DK177944B1 - Controlling adhesive spew upon assembly of bonded components - Google Patents

Abstract

A dam profile for controlling adhesive spew when components are bonded together is shaped to extend around a free edge of one of the components. The dam profile has a head defining a barrier wall of convex cross-sectional curvature that imparts a beneficial concave cross-sectional curvature to an edge of the adhesive disposed between adherend surfaces of the components. The dam profile also has an anchor formation for attachment to a support surface on an opposite side of the component with respect to its adherend surface, allowing the head of the dam profile to move past the free edge during assembly movement to avoid distortion of the components.

Description

Controlling adhesive spew upon assembly of bonded components

This invention relates to the assembly and bonding together of components, and in particular to controlling the extent and cross-sectional shape of adhesive spew when components are brought together for bonding.

In this specification, the invention will be exemplified with reference to a 'cup and cone' joint used between a root and a spar of a wind turbine blade. While the invention has particular advantages in that demanding application, it should be understood that the invention may be used in other applications in which components are bonded together by an intermediate layer of adhesive.

To put the invention into context and to explain certain problems suffered by the prior art, reference will first be made, by way of example, to Figures 1 to 5 of the accompanying drawings, in which:

Figure 1 is an enlarged perspective view showing a cup and cone joint used between a root and a spar of a wind turbine blade, before assembly;

Figure 2 is a perspective view of the root and spar after assembly;

Figure 3 is an enlarged perspective view in longitudinal section through the assembled cup and cone joint of the root / spar assembly shown in Figure 2;

Figure 4 is an enlarged schematic longitudinal sectional view of the cup and cone joint before assembly, with an adhesive surface of a male part supporting an adhesive layer facing an opposing adhering surface of a female part; spirit

Figure 5 is a further enlarged detail view of the cup and cone joint after assembly, showing a spew detail of adhesive forced from between the adherent surfaces of the male and female parts.

Referring initially to Figures 1 and 2, a hollow root 10 and a hollow box spar 12 are bonded together in longitudinal alignment on a common central longitudinal axis 14 to serve together as the principal structural member of a wind turbine blade. Of course, the complete blade will also comprise a shell for its aerodynamic and structural properties but this shell has been omitted from the drawings.

The spar 12 resists bending loads experienced by the blade in use, largely due to aerodynamic lift and gravity forces, and transmits loads through the root 10 to the rotor hub structure of the wind turbine. The joint 16 between the root 10 and the spar 12 is clearly of critical importance and requires careful design to resist fatigue in view of the cyclic loading that will be experienced by the blade during its long service life.

The spar 12 is typically made by a lay-out method in a mold. It comprises a pair of spar caps 18 having unidirectional fibers running along the length of the spar 12, joined by a pair of shear webs 20. The resulting cross-section of the spar 12 is near-rectangular although it can be seen that the spar caps 18 and the shear webs 20 are slightly convex in section.

The root 10 is typically made by winding filaments around a mandrel. The root 10 is near-rectangular in cross-section at its outermost end to match the cross-section of the spar 12 but, at its innermost end, it is circular in cross-section to be bolted to a pitch bearing in the rotor hub structure.

As best appreciated in Figures 3 and 4, the joint 16 used between the root 10 and the spar 12 in Figures 1 and 2 involves longitudinal overlap between opposing interface surfaces of the respective components. This overlap defines a lap region bounded by lap ends.

If the joint 16 is between male and female components in this example, the interface surfaces are described here as a female adhesive surface 22 and a male adhesive surface 24. An intermediate layer of adhesive 26 visible in Figure 4 is disposed between, and upon assembly of the joint 16 bonds to both of, the adhesive surfaces 22, 24. Typically the adhesive 26 is an epoxy adhesive although this is not essential.

In this example, the root 10 defines the female adherent surface 22 and the spar 12 defines the male adherent surface 24. Thus, the female adherent surface 22 surrounds an inner end of the spar 12 defining the male adherent surface 24; or, expressed another way, the male adhering surface 24 fits within an outer end of the root 10 defining the female adhering surface 22.

The joint 16 shown here is a form of scarf joint, in that the overlapping adhesive surfaces 22, 24 have complementary inclinations relative to the central longitudinal axis 14. Specifically, the female adhesive surface 22 of the root 10 diverges from the central longitudinal axis 14 as the wall thickness of the root 10 tapers towards the blade tip. Conversely, the male adherent surface 24 of the spar 12 is defined by an inwardly-inclined end portion 28 of the spar 12, such that the male adherent surface 24 converges with the central longitudinal axis 14 moving away from the blade tip.

