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Title:
AN ASSEMBLY UNIT WITH A RETAINER FOR RETAINING A BOLT
Document Type and Number:
WIPO Patent Application WO/2019/201402
Kind Code:
A1
Abstract:
A method for assembling an assembly unit (19) is disclosed. A flexible item (1) is provided, the flexible item (1) having a dimension in a plane being significantly larger than a dimension perpendicular to the plane. The flexible item (1) is rolled into a substantially cylindrical shape, thereby forming a retainer (11). A bolt (8) is provided, and the bolt (8) and the retainer (11) are inserted into a through-going hole (17) formed in a component (15), such as a flange of a wind turbine component, in such a manner that a portion of the bolt (8) is placed inside the retainer (11). The size of the retainer (11) can be customized to fit the dimensions of bolt (8) and through-going hole (17). The bolt (8) is retained in the assembly unit (19), e.g. during transport.

Inventors:
PAUL, Hans-Christoph (Nordlundvej 166, 7330 Brande, 7330, DK)
Application Number:
DK2019/050118
Publication Date:
October 24, 2019
Filing Date:
April 12, 2019
Export Citation:
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Assignee:
VESTAS WIND SYSTEMS A/S (Hedeager 42, 8200 Aarhus N, 8200, DK)
International Classes:
F16B5/02; F03D13/00; F16B41/00
Foreign References:
US3474847A1969-10-28
US3156281A1964-11-10
DE19818369A11999-07-08
US6309156B12001-10-30
DE102012024823A12014-06-26
US6623226B22003-09-23
DE102010010297A12011-02-03
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Claims:
CLAIMS

1. A method for assembling an assembly unit (19), the method comprising the steps of: providing a flexible item (1), the flexible item (1) having a dimension in a plane being significantly larger than a dimension perpendicular to the plane,

- rolling the flexible item (1) into a substantially cylindrical shape, thereby forming a retainer (11), providing a bolt (8), and - inserting the bolt (8) and the retainer (11) into a through-going hole (17) formed in a component (15), in such a manner that a portion of the bolt (8) is placed inside the retainer (11).

2. A method according to claim 1, wherein the step of inserting the bolt (8) and the retainer (11) into a through-going hole (17) comprises inserting the retainer (11) into the through-going hole (17) and subsequently placing a portion of the bolt (8) inside the retainer (11).

3. A method according to claim 1, wherein the step of inserting the bolt (8) and the retainer (11) into a through-going hole (17) comprises the steps of:

- placing a portion of the bolt (8) inside the retainer (11), and subsequently inserting the bolt (8) along with the retainer (11) into the through-going hole (17).

4. A method according to claim 3, wherein the steps of rolling the flexible item (1) and placing a portion of a bolt (8) inside the retainer (11) are performed simultaneously by rolling the flexible item (1) around the portion of the bolt (8).

5. A method according to any of the preceding claims, further comprising the step of cutting the flexible item (1) from a band of flexible material.

6. A method according to claim 5, wherein the step of cutting the flexible item

(I) is performed after the step of placing a portion of a bolt (8) inside the retainer (11).

7. A method according to any of the preceding claims, further comprising the step of applying grease between the retainer (11) and the bolt (8).

8. A method according to any of the preceding claims, wherein the step of providing a flexible item (1) comprises providing the flexible item (1) with a plurality of hinges (2) allowing the flexible item (1) to bend around at least one axis.

9. A method according to any of the preceding claims, further comprising the step of fixating the retainer (11) relative to the bolt (8).

10. A method according to claim 9, wherein the step of fixating the retainer (11) relative to the bolt (8) comprises applying mechanical fixation means (14) around the retainer (11) and the bolt (8).

11. A method according to any of the preceding claims, wherein the retainer

(II) is provided with a plurality of teeth (3) arranged on a surface facing the bolt (8), the teeth (3) being configured for, in cooperation with a threaded portion (9) of the bolt (8), maintaining the axial position of the retainer (11) relative to the bolt (8).

12. A method according to any of the preceding claims, wherein the retainer (11) is provided with a plurality of protruding portions (5) arranged on a surface facing away from the bolt (8), the protruding portions (5) extending

substantially along an axial direction of the retainer (11).

13. A method according to any of the preceding claims, wherein the step of providing a flexible item (1) comprises providing a flexible item (1) made from a resilient material.

