Abstract:
An apparatus for shot peening blade mounting areas on a disc of a rotor includes a peening nozzle unit which streams shot peening media along a longitudinal axis. The unit includes a nozzle outlet which extends at least partially in a circumferential direction of the unit, and a deflection arrangement with a deflection area for the media. The deflection area is at least partially cone or half-hyperboloid shaped, such that the media passes the nozzle outlet over an angle range in circumferential direction after being deflected by the deflection arrangement. A method for shot peening the blade mounting areas positions the unit in a slot profile of a blade mounting area and guides the unit along the contour of the slot profile with the nozzle outlet facing the contour of the slot profile to approximately uniformly peen the contour of the slot profile.

Description:
This application claims priority to European Patent Application No. 13 183 938.3 filed Sep. 11, 2013, the entirety of which is incorporated by reference herein. 
     FIELD OF THE INVENTION 
       [0001]    The invention relates to an apparatus for shot peening of blade mounting areas on a rotor arrangement disc by means of a shot peening media as described in the claims, and to a method for controlled shot peening of blade mounting areas on a disc of a rotor arrangement as described in the claims. 
       BACKGROUND OF THE INVENTION 
       [0002]    Rotors of gas turbines, in particular aircraft gas turbines, comprising a rotor disc and blades arranged in circumferential direction around the disc are widely known from practical experience. Typical blades are inserted with a dovetail shaped blade root into also dovetail shaped blade mounting areas on the disc. The dovetail of a turbine blade typically includes corresponding pairs of upper and lower dovetail lobes or tangs in a fir tree configuration. Correspondingly, the perimeter of the rotor disk includes a row of axial dovetail slots defined between corresponding disk posts having complementary upper and lower supporting lobes or tangs. 
         [0003]    In order to make the blade mounting areas durable and failsafe it is known to strain-harden the surface of the blade mounting areas by shot peening. With this method, a for example balk-shaped shot peening media is blasted or peened, respectively, with high velocity against the surface of the blade mounting area. Said method allows the improving of the mechanical features of the component and the inducing of inherent compressive stress into the surface of the component such that the danger of crack formation and propagation in the component is reduced, and the fatigue strength and the life time of the blade mounting areas are increased. 
         [0004]    Due to the contour of the blade mounting area profile like a dovetail or a fir-tree profile, there is a very limited accessibility for a shot peening device. Currently, shot peening of blade mounting areas is performed by using nozzles which are fitted on specific retaining fixtures and peen the blade mounting areas from the outside with a shower-like media stream. During the peening, the peening stream of the nozzles is directed substantially perpendicular to a slot bottom of the blade mounting area. Due to the unique contour shape of the blade mounting area, several areas are hit very well by the peening stream, however some very poorly. An area of difficult accessibility are the pressure flanks of the blade mounting area which are hit by the shot peening media in particular via rebounds from the slot bottom. Therefore, peening with standard outside peening nozzles from outside the component results in a non-uniform peening treatment since the slot bottom and the pressure flange are unequally exposed to the peening stream. In particular for dovetail profiles the unequal alignment of the pressure flange and the slot bottom against the peening stream is a determining factor. 
         [0005]    For providing sufficient strengthening of the pressure flanks with shot peening, it is known to peen the slot bottom very intensively, so that the pressure flanks are peened by the rebounds from the slot bottom with a desired intensity. However, this method may result in a damaging of the slot bottom. Further, no uniform shot peening treatment of the whole blade mounting area in terms of peening intensity, peening coverage, originated surface roughness and residual stresses in the component surface is possible due to the unfavorable hit angel of the peening stream onto the blade mounting area surface. 
         [0006]    From DE 10 2008 010 847 A1 it is known to shot peen blades of blade integrated discs (blisks) with a dual-nozzle unit from a suction side and a pressure side of the blade in one step. For making that possible each peening nozzle has a planar deflection area arranged with an angle to a longitudinal axis of each peening nozzle which redirects peening shot media from moving mainly along the longitudinal axis to a direction essentially vertically to the longitudinal axis. Therefore, the peening shot media can be shot from both sides simultaneous against the both sides of the surface of the blade. 
         [0007]    Ultra-Sonic-Peening is another possible method to strengthen the surface of a blade mounting area. With this method, the treated component surface and a chamber create a hermetically sealed area where an Ultra-Sonic-Peening source imparts a small volume media stream on the part surface randomly, thereby strengthening it. It is a disadvantage of this method that material damages may occur due to the rather big size of the peening elements which may cause deformations in areas with thin material. Further, applying this method is quite costly as for each type of contour a separate chamber is required. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to provide an apparatus and a method for shot peening of blade mounting areas on a rotor arrangement disc by which a more uniformly strengthened surface of the blade mounting area can be achieved in a simple manner and preferably in one process step. 
