GB2115075A

GB2115075A - Concrete structure e.g. a rotor blade

Info

Publication number: GB2115075A
Application number: GB08302209A
Authority: GB
Inventors: Arthur John Slemmons
Original assignee: SRI International Inc; Stanford Research Institute
Current assignee: SRI International Inc
Priority date: 1982-02-01
Filing date: 1983-01-27
Publication date: 1983-09-01
Also published as: JPS58135379A; SE8205615L; GB8302209D0; AU8809582A; DE3232361A1; NL8300164A; SE8205615D0; GB2115075B; DK387882A

Abstract

A concrete mix containing fibres is sprayed onto a surface 12 of a female mould 10 to form a thin layer 13. Preferably, a male mould 14 is then inserted over the layer of wet concrete and a thin layer 15 of concrete is sprayed onto the male mould 14 to form a beam or spar which is integral with the layer 13 applied to the female mould 10. A monolithic concrete element is thus produced. Another such element is similarly formed and the two elements are cemented together to form a tubular structure, e.g. a rotor blade for a wind turbine. Reinforcement rods may be incorporated, e.g. in the two beams or spars, and placed in tension to place the structure in compression. <IMAGE>

Description

SPECIFICATION Rotor blades, rotor blade components and methods of forming such components and other components and structures This invention relates to rotor blades, rotor blade components and methods of forming such components and other components and structures. More particularly, but not exclusively, the invention relates to the construction of blades for wind turbine rotors intended for use in wind turbines which in turn are intended for use to generate power from the wind.

Wind turbines are becoming of increasing importance as sources of power. To generate significant power the rotor blades must be large and must present a large surface to the wind. For example, large wind turbines can have a diameter of about 37m (about 120 feet) and the blades can have a length of about 18.5m (about 60 feet). The blades may have a width tapering from about 2.4m (about 8 feet) at the hub end of the blade to 0.6m (about 2 feet) the tip of the blade. The blades normally have a twist about a radial axis.

Such blades are preferably stiff and iight in weight and they must have adequate ultimate and fatigue strengths for the intended use. The sizes of such rotor blades are such that the cost of materials of construction is a significant factor. Additionally, the labour for the assembly of different subassemblies of different materials can also be significant.

In co-pending US Patent Application No.184208, filed on 5 September 1980 and entitled "Solar Collector Construction", and in another (continuation-in-part) co-pending US Patent Application No.

283 799, filed on 20 July 1981 and entitled "Radiation Reflector Construction", a technique is described for producing solar reflectors and radar antennas. This technique involves the spraying of fibre reinforced concrete, such as glass fibre reinforced concrete, onto a mould and the fabrication of reinforcing beams by the same technique. A monolithic structure results which has adequate strength and which is more economical than similar structures made of wood, metal, reinforced plastics, or a combination thereof. The inventor has now found a two-piece bonded beam construction using such spray technique can be used to advantage in the fabrication of blades for wind rotors and other structures.

According to a first aspect of the invention there is provided a rotor blade component having an aerodynamic surface and comprising a thin, monolithic layer of reinforced concrete composite forming a body of the component.

According to a second aspect of the invention there is provided an elongate rotor blade formed by a pair of blade components each having a first, aerodynamic surface and a second surface, said second surfaces being secured together and each component being constructed monolithically of reinforced concrete.

According to a third aspect of the invention there is provided a method of forming a component of an aerodynamic rotor blade, the method comprising applying a thin layer of a wet concrete mixture to a surface having a desired aerodynamic shape and configuration, said surface being a surface of an open mould cavity of a female mould, and removing the resulting concrete structure from the mould after the concrete has hardened.

According to a fourth aspect of the invention there is provided a method of forming a component of a tubular concrete structure, the method comprising the following steps: a) applying a thin layer of wet concrete mix to a surface having the desired configuration, said surface being a mould surface presented by an open mould cavity of a female mould, b) applying to the exposed surface of said layer, while it is still malleable, a male mould extending lengthwise of the female mould and projecting from said layer, c) applying to the exposed surface of the male mould a thin layer of wet concrete mix and causing such layer to unite with the first-mentioned layer thereby forming a monolithic concrete structure including the layer applied to the surface of the female mould and the layer applied to the surface of the male mould, and d) separating the resulting monolithic structure and the mould after the structure has hardened.

