U.S. patent application number 12/935236 was filed with the patent office on 2011-04-28 for wind turbine blade.
Invention is credited to Paul Rudling.
Application Number | 20110097211 12/935236 |
Document ID | / |
Family ID | 39386953 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110097211 |
Kind Code |
A1 |
Rudling; Paul |
April 28, 2011 |
WIND TURBINE BLADE
Abstract
A wind turbine blade is disclosed, at least 50% of the surface
of which is covered with a self-adhesive, thermoplastic film. A
method of manufacturing and repairing such a wind turbine blade is
also disclosed. A two layer thermoplastic film suitable for
covering the surface of a wind turbine blade is also disclosed. The
film comprises a surface layer and a lower layer. The surface layer
comprises 50% to 85% of polyvinylidene fluoride (PVDF), wherein up
to 30% of the polyvinylidene fluoride may be replaced by
hexafluoropropylene (HFP); and 10% to 45% polymethyl methacrylate
(PMMA). The lower layer comprises 10% to 45% of a polyvinylidene
fluoride (PVDF) polymer, wherein up to 30% of the polyvinylidene
fluoride may be replaced by hexafluoropropylene (HFP); and 50% to
85% PMMA. Optionally the surface and/or lower layer comprises up to
8% UV stabilisers/absorbers; up to 10% matting agent; and up to 40%
of an inorganic pigment. The film has an initial gloss of less than
30% when measured with a reflectometer at a angle of 60
degrees.
Inventors: |
Rudling; Paul; (Calbourne,
GB) |
Family ID: |
39386953 |
Appl. No.: |
12/935236 |
Filed: |
March 30, 2009 |
PCT Filed: |
March 30, 2009 |
PCT NO: |
PCT/GB2009/000851 |
371 Date: |
December 9, 2010 |
Current U.S.
Class: |
416/229R |
Current CPC
Class: |
B32B 27/40 20130101;
B32B 2307/514 20130101; B32B 2307/58 20130101; B32B 2307/41
20130101; B32B 2307/72 20130101; Y02P 70/50 20151101; B32B 2603/00
20130101; Y02P 70/523 20151101; B32B 27/308 20130101; B32B 2307/726
20130101; Y02E 10/721 20130101; B32B 27/08 20130101; B32B 27/304
20130101; B32B 2307/536 20130101; B32B 27/20 20130101; B32B 27/30
20130101; Y02E 10/72 20130101; B32B 2264/102 20130101; B32B 2270/00
20130101; B32B 27/322 20130101; F03D 1/065 20130101; B32B 2307/712
20130101; B32B 2307/558 20130101; Y10T 428/24942 20150115; B32B
27/18 20130101; Y10T 29/49336 20150115; B32B 2307/724 20130101 |
Class at
Publication: |
416/229.R |
International
Class: |
F04D 29/18 20060101
F04D029/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2008 |
GB |
0805713.5 |
Claims
1.-38. (canceled)
39. A wind turbine blade at least 50% of the surface of which is
covered with a self-adhesive, thermoplastic film, wherein the film
is applied in a number of strips.
40. The wind turbine blade according to claim 39, wherein the film
is applied in a number of strips arranged to reduce the complexity
of curvature of each strip.
41. The wind turbine blade according to claim 39, wherein the edge
of one strip overlaps with the edge of an adjacent strip.
42. The wind turbine blade according to claim 39, wherein edges of
adjacent strip do not overlap and the join is covered with a
further strip of thermoplastic film.
43. The wind turbine blade according to claim 39, wherein edges of
adjacent strips do not overlap and the join is painted with a PVDF
paint.
44. The wind turbine blade according to claim 39, wherein the
thermoplastic film comprises at least one of an aliphatic
polyurethane, a vinyl, an acrylic or a fluorinated
thermoplastic.
45. The wind turbine blade according to claim 39, wherein
substantially all of the blade is covered with the film
covering.
