Tower section production process

Abstract

The application relates to wind turbine tower section production methods and in particular to methods of manufacturing a plurality of elongate tower segments for forming a wind turbine tower section, the tower section constructed from a plurality of elongate tower segments connected along their respective longitudinal edges. The tower section is formed from a plurality of cans connected end to end and is divided into elongate segments by cutting along two or more cut lines extending along the length of the tower. A method of providing a horizontal flange at the end of a wind turbine tower is also discussed, as is a vertical flange preassembly including a pair of vertical flanges for connecting the longitudinal edges of adjacent first and second tower segments.

Claims

1. A method of manufacturing a wind turbine tower section, comprising: forming a plurality of elongate tower segments, the tower section being constructed by connecting the plurality of tower segments along their respective longitudinal edges, wherein the step of forming a plurality of elongate tower segments further comprises: forming each of a plurality of cans by rolling a metal sheet into a tube having a longitudinal seam formed by welding first and second opposed edges of the rolled sheet, wherein at least some of the welded seams comprise tack welds; connecting the plurality of cans end to end; and cutting along two or more cut lines extending along a length of the connected plurality of cans to divide the connected plurality of cans into the plurality of elongate tower segments, wherein the step of cutting along two or more cut lines comprises cutting along the longitudinal seams through the tack welds.

2. The method of claim 1, wherein the step of cutting along two or more cut lines comprises cutting along the longitudinal seam of each of the plurality of cans.

3. The method of claim 1, wherein the connected plurality of cans comprise two or more longitudinal section cut indication lines indicating where the two or more cut lines are to be made during the step of cutting.

4. The method of claim 3, wherein the section cut indication lines are at least partially defined by one or more cut indication marks arranged on the outer surface of one or more of the plurality of cans.

5. The method of claim 4, wherein the step of connecting the plurality of cans further comprises aligning the longitudinal seam of at least one can having tack welds with a cut indication mark on the outer surface of an adjacent can such that at least one of the section cut indication lines is at least partially defined by the longitudinal seam.

6. The method of claim 4, wherein prior to forming the cans each unrolled sheet is cut to an appropriate size and shape using a cutting device, and wherein the step of applying one or more cut indication marks comprises cutting one or more cut indication marks into the surface of the unrolled sheet.

7. The method of claim 6, wherein the cutting device comprises a CNC-operated plasma cutter.

8. The method of claim 1, further comprising the step of circumferentially offsetting the longitudinal seams of adjacent cans before connecting the plurality of cans.

9. The method of claim 1, wherein the length of each of the tack welds is from about 10 mm to about 30 mm.

10. The method of claim 1, wherein the tack welds are applied at intervals of from about 100 mm to about 300 mm.

11. The method of claim 1, wherein the plurality of cans are connected end to end by welding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a front view of a utility-scale wind turbine;

(3) FIG. 2 is a perspective view of a tower section comprising three longitudinal segments bolted together in the lateral direction;

(4) FIG. 3 is a detailed view of the encircled region shown in FIG. 2;

(5) FIG. 4 is a plan view of a steel plate used in the manufacture of a tower section;

(6) FIG. 5 is a perspective view of a manufacturing process using the steel plate of FIG. 4;

(7) FIG. 6 is a perspective view of a can formed using the process of FIG. 5;

(8) FIG. 7 is a side view of a tower section formed using a plurality of cans;

(9) FIG. 8 is a partial end view of a tower section during manufacture;

(10) FIG. 9 is a cross sectional view taken through line 9-9 in FIG. 8;

(11) FIG. 10 is a perspective view of a set of vertical flanges for a tower section;

(12) FIG. 11 is a partial cross sectional view showing the set of vertical flanges of FIG. 10 attached to a tower section;

(13) FIG. 12 is a perspective view of a first method of cutting a tower section into segments;

(14) FIG. 13 is a detailed view of the cutting apparatus used in the method of FIG. 12; and

(15) FIG. 14 is a perspective view of a second method of cutting a section into segments.