Viewed around the cross-sectional perimeter of the root 10 and the spar 12, the adherent surfaces 22, 24 are frustums that are largely frusto-pyramidal. The adherent surfaces 22, 24 are also somewhat frusto-conical due to the slightly convex section of the spar caps 18 and the shear webs 20. It can therefore be appreciated how the female adherent surface 22 of the root 10 is akin to a cup and the male adhering surface 24 of the spar 12 is akin to a cone shaped to fit tightly into that cup.

The scarf joint configuration maximizes the interface area of the joint 16 for the benefit of its strength and enables the joint 16 to be assembled simply by pressing together the root 10 and the spar 12 along the central longitudinal axis 14 around the adhesive 26. Thus, the direction of relative movement during assembly of the root 10 and the spar 12 intersects the longitudinal cross-section of the adhering surfaces 22, 24. Assembly involves a linear translation between the root 10 and the spar 12 and, momentarily, some shear in the layer of adhesive 26 as the adhesive surfaces 22, 24 bear against each other through the adhesive 26 with a wiping or sliding action.

As best shown in the further enlarged views of Figures 4 and 5, the wall thickness of the end portion is 28 tapers away from the blade tip, with the result that the spar 12 terminates at a very thin free edge 30 relative to the thickness of the opposed part of the root 10.

The intermediate layer of adhesive 26 is shown in Figure 4 supported by the male adhesive surface 24 before assembly of the joint 16. Before curing, the adhesive 26 has the consistency of a paste. Consequently, when the root 10 and the spar 12 are pressed together along the central longitudinal axis 14, the adhesive 26 is squeezed between the adherent surfaces 22, 24 and flows to migrate along the lap region driven by the narrowing gap between those surfaces 22, 24th

As shown in Figure 5, some of the adhesive 26 oozes out at least one end of the lap region as a spew detail. The spew forms a bead 32 at the internal lap end with a bulbous convex cross-section. The bead 32 projects beyond the free edge 30 at the end portion 28 of the spar 12, and around the junction between the inclined female adherent surface 22 and the inner surface 34 of the root 10. In effect, therefore, the bead 32 extends the adhering surface 22 onto the inner surface 34 of the root 10.

Whilst the bead 32 slightly enlarges the area of the interface between the adhesive 26 and the root 10, there are very sharp changes in cross-sectional shape at the intersections between the bead 32, the root 10 and the spar 12. Indeed, the internal entry angle θι through the adhesive 26 between the bead 32 and the root 10 exceeds 90 ° and the corresponding internal entry angle Θ2 between the bead 32 and the spar 12 exceeds 180 °. These severe discontinuities cause undesirable stress concentrations around the bond line when the blade is loaded in use, which tends to impair its fatigue life.

Where possible, a spew detail may be re-worked before or, less preferably, after the adhesive 26 has cured, for example to re-shape it into a fillet shape with a generally triangular cross-section. Spew at the external lap end can be shaped flush with the outer surfaces of the root 10 and the spar 12 but a small step will remain between the inner surfaces of the root 10 and the spar 12 at the internal lap end.

Re-working a spew detail at an external lap end is straightforward, if undesirable. However, health and safety restrictions and ergonomic considerations mean that it is difficult at best, and indeed may be impossible, to re-work a spew detail on an internal lap end in a confined space within a hollow component. This applies especially to 'wet work' before the adhesive has cured.

If less adhesive 26 is used to reduce or eliminate spew at an internal lap end, there is a risk that the adhesive 26 will fail to migrate fully along the lap region to fill the external lap end. Of course, this would weaken the joint and introduce a further undesirable discontinuity.

It is known in the prior art to employ a dam to confine adhesive within the lap region to prevent or control spew. For example, it is known to use a jig to hold a dam at the lap end against an edge of a component being bonded, but this is not practical in the example shown in Figures 1 to 5.

