Patent Application
20160009005
The invention relates generally to the field of wind turbines, and more particularly to a method of manufacturing a wind turbine blade.
Wind turbine blades may be formed using a wind turbine blade mold that includes two outer mold parts that fit together around a mandrel. When so arranged, the two outer mold parts and the mandrel define a cavity that takes the profile of the wind turbine blade to be formed. Fibers are positioned within the cavity, and a curable material (such as an epoxy resin) is injected into the cavity. Injection of the curable material may be expedited by various techniques, such as by using a vacuum to draw the curable material through the cavity.
The industry is trending towards larger wind turbines. A larger wind turbine may require a larger blade, and with an increase in blade size is an exponential increase in a structural volume and/or mass of a root section of the blade. Due to this increase in mass and volume, there are growing manufacturing issues associated with the root section. Consequently, there is room in the art for improvement.
The invention is explained in the following description in view of the drawings that show:
The present inventors have recognized that the increasing size and mass of the wind turbine blade casting is creating a root section of the casting so large that it is deforming under its own weight during the curing process. The resulting deformation of the root section from its design profile causes the root section to cure in a deformed/non-optimal profile.
A root section having an undesired cured profile gives rise to a number of issues, including, but not limited to: additional circumferential fatigue and buckling issues; tolerances beyond accepted criteria leading to difficulty when connecting the root section to a hub of the wind turbine; and bending stresses in the bolts connecting the root section to the hub. Each of these issues increases the likelihood of a failure in the wind turbine.
The present inventors have devised an innovative method for reducing and/or eliminating this gravity-induced deformation altogether. The inventors propose to repeatedly reposition the mold while the curing material cures. By repositioning the mold, a rate of deformation for any given location can be reduced, and previously formed deformations can be decreased in size.
In an exemplary embodiment of the method disclosed herein,
In an exemplary embodiment of the method disclosed herein,
While this exemplary embodiment shows three mold positions 40, 60, 70, there may be as many or as few mold positions as is deemed desirable. Further, the amount of angular displacement need not be limited to ninety or one hundred eighty degrees, but may be any amount deemed desirable. Likewise, the mold 12 may be rotated the same direction between stops, or it may be rotated in alternating directions between stops, or it may be rotated in any sequence of directions deemed desirable. In an exemplary embodiment, a stepper motor may be used and the mold rotated by a discrete angular displacement, stopped, and the process repeated as many times as desirable, from one stop during the curing to as many stops as the configuration will permit during the curing. The discrete angular displacements may be equal between each stop, or some or all may be unequal. Likewise, the dwell times for each stop may be equal, or some or all may be unequal. Further, the direction of rotation may be the same between stops, may alternate, or may follow any pattern. Consequently, the movement may follow a predetermined pattern of angular displacements, rotation directions, and stops, and/or it may determine the next best angular displacement, rotation direction, and dwell time based on feedback from the sensors monitoring the curing and deformation. As more stops are utilized, more of the casting 18 may deform, but the actual profile deviates less, on average, from the design profile.
Further, the mold 12 may be held in any of the stopped positions for any amount of time. In an exemplary embodiment, the shortest amount of time would be the minimum amount of time necessary to change directions and start rotating the mold 12 in the other direction. In this exemplary embodiment the mold 12 may simply be rotated for a selected angular displacement, stopped long enough to permit a change in direction of rotation, and then rotated for another selected angular displacement. These minimum stop times may not be used, or may be used for some or all of the stops.
Alternately, there may be two or more winches 82 at each end 88 and the mold 12 can be rotated by retracting one winch cable and extending the other. Alternately, the weight of the mold 12 may be supported by a stand arrangement 24, while the winches effect the rotation. Any combination can be used so long as it is capable of supporting the mold 12 and rotating the mold 12 about its long axis 26.
In addition to the above advantages, the method may be useful to help distribute the curable material 42 throughout the cavity 20. There is a limit as to, for example, how much vacuum can be applied to the mold 12 and its associated components (mandrels, vacuum bags, injection system etc.). As blades get larger, problems are encountered, and even more problems are anticipated, when a fixed vacuum pressure is required to pull large amount of curable material 42 (such as epoxy resin) through a larger (and exponentially increasing) volume of fibers, (such as glass fibers). This increases the chances that the curable material 42 will not fully permeate the cavity 20, possibly leaving dry spots. These dry spots require special attention after the molding process, and thereby incur time and expense. By rotating and then stopping the mold 12, the force of gravity on the curable material 42 can be used to guide the curable material 42. This process can then be used to ensure the curable material 42 reaches all areas of the cavity 20, and thus dry spots can be mitigated or eliminated altogether. In this manner the rotation helps distribute the curable material 42 not through centrifugal forces, but instead by orienting the cavity 20 in such a way as to allow gravity to cause the distribution. Centrifugal forces may be negligible during rotation and nonexistent when the mold is stopped.