46. The wind turbine blade according to claim 39, wherein the
thermoplastic film comprises a two layer structure having an outer
layer with enhanced weather resistant properties compared to the
inner layer.
47. The wind turbine blade according to claim 46, wherein the inner
layer has enhanced adhesion properties compared to the outer
layer.
48. The wind turbine blade according to claim 46, wherein the inner
and outer layers include polyvinylidene fluoride (PVDF) and
polymethyl methacrylate (PMMA) with the outer layer having more
PVDF than PMMA and the inner layer having more PMMA than PVDF.
49. The wind turbine blade according to claims 46, wherein the
layers are co-extruded.
50. The wind turbine blade according to claim 39, wherein the
thermoplastic film has an initial gloss of less than 30% when
measured with a reflectometer at an angle of 60.degree. with
respect to the film surface.
51. The wind turbine blade according to claim 39, wherein the
thermoplastic film is less than 300.about.m thick, and preferably
from 50 to 150.about.m thick.
52. The wind turbine blade according to claim 39, wherein the
thermoplastic film is porous such that it is air permeable and
water impermeable.
53. The wind turbine blade according to claim 39, wherein the
adhesive is an acrylic or silicon based adhesive.
54. A method of manufacturing a wind turbine blade comprising
moulding the blade body and adhering a thermoplastic film to at
least 50% of the surface of the body, wherein the film is applied
in a number of strips.
55. A method of repairing a wind turbine blade comprising adhering
a thermoplastic film to at least 50% of the surface of a worn blade
body, wherein the film is applied in a number of strips running
between the leading and trailing edges of the blade.
56. The method of manufacturing or repair according to claim 54,
wherein the film is applied in a number of strips arranged to
reduce the complexity of curvature of each strip.
57. The method of manufacturing or repair according to claim 54,
wherein the edge of one strip overlaps with the edge of an adjacent
strip.
58. The method of manufacturing or repair according to claim 54,
wherein edges of adjacent strip do not overlap and the join is
covered with a further strip of thermoplastic film.
59. The method of manufacturing or repair according to claim 54,
wherein edges of adjacent strips do not overlap and the join is
painted with a PVDF paint.
60. The method of manufacturing or repair according to claim 54,
wherein the thermoplastic film is heated shortly before and/or
during its application to the blade body.
61. A wind turbine blade manufactured according to the method of
claim 54.
Description
[0001] The present invention relates to a wind turbine blade, and
more specifically, to an improved surface coating for a wind
turbine blade.
[0002] The coating on the surface of a wind turbine blade is
exposed to a harsh environment of abrasion, UV, humidity,
corrosion, cyclical stresses, and extreme temperature fluctuation
and requires a high performance material. Coatings need to retain
performance for up to 20 years, putting them in a higher
performance and different specification bracket than most
civil/automotive applications and additionally they need to be of a
cost significantly lower than products typically found in aerospace
applications.
[0003] Wind turbine blades are normally formed from a glass-fiber
reinforced polymer composite. They may be formed from fiberglass
composites, polyester, vinylester or carbon and wood with
fiberglass in an epoxy matrix. Epoxy-based composites are of use
because they deliver a combination of environmental, production,
and cost advantages over other resin systems. Carbon
fiber-reinforced load-bearing spars can be introduced into the
blade as a cost-effective means for reducing weight and increasing
stiffness.
[0004] Wind turbine blades have complex surface topographies to
optimize the aerodynamic efficiency of the rotor, to keep the
generator within its speed and torque limits, to keep the rotor and
tower within their strength limits and to reduce noise and drag.
Accordingly, surface coatings that have conventionally been applied
to wind turbine blades have focused on painted compositions and
in-mold coatings. Such coatings can be relatively quickly
applied.
