Patent Description:
Generally, a wind turbine includes a turbine that has a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower.

In a wind turbine, rotor blades are large-scale integral hybrid structures. For a large part they are made of composites, with bolted blade-hub connections and integrated lightning protection, and including various types of composite structural materials and elements. Each rotor blade may include a number of hollow composite components, for example, a hollow spar such as a box spar or D-spar.

With conventional processes for manufacturing hollow composite structures, a mandrel is used to define the hollow space. Fiber material or sheets, such as prepreg glass fiber material, are laid up on the mandrel within a first mold part, wherein the position and shape of the fibre material on the mandrel essentially defines the composite part. A second mold part completes the mold, and the fiber material can be cured in a conventional vacuum resin curing process. This process can be used in the production of strong and light-weight composite structures of wind turbine rotor blades.

<CIT> describes a method in accordance with the preamble of claim <NUM> for producing a hollow composite structure, such as a spar beam for use in a wind turbine blade, includes placing fiber reinforcement material around a mandrel within a mold, and curing the fiber reinforcement material. The mandrel is formed from a compressible material having a rigid neutral state with a rigidity to maintain a defined shape of the mandrel during lay up and curing of the fiber reinforcement material. Subsequent to curing, a vacuum is drawn on the mandrel to compress the compressible material so that the compressed mandrel can be drawn out through an opening in the composite structure, the opening having a size such that the mandrel could not be withdrawn through the opening in the rigid neutral state of the mandrel.

Thus, there is a need for an improved mandrel for producing a hollow composite component of a wind turbine rotor blade.

According to an aspect, there is provided a mandrel for producing a hollow composite component of a wind turbine rotor blade, the mandrel including a core of a first material, an outer layer of a second material arranged radially outward of the core, the second material being more compressible than the first material, and a first intensifier member for intensifying a pressure on a first inner area of a lay-up, the first intensifier member being arranged at least partially radially outward of the core, wherein a first outer surface of the first intensifier member and a second outer surface of the outer layer, together, forms a defined shape corresponding to a desired inner shape of at least a portion of the hollow composite component.

According to a further aspect, there is provided a method for producing a hollow composite component of a wind turbine rotor blade, using a mandrel as described herein, the method including placing the lay-up around the mandrel within a mould, and performing an in-mould curing process.

According to another aspect, there is provided a hollow composite component of a wind turbine rotor blade manufactured using a mandrel as described herein.

These and other aspects, embodiments, examples and advantages of the present invention will become better understood with reference to the following description and appended claims.

A full and enabling disclosure, including the best mode thereof, directed to the person skilled in the art, is set forth in the specification, which makes reference to the appended figures, in which:.

Reference now will be made in detail to embodiments, one or more examples of which are illustrated in the drawings. Each example is provided for explaining the present disclosure. Features illustrated or described as part of one example or embodiment can be used with another example or embodiment.

As discussed above, the present invention is directed to an improved mandrel for producing a hollow composite component of a wind turbine rotor blade, such as a spar beam.

Composite materials generally comprise a fibrous reinforcement material embedded in a matrix material, such as a polymer or ceramic material. The reinforcement material typically serves as the load-bearing constituent of the composite material, while the matrix material protects the reinforcement material, maintains the orientation of its fibers and serves to dissipate loads to the reinforcement material. Polymer matrix composite (PMC) materials are typically fabricated by impregnating a fabric with a resin, followed by curing. Prior to impregnation, the fabric may be referred to as a "dry" fabric and typically comprises a stack of two or more fiber layers (plies or sheets). Depending on the intended application and the matrix material used, the fiber layers may be formed of a variety of materials, for example, carbon (e.g., graphite), glass (e.g., fiberglass), polymer (e.g., Kevlar®), and ceramic (e.g., Nextel®) fibers.

In composites manufacturing, it is beneficial to produce a well-compacted laminate that has a prescribed resin-to-fiber ratio and is free of voids or flaws. Common challenges include surface porosity, voids, resin-rich areas, and bridging.

Mandrels comprising compressible material are susceptible to bridging. Bridging is when the initial, or first, fabric ply pulls away from a defined feature, e.g. a corner, and spans across, rather than remaining tightly adhered thereto. Bridging may result in resin richness, which is an undesired agglomeration of excess resin beneath the first ply of fabric that can locally weaken the laminate.