Another approach is to fix a dam to one of the adhering surfaces parallel to its free edge and facing the other of the adhering surfaces. The height of the dam bridges the gap between the adhesive surfaces as the components are brought together and determines the thickness of the adhesive layer. However, if used between the adhesive surfaces 22, 24 of the example shown in Figures 1 to 5 to prevent spew at the internal lap end, a dam would tend to distort the thin laminate at the end portion 28 of the spar 12. Specifically, the dam would cause the end portion 28 of the spar 12 to hinge or flex away from the root 10 to which the spar 12 is being bonded. Such a dam would also reduce the area of the interface between the adhesive 26 and the root 10. Indeed, such a dam may prevent adhesive migration fully along the lap region, which would weaken the joint and cause discontinuity at the internal lap end.

Typically, a dam can be used only where the parts being bonded are pressed against each other in a direction largely orthogonal to the adhesive surfaces so as to compress the adhesive layer without much shearing. In view of the linear translation between the root 10 and the spar 12 and the shallow inclination of the adhesive surfaces 22, 24 relative to the direction of translation, known dams are incompatible with the wiping or sliding action as the adhesive surfaces 22, 24 bear against each other through the adhesive 26. If used in these circumstances, a dam fixed to one of the adhesive surfaces 22, 24 will tend to peel back into the adhesive 26, creating a greater discontinuity and imparting a disadvantageous cross-sectional shape to the edge of the adhesive extending along the bond line. WO2010 / 023140 describes a joint between adhesively-bonded components that comprise respective adhesive surfaces joined by adhesive, wherein at least one of the components has a free edge disposed between the adhesive surface and a support surface of that component. The present invention is characterized by a dam profile extending around the free edge of that component comprising an anchor formation attached to the support surface and a head which presents a barrier wall of convex cross-sectional curvature to impart concave cross-sectional curvature to an edge of the adhesive disposed between the adhesive surfaces. The concave cross-sectional curvature of the edge of the adhesive reduces stress concentrations and maximizes fatigue life.

To avoid distortion of the component to which the dam profile is attached, the anchor formation is preferably attached to a support surface on an opposite side of the component with respect to the adhering surface. So, the anchor formation is preferably flexible. This allows the head to slide past the free edge when the other component bears against the head during assembly of the components. For example, the anchor formation may be attached to the support surface at a free end region and be free to move away from the support surface at a base region. It is also possible for the head of the dam profile to be flexible to deform when the other component bears against the head.

The head may engage resiliently with the free edge to locate the barrier wall in relation to the adhering surface, with a channel of the dam profile embracing the free edge between the anchor formation and the barrier wall.

The inventive concept embraces a related dam profile for controlling adhesive spew when components are brought together for bonding. That dam profile is shaped to extend around a free edge of a component and comprises an anchor formation for attachment to a support surface of the component and a head having a barrier wall of convex cross-sectional curvature. The anchor formation suitably extends tangentially with respect to the barrier wall; for example, the dam profile may be generally of P-section, comprising a head of circular or elliptical cross-section defining the barrier wall and a leg extending from the head defining the anchor formation.

The inventive concept also embraces a joint made using the dam profile as described, whether or not the dam profile remains attached to a component. In this sense, the invention may be described as a joint between adhesively bonded components which comprise respective adhesive surfaces joined by adhesive, wherein: at least one of the components terminates in a free edge; and an edge of the adhesive has concave cross-sectional curvature extending between the adhesive surfaces from the free edge of one component to the other component, that curvature defining an internal angle through the adhesive of less than 90 ° with respect to at least one of the the adhering surfaces.

The joint of the invention may be a scarf joint in which the adhering surfaces have complementary inclinations relative to an assembly direction that brings the components together to compress the adhesive between them. In that case, the free edge of one of the components may be defined by a thin end portion which extends generally in parallel to the adherent surface of the other component and comprises opposed faces both correspondingly inclined relative to the assembly direction, one of which faces defines the adherent surface of that component.

The inventive concept extends to a structure comprising at least two components joined by a joint of the invention or comprising a dam profile of the invention. The inventive concept also embraces a method of forming a joint between components that comprise respective adhesive surfaces, at least one of those components having a free edge, the method comprising: attaching a dam profile to at least one of the components to extend around its free edge and to place a head of the dam profile beside its adherent surface, that head having a barrier wall of convex cross-sectional curvature; and imparting concave cross-sectional curvature to an edge of adhesive disposed on that adhesive surface by virtue of conforming contact between the adhesive and the barrier wall. The adhesive may be brought into conforming contact with the barrier wall before or during assembly of the components, whereupon the barrier wall constrains migration of the adhesive in one direction as the adhesive is squeezed between the adhering surfaces during assembly of the components. This promotes migration of adhesive between the adhering surfaces in an opposite direction.

In summary, therefore, the invention contemplates a dam profile for controlling adhesive spew when components are bonded together is shaped to extend around a free edge of one of the components. The dam profile has a head defining a barrier wall of convex cross-sectional curvature that imparts a beneficial concave cross-sectional curvature to an edge of the adhesive disposed between adherent surfaces of the components. The dam profile suitably also has an anchor formation arranged for attachment to a support surface on an opposite side of the component with respect to its adhering surface, allowing the head of the dam profile to move past the free edge during assembly movement to avoid distortion of the components.

Reference has already been made to Figures 1 to 5 of the accompanying drawings to put the invention into context and to explain certain problems suffered by the prior art. In order that the invention may be more readily understood, reference will now be made to Figures 6 to 9 of the drawings, in which:

Figure 6 is an enlarged schematic longitudinal sectional view corresponding to Figure 4 but showing a dam profile in accordance with the invention attached to the male part to control spew of adhesive upon assembly of the cup and cone joint;

Figure 7 corresponds to Figure 6 but shows the male and female parts being brought together around the intermediate adhesive layer carried by the male part while the dam profile controls spew of the adhesive;

Figure 8 is a further enlarged detail view showing how the dam profile may deform and move relative to the male part during assembly of the joint; spirit

Figure 9 is a further enlarged detail view of the joint after assembly and with the dam profile removed, showing how the extent and cross-sectional profile of adhesive spew may be controlled in accordance with the invention.

In the following description accompanying Figures 6 to 9, the root 10 and the spar 12 are identical to those shown in Figures 1 to 5 and they are assembled in much the same way. Consequently, like numerals are used for similar parts. This immediately illustrates one advantage of the invention, which is that there is no need to adapt the components being joined.

Figures 6 to 8 show a dam profile 36 in accordance with the invention shown here attached to the end portion 28 of the spar 12. The dam profile 36 is positioned and arranged to serve as a barrier that controls the extent of spew of the adhesive 26 when the root 10 and the spar 12 are brought together for bonding. Also, the dam profile 36 is shaped to maintain, or to impart, a desired cross-sectional shape in the adhesive 26 at the bond line where the adhesive 26 terminates at an end of the lap region.

The dam profile 36 is a P-section extrusion of flexible, resilient foam rubber comprising a tubular head 38 and an integral anchor web 40 that is cantilevered from the head 38 as a tangentially extending flap. The cross-sectional shape of the dam profile 36 therefore comprises a circle or ellipse corresponding to the head 38, and a leg corresponding to the anchor web 40 extending tangentially from the circle or ellipse. The head 38 and the anchor web 40 intersect at an acute angle to define a channel 42 extending along the dam profile 36.

In use, the anchor web 40 is adhesively attached to the end portion 28 of the spar 12 near its free edge 30. Specifically, the anchor web 40 is attached to a support surface 44 of the end portion 28 as opposed to the male adhering surface 24 The free edge 30 of the end portion 28 is received in the channel 42 between the head 38 and the anchor web 40.

When attached to the support surface 44 in this way, the anchor web 40 provides resilient support to the head 38, which is positioned such that a convex-curved barrier wall 46 of the head 38 bulges slightly into the lap region bounded by the male interface surface 24. In doing so, the barrier wall 46 is positioned to impart a desired cross-sectional shape to the adhesive 26 at the bond line. This will be explained further below with reference to Figure 9 of the drawings. In this position, the barrier wall 46 engages resiliently with the free edge 30 of the end portion 28 to provide further support and location for the head 38.

The adhesive 26 shown in Figure 6 is applied to the male adhesive surface 24 after attaching the dam profile 36 to the end portion 28 of the spar 12. The head 38 of the dam profile 36 confines the adhesive 26 as the adhesive 26 fills gaps between the head 38 and the end portion 28, to lie in close conformity with the barrier wall 46 of the head 38. The adhesive 26 therefore extends to the free edge 30 of the end portion 28 and conforms to the shape of the barrier wall 46 It will be noted that the adhesive 26 is applied to the male adhesive surface 24 in a layer which is slightly shallower than the height of the barrier wall 46.

Figure 7 shows the root 10 and the spar 12 being pressed together during assembly. The head 38 of the dam profile 36 initially bears against the female adhering surface 22 near its junction with the inner surface 34 of the root 10.

Initially, upon encountering the female adhering surface 22, the head 38 of the dam profile 36 tilts back slightly into the adhesive 26. This further promotes conforming contact between the adhesive 26 and the barrier wall 46 of the head 38. However, by virtue of embracing the free edge 30 at the end portion 28 of the spar 12, the dam profile 36 cannot peel back into the adhesive 26 to the extent suffered by dams of the prior art.

The head 38 of the dam profile 36 also flattens slightly upon encountering the female adhering surface 22, becoming increasingly elliptical or ovate. This deformation reduces the height of barrier wall 46 until eventually it matches the thickness of the layer of adhesive 26, whereupon the adhesive 26 comes into contact with the female adhesive surface 22 as shown in Figure 7.

The layer of adhesive 26 is shown in Figure 7 being squeezed between the adhesive surfaces 22, 24; As a result, the adhesive 26 has flowed to migrate along the lap region to the external lap end 48. Here, any spew of adhesive 26 can readily be flattened off to lie flush with the exterior of the root 10 and spar 12 as shown. Effective migration of the adhesive to fill the lap region is assured because the barrier wall 46 of the head 38 blocks spew of the adhesive 26 from the internal lap end. Again, this promotes conforming contact between the adhesive 26 and the barrier wall 46.

Figure 8 shows the root 10 and the end portion 28 of the spar 12 in a fully assembled position. Here, the dam profile 36 on the end portion 28 has slid past the female adhering surface 22 and onto the adjacent inner surface 34 of the root 10.

It will be noted in Figure 8 that the anchor web 40 of the dam profile 36 is only attached to the support surface 44 at a free end region 50. This leaves a base region 52 of the anchor web 40 free to flex away from the support surface 44 as shown. To provide clearance for this movement, the free edge 30 of the end portion 28 is spaced slightly from the base of the channel 42 defined by the line of intersection between the head 38 and the anchor web 40. The head 38 may also deform slightly to pass the free edge 30.

If the head 38 of the dam profile 36 is decoupled from the end portion 28 of the spar 12 to be able to slide past the free edge 30 to some extent, the barrier wall 46 of the head 38 contains the adhesive 26 effectively without forcing the thin laminate of the end portion 28 of the spar 12 to flex away from the root 10. This is an advantage over prior art dams in which the dam is supported between the adhering surfaces.

Referring finally to Figure 9, this shows the dam profile 36 removed from the end portion 28 of the spar 12. It can be seen how the convex-section barrier wall 46 of the head 38 has imparted a desired cross-sectional shape in the edge of the adhesive 26, at the bond line where the adhesive 26 terminates at the internal lap end. Specifically, the disadvantageous bulbous bead 32 shown in Figure 5 has been replaced by a concave, smoothly-radiused cross-sectional shape 54 that remains concave between the free edge 30 of the end portion 28 and the inner surface 34 of the root 10. This is achieved with no need for re-working.

In effect, the cross-sectional shape 54 at the edge of the adhesive 26 extends the adherent surface 22 onto the inner surface 34 of the root 10. By extending onto the inner surface 34 in this way, the shape 54 beneficially enlarges the area of the the interface between the adhesive 26 and the root 10. Yet, the shape 54 avoids the sharp cross-sectional changes that favor the prior art. It can be seen that the internal entry angle θ3 through the adhesive 26 between the adhesive 26 and the inner surface 34 of the root 10 is very much less than 90 ° and that the corresponding internal entry angle © 4 between the adhesive 26 and the end portion 28 of the spar 12 is also less than 90 °. These favorable entry angles minimize stress concentrations around the bond line when the wind turbine blade is loaded in use, which enhances its fatigue life.

Variations are possible within the inventive concept. For example, the dam profile 36 may be attached to the end portion 28 before or after the adhesive 26 is applied to the male adhesive surface 24. It is also possible to leave a gap between the head 38 of the dam profile 36 and the adjacent edge of the adhesive 26 before the root 10 and the spar 12 are assembled. In that case, the adhesive 26 is squeezed between the adhesive surfaces 22, 24 upon assembly to migrate into close conformance with the convex barrier wall 46 of the head 38.

The adhesive attachment of the dam profile 36 to the spar 12 may be temporary, to be removed when the adhesive 26 has cured, or to remain permanently in place after the adhesive 26 is cured. The latter option is preferred because the dam profile 36 may be inaccessible after assembly of the root 10 and the spar 12. Also, if left in situ, the dam profile 36 may help protect the adhesive 26 during the service life of the wind turbine leaves.