[0005] Wind turbine blades are typically coated using either a
gelcoat, or are painted. Gelcoat is applied directly into the mould
during manufacture of the blade and is formulated from a chemical
backbone compatible with the substrate laminate, which is usually a
polyester, vinylester or an epoxy resin. Painted finishes are
normally achieved using variations of cross-linked polyurethane
paint, usually supplied as two components (with a polyol and, or
polyester resin base and an aliphatic isocyanate curing agent).
These are mixed prior to application and the chemical reaction
produces the cross linked polyurethane polymer. Some blades use a
combination of both gelcoat applied into the mould and paint
applied to the blade after demoulding. This gives additional
service life to the surface.
[0006] Some wind turbine blades have their leading edges taped with
impact resistant tape, which is often applied to older blades to
repair them.
[0007] The shortcomings of current technology are as follows:
[0008] With so-called `in mould` technology such as gelcoat it is
very difficult, if not impossible, to achieve a perfect surface
straight out of the mould. Practically, any small variances in
mixing quality, viscosity, humidity, substrate condition and
operator skill can lead to a large number of cosmetic defects out
of the mould but also a number of adhesion problems when in
service. In reality a large amount of time and labour (around a
third of the labour required to produce the blade) is spent
repairing defects in the surface of these blades prior to use and
filling manufacturing joins from the mould itself resulting in a
cost increase in the blade. These problems, and the probability of
a defect in the surface only increases with increasing blade
size.
[0009] Painting as a process, in particular spraying, is a very
wasteful process and requires a lot of operator skill in order to
ensure a consistent coating. Furthermore, painted surfaces tend to
lack cohesive strength and durability. Polyurethane coating systems
used for wind turbine blades are solvent based and when these are
sprayed a large amount of hazardous organic solvent (typically 50%
by weight), is released into the atmosphere. Spraying of
polyurethanes is also a potentially hazardous operation both for
workers and the environment due to the isocyanate component in the
curing agent which is a sensitising agent and great care has to be
taken to prevent fumes of isocyante being inhaled by the operators
involved in the spraying operation.
[0010] The inventors have found that paint type coatings for
turbine blades tend to be insufficiently durable to protect wind
turbine blades. Furthermore, paint treatments do little to smooth
the surface of any irregularities resulting from in-mold defects.
Therefore, paint treatments require extensive preparation of the
blade surface before a painted surface coating can be applied. If
the paint is applied too thinly then imperfections on the surface
of the blade can lead to minor defects in the paint which can
dramatically reduce the expected lifetime of the blade.
[0011] In addition it is found that, although aliphatic
polyurethanes are the highest performing paints available for
coating wind turbines, it is often necessary to repair such a
coating after little more than five years in service (depending on
operating conditions). This is extremely costly and adds additional
cost to the service life of the blade as the necessary working life
of a wind turbine blade is 20 years.
[0012] According to the present invention, there is provided a wind
turbine blade at least 50% of the surface of which is covered with
a self-adhesive thermoplastic film.
[0013] By applying a self-adhesive thermoplastic film to the blade,
the need for a gelcoat or paint is eliminated. It is estimated that
the thermoplastic film will take a similar time to apply as the
gelcoat and/or paint. However, it does not require any further
treatment once it has been applied, thereby reducing significantly
the work involved in finishing the blade. In order to save costs it
is preferred that no further coating (paint or otherwise) is
applied to the thermoplastic film. Furthermore, less preparatory
work needs to be performed before the film is applied, such as
smoothing the surface of the blade. The film serves a dual purpose
of protecting the blade and can also be used to cover over any
minor imperfections, such as pores, in the surface of the blade.
Also, the thickness of the film is precisely controlled in advance
of its application to the blade ensuring that a surface with a
uniform thickness is produced. Film manufacturing techniques allow
the composition of the film to be precisely controlled and even to
vary across the thickness of the film. The possibility of having
variable or poor weathering performance over the lifetime of the
blade due to variability in coating production/application
processes is therefore almost completely eliminated.
