U.S. patent application number 12/102506 was filed with the patent office on 2009-10-01 for wind turbine blade.
Invention is credited to Paul Rudling.
Application Number | 20090246033 12/102506 |
Document ID | / |
Family ID | 39386953 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090246033 |
Kind Code |
A1 |
Rudling; Paul |
October 1, 2009 |
WIND TURBINE BLADE
Abstract
There is provided a wind turbine blade at least 50% of the
surface of which is covered with a self-adhesive thermoplastic
film. By applying a self-adhesive thermoplastic film to the blade,
the need for a gelcoat or the 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. 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.
Inventors: |
Rudling; Paul; (Calborne,
GB) |
Correspondence
Address: |
PATTERSON & SHERIDAN, L.L.P.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
39386953 |
Appl. No.: |
12/102506 |
Filed: |
April 14, 2008 |
Current U.S.
Class: |
416/241A ;
29/889.7; 428/212 |
Current CPC
Class: |
B32B 27/20 20130101;
Y02P 70/523 20151101; B32B 2307/558 20130101; Y10T 428/24942
20150115; B32B 27/308 20130101; B32B 2603/00 20130101; B32B 27/322
20130101; Y02E 10/72 20130101; Y10T 29/49336 20150115; B32B 27/304
20130101; B32B 2307/726 20130101; B32B 27/40 20130101; B32B 2270/00
20130101; B32B 2307/724 20130101; Y02P 70/50 20151101; B32B 27/30
20130101; B32B 2307/536 20130101; B32B 2307/58 20130101; F03D 1/065
20130101; B32B 27/08 20130101; B32B 2307/514 20130101; Y02E 10/721
20130101; B32B 2307/41 20130101; B32B 2307/712 20130101; B32B
2307/72 20130101; B32B 2264/102 20130101; B32B 27/18 20130101 |
Class at
Publication: |
416/241.A ;
29/889.7; 428/212 |
International
Class: |
B63H 1/26 20060101
B63H001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2008 |
GB |
0805713.5 |
Claims
1. A wind turbine blade at least 50% of the surface of which is
covered with a self-adhesive, thermoplastic film.
2. The blade according to claim 1, wherein substantially all of the
blade is covered with the film.
3. The blade according to claim 1, wherein the thermoplastic film
comprises a two layer structure having an outer layer with enhanced
weather resistant properties compared to the inner layer.
4. The blade according to claim 3, wherein the inner layer has
enhanced adhesion properties compared to the outer layer.
5. The blade according to claim 3, 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.
6. The blade according to claim 3, wherein the layers are
co-extruded.
7. The blade according to claim 1, 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.
8. The blade according to claim 1, wherein the thermoplastic layer
is less than 300 .mu.m thick.
9. The blade according to claim 1, wherein the film is porous such
that it is air permeable and water impermeable.
10. The blade according to claim 1, wherein the adhesive is an
acrylic adhesive.
11. 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.
12. The method of manufacturing according to claim 11, wherein the
film is applied in a number of strips running between the leading
and trailing edges of the blade.
13. The method of manufacturing according to claim 11, wherein the
film is applied in a number of strips arranged to reduce the
complexity of curvature of each strip.
14. The method of manufacturing according to claim 12, wherein the
edge of one strip overlaps with the edge of an adjacent strip.
15. The method of manufacturing according to claim 12, wherein
edges of adjacent strip do not overlap and the join is covered with
a further strip of thermoplastic film.
16. The method of manufacturing according to claim 12, wherein
edges of adjacent strip do not overlap and the join is painted with
a PVDF paint.
17. The method of manufacturing according to claim 11, wherein the
thermoplastic film is heated shortly before and/or during its
application to the blade body.
18. The method of manufacturing according to claim 11, wherein the
blade body is wetted with a suitable fluid shortly before the
application of the thermoplastic film to the blade body.
19. The method of manufacturing according to claim 11, wherein the
film is trimmed before its application to the blade body.