         [0009]    The object is achieved by the present invention with an apparatus and method according to the features described herein. 
         [0010]    Further advantages, features, and measures are listed herein. The features and measures listed herein can be combined with one another in advantageous ways. 
         [0011]    According to the present invention an apparatus for shot peening of blade mounting areas on a disc of a rotor arrangement comprises a peening nozzle unit which is operatively connectable with a movement device and allows the streaming of a shot peening media along a longitudinal axis from a first end to a second end of the peening nozzle unit, wherein the peening nozzle unit comprises a nozzle outlet which extends at least partially in circumferential direction of the peening nozzle unit, and wherein the peening nozzle unit comprises a deflection arrangement with a deflection area for the shot peening media. The deflection area is at least partially cone or half-hyperboloid shaped over at least a part of the circumferential direction of the peening nozzle unit, such that shot peening media streaming in direction of the longitudinal axis of the peening nozzle unit is passing the nozzle outlet over an angle range in circumferential direction after being deflected by the deflection arrangement. The deflection arrangement is designed as a separate component, and is connected to a cross-member of the peening nozzle unit which is arranged transverse to the longitudinal axis of said nozzle unit. The cross-member forms the second end of the peening nozzle unit and is connected to a particularly cylindrical shaped peening media nozzle base of the nozzle unit via a web. 
         [0012]    The shot peening method according to the invention uses a peening nozzle unit of an apparatus for shot peening of blade mounting areas. This peening nozzle unit is positioned in a slot profile of the respective blade mounting area, and is controlled guided along the contour of the slot profile with a nozzle outlet facing the contour of the slot profile such that the contour of the slot profile is uniformly or at least approximately uniformly peened. 
         [0013]    With using the invention, a blade mounting area profile can be entirely and uniformly impacted by the peening stream, and therefore, uniformly peened. The blade mounting area can be simultaneously peened within its profile cross-section at its pressure flanges, the radius between pressure flange and a slot bottom, and the slot bottom itself with identical peening parameters, i.e. for example a hit angle of the shot peening media stream to the pail surface, and the distance from the nozzle outlet to the part surface. Each blade mounting area can be peened individually with identical peening parameters. 
         [0014]    By use of the invention the peening media stream can be guided directly and controlled onto the part surface without turbulence and peening shadows, and the entire profile of the blade mounting area, in particular a typical dovetail or fir tree profile can be peened uniformly from inside the profile. 
         [0015]    The inventive deflection arrangement can be manufactured in a simple manner at low costs, and can be fixed to the cross-member of the peening nozzle unit by appropriate fastening means, like a screw for example. 
         [0016]    The at least partially cone or mushroom-like half-hyperboloid shaped deflection area of the peening nozzle unit allows advantageously the peening of a wide angle range of the blade mounting area in a single process step. Thus, a uniform peening result in terms of peening intensity, peening coverage, originated surface roughness and residual stresses in the component surface is achieved in a short process time. 
         [0017]    Compared to Ultra-Sonic-Peening the presented apparatus and method are cost saving and applicable for various geometric forms of blade mounting areas. To strengthen the part surface with Ultra-Sonic-Peening, relatively large media are necessary to create the required kinetic energy. Due to the smaller size of the peening media, the invention allows the treatment of smaller fillet radii. In addition, small part edges can be treated without danger to be deformed by large media. 
         [0018]    In a preferred embodiment of the apparatus according to the invention, the full circumference of the deflection arrangement is provided with the deflection area. Hereby all surfaces of the blade mounting area profile including the slot bottom, the pressure flanks and the radii between slot bottom and pressure flanks can be strain-hardened when inserting the nozzle unit into the profile of the blade mounting area and leading therein in longitudinal extension direction of the blade mounting area. 
         [0019]    Advantageously, the deflection arrangement is designed as an at least substantially rotation-symmetric, in particular full rotation-symmetric component in order to achieve an utmost uniformly distributed deflection of the peening shot media. Hereby, the peening elements of the shot peening media comprise substantially the same velocity and energy, and an interaction of the peening elements as well as a change of their characteristics after deflection can be avoided. Further, turbulences and peening shadows can be avoided. 
         [0020]    It is advantageous if the web covers only a small circumferential area of the nozzle unit. The thinner the web or fillet is designed, the less limited is the effective angle range of the nozzle outlet and thereby the treatment area. For example, the web which can be formed integrally with the cross-member may cover an angle of about 20° or 30° of the perimeter. 