DETAILED DESCRIPTION

(16) FIG. 1 illustrates a modern utility-scale wind turbine 10 comprising a tower 11 and a wind turbine nacelle 12 positioned on top of the tower 11. The wind turbine rotor 13, comprising three wind turbine blades 14, is connected to the nacelle 12 through a low speed shaft (not shown) which extends out of the front of the nacelle 12. The different components of the wind turbine 10 are usually transported separately to the site and assembled there. To facilitate transportation, tower 11 is constructed from a number of tower sections 15 connected end-to-end, as shown. The sections 15 are provided with horizontally orientated flanges (see FIGS. 2 and 3) extending either inwardly or outwardly from the periphery of their open ends by which adjacent sections can be connected. In practice, opposing horizontal flanges of adjacent sections 15 are brought together at the site using lifting machinery, such as a tower crane, and the vertical sections 15 are then secured to one another using bolts passing through bolt holes in the horizontal flanges.

(17) As is known from Applicant's WO2004/083633 A1, which was filed on 19 March 2003 and is herein incorporated by reference, it is known to form the tower sections 15 from a number of individual segments which are connected at the site. One or more of the sections 15 may be divided into two or more segments which combine to form the complete section 15, as discussed below with reference to FIGS. 2 and 3.

(18) FIGS. 2 and 3 illustrate a section 15 of a wind turbine tower. Tower section 15 comprises a plurality of lengths of shell 16, commonly referred to as cans, that are formed from rolled steel plate and joined together along their abutting upper and lower edges by welding. The section 15 is provided with a horizontally orientated flange 17 extending inwardly from the periphery of each of its ends. Each horizontal flange 17 includes a number of bolt holes 18 by which adjacent sections can be connected by passing bolts through adjacent bolt holes 18.

(19) In this example, section 15 is formed from a plurality of cans 16 joined together along abutting upper and lower edges. However, in alternative examples, the tower section may be formed from a single can. The number of cans in a tower section is generally dependent on the required length of the section.

(20) The tower section 15, and each of the cans 16 from which it is formed, is divided into three longitudinal segments 19 that combine in the assembled tower to form the complete section 15. The three segments 19 are joined together along their longitudinal edges at three longitudinal joins 20. Each segment 19 includes at opposite edges vertical flanges 21 extending inwardly from its interior surface in the region of the longitudinal joins 20. The vertical flanges 21 include a large number of bolt holes by which adjacent segments 19 are secured to one another using bolts 22 passed through the bolt holes in adjacent vertical flanges 21. The vertical flanges 21 are welded to the segments 19 at a distance from their longitudinal edges so that an elongate spacer bar or bushing can be sandwiched between the vertical flanges 21 when they are tightened together.

(21) In this example, the segments 19 have substantially the same arc length and therefore subtend substantially the same angle with respect to the centre of the tower section 15. In alternative embodiments, it may be preferable to divide the tower section 15 into segments of unequal arc lengths.

(22) Throughout the specification, the use of the terms vertical and horizontal with regard to the sections and the flanges refers to their orientation once installed in the tower, and is not therefore intended to be used in a limiting way with regard to the method of production or assembly. As will be explained below, the cutting and reassembly processes are more conveniently carried out while the tower section is laid horizontally.

(23) In alternative examples each tower section may be formed of more or fewer than three segments. Further, the number of segments from which each section is formed may differ depending on where in the tower the section will be located. As the diameter of the tower is generally largest at the bottom, the tower sections for this part of the tower may be divided into more segments than sections from the top of the tower where the diameter is smaller.

(24) For example, a section towards the base of the tower may comprise four segments, while the sections or sections at the top may comprise only two segments. When assembling the tower, joining the segments together into the tower sections is preferably carried out before the step of assembling the tower sections into the tower. The segments may be arranged horizontally while they are joined to one another. The longitudinal joins of adjacent segments may be aligned or offset in the circumferential direction.

