Patent Application
20120279065
The present exemplary embodiment relates to a method for extracting barrel nuts that are bonded in the root of a wind turbine blade. This disclosure finds particular application in conjunction with maintaining the blade root to hub mechanical connection of a wind turbine blade, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also applicable to other similar applications.
A typical utility-scale, horizontal axis wind turbine includes a set of rotor blades mounted to a hub. Two or three or possibly more blades could be used. The blades are aerodynamically designed to interact with the wind to generate a moment force and turn the hub. The hub and the blades together as an assembly (with other components) are typically referred to as the rotor. The rotor is connected to a main shaft and transfers torque to the main shaft, the main shaft may in turn be connected to a speed increasing gearbox that drives an electrical generator, or the main shaft can be directly connected to the electrical generator without a gearbox. The main shaft and its bearings, the gearbox, and the generator are typically mounted on a large base that is positioned inside of a nacelle assembly. The nacelle assembly forms a mostly enclosed structure around all of these machine parts. The nacelle assembly and machine base are typically mounted on top of a tower and can rotate, or yaw, relative thereto to align the rotor blades with the wind direction. Various different designs and topologies are, of course, possible for a wind turbine.
In many wind turbines, the rotor blade is mechanically attached to the hub via studs and barrel nuts.
The root end of the blade can form a relatively thin annular wall that extends from the root end towards the hub. The wall has an exterior annular surface, an interior annular surface and a circular end surface that connects the interior and exterior surfaces. The circular end surface is radially arranged around a central longitudinal axis of the blade, as seen in
Barrel nuts are positioned in the barrel nut bores. As is known, the barrel nuts have an internally threaded hole for a threaded connection to a stud. A stud is pushed through the respective stud bore and threaded to the barrel nut to firmly mechanically attach the studs to the root end of the blade.
From time to time, it may be necessary to remove and replace a barrel nut. The barrel nuts are often glued into position in the barrel nut bores and sealed by epoxy or other materials. This makes removal of the barrel nuts difficult.
One manufacturer of rotor blades recommends a process to heat the end of the barrel nut to be removed. The heat is used to loosen the epoxy material, allowing the barrel nut to be broken free and removed. More specifically, the process involves removing any sealant located around the exterior face and interior face of the barrel nut in the root end. A heater is then applied to the exposed ends of the barrel nut. A C-shaped clamping fixture spans the circular end surface of the root to engage the exterior surface and interior surface of the root end. The C-shape clamping fixture firmly holds a heating element in place against one or both of the exterior face and interior face of the barrel nut. In some instances, the heating element increases the temperature of the exterior or interior face of the barrel nut to a temperature higher than 90° C. to a maximum of approximately 320° C. to reduce the strength or adhesion of the surrounding epoxy. When the barrel nut and the surrounding epoxy is sufficiently heated and softened, the heating element and clamping fixture are removed. Then a second generally C-shaped fixture is employed to break the barrel nut free and force it out of the bore. The second fixture, like the first, spans the circular end surface to engage the interior and exterior surface of the root end. The fixture pushes against the interior end of the barrel nut, and clamps against the exterior surface of the root end, pushing the barrel nut out of its bore and out from the exterior surface. Of course, pushing in the opposite direction toward the interior and the central axis of the blade is also possible.
This existing method and these existing fixtures for removing barrel nuts work as long as the fixtures can span the blade end surface to engage the interior and exterior surfaces of the blade root. However, in some cases, it may be necessary to remove a barrel nut while the blade is attached to the hub, and in such a case, the existing method and fixtures will not work. In this case, the circular end surface abuts the hub and prevents the first and second C-shaped fixtures from engaging the interior and exterior surfaces of the root end. To use the existing method and C-shaped fixtures, the blade must be removed from the hub, and also preferably lowered to the ground. This requirement is a significant disadvantage.
Another disadvantage of the existing method is that the C-shaped fixtures are quite heavy and bulky, and difficult to hoist into position relative to the rotor blade which are also quite large.
Yet another disadvantage of the prior art method and assembly is that heating the exterior or interior face of the barrel nut requires a large amount of energy and heat to reduce the strength of the surrounding epoxy.
For the foregoing reasons, and others, there remains a need for an improved method and apparatus for efficiently removing barrel nuts used for securing studs to a rotor blade.
In one embodiment, the present disclosure pertains to a method for removing barrel nuts used for securing studs to a turbine blade. The method includes connecting an extractor assembly connected to a barrel nut for mechanically securing a stud located about a root end of a turbine blade, the barrel nut being anchored to the root end of the turbine blade. The extractor assembly includes a structural body and a removal device having an internal heating element. The barrel nut is heated through the removal device to a predetermined temperature. The adhesion of the barrel nut to the turbine blade is overcome and the barrel nut is extracted from the turbine blade.
In another embodiment, the present disclosure pertains to a method of removing barrel nuts used for securing studs to a turbine blade while the turbine blade is attached to a hub. The method includes connecting a heating an removal device to the barrel nut while the barrel nut is secured to a root end of a turbine blade. The heating device includes a heating body having a first portion in thermal communication with the barrel nut. The barrel nut is simultaneously heated and extracted from the turbine blade and the attachment of the turbine blade to the hub is maintained.
In still another embodiment, provided is an apparatus for extracting barrel nuts used for securing studs to a turbine blade, the apparatus comprising a structural body for bracing between a barrel nut to be removed from a turbine blade and a removal device. The structural body including a closed end surface, an open end surface defining a cavity configured to accept said barrel nut. A heating element is operatively adapted to provide heat to the barrel nut. The removal device cooperates with the closed end surface opposite the open end surface of the body, the removal device being coupled to the barrel nut.