14. A method according to any of the preceding claims, wherein the flexible item (1) is provided with a chamfered edge (7), and wherein the step of inserting the bolt (8) and the retainer (11) into the through-going hole (17) comprises entering the chamfered edge (7) firstly into the hole (17).

15. A method according to any of the preceding claims, further comprising the step of transporting the assembly unit (19) to an installation site. 16. A method according to any of the preceding claims, further comprising the steps of:

- arranging the assembly unit (19) adjacent to an additional component (16) having at least one through-going hole (18) formed therein,

- moving the bolt (8) in an axial direction into a through-going hole (18) of the additional component (16), and applying a nut to the bolt (8) and tensioning the bolt (8), thereby assembling the component (15) and the additional component (16).

17. An assembly unit (19) comprising : a component (15) having at least one through-going hole (17) formed therein at least one bolt (8), each bolt (8) being mounted in one of the trough- going holes (17), and at least one retainer (11) being mounted in one of the through-going holes (17) between an inner wall of the through-going hole (17) and a bolt (8) mounted in the through-going hole (17), wherein the retainer (11) is formed by rolling into a substantially cylindrical shape a flexible item (1) having a dimension in a plane being significantly larger than a dimension perpendicular to the plane.

18. An assembly unit (19) according to claim 17, wherein the retainer (11) is provided with one or more grease reservoirs (4) formed in a surface of the retainer (11) which faces the bolt (8).

19. An assembly unit (19) according to claim 17 or 18, wherein the retainer (11) is provided with a plurality of hinges (2) extending substantially along an axial direction of the retainer (11). 20. An assembly unit (19) according to any of claims 17-19, wherein the component (15) is or forms part of a wind turbine generator.

21. An assembly unit (19) according to claim 20, wherein the component (15) is or forms part of a flange-to-flange connection in a wind turbine generator.

Description:
AN ASSEMBLY UNIT WITH A RETAINER FOR RETAINING A BOLT

FIELD OF THE INVENTION

The present invention relates to a method for assembling an assembly unit comprising a component having at least one through-going hole formed therein, at least one bolt mounted in one of the through-going holes and at least one retainer for retaining the bolt in the through-going hole. The present invention further relates to such an assembly unit.

BACKGROUN D OF THE INVENTION

Large components, such as tower sections of a wind turbine, may be assembled via flanges formed on the components being provided with a plurality of through-going holes, and by means of bolts or the like extending through corresponding holes formed in each of the flanges. The larger the components are, the larger and heavier the bolts will be.

Normally, the components will be arranged adjacent to each other on site, and the bolts will subsequently be arranged in the through-going holes in order to assemble the components. In the case that the bolts are large and heavy, handling the bolts on site in this manner is inconvenient and takes time.

Furthermore, in the case that the assembly position is elevated from the ground, for instance when the components are tower sections of a wind turbine tower, the bolts may need to be lifted to the level of the assembly position by a crane, and a platform arranged at this level must be designed for carrying the entire weight of all of the required bolts in a single region. This adds to the costs of the structure which the components form part of as well as to the time during which a crane is required. Since the costs involved with using large cranes are considerable, this also adds to the costs of assembling the structure.

It is therefore desirable to provide a system which allows separate handling of the bolts on site to be dispensed with. It is further desirable that a system as outlined above can be provided in a manner which allows bolts and through-going holes of varying diameter to be used, in an easy and cost effective manner.

US 6,623,226 B2 discloses an assembly unit including at least one component and at least one screw including a shank at least partially including a thread. The component for each screw includes a through-hole. At least one bush is associated with the at least one screw, and it is designed and arranged to be insertable into the respective through-hole.

DE 10 2010 010 297 A1 discloses a fastening system and a method for mounting wind turbine components. The system comprises a bolt to be inserted into a through-going hole in a component. A grommet is arranged in contact with the bolt in order to retain the bolt in the through-going hole.

DESCRIPTION OF THE INVENTION

It is an object of embodiments of the invention to provide an assembly unit which allows separate handling of bolts at an installation site to be dispensed with.

It is a further object of embodiments of the invention to provide an assembly unit which is capable of carrying bolts along with a component from a

manufacturing site to an installation site. It is an even further object of embodiments of the invention to provide a method for assembling two components without requiring separate handling of a plurality of bolts on site.

