blade material surrounding the bore is removed using a removing tool and that at least one shim plate is attached to the processed front surface surrounding the bore.

According to embodiments of the invention the root material at the root front surface is partially removed by processing the front surface with a removing tool. This allows to remove the material surrounding the bore and allows especially to remove the material in areas where wear is given, while areas which are still intact do not need to be processed.

After removing the worn material at least one shim plate is attached to the processed area of the front surface, which shim plate is designed to surround the bore.

The inventive method allows for an easy, fast and, if necessary, only local repair of the root front surface and providing a new surface area with the attached shim plate. Also, a tension area at the root may be secured by means of the shim plate, which, as depicted above, surrounds the bolt bore. This is especially advantageous when the inventive repair is done together with an exchange of a blade bearing seal, because any leakage may be stopped and any further leakage, which could enter the bore respectively the bolt in the front surface region may be prevented. Thus, embodiments of the invention not only allow for repairing respectively restoring a correct surface for attaching the blade root to the hub respectively the sealing but also for tensioning the bolts and stopping further leakage and thus any resulting wear problems.

According to embodiments of the invention a removing tool is used for processing the root front surface. During this processing state only an area surrounding one bore may be processed with the tool. This is possible, especially when wear is only given in a smaller local area around certain bores. During this process for example a ring-shaped area of root surface material around the bore is removed, thus a kind of ring-shaped recess of groove is realized for accommodating a ring-shaped shim plate. In case two or more neighbouring hole areas need to be processed, it is possible that the material is removed again in a ring-shaped form, but the respective ring-shaped grooves or reaseses overlap each other. In this case for example ring shaped shim plates may be used, which have an adapted outer circumference with one half-moon recess into which the neighbouring plate engages.

In an alternative to the above mentioned single processed area, it is possible that an area surrounding several bores is processed. This may be done if the area surrounding several neighbouring bores is worn in order to accelerate the material removal stage.

The shim plate or the shim plates, which are used, may have different shapes. For example, a shim plate may be used having only one opening, which shim plate surrounds only one bore. This shim plate has a ring shape respectively is disc-like with the central hole. In an alternative a shim plate having more than one opening, surrounding more than one bore may be used. This elongated shim plate is used when a larger material area at the root front surface is removed, which larger shim plate covers the whole area. In this case only one shim plate needs to be attached, but not several shim plates.

A shim plate, having only one opening, may have a ring form, an oval form, a rectangular or polygonal form. A ring-shaped shim plate is used, which is easy to produce, and which may also easily be inserted into the circular groove or recess in a form fit, an embodiment, to which is referred afterwards.

If a shim plate having more than one opening is used, this shim plate has a bended form according to the radius of the root front surface in order to follow the curvature of the root. The shim plate may have a rectangular or polygonal form, it may also have a free form or may be provided with round ends, especially when a rectangular or polygonal form is used. In case a free form is used, this free form may for example comprise ring shaped sections, in which the opening is provided, which sections are connected via bridging bars or the like.

While it is possible to remove the root material completely around the bore respectively to the bore, it is in an alternative also feasible to process the root front surface that a material ring of unprocessed surface material remains around the bore and that the opening in the or each shim plate has at least the same or a larger diameter as the remaining material ring. This remaining material ring is an area which avoids removed material falling into the bore.

As mentioned above, the shim plate is attached to the processed root front surface, with the opening of the shim plate being concentric to the bore, so that the shim plate surrounds the bore. While it is preferable to arrange only one layer of a shim plate at the front surface, it is also possible to arrange two or more shim plates stacked above each other. This for example allows to adjust the total height of the shim plate stack in order to adjust it to the depth of the recess or area where the material was removed. The shim plates may be provided in a set comprising several shim plates having different thickness, for example within a range of 0.1-10.0 mm, so that it is possible to very precisely adjust the stack height.

According to a preferred embodiment of the invention it is possible to insert the or each shim plate with a form fit into the processed route front surface. As already mentioned above, a rotating removal tool, for example a milling tool, is used, which allows to process a circular ring-shaped groove or recess around the bore. In this case the or each shim plate may easily be form fitted into this recess by using a round, disc-like or ring-like shim plate. In case the processed ring-shaped areas slightly overlap the form fit shim plates have an adapted outer circumference with one half-moon recess into which the neighbouring plate engages. This form fit allow for a slight fixation of the respective shim plate, which is additionally also fixed to the root by means of a fixation device, for example a screw, which is screwed into the root front surface. It may also be fixed by means of a glue or the like.

The shim plate or the stacked shim plates are arranged flush with the unprocessed front surface. This secures that, after the final repair, the root front surface has a uniform surface respectively a uniform plane. It is also possible that the shim plate or the plate stacked very slightly extents above the unprocessed surface, while it should not be lower than the surface, as in this case an opening remains into which again any harming lubricant or the like may enter.