The invention may also be used to construct modular blades. For example, the joint may be used when a tip portion of a wind turbine blade is connected to the main portion of a wind turbine blade.

Claims (17)

An assembly of adhesive bonded components (10, 28) comprising corresponding adhesive surfaces (22, 24) assembled by adhesive (26), wherein: at least one of the components has a free edge (30) disposed between the adhesive surface and a support surface (44) for this component; characterized by a barrier profile (36) extending around the free edge (30) of this component comprising an anchorage (40) secured to the support surface and a head (38) showing a barrier wall of a convex curvature cross section to impart a concave curvature cross-section to an edge of the adhesive disposed between the adhesive surfaces. Assembly according to claim 1, wherein the support surface (44) is on an opposite side of the component relative to the adhesive surface (24). The assembly of claim 1 or claim 2, wherein the anchorage (40) of the barring profile (36) is flexible to allow the head (38) to move past the free edge (30) relative to the support surface (44), when the other component is in contact with the head during assembly of the components. The assembly of claim 3, wherein the anchorage (40) is attached to the support surface (44) at a free end region of the anchorage and is free to move away from the support surface at a base region of the anchorage. Assembly according to any of the following claims, wherein the head (38) of the barring profile (36) is flexible and can be deformed when the second component abuts the head during assembly of the components. Assembly according to any one of the following claims, wherein the head (38) elastically engages the free edge (30) as a channel (42) of the barrier profile (36) encloses the free edge between the anchorage and the barrier wall. A barrier profile (36) for controlling adhesive (26) when assembling components for bonding, wherein the barrier profile is formed to extend around a free edge (30) of a component (28) and includes an anchor (40) for attachment to a support surface of the component and a head (38) having a barrier wall of convex cross-section curvature. The barrier profile (36) according to claim 7, wherein the anchorage (40) extends tangentially to the barrier wall. A barrier profile (36) according to claim 7 or claim 8, generally having a P-section comprising a head (38) of circular or elliptical cross-section defining the barrier wall and a leg extending from the head defining the anchorage (40). An assembly of adhesive bonded components (10, 28) comprising corresponding adhesive surfaces (22, 24) assembled by adhesive (26), wherein: at least one of the components (28) ends at a free edge (30); and an edge of the adhesive has a concave cross-sectional curvature extending between the adhesive surfaces from the free edge of one component to the other component, the curvature defining an internal angle through the adhesive of less than 90 ° to at least one of the adhesive surfaces; characterized in that the joint is a blade joint, where the adhesive surfaces (22, 24) have complementary slopes relative to a joint direction bringing the components together to compress the adhesive (26) between them. The assembly of claim 10, wherein the free edge of one of the components is defined by a thin end portion which generally extends parallel to the adhesive surface of the other component and comprises opposing surfaces both inclined correspondingly to the assembly direction, of which one surface defines the adhesive surface of this component. A method of forming a joint between components (10, 28) comprising corresponding adhesive surfaces (22, 24), wherein at least one of said components has a free edge (30), characterized in: a barrier profile (36) for at least one of the components to extend around its free edge (30) and to place a head (38) of the barrier profile adjacent to its adhesive surface, said head having a barrier wall of convex cross-section curvature; and imparting a concave cross-sectional curvature to an edge of adhesive disposed on said adhesive surface by virtue of conformal contact between the adhesive and the barrier wall. The method of claim 12, which comprises moving the head (38) of the barring profile (36) past the free edge of one component in response to the other component abutting the head during assembly of the components. The method of claim 12 or claim 13, which comprises deflecting the barrier wall toward the adhesive (26) disposed on the adhesive surface (24) of one component in response to the other component abutting the head (38) below. assembly of the components. A method according to any one of claims 12 to 14, which comprises contacting the adhesive (26) with the barrier wall prior to assembling the components. A method according to any one of claims 12 to 15, wherein the barrier wall restricts migration of the adhesive (26) in one direction as the adhesive is pressed between the adhesive surfaces (22, 24) during assembly of the components, thereby promoting adhesive migration between the adhesive. the surfaces in an opposite direction. A method according to any one of claims 12 to 16, wherein the components are assembled in an assembly direction which intersects complementary inclined adhesive surfaces.