         [0021]    In order to achieve a maximum angle of peening media distribution, the nozzle outlet may be formed extending over the full circumference of the nozzle unit with exception of the circumferential area covered by the web or fillet if such one is provided. 
         [0022]    The deflection area is preferably inclined towards the longitudinal axis of the nozzle unit in movement direction of the shot peening media by an angle of at least 30°, in particular circa 45°. The smaller the chosen inclination angle, the smaller is the energy loss of the peening media when being deflected at the deflection area. The skilled person may select the deflection angle most appropriate for the respective application in dependence of the desired characteristics of the peening media stream and the desired surface characteristics. 
         [0023]    In an advantageous embodiment, the deflection arrangement of the inventive apparatus may comprise an area which extends at least approximately in direction of the longitudinal axis of the nozzle unit, and which comprises a tip directed against the movement direction of the shot peening media. Hereby, an cross section angle of the tip may be in a range between 40° and 60°. 
         [0024]    In order to facilitate the joining of the deflection arrangement and the nozzle unit, a chamber-bevel can be provided on the deflection arrangement at its end portion facing the cross-member and/or on the cross-member at its side facing the nozzle outlet. 
         [0025]    The deflection arrangement and/or the peening media nozzle base of the nozzle unit is preferably made of hardened steel. An advantageous steel is known in the Register of European Steels under material number 1.2379 X153CrMoV12. The used materials should have a Rockwell hardness higher than 60 HRC. 
         [0026]    In a preferred embodiment of the inventive apparatus, the peening nozzle unit is dimensioned for insertion, at least with its deflection arrangement, into a slot profile, particularly with a dovetail-like or fir tree-like contoured cross-section, of the blade mounting area. 
         [0027]    For accurate and repeatable process results also on a plurality of blade mounting areas, the movement device or the nozzle device assembled to the movement device, respectively, is preferably connected to a control unit which is programmed according to the geometric parameters of the blade mounting area such that the peening nozzle unit is guided at least with its deflection arrangement within a profile of the blade mounting area along its contour. 
         [0028]    In a preferred embodiment of the inventive method, the peening nozzle unit is controlled guided substantially in extension direction of the blade mounting area by controlled driving the movement device. Hereby, the peening nozzle unit can, at least substantially, be aligned with its longitudinal axis to the extension direction of the blade mounting area during peening operation. 
         [0029]    Advantageously, the guiding of the peening nozzle unit is performed in dependence of signals of a controlling unit which controls the guiding of the peening nozzle unit according to stored geometric parameters of the blade mounting area profile, in particular dovetail or fir-tree like profiles. 
         [0030]    If a peening nozzle unit used with a cone or hyperboloid shaped deflection arrangement joint to other parts of the nozzle unit by a web or fillet covering a part of the perimeter of the nozzle unit and its deflection arrangement, the inventive method is advantageously performed by controlled guiding the nozzle unit within the blade mounting area profile with the fillet on a side of the nozzle unit facing away the surface to be peened. 
         [0031]    The features, functions and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments. Advantageous embodiments as well as a preferred mode of use, and further details and advantages thereof will best be understood by reference to the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  schematically shows a perspective view of an apparatus for controlled shot peening of blade mounting areas on a rotor arrangement disc of an aircraft gas turbine; 
           [0033]      FIG. 2  schematically shows a perspective view of the apparatus of  FIG. 1  during peening operation on a blade mounting area of a partly shown disc of a rotor; 
           [0034]      FIG. 3  schematically shows in more details a part of  FIG. 3  another point of view; 
           [0035]      FIG. 4  shows a simplified perspective view of a part of  FIG. 2  a further point of view; 
           [0036]      FIG. 5  is a longitudinal cross-section of a peening nozzle unit of the apparatus shown in  FIG. 1  to  FIG. 4 ; 
           [0037]      FIG. 6  is a simplified top view of peening nozzle unit of  FIG. 5 ; and 
           [0038]      FIG. 7  shows a further embodiment of a peering nozzle unit for the apparatus of  FIG. 1  in a longitudinal cross-section. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]      FIG. 1  shows an apparatus  1  for controlled shot peening of part surfaces which comprises a peening nozzle unit  5  connected to a movement device  3 . The movement device  3  is holding the peening nozzle unit  5  and guiding said unit preferably by means of a robot, e.g. a typical 6-axis robot, in dependence of geometric data output by a control unit  4  of the movement device  3 . 
