WO2011069511A1

WO2011069511A1 - Heating apparatus

Info

Publication number: WO2011069511A1
Application number: PCT/DK2010/050333
Authority: WO
Inventors: Mohan Raj Krishnaswamy; Saravanan Periyasamy
Original assignee: Vestas Wind Systems A/S
Priority date: 2009-12-09
Filing date: 2010-12-08
Publication date: 2011-06-16

Abstract

A heating apparatus comprising a heater cell (24) arranged to accommodate a member of a wind turbine (2), the member having at least one portion (4) to be heated is provided. The heater cell (24) comprises a housing (27), a heater face (42 and a plurality of infrared heat sources (44) located on the heater face (42). The heater cell (24), defines a heating cavity (25) delimited by the housing (26) and the portion to be heated. In use the heater cell (24) defines a heating cavity (25) formed by the housing (26) and a said member to be heated. An efficient heat treatment apparatus is provided.

Description

HEATING APPARATUS

The present invention relates to a heating apparatus for at least a portion of a member of a wind turbine in particular, but not exclusively, to heating apparatus for heat treatment of wind turbine rotor blades at a wind turbine hub. A specific aspect of the invention relates to a heating apparatus for the circumference of a root end of a wind turbine blade.

Wind turbine rotor blades are typically made from one or more composite materials. The composite material is generally a laminated material, whereby layers of reinforcing material are bonded to one another with a resin and, subsequently, cured to consolidate a component, for example a wind turbine rotor shell.

Wind turbine rotor blades and components formed of composite materials do not have the structural integrity to provide a secure fixing mechanism into which, for example, threaded bolts may be directly inserted. A hole may be tapped into the composite material of the blade to provide a complementing thread upon which a bolt may achieve a secure purchase. However, when an interface between the bolt and the root is exposed to relative movement between the rotor hub and the rotor blade, the composite material would be too soft to prevent movement by the bolt and deterioration of the composite material would occur either through a crumbling or a delamination failure mechanism.

For this reason, it is known for wind turbine rotor blades to comprise internally threaded metal inserts which are embedded into the root portion of the blade. Fixing bolts may be used in combination with these inserts to achieve a secure connection between the rotor hub and the rotor blade. Figure 1 illustrates a conventional rotor blade configuration whereby a rotor blade 2, comprising composite material, has, at its root end portion 4, a plurality of inserts 6. Figure 2 illustrates in cross section the rotor blade 2 of Figure 1 attached to a rotor hub 8 of a wind turbine assembly, of which only a portion, including bearings 10, is shown in Figure 2.

The inserts 6 are introduced into the rotor blade 2 during manufacture thereof and secured and embedded therein. The blade 2 may be made up in sheet layers and cured without the inserts present. Holes for receiving the inserts are subsequently machined into the root portion 4 of the rotor blade 2. Inserts are introduced into these holes in the presence of an adhesive material such that they become securely bonded in place. Each insert 6 is generally made from metal. Adhesives suitable for bonding metal and laminate can be used to secure the insert 6. The bonding and curing of suitable adhesives can present particular challenges in manufacture, for example some adhesives require a long period of time to set or require a high temperature step to cure the bond between the metal and the laminate and embed the insert 6 securely. Electrical heaters can be used to provide heat to cure the bond however an electrical heating element may be slow to heat up to an operating temperature, requiring a pre-heating stage. This means the operation of the element may be inefficient.

The material properties of the metal of the insert 6 and the composite blade vary significantly, in particular the stiffness which is quantified by Young's modulus.

In operation, aerodynamic loads are exerted on each rotor blade 2 and the rotor hub is rotatably driven. Significant levels of dynamic structural loading are transmitted between the rotor hub 8 and each rotor blade 2. This axial load is carried by the inserts 6 and is transmitted to the surrounding composite material of the rotor blade 2 adjacent to a tip end of the insert 6. Significant local stress is, therefore, experienced in the composite material at the insert 6. A loose fit or a flaw in the fit between the blade 2 and the insert 6 can lead to increased loading experienced in the region surrounding the insert and greater loading and stress on other inserts. The accumulation of stress in the region may, in the extreme, lead to catastrophic failure of the insert 6 and/or the rotor blade 2.

It is desired that a secure reliable fix is produced and maintained between the blade 2 and the insert 6 embedded therein to avoid blade failures. It is desirable to provide an alternative heating apparatus which avoids some of the aforementioned disadvantages thus improving the efficiency and reliability of a fixing and heat treatment process.

According to a first aspect, the present invention provides a heating apparatus comprising a heater cell arranged to accommodate at least a portion of a member of a wind turbine, the member having at least one portion to be heated; the heater cell comprising a housing, a heater face and at least one infrared heat source located on the heater face, the heater cell defining a heating cavity delimited by the housing and a said member,

wherein the at least one infrared heat source is arranged substantially opposite to a respective of the at least one portion to be heated. Preferably, where there are a plurality of portions to be heated, there are a plurality of infrared heat sources. The heating cavity may be delimited by a wind turbine blade root. By providing a heater cell suitable for accommodating a part to be heated, such as a part of a wind turbine assembly and a plurality of infrared heat sources, the heating process and curing can be efficient. The infrared heat sources or elements provide accurate, efficient sources of heat that can be well controlled. Indirect heating of the surroundings can be avoided as the emission wavelength spectrum of the heat source can be matched to the absorption wavelength spectrum of the portion to be heated.

The heater cell provides a contained space in which to carry out a heat treatment and the containment reduces turbulence and external factors that may cool or influence the surrounding environment. The heater face may comprise part of the housing. The plurality of infrared heat sources may be arranged in a ring. The location and arrangement of the heat sources in a direct position close to the portion to be heated provides control of the heating process and reduces heating zones and variations in the heater cell environment. In addition, the ramp up and ramp down periods during which time a desired temperature has yet to be reached is reduced. The heating of a portion or the curing of an adhesive becomes predictable and the desired temperature and set or cured stage of an adhesive can be achieved quickly.

The heating apparatus may have an electrical heat source. The electrical heat source is in addition to the infrared heat sources. Thus the heating apparatus has heater redundancy and there will be no zero or down time in manufacture if one heat source breaks down. The switch to an alternative heat source may be automatic or manual.

The heating apparatus may have an air inlet and an air outlet arranged to create airflow through the cavity. The air inlet and the air outlet may comprise respectively, an air inlet pipe and an inlet valve and an air outlet pipe and an exhaust valve. The valves can provide a defined and controlled volume of air flow flowing through the heater cell cavity. The controlled environment may be pressurised to a pressure of at least 1 bar, and may be in the range from 1.02 bar to 1.3 bar. Controlled air flow through the heater cell can create an environment facilitating cooling if required for a curing process. By increasing the pressure in the cavity during the heating process higher temperatures can be reached efficiently.

The heating apparatus may include a fan, and preferably a controller and monitoring apparatus. The information may be used for a database, system tracking, temperature change tracking and recordal purposes and can be managed in real time and integrated with manufacturing automation.

According to a second aspect, the present invention provides a heating apparatus comprising a heater cell arranged to accommodate at least a portion of a member of a wind turbine, the member having at least one portion to be heated; the heater cell comprising a housing, a heater face and a plurality of infrared heat sources located on the heater face, wherein in use the heater cell defines a heating cavity formed by the housing and a said member. According to a third aspect, the present invention provides a method of heating a member of a wind turbine, the member having at least one portion to be heated with the aforementioned heating apparatus.

According to a fourth aspect, the present invention provides a member of a wind turbine, the member having at least one portion heat treated by the aforementioned method.

The present invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 represents a schematic of a member, i.e. the root of a rotor blade, of a wind turbine;

Figure 2 represents a cross section of the rotor blade of Figure 1 in a portion of a wind turbine assembly;

Figure 3A illustrates an insert embedded in the rotor blade of Figure 1 in a first configuration;

Figure 3B illustrates an insert embedded in the rotor blade of Figure 1 in a second configuration; and

Figure 4 illustrates the heating apparatus of the present invention in an open, exposed arrangement.

Figure 2 illustrates a portion of a conventional rotor blade of the type shown in Figure 1 , and as described above for connecting a rotor blade 2 to a rotor hub 8. A single insert 6 is shown in Figures 2 and 3, and a bore 12 is formed within the insert 6 for receiving a bolt 14. A portion 16 of the bore 12 is tapped such that a threaded portion 18 is formed to cooperate with a correspondingly threaded portion of the bolt 14 for securing the rotor blade 2 to the rotor hub 8. In this example, each insert is made from metal such as steel however, alternative materials having a suitable stiffness and machineability properties, such as reinforced plastics material, could be used,

Figure 3A and 3B illustrate the installation of an insert into the blade 2, wherein one end of the insert 6 is located flush with the extreme root end 4 of the rotor blade 2 and the insert 6 extends axially into the material of the rotor blade. Figure 3A represents an insert introduced into the blade 2 during manufacturing of the blade such that the blade material formed about the insert 6. In Figure 3B the insert 6 is accommodated within hole 20 in an already fabricated blade 2. Hole 20 having been subsequently machined into the root portion 4. Space 22 in between insert 6 and the inner wall of hole 20 can accommodate a curable adhesive introduced (in the direction of the arrows) into the hole 20 to secure the inserts in the bulk material.

Figure 4 illustrates an embodiment of the heating apparatus of the present invention for curing material to secure the inserts of Figure 3A and 3B within the blade 2.

The heating apparatus comprises a heating chamber or heater cell 24 comprising an inner heating cavity 25 surrounded by an outer housing 26. The outer housing 26 includes a front wall 28, upper wall 30, lower wall 32 and side walls 34, 36. An opening 38 is located at the front wall 28 of the housing 26. The opening 38 is sized for accommodation of a member requiring heat treatment, such as, in the preferred embodiment described hereafter, the root end of a blade of a turbine assembly. The opening 38 is established by any suitable procedure such as cutting or machining. The accommodation of the root end within the housing 26, is such that the outer surface of the blade member is substantially flush to the edge of the opening 38 in the front wall 28 and there are no gaps in the front wall 28 around the blade member. Alternatively, a suitable flexible collar might be provided along the circumference of the opening 38, so as to provide an air tight interface between the blade root and the front wall 28. The blade itself comprises a glass composite material, having a plurality of inserts 6 embedded therein or laid up within, by known techniques as illustrated in Figure 3A and Figure 3B. As such the inserts require heat treatment as part of the blade fabrication process.

A rear wall 40 of the heater cell 24 is located substantially opposite front wall 28. The rear wall 40 comprises a heater face 42 having a number of Infrared heat sources 44 located thereat and embedded therein. In the embodiment illustrated there are 24 heat sources arranged in a circular pattern of a ring. Different numbers and different arrangements of the heat sources 44 are envisaged for other applications and situations. The rear wall 40 is joined to the rearmost portions of the walls (30, 32, 43, 36) of the housing 26, by a hinge or other suitable means. Thus the heater cell 24 defines the heating cavity 25 as that delimited by the inner surfaces of the walls 28, 30, 32, 34, 36 of the housing 26, the heater face 42 and the blade 2 accommodated at the front wall 28.

The ring shape or circular pattern is arranged such that each heater element 44 in the ring corresponds in an opposing manner to an insert portion of the root end 4 of the blade to be heat treated.

The heater cell 24 further comprises an air inlet and an air outlet arranged at the housing 26 and arranged in communication with the cavity 25 to create an airflow through the heater cell 24. The air inlet comprises an air inlet pipe 46 and an inlet valve 48 and the air outlet comprises an air outlet pipe 50 and an exhaust valve 52. The gas flow within the heater cell 24 is controlled and maintained at above atmospheric pressure by the inlet valve 48 and exhaust valve 52. The pressure in the heating cavity 25 of the preferred embodiment is in the range from 1.02 bar to 1.3 bar.

In use, heat treatment and curing is required at the root end 4 of a blade 2 comprising composite material having an opening into which a metal insert 6 is fitted. In this example, the insert 6 undergoes an adhesive injection process as illustrated in Figure 3B. The resultant adhesive flow path is such that it flows into the opening 20 in the root end 4 of the blade 2, around the outside of the insert 6 and anchors the insert 6 within its opening 20.

Operation of the heating apparatus includes locating the member to be heat treated within the heater cell 24, by accommodating the rotor blade into the front face at opening 38 or otherwise and sealing the cavity with the heater face 42 located opposite to the front wall 28.

The orientation of the heater face 42 of the cavity 25 is such that each one of the infrared heat sources is arranged substantially opposite to an insert of the blade root and adhesive to be heat treated. Thus, in the present example the blade root has 24 openings 20, with an insert 6 and an adhesive component in each opening 20 and a corresponding 24 infrared heat sources located close to and opposite to each one of the portions to be heated. Upon delivery of power to the heat sources to generate and emit infrared radiation, each source directly heats its corresponding insert and adhesive layer, causing curing of the adhesive and/or composite material and curing of the bond between the blade and the insert. The heat is transferred swiftly and in a direct manner and, unlike techniques of heating with electrical heater elements, the heat is not dissipated to warm surrounding air flow or apparatus. The direct infrared heating means that the heat is absorbed in the glue adhesive straight away. The direct heat applied to the area cures the adhesive, fixing the insert rigidly in place within the blade root such that fixing bolts may be secured into the internally threaded metal inserts and used to give a secure connection between the root end 4 of the rotor blade 2 and the rotor hub 8. The heating apparatus comprises material such as steel or other metal that can withstand the curing temperatures experienced within the heater cell.