(25) The present invention provides methods for manufacturing a segmented section of a wind turbine tower of the type illustrated in FIGS. 2 and 3 in a quicker and more accurate manner. In particular, FIGS. 4 to 6 illustrate an improved method for manufacturing a can for forming a wind turbine tower section divided into two or more segments, FIG. 7 illustrates an improved method for forming a wind turbine tower section from a plurality of cans, FIGS. 8 and 9 illustrate an improved method for providing a horizontal flange to the end of a wind turbine tower section, FIGS. 10 and 11 illustrate an improved method for providing a set of vertical flanges to a wind turbine tower section, and FIGS. 12 to 14 illustrate two improved methods for cutting a wind turbine tower section into two or more segments.

(26) FIGS. 4 to 6 illustrate an improved method according an aspect of the invention for manufacturing a can for forming a wind turbine tower section divided into three segments. The can 16 is formed from a planar metal plate 24 which is cut into the desired size and shape using a conventional cutting process, for example, using a plasma cutter operated by a CNC (computer numerical control) process. Steel is by far the most commonly used material for metal towers, but other metals and alloys might be used, and the expression metal used herein is intended to encompass metal and alloys thereof. The steel plate 24 may be formed from a single sheet, or from two or more separately manufactured sheets which are welded together to form the plate (for example particularly for the latest very large turbines). As shown in FIG. 4, the cut steel plate 24 has slightly arc-shaped upper and lower edges 25 and straight side edges 26, so that it will form a truncated cone when the side edges 26 are brought together. The curvature of upper and lower edges 25 is exaggerated in FIG. 4 for illustrative purposes. In alternative embodiments, the plate 24 could have an alternative shape corresponding to the shape of can required. For example, where a cylindrical can is required, the plate could be rectangular.

(27) During the process of cutting the plate 24 into the required shape, two longitudinal cut indication lines 27 are marked onto the surface of the plate 24 by the plasma cutter as part of the CNC process to visually divide the area of the plate 24 into three equally sized shell segments 28. The cut indication lines 27 do not extend through the thickness of the plate 24 but indicate where the plate 24 should be cut in a subsequent cutting operation. The cut indication lines 27 are straight and extend between the arc-shaped upper and lower edges 25.

(28) Once the cut indication lines 27 have been marked on the surface of the plate 22, the plate 24 is placed in a conventional rolling mill where it is rolled into a truncated cone shaped can 16, having the cut indication lines 27 on the outside, by bringing the side edges 26 together to form a longitudinal join. In accordance with an aspect of the invention the side edges 26 are then welded together to form a welded longitudinal seam 29 to keep the structure of the can 16 stable during subsequent production steps, specifically by applying tack welds 30 at intervals along the length of the seam 29. In certain embodiments, the length of each tack weld 30 is from between 10 mm to 30 mm and preferably about 20 mm. In certain embodiments, the tack welds are applied at intervals of from 100 mm to 300 mm, preferably about 200 mm. In a preferred embodiment, a tack weld of about 20 mm in length is applied at about every 200 mm along the longitudinal seam. The can 16 can then be used to form a wind turbine tower section, either on its own or in combination with further cans 16, as discussed below in relation to FIG. 7. The resulting section can be divided into three shell segments by cutting along the cut indication lines 27 and along the longitudinal seams 29 of the cans 16 from which it is formed, as discussed below in relation to FIGS. 12 to 14. By applying the cut indication lines 27 as part of the CNC process, time can be saved and the accuracy of the subsequent cut can be improved. By tack welding the longitudinal seam 29, rather than applying a continuous weld, the section can be more quickly formed as the welding time is reduced. The use of tack welds can also reduce the amount of testing subsequently required on weld integrity (typically NDT testing). Furthermore, the formed section can subsequently be cut into the segments more quickly by cutting along the tack welded longitudinal seams 29 of the cans 16, given that less material is required to be cut through.

(29) The above process describes the use of tack welds on all longitudinal seams. However, it may be arranged that only certain longitudinal seams are tack-welded, whilst others are fully welded. Alternatively, tack welding may be used on only a proportion of any particular seam, with the remainder having a full weld.

