GB2254382A

GB2254382A - Wind turbine blades

Info

Publication number: GB2254382A
Application number: GB9202630A
Authority: GB
Inventors: Ir Henry Bert Lawson-Tancred
Original assignee: LAWSON TANCRED SIR HENRY BERT
Current assignee: LAWSON TANCRED SIR HENRY BERT
Priority date: 1991-02-07
Filing date: 1992-02-07
Publication date: 1992-10-07
Also published as: GB9102665D0; GB9202630D0

Abstract

A windmill blade is formed by moulding a foamable resin aerofoil 12 about a tubular steel spar 10 which may be rectangular in section (fig 1) or comprise a circular section having fins (fig 2). The spar may be provided with one or a plurality of spaced aerofoil cross section bulkheads (16). The foamable resin may be expoxy based with organosilicon compound foaming additives or it may be a syntatic epoxy resin with a low density filler. Details of alternative foams and handovers are given. <IMAGE>

Description

TURBINE BLADES This invention relates to a method of construction for turbine blades for either horizontal or vertical axis windmills used for power generation and which blades are usually shaped to a teardrop aerofoil profile.

A well-known construction method is to first manufacture a two-piece mould conforming to the desired shape of the aerofoil. The finished article is then made in two halves which are subsequently joined together. Into the mould is first placed a layer of epoxy resin followed by a layer of glass fibre matting which will bond with and strengthen the resin. After this operation, a further layer of resin is laid on top of the glass fibre matting followed by another layer of glass fibre matting, and so on until the resulting laminate of resin-glassfibre matting-resin has reached the required thickness. If the mould is made correctly, the surface finish of the resin after de-moulding will be of the required smoothness.

A refinement of the above technique allows for further strength reinforcement by the inclusion of strength producing components like steel bars in the matting, at points where reinforcement is required. The end-result being bonding of the steel with the resin and glassfibres to form a blade of great strength and capable of being made to conform to the shape of article required.

A disadvantage of the above manufacturing method is the time and skill needed to perform the functions described. A further and more serious disadvantage arises where the turbine control systems in the windmill generator uses a stall technique. This is likely to cause turbine buffeting unless blades can be provided with very small deflections which are unobtainable using laminated construction methods.

The present invention reduces the labour content as compared to hitherto conventional manufacturing techniques and thus reduces turbine blade costs as well as providing blades having the degree of stiffness required for compabilitlity with various control systems.

The invention comprises a blade for a windmill comprising an elongate spar adapted to be secured to the hub of a windmill supporting a foamed resin constituting at least part of an aerofoil cross-section.

The metal spar is preferably of steel and preferably is rectangular, e.g. square, in cross-section.

In order to reduce the weight it is also preferably hollow, i.e. tubular.

In order to provide the aerofoil blade, a foamed epoxy resin is moulded around the metal spar, leaving sufficient exposed to enable it to be fixed to the hub of a windmill. The metal spar preferably extends almost the whole length of the aerofoil blade so that the tip can be produced in the desired smooth shape with the foamed resin.

The foamed epoxy resin is preferably one that can be made using little or no heat, thereby allowing the blade to be made in situ if desired. It is also one which preferably does not produce high internal pressures because of the large size of the mould, which can be 15-30 metres long or more. The foam is preferably a closed cell foam with a cell size not greater than 3 mm, preferably 0.1 to 0.5 mm.

The foamed resin may be one foamed by the addition of an organosilicon compound containing at least one hydrogen atom directly bonded to silicon to curable epoxy resin compositions which contain aliphatic primary or secondary amine groups or which contain both Lewis bases and hydroxyl groups (or generate hydroxyl groups during the curing reaction). The mixture is allowed to expand into a foam and then to cure in the normal way.

Suitable organosilicon compounds containing one or more Si-H linkages are, for example, silanes such as those of formula RlR2R3Si-H where R1,R2 and R3 may be the same or different and represent alkyl, alkoxy or aryl groups; cyclic siloxanes such as tetraalkylcyclotetrasiloxanes; and linear di- or polysiloxanes such as tetra-alkyldisiloxanes and polysiloxanes containing silicon-bonded organic radicals in addition to the silicon-bonded hydrogen atoms, for example methyl phenyl polysiloxanes, methyl vinyl polysiloxanes and methyl hydrogen polysiloxanes having terminal trimethylsiloxy groups.

The amount of organosilicon compound used in the process of the invention will vary depending on the proprtion of hydroxyl groups contained in the curable epoxy resin composition or formed during the curing reaction. Clearly, not more than one equivalent of -Si-H groups will be used per equivalent of hydroxyl groups. Ordinarily, not more than about 10% by weight of organosilicon compound is used based on the weight of epoxy resin, the actual amount being determined by the degree of foaming required.

The term "epoxy resin" denotes a substance containing on average more than one 1,2-epoxy group per molecule. Such substances include, for example: polyglycidyl ethers of polyalcohols such as butane-1,4,- diol or glycerol, of N-arylethanolamines such as N-phenyldiethanolamine, of polyhydric phenols such as resorcinol, 2, 2-bis (4-hydroxyphenyl ) propane (bisphenol A) and of condensation products of aldehydes with phenols (novolaks); polyglycidyl esters of polycarboxylic acids such as phthalic acid, adipic acid or maleic acid; aminopolyepoxides such as are, for example, obtained by the dehydrohalogenation of the reaction products of epihalohydrins and primary or di-secondary amines such as m-xylylenediamine, piperazine, analine, 4,4'-diaminodiphenylmethane or 4,4, -methylaminophenylmethane; and products obtained by the complete or incomplete epoxidation of ethylenically unsaturated cyclic or acyclic polyolefines. Preferred epoxy resins are polyglycidyl ethers of dihydric phenols, those derived from bisphenol A or bisphenol F being particularly preferred.

The preferred hardener for the epoxy resin is based on aliphatic amines such as ethylenediamine, triethylenetetramine, trimethylhexamethylenediamine, iso-phoronediamine, N-diethylaminopropylamine, piperidine, N-(2-aminoethyl)piperazine, N-(3-amino propyl)cyclohexylamine, m-xylylenediamine, polyoxypropylenepolyamines or 2,4,6-tris(dimethylaminomethyl)phenol.

These amines may be present in their unmodified form or may be modified by reaction with sub-stoichiometric levels of co-reactants such as carboxylic acids, epoxy compounds or acrylic-functional compounds. Such hardeners usually cure the epoxy resin without the need for heating, which is an important advantage in the present invention.

The above described aliphatic amines and their modificants may advantageously be blended with aromatic polyamines such as 4,4'-diaminodiphenylmethane or m-phenylenediamine.

Alternatively, the hardener may consist of a dicarboxylic acid anhydride such as methyltetrahydrophthalic anhydride in conjunction with a Lewis base such as benzyldimethylamine or triphenylphosphine. Such hardeners, however, suffer from the disadvantage of requiring a high temperature cure.

Instead of using a silicon foaming agent as above, a syntactic epoxy foam may be used. In this case the foam is provided by the use of hollow microsphere fillers in the resin. Suitable microsphere fillers include glass, pulverised fly ash, phenolic microballoons and other polymeric microballoons.

The foams may also contain plasticisers such as dibutyl phthalate, foam-stabilising agents such as polyvinyl formals, fillers, colouring agents, antioxidants, UV absorbers and, as reactive diluents, monoepoxide compounds such as phenyl glycidyl ether or butyl glycidyl ether.

The foams may further contain mineral fillers such as calcium carbonate or aluminium oxide trihydrate which serve to moderate the temperature rise resulting from the evolution of heat during the exothermic curing reaction.

In order to improve the resistance of the blades to W radiation and erosion, the blade is preferably given a tough, W-resistant coating. This may be produced by applying a gel coat resin to the mould used to make the blade and then, when the gel coat has partially hardened, carrying out the foaming in order to bind the gel coat to the foam. Preferably the coating is applied by conventional brush, spray or roller techniques to the blade after it has been demoulded.

The coating is preferably a polyurethane, for instance a polyester-polyurethane.

The invention is described by reference to the accompanying -drawings in which Figure 1 shows a section through a blade of the invention; and Figure 2 shows a metal spar.

Figure 1 shows metal spar 10 surrounded by epoxy foam 12 in the shape of an aerofoil. The blade is symmetrical along its length, being twistless, but it generally tapers from the end near the hub of the windmill to the tip.

