Abstract:
The invention relates to a method of producing large parts based on composite materials, such as the roots of blades for wind generators. The inventive method comprises the following steps consisting in: helically winding a band of fibre- and resin-based composite material around a mould; applying a removable protective sheet to the surface of the body; applying a heat-shrinkable strip to the sheet; compacting the laminate thus formed under a vacuum; curing the resin; aligning the cured body, machining the transverse surface to be applied to the blade and forming axial housings in said surface; and positioning and affixing inserts in the axial housings in order to secure the blade.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a method of producing large parts based on composite materials, and is especially applicable to the manufacture of the roots of blades for wind generators. 
         [0002]    More specifically, the inventive method includes helically winding a band of fibre- and resin-based composite material around a mould and finally subjecting it to a curing operation. 
       BACKGROUND OF THE INVENTION 
       [0003]    The known methods for manufacturing large parts based on composite materials are generally based on the use of continuous fibres impregnated with resin, which are wound around a mandrel or mould. In this sense we can indicate for example the U.S. Pat. No. 5,993,717, related to a procedure for manufacturing reinforced composite profiles, with open or closed sections, in which the reinforcing fibres pass through a resin bath, together with reinforcing threads or rods, to then penetrate into a mould where the profile is shaped and cured. 
         [0004]    In the same sense we can cite the EP 1056587, related to the manufacture of floating bodies from reinforced synthetic resins with continuous fibres and made with winding machines. 
         [0005]    The manufacture of large resin parts is also known, where the reinforcement elements consist of bands or strips of fibres. In this sense we can cite the ES 2089965, related to a procedure for manufacturing aerodynamic profiles for wind turbine blades, which consists in coating moulds with complexes of fibres impregnated with synthetic resins, later combining all the covered moulds. The fibre complexes can be shaped on the moulds, for example based on stratified layers of reinforced fibres, supplied in strips with single-direction fibres that are preimpregnated with synthetic resins. Also in this case the fibres are preimpregnated and, in addition, the strips or bands of fibres are extended across the mould and the mould forms part of the profile that you wish to obtain. 
       DESCRIPTION OF THE INVENTION 
       [0006]    The object of this invention is to be able to obtain large parts using complex materials, based on reinforcing fibres and resins, in which the reinforcing fibres comprise bands of undefined length, which are applied to a mould, on which the curing takes place and from which the part to shape is separated, obtained only with the complex material and without other supporting or reinforcing elements being part of it. 
         [0007]    According to a first characteristic of the invention, the parts are shaped on a mould, by helically winding a band of complex material around this mould, until achieving the desired laminate. 
         [0008]    This winding can be performed with the mould in a winding machine, which can rotate the mould along its axis, while the spools of the band of complex material move linearly in a carriage, parallel to the mould. 
         [0009]    The laminate of the part is achieved by combining the linear movement of the spool carriage and the turning movement of the mould along its axis. Thus, with successive sweeps, you can achieve the required laminate thickness on every area or section of the mould by regulating the length of each sweep. While the laminate is being formed, the band is maintained at a homogenous voltage, to avoid wrinkling. 
         [0010]    According to another characteristic of the invention, the band of complex material consists of a stratification formed by alternate layers of fibre and resin strips. These bands will preferably be composed of two external layers of fibre and an intermediate layer of resin. The resin will be in solid state until the moment it is used, so the band must be kept at temperatures lower than 5° C. To apply the band to the mould, this band must be heated to a temperature of between 15 and 20° C., so the resin reaches a doughy or semi-liquid state. 
         [0011]    Before starting to wind the band, the surface of the mould must be prepared by cleaning it, applying a demoulding agent and placing thermocouples to verify temperatures in the subsequent stage of curing the resin. 
         [0012]    Once the laminate is complete, the whole surface is covered with a removable protective sheet. This sheet may be a band that is wound helically around the laminate, with the longitudinal edges partially overlapping and tensed so that it fits over the surface of the laminate. The protective sheet has a double function, on one hand it protects the laminate from dirt and, on the other, makes the surface of the laminate rough enough for the layers applied in later operations to adhere correctly, as indicated below. 
         [0013]    Then a heat-shrinkable strip is wound helically around the protective sheet, tensed and with the longitudinal edges partially overlapping, forming a continuous cover through which passages are formed to evacuate the air and let the resin sweat, passages that may be achieved by placing a strip of permeable material between certain successive turns of the band, transversally to it. 