According to a fifth aspect of the invention there is provided a method of forming a tubular concrete structure, the method comprising the following steps: a) forming a first tubular element by applying a thin layer of wet concrete mix to a mould cavity of a female mould having a mould surface shaped to a desired configuration, such step resulting in a first tubular element having a first surface in contact with and shaped by the female mould and having also a second surface which is exposed in the mould, b) allowing the concrete layer to harden, c) separating the first tubular element from the mould, d) similarlyforming a second tubular element by steps a), b), and c), and e) bringing the first and second tubular elements together with their second surfaces in contact with one another and securing the elements together to form the tubular concrete structure.

According to a sixth aspect of the invention there is provided a method of forming a tubular concrete structure, the method comprising the following steps: a) forming a first tubular element by applying a thin layer of wet concrete to a mould cavity of a female mould having a mould surface shaped to a desired configuration, such step resulting in a first tubular element having a first surface in contact with and shaped by the female mould and having also a second surface which is exposed in the mould, b) applying to the surface of the concrete layer, before it hardens, a male mould extending longitu dinallyofthefemale mould, c) applying a thin concrete layer to the surface of the male mould and causing such layer to be integral with the layer of concrete applied to the female mould, d) allowing the concrete to harden, e) separating the first tubular element from the female mould, f) similarly forming a second tubular element by a repetition of steps a), b), c), d) and e), and g) bringing the first and second tubular elements together with their second surfaces in contact with one another and securing the elements together to form the tubular concrete structure.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a mould structure employed in the fabrication of a monolithic part or section of a rotor blade for a wind turbine, showing a fragment of the bare mould structure and a fragment of the completely moulded part or section of the rotor blade, a normal twist of the blade mould not being shown; Figures2to 6 are cross-sections taken through the mould of Figure 1, showing successive stages in the fabrication of the monolithic part or section of the rotor blade, the cross-section in these figures being along the line 2-2 of Figure 1; Figures 7, 8 and 9 are views in similar crosssection showing completion of the rotor blade section fabrication operation;; Figure 10 shows two halves or sections of the rotor blade brought together; Figure 11 is an end view (a hub end) of the rotor blade of Figure 10, showing an end plate in position; Figure 12 is an explosed view of the rotor blade, showing reinforcement rods, a hub plate and a tip plate; Figure 13 is a perspective view of a wind turbine rotor employing rotor blades as shown in the preceding figures; Figure 14 is a perspective view of a different type of wind turbine rotor employing vertical rotor blades having an elliptical cross-section; Figure 14A is a fragmentary perspective view of one of the rotor blades of the rotor of Figure 14; Figure 15 is a view similar to Figure 10, but showing a rotor blade (in cross-section) which is small and does not require a beam or spar; and Figure 16 is a view similar to that of Figure 10 but showing a different placement of the reinforcement rods.

Figures 2 to 6 of the drawings shows a female mould 10 in cross section, the mould 10 being made of the material 11 which may be, for example, wood, metal or plastics, and which is carved, moulded or machined to provide a cavity 12 of desired shape and dimensions. It will be seen by reference to Figure 1 that the mould cavity 12 is tapered so that there is a hub end at the left in Figure 1 and a tip at the right.

A suitable release agent, e.g., a hydrocarbon fluid is applied to the surface of the mould cavity 12.

Then, a graduated thickness layer 13 of a concrete or mortar mix composed of sand, hydraulic cement, for example Portland cement, and water in suitable proportions, is applied. Preferably, the mix also contains fibre reinforcements such as glass fibres, organic polymer fibres such as polypropylene, or other fibres commonly used to reinforce composite materials. The material is preferably applied by means of a spray gun of a well known type such as is used for spray coating walls of swimming pools.The gun ejects the mortar or concrete mixture at a rapid rate and is equipped with a spool of fibre roving and chopper means which chops the moving into small lengths as the mortar mix is sprayed, causing the cut pieces of fibre to be mixed intimately with the mortar or concrete. Alkaii resistant glass fibres can be used, the fibre being made from zirconia sands and available under the trade mark "Cem-FIL". This results in a monolithic layer 13 of fibre concrete composite.

Referring now to Figure 4, a male mould member 14 is placed on the surface of the layer 13 before it has hardened excessively. The shape of the male mould member 14 in cross-section may be that of a polygon with diverging sides, as shown. However, other shapes may be used. The male mould member 14 may be made of coated cardboard, wood, metal, plastics, foamed plastics or other suitable material. It is preferably a material having a surface which does not adhere to the hard and cured concrete, or it is coated with a release agent which performs the same function whereby it can be removed at an appropriate stage as described below. However, the male mould member 14 may remain in the structure.

The member 14 has a tapered shape, as shown in Figure 1, to provide shoulders such as those shown at 14a and 14b.