(30) Referring to FIG. 7, an improved method according to the invention for forming a wind turbine tower section from a plurality of cans is provided. To form the tower section 15, a number of cans 16 are positioned end-to-end and rotated to line up their respective longitudinal tack-welded seams 29 with the cut indication lines 27 of adjacent lengths of shell 16. The aligned cut indication lines 27 and longitudinal seams 29 define three continuous, longitudinal section cut indication lines 31. The section cut indication lines 31 show where the section 15 should be cut in order to divide it into separate longitudinal segments. In this embodiment, each can 16 is rotated about its longitudinal axis by 120 degrees relative to the preceding can 16. Consequently, the section cut indication lines 31 are each defined by a combination of cut indication lines 27 and longitudinal seams 29 of the cans 16. Additionally, the longitudinal seam 29 of each can 16 is offset by 120 degrees from the longitudinal seam 29 of the adjacent cans 16. Once adjacent cans 16 are positioned correctly, they are welded together along their abutting upper and lower edges. This welding of adjacent cans may be carried out as each can is brought alongside the earlier, or alternatively, some or all cans may be aligned together before welding.

(31) By offsetting the longitudinal seam 29 of each can 16 by 120 degrees from the longitudinal seam 29 of the adjacent cans 16, the resulting structure is more stable. Horizontal and vertical flanges can then be provided to the section as discussed below in relation to FIGS. 8 to 11 and the section divided into segments by cutting along the section cut indication lines 31, as discussed below in relation to FIGS. 12 to 14.

(32) FIGS. 8 and 9 illustrate an improved method according to the invention for providing a horizontal flange to the end of a wind turbine tower section. Rather than providing a conventional unitary flange which is welded onto the section and subsequently cut when the longitudinal cuts are made, the horizontal flange 17 according to an aspect of the present invention the flange is formed from three separate flange segments 32, each having the shape of part of an annulus, which are brought together to form the horizontal flange 17. In this embodiment, the three flange segments 32 have arc lengths which are substantially equal and which correspond to the arc lengths of the three segments into which the section 15 will be divided. Alternatively, the arc lengths of the flange segments may be smaller or larger than the arc lengths of the segments into which the section will be divided and/or may be unequal.

(33) Prior to welding to the end of the section 15, the flange segments 32 are positioned together in the shape of the horizontal flange 17 and temporarily held together using a flange alignment plate 33 across each junction between adjacent flange segments 32. In this embodiment, the flange alignment plates 33 each include four bolt holes 34 for connecting the flange alignment plates 33 to the flange segments 32. The flange segments 32 are secured together by aligning the bolt holes 34 of the flange alignment plates 33 with the bolt holes 18 of two flange segments 32 and passing a bolt through each of the bolt holes 34 of the flange alignment plates 33 and the adjacent bolt holes 18 of the flange segments 32. When bolted together, the flange segments 32 are preferably separated by a small gap 35. The assembled horizontal flange 17 is then placed at an end of the tower section 15 so that each junction between adjacent flange segments 32 is aligned with a section cut indication line 31. The horizontal flange 17 is then welded to the end of the tower section 15, as shown in FIG. 9. The flange alignment plates 17 are then removed. The gap 35 allows that when the tower section 15 is cut longitudinally the cutting tool passes through the flange at the position of the gap thereby avoiding or reducing the amount of material to cut through.

(34) FIGS. 10 and 11 illustrate an improved method according to the invention for providing a vertical flange set 36 to a wind turbine tower section 15. The set of vertical flanges 36 comprises two parallel, vertical flanges 21 arranged to secure adjacent segments of a tower section together along their longitudinal edges. Prior to their attachment to the vertical section 15, the vertical flanges 21 are metallized with a suitable coating, with the exception of the region in which the flanges 21 will be welded to the section 15. The vertical flanges 21 are then preassembled as a set 36 by aligning the bolt holes 22 of the two vertical flanges 21 and passing bolts through the bolt holes 22 to secure the flanges together. The preassembly of the set of vertical flanges 21 does not necessarily require the assembly of the flanges 21 at every adjacent bolt hole 22. In this embodiment, the flanges 21 are bolted together at every second bolt hole 22. In other embodiments, the flanges may be bolted together at different intervals, which may or may not be uniform along the length of the flanges. At least some of the bolts are each passed through an elongate bushing 23 which is sandwiched between the vertical flanges 21 as they are tightened together so that the vertical flanges are offset by the length of the bushing 23, as shown in FIG. 11, to correctly space the flanges 21.