It is an even further object of embodiments of the invention to provide a method for assembling two components which allows for variations in bolt size. According to a first aspect the invention provides a method for assembling an assembly unit, the method comprising the steps of: - providing a flexible item, the flexible item having a dimension in a plane being significantly larger than a dimension perpendicular to the plane,

- rolling the flexible item into a substantially cylindrical shape, thereby

forming a retainer, - providing a bolt, and

- inserting the bolt and the retainer into a through-going hole formed in a component, in such a manner that a portion of the bolt is placed inside the retainer.

The method according to the first aspect of the invention is a method for assembling an assembly unit. The assembly unit comprises a component, at least one bolt and at least one retainer. The component has at least one through-going hole formed therein, the at least one bolt is arranged in the at least one hole, and the at least one retainer is arranged in the at least one through-going hole between the at least one bolt and an inner wall of the through-going hole. In the present context the term 'through-going hole' should be interpreted to mean a hole which extends through the component, from one side of the component to another, allowing passage through the component, via the through-going hole.

In the method according to the first aspect of the invention, a flexible item is initially provided. In the present context the term 'flexible item' should be interpreted to be an item which is able to bend in at least one direction, such as around at least one axis. The flexibility properties of the flexible item may be inherent properties of the material of the flexible item, or they may be the result of design details of the flexible item. This will be described in further detail below.

The flexible item has a dimension in a plane being significantly larger than a dimension perpendicular to the plane. Accordingly, the flexible item substantially extends in the plane, i.e. it forms a flat and substantially sheet like structure. Next, the flexible item is rolled into a substantially cylindrical shape. In the present context the term 'cylindrical shape' should be interpreted to mean a shape which has a constant cross section along a direction defined by a cylinder axis. The cylindrical shape is preferably a circular cylindrical shape, where the constant cross section is in the form of a circle. However, it is not ruled out that the constant cross section has another suitable shape. The cylindrical shape forms a retainer.

A bolt is provided, and the bolt and the retainer are inserted into a through- going hole formed in a component, in such a manner that a portion of the bolt is placed inside the retainer. Thereby an assembly of the component, the bolt and the retainer is formed.

Since portion of a bolt is placed inside the retainer, the retainer is positioned around a portion of the bolt. The portion of the bolt is thereby arranged inside a perimeter defined by the cylindrical wall of the retainer. The portion of the bolt being placed inside the retainer is preferably a threaded shaft of the bolt.

Furthermore, since a portion of the bolt is placed inside the retainer, and the bolt as well as the retainer have been inserted into the through-going hole, the retainer is positioned between the bolt and an inner wall of the through-going hole, i.e. the retainer is in contact with the inner wall of the through-going hole as well as with the bolt. Thereby the retainer keeps the bolt in position in the through-going hole. Accordingly, the retainer ensures that the bolt can be kept in position in the through-going hole, even during transport of the component. Thus, bolts can be mounted in through-going holes of the component, e.g. at a manufacturing site, and the component can subsequently be transported to an installation site, with the bolts mounted therein. Thereby individual handling of the bolts at the installation site is avoided. For instance, in the case that the component needs to be lifted to an elevated installation position, the component and all of the bolts can be lifted in a single lifting operation, thereby reducing the number of lifting operations and the time during which a crane is required.

Furthermore, the time required for joining the component to another component is reduced, because it is not necessary to insert the bolts individually on site. Since the retainer is formed by rolling a flexible item, the retainer can easily be provided with dimensions which match the bolt and the through-going hole which are used in a given case. Thereby a number of different assembly units, having bolts and through-going holes with differing dimensions, can be provided with retainers as described above, without having to provide variously sized retainers matching the dimensions of each bolt/through-going hole pair. Thereby customised retainers can be provided at low cost.

The step of inserting the bolt and the retainer into a through-going hole may comprise inserting the retainer into the through-going hole and subsequently placing a portion of the bolt inside the retainer.

According to this embodiment, the retainer and the bolt are inserted separately into the through-going hole, i.e. the insertion is performed in two steps. Thus, initially the retainer is positioned in the through-going hole in abutment with the inner wall of the through-going hole. Subsequently, the bolt is inserted into the through-going hole and into the retainer in one step, thereby placing a portion of the bolt inside the retainer which is already positioned inside the through-going hole.