Accordingly, in a production of a hollow composite component, bridging can be an issue. The size of the radius is important, e.g. in internal corners. For example, it can be more difficult with an internal corner with a smaller radius.

The issue of bridging, such as in an inner corner, results in resin build up, and glass bridging away. This results in additional weight, as resin is heavy, and increased risk of cracking, as resin build up results in increased exothermic heat. Since wind turbine rotor blades are weight sensitive, additional weight is undesirable. Additionally, sub-standard components, e.g. due to cracked resin or sub-standard curing, are typically not repairable, and results in scrapped parts. At the least, resin build up can thermally degrade the part, and further, negatively affect safe temperature limits, e.g. ramp up, cycling.

Accordingly, it is desirable to provide a mandrel comprising compressible material, the mandrel for producing a hollow composite component of a wind turbine rotor blade, where the mandrel is improved with respect to a desired shape of the hollow composite component having a defined feature, e.g. a corner.

The following provides some further description, which may be understood with reference to <FIG>.

The mandrel includes a core <NUM> of a first material and an outer layer <NUM> of a second material. The first material and the second material are compressible materials. The second material is more compressible than the first material. A compressible material may be understood as a material having a non-compressed state and a compressed state.

A compressible material may be understood as a material capable of being in a non-compressed state, in which the compressible material forms a defined shape. A compressible material may be understood as a material capable of being in a non-compressed state, in which the compressible material has sufficient rigidity to maintain a defined shape during lay up and curing of fiber reinforcement material placed around the mandrel.

A compressible material may be understood as a material capable of being transformed into a compressed state upon application of a vacuum thereto. A compressible material may be understood as a material having sufficient elasticity to return to a non-compressed state upon release of the vacuum applied thereto.

The first outer surface <NUM> of the first intensifier member <NUM> and the second outer surface <NUM> of the outer layer <NUM>, together, forms a defined shape corresponding to a desired inner shape of at least a portion of the hollow composite component.

The pressure on the first inner area of the lay-up may be understood as a compressive force on the lay-up. It may be understood that a mould or a part of the mould, around the mandrel and the lay-up, in combination with a vacuum applied to the lay-up enables the pressure or compressive force to the first inner area of the lay-up. It may be understood that the depression or the opening of the core <NUM> acts as cylinder walls.

'Lay-up' may be understood as material(s) forming or for forming at least a portion of the hollow composite component. In particular, 'lay-up' may be understood as fiber fabric and/or composite materials. In an example, the hollow composite component is a part of a spar beam component, a spar beam component, a part of a spar beam, or a spar beam. A hollow composite component, in particular a spar beam as described herein, may be understood as being manufactured to become an inner part of a wind turbine rotor blade.

'Lay-up' may be understood to comprise or contain material in a state prior to final or complete curing, for example, comprising or containing uncured material, pre-cured material, and/or partially-cured material.

'Lay-up' may be understood as layers of material. In particular, 'lay-up' may be understood to include plies, for example, mineral plies, polymer plies, glass plies, metallic plies, carbon plies). 'Lay-up' may be understood to include fibers, for example, mineral fibers, polymer fibers, glass fibers, metallic fibers, carbon fibers.

It may be understood that polymer fiber may include aromatic polyamides, polyethylene, polyurethane and/or aramide fibers. It may be understood that the fibers may be in the form of unidirectional or multidirectional fibers, prepregs, fiber boards, or fiber mats.

In an example, 'lay-up' includes dry glass/carbon fabrics, and/or pre-preg.

In an example, 'lay-up' includes pre-fabricated material(s).

The description `a first intensifier member for intensifying a pressure' may be understood as a first intensifier member <NUM> for providing a higher pressure or a larger force than a pressure or a force provided if the first intensifier member is replaced by a member of the second material.

For example, in a case where the outer layer <NUM> is arranged also in the position in which the first intensifier member <NUM> is otherwise arranged, the pressure or the force provided by the extended outer layer in the position in which the first intensifier member <NUM> is otherwise arranged, is less than the pressure or the force provided by the first intensifier member <NUM> in said position.

In an example, the first outer surface <NUM> of the first intensifier member <NUM> is a surface configured to be proximate to the first inner area of the lay-up. In an example, the first outer surface <NUM> of the first intensifier member <NUM> is arranged (most) distal from the core.

In an example, the second outer surface <NUM> of the outer layer <NUM> is a surface configured to be proximate to a second inner area of the lay-up. It may be understood that the second inner area of the lay-up is proximate to the first inner area of the lay-up.