(35) The preassembled vertical flanges 21 are then placed inside the tower section 15 and aligned with an associated section cut indication line 31. When aligned, the vertical flanges 21 run parallel to the section cut indication line 31 with one of the vertical flanges 21 on either side of the section cut indication line 31. Each vertical flange 21 is then welded in position using a welding tractor (not shown), for example by welding on a single side of each vertical flange 21. The same process is repeated to provide additional sets of vertical flanges along the remaining section cut indication lines.

(36) FIGS. 12 and 13 illustrate an improved method according to the invention for cutting a wind turbine tower section into two or more segments using portable milling units 37. Each portable milling unit 37 includes a circular milling head 38 mounted on a carrier 39 running along two parallel rails 40. The portable milling unit 37 further includes a conveyor mechanism 41 for moving the carrier 39 along the rails 40 and number of electromagnets 42 on the underside of the rails 40 for attaching the rails to the vertical section 15. The carrier 39 includes a depth adjustment mechanism 43 for varying the cutting depth of the milling head 38.

(37) As shown in FIG. 12, tower section 15 is positioned in a support unit 44 such that its longitudinal axis is substantially horizontal. The support unit 44 has rollers 45 for rotating the section 15 about its longitudinal axis. In this embodiment, the rollers 45 are driven by a motor (not shown) operated by remote control to rotate the section 15. In alternative embodiments, the section 15 may be rotated on the rollers by other suitable means, for example manually. In this embodiment, the rolling mill used to shape the lengths of shell also functions as the support unit 44. In alternative embodiments, the support unit 44 may be a separate unit.

(38) To attach the portable milling units 37 in place, a first portable milling unit 37 is mounted on a frame 46 to the side of the section 15 and tilted at an angle so that the underside of each of the rails 40 is in close proximity to the outside wall of the section 15. In this embodiment, the frame 46 has frame adjustment levers 47 for manually adjusting the position and tilt of a portable milling unit on the frame 46. In alternative embodiments, one or both of the position and tilt of a portable milling unit on the frame may be fixed. Alternatively, one or both of the position or tilt of a portable milling unit 37 on the frame may be adjusted by means of hydraulics, pneumatics, or one or more motors. Further, in this embodiment, the frame 46 is static and has feet 48 on which it rests. In alternative embodiments, the frame may be provided with wheels such that it is moveable, either by manual pushing or pulling, or with driving means such as a motor.

(39) To align the first portable milling unit 37 with the section cut indication line 31, the section 15 is rotated on the rollers 45 about its longitudinal axis until the first section cut indication line 31 is aligned with the milling head 38 and the electromagnets 42 on the underside of the rails 40 are activated to clamp the first portable milling unit 37 in place against the outside wall of the vertical section 15. In this embodiment, the portable milling unit 37 is clamped to the vertical section 15 when the section cut indication line 31 is due to cut is in approximately the four o'clock position as viewed from one of the ends of the section 15 and as shown in FIG. 12. In alternative embodiments, the frame 46 may be arranged to clamp the portable milling unit 37 to the section 15 when the section cut indication line 31 is in a different position. Once the first portable milling unit 37 is clamped in place, the section 15 is rotated 120 degrees about its longitudinal axis and a second portable milling unit 37 is placed in the frame 46 so that its milling head 38 is aligned with the second section cut indication line 31. As with the first portable milling unit 37, the electromagnets 42 on the underside of the rails 40 of the second portable milling unit 37 are activated to clamp it in place against the outside wall of the vertical section 15. This process is repeated to attach a third portable milling unit 37 in line with the third section cut indication line 31.

(40) Once in place, the milling head 38 of each portable milling unit 37 is operated to cut into the section 15 and is conveyed along the section cut indication line 31 by moving the carrier 39 along the rails 40. The speed at which the carrier 39 moves along the rails 40 can be adjusted according to the thickness of the section being cut. Where the length of the section 15 being cut is longer that the rails 40, as is the case in FIG. 12, the portable milling units 37 must repositioned after a cutting operation to continue cutting along the remaining portions of the section cut indication lines 31 in a repeat of the process outlined above.

(41) Although the above process is described in relation to first second and third portable milling units 37 over first second and third section cut indication lines 31, fewer or more than three portable milling units 37 may be used to cut a particular section into segments. For example, a single portable milling unit may be used for all of the lines. Alternatively, to reduce the time taken to cut a particular section into segments, multiple portable milling units 37 may be used to simultaneously cut along a single section cut indication line 31.

(42) FIG. 14 illustrates an improved method according to the invention for cutting a wind turbine tower section into two or more segments using a fixed milling unit 49. As with the method described above in relation to FIGS. 12 and 13, tower section 15 is positioned in support unit 44 such that its longitudinal axis is horizontal. The support unit 44 is the same as described above in relation to FIGS. 12 and 13. The fixed milling unit 49 includes a circular milling head 50 mounted on a carrier 51 running along two parallel rails 52 fixed to the ground adjacent to the support unit 44 and running parallel to the section 15 being cut. The milling head 50 is mounted on the carrier 51 at an angle. In this embodiment, the milling head 50 is tilted on the carrier 51 at approximately 45 degrees from vertical. In alternative embodiments, the milling head may be tilted at a different angle, depending on the position of the milling head relative to the section and the required angle of cut. The fixed milling unit 49 further includes a conveyor mechanism (not shown) for moving the carrier 51 along the rails 52. The cutting depth, position, tilt angle, or any combination thereof of the milling head 50 may be adjustable to allow the milling unit 49 to be used with vertical sections of differing geometry. For example, the milling head 50 may be adjusted using manual levers, or by means of hydraulics, pneumatics, or one or more motors.

(43) To align the milling unit 49 with a section cut indication line 31, the section 15 is rotated on the rollers 45 about its longitudinal axis until the first section cut indication line 31 is aligned with the milling head 50, as shown in FIG. 13. The milling head 50 is then operated to cut into the section 15 and the carrier 51 is moved along the rails 52 so that the milling head 50 cuts along the length of the first section cut indication line 31. The carrier 51 is then withdrawn and returned to the start position while section 15 is rotated along its longitudinal axis to align the next section cut indication line 31 with the milling head 50. The milling head 50 is then operated to cut into the section 15 and the carrier 51 again moved along the rails 52 so that the milling head 50 cuts along the length of the section cut indication line 31. This process is repeated for the third section cut indication line 31 to divide the section 15 into three individual segments.

(44) In this embodiment, the milling head 50 is withdrawn from the cutting position while returning to the start position. In alternative embodiments, the milling head 50 may be arranged to cut in both directions of travel to reduce processing time. In such embodiments, the section may be rotated to align the milling head 50 with the next section cut indication line 31 before the milling head 50 is returned to the start position. The milling head 50 can then be operated to cut through the next section cut indication line 31 when returning to the start position after having cut thought the first section cut indication line 31.

(45) Alternatively, the milling head 50 may be rotated so that it can be used on two production lines, one on either side of the rails. This enables a reduction in down time as the milling unit can be used on a second side of the rails while other operations are carried out on the first side of the rails. Where the milling head is arranged to cut in both directions, this also enables the milling head 50 to alternative between tower sections on either side of the rails, for example to cut through a first tower section in one direction and to cut through a tower section on the opposite side of the rails in the opposite direction when returning to the start position.