When the mold 12 is rotated and stopped in a manner that also guides the curable material 42, then the motion is serving a dual purpose: to mitigate/prevent deformation, and to aid in the distribution of the curable material 42. In such an exemplary embodiment, movement characteristics such as the magnitude of the angular displacement between stops, the time taken to accomplish the angular displacement, and the dwell time at the stops etc. may take into consideration deformation factors as well as distribution factors. Since the curable material 42 flows through the entire cavity 20, from a base of the blade to a tip of the blade, and since the blade is not symmetric along its length, and since the injection points for the curable material and the vacuum points may not be uniformly distributed around the cavity 20, it may be that at times the distribution factors take priority over the deformation factors.
For example, there may be a particular angular position that is favored in order to facilitate distribution of the curable material 42 due to an asymmetric shape of the casting 18 at, for example, the max-cord portion of the casting 18. To properly distribute the curable material 42, perhaps the mold 12 might need to maintain the particular angular position for a time longer than deformation factors alone would permit. The result is the necessary distribution of the curable material 42 at the example max-cord portion of the casting 18, but at the expense of greater deformation of the root portion during that stop. However, once the curable material 42 is distributed as necessary, the deformation factors may then take priority, and the extra deformation incurred may be mitigated and/or removed. When all factors are considered, such as when the particulars of the root section of the casting 18 are taken into account, and/or when there are multiple factors being considered simultaneously, such as deformation factors and distribution factors, it is evident that the movement characteristics may be varied in any manner necessary to accomplish the deformation mitigation and/or distribution etc. The resulting motions may not appear to be symmetric, or to have an apparent pattern, and this is within the scope of the disclosure.
In addition, the root section or any section may be monitored during the casting and curing operations for deformation and the movement characteristics may be adjusted in response to a detected deformation. A sensor such as a strain gauge or an optical gauge etc may compare a design profile to an existing profile, and or may monitor a change in the profile in one or all angular positions of the mold 12. A processor may receive sensor inputs regarding the deformation and may be programmed to adjust the movement characteristics in response to the sensor inputs. For example, perhaps experience indicates a particular amount of deformation may be expected under certain conditions. A base pattern of movement may be developed for the casting and curing operations. However, the processor may be configured to adjust from the base pattern in response to the deformation sensed during the instant casting and curing operation. Alternately, the processor may be configured to alert so an operator can make manual adjustments.
Similarly, the casting may be monitored while the curable material 42 is infused into the cavity 20 and the movement characteristics may be adjusted in response to less than expected distribution. A sensor such as an optical gauge or a pressure gauge etc. may be used to check for the presence of the curable material 42. The sensor may be positioned, for example, in a location where it is known to be difficult for the curable material 42 to reach. The same processor or a separate processor may receive the sensor inputs regarding the distribution of the curable material 42 and may be programmed to adjust the movement characteristics in response to the sensor inputs. The processor may also be programmed to select the best movement characteristics given the sometimes conflicting deformation and distribution parameters. Alternately, the processor may be configured to alert so an operator can make manual adjustments.
The method disclosed herein may be used in conjunction with other known techniques, such as by adding additional layers of fiber, and/or adding stiff interfaces in the ply layup. However, an advantage of the method disclosed herein is that it does not add mass and complexity to the blade like the conventional techniques do. It is also possible to rotate and stop the mold 12 about a short axis of the mold 12. This may be particularly helpful in aiding the distribution of the curable material 42.
From the foregoing it can be seen that the inventors have devised a simple, yet effective method for tolerance control of a root section of a wind turbine blade casting. Wind turbine castings made using this method have an average actual profile that is closer to the design profile, and have better distribution of the curable material 42. Better average adherence to the design profile reduces circumferential fatigue and buckling issues, improves ease of connection to the hub, and reduces bending stresses in the bolts that connect the blade to the hub. In addition, the method enables greater distribution of the curable material, and this reduces rework necessary to fill in dry spots. This represents a cost and time savings. Consequently, the method represents an improvement in the art.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