It may be understood that the first outer surface <NUM> of the first intensifier member <NUM> and the second outer surface <NUM> of the outer layer <NUM> share a common edge.

It may be understood that the first intensifier member <NUM> having the hollow portion <NUM> in an expanded state, and the outer layer <NUM> in a non-compressed state, together, forms the defined shape corresponding to the desired inner shape of the at least a portion of the hollow composite component.

It may be understood that the defined shape (formed by the first outer surface <NUM> of the first intensifier member <NUM> and the second outer surface <NUM> of the outer layer <NUM>, together), and the desired shape (of the at least a portion of the hollow composite component) is when the lay-up is laid-up on the mandrel, in particular, during (in-mould) curing process.

In an example, the defined shape (of the mandrel) and the desired shape (of the hollow composite component) are of the mandrel and hollow composite component, respectively, during (in-mould) curing process.

It may be understood that the second inner area of the lay-up and the first inner area of the lay-up share a common edge.

It may be understood that the lay-up, laid-up on the mandrel, including the first outer surface <NUM> of the first intensifier member <NUM> and the second outer surface <NUM> of the outer layer <NUM>, is cured to form at least a portion of the hollow composite component, wherein the at least a portion of the hollow composite component has the desired inner shape corresponding to the defined shape formed by the first outer surface <NUM> of the first intensifier member <NUM> and the second outer surface <NUM> of the outer layer <NUM>.

Accordingly, the performance of the mandrel is improved with respect to a desired shape of the hollow composite component, having a defined feature, e.g. a corner. Accordingly, a desired shape of the hollow composite component can be better achieved. Accordingly, undesirable effects, such as bridging, may be better avoided.

According to an embodiment, the first intensifier member <NUM> comprises a hollow portion <NUM> expandable by a pressurizing fluid.

In an example, the hollow portion <NUM> is inflatable. In an example, the hollow portion <NUM> may be understood as an inflatable portion. In an example, a pressurizing fluid is a gas (e.g. air, nitrogen), or a liquid (e.g. water).

According to an embodiment, the hollow portion <NUM> is arranged proximate to the core <NUM>, and/or wherein the hollow portion <NUM> is at least partially surrounded by the core <NUM>.

In an example, the hollow portion is arranged at a first end of the first intensifier member <NUM>, proximate to the core <NUM>.

In an example, the core <NUM> comprises a depression or an opening, e.g. a recess, a cavity, a slot, a groove or a channel.

In an example, the depression of the core <NUM> or the opening of the core <NUM> is configured for holding the first intensifier member <NUM>.

In an example, the depression or opening of the core <NUM> has an inner shape complementing a shape of a portion of the first intensifier member <NUM>.

In an example, the depression or the opening is oriented in a direction in which the intensified pressure is to be applied to the first inner area of the lay-up.

In an example, the depression or the opening is oriented in a direction of the first inner area of the lay-up.

In an example, an axis of the depression or the opening of the core <NUM> is oriented in a direction of the first inner area of the lay-up, the axis being in a cross-sectional plane of the core <NUM>, the axis preferably being an axis of symmetry of the depression or the opening.

According to an embodiment, the hollow portion <NUM> is fluidly isolated from the core <NUM> and rest of the first intensifier member <NUM>. In an example, the hollow portion <NUM> is fluidly isolated from the rest of the first intensifier member <NUM> and/or from the core <NUM> and/or the outer layer <NUM>.

In an example, the hollow portion forms a fluidly sealed volume, apart from a port.

It may be understood that the port can be in an open state, e.g. to allow pressurizing fluid to pass through the port, and in a closed state, e.g. to block pressurizing fluid from passing through the port.

In an example, the first intensifier member <NUM> is less compressible or more rigid relative to the outer layer <NUM>. In an example, the first intensifier member comprises a material less compressible than the second material of the outer layer <NUM>.

Accordingly, a pressure acting on the first inner area of the lay-up proximate to the first intensifier member <NUM>, is intensified relative to (or is larger than) a pressure acting on the second inner area of the lay-up proximate to the outer layer <NUM>, during the curing process, e.g. curing in an autoclave.

As an illustrative example, the hollow portion <NUM> is a <NUM> inch thick discharge hose providing radial expansion of <NUM> inch.

According to an embodiment, the hollow portion <NUM> comprises at least one from the following group: drop stitches <NUM>; <NUM>, continuous fibers, and reinforcement, for defining a shape of the hollow portion <NUM> in an expanded state <NUM>.

In an example, the hollow portion <NUM>, in an expanded state <NUM>, has a defined shape for intensifying the pressure on the first inner area of the lay-up. In an example, the first inner area of the lay-up comprises a defined feature, e.g. a corner.

In an example, the hollow portion <NUM> has a shape, e.g. in cross-section, circular or triangular, and/or is arranged, such that, when in an expanded state <NUM>, intensifies the pressure on the first inner area of the lay-up, at the point of smallest radius, or along the axis of, of the defined feature, e.g. at the apex of the corner.

The first material of the core <NUM> may be a foam material, for example closed-cell foam.

Generally, the first material of the core <NUM> may be (further comprising) a non-compressible material, such as a plastic or wood core. For example, the core <NUM> may be rigid. In another example, the core <NUM> may be hollow, e.g. having an outer (rigid) structure, with an empty inner portion, or with an inner portion that is filled with a fluid, in particular air. For example, the empty inner portion may form more than <NUM>%, by volume, of the core <NUM>.

The first material may be at least one of the following: polymeric, rubber, polyethylene (EPE, XLPE), EVA, polypropylene, polystyrene, Closed Cell EPDM Foam Rubber, preferably crosslinked polyethylene; density of at least <NUM> lb. per cubic foot, preferably at least <NUM> lbs. per cubic foot; density of at most <NUM> lbs. per cubit foot, preferably at most <NUM> lbs. per cubic foot; as a particular example: Minicell® L200 or cross-linked polyethylene.

According to an embodiment, the first intensifier member <NUM> comprises a first intermediate portion <NUM> of a third material less compressible than the second material of the outer layer <NUM>, preferably wherein the first intermediate portion <NUM> comprises closed shell foam.

It may be understood that the first intermediate portion <NUM> is less compressible or more rigid, relative to the outer layer <NUM>, and/or relative to the core <NUM>.

Accordingly, the first intermediate portion <NUM> enables the transmission of the pressure intensification on the first inner area of the lay-up.

According to an embodiment, the first intensifier member <NUM> comprises a second intermediate portion <NUM> less compressible than the first intermediate portion <NUM>, the second intermediate portion <NUM> being arranged proximate to the first outer surface <NUM> or having a surface forming the first outer surface <NUM>.

In an example, the second intermediate portion <NUM> is incompressible or rigid. It may be understood that the second intermediate portion <NUM> is less compressible or more rigid, relative to the first intermediate portion, relative to the core <NUM>, and/or relative to the outer layer <NUM>.

In an example, the second intermediate portion <NUM> has an outer surface of a defined shape corresponding to the desired inner shape of at least a portion of the hollow composite component.

Accordingly, the second intermediate portion <NUM> enables the pressure intensification on the first inner area of the lay-up.

In an example, there may be a plurality of first intensifier members <NUM>. In an example, a first intensifier member <NUM> and at least one further intensifier member, arranged in respective positions. In an example, the at least one further intensifier member may be according to embodiments and examples of the first intensifier member <NUM> as described herein.

According to an embodiment, the core <NUM> comprises closed shell foam, and/or wherein the outer layer <NUM> comprises open shell foam.

The second material of the outer layer <NUM> may be a foam material, for example open-cell foam. The second material is more compressible than the first material.

The second material may have a lower density than the first material. The second material may be less rigid than the first material.

The second material may be at least one of the following: polymeric, rubber, polyurethane, reticulated polyurethane, PVC, nitrile, EPDM; density of at least <NUM> lb. per cubic foot, preferably at least <NUM> lbs. per cubic foot; density of at most <NUM> lbs. per cubit foot, preferably at most <NUM> lbs. per cubic foot; as a particular example: Lux-HQ® or Lux® foam.

In an example, there may be a plurality of outer layers <NUM>. In an example, an outer layer <NUM> and at least one further outer layer, arranged in respective positions. In an example, the at least one further outer layer may be according to embodiments and examples of the outer layer <NUM> as described herein.

The core <NUM> may be understood to be a support (or a base) for the outer layer <NUM> and/or the first intensifier member <NUM>. In an example, the outer layer <NUM> and/or the first intensifier member <NUM> are/is arranged radially outward of the core <NUM>. In an example the outer layer <NUM> and/or the first intensifier member <NUM> are/is arranged on the core <NUM>.