As an alternative, the step of inserting the bolt and the retainer into a through- going hole may comprise the steps of: - placing a portion of the bolt inside the retainer, and

- subsequently inserting the bolt along with the retainer into the through- going hole.

According to this embodiment, the bolt and the retainer are inserted into the through-going hole together, i.e. the insertion is performed in a single step. Thus, according to this embodiment, a portion of the bolt is initially placed inside the retainer, i.e. the retainer is positioned around the bolt. Subsequently, the retainer, with the bolt positioned inside, is inserted into the through-going hole in one step. The steps of rolling the flexible item and placing a portion of the bolt inside the retainer may be performed by first rolling the flexible item and then placing the portion of the bolt inside the retainer formed thereby. In this case the portion of the bolt may be placed inside the retainer before the retainer is inserted into the through-going hole, or it may be placed inside the retainer after the retainer has been inserted into the through-going hole, as described above.

As an alternative, the steps of rolling the flexible item and placing a portion of a bolt inside the retainer may be performed simultaneously by rolling the flexible item around the portion of the bolt. According to this embodiment, the flexible item is wrapped directly around the portion of the bolt while the cylindrical retainer is formed. Thereby it is ensured that the cylindrical retainer exactly matches the dimensions of the bolt in an easy manner.

The method may further comprise the step of cutting the flexible item from a band of flexible material. According to this embodiment, the flexible item is cut from a larger piece of flexible material, in the form of a band of flexible material. Thereby the flexible item can be cut to have exactly the size required under the given circumstances. This minimises waste of material.

The step of cutting the flexible item may be performed after the step of placing a portion of a bolt inside the retainer. According to this embodiment, a portion of the band of flexible material may be rolled around the portion of the bolt until a cylindrical shape has been formed which exactly surrounds the portion of the bolt. Then the band of flexible material may be cut, thereby cutting the rolled flexible item from the band of flexible material and forming the retainer.

The process of rolling the flexible item and cutting the flexible item from the band of flexible material may be automated using suitable equipment which rolls the flexible item, e.g. including rotating the bolt, and cuts the flexible material when the flexible item has been rolled around the bolt.

As an alternative, the step of cutting the flexible item from a band of flexible material may be performed prior to the step of rolling the flexible item. This is, e.g., relevant in embodiments where the retainer is inserted into the through- going hole before the portion of the bolt is placed inside the retainer.

The method may further comprise the step of applying grease between the retainer and the bolt. Thereby grease is automatically applied to the portion of the bolt which is arranged in contact with the retainer. This is very relevant when the portion of the bolt being placed inside the retainer is a threaded shaft of the bolt. Such threaded shafts need to have grease applied thereto in order to allow the bolt to be smoothly joined with a corresponding nut.

The grease could be applied directly to the bolt or directly to a surface of the flexible item, prior to placing a portion of the bolt inside the retainer. Applying the grease via the bolt or the flexible item is a very easy manner of applying grease to the threaded shaft of the bolt.

The surface of the flexible item which is facing the bolt may be provided with grease reservoirs arranged to accommodate grease. In the case that grease is applied directly to the bolt, the grease reservoirs may be used for collecting excess grease. In the case that grease is applied directly to the flexible item, the grease may be applied via the grease reservoirs, and may be accommodated there until the bolt has been placed inside the retainer.

The grease could, e.g., be applied to the bolt or to the surface of the flexible item as part of an automatic process where the flexible item is rolled around the bolt and possibly cut from a band of flexible material.

The step of providing a flexible item may comprise providing the flexible item with a plurality of hinges allowing the flexible item to bend around at least one axis. According to this embodiment, the flexible item may be made from a material which is rigid, and which would therefore normally not allow the flexible item to be bent. However, the plurality of hinges will apply the required flexibility to the item, allowing it to be bent into the cylindrical shape. Each hinge may interconnect two segments or chain members which can pivot relative to each other via the hinge. The hinges may each define a hinge axis about which a pivoting hinge

movement is performed. The hinge axes are preferably aligned with respect to each other, thereby defining a direction about which the flexible item can be bent. The hinge axes may advantageously be arranged substantially along the axial direction of the cylindrical shape of the retainer.

The hinges may be formed as an integral part of the flexible item, for instance as portions of the flexible item with a reduced material thickness, such as grooves. As an alternative, the hinges may be separate parts which interconnect individual segments or chain members. For instance, the segments or chain members may be clicked together, via the hinges.