         [0014]    Then it is compacted under a vacuum, using a process that is known in itself, that may include the successive use of a bleeder; an aerator, constituted by a layer of absorbent material, which will be responsible for absorbing the resin that the laminate may sweat through the joints of the bleeder and its edges; and a vacuum cover or bag that covers the whole lateral surface of the assembly and is sealed. 
         [0015]    Between the bleeder and the vacuum bag, intercommunicated longitudinal and transversal vacuum passages are formed through which the air can be extracted. Also on the layer of absorbent material, before forming the vacuum bag, thermocouples and tubes to extract air will be placed, tubes that start in the vacuum passages, pass over the layer of absorbent material and leave through the end sections. In addition, a tube passes through the vacuum and will be connected to a vacuum gauge at a later stage when the vacuum is created, by connecting the air extraction tubes to a vacuum pump. The seal of the plastic sheet that shapes the vacuum bag, between its edges and with the layer of absorbent material and the seal where the thermocouples and air extraction tubes exit, may be chromed. 
         [0016]    After achieving the degree of vacuum inside the vacuum bag, the curing of the laminate resin begins, maintaining the compacting due to the vacuum and applying heat to the exterior of the shaped body and also to the interior, through the mould. This may be done inside a curing oven, monitoring the temperature with the thermocouples that had previously been fitted, which enables the curing stage to be carried out independently from the interior and exterior of the laminate, controlling the curing from the inside out. 
         [0017]    Once the resin has been cured and after the assembly has been removed from the curing oven, the vacuum bag, the layer of absorbent material with the air passages, thermocouples and vacuum or air extraction tubes are removed, to finally demould the body. To do this and to remove the excess material formed during the lamination on the side with the greatest section, two peripheral cuts will be made close to the greatest end section, which reach the mould and establish two rings, one at the end, which is separated by axial cuts for example to subdivide the ring into two or more separable sectors, and an intermediate ring that will rest on fixed supports while the mould is removed by pushing axially from the side opposite this ring. Thus the demoulding is carried out by acting on the mould, moving it with respect to the body or laminate obtained, which rests on fixed transverse supports, through the intermediate ring. When the mould is removed, this intermediate ring is released and separated from the moulded body. 
         [0018]    So that the transverse cuts on the moulded body to obtain these rings do not affect or reach the surface of this mould, a peripheral channel is formed on the surface of the mould, near the end section. The channel shall be a little wider than the separation between the cuts that establish the rings and shall coincide with the position where these cuts are made. In this channel, before starting to wind the band of composite materials, a soft filler material is placed, such as cork, which will be covered with a impervious sheet that is flush with the lateral surface of the mould. Thus, when making the transverse peripheral cuts in the moulded body, the cutter may exceed the thickness of this without affecting the mould, as it will hit the cork filler of the peripheral channel. 
         [0019]    Then, the moulded body is subjected to an alignment process and the transverse surface to be abutted to the blade is machined, to obtain a flat surface perpendicular to the axis of the body. Axial housings are made in this surface and inserts are placed into them and affixed, for securing to the blades. 
         [0020]    The aforementioned axial housings are obtained by machining in several stages to achieve a conical internal section and a cylindrical external section. 
         [0021]    The inserts will be tubular, with an external shape and section that coincide with the inserts. 
         [0022]    The laminating operation and at least the operations after the shaping of this laminate, such as the stages of vacuum, curing, demoulding, aligning, machining and affixing inserts, are performed at fixed or different work stations, to which the mould will be successively transported. This allows different operations to be performed at different work stations at the same time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The characteristics of the invention procedure can be understood better with the following description of an example, with reference to the attached drawings, where: 
           [0024]      FIG. 1  shows a plan view diagram of an installation for the helical winding of laminate strips around the mould where the laminate is shaped. 
           [0025]      FIG. 2  corresponds to Detail A of  FIG. 1 , in section, once the process of shaping the laminate has finished, with the vacuum bag and before the curing process. 
           [0026]      FIG. 3  shows a plan view of the assembly in  FIG. 2 , with the vacuum bag. 
           [0027]      FIG. 4  is a diametral section of the mould with the laminate or shape on it, in a stage prior to demoulding. 