The depth, to which the root front surfaces is processed, may be within the range of 0.1-10 mm relative to the unprocessed root front surface. Also, the or each shim plate may have a thickness of 0.1-10 mm, while the thickness of a single shim plate may be smaller than the processed depth due to the possibility to stack several shim plates.

As already mentioned above, it is possible to fix the shim plate or the stacked shim plate when being attached at the root by means of a fixation device, even if no form fit is given. This fixation device may be, as mentioned, for example a screw or an adhesive or the like.

In a preferred embodiment a shim plate having a sealing provided at least at the side facing away from the root front surfaces used. This seal is attached to the surface of the hub or the bearing. As this sealing surrounds the opening of the shim plate it also surrounds the bore and thus is a sealing area which additionally prevents any harming lubricant from entering the area of the bolt. It is also possible to provide both sides of the sealing plate with respective sealing means. In case several shim plates are stacked, at least the outermost shim plate is provided with the sealing, while also sealings may be provided at the other shim plates for providing respective sealing levels also within the stack.

A sealing may be realized in form of an O-ring when ring or disc-shaped sealing plates are used. These sealing rings are arranged close to the outer circumference of the respective shim plate. If larger shim plates surrounding several holes are used, also an O-ring, which is arranged close to the outer circumference, may be used. In an alternative to such an O-ring, also a paste-like, curable sealing means may be used. A third alternative is a sealing tape which is attached to the respective plate. For attaching the respective sealing, no matter what it is, a small groove may be provided in the surface of the sealing plate, into which groove the sealing means is attached.

The shim plate may be of various material, for example metal or an appropriate polymer (plastic). Also, a shim plate made of a composite material, for example comprising metal and polymer layers or a combination of a metal and a fibre material or the like may be used, while also pure fibre material plates may be used.

As already mentioned above, the removal tool is used for removing the worn surface material. A rotating tool like a milling tool is used. This rotating tool allows an easy preparation of the respective mentioned circular grooves or recesses surrounding a bore, or, when the working radius of the milling tool is large enough, for processing also larger areas of the front surface.

The removing tool may be attached to the root by means of a clamping mechanism engaging at the inner and outer surface of the root. This engaging mechanism may comprise holding brackets or clamping arms, which are firmly attached or clamped against the walls of the root for firmly fixing the tool. In an alternative it is also possible that the tool is fixed to the root by means of one or two bolts inserted into bores adjacent to the area to be processes. In this embodiment respective bolts are screwed into the transverse fixation bolts, into which, when mounted, the blade bolts are screwed.

In another embodiment a removing tool comprising a tool frame which is to be attached to the plate and an exchangeable tool head is used. This allows to simply change the tool head comprising the milling part for switching from a tool processing a smaller area like only an area around one hole to a tool used for processing larger areas.

Finally, it is preferably to use a tool with a processing dust removal device like a suction device or a kind of reservoir into which the dust accumulates.

Aside the method for repairing the root embodiments of the invention also refers to a rotor blade for a wind turbine, with a root comprising several bores for receiving a bolt and extending from the root front surface into the blade. This rotor blade is characterized in that the root is repaired according to the method depicted above with at least one shim plate arranged at the root front surface.

DETAILED DESCRIPTION

FIG.1shows a principle sketch of a rotor blade1for a wind turbine, comprising a root2, which root2is attached to the hub respectively a pitch bearing arranged at the hub.

The root2comprises a root front surface3, where several bores4are provided, into which respective bolts are inserted used for fixing the rotor blade1to the hub respectively the bearing, which bolts are screwed in respective threaded bores of fixation bolts5fixed to the root2and extending transverse to the respective bores4.

In an area6around the bore4shown in the middle of the depicted example the front surface3respectively the surface material is worn, as depicted by the lines resembling to some kind of cracks or the like. This area is harmful, as a lubricant or like grease or the like from the pitch bearing, which leaks the bearing respectively the bearing seal, may ingress this area6and thus may further wear this area resulting also in wear of the bolt, which may rust and, in worst case, finally break. To repair this area6a removal tool, which is disclosed in further detail later on, is used.

With this tool a circular groove or recess7, seeFIG.2, surrounding the bore4is removed. The diameter of the recess7, and thus the working zone of the removal tool, a milling tool, is adjusted to the dimension of the area6.

After removal of the worn material a shim plate8having in this embodiment also a ring shaped or disc shaped form is inserted into the recess7. The shim plate8comprises an opening9which has at least the same diameter as the bore4, but may have also a slighter larger diameter, as it is possible to process the root front surface3in a way that a material ring, which is unprocessed, may remain surrounding the bore4.

Nevertheless, after providing the recess7the shim plate8is inserted into the recess7, with the opening9being concentric to the bore4. Due to the corresponding geometry the shim plate8is inserted in a form fit manner in the recess7. It may be fixed in the recess7with the fixation means like a screw or an adhesive or the like.