20. The method of manufacturing according to claim 11 of making a
blade according to claim 1.
21. 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
polyvinylidene fluoride 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 polyvinylidene fluoride
may be replaced by hexafluoropropylene (HFP); (g) 50% to 85% PMMA;
(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; wherein the film has an initial gloss of less than 30%
when measured with a reflectometer at an angle of 60 degrees.
22. The two layer film according to claim 21 wherein the upper
layer has a thickness between 40 and 240 .mu.m and the lower layer
has a thickness between 10 and 60 .mu.m.
23. The two layer film according to claim 21, wherein the UV
stabilisers are based on ultrafine `nano` titanium dioxide
materials containing surface modified inorganic oxide
particles.
24. The two layer film according to claim 21, wherein the PVDF
contains up to 30% HFP.
25. The two layer film according to claim 21, further comprising
adhesive on the lower layer.
26. The two layer film according to claim 21, wherein there is at
least 0.5% matting agent in at least one layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of Great Britain patent
application serial number 0805713.5, filed Mar. 28, 2008, which is
herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a wind turbine blade, and
more specifically, to an improved surface coating for a wind
turbine blade.
[0004] 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 be of a cost
significantly lower than products typically found in aerospace
applications.
[0005] 2. Description of the Related Art
[0006] 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.
[0007] Some wind turbine blades have their leading edges taped with
impact resistant tape, which is often applied to older blades to
repair them.
[0008] The shortcomings of current technology are as follows:
[0009] 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.
[0010] 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. 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.
[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.
SUMMARY OF THE INVENTION
[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 the 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. 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,
PVDF; PVDF+HFP copolymer; THV (PVDF, HFP, TFE); PVF; FEP (TFE,
HFP); PFA (TFE, PFVE); CTFE; CTFE+VF2/HFP or a combination of
these.
[0015] The thermoplastic may be a single layer, but it is
preferably formed of a two layer structure having an outer 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. This facilitates the
adhesion of the film to the blade.
[0016] 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.
[0017] 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.
[0018] 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 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).
[0019] All of the percentages recited for the composition of the
film material are by weight percentages for the film excluding the
adhesive layer.
[0020] 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.
[0021] The thickness of the thermoplastic film (excluding the
adhesive) is preferably less than 300 .mu.m, and preferably between
50 and 150 microns thick.
[0022] 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.
[0023] The adhesive is preferably a pressure sensitive adhesive
such as a rubber, acrylic, modified acrylic (tackifier modified) or
silicone adhesive.
[0024] 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.
[0025] 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.
[0026] 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
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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;
[0033] (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;
[0034] 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.
[0035] Preferably the upper layer has a thickness between 40 and
240 microns and the lower layer has a thickness between 10 and 60
microns.
[0036] Preferably the UV stabilisers are based on ultrafine `nano`
titanium dioxide materials containing surface modified inorganic
oxide particles.
[0037] Preferably the PVDF contains up to 30% HFP.
[0038] Preferably the film further comprises adhesive on the lower
layer.
[0039] It should be understood that any of the preferred features
of the method referred to above may be applied in combination with
any of the preferred features of the blade referred to above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0041] FIG. 1 is a schematic plan view of an entire blade;
[0042] FIG. 2 is a cross-section of a first example of a join
between adjacent strips;
[0043] FIG. 3 is a cross-section to a second example of a join
between adjacent strips;
[0044] FIGS. 4A-E show a number of different configurations of
strips that could be used;
[0045] FIGS. 5A-E show similar configurations to those of FIGS.
4A-E but include an edge protection strip;
[0046] FIG. 6 is a cross-section that refers to an example of a
film and the underlying blade; and
[0047] FIG. 7 is a cross-section through a second example of a film
and the underlying blade.
DETAILED DESCRIPTION
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] In all cases, the thermoplastic film 6 is preferably between
50 and 300 microns thick.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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
coatadhesive onto the lower surface before the film is wound on to
a roll ready for transportation.
[0061] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *