METHOD OF MASKING A MOULD FOR MOULDING A WIND TURBINE BLADE SHELL PART

A method of masking a mould for moulding a wind turbine blade shell part, the method comprising the steps of: arranging a masking device in a mould so that the masking device covers the non-coating zone of the mould surface, spraying a coating onto a mould surface of the mould so that the coating is applied to a coating zone of the mould surface and prevented from being applied to a non-coating zone of the mould surface by the arrangement of the masking device, and removing the masking device from the mould so that the non-coating zone is exposed. The masking device is configured so that, upon terminating spraying of the coating at the first longitudinal boundary of the coating zone, a lip portion of the masking device is separated from the coating applied on the coating zone by a gap.

TECHNICAL FIELD

The present disclosure relates to a method of masking a mould for moulding a wind turbine blade shell part.

BACKGROUND

Modern day wind turbine blades typically comprise multiple shell parts, such as suction and pressure side shell parts, that are bonded together to form a closed shell. When moulding such wind turbine blade shell part in a mould, the first step is typically to apply a coating to a mould surface of the mould. This applied coating becomes part of the outer coating of the wind turbine blade after the shell part has been infused and cured. However, at this stage, coating is typically not desirable near the bond line to ensure good bonding of the shell parts. Thus, when applying coating on the mould surface, care is taken to avoid applying coating on a non-coating zone of the mould surface adjacent to a longitudinal mould edge of the mould. In prior art methods this is often achieved by arranging a strip of masking tape on the non-coating zone, applying the coating to the coating zone, and then removing the masking tape. Such a method works reasonably well when the masking tape is removed before the coating dries but often leaves a rather sharp step in coating thickness at the boundary. If the masking tape is not removed before coating is dry, the removal of the masking tape often results in peeling of the coating on the coating zone leaving a jagged boundary. This can especially be a problem when the coating is applied autonomously since often the coating is applied in a single pass and afterwards the masking tape can be removed.

After moulding the shell part in the mould, the wind turbine blade is bonded along the bond line and another round of coating is applied to the bond line and the non-coated zone to achieve a uniform outer coating of the wind turbine blade. However, a sharp step in coating thickness at the boundary of the coating zone makes it difficult to provide a uniform coating thickness. In some cases, further post-processing is required such as grinding or sanding the sharp step to a gentle slope. Likewise, when the boundary of the coating zone is jagged, burdensome post-processing can be required, e.g. a full sanding of the boundary to achieve a substantial straight boundary, or even discarding the applied coating and reapplying to the mould surface if observed prior to moulding the shell part.

SUMMARY

On this background, it may be seen as an object of the present disclosure to provide a method of masking a mould for moulding a shell part for a wind turbine blade which at least mitigates some of the above drawbacks of the prior art.

One or more of these objects may be met by aspects of the present disclosure as described in the following.

A first aspect of the present disclosure relates to a method of masking a mould for moulding a shell part for a wind turbine blade, the wind turbine comprising an aerodynamic shell body with a suction side shell part and a pressure side shell part that extends in a longitudinal direction between a root and a tip and in a transverse direction between a leading edge and a trailing edge, wherein the method comprises the steps of:providing:a mould for moulding a shell part, such as the suction or pressure side shell part, of the wind turbine blade, the mould comprising a mould surface having a longitudinal mould edge, a coating zone, and a non-coating zone, the coating zone having a first longitudinal boundary arranged towards the non-coating zone, and the non-coating zone extending longitudinally and extending from the longitudinal mould edge to a second boundary towards the coating zone, anda masking device comprising a lip portion including a longitudinal masking edge preferably extending along the longitudinal direction:arranging the masking device in the mould so that the masking device covers the non-coating zone of the mould surface and so that the longitudinal masking edge of the masking device delimits the first longitudinal boundary of the coating zone:spraying a coating, such as a gelcoat, onto the mould surface so that the coating is applied to the coating zone, and so that coating is prevented from being applied to the non-coating zone by the arrangement of the masking device; andremoving the masking device from the mould so that the non-coating zone is exposed:

wherein the masking device is configured so that, upon terminating spraying of the coating at the first longitudinal boundary of the coating zone, the lip portion of the masking device is separated from the coating applied on the first longitudinal boundary of the coating zone by a gap.