[0014] Some advantages would be achieved by the film being applied
to a significant proportion of the wind turbine blade with
conventional techniques being used to coat the remainder of the
blade. However, preferably, substantially all of the blade is
covered with the film. The thermoplastic film may be alphatic
polyurethane, vinyl, acrylic or fluorinated thermoplastics such as,
polyvinylidene fluoride (PVDF); tetrafluoroethylene (TFE);
Hexafluoropropylene (HFP); PVDF+HFP copolymer; THV (PVDF, HFP,
TFE); polyvinyl fluoride (PVF); FEP (TFE, HFP); perfluoroalkoxy or
PFA (TFE, PFVE); chlorotrifluoroethylene (CTFE); CTFE+VF2
(difluoroethylene)/HFP, or a combination of two or more of any of
these. Fluorinated polymers are particularly preferred as they are
water and dirt repellent.
[0015] The thermoplastic film is preferably a self-supporting
thermoplastic laminar. That is, the film is preformed as a sheet
which has structural integrity on its own before it is applied to
the blade. The integrity of the film eases the application of the
film to the blade and reduces the likelihood of the film being
damaged during the film application process.
[0016] It is preferred that the uppermost surface of the film
exposed to the atmosphere once applied to the blade is hard wearing
and resilient. Accordingly, at least the surface of the film is
preferably formed of a high density thermoplastic. The
thermoplastic below the surface can be of a lower density to save
cost.
[0017] The thermoplastic film may be a single layer, but it is
preferably formed of a two layer structure having an outer (or
surface) layer with enhanced UV, erosion, dirt shedding and weather
resistant (latterly referred to throughout as `weather resistant`)
properties compared to the inner layer. This allows weather
resistant material which may be relatively expensive, to be
concentrated towards the outer surface of the film where it is most
effective. With the two layer structure, the inner layer preferably
has enhanced adhesion properties compared to the outer layer. When
a fluorinated polymer is used in the thermoplastic film this can
reduce the adhesive properties of the film and so it is preferred
that any fluorinated polymer is concentrated more in the surface
layer than the inner layer. This facilitates the adhesion of the
film to the blade.
[0018] It is preferred that the outer layer is formed of a high
density thermoplastic. This helps to provide the finished blade
with point impact resistance and a high weathering resistance. It
has also been observed that providing a coating with a degree of
flexible strength helps to provide a smooth coating across the
surface of the blade. By "high density" it is understood that the
thermoplastic has a density of at least 1.1 g/cc, as measured
according to ISO 1183. It is preferred that the surface density is
from 1.3 to 3 g/cc and more preferably from 1.7 to 1.9 g/cc. It has
been found that the high density thermoplastic allows for the
provision of highly durable, relatively thin films without adding
too much weight to the blade. Above 3 g/cc it has been found that
the film becomes more difficult to handle and apply. High density
polymers are generally not suitable for application by painting
methods.
[0019] It is also preferred that the thermoplastic film is formed
by extrusion. When the film comprises a two layer structure the
layers may be formed by coextrusion. For ease of manufacture, the
film can also be extruded with an adhesive on one surface.
Extrusion is particularly preferred as it allows for the provision
of an axially oriented film. The degree of axial orientation that
can be provided by extrusion of the film helps to provide the
thermoplastic film with increased durability.
[0020] It is preferred that the thermoplastic film, in particular
the outer layer (if a two layer structure is used), exhibits a melt
flow rate (ASTM D1238, 230.degree. C., 2.16 kg) of 20 g/10 mins or
less. Preferably the melt flow rate is between 1 g/10 min and 15
g/10 min and most preferably about 8 g/10 min. High melt flow rate
thermoplastics, such as waxes, are not suitable for use in the
present invention. Such thermoplastics do not provide a wear
surface that is sufficiently durable for use on a wind turbine
blade.
[0021] The thermoplastic film preferably has a Shore D hardness (2
mm thick; ASTM D2240) of at least 20. More preferably the hardness
is from 40 to 100 and most preferably about 60. The hardness of the
surface layer helps to protect the surface of the blade against any
impacts or point damages, for example, during transport after
manufacture.