Referring to Figure 5, another layer 15 of concrete is applied, preferably by the same spray technique, over the mould member 14 so that it is continuous with the layer 13.

It is preferred to agitate the layer 13 before the mould member 14 is applied and to agitate the layer 15 to eliminate air bubbles. This may be done by a standard procedure in which a perforated form of appropriate shape, e.g. expanded metal, is placed over the concrete layer, and an agitator or vibrator is used to vibrate the perforated form. The function of the agitation in conjunction with the perforated form is to ensure that the small lengths of fibre are in intimate contact with the concrete and also to remove air bubbles so that no appreciable amount of voids is left in the fibre concrete layer.

Referring now to Figure 6, mould members 16 are inserted on opposite sides of the mould member 14.

The mould members 16 conform to the cavities on either side of the mould member 14. The mould members 16 may be of similar construction to the mould member 14. Then, a top cover and mould member 17, having an inner surface which is flat except for downwardly extending semicircular ribs 18, is laid across the mould 10 and the partially fabricated concrete structure in the manner shown in Figure 6. The mould members 16 and 17 may be integral with one another or they may, as shown, be separate pieces.

It will be understood that the mould members 14 and 16 will be tapered and that the ribs 18 may be fewer in number at different parts of the mould member 17 to accommodate the taper of the concrete layer 15. Also, it will be understood that each mould may be integral or it may be made in sections which are held together by suitable means such as clamps. It will further be understood that the steps shown in Figures 4,5 and 6 will be carried out while the concrete layers 13 and 5 are still soft enough to take the shapes impressed upon them by the moulds 16and 17.

After a suitable interval, when the concrete has set and hardened sufficiently, the moulded structure is removed by removing the top mould member 17 and removing the structure from the mould cavity 12. The mould member 14 may be removed by pulling it from the hub end and the mould member 16 and 17 may be removed by lifting them. As noted above, the mould member may be left in place, as may the mould members 16, in particular if they are of inexpensive, disposable construction such as coated cardboard or plastics foam.

There results a monolithic blade section structure as shown at 25 in Figure 7, which structure comprises an interior cavity 26, open side cavities 27 and 28, flat side surfaces 30 and 31 and a median portion 32 having longitudinal grooves 33 separated by surfaces 34. The surfaces 30,31 and 34 lie in the same twisted planar surface. The twist is desirable to maintain an optimum angle of attack of the blade section to an air stream for all radial points on a rotor blade formed from the blade section.

The layer 14 forms a body of the blade section structure 25 and the layer 15 forms an internal beam or spar extending lengthwise of the structure 25 and cast monolithicaily with the layer 14.

Referring now to Figure 8, the surfaces 30,31 and 34 are coated at 35 with a suitable adhesive such as acrylic copolymer/water emulsions or two part epoxy adhesives such as Aquatapoxy (trade mark).

Referring now to Figure 9, steel reinforcement rods or cables 36 are laid in the grooves 33.

Referring now to Figure 10, a second structure 25a is shown. this is similar to the structure 25, except that it may be a mirror image of the structure 25, and it will be constructed similarly. If an aerodynamic surface 40 of the structure 25 differs from an aerodynamic surface 40a of the structure 25a the mould cavities 12 will differ for the two structures.

The mating surfaces 30,31 and 34 with the adhesive layer 35 are brought together and pressure is applied as indicated by the arrows, e.g. in a press. A unitary rotary blade 42 results, the blade having cavities 26, 43and44.

The surfaces 40 and 40a may be treated with a water-proofing, sealing agent such as a water-based acrylic paint.

Referring now to Figure 12, which is an exploded view showing the lower and upper halves 25 and 25a of the rotor blade 42, the ends of the rods 36 are threaded and, as will be seen, washers 50 and nuts 51 are provided at shoulders 53 to anchor outer, shorter rods 36 within the blade. A hub plate 54 is formed with bolt holes 55 to receive the threaded ends of the rods 36. Washers 56 and nuts 57 are applied to the protruding threaded ends of the rods 36. A hub 58 has a mounting flange 59 with bolt holes 60 whereby the rotor blade 42 may be mounted on a shaft of wind rotor. A tip plate 61 is provided with similar bolt holes and is bolted to the tip of the blade by washers and nuts applied to the protruding ends of the rods 36. The rods are placed in tension whereby the concrete structure is placed in compression. As is well known, concrete is strong in compression.For example, carbon fibre reinforced neat cements (without sand) have demonstrated a fatigue strength of 69 MPa, equal to 10,000 Ibf/in2, (zero to compression) at over 108 cycles and are suitable for use in the present application.