           [0028]      FIG. 5  is a profile view of the laminate, after removing the mould, seen from its larger base. 
           [0029]      FIG. 6  is a partial longitudinal section of the wall of the laminate, taken according to the cutting point VI-VI in  FIG. 5 . 
           [0030]      FIG. 7  is a front lateral view of the shaped laminate on the mould, according to a variation of execution. 
           [0031]      FIG. 8  corresponds to Detail B of  FIG. 7 , in section and at a greater scale. 
       
    
    
     DETAILED DESCRIPTION OF A METHOD 
       [0032]    The example represented in the drawings corresponds to the manufacture of a root of a wind turbine blade, with a tubular structure, which is obtained from a mould that is also tubular. To obtain this part, start by fitting the mould  1 ,  FIG. 1 , onto a winding machine, between a jaw chuck  2  and a counterpoint  3 . This model also includes a carriage  4  that can carry spools  5  of a band of composite material  6 , with which the root will be laminated. The carriage  4  can move linearly along a base  7  parallel to the axis of the mould  1 . 
         [0033]    Combining the rotation of the axis  1  with the linear movement of the carriage  4 , the band  6  is wound helically around the mould  1 , achieving the thickness of laminate required for each area or section of the mould. The band  6  will be maintained with a uniform voltage to avoid wrinkling and to achieve a homogenous laminate. 
         [0034]    The band  6  of composite material will be made up of a stratification formed by two layers of fibre with a layer of resin between them. 
         [0035]    After winding the band  6 , a stratification is obtained, which is indicated in  FIG. 2  with the number  8 . On this stratification, keeping it on the mould  1 , a removable protective sheet  9  is applied, which shall be porous to resin but shall prevent dirt reaching the surface of the stratification  8 . A heat-shrinkable strip is wound helically around this protective sheet to form a continuous cover  10 , which will help the compacting of the laminate  8  in the later curing process. As this strip is not porous, discontinuities are created at certain points, for example by alternating with strips of permeable material, which create passages through which air can pass and the resin can sweat. 
         [0036]    A bleeder  11  is placed on this cover, constituted by a sheet of plastic with small holes that do not let the resin through, but do let air pass. The bleeder is later covered with an aerator  12 , constituted by a layer of absorbent material, for example a blanket of non-woven fibre. The bleeder will be responsible for absorbing the resin that may be sweated by the laminate through the joints of the bleeder and its edges. 
         [0037]    Finally, a vacuum bag  13  is formed on the bleeder  12 , made up of an impervious sheet placed around the bleeder  12 , with the longitudinal edges sealed together and the transverse edges sealed to the bleeder  12  with a sealant  14  applied adjacent to the transverse sections of the assembly. 
         [0038]    Between the vacuum bag  13  and the bleeder  12  there are thermocouples  15  whose cables  16  can exit through the layer of sealant  14 . Also between the bag  13  and the bleeder  12  there are air extraction tubes  17  that may also protrude through the sealant  14 . The tubes  17  leave from passages  18  formed between the bleeder  12  and the bag  13  that pass longitudinally and peripherally and are connected together. These passages  18  can be formed, for example, by strips of mesh positioned on the blanket that forms the bleeder  12 . 
         [0039]    As you can see in  FIG. 2 , before starting to wind the band  6 , thermocouples  19  are fitted on the mould  1 . The conductors  20  exit towards the same side as the conductors  16  of the thermocouples  15 . 
         [0040]    Thus the bag  13  is fully sealed against the bleeder  12  and a tube passes through an intermediate point, not represented, that ends inside between this bag and the bleeder  12 . It is connected to a vacuum gauge on the outside, to monitor the degree of vacuum that is created inside the bag  13  when the tubes  17  are connected to a vacuum pump. Once the minimum vacuum required has been reached, the mould  1  with the body shaped on it using the laminate  8 , the different layers described and the vacuum bag is transported to a curing oven, where heat is applied to the exterior of the body and also to the interior through the mould  1 , monitoring the temperature using thermocouples  15  and  19 , to achieve independent interior and exterior curing. 