In an example, the outer layer <NUM> and/or the first intensifier member <NUM> are/is bonded to the core <NUM>, e.g. using rubber glue. In an example, the outer layer <NUM> and the first intensifier member <NUM> are bonded to each other, e.g. using rubber glue.

It may be understood that the first intensifier member <NUM> is configured for intensifying a pressure on a first inner area of a lay-up.

For example, the first intensifier member <NUM> is arranged at least partially radially outward of the core. For example, the first intensifier member <NUM> has an inner radial position within a radial extent of the core.

In an example, the first intensifier member <NUM> is arranged extending from a radial position within a radial extent of the core, or from an outer surface of the core <NUM>.

Accordingly, the core acts as a constraint to control the direction of force effected by the first intensifier member <NUM> on the lay up (on the first inner area of the lay-up).

According to an embodiment, an outer skin portion <NUM> of the first intensifier member <NUM> forming the first outer surface <NUM> is more rigid than the first intermediate portion <NUM> of the first intensifier member <NUM>.

According to an embodiment, an outer skin portion <NUM> of the first intensifier member <NUM> forming the first outer surface <NUM> is more rigid than a portion of the outer layer <NUM> forming the second outer surface <NUM> of the outer layer <NUM>.

In an example, the outer skin portion <NUM> has a rigidity module at least an order of magnitude larger than a rigidity modulus of the first intermediate portion <NUM>, the core <NUM>, and/or the outer layer <NUM>.

In an example, the outer skin portion <NUM> is of a rigid material, e.g. fiber-reinforced plastic. In an example, the outer skin portion <NUM> is incompressible or rigid.

In an example, the outer skin portion <NUM> has an outer surface of a defined shape corresponding to the desired inner shape of at least a portion of the hollow composite component.

Accordingly, the outer skin portion <NUM> enables the pressure intensification on the first inner area of the lay-up.

According to an embodiment, the first outer surface <NUM> of the first intensifier member <NUM> comprises a feature with a radius smaller than a radius of any feature of the second outer surface <NUM> of the outer layer <NUM>.

In an example, the first outer surface <NUM> of the first intensifier member <NUM> is a discontinuous surface or a non-flat surface.

Accordingly, the performance of the mandrel is improved with respect to a desired shape of the hollow composite component, having a defined feature, e.g. a feature with a small radius, e.g. a corner. Accordingly, a desired shape of the hollow composite component can be better achieved. Accordingly, undesirable effects, such as bridging, may be better avoided.

In an example, a first rigid surface portion <NUM> is arranged on a radially proximal side of the hollow portion <NUM>. In an example, a second rigid surface portion <NUM> is arranged on a radially distal side of the hollow portion <NUM>.

Accordingly, the first rigid surface portion <NUM> and the second rigid surface portion <NUM> enables the directed transmission of the pressure intensification on the first inner area of the lay-up.

The term 'radially proximal' may be understood as proximate to the center (of the core <NUM>), in a radial direction, or proximate to the core <NUM>, in a radial direction. The term `radially distal' may be understood distant from the center (of the core <NUM>), in a radial direction, or distant from the core <NUM>, in a radial direction.

The term `radial direction' may be understood as a direction extending outward from a center of the core <NUM> or from a center of the mandrel, in a cross-sectional plane of the core <NUM> or in a cross-sectional plane of the mandrel.

The term 'radial' may be understood to be along a direction extending outward from a center of the core <NUM> or from a center of the mandrel, in a cross-sectional plane of the core <NUM> or in a cross-sectional plane of the mandrel.

According to an embodiment, a thickness dimension of the outer layer <NUM> is configured to enable extraction of the mandrel from the hollow composite component, and/or wherein a thickness dimension of the outer layer <NUM> is configured based on a compressibility of the second material of the outer layer <NUM> and a geometry of the hollow composite component.

Accordingly, the compressed mandrel, having a reduced cross-sectional size, particularly due to the compression of the outer layer <NUM>, can be withdrawn from the hollow composite structure, post-curing. It may be understood that the mandrel could not be withdrawn from the hollow composite structure, post-curing, when the mandrel is not compressed, i.e. when the mandrel is in a non-compressed state.

Accordingly, a compressible mandrel, as described herein, may be understood to enable extraction of the mandrel from the hollow composite component, post-curing. Since a compressible mandrel is at particular risk of undesirable effects, such as bridging, due to its compressibility, a compressible mandrel, provided with a pressure intensifier member, as described herein, enables a compressible mandrel to achieve a shape definition similar to a rigid mandrel, yet still having the benefits of a compressible mandrel.