Figure 13 shows a complete wind turbine rotor that comprises a tower 71 to the top of which is secured an electric generator 72 having a shaft 73 on which a rotor 74 is mounted, such rotor comprising three of the rotor blades 42. A lesser or greater number of blades may be used.

Figure 14 shows a different type of wind turbine rotor 80 that comprises a shaft 81 on a base 82. Rotor blades 83 are mounted on the shaft 81 by means of plates. One of the rotor blades 83 is shown in Figure 14A. As will be apparent, the blade 83 is constructed of two halves 85, which are similar. The two halves 85 are joined by means of an adhesive. Reinforcement rods 87 and end plates 88 are shown. The rotor blade halves 85 are constructed like the structures 25 and 25a and are joined in like manner.

Figure 15 shows a cross-section similar to that of Figure 10 of a rotor blade 90. The rotor blade 90 is made of two halves 91 and 91a joined at 92 by adhesive and with reinforcement rods 93 which are placed in tension. The blade 90 is small enough that it does not require a beam or spar.

Figure 16 shows a rotor blade 100 having parts similar to those of the blade 42 in Figure 10 and with parts similarly numbered, but the reinforcement rods 36 are placed differently.

It will be apparent that new and useful rotor blades and rotor blade components have been described.

The blades are made of economical material (fibre/ concrete composite) and they have sufficient bending and fatigue strength for the purpose when held in compression by the rods or tension members. The tension members can be of fibre resin composite construction or be cables. The rods will be placed in tension after the rotor blade is formed. Such tension will place the final concrete material in compression, which adds materially to the bending and fatigue strength ofthefibre/concrete composite material.

It will also be apparent that the constructional technique described above may be employed to fabricate tubular members other than rotor blades.

Claims

1. A rotor blade component having an aerodynamic surface and comprising a thin, monolithic layer of reinforced concrete composite forming a body of the component.

2. A rotor blade component according to claim 1, wherein the composite is reinforced with fibres.

3. A rotor blade component according to claim 2, wherein the fibres are short fibres.

4. A rotor blade component according to claim 1, claim 2 or claim 3, including an internal beam extending lengthwise of the component and cast of fibre/concrete composite monolithically with the concrete composite material forming the aerodynamic surface.

5. A rotor blade component according to any one of claims 1 to 4, wherein the component has a second surface opposite the aerodynamic surface, such second surface being capable of mating with a similar surface of a similar rotor blade component to form a complete rotor blade.

6. An elongate rotor blade formed by a pair of blade components each having a first, aerodynamic surface and a second surface, said second surfaces being secured together and each component being constructed monolithically of reinforced concrete.

7. A rotor blade according to claim 6, wherein the concrete is reinforced with fibres.

8. A rotor blade according to claim 7, wherein the fibres are short fibres.

9. A rotor blade according to claim 6, claim 7 or claim 8, wherein each component is formed with an interior beam extending lengthwise of the component and the two beams are face to face and cooperate to provide a single beam extending lengthwise of the rotor blade, the beam being of fibre reinforced concrete construction and the entire concrete body and beam of each component being monolithic.

10. A rotor blade according to claim 9, wherein the beam is provided with longitudinal reinforcement members.

11. A rotor blade according to claim 10, wherein the longitudinal reinforcement members are in the form of rods which are under tension.

12. A method of forming a component of an aerodynamic rotor blade, the method comprising applying a thin layer of a wet concrete mixture to a surface having a desired aerodynamic shape and configuration, said surface being a surface of an open mould cavity of a female mould, and removing the resulting concrete structure from the mould after the concrete has hardened.

13. A method according to claim 12, wherein the concrete is reinforced.

14. A method according to claim 13, wherein the concrete is reinforced with fibres.

15. A method according to claim 14, wherein the fibres are short fibres.

16. A method according to any one of claims 12 to 15, wherein the concrete is applyied by spraying.

17. A method of forming a component of a tubular concrete structure, the method comprising the following steps: a) applying a thin layer of wet concrete mix to a surface having the desired configuration, said surface being a mould surface presented by an open mould cavity of a female mould, b) applying to the exposed surface of said layer, while it is still malleable, a male mould extending lengthwise of the female mould and projecting from said layer, c) applying to the exposed surface of the male mould a thin layer of wet concrete mix and causing such layer to unite with the first-mentioned layer thereby forming a monolithic concrete structure including the layer applied to the surface of the female mould and the layer applied to the surface of the male mould, and d) separating the resulting monolithic structure and the mould after the structure has hardened.

