Abstract:
A method for hardening a surface of a component in a wind turbine is disclosed. The component to be hardened includes a surface and the surface is applied with a blasting material by ultrasound waves. The component is a part of a drive or a drive housing, a bearing surface, a gear wheel or a pinion. The ultrasound waves are emitted with the aid of a piezo electric transducer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of German application No. 10 2010 006 094.1 filed Jan. 28, 2010, which is incorporated by reference herein in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for hardening the surface of a component in a wind turbine, in particular the surface outer layer of a component in a wind turbine. 
       BACKGROUND OF THE INVENTION 
       [0003]    Microscopic cracks in the respective part frequently appear, as a result of high Hertzian pressure, in heavily loaded regions of drives, for instance in heavily stressed regions of bearing surfaces of drives or tooth flanks of gear wheels. Microscopic cracks of this type may result in premature faults and corresponding failures of the respective part. The crack formation frequently occurs on the outer surfaces and/or in the region of the periphery of the heavily loaded contact surfaces. Micro defects of this type reduce the operating time and the service life of the respective part, for instance of the drive and the drive housing. In numerous plants, for instance in wind turbines, the thus necessary replacement of the respective component, for instance of the drive or parts thereof, is generally complicated and expensive. 
         [0004]    The hardening processes and processing technologies used to date, such as rolling, hard turning or blasting material peening, do not achieve increased internal stress particularly of the heavily loaded contact regions and therefore reduce the high tensile load. Only internal stresses of a maximum of 400 MPa can currently be achieved. 
         [0005]    DE 10 2007 009 470 A1 and WO 93/20247 A1 describe methods for the surface peening, in particular for the ultrasound ball peening of a part, in particular a gas turbine. Ultrasound blasting material peening is characterized in that a sub-region of the surface of a part is hardened by applying a blasting material. The blasting material preferably consists of small balls with a diameter of less than 4 mm. 
       SUMMARY OF THE INVENTION 
       [0006]    The object of the present invention consists in providing an advantageous method for hardening the surface of a component in a wind turbine. This object is achieved by a method as claimed in the independent claim. The dependent claims contain further advantageous embodiments of the invention. 
         [0007]    The inventive method for hardening the surface of a component in a wind turbine is characterized in that the component to be hardened has a surface and the surface is applied with a blasting material by means of ultrasound waves. The component to be hardened can be in particular parts of bearings or the drive of the wind turbine. In particular, the component can include a part of a drive or a drive housing, a bearing surface, in particular of a bearing, for instance a bearing surface of a roller bearing, or of a drive, a gear wheel or a pinion, in particular a drive pinion. The component to be hardened can be in particular a tooth flank of a gear wheel. 
         [0008]    By means of ultrasound blasting material peening, in other words applying the surface to be hardened with a blasting material by means of ultrasound waves, the internal stress of the respective component is increased and the susceptibility to cracking is thus reduced. The service life and the operating time of the respective component are increased in this way by approximately 20%. 
         [0009]    The ultrasound waves can preferably be emitted with the aid of a piezo electric transducer. For instance, ultrasound waves can be emitted with a frequency between 10 kHz and 30 kHz, preferably 20 kHz. It is particularly advantageous if the ultrasound waves are amplified. This can take place for instance with the aid of an acoustic amplifier. 
         [0010]    The blasting material can preferably include a relatively heavy material, like for instance tungsten carbide, and/or consist of tungsten carbide. In addition, the blasting material can include balls. The blasting material can preferably include balls with a diameter of more than 1 mm, advantageously with a diameter of more than 5 mm, or can exclusively consist of blasting balls with a diameter of more than 1 mm, advantageously with a diameter of more than 5 mm. It has emerged that the use of tungsten carbide balls and the use of balls with a relatively large diameter, in particular of more than 5 mm, can achieve particularly high internal compressive stress results, since the balls are in this case embodied in a relatively large and heavy fashion. 
         [0011]    With the aid of the inventive method, internal stresses, in particular of bearing surfaces of wind turbine bearings and wind turbine drives, for instance gear wheel drive systems, of more than 800 MPa can be achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further features, characteristics and advantages of the present invention are described in more detail below with reference to an exemplary embodiment with respect to the appended figures. Here the described features are advantageous both individually and also in combination with one another. 
           [0013]      FIG. 1  shows a schematic representation of a wind power plant. 
           [0014]      FIG. 2  shows a schematic representation of a first cross-section through a part of an apparatus for implementing the inventive method on a gear wheel. 
           [0015]      FIG. 3  shows a schematic representation of a second cross-section through a part of an apparatus for implementing the inventive method on a gear wheel. 
           [0016]      FIG. 4  shows a schematic representation of a first cross-section through a part of an apparatus for implementing the inventive method on the interior surface of a roller bearing outer ring. 
           [0017]      FIG. 5  shows a schematic representation of a second cross-section through a part of an apparatus for implementing the inventive method on the inner surface of a roller bearing outer ring. 
           [0018]      FIG. 6  shows a schematic representation of a first cross-section through a part of an apparatus for implementing the inventive method on the outer surface of a roller bearing inner ring. 
           [0019]      FIG. 7  shows a schematic representation of a second section through a part of an apparatus for implementing the inventive method on the outer surface of a roller bearing inner ring. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    An exemplary embodiment of the invention is described in more detail below with the aid of  FIGS. 1 to 7 .  FIG. 1  shows a schematic representation of a wind power plant  1 . The wind power plant  1  includes a tower  2 , a pod  3  and a rotor hub  4 . The pod  3  is arranged on the tower  2 . The rotatably mounted rotor hub  4  is arranged on the pod  3 . At least one rotor blade  5  is fastened to the rotor hub  4 . The wind power plant  1  typically includes two or three rotor blades  5 . 