         [0041]    After the curing you have an assembly like that represented in  FIG. 4 , which includes the mould  1  and the laminate  8  with the aforementioned layers. Then it is necessary to proceed to the demoulding, for which the mould with the laminate is moved to a cutting and demoulding machine, the auxiliary materials that help the curing, such as the vacuum bag, the layer of absorbent material with the air passages  18 , thermocouples  15  and vacuum or air extraction tubes  17  are removed. Then it will be necessary to remove the excess material formed on the side with the greater section during the laminating. To do this, two transverse cuts  22  and  23  are made all around the body  8 , near the end section with the bigger diameter, cuts that must go through the whole thickness of the body  8  and that establish an end ring  24  and an intermediate ring  25 . 
         [0042]    To avoid damaging the surface of the mould  1  when making the cuts  22  and  23 , there is a peripheral channel  26 ,  FIGS. 2 and 4 , in the area of the cuts, which is filled with a soft material such as cork  27  before starting to helically wind the band  6 . The filler material  27  is covered with an impervious sheet or layer  28  flush with the surface of the mould  1 . Thus the cutting points  22  and  23 , as you can see in  FIG. 2 , can exceed the height corresponding to surface of the mould  1 , partially penetrating the filler material  27 , which allows all the cuts to be made safely and rings  24  and  25  to be formed ready for demoulding process, as described below. 
         [0043]    For the demoulding, axial cuts are made in the external ring  24 , so that it comprises two or more sectors that can be easily separated from the mould  1 . Then the intermediate ring  25  is supported by means of its flat surface on fixed position limiters  30  and the mould  1  is pushed in the direction of arrow D, thus easily managing to demould the part and, during this operation, removing ring  25 . 
         [0044]    Once the part is demoulded, it is necessary to obtain, on the side with the greatest section, a flat surface perpendicular to the axis of the part. For this purpose the demoulded part is transported to an alignment station, where the part is oriented to the correct position, where it is immobilised. Then the transverse surface  31  that corresponds first with cut  23  is machined until a flat surface perpendicular to the axis of the body  8  is obtained. Next, in surface  31 , axial housings  32  are formed for inserts  33  to be placed and affixed, which are for securing the body or root  8  in the blade of the wind turbine. 
         [0045]    To place the inserts, adhesive is applied to them and once the axis of the housing and the insert are aligned, the inserts  33  are inserted into the housings  32  by means of a continuous rotational movement, which prevents air bubbles forming, filling the whole space that may be between the housing  32  and the insert  33  with adhesive  34 . In addition, adhesive  35  is also applied around the insert  33  and this adhesive is cured by moving the part to a curing oven. The curing temperature can be monitored by a thermocouple previously inserted into insert  33  using stoppers. Once the resin is cured, the stoppers and the Thermocouple are removed. 
         [0046]    Once this process is finished it is time to face the inserts  33 . For this purpose the part is moved to a facing machine and, once fitted on the bedplate, the insert that protrudes most is selected, to establish a starting point for the facing. Then the facing is begun, with as many sweeps as necessary until the surface all the inserts are all on the same plane, perpendicular to the axis of the body. 
         [0047]    With the aforementioned process, you now have a part that forms the root of the blade, with a structure that is resistant enough for the role it must fulfil. As a process verification, a test of traction and of the thread of the inserts  33  can be carried out. 
         [0048]    It is possible to make the whole process of shaping the laminate or body  8  on a symmetrical mould  36 ,  FIG. 7 , equivalent to two moulds  1  as in  FIG. 1  joined at the larger base. In this case the channel  26 ,  FIG. 8 , shall be made to coincide with the intermediate area of the mould and it shall also be filled with cork  27  or similar. Only one peripheral cut shall be made  37 , through which an element will be inserted which can push in directions E or F of  FIG. 8  to demould the bodies  8  and  8 ′ shaped on it. 
         [0049]    As you can see in  FIG. 6 , the housings  32  for the inserts  33  may include an external cylindrical section  37  and an internal conical section  38 , decreasing towards the bottom. A conical coaxial core  39  protrudes from this base, with a decreasing section that limits a ring-shaped space with the wall of the housing. For its part, the insert  33  is tubular, which coincides with the housing, and has a section  40  in which the wall is thinner, to fit into the aforementioned ring-shaped space, between the wall of the housing  32  and the core  39 . 
         [0050]    The housings  32  are machined in successive operations, to obtain cylindrical  37  and conical  38  sections. 
         [0051]    The insert  33  will also include an internal threaded section  41  that can be protected with stoppers  42  until the moment of assembly.