As an alternative, the flexible item may be made from a flexible material which in itself allows the flexible item to be bent into the cylindrical shape.

The method may further comprise the step of fixating the retainer relative to the bolt. According to this embodiment, it is ensured that the retainer remains in contact with the bolt and that the bolt remains inside the retainer. The fixation may be permanent in the sense that it is allowed to remain on the retainer and the bolt after the bolt has been inserted into the through-going hole.

Alternatively, it may be removed, e.g. when the bolt has been inserted into the through-going hole or immediately prior to inserting the bolt into the through- going hole.

The step of fixating the retainer relative to the bolt may comprise applying mechanical fixation means around the retainer and the bolt. According to this embodiment, the retainer is fixated relative to the bolt in a mechanical manner. The mechanical fixation means could, e.g., include a clamp, adhesive tape, a rubber band, a wire, or any other suitable kind of mechanical fixation means.

As an alternative, the retainer may be fixated relative to the bolt in a non- mechanical manner, e.g. by permanently joining ends of the flexible item, e.g. by means of glue, heat treatment, etc. It should be noted that in the case that mechanical fixation means is supposed to remain around the retainer and the bolt when the bolt and retainer are positioned in the through-going hole, the frictional properties of the mechanical fixation means should preferably be such that the overall frictional properties of the retainer are not affected, or are only affected to a limited extent. This will ensure that the retainer is still capable of retaining the bolt with respect to the through-going hole. As an alternative, the mechanical fixation means may be removed immediately prior to inserting the bolt and/or the retainer in the through-going hole.

As an alternative to fixating the retainer relative to the bolt, the bolt and the retainer may be inserted into the through-going hole while grapping the retainer and the bolt, e.g. by means of a robotic gripper or manually. As another alternative, the retainer may be held manually in the rolled form while being inserted into the through-going hole. Once the retainer has been positioned in the through-going hole, the cylindrical shape of the retainer will be maintained by the inner wall of the through-going hole, and the bolt can be subsequently inserted into the through-going hole and the retainer as described above.

The retainer may be provided with a plurality of teeth arranged on a surface facing the bolt, the teeth being configured for, in cooperation with a threaded portion of the bolt, maintaining the axial position of the retainer relative to the bolt. According to this embodiment, the retainer is firmly kept in place with respect to the bolt, once the portion of the bolt has been placed inside the retainer.

The teeth may extend along a direction being substantially perpendicular to an axial direction of the retainer, for instance following a pitch defined by the threaded portion of the bolt. Thereby the teeth can be arranged in valleys defined by the thread, and the retainer is prevented from performing direct axial movements relative to the bolt, due to engagement between the teeth and the thread. However, it may still be possible to move the retainer in an axial direction relative to the bolt by rotating the bolt or the retainer, thereby causing the teeth to move along the thread of the bolt. The teeth may have an elongated shape, in the sense that they define a length. In this case each of the teeth may be arranged along a portion of a valley of the thread. Alternatively, the teeth may have a point like shape. For instance, the teeth may be in the form of dimples or the like.

Alternatively or additionally, the retainer may be provided with a plurality of protruding portions arranged on a surface facing away from the bolt, the protruding portions extending substantially along an axial direction of the retainer. Since the protruding portions are arranged on a surface facing away from the bolt, they will be facing an inner surface of the through-going hole when the bolt and the retainer have been inserted into the through-going hole.

The protruding portions may be used for taking up small tolerances of the through-going holes. For instance, they may be configured to be scraped off during insertion of the bolt and the retainer into the through-going hole, due to contact between the protruding portions and an edge of the through-going hole. In this case some or all of the protruding portions will be removed, thereby reducing the outer diameter of the retainer, in the case that the diameter of the through-going hole is smaller than expected. On the other hand, in the case that the diameter of the through-going hole is larger than expected, the protruding portions remain on the retainer, thereby maintaining an outer diameter of the retainer which is defined by the protruding portions. This even further ensures that the retainer can be applied to bolts and through-going holes of varying size. Furthermore, the requirements to tolerances of the parts, in particular with respect to the dimensions of the through-going hole and the bolt, can be lowered, thereby reducing the manufacturing costs.