         [0021]    The wind power plant  1  also includes at least a rotational axis  6 , a main bearing  30 , a drive  7 , a brake  8  and a generator  9 . The rotational axis  6 , the main bearing  30 , the drive  7 , the brake  8  and the generator  9  are arranged inside the pod  3 . A center to center difference is essentially possible in the drive  7 . Different components can therefore have different rotational axes. In addition, the wind power plant  1  can also be embodied without drives. 
         [0022]      FIG. 2  shows a schematic representation of a cross-section through part of an apparatus for implementing the inventive ultrasound shot peening method. The apparatus includes a peening chamber  10 , within which the shot peening is implemented. Part of a component to be hardened, in the present exemplary embodiment part of a drive pinion  11 , is arranged within the peening chamber  10 . The drive pinion  11  includes a rotational axis  13 .  FIG. 2  shows a cross-section through the drive pinion  11  along the rotational axis  13 , in other words an axial cross-section. The drive pinion  11  includes a number of teeth  24 , of which at least one part is arranged within the peening chamber  10 . The surface to be hardened of the teeth  24  of the gear pinion  11  is identified with reference character  26 . 
         [0023]    At least one part of a sonotrode  17  is also arranged within the peening chamber  10 . The sonotrode  17  is preferably arranged opposite the surface  26  to be hardened. The sonotrode  17  is connected to an amplifier  16 , preferably an acoustic amplifier. The amplifier  16  is also connected to a transducer, preferably in the form of a piezo electric emitter. 
         [0024]    A cavity  27  is disposed between the sonotrode  17  and the drive pinion  11  within the peening chamber  10 . A number of balls  18  are arranged in this cavity  27 . The balls  18  preferably consist of tungsten carbide. The balls  18  advantageously have a diameter of more than 1 mm, preferably of more than 5 mm. A homogenous hardening of the surface  26  is herewith achieved. 
         [0025]    In order to implement the inventive method, ultrasound waves with a frequency between 30 kHz and 10 kHz, advantageously with a frequency of 20 kHz, are generated with the aid of the transducer  14 . The ultrasound waves are then amplified with the aid of the acoustic amplifier  16 . The amplified ultrasound waves are transmitted by means of the sonotrode into the peening chamber  10 , and/or into the cavity  27  disposed therein. The ultrasound waves cause the balls  18  inside the peening chamber  10  to vibrate and move inside the peening chamber  10 . The balls  18  are in this way reflected by the surface of the sonotrode  17 , by the surface  26  to be hardened and by the walls of the peening chamber  10 . In addition, the balls  18  collide with one another. As a result of the random scattering of the balls  18 , a homogenous treatment of the surface  26  to be hardened is achieved. 
         [0026]      FIG. 3  shows a schematic representation of a cross-section according to  FIG. 2  through an apparatus for implementing the inventive method. Contrary to  FIG. 2 , the drive pinion  12  is shown in  FIG. 3  in a radial cross-section, in other words in a cross-section at right angles to the rotational axis  13 . The view of the remaining parts in  FIG. 3  can essentially correspond to the cross-section shown in  FIG. 2 , with only the part  11  and/or  12  to be hardened being arranged differently. Alternatively the cross-section shown in  FIG. 3 , in respect of all parts, may be a cross-section at right angles to the cross-section shown in  FIG. 2 . The longitudinal axis of the apparatus is identified in both  FIGS. 2 and 3  with reference character  15 . 
         [0027]    The teeth  24  of the drive pinion  12  shown in  FIG. 3  include tooth flanks  25 . With the aid of the inventive method, the tooth flanks  25  can in particular be effectively hardened, since as a result of the random scattering of the balls, the whole surface to be hardened can be evenly treated. 
         [0028]      FIGS. 4 and 5  show a cross-section through part of an apparatus for implementing the inventive method.  FIGS. 4 and 5  show the hardening of the inner bearing surface  21  of a roller bearing outer ring  19  and/or  20 . Here the roller bearing outer ring  19  in  FIG. 4  is shown in an axial cross-section in respect of a rotational axis  23 .  FIG. 5  shows the roller bearing outer ring  20  in a radial cross-section in respect of the rotational axis  23 . Similarly to the embodiments rendered in conjunction with  FIGS. 2 and 3 ,  FIGS. 4 and 5  may be two cross-sections arranged at right angles to one another and the same arrangement or however the same cross-section, with the roller bearing outer ring  19  and/or  20  being arranged differently. 
         [0029]    The same applies to  FIGS. 6 and 7 , in which a cross-section is shown through an apparatus for hardening the outer bearing surface  22  of a roller bearing ring  28  and/or  29 .  FIG. 6  shows part of the roller bearing inner ring  28  in an axial cross-section in respect of the rotational axis  23 , while  FIG. 7  shows part of the roller bearing inner ring  29  in a radial cross-section in respect of the rotational axis  23 . 
         [0030]    The inventive method described in conjunction with  FIG. 2  can be implemented in a similar fashion with the aid of the embodiments shown in  FIGS. 3 to 7 . 
         [0031]    As a result, an internal stress of the surface of the drive pinion  11 ,  12 , in particular of the surface of the tooth flanks  25 , of the outer bearing surface  22  and of the inner bearing surface  21  of the roller bearing ring  19 ,  20 ,  28 ,  29  of more than 800 MPa can be achieved with the aid of the inventive method.