         [0040]    The peening nozzle unit  5  comprises a cylindrical peening nozzle base  7  which can be seen e.g. in  FIG. 5 . The peening nozzle base  7  is designed tube-like for leading a shot peening media  9  which comprises in particular ball-shaped peen particles  11  of metal, glass, ceramic or another appropriate material. 
         [0041]    Coming from a (not-shown) peen particles source, the shot peening media  9  is entering the peening nozzle base  7  at an inlet port  13  which is forming a first end of the peening nozzle unit  5 . From said inlet port  13 , the shot peening media  9  is accelerated within the peening nozzle base  7  substantially parallel to a longitudinal axis  25  of the peening nozzle  5  in direction of a nozzle outlet  15 . 
         [0042]    In the region of the nozzle outlet  15 , a deflection arrangement  17  is provided which has the design of a deflector cone and is fixed by a screw connection  23  to a disc-shaped cross-member  21  which forms a second end of the peening nozzle unit in longitudinal direction. Said cross-member  21  is connected to the peening nozzle base  7  by means of a web or fillet  19 . In the cross-section shown in  FIG. 5 , the cross-member  21  and the web  19  are forming substantially a L-shape, and are integral parts of the peening nozzle  5 . 
         [0043]    In the shown embodiments, the deflection arrangement  17  is a rotation-symmetric body positioned coaxially to the longitudinal axis  25  of the peening nozzle base  7 ,  1 ,e, centered in the peening nozzle  5 . Further, the deflection arrangement  17  comprises a nail-like shape with a head portion  27  by which the deflection arrangement  17  is connected with the cross-member  21 . 
         [0044]    On a side of the deflection arrangement  17  facing the first end of the nozzle unit  5  with the inlet port  13 , the deflection arrangement  17  comprises a cylindrical shaft  29  which is centered in the peening nozzle base  7  and which comprises a tip or point  31  facing the inlet port  13 . Said tip  31  is cone-shaped with a cross-section angle  33  of about 60° in the shown embodiment. 
         [0045]    At its head portion  27 , the deflection arrangement  17  comprises an inclined deflection area  39  which is joining a cylindric lateral area  35  of the shaft  29  with a transition radius  37 . 
         [0046]    Here, the deflection area  39  is cone-shaped, i.e. radially inclined towards the longitudinal axis  25  of the nozzle unit  5  by an angle  41  of approximately 45°, and abuts the lateral area  35  of the shaft  29  by a transition radius  37  of R5. 
         [0047]    In another embodiment the surface of the deflection area can also be curved radially outwards, forming a mushroom-like half-hyperboloid. 
         [0048]    In order to facilitate the inserting of the deflection arrangement  17  into the peening nozzle unit  5  through the nozzle outlet  15 , the deflection arrangement  17  is provided with a circular chamber-bevel or bezel  43  at its head portion side  27  facing the cross-member  21 . Further, also the cross-member  21  is designed with a chamber-bevel  45  at its edge facing the nozzle outlet  15 . 
         [0049]    In operation, the shot peening media  9  is streaming from the inlet port  13  in direction of the longitudinal axis  25  of the peening nozzle base  7  towards the deflection area  39  as shown by arrows in  FIG. 5 . At the deflection area  39 , the peen particles  11  of the shot peening media  9  bouncing against the deflection area  39  or the transition radius  37  are deflected and rebounded from the deflection arrangement  17 . In the area of the transition radius  37 , the blasted peen particles  11  are deflected with different angles towards the longitudinal axis  25  depending on their bouncing point. Therefore, peen particles  11  having a different radial distance towards the longitudinal axis  25  of the nozzle unit  5  are blasted with different deflection angles through the fan-shaped nozzle outlet  15 . 
         [0050]    In the embodiments shown in the drawings, the inclination of the deflection area  39  and the transition radius  37  are chosen such that the relation between the deflection angle and the impact on the surface of the component, i.e. an energy loss of the peen particles, is an advantageous compromise between these parameters. 
         [0051]    The shown deflection arrangement  17  with the deflection area  39  and the radius  37  is a full rotation-symmetric component, thus, the peen particles  11  are deflected by the deflection arrangement  17  around its perimeter in all radial directions. Hereby, the peen particles  11  are approximately uniformly distributed in circumferential direction so that the deflected peen particles  11  are providing approximately the same velocity and energy. Only the few peen particles  11  which are rebounded into direction of the web  19  are prevented by the web  19  from streaming out of the peening nozzle unit  5 . Due to the ball-shaped design of the peen particles  11 , the web  19  is not significantly strained by abrasion when hit by the peen particles  11 . As the peening nozzle unit  5  with the deflection arrangement  17  is made of hardened steel with a Rockwell hardness higher than 60 HRC, the overall wear and abrasion of the peening nozzle unit  5  is very low. 