According to an aspect, there is provided a method for producing a hollow composite component of a wind turbine rotor blade, using a mandrel as described herein, the method including placing the lay-up around the mandrel within a mould, and performing an in-mould curing process.

Placing the lay-up around the mandrel within a mould <NUM> may be understood as a fiber material lay up process. In an example, the lay-up is laid-up in a mould or in a part of a mould. In an example, a mandrel is arranged on the laid-up lay-up. In an example, the laid-up lay-up with the mandrel arranged atop is arranged around the mandrel.

Performing an in-mould curing process <NUM> may be understood as following a resin infusion process. It may be understood that a resin infusion process is performed after drawing, in the mould, a vacuum.

According to an embodiment, the method for producing a hollow composite component of a wind turbine rotor blade comprises activating the first intensifier member <NUM>, at least during the in-mould curing process, preferably before the in-mould curing process.

According to an embodiment, activating the first intensifier member <NUM> comprises fluidly pressurizing a hollow portion of the first intensifier member.

In an example, a gas or liquid pump may be fluidly connected to the hollow portion <NUM>. In an example, the hollow portion may be pressurized using the gas or liquid pump.

In an example, fluidly pressurizing a hollow portion of the first intensifier member comprises pumping a gas or liquid into the hollow portion of the first intensifier member. In an example, the hollow portion is in a fluidly pressurized state or expanded state when a pressure of the fluid in the hollow portion reaches an upper pressure limit of the hollow portion.

According to an embodiment, the method for producing a hollow composite component of a wind turbine rotor blade comprises extracting the mandrel <NUM> from the composite component.

According to an embodiment, extracting the mandrel <NUM> comprises deactivating the first intensifier member <NUM> and drawing a vacuum on the mandrel <NUM>.

According to an embodiment, deactivating the first intensifier member <NUM> comprises releasing fluid pressure to the first intensifier member, after the in-mould curing process.

According to an embodiment, activating the first intensifier member <NUM> comprises effecting a first pressure, by the first intensifier member, on the first inner area of the lay-up, that is higher than a second pressure, by the outer layer, on a second inner area of the lay-up that is proximate to the first inner area.

Accordingly, the pressure is intensified at least during curing of the lay-up. Accordingly, a desired shape of the hollow composite component can be better achieved.

According to an aspect, there is provided a hollow composite component of a wind turbine rotor blade manufactured using a mandrel as described herein.

The following provides some further description, which may be understood with reference to <FIG> and <FIG>.

In an example, a hollow composite component of a wind turbine rotor blade as described herein, is (e.g., a part of) a spar beam component, e.g. first spar member <NUM> or third spar member <NUM>.

In an example, the first spar member <NUM> is a hollow spar member, integrated into the structure of the wind turbine rotor blade <NUM>. In another example, the first spar member <NUM> is composed of a plurality of components, including at least one hollow composite component.

In an example, the third spar member <NUM> is a hollow spar member arranged within a receiving section, e.g. first spar member <NUM>, of a wind turbine rotor blade <NUM>.

In an example, the second spar member <NUM> may include a hollow composite component, for example a hollow spar web which may be arranged between spar caps.

In an example, a wind turbine rotor blade <NUM> may be as depicted in <FIG>.

As an illustrative example, a core is formed of a harder, less compressible foam. As an illustrative example, the mandrel is cut to the profile of the inner mould line of the hollow composite component, minus the offset for the bulked lay-up. As an illustrative example, the mandrel is also offset to allow a layer of more compressible open cell forming the outer layer.

As an illustrative example, this outer layer thickness is defined by the amount of compression needed to extract the mandrel from the hollow composite component. As an illustrative example, the thickness of this outer layer is in accordance or based on the geometry of the hollow composite component.

As an illustrative example, in the areas of the lay-up that need higher compression, a pressurizable member is provided. As an illustrative example, this pressurizable member may have a constrained shape when pressured or the movement of which may be constrained to a specific direction, i.e. a vector of force is provided.

As an illustrative example, the core is used to control the vector of force and orient the vector of force at the desired location of the lay-up.

As an illustrative example, the outer layer is compressible. As an illustrative example, by vacuuming down the air inside the mandrel, the foam is compressed, and the mandrel size is reduced, allowing the mandrel to be extracted from the hollow composite component in which the mandrel would otherwise be die locked.