18. A method according to claim 17, wherein the application of concrete is by spraying.

19. A method according to claim 17 or claim 18, wherein the concrete is reinforced with fibres.

20. A method according to claim 19, wherein the fibres are short fibres.

21. A method according to any one of claims 17 to 20, wherein the mould surface of the female mould is designed to form an aerodynamic surface of a rotor blade.

22. A method of forming a tubular concrete structure, the method comprising the following steps: a) forming a first tubular element by applying a thin layer of wet concrete mix to a mould cavity of a female mould having a mould surface shaped to a desired configuration, such step resulting in a first tubular element having a first surface in contact with and shaped bythefemale mould and having also a second surface which is exposed in the mould, b) allowing the concrete layer to harden, c) separating the first tubular element from the mould, d) similarly forming a second tubular element by steps a), b), and c), and e) bringing the first and second tubular elements together with their second surfaces in contact with one another and securing the elements together to form the tubular concrete structure.

23. A method according to claim 22, wherein the concrete layer is applied by spraying.

24. A method according to claim 22 or claim 23, wherein the concrete is reinforced with fibres.

25. A method according to claim 24, wherein the fibres are short fibres.

26. A method according to any one of claims 22 to 25, wherein the mould surface or surfaces of the female mould or moulds are designed to form aerodynamic surfaces of a rotor blade.

27. A method of forming a tubular concrete structure, the method comprising the following steps: a) forming a first tubular element by applying a thin layer of wet concrete to a mould cavity of a female mould having a mould surface shaped to a desired configuration, such step resulting in a first tubular element having a first surface in contact with and shaped by the female mould and having also a second surface which is exposed in the mould, b) applying to the surface of the concrete layer, before it hardens, a male mould extending longitudinally of the female mould, c) applying a thin concrete layer to the surface of the male mould and causing such layer to be integral with the layer of concrete applied to the female mould, d) allowing the concrete to harden, e) separating the first tubular element from the female mould, f) similarly forming a second tubular element by a repetition of steps a), b), c), d) and e), and g) bringing the first and second tubular elements together with their second surfaces in contact with one another and securing the elements together to form the tubular concrete structure.

28. A method according to claim 27, wherein the layers of concrete are applied by spraying.

29. A method according to claim 27 or claim 28, wherein the concrete is reinforced with fibres.

30. A method according to claim 29, wherein the fibres are short fibres.

31. A method according to any one of claims 27 to 30, wherein steps a) and b) result in a second surface which is planar and comprises first and second segments formed by edges of the firstmentioned layer of concrete and a third segment formed by an upper surface of the layer of concrete applied to the male mould, and wherein before the concrete has hardened longitudinal grooves are formed in the third segment, the method also including the step of placing elongate reinforcement members in the grooves of one of the rotor elements, fitting the other element over such members to enclose them by the two sets of grooves, securing the two elements together, adding end plates and tensioning the rods.

32. A method according to any one of claims 27 to 31,wherein the mould surface or surfaces of the female mould or moulds are designed to form an aerodynamic surface of a rotor blade.

33. A rotor blade component substantially as herein described with reference to Figures 1 to 9, or Figures 1 to 9 as modified by Figure 14A, Figure 15 or Figure 16, of the accompanying drawings.

34. An elongate rotor blade substantially as herein described with reference to Figures 1 to 12, or Figures 1 to 12 as modified by Figure 14A, Figure 15 or Figure 16, of the accompanying drawings.

35. Awind turbine substantially as herein described with reference to Figure 13 or Figure 14 of the accompanying drawings.

36. A method of forming a component of a tubular concrete structure, the method being substantially as herein described with reference to Figures 1 to 9, or Figures 1 to 9 as modified by Figure 14A, Figure 15 or Figure 16, of the accompanying drawings.

37. A method of forming a rotor blade component, the method being substantially as herein described with reference to Figures 1 to 9 or Figures 1 to 9 as modified by Figure 14A, Figure 15 or Figure 16, of the accompanying drawings.

38. A method of forming a tubular concrete structure, the method being substantially as herein described with reference to Figures 1 to 12, or Figures 1 to 12 as modified by Figure 14A, Figure 15 or Figure 16, of the accompanying drawings.

39. A method of forming a rotor blade, the method being substantially as herein described with reference to Figures 1 to 12, or Figures 1 to 12 as modified by Figure 14A, Figure 15 or Figure 16, ofthe accompanying drawings.