         [0052]    As shown more detailed in  FIG. 2  to  FIG. 4 , the peening nozzle unit  5  is used for the strain-hardening of blade mounting areas  51  on a fan disc or a turbine disc  53  of a rotor arrangement  55  of an gas turbine. Hereby, the peening nozzle unit  5  is controlled guided by the movement device  3  substantially in extension direction of the blade mounting area  51  of the disc  53 . Each blade mounting area  51  comprising a slot bottom  57 , lateral pressure flanks  59  and a radius  61  connecting the slot bottom  57  with the pressure flanks  59  can be peened from inside by means of the peening nozzle unit  5 . For this, the peening nozzle unit  5  is driven by the robot of the movement device  3  into an interior space  63  of the blade mounting area profile such that the peen particles  11  are bouncing against the surfaces of the slot bottom  57 , the pressure flanks  59 , and the radius  61  after streaming out of the nozzle outlet  15 . During this operation, the web  19  is positioned on a side of the nozzle unit  5  facing away from the slot bottom  57 . Hereby, a whole surface  65  of the blade mounting area  51  can be peened by the peening nozzle unit  5  in a single movement operation of the peening nozzle unit  5  along the profile contour of the blade mounting area. 
         [0053]    After the treatment the endurance strength of the rotor arrangement  55  is improved, and an effective prevention of a crack formation and crack propagation is achieved. Further, as the peen particles  11  are comprising substantially the same velocity and energy, the whole surface  65  of the blade mounting area is highly uniformly peened in regard of peening intensity, peening coverage, originated surface roughness and residual stresses in the component surface  65 . 
         [0054]      FIG. 7  shows an alternative embodiment of a peening nozzle unit  81  which comprises a substantially analog structure to that of the peening nozzle unit  5 . However, the peening nozzle unit  81  of  FIG. 7  differs in the design of a deflection arrangement  83  from the embodiment shown in the previous figures. In the following, only the features are described in detail in which the deflection arrangement  83  differs from the deflection arrangement  27  of the embodiment shown in  FIGS. 5 and 6 . The further constructional features comply with these of the first embodiment. 
         [0055]    The deflection arrangement  83  comprises a deflection area  85  which is inclined towards the longitudinal axis  25  of the peening nozzle unit  83  by an angle  87  of 30°. Thereby, the peen particles  11  are less deflected by the deflection arrangement  83  and are moved with a higher velocity and energy through the nozzle outlet  15  while having the same starting velocity as the peen particles  11  in the previous described embodiment. 
         [0056]    Further, the deflection arrangement  83  is more cone-shaped than nail-shaped with a head portion  95  facing the cross-member  21  of the nozzle unit  81  and a shaft  29  which is conically tapered towards the inlet port  13  of the nozzle unit  81  and which is shortened compared to the deflection arrangement of the previous described embodiment. The head portion  95  of the deflection arrangement  83  as well as the cross-member  21  is providing a chamber-bevel  97  or  99  respectively for easier installation. 
         [0057]    The shaft  89  comprises a tip  93  which is centered in the peening nozzle base  7  and is shaped with a cross section angle  95  of about 40°. Also here, the surface of the shaft  89  is joining the conical surface of the head portion  95  by a transition radius  95 . 
         [0058]    The whole peening nozzle unit  81  of  FIG. 7  is smaller dimensioned compared to the peening nozzle unit  5  of  FIG. 1  to  FIG. 6 , and therefore, the smaller peening nozzle unit  81  is especially suitable for use in smaller dimensioned blade mounting areas  51 .
     1  Apparatus     3  Movement device     5  Peening nozzle unit     7  Peening nozzle base     9  Shot peening media     11  Peen particles     13  Inlet port     15  Nozzle outlet     17  Deflection arrangement     19  Web     21  Cross-member     23  Screw connection     25  Longitudinal axis     27  Head portion of the deflection arrangement     29  Shaft of the deflection arrangement     31  Tip of the shaft     33  Tip angle     35  Surface of the shaft     37  Radius     39  Deflection area     40  Angle     41  Angle     43  Chamber-bevel     45  Chamber-bevel     51  Blade mounting area     53  Disc     55  Rotor arrangement     57  Slot bottom     59  Pressure flank     61  Radius     63  Interior space     65  Surface of blade mounting area     81  Peening nozzle unit     83  Deflection arrangement     85  Deflection area     87  Angle of the deflection area     89  Shaft     91  Angle     93  Tip of the shaft     94  Radius     95  Head portion of the deflection arrangement     97  Chamber-bevel     99  Chamber-bevel