In the case that the retainer is fixated relative to the bolt by means of

mechanical fixation means, the mechanical fixation means may advantageously be arranged in a zone with no protruding portions.

The step of providing a flexible item may comprise providing a flexible item made from a resilient material, such as a plastic material. According to this embodiment, the flexible properties of the flexible item originate at least partly from properties of the material of the item. The flexible item may be provided with a chamfered edge, and the step of inserting the bolt and the retainer into the through-going hole may comprise entering the chamfered edge firstly into the hole. According to this embodiment, the part of the retainer which is initially introduced into the through-going hole has a slightly smaller outer diameter than the rest of the retainer, due to the chamfered edge. This makes it easier to insert the retainer, possibly with the bolt placed therein, into the through-going hole.

The method may further comprise the step of transporting the assembly unit to an installation site. According to this embodiment, the component is transported to the installation site with one or more bolts retained in the through-going holes. As an alternative, the method may be performed at the installation site before hoisting the component to an elevated mounting position.

The method may further comprise the steps of:

- arranging the assembly unit adjacent to an additional component having at least one through-going hole formed therein,

- moving the bolt in an axial direction into a through-going hole of the

additional component, and

- applying a nut to the bolt and tensioning the bolt, thereby assembling the component and the additional component. Thereby the two components can be assembled without requiring individual handling of the bolts at the installation site. As an alternative to applying a nut, the bolt may instead be screwed directly into the additional component.

The step of moving the bolt in an axial direction may be performed by pushing the bolt linearly in the axial direction. As an alternative, the step of moving the bolt in an axial direction may be performed by rotating the bolt, thereby causing a relative movement between a threaded portion of the bolt and one or more teeth arranged on a surface of the retainer facing the bolt, which advances the bolt in an axial direction. According to a second aspect the invention provides an assembly unit

comprising :

- a component having at least one through-going hole formed therein,

- at least one bolt, each bolt being mounted in one of the trough-going holes, and

- at least one retainer being mounted in one of the through-going holes between an inner wall of the through-going hole and a bolt mounted in the through-going hole, wherein the retainer is formed by rolling into a substantially cylindrical shape a flexible item having a dimension in a plane being significantly larger than a dimension perpendicular to the plane.

The assembly unit according to the second aspect of the invention has been assembled using the method according to the first aspect of the invention. The remarks set forth above are therefore equally applicable here. In particular, since the retainer is formed by rolling a flexible item into a cylindrical shape, the size of the retainer can be adjusted to match the dimensions of the bolt and the through-going hole.

The retainer may be provided with one or more grease reservoirs formed in a surface of the retainer which faces the bolt. According to this embodiment, grease may be provided between the bolt and the retainer, as described above with reference to the first aspect of the invention. For instance, grease may be applied to the bolt prior to placing a portion of the bolt inside the retainer, in which case the grease reservoirs may be used for collecting excess grease. Alternatively, grease may be provided directly to the grease reservoirs prior to placing a portion of the bolt inside the retainer, and possibly prior to rolling the flexible item into a substantially cylindrical shape. Applying grease between the bolt and the retainer in this manner ensures that grease is applied to the portion of the bolt, e.g. a threaded shaft, which is arranged in contact with the retainer.

The retainer may be provided with a plurality of hinges extending substantially along an axial direction of the retainer. As described above, such hinges provide the required flexibility of the flexible member, allowing it to be rolled into a substantially cylindrical shape, without requiring flexible properties of the material of the flexible item.

The component may be or form part of a wind turbine generator, such as a wind turbine tower section, a hub, a main shaft, a main bearing housing, a wind turbine blade, a gearbox, or any other suitable part of a wind turbine generator which needs to be assembled with another part.

The component may be or form part of a flange-to-flange connection in a wind turbine generator. This could, e.g., be in the form of a tower flange of a wind turbine tower section, or it could be in the form of a flange-to-flange connection of any of the wind turbine components mentioned above.