Metal spar 10 may be a square section steel tube as shown in Figure 1 or it may have tapering fins 14 extending along its length as shown in Figure 2. The fins 14 may be welded or bolted on to steel tube 10.

Also shown in Figure 2 is bulkhead 16. Only one bulkhead is shown although, depending on the length of steel tube 10, more than one may be present. Both the bulkhead(s) and fins may be of steel. The bulkhead 16 helps to keep the foam resin firmly in place around tube 10, although in many cases the adhesion of the resin to the tube is sufficient without needing a bulkhead.

In order to make a blade, tube 10 is positioned inside a mould which is preferably in two parts which are joined together by a hinge. Tube 10 is held in place by suitable fixtures in the mould. The mould is then closed and the curable resin composition is pumped in via suitable inlets. The resin is then allowed to foam and cure, or if a syntactic foam is used, it is simply allowed to cure.

Once the resin is cured, the mould is opened, the blade is removed, and smoothed off as required e It may then be coated with a UV absorbent coat if such a coat has not already been provided in the mould.

The resulting blade is able to withstand all the aerodynamic stresses exerted during use without any failure of the spar, the epoxy foam or the adhesion between the spar and the epoxy foam.

Claims

1. A windmill comprising an elongate spar adapted to be secured to the hub of a windmill supporting a foamed resin constituting at least part of an aerofoil cross-section.

2. A blade according to claim 1, in which the spar is embedded in the foamed resin.

3. A blade according to claim 1 or claim 2, in which the resin comprises an epoxy resin.

4. A blade according to any one of claims 1 to 3, in which the spar is of metal.

5. A blade according to claim 4, in which the spar is of steel.

6. A blade according to any one of claims 1 to 5, in which the spar is of non-circular cross-section.

7. A blade according to claim 6, in which the spar is of rectangular cross-section.

8. A blade according to any one of claims 1 to 7, in which the spar is hollow.

9. A blade according to any one of claims 1 to 8, of which the spar has at least one bulkhead.

10. A blade according to any one of claims 1 to 9, of which the spar has at least one lengthwise-extending fin.

11. A blade according to any one of claims 1 to 10, in which the foamed resin is formed by the addition of an organosilicon compound, containing at least one hydrogen atom bonded directly to silicon, to a curable epoxy resin composition which contains aphatic primary or secondary amine groups, or which contains both a Lewis base and hydroxyl groups which are originally present or are generated during the curing reaction, allowing the mixture to expand into a foam and then curing it.

12. A blade according to any one of claims 1 to 10, in which the resin comprises a syntactic foamed resin containing hollow microsphere filler.

13. A blade according to any one of claims 1 to 12, in which the foam is a closed cells foam with a cell size of 0.1 to 0.5 mm.

14. A blade according to any one of claims 1 to 13, of which the foamed resin is coated with a UV-resistant coating.

15. A blade according to claim 14, in which the coating comprises polyurethane.

16. A method for making a blade for a windmill comprising attaching to an elongate spar a foamed resin constituting at least part of an aerofoil cross-section.

17. A method according to claim 16, in which the spar is positioned in a mould and the resin shaped in the mould.

18. A method according to claim 17, in which the resin comprises a curable epoxy resin.

19. A method according to claim 17 or claim 18, in which the resin is foamed in the mould.

20. A method according to claim 19, in which the resin is formed by the addition of an organosilicon compound, containing at least one hydrogen atom directly linked to silicon, to a curable epoxy resin composition which comprises aliphatic primary or secondary amine groups or which contains a Lewis base and hydroxyl groups which are originally present or which are generated during the curing reaction.

21. A method according to claim 18, in which the resin is a syntactic foamed epoxy resin composition containing hollow microsphere fillers.

22. A method according to any one of claims 16 to 21, in which the mould defines at least part of the external shape of the blade.

23. A method according to claim 22, in which the mould is of aerofoil cross-section and the spar is embedded in the resin.

24. A method according to claim 22 or claim 23, in which the interior of the mould is coated with a UV resistant coat before the resin is introduced into the mould such that the coat is attached to the resin.

25. A method according to any one of claims 16 to 24, in which a W resistant coat is applied to at least exposed resin parts of the blade after demoulding.

26. A method according to claim 24 or claim 25, in which the coat is a polyurethane gel coat.

27. A blade substantially as hereinbefore described with reference and as illustrated in the accompanying drawings.