[0022] One way of achieving the enhanced weather resistant
properties of the outer layer and enhanced adhesion properties of
the inner layer is for the inner and outer layers to be made of
polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA)
with the outer layer having more PVDF than PMMA and the inner layer
having more PMMA than PVDF.
[0023] The two layers may be manufactured separately and fused or
adhered together. However, preferably, the two layers are
co-extruded. This is particularly suitable for a PVDF and PMMA
composition as they are very suitable for co-extrusion.
[0024] The thermoplastic film preferably contains pigmentation,
and/or fillers to give the film the desired colour. As most wind
turbine blades are required to be white this pigmentation is
normally achieved by the addition of suitable surface coated grade
of rutile titanium dioxide. The opacity of the film can be measured
by observing its radiation transmission properties. In particular,
the extent to which visible light is transmitted can be measured.
0% opacity indicates that the film is completely clear and that all
the light is transmitted. 100% opacity indicates that the film is
completely opaque and that no light is transmitted.
[0025] The film preferably also contains amounts of a UV absorber
present in levels from 0.1% to 5% based on the film weight. The
purpose of the UV absorber is to prevent the passage of damaging UV
radiation through the film and into the adhesive layer. The UV
absorber may be used singly or may be a combination of two
different types of UV absorber to obtain optimal results. Examples
of such a combination would be a benzophenone and a hindered amine
light stabiliser that can act together in a synergistic manner.
Another suitable UV absorber for the thermoplastic film is nano
titanium dioxide containing surface modified inorganic oxide
particles. This can be extremely effective in such a film and has
the additional benefit that it is complete stable in the polymer
and cannot suffer from "migration" effects. Such migration effects
can be volatilisation during film manufacture causing plate-out
effects on the extrusion die, or migration effects in service that
can lead to reduced weathering performance or even dissbondment of
the film. Such a nano titanium dioxide would be present in the film
at between 0.1% and 8% of the film weight (excluding the
adhesive).
[0026] All of the percentages recited for the composition of the
film material are by weight percentages for the film excluding the
adhesive layer.
[0027] For a wind turbine blade, it is desirable that the blades do
not have a high gloss and/or high reflectance as this causes an
unacceptable nuisance in the finished product when the blades are
in service. Therefore, preferably, this effect is minimised by
surface treating the film, for example by applying a cold roller to
the film as it is extruded and/or by a matting agent incorporated
into the film. A suitable matting agent would be a light stable
acrylic resin of controlled particle size.
[0028] The thickness of the thermoplastic film (excluding the
adhesive) is preferably less than 300 .mu.m, and preferably between
50 and 150 microns thick. It has been found that films of these
thicknesses are sufficiently durable.
[0029] When applying the film to the blade, care must be taken to
avoid air bubbles becoming trapped between the film and the blade.
The film may therefore be porous such that it is air permeable and
water impermeable as this helps prevent the formation of air
bubbles during the manufacturing process.
[0030] The adhesive is preferably a pressure sensitive adhesive
such as a rubber, acrylic, modified acrylic (tackifier modified) or
silicone adhesive. It is preferred that the adhesive does not
require thermal activation and can be applied at temperatures
between 5 and 35 degrees. Photo-activated adhesives (including
initiators) may be used which can be cured by exposure to radiation
after the film has been applied.
[0031] The invention also extends to a method of manufacturing a
wind turbine blade comprising moulding the blade body and adhering
a thermoplastic film to at least 50% of the surface of the
body.
[0032] The invention also extends to a method of repairing a wind
turbine blade by adhering a thermoplastic film to at least 50% of
the surface of the body. Any steps disclosed herein relating to the
manufacture of a wind turbine blade apply equally to the repair of
a wind turbine blade.