FIG.4shows a sectional view of the blade root2along the lines IV-IV inFIG.3. It shows that the shim plate8is inserted with a form fit in the recess. The depth of the recess7, which may be between 0.1-10 mm, and the height of the shim plate8are the same, so that the surface10of the shim plate8flushes with the unprocessed root front surface3.

FIG.4shows a dashed line11extending through the shim plate8. This line shall indicate, that it is also possible to stack two separate shim plates8above each other, in case of need also more than two shim plates, having the same geometry. The shim plates8may have the same thickness or a varying thickness. It is possible to provide a whole set of shim plates having varying thicknesses, from a very low thickness of for example 0.1 mm to a remarkably high thickness of 10 mm. With this set it is possible to precisely adjust the overall height of the shim plate stack in order to flush the surfaces10and3. The stacked shim plates may also be fixed to each other or with one common fixation screw.

FIG.4shows an embodiment of a rotor blade1with a root2and a root front surface3, in which respective bores4are provided. In this embodiment the removal or milling tool has a remarkably large working diameter, which is indicated by the dashed lines12. The working diameter overlaps. This allows for producing a relatively large recess7extending or surrounding several bores4, in the shown embodiment it covers three bores4.

FIG.5also shows a shim plate8of another embodiment, which is formed according to the geometry of the recess7shown inFIG.4. It is, according to the curvature of the root2, bent and has rounded edges13corresponding to the edge geometry of the recess7.

Similar to the previously described embodiment this shim plate8is inserted into the recess7and fixed by screwing or gluing or the like. It covers the whole area respectively recess7, thus repair the worn surface area surrounding several bores4.

Also, in this embodiment it is possible to stack several identically shaped shim plates8, as already mentioned toFIG.4.

FIG.7shows a principle sketch of a removal tool14, here a milling tool, which is attached to the root2and which is used for preparing a recess according to the embodiment ofFIG.2. The removal tool4comprises a tool frame15which is, seeFIG.8, fixed to the root2by means of bolts16which are inserted into bores4adjacent to the bore4which is processed. These bolts16are screwed into the respective fixation bolts5.

FIG.8shows only the tool frame15but not the tool head17, which is also shown inFIG.6. The tool head17comprises a processing dust removal device18, here in form of a box, to which for example a suction device like a vacuum cleaner may be attached. This is to avoid any processing dust falling in the processed bore4.

As the tool head17is removeable from the tool frame15it is possible to change the tool head if need be, thus using a tool head which provides recesses according toFIG.2or change the tool head17to a head with a larger working diameter for preparing recesses according toFIG.5.

FIG.7shows a front view of the root front surface3showing a bore4in the unprocessed root front surface3and a bore4with a processed recess7surrounding it. In this embodiment a remaining ring19of unprocessed surface material surrounds the bore4. The shim plate8, one of which is shown inFIG.8, form fits into this recess7and therefore has a diameter of its opening9which corresponds to the outer diameter of the remaining material ring19.

In the situation shown inFIG.7the removal tool14is attached to the root2and processes another bore4.

The result of these processing stages is shown inFIG.8, with the recess7milled around the bore4. For preparing the remaining material ring19a sleeve20may be used which is inserted into the bore4and which defines the outer diameter of the material ring19respectively covers it while the recess7is milled.

FIG.9shows the root front surface3with two shim plates8form fitted into the respective recesses7. As mentioned before the surfaces10of the respective shim plates8flush with the front surface3or very slightly extend over this front surface.

When the repair is finished the rotor blade1can be remounted. After attaching it to the hub respectively the bearing the unprocessed root front surface3and the shim plate surfaces10are tightly fixed against the corresponding hub or bearing surface. As the shim plate surface10is new and completely unworn, any ingress of harming lubricant like grease, water or the like to the secured bore4is avoided.

FIG.10shows another embodiment of shim plate8.FIG.10shows the root front surface3with three bores4and with three recesses7provided in the root front surface3leaving a remaining material ring19around the respective bore4. As shown the recesses7slightly overlap. For form fitting the respective shim plates8it is necessary to adapt their geometry. Due to the overlap each shim plate8comprises a half moon like recess20into which the adjacent shim plate8engages.

Furthermore, each shim plate8comprises a sealing21, here in form of an O-ring which is inserted into a respective groove22provided close to the outer circumference of the respective shim plate8. This sealing21abuts the respective adjacent surface of the hub respectively the bearing and tightly seals the area of the respective bore4to the surrounding avoiding any ingress of harming substances.

Aside an O-ring it is possible to use a paste-like, curable sealing means filled in the respective groove22or a sealing tape or the like.

FIG.10also shows respective fixation means23in form of screws which extend through respective openings in the respective shim plates8and which are screwed in the bottom of the respective recess7for fixing the shim plate8. Aside such a screw also an adhesive may be used.

Finally,FIG.11shows a wind turbine24, comprising a nacelle25arranged at a tower26. The nacelle25comprises a hub26, to which several inventive rotor blades1are attached, after they were repaired according to the inventive method.