(46) In both methods of cutting the tower section discussed above, the section 15 remains assembled after the cutting process has been completed, due to the fact that the vertical flanges 21 between each segment are bolted together prior to cutting. This improves the ease of handling of the section during cutting. The bolting of the segments together prior to cutting also ensures that the vertical flanges 21 will align correctly when the section 15 is reassembled, for example after transportation.

(47) Since the longitudinal seams 29 of the cans forming the section 15 are aligned with the section cut indication lines 31 and are tack welded, rather than welded fully, the section can be cut into segments more easily and quickly with less material being removed. Similarly, where separate flange segments 32 are provided to form the horizontal flange 17, the cutting process can be sped up by separating each of the flange segments 32 by a small gap 35 and aligning the gaps with the section cut indication lines 31.

(48) Due to the significant dimension of the tower section when it is supported horizontally typically at opposite ends, for example on a roller bed, the section will deform under its own weight, bowing down between the supports; for example, a tower section of some 30 m may exhibit a maximum vertical deflection at its midpoint between supports of 120 mm. As a result of this deflection, in order to effect cuts along the section which result in straight sided segments in the un-deformed tower section for example when it is vertically orientated, cutting lines which compensate for this deflection must be followed. The section cut indication lines 31 will deform with the tower section and still indicate the cutting paths to be followed. The deflection will vary with the position of the cut. A cut made at a 6 o'clock or 12 o'clock position (assuming a radial cut) will require linear (vertical) displacement of the cutting head axis in a direction parallel to the plane of the cutting blade or perpendicular to its axis to follow the curve of the deflection. A cut made at a 3 o'clock or 9 o'clock position would need a tilting of the cutting blade axis. A cut made at an intermediate position for example 4 o'clock or 8 o'clock will require a more complex movement whereby the blade axis is both tilted and displaced to follow the curve of the cut indication line 31.

(49) The adjustment needed to in order to effect the precise movement of the cutting head to follow the curved cut line depends on the type of cutting or milling unit, and the manner of mounting of the cutting or milling head. A fixed unit fixed relative to the ground will require the milling head to be driven along the curve to follow the curved cut line. A mobile unit directly mounted on the tower section itself may need more limited adjustment if the mounting of the milling head itself follows the deflection of the tower; for example, if a mobile unit is used secured onto the tower surface where the head is on rails which follow the tower and/or where the unit progressively moved along the length of the tower section as the cut is made this may be set to follow the curve of the cut indication line 31 with limited adjustment of depth of cut or cutting head axis.

(50) Once the tower section has been cut into segments it can be surface treated either in an assembled or disassembled condition, depending on the capabilities of the tower production facility. In one embodiment, the section is surface treated in an assembled condition. By cutting the section using a milling head, the cut surface can be surface treated, painted, or both, without requiring additional preparation steps, such as grinding or blasting, which may be required, for example if the section were cut using a plasma torch.

(51) Various modifications to the example embodiments described above are possible and will occur to those skilled in the art without departing from the scope of the invention which is defined by the following claims.

LIST

(52) 10. Wind turbine 11. Tower 12. Nacelle 13. Rotor 14. Blades 15. Vertical tower section 16. Can 17. Horizontal flange 18. Bolt hole in the horizontal flange 19. Longitudinal segment 20. Longitudinal join 21. Vertical flange 22. Bolt in the vertical flange 23. Bushing 24. Steel plate 25. Upper or lower edge 26. Side edge 27. Cut indication line 28. Shell segment 29. Longitudinal seam 30. Tack weld 31. Section cut indication line 32. Flange segment 33. Flange plate 34. Bolt hole in the flange plate 35. Gap 36. Vertical flange set 37. Portable milling unit 38. Milling head 39. Carrier 40. Rail 41. Conveyor mechanism 42. Electromagnet 43. Depth adjustment lever 44. Support unit 45. Roller 46. Frame 47. Frame adjustment lever 48. Feet 49. Fixed milling unit 50. Milling head 51. Carrier 52. Rail