[0033] Wind turbine blades may become worn through exposure to the
weather or by impact with wind-born debris and it may be necessary
to repair the blade. It is possible when performing the repair to
fit a conventional blade with a thermoplastic film. Alternatively,
the step of repair may involve repairing a blade according to the
present invention by removing a previous thermoplastic film and
replacing it with a new thermoplastic film in accordance with the
films of the present invention.
[0034] The film is preferably applied to the blade body in a number
of strips running between the leading and trailing edges of the
blade. The film can also be preferably applied in a manner with the
strips oriented such that the complexity of the curvature in which
the film is applied can be markedly reduced.
[0035] The edge of one strip may overlap with the edge of an
adjacent strip. Alternatively, the edges of adjacent strips do not
overlap and the join is covered with a further strip of
thermoplastic film, painted with acrylic or epoxy adhesive, painted
with a PVDF paint or hot welded together. It is preferred that any
surface painting is restricted to the immediate area of a seam or
join between strips of the film.
[0036] Similar considerations may apply at the leading and trailing
edges where the adjacent strips may either overlap or the join may
be covered with a further strip of thermoplastic film extending
along the edge.
[0037] Surprisingly, the inventors have found that applying the
thermoplastic film in strips does not interfere with the
performance of the finished turbine blade. It had been speculated
that the seams and overlaps could result in surface irregularities
and increase drag and/or noise. The thermoplastic film of the
present invention is sufficiently thin and the self supporting
laminar of the film is sufficiently resilient, that these
disadvantages are not observed. Rather, the film serves to increase
the durability of the turbine blade and to provide a smooth and
efficient blade surface.
[0038] The method preferably also includes the step of heating the
thermoplastic film shortly before when/or during its application to
the blade body. This is preferably done by blowing hot air onto the
film. This increases the flexibility of the film allowing it to be
applied more easily to the surface of the blade. In view of the
self-adhesive nature of the film preferably no heating of the film
is required once the film has been applied to the blade
surface.
[0039] The film can be applied `dry` to the blade surface or `wet`
utilising water or other suitable fluid to enable the film to be
more easily positioned without creasing or trapping air.
[0040] The film may be supplied in a number of sections each being
specially shaped to fit on an appropriate section of the blade.
Preferably, however, the film is applied from a roll. In this case,
the film may be trimmed before its application to the blade body.
This is particularly useful, for example, around the root of the
blade which has a complex shape.
[0041] The thermoplastic film may be applied to a full length
moulding of the blade. However, it is also possible that the blade
is made up of a plurality of modules as disclosed in our earlier
application GB 0717690.2. In this case, the thermoplastic film may
either be applied to the individual modules before they are
assembled into the finished blade, or the modules may be assembled
before the film is applied.
[0042] According to a third aspect of the invention, there is
provided a two layer thermoplastic film comprising an upper layer
and a lower layer, wherein:
the upper layer comprising (a) 50% to 85% of polyvinylidene
fluoride (PVDF), wherein up to 30% of the PVDF may be replaced by
hexafluoropropylene (HFP); (b) 10% to 45% polymethyl methacrylate
(PMMA); (c) optionally up to 8% UV stabilisers and/or absorbers;
(d) optionally up to 10% matting agent; and (e) optionally up to
40% of an inorganic pigment; the lower layer comprising (f) a
polymer of 10% to 45% of (PVDF), wherein up to 30% of the PVDF may
be replaced by hexafluoropropylene (HFP);
(g) 50% to 85% PMMA;
[0043] (h) optionally up to 8% UV stabilisers/absorbers; (i)
optionally up to 10% matting agent; and (j) optionally up to 40% of
an inorganic pigment;
[0044] wherein the film has an initial gloss of less than 30% when
measured with a reflectometer at an angle of 60.degree. with
respect to the film surface.
[0045] Preferably components (a) and (f) are copolymers of PVDF and
hexafluoropropylene in the recited amounts. That is, the components
are copolymers containing monomers of each of the named
polymers.