It is to be understood that the detailed figures are for purposes of illustrating exemplary embodiments only and are not intended to be limiting. Additionally, it will be appreciated that the drawings are not to scale and that portions of certain elements may be exaggerated for the purpose of clarity and ease of illustration.
In accordance with the present disclosure, a method is provided for maintenance of barrel nuts fixed in bores in a rotor blade of a wind turbine. The disclosed method is particularly related to the removal of a barrel nut 200 from a root end 120 of the wind turbine blade 140 so that it can be replaced with a new barrel nut.
With reference to
With reference to
The wind turbine blade 140 changes shape from the root end 120 toward the blade tip 70 until it assumes an air foil shaped configuration as illustrated in
As shown in
From time to time, it may be necessary to remove the barrel nut 200 for service, and potentially replace it with a new barrel nut. For example, when the internal threads 206 of the barrel nut 200 become damaged or due to mechanical or cyclic failure of the barrel nut 200 and stud 150 assembly. Other reasons why it may be necessary to replace a barrel nut include excessive corrosion, a defective barrel nut lot and lightning damage—as one barrel nut on each blade has a bolted connection to the blade or turbine lightning arrest system. Additionally, if the rotor blade 140 is attached to the hub 30, it is highly desirable to remove the barrel nut 200 from inside of the blade 140 and hub 30 only, without needing access to the outside surface of the blade 140. Otherwise, the whole blade 140 has to be removed from the hub 30 to remove and replace the barrel nut 200 and this is extremely expensive and time consuming.
As shown in
A locking nut 365, a torque nut 370 and torque washer 375 can be provided along shaft threads 355 of pull rod 330. Locking nut 365 is threadedly engaged to pull rod 330 and can be located within hollow interior 310 of cylindrical body 305, as shown in
With reference now to
With reference to
Bore hole 400 may generally be of any desired diameter and length, however, it should be appreciated that the bore hole 400 is sized such that at least a portion of shaft threads 355 of the pull rod are inserted within bore hole 400 to threadingly engage an inner surface 405 of bore hole 400. In one embodiment, the bore hole 400 extends along a common central axis of barrel nut 200. Further, the inner surface 405 of bore hole 400 can be tapped or threaded to firmly engage at least a portion of shaft threads 355. An optional second bore hole 410 may be drilled on exposed surface 385 through at least a portion of barrel nut 200 to house thermocouple 380. It should be appreciated that a length of bore hole 400 can be greater than a length of second bore hole 410.
With reference again to
The closed end 347 of pull rod 330 is then inserted in bore hole 400 and at least a portion of shaft threads 355 engage inner surface 405. Locking nut 365 is axially tightened around pull rod 330 until locking nut 365 firmly abuts exposed surface 385. The locking nut 365 is provided to securely engage the pull rod 330 to the barrel nut 200. In one embodiment, high temperature grease is applied to pull rod 330 and inner surface 405 prior to insertion to assist in heat transfer. Further, in another embodiment, pull rod 330 is inserted no less than 4½″ (11.43 cm) through barrel nut 200.
Cylindrical body 305 is slid partially over pull rod 330 whereby base rim 320 abuts the root end 120 of the blade 140. Base rim 320 can have a diameter that is greater than a diameter of barrel nut 200 to allow barrel nut 200 to at least partially occupy hollow interior 310 when removed from root end 120. This is illustrated in
Both heating element 350 and thermocouple 380 are electronically connected to a controller and a power source (not shown). Heating element 350 is activated and provides consistent heat to barrel nut 200 until it reaches a predetermined temperature. In one embodiment, the temperature controller can be set to a value between 70° C. and 80° C., but preferably 75° C. A temperature profile readout is provided by thermocouple 380. When the temperature profile readout reaches approximately 70° C., a user can apply a tightening force to torque nut 370 thereby placing tension on barrel nut 200. The tightening force can be applied by a manually operated tool, such as a wrench 412. In one embodiment, the force applied is less than or equal to 100 ft-lbs (138.3 Newton-meters) of torque. The torque provided overcomes an adhesion of barrel nut 200 to root end 120. Once the barrel nut 200 begins to move, the torque nut 370 is rotated until barrel nut 200 is completely extracted. The heat provided may also cause longitudinal deformation of barrel nut 200 along a central axis thereby decreasing the width of barrel nut 200 and further adding to the ease of extracting barrel nut 200.
With reference now to
In one embodiment, barrel nut 200 can be 4½″ (12.07 cm) long. A diameter of bore hole 400 can be ½″ (1.27 cm). Further, the length of bore hole 400 can be 4½″ (11.43 cm) to allow for sufficient exposure of surface area between pull rod 330 and bore hole 400. In this embodiment, inner surface 405 can be threaded approximately 1″ (2.54) deep from exposed surface 385 of the barrel nut 200 for sufficient threaded engagement with pull rod 330. Additionally, second bore hole 410 can have a 1/16″ (0.42 cm) diameter for thermocouple 380. Notably, these measurements are approximations and other dimensions are also contemplated.
Disclosed has been a method of removing barrel nuts from a wind turbine blade 140 to maintain a sufficient mechanical connection between the root end 120 and a plurality of studs 150. The disclosed method allows removal of barrel nuts from a turbine blade while the blade remains mounted to the hub 30 or on an associate pitch bearing mounted to the hub 30, since access is only needed to the interior face of the turbine blade root end. Thus, the turbine blade can remain in a field service environment during the removal and maintenance of the barrel nut 200 and stud 150. Of course, it is also possible to remove barrel nuts 200 form a turbine blade 140 in a manufacturing environment.
The disclosure has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiments be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