By arranging the masking device so that a gap between the wet coating and the lip portion of the masking device is present when terminating spraying of coating may provide the advantage of allowing the coating to dry without risking peeling off parts of the coating when subsequently removing the masking device from the mould. Accordingly, the quality of the moulded wind turbine blade shell part is improved. Allowing the masking device to stay on the mould for an extended period while the coating dries may further increase the flexibility of the coating process. For instance, an operator can perform other tasks while the coating dries instead of being required to promptly remove the masking device after coating application. Further, such a method may allow the spray coating process to be automated, e.g. by a spray coating robot, while the masking device may still be manually removed. In some automated spray coating processes, operators are not allowed near the mould while the spray coating robot applies the coating. Therefore, the coating applied at one end of the mould may dry before an operator can remove the masking device and before the spray coating process has finished. The present method advantageously provides a gap between the lip portion of the masking device and the applied coating that allow removal of the masking device even when the applied coating has dried without risking peeling of the dry coating.

In the context of the present disclosure, both the mould and the resulting shell part for a wind turbine blade extend along the same longitudinal direction.

Additionally or alternatively, the mould surface may comprise a transition zone that extends longitudinally along the longitudinal direction. The transition zone may extend from the first longitudinal boundary of the coating zone to the second boundary of non-coating zone. The lip portion may be arranged so that during spraying of the coating at the first longitudinal boundary, coating is partially applied through the gap to the transition zone beneath the lip portion of the masking device. The lip portion of the masking device may be arranged so that a coverage and/or thickness of the coating applied to the transition zone gradually decreases from the first longitudinal boundary of the coating zone, e.g. 100% coverage and/or 100% of the coating thickness on the coating zone, to the second boundary of the non-coating zone, e.g. so that no coating is present on the second boundary.

Compared to a prior art method resulting in a sharp boundary line between the coating zone and the non-coating zone, such as a method involving masking tape, a transition zone with gradual coating coverage may prove advantageous in a post-moulding process. After bonding the suction and pressure side shell parts along a bond line, a second coating similar or identical to the coating applied to individual shell parts is applied to the area delimited by the first longitudinal boundary of the suction side shell part and the first longitudinal boundary of the pressure side shell part. When the shell parts include a transition zone, the second coating can be applied on transition zones along with the non-coating zones of the shell parts to achieve a uniform coating. Such a uniform coating avoids edges or coating thickness steps between the coating zones and the non-coating zones of the shell parts. In particular, the method may advantageously avoid a coating thickness step at the first longitudinal boundaries or a post-process of eliminating such a step. The present method instead provides a coating that gradually increases in coverage and/or thickness from the non-coating zone to the coating zone that advantageously allows easy post-moulding process of applying the second coating to obtain a uniform coating on the entire surface of the suction and pressure side shell parts including on the bond line.

Additionally or alternatively, the coverage of the coating applied to the transition zone may decrease from 100% at the first longitudinal boundary to 0% at the second boundary. The first longitudinal boundary and the second boundary may be parallel and may be separated by a distance of 0.5-10 cm, preferably 1-5 cm, more preferably 2-3 cm.

Additionally or alternatively, the masking device may be biased to urge the lip portion away from the mould surface so that, upon terminating spraying of the coating at the first longitudinal boundary of the coating zone, the lip portion returns to a position in which the lip portion of the masking device is separated from the coating applied on the first longitudinal boundary of the coating zone by the gap.

Additionally, the lip portion may have a resting position in which the lip portion extends non-parallel to and/or is angled away from to mould surface.

Additionally or alternatively, the masking device may comprise a body portion and a separation element. The separation element may be arranged between the body portion and the lip portion of the masking device and at a distance to the longitudinal masking edge. Further, the step of arranging the masking device in the mould may comprise contacting the separation element with the non-coating zone of the mould surface so that the gap separating the lip portion of the masking device from the coating applied on the first longitudinal boundary of the coating zone is provided by the separation element.

During spraying of the coating on the coating zone, especially near or at the first longitudinal boundary, pressure is applied to the masking device forcing it towards the mould surface. By including such a separation element, the pressure is transmitted to the mould surface via the separation element so as to provide the gap between the lip portion of the masking device and the coating applied on the first longitudinal boundary of the coating zone during and upon termination of the application of coating on the coating zone near or at the first longitudinal boundary.

Additionally, the separation element may be formed by a protrusion of the masking device and wherein the separation element preferably contacts the mould surface non-adhesively. Alternatively, the separation element may be formed separately from the masking device, and the separation element may preferably adhesively contact the mould surface.

By providing the masking device with a protrusion forming the separation element allows handling of the masking device as a single entity thus easing arrangement of the masking device in the mould. Further, in a typical mould setup, the mould surface is coated with a slip coating which allows the moulded shell part to more easily be removed from the mould without sticking to the mould. By contacting the separation element non-adhesively with the mould surface may allow a wider range of slip coatings on the mould surface since the slip coating does not have allow the separation element to stick to the mould surface. Further, such a separation element may allow easy removal of the mould device.

Additionally or alternatively, the method may comprise a step of arranging one or more clamps on the masking device so as to clamp the masking device to the mould surface.

This may reduce or eliminate the risk of the masking device being dislocated by pressure applied by the coating spraying process.

Additionally or alternatively, the gap between the lip portion of the masking device and the coating applied on the first longitudinal boundary of the coating zone may be at least 0.1 mm, preferably at least 0.5 mm, more preferably at least 1.0 mm.

Additionally or alternatively, the gap between the lip portion of the masking device and the mould surface may be at least 1.0 mm, preferably at least 1.5 mm, more preferably at least 2.0 mm.

Additionally or alternatively, a width of the non-coating zone from the longitudinal mould edge to the second boundary may be in the range of 100-500 mm, preferably in the range of 200-400 mm.

Additionally or alternatively, the width of the non-coating zone in a tip region of the mould may be in the range of 200-300 mm, and/or the width of the non-coating zone in a root region of the mould may be in the range of 300-400 mm.

Additionally or alternatively, the masking device may comprise a plurality of individual masking elements each having a lip portion with a longitudinal masking edge. The step of arranging the masking device in the mould may comprise arranging the plurality of masking elements so that longitudinal masking edge of each masking element extends in parallel and substantially coincides to delimit the first longitudinal boundary of the coating zone.

Such a method may be especially advantageous for moulds for longer wind turbine blades as each masking element may be made of a size and weight that can be handled by a single operator.

Additionally or alternatively, the masking device may comprise or consist essentially of a polymer material, such as silicone or EPDM rubber.

Additionally or alternatively, the step of arranging the masking device in the mould may comprise attaching the masking device to the mould, e.g. to a mould flange of the mould. This step may be achieved by attaching the plurality of clamps to the masking device thus clamping the masking device to the mould surface of the mould.

A second aspect of this disclosure relates to a masking device for use in a method according to the first aspect of present disclosure.

A third aspect relates to a use of a masking device in a method according to the first aspect of the present disclosure.

A person skilled in the art will appreciate that any one or more of the above aspects of this disclosure and embodiments thereof may be combined with any one or more of the other aspects of this disclosure and embodiments thereof.

DETAILED DESCRIPTION OF THE INVENTION

In the following figure description, the same reference numbers refer to the same elements and may thus not be described in relation to all figures.

FIG.1illustrates a conventional modern upwind wind turbine2according to the so-called “Danish concept” with a tower4, a nacelle6and a rotor with a substantially horizontal rotor shaft which may include a tilt angle of a few degrees. The rotor includes a hub8and three blades10extending radially from the hub8, each having a blade root16nearest the hub and a blade tip14furthest from the hub8.

FIG.2shows a schematic view of an exemplary wind turbine blade10. The wind turbine blade10has the shape of a conventional wind turbine blade with a root end17and a tip end15and comprises a root region30closest to the hub, a profiled or an airfoil region34furthest away from the hub and a transition region32between the root region30and the airfoil region34. The airfoil region has a tip region36closest to the tip15of the blade. The blade10comprises a leading edge18facing the direction of rotation of the blade10, when the blade is mounted on the hub8, and a trailing edge20facing the opposite direction of the leading edge18.

The airfoil region34(also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region30due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade10to the hub. The diameter (or the chord) of the root region30may be constant along the entire root region30. The transition region32has a transitional profile gradually changing from the circular or elliptical shape of the root region30to the airfoil profile of the airfoil region34. The chord length of the transition region32typically increases with increasing distance r from the hub. The airfoil region34has an airfoil profile with a chord extending between the leading edge18and the trailing edge20of the blade10. The width of the chord decreases with increasing distance r from the hub.

A shoulder38of the blade10is defined as the position, where the blade10has its largest chord length. The shoulder38is typically provided at the boundary between the transition region32and the airfoil region34.

It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

The blade10is typically made from a pressure side shell part24and a suction side shell part26that are glued to each other along bond lines28at the leading edge18and the trailing edge20of the blade to form an aerodynamic shell body of the wind turbine blade10.

FIG.3illustrates a mould40for moulding a shell part, such as the suction side shell part26or pressure side shell part24of the wind turbine blade10(as shown inFIG.2). The mould40has a root region30for moulding the root16of the wind turbine blade10and a tip region36for moulding the tip14of the wind turbine blade10. The mould40comprises a mould surface41with a longitudinal mould edge42, a coating zone44, a transition zone48, and a non-coating zone46. The coating zone44has a first longitudinal boundary45arranged towards the non-coating zone46. The non-coating zone46extends longitudinally along the mould40and further extends from the longitudinal mould edge42to a second boundary47towards the coating zone44. The transition zone48extends from the first longitudinal boundary45of the coating zone44to the second boundary47of non-coating zone46.