[0046] Preferably the upper layer has a thickness between 40 and
240 microns, more preferably 60 and 200 microns and the lower layer
has a thickness between 2 and 60 microns, more preferably between
10 and 40, and most preferably between 2 and 20 microns. In a
preferred embodiment the upper layer is between 60 and 240 microns
and the lower layer is between 2 and 10 microns.
[0047] Preferably the UV stabilisers are based on ultrafine `nano`
titanium dioxide materials containing surface modified inorganic
oxide particles.
[0048] Preferably the PVDF contains up to 30% HFP or is a copolymer
of 70% PVDF and 30% HFP.
[0049] Preferably the film further comprises adhesive on the lower
layer.
[0050] Preferably the film has an opacity of 60% or greater, more
preferably 80% of greater. It is advantageous for the film to be
opaque as it transmits very little light, and therefore reflects,
scatters, or absorbs most of it. This helps to make the wind
turbine blade less conspicuous.
[0051] It should be understood that any of the preferred features
of the above method or manufacture of repair may be applied in
combination with any of the preferred features of the blade
referred to above. Furthermore, any features disclosed in respect
of the film of the present invention can be applied in combination
with any of the preferred features of the blade.
[0052] In a fourth aspect, the present invention also encompasses
the use of the above-described films for use as a covering of a
wind turbine blade. It is preferred that the film is arranged so
that the upper layer corresponds to the surface layer of the blade
and is exposed to the atmosphere in use.
[0053] An example of a wind turbine blade in accordance with the
present invention will now be described with reference to the
accompanying drawings, in which:
[0054] FIG. 1 is a schematic plan view of an entire blade;
[0055] FIG. 2 is a cross-section of a first example of a join
between adjacent strips;
[0056] FIG. 3 is a cross-section to a second example of a join
between adjacent strips;
[0057] FIGS. 4A-E show a number of different configurations of
strips that could be used;
[0058] FIGS. 5A-E show similar configurations to those of FIGS.
4A-E but include an edge protection strip;
[0059] FIG. 6 is a cross-section that refers to an example of a
film and the underlying blade; and
[0060] FIG. 7 is a cross-section through a second example of a film
and the underlying blade.
[0061] A wind turbine blade is shown in FIG. 1. The basic body of
the blade may be formed in accordance with conventional techniques
in which full length mouldings of each half are made and the two
halves are joined together in a clam shell-like construction.
Alternatively, the blades may have a modular construction as
described in our earlier GB application number 0717690.2.
[0062] The present invention is concerned only with the surface
coating. As can be seen from FIG. 1, the blade is covered with a
number of strips 1 of self-adhesive of thermoplastic material 6 and
adhesive 4. Each strip extends from the leading edge 2 to the
trailing edge 3. The opposite side of the blade corresponds to
this. At these leading and trailing edges 2, 3 the strip on one
side may overlap slightly with the strip on the opposite side or a
further thin strip may be provided along the edge to cover the join
between strips in a similar manner to that described in the
reference to FIGS. 2 and 3 below.
[0063] As can be seen from FIG. 1, each strip overlaps with an
adjacent strip. The join between the two is shown in more detail in
FIG. 3. Adhesive 4 is provided on the lower surface of each strip
and will adhere to the underlying blade surface 5. At an overlap
portion strip 1 adheres to the surface of the adjacent
thermoplastic film 6 as shown. An alternative is shown in FIG. 2 in
which adjacent strips 1, 1 abut one another and a further strip 7
with adhesive 8 of the same or a similar material runs along the
join. The thickness of the material is such that the overlap
portion or the further thin strips do not have a significant effect
on the performance of the blade. As an alternative, the join shown
in FIG. 3 may be painted, for example with a PVDF paint and,
indeed, this is the current preference.
[0064] The strips 1 are supplied on a roll. The strips may have a
backing material covering the adhesive that is peeled off before
the strip is applied to the blade surface. However, no backing
material is necessary if the top surface of the film 1 is of a
material that does not adhere to the adhesive. An appropriate
amount is unrolled and, if necessary, trimmed to the correct shape.
