Abstract:
A flow-conducting component such as a pump impeller is provided. Passages between vanes of the flow-conducting component include notches in the form of transitions between the vane and a common surface, such as a cover disk. The notches include a transition surface having a geometric configuration determined in accordance with a calculated load spectrum along at least a portion of the length of the notch and in accordance with a particular geometric pattern.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage of PCT International Application No. PCT/EP2015/067235, filed Jul. 28, 2015, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2014 215 089.2, filed Jul. 31, 2014, the entire disclosures of which are herein expressly incorporated by reference. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
       [0002]    The present invention relates to the geometric configuration of a flow-conducting component as well as the production of a such component. 
         [0003]    Flow-conducting components are known in various embodiments. Depending upon operating conditions, that is to say operating pressure, conveying medium, medium temperature or the like, the component is manufactured from specific materials. The static construction of the housing is likewise greatly dependent upon the field of use. 
         [0004]    At sections which are particularly loaded and above all at the transitions between different sections, in particular mechanical stresses can be built up which lead to shortening of the service lives. Stresses can be substantially reduced by an advantageous configuration of the notch, but this necessitates processing of the transition section with tools. 
         [0005]    European patent publication no. EP 1 785 590 A1 shows the configuration and production of an impeller of a pump or turbine, wherein attention is focused in particular on the design of the notches. The impeller is welded in a plurality of locations, wherein stresses are directly prevented. During production, the procedure necessitates access to the notches with corresponding tools. 
         [0006]    Both casting technology and also joining technology quickly reach the limits for flow-conducting components, since in some instances the notches are accessible only with difficulty and/or are not directly accessible at all from the exterior. This leads to considerable restrictions in the configuration of the geometry of the component. 
         [0007]    The object of the invention is to find and to apply, for the mechanical loading at the transition points of a flow-conducting component, especially in the region of the notches, a geometric configuration which can be produced simply and cost-effectively. 
         [0008]    The solution provides that the load spectrum of the notch is determined based on calculations, forming the notches geometrically according to their mechanical load, in particular where they are accessible only with difficulty and/or are not directly accessible at all from the exterior. 
         [0009]    In this case it is advantageous that the design of the flow-conducting part, which may for example be an impeller for a centrifugal pump, can be free from the restriction of conventional requirements. Limitations due to casting technology and/or joining processes do not have to be taken into consideration, since only the mechanical and hydraulic properties are significant. Such freedom from traditional design principles enables a completely new configuration of the impeller. 
         [0010]    In a further embodiment, in the flow-conducting component the notch is configured so that a transition in the component from a first section A to a second section B encloses an angle α. The angle bisector of the angle α is ascertained, wherein along this angle bisector a point P is determined. In each case a perpendicular of one of the arms (A, B) forming the angle α passes through the point P. Through the point P a straight line is applied to the respective perpendicular with an angle of 45°, wherein by the intersection of these straight lines with the respective arms (A, B) in each case a distance (S, S′) is fixed. The respective centers fix the points Q, Q′, wherein at the points Q, Q′ in each case straight lines are applied with an angle of 22.5° to the distances S, S′, intersecting the arms (A, B) in the points R, R′. The envelope E, E′ of this structure predetermines the geometric configuration of the notch. 
         [0011]    This simple construction method makes it possible very simply to determine a geometry which in a direction-dependent manner takes into account the differential mechanical load in the component. Impinging forces are analyzed under the effect of the conveyed medium and the operating conditions provided, wherein minimum and maximum values are determined. According to these values the mechanical stability required for the impeller is determined. The method of calculation predetermines the geometric configuration and thus also the use of material and the machining of workpieces. 
         [0012]    In an advantageous embodiment the flow-conducting component is produced by a generative process, wherein in particular metal powders are joined to form a component by a beam melting process such as for example laser or electron beam melting. This has the advantage that the impeller can be produced very simply and nevertheless in a very stable manner. Said processes enable the production of fluid-tight components with the possibility of substantial details. In this process a special surface structure can be additionally applied to the components, for example a shark skin which additionally improves the mechanical and hydraulic properties. 
         [0013]    In a further advantageous embodiment, in the flow-conducting component at least one notch is arranged in the interior of the component, in particular in a cavity and/or an undercut. This has the advantage that in the geometric configuration of the component locations can be advantageously formed which are not accessible for the mechanical post-processing. This detailed configuration enables the production of components which are mechanically more resilient with a reduced use of material. 
         [0014]    In a further embodiment the flow-conducting component is a pump component, in particular of a centrifugal pump. The geometric configuration is advantageous in particular in the case of impellers and/or guide wheels of centrifugal pumps. These parts are subjected to particularly high mechanical loads. The transitions between a guide/impeller vane and a cover disc are sometimes accessible with great difficulty. In a centrifugal pump, in addition to the purely geometric overall structure the surfaces of the individual impeller vanes can of course also be freely configured, so that the boundary layer between the impeller and the fluid can be influenced. In the case of inducers it is also possible inter alia to make components hollow, so that considerable savings of material are possible. The component must then obtain its mechanical stability through the corresponding configuration of the struts inside the hollow spaces, as well as the transitions between mechanically stabilizing sections according to the above design rule. 
         [0015]    In a further advantageous embodiment the component is produced from an iron-based material. This enables a simple and cost-effective production on tools which are already ready for mass production. The iron-based material is advantageously an austenitic or martensitic or ferritic or duplex material. This enables the production of corrosion-resistant components. The production of the powders required for the aforementioned high-energy beam processes is likewise cost-effective and simple. This is even more apparent if the iron-based material is advantageously a gray or spheroidal graphite iron material. 
         [0016]    Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  illustrates geometric relationships of a flow-conducting component in accordance with the present invention. 
           [0018]      FIGS. 2A, 2B  illustrate oblique views of a flow-conducting component in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows an arbitrary location at which the contour of a component transitions from a first zone  1  discontinuously into a second zone  2 , wherein the two sections enclose an angle  3 . At this point of discontinuity considerable stresses develop which can be influenced significantly by a suitably designed geometric configuration. In the case of a predefined breaking point the stresses can be used in order to allow the component to break in a targeted manner at the point of discontinuity under a threshold load. Usually, however, the opposite is desirable, and the point of discontinuity should be sufficiently resilient against the applied forces. A so-called engineer&#39;s notch is traditionally provided here which shapes the sharp angle by a curve with a chosen radius. 
         [0020]    With reference to various observations in nature, a method for designing the notch has been developed which is simple to construct and nevertheless absorbs the forces at the point of discontinuity so that the loads of the component can be very considerably reduced with minimal expenditure on design and manufacture. In this connection an angle bisector  4  is defined through the angle  3 . A point  5  is selected on this angle bisector  4 . Through this point  5  the straight lines  6  and  7  are placed perpendicular to the sections  1  and  2 . With respect to these straight lines  6  and  7 , at the point  5  straight lines which intersect the sections  1  and  2  are applied at the angle  8  of 45°, wherein the intersection point  11  is fixed in the section  2 . The distance between the point  5  and the point  11  is halved, so that the point  9  is obtained, at which a straight line is applied at the angle  10  of 22.5° and intersects the section  2  at point  13 . The distance between the point  9  and the point  5  is again halved, so that the point  12  is obtained, at which a straight line is applied at the angle  14  of 12.2° and intersects the section  2  at point  15 . The envelope of this structure produces a contour which has different points of discontinuity. This would be rather disadvantageous for machining. In a generative production method, where the workpiece is produced by linking together individual volume elements or material layers, operating in discrete units, such a structure can be ideally implemented in a workpiece. 
         [0021]    The presented structure is based upon a non-symmetrical loading of a component. If the component were symmetrically loaded, for example by alternating left/right running, then the structure can be supplemented symmetrically in the direction of the first section  1  in an analogous manner. 
         [0022]      FIGS. 2A, 2B  show an example of an application for the method of construction and production according to the invention. In  FIG. 2 a    an impeller  16  is illustrated, such as is used for example in a centrifugal pump. The impeller  16  has a hub region  17  and a cover disc  20 . Further details can be seen from  FIG. 2 b   . The impeller vanes  18  and a further cover disc can be seen here. Such an impeller with the two cover discs  20  and  19  is designated as a closed impeller. Both in the region of the impeller hub  17  and also in the region of the cover discs  19  and  20 , in each case the impeller vanes  18  have transitions  21  and  22  which correspond to the ones described in  FIG. 1 . In the region of the cover disc  19  the transition  21  can be described so that the surface of the cover disc  19  constitutes the first section  1  and the impeller  16  constitutes the second section  2 . The forces occurring at the point of discontinuity between the two sections  1  and  2  can be the determined from the parameters of the impeller, the liquid of the pump and the application. With reference to these forces the point  5  is fixed in the notch to be constructed. The notch is constructed with this point. If the impeller  16  is produced for example in a  3 D printing process, the contours of the transitions  21  and  22  can be produced at each location on the impeller with the precision of the resolution of the printing process, without any post-processing being necessary. This particularly advantageous contour, which could not be produced with corresponding accuracy of shape by conventional cutting processes, can be constructed even at locations which could not even be reached with tools for post-processing, which initially is not directly apparent from  FIG. 2 . 
         [0023]    The presented construction and production principle links the effect of a generic  3 D printing production method, which operates in principle with separate elements in which individual voxels or layers on a workpiece are joined, with a method for optimizing a discontinuous surface geometry. As a result it is possible to omit a further post-processing of the workpiece, in which the individual layers of the production must be “smoothed” to give a continuous body. 
         [0024]    The application in the illustrated closed impeller already shows the advantages in the production and the potential for saving material with careful design. Particularly advantageously, the method according to the invention can be applied in an interior which is no longer accessible at all from the exterior after production. 
         [0025]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  first section 
           2  second section 
           3  angle 
           4  angle bisector 
           5  point 
           6  right angle 
           7  right angle 
           8  angle of 45° 
           9  point 
           10  angle of 22.5° 
           11  intersection point 
           12  point 
           13  point 
           14  angle of 12.25° 
           15  point 
           16  impeller 
           17  impeller hub 
           18  impeller vanes 
           19  cover disc 
           20  cover disc 
           21  transition 
           22  transition