The process is performed in a pressurised atmosphere, controlled by an air inlet and an air outlet in the heater cell, and at above atmospheric pressure for improved efficiency of the heating process. Specifically, air flow into and out of the cavity is controlled by an air inlet value 48 and an air outlet valve 52. An incoming air flow is routed through the heater housing and heating cavity and exits through the air exhaust pipe 50. Internal fans 54, 56 located in the heater face 42 provide assistance for moving the air flow across the heating area and through the heating cavity 25. The heater cell 24 is held above atmospheric pressure. In the preferred embodiment the pressure is slightly above atmospheric pressure at between 1.02 bar to 1.3bar. By increasing the pressure in the oven during the heating process higher temperatures can be reached efficiently. A pressurised cell will therefore use energy more efficiently and reach the desired temperature more quickly than an unpressurized cell by the gas properties and gas constant.

An additional, electrical heater element is provided as an additional heat source if required. The controller provided controls the heating process and length of heating time and heater power used for each infrared heat source. Additional elements of control are the infrared emission wavelength and frequency, heater source status checking, heat zone control and maintenance schedules.

The invention has been described with reference to specific examples and embodiments. However, it should be understood that the invention is not limited to the particular example disclosed herein but may be designed and altered with the scope of the invention in accordance with the claims.

In the embodiment described above each respective insert is configured to receive a single bolt, however, in an alternative embodiment, the insert could be elongated and configured to receive two or more bolts.

There may be an alternative set or number or orientation of infrared heaters than in the preferred embodiment described. Alteration may be required for the size of area to be cured or the material to be cured.

For example the operating temperature and pressure range, the number of inlets and outlets and the number and position of fans for curing purposes may be altered as required for the materials and process of choice. The curing process is applicable to a variety of parts and components from the wind turbine assembly field.

Claims

1. A heating apparatus comprising a heater cell arranged to accommodate at least a portion of a member of a wind turbine, the member having at least one portion to be heated;

the heater cell comprising a housing, a heater face and at least one infrared heat source located on the heater face, the heater cell defining a heating cavity delimited by the housing and a said member,

wherein the at least one infrared heat source is arranged substantially opposite to a respective of the at least one portion to be heated.

2. A heating apparatus according to Claim 1 , wherein the heating cavity is delimited by a wind turbine blade root.

3. A heating apparatus according to Claim 1 or Claim 2, wherein the heater face comprises part of the housing.

4. A heating apparatus according to any one of claims 1 , 2 or 3, wherein the plurality of infrared heat sources are arranged in a ring.

5. A heating apparatus according to any preceding claim, wherein the heating apparatus further comprises an electrical heat source.

6. A heating apparatus according to any preceding claim, further comprising an air inlet and an air outlet arranged to create an airflow through the cavity.

7. A heating apparatus according to Claim 6, wherein the air inlet and the air outlet comprise respectively an air inlet pipe and an inlet valve and an air outlet pipe and an exhaust valve.

8. A heating apparatus according to Claim 6 or Claim 7, wherein the airflow is such that the cavity is pressurised.

9. A heating apparatus according to any one of claims 6, 7 or 8, wherein the cavity pressure is at least 1 bar, and is preferably in the range from 1.02 bar to 1.3 bar.

10. A heating apparatus according to any preceding claim, wherein at least one fan is located within the housing.

11. A heating apparatus as claimed in any preceding claim, wherein the heating apparatus further comprises a controller arranged to control at least one of the plurality of infrared heat sources to generate and emit an infrared radiation signal.

12. A heating apparatus as claimed in claim 11 , wherein the controller is arranged to control the rate of generation of the radiation signal so as to control the power and intensity of radiation emitted by the heat source.

13. A heating apparatus as claimed in any preceding claim, wherein the heating apparatus further comprises a monitor system arranged to monitor any one or more of the power and intensity of the radiation signal, a temperature, a pressure, or a turbulence of the airflow, in the heating cavity and a condition of a said portion to be heated.

14. A heating apparatus comprising a heater cell arranged to accommodate at least a portion of a member of a wind turbine, the member having at least one portion to be heated; the heater cell comprising a housing, a heater face and a plurality of infrared heat sources located on the heater face, wherein in use the heater cell defines a heating cavity formed by the housing and a said member.

15. A method of heating a member of a wind turbine, the member having at least one portion to be heated utilising the apparatus as claimed in any preceding claim.

16. A member of a wind turbine, the member having at least one portion heat treated by the method of Claim 15.