Before applying a coating to the coating zone44, the mould40is masked. This is performed by providing a masking device50comprising a lip portion52including a longitudinal masking edge53extending along the longitudinal direction of the mould40. The masking device50is then arranged in the mould40as shown inFIG.4. In the present embodiment, the masking device50is divided into separate masking elements57but the masking device50may in other embodiments be formed in one piece. A plurality of clamps60that reaches around the mould flange43and forcing the masking device50onto the mould surface41thereby attaching the masking device to the mould40. In this arrangement, the masking device50covers the non-coating zone46of the mould surface41by overlapping the transition zone48and extending to the first longitudinal boundary45of the coating zone44as best seen inFIGS.6A-6D. Thus, the longitudinal masking edge53of the masking device50delimits the first longitudinal boundary45of the coating zone44. Further, a gap G separates the lip portion52of the masking device50and the first longitudinal boundary45of the coating zone44. The gap G as measured from the mould surface41to the longitudinal masking edge53is at least the maximum coating thickness together with a safety tolerance, such as between 1.0-10 mm. The masking device is configured so that, upon terminating spraying of the coating at the first longitudinal boundary45of the coating zone44, the lip portion52of the masking device50is separated from the coating70(as shown inFIG.5) applied on the first longitudinal boundary45of the coating zone44by the gap G. This can be achieved by the masking devices50as shown inFIG.6A-6Dwhich are discussed in more detail below. In principle, the gap G needs only be present while the coating has not yet dried. Thus, in some embodiments, the lip portion52is forced to contact the mould surface41by the spray force of the coating being applied but once the spray force stops, the lip portion returns to its original shape to provide the gap G between the lip portion52and the mould surface41. After application of the coating and even after the coating has dried, the masking device50can be removed from the mould40to reveal the zones44,46,48of the mould surface41. As shown inFIG.5, a full layer of coating has been applied onto the coating zone44, while a layer of coating that gradually decreases in thickness and/or coverage has been applied to the transition layer48(which is often seen as a “cloudy” or spotted layer), and no coating has been applied to the non-coating zone46. The coverage of the coating applied to the transition zone48decreases from 100% at the first longitudinal boundary45to 0% at the second boundary47. The first longitudinal boundary45and the second boundary47are parallel and may in some cases be distanced from each other by 2-3 cm.

Turning toFIGS.6A-6D, four embodiments of a masking device50are shown. All embodiments of the masking device50have an attachment portion55which is fixed to the mould40, in particular the mould flange43. However, different embodiments are envisioned but not shown in which the masking device is suspended in the mould40without being necessarily fixed to the mould40. The coating is sprayed substantially perpendicularly to the coating zone44via a spray nozzle72as schematically shown in the figures.

InFIG.6A, a first embodiment of the masking device50is shown in which both the body portion51and the lip portion52extend along the longitudinal direction (through the plane ofFIG.6A) and along a transverse direction (in the plane ofFIG.6A). The body portion51lies substantially flat against the mould surface41and the lip portion52curved outwards away from the mould surface41. The masking device50has sufficient weight and stiffness so that during spraying of the coating, the gap G does not substantially diminish and is thus preserved during the application of the coating. Such sufficient weight and stiffness depend on the spray force of the spray nozzle72and on the characteristics of the coating.

The second embodiment shown inFIG.6B, differs from the first embodiment shown inFIG.6Ain that a body joint56is arranged between the body portion51and the attachment portion55. This body joint56allows the body portion51to flex about the body joint56relative to the attachment portion55. This enables the provision of a relatively rigid body portion51and lip portion52while allowing the body portion51and the lip portion52to conform to the changing gradient of the mould surface41along the longitudinal direction (through the plane of theFIG.6B). The body joint56can be provided as a hinge, such as a living hinge.

Turning toFIG.6C, a third embodiment of the masking device50is shown. The third embodiment of the masking device50comprises a protrusion54arranged between the lip portion52and the body portion51. The protrusion54contacts the mould surface41at the second boundary47and prevents the lip portion52from being forced to contact the mould surface41when coating is sprayed at the first longitudinal boundary45by the spray nozzle72. Thus, the protrusion47maintains the gap G during coating application.

Lastly, a fourth embodiment is shown inFIG.6D. The fourth embodiment differs from the first embodiment in that the lip portion52, in its resting position as shown inFIG.6D, is angled outwardly, away from the mould surface41, so that when coating is applied and a spray force urges and deforms the lip portion52towards the mould surface41, the angling of the lip portion52ensures that the lip portion52resists this deformation towards the mould surface41. Thus, during coating application, the gap G is reduced but still maintained. In this embodiment, the body portion51preferably mates with the non-coating zone46of the mould surface41.