In the case that the component is or forms part of a tower flange of a wind turbine tower section, the wind turbine tower section needs to be assembled with another wind turbine tower section, via tower flanges formed on the two wind turbine tower sections. Since bolts can be retained in the through-going holes formed in one of the tower flanges, as described above, it is possible to insert the bolts into the through-going holes at the manufacturing site and to transport the wind turbine tower section to an installation site of the wind turbine with the bolts retained in the through-going holes. Furthermore, the tower section can be lifted into position along with the bolts, and the bolts can subsequently be moved into the through-going holes of the other wind turbine tower section. Accordingly, only one lifting operation is required for lifting the wind turbine tower section and the bolts to the installation position, no individual handling of the bolts is required, and no part of a working platform arranged inside the wind turbine tower needs to be dimensioned to carry all of the bolts at once. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the accompanying drawings in which

Fig. 1 is a perspective view of a flexible item for an assembly unit according to an embodiment of the invention,

Fig. 2 is a detail of the flexible item of Fig. 1,

Fig. 3 is a perspective view of the flexible item of Figs. 1 and 2, seen from the opposite side,

Figs. 4-9 illustrate method steps of a method according to an embodiment of the invention, and

Figs. 10 and 11 illustrate assembly of two components using an assembly unit and a method according to embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a flexible item 1 for an assembly unit according to an embodiment of the invention. The flexible item 1 is provided with a plurality of hinges 2 in the form of portions of the flexible item 1 with a smaller material thickness than the rest of the flexible item 1. Segments arranged on opposite sides of a hinge 2 are allowed to pivot relative to each other via the hinge 2. Accordingly, the plurality of hinges 2 ensure that the flexible item 1 can be bent around an axis (not shown), i.e. the hinges 2 provide the required flexibility to the flexible item 1.

The flexible item 1 is further provided with a plurality of teeth 3, each extending along a direction which is substantially perpendicular to the direction of the hinges 2. The teeth 3 are configured to engage a threaded portion of a bolt in a manner which will be described in further detail below. When the teeth 3 are arranged in engagement with a threaded portion of a bolt, the bolt is prevented from moving in an axial direction relative to the flexible item 1.

Furthermore, a plurality of grease reservoirs 4 is formed in the flexible item 1. The grease reservoirs 4 are configured to accommodate grease which is used for lubricating a part of a bolt being arranged in contact with the flexible item 1, e.g. a threaded portion of the bolt. Thereby it can easily be ensured that the bolt is suitably lubricated.

Fig. 2 is a detailed view of the flexible item 1 of Fig. 1. The hinges 2, the teeth 3 and the grease reservoirs 4 can be easily seen. Furthermore, it can be seen that the flexible item 1 comprises a plurality of protruding portions 5 arranged on an opposite side of the flexible item 1. These will be described in further detail below with reference to Fig. 3.

Fig. 3 is a perspective view of the flexible item 1 of Figs. 1 and 2, seen from an opposite side. The hinges 2 and the protruding portions 5 can be clearly seen. Each of the protruding portions 5 extends along a direction which is substantially parallel to the direction of the hinges 2. Approximately in the middle of the flexible item 1 a zone 6 is defined in which there are no protruding portions 5. This will be described in further detail below with reference to Figs. 4-9.

The side of the flexible item 1 which is shown in Fig. 3 is configured to be arranged in such a manner that it faces away from a bolt, when the flexible item 1 is rolled to form a retainer and has a bolt placed therein. When the retainer is inserted into a through-going hole of a component, and a bolt is placed therein before or after inserting the retainer, the side of the flexible item 1 which is shown in Fig. 3 faces an inner wall of the through-going hole. Accordingly, the protruding portions 5 will be facing the inner wall of the through-going hole. The protruding portions 5 may be used to take up small tolerances of the through- going hole. For instance, in the case that the diameter of the through-going hole is slightly smaller than expected, the protruding portions 5 may be scraped off when the bolt and the retainer are inserted into the through-going hole, thereby reducing the outer diameter of the retainer. On the other hand, in the case that the diameter of the through-going hole is somewhat larger, the protruding portions 5 remain on the flexible item 1, and the larger outer diameter of the retainer is maintained. The maximum diameter of the through-going hole should, in any case, be less than the diameter of the circumscribed circle of the retainer. The flexible item 1 is further provided with a chamfered edge 7. When the flexible item 1 has been rolled into a retainer, and the retainer is being inserted into a through-going hole of a component, the chamfered edge 7 is inserted firstly into the through-going hole. The chamfered edge 7 provides a slightly smaller outer diameter of the retainer than the remaining part of the retainer, and this makes it easier to introduce the retainer, possibly with the bolt placed therein, into the through-going hole.