As an illustrative example, a less compressive component makes the core of the mandrel. As an illustrative example, the core acts as a support for the compressible layers as well as a constraint that control the direction in which the compressive force is applied to the lay up.

As an illustrative example, the slot in the core is oriented in the direction in which the pressure is applied to the laminate. As an illustrative example, the slot in the core acts as cylinder walls.

As an illustrative example, the slot in the core is filled with an expandable element that provides directional movement and/or pressure. As an illustrative example, the expandable element is covered by harder and/or less compressible foam, or even solid rigid components if needed, to pinpoint the area that needs to be compressed.

As an illustrative example, an outside layer is made of compressible open cell material that can be considerable reduced in size under compression or vacuum allowing the extraction of the mandrel out of an otherwise die locked shape.

As an illustrative example, the mandrel includes foams of different firmness. As an illustrative example, a first foam is provided for the all-around cover and a second foam firmer than the first foam is provided for the corners.

As an illustrative example, a combination of open-cell foam and closed-cell foam is provided for the corners.

It is beneficial to provide a mandrel design allowing the manufacturing of a hollow die lock composite part. A collapsible mandrel beneficially facilitates extraction. A mandrel incorporating intensifiers which may be pneumatically activated and which can provide controlled linear movement to intensify pressure in specific areas such as corners or other geometry that necessitate very good definition is beneficial.

The use of various density and compressibility closed cell foam, various density and compressibility open cell foam, composite rigid components, as well as inflatable/expandable components constrained in a way to control the direction of the movement providing the pressure is beneficial.

It is beneficial to provide a pressurized mandrel shape constrained and controlled in a way that defines the final shape thereof. Internal and external reinforcement, such as drop stitches, continuous fibers and fabrics, may be used to achieve such a final shape.

A highly directional movement ensuring the critical area of the part is well defined while still allowing enough collapsibility or compression to allow extraction of a die lock part is beneficial.

It is thus beneficial to combine the ability to apply pressure in a specific area of a part while still being compressible enough to allow extraction out of a hollow die lock composite structure. In general, in compressible mandrels, expansion is uniform.

It is beneficial to control where the pressure is applied to avoid bridging of glass fabric. In general, inflatables do not constrain expansion. It is thus provided a mandrel with precise control where pressure is applied while still being able to be collapsed sufficiently to offset the die lock and allow for extraction.

It is thus described a mandrel which allows precise control of the axis of the force applied, by constraining the expansion in a specific direction, through the use of different compressibility components or internal constraints to the expanding structure, such as drop stitches or other reinforcements.

It has been discovered, that in a spar beam moulded for a pin joint for a wind turbine, inside radii is critical for reducing fatigue resistance of the part. It has been discovered that these radii are critically controlled by the way the glass is laid up. It has been discovered that this is extremely operator dependent.

It has been discovered that it is one of the most important cause of scrap part, and that it is actually generally impossible to repair the inside of such a hollow part.

Accordingly, it is described a mandrel which controls the direction of force by intensifiers. It is beneficial to use hollow shapes that can be pressurized with a gas or liquid but which is constrained to a final shape when pressurized. This can beneficially be achieved by internal reinforcement, fabric, or drop stitches that define the final pressurized shape and prevent expansion in directions where no compression is wanted or needed.

It has been discovered that such a mandrel is much more resource efficient than a mechanical apparatus. It has been discovered that such a mandrel is much more flexible as there are very few solid/rigid components. It has been discovered that such a mandrel requires a lot less precision, being much more permissive in not constraining axes.

A solid mandrel having (mechanical) activators to apply pressure in specific areas are generally very complex, less flexible and much less resource efficient.

Claim 1:
A mandrel for producing a hollow composite component of a wind turbine rotor blade, the mandrel comprising:
a core (<NUM>) of a first material;
an outer layer (<NUM>) of a second material arranged radially outward of the core (<NUM>), the second material being more compressible than the first material; and characterized by
a first intensifier member (<NUM>) for intensifying a pressure on a first inner area of a lay-up, the first intensifier member (<NUM>) being arranged at least partially radially outward of the core (<NUM>),
wherein a first outer surface (<NUM>) of the first intensifier member (<NUM>) and a second outer surface (<NUM>) of the outer layer (<NUM>), together, forms a defined shape corresponding to a desired inner shape of at least a portion of the hollow composite component.