Hot air is then blown onto the strip to make it flexible and the
strip is then applied to the blade surface. The strip is initially
adhered at a location close to one of the edges 23 and are
progressively adhered across the blade with the operator being
careful to ensure that no air is trapped as the film is
progressively adhered.
[0065] FIGS. 4A-E show various configurations of the strips which
may be applied to a blade. The blades may have the same
configuration of strips on both sides, or they may be different.
The strips may run across the blade (FIG. 4A), along the blade
(FIG. 4B) or diagonally (FIG. 4C). Alternatively, the root end of
the blade, which has the greatest curvature may be provided with a
different configuration of strips from the remainder of the blade.
In FIG. 4D the root end of the blade is covered with a number of
triangular strips which converge adjacent to the root end. These
strips offer the greatest degree of conformity with the blade
curvature and this example will be most useful for a relatively
un-pliable material. However, in the example of FIG. 4D the strips
either need to be supplied pre-cut, or if they are taken from a
roll, require a considerable amount of trimming and this example
will be more difficult to produce in practice. As a compromise, the
example of FIG. 4E provides reasonably good conformity in the
curved regions, but the strips can be used from a roll with
relatively little trimming.
[0066] The examples of FIGS. 5A to 5E are similar to those shown in
the corresponding FIG. 4 representations. The only different is
that the leading edge is provided with a protective strip 1A. This
extends to both sides of the blade and therefore provides good
weather proofing at the leading edge where it is most required.
[0067] The current preference is for the configuration shown in
FIG. 5A as this has a weather proofing strip 1A on the leading
edge, and also the transverse arrangement of strips 1 ensures that
the seams between adjacent strips lie substantially in the
direction of travel of the blade thereby minimising any
turbulence.
[0068] The nature of the thermoplastic film and adhesive will now
be described in greater detail with reference to FIGS. 6 and 7.
FIG. 6 is a cross-section through the blade surface and a first
film consisting of adhesive 4 layer and a thermoplastic film 6
which has a single layer. FIG. 7 is similar except that the
thermoplastic film 6 has separated into upper 9 and lower 10
layers.
[0069] In all cases, the thermoplastic film 6 is preferably between
50 and 300 microns thick.
[0070] For the single layer of FIG. 4, the thermoplastic film
preferably consists of 45.9% of polyvinylidene fluoride, 25.5%
PMMA, 1.5% UV stabilisers and absorbers, 1.5% matting agent and
25.6% inorganic pigment.
[0071] For the double layer of FIG. 5, the upper layer preferably
consists of 52.8% of polyvinylidene fluoride (15% of which is HFP),
22% PMMA, 1.5% UV stabilisers and absorbers, 1.5% matting agent and
22.2% inorganic pigment to give sufficient colour and opacity. The
lower layer preferably consists of 22% of polyvinylidene fluoride
(15% of which is HFP), 52.8% PMMA, 1.5% UV stabilisers and
absorbers, 1.5% matting agent and 22.2% inorganic pigment to give
sufficient colour and opacity.
[0072] For the double layer of FIG. 5 the upper layer is of a
thickness between 5 and 295 microns and the lower layer is of a
thickness between 5 and 295 microns. With the upper layer
preferably being between 40 and 240 microns and the lower layer
preferably being between 10 and 60 microns.
[0073] The film may be extruded (in the case of the FIG. 4 example)
or co-extruded (in the case of the FIG. 5 example) using an
extruder which is well known, for example the type of co-extruder
used to manufacture UPVC windows. The extruded material may then be
subjected to a second surface treatment such as a cold roller to
produce the desired lack of reflectiveness of the upper surface.
The film can then also preferably pass through a second process to
coat adhesive onto the lower surface before the film is wound on to
a roll ready for transportation.
* * * * *