Figs. 4-9 illustrate method steps of a method according to an embodiment of the invention. In Fig. 4 a flexible item 1 is provided. The flexible item 1 is provided with a plurality of hinges and a plurality of grease reservoirs 4. The flexible item 1 could, e.g., be of the kind illustrated in Figs. 1-3.

The flexible item 1 may be provided as a long band from which the flexible item 1 can be cut to length.

Alternatively, the flexible item may be provided as sheets of the required length.

In Fig. 5 the flexible item 1 has been rolled around a bolt 8 comprising a threaded portion 9 and a head 10. Thereby a retainer 11 with a substantially cylindrical shape has been formed from the flexible item 1. This is possible because the hinges 2 allow the flexible item 1 to bend around an axis which is substantially parallel to an axial direction defined by the bolt 8.

Furthermore, grease has been applied to the grease reservoirs 4 of the flexible item 1, prior to rolling the flexible item 1 around the bolt 8, by means of a grease applicator 12. Thereby it is ensured that the threaded portion 9 of the bolt 8 is properly lubricated. In Fig. 6 the flexible item 1 is cut by means of a cutting tool 13, and thereby a retainer 11 of a size which exactly matches the size of the threaded portion 9 of the bolt 8 is obtained. In Fig. 7 the cutting has been completed, and the retainer 11 has thereby been separated from the remaining part of the flexible item 1. In Fig. 8 a mechanical fixation means 14 is being applied to the outer surface of the retainer 11 in order to fixate the retainer 11 relative to the bolt 8. In the case that the flexible item 1 is of a kind having protruding portions 5 (shown in Fig. 3) arranged on the side of the flexible item 1 which faces away from the bolt 8, e.g. the flexible item 1 illustrated in Figs. 1-3, then the mechanical fixation means 14 could advantageously be arranged in a zone 6 (shown in Fig. 3) with no protrusions 5. Thereby it is ensured that the outer diameter of the retainer 11 is defined by the protruding portions 5, and not by the mechanical fixation means 14.

The mechanical fixation means 14 could, e.g., be in the form of a clamp, adhesive tape, a rubber band, a wire, etc.

Fig. 9 is a side view of the bolt 8 with the retainer 11 mounted on the threaded portion 9 thereof.

As an alternative to the method illustrated in Figs. 4-9, a flexible item could be cut from the sheet and rolled into a cylindrical shape, thereby forming a retainer which is inserted into a through-going hole of a component. Subsequently, the bolt may be inserted into the through-going hole, while placing a portion of the bolt inside the retainer which is already positioned in the through-going hole.

Fig. 10 and 11 illustrate assembly of two components 15, 16, using an assembly unit 19 and a method according to embodiments of the invention. The

components 15, 16 are in the form of flanges of wind turbine tower sections to be joined to each other during erection of a wind turbine.

In Fig. 10 the first component 15 and the second component 16 are arranged with a distance, i.e. the second component 16 is in the process of being arranged adjacent to the first component 15. A plurality of bolts 8 are arranged in through-going holes 17 formed in the first component 15 by means of retainers (not visible). The retainers may have been provided on the bolts 8 in the manner described above with reference to Figs. 4-9, or the retainers may have been inserted into the through-going holes 17 first, and the bolts 8 may have been subsequently inserted into the through-going holes and the retainers, as described above. Accordingly, the bolts 8 are retained in the shown positions during transport and installation, even when they are arranged with the bolt head pointing downwards, as shown in Fig. 10. The second component 16 is also provided with a plurality of through-going holes 18. However, no bolts are arranged in these through-going holes 18.

In Fig. 11 the second component 16 has been arranged adjacent to the first component 15 in such a manner that the through-going holes 17 formed in the first component 15 are aligned with the through-going holes 18 formed in the second component 16. Accordingly, the first component 15 and the second component 16 are ready to be assembled by means of the bolts 8 arranged in the through-going holes 17 of the first component 15.

In order to achieve this, the bolts 8 are moved in an upwards direction, towards the second component 16. This may, e.g., be obtained by rotating the bolts 8, thereby advancing them forward via an engagement between threaded portions of the bolts 8 and teeth formed on inner surfaces of the retainers. Thereby each of the bolts 8 enters a through-going hole 18 formed in the second component 16, while the retainers remain in the through-going holes 17 of the first component 15.




 
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