Abstract:
A method for producing a centrifugal pump impeller having a base plate, which is a single piece with pump blades and a cover plate, which consists of a thermoplastic material, wherein contact areas are available, which are heated and melted by means of ultrasonic excitation and form a close bonded connection after cool-down. The objective of the invention is to ensure inherent stability with the individual parts and a simple and reliable pre-assembly as well as a fixed mechanical connection, wherein only a small amount of excitation energy is required, with a centrifugal pump impeller comprising a base plate and cover plate.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
       [0001]    The invention relates to a method for producing a centrifugal pump impeller having a base plate, which is a single piece with pump blades and a cover plate. 
       (2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
       [0002]    Ultrasonic welding methods have long been used to join together thermoplastics. This is part of the group of friction welding methods and they differ by the type of friction generation. With friction welding, generally a quick rotary movement of a part to be joined together is executed upon contact with the second part to be joined together and thereby sufficient heat is generated in order to melt the joining zone. For parts that are not rotationally symmetrical, friction welding is not usable or is used only in rare cases. In this case, the ultrasonic welding method is better, because oscillations of very low amplitude are used here to obtain the friction heat and therefore even complicated shapes can be used as the welding zone. However, it is important that it be possible to keep the ultrasonic energy concentrated onto as small a friction surface as possible. 
         [0003]    U.S. Pat. No. 8,793,872 discloses a centrifugal pump impeller in which the pump vanes are equipped with narrow rib-like protrusions and the cover plate forms a smooth cone-shaped surface. The smooth surface means that there is no possibility of simple pre-adjustment and pre-assembly of the parts to be joined together. In addition, there may be molding inaccuracies during cool-down of the cast cover plate. 
         [0004]    An object of the present invention is to ensure inherent stability with the individual parts and a simple and reliable pre-assembly as well as a fixed mechanical connection, wherein only a small amount of excitation energy is required, with a centrifugal pump impeller comprising a base plate and cover plate. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The objective of the present invention is achieved according to a method for producing a centrifugal pump impeller having a base plate, which is a single piece with pump blades and a cover plate, which consists of a thermoplastic material, wherein contact areas are available, which are heated and melted by means of ultrasonic excitation and form a close bonded connection after cool-down. 
         [0006]    The ribs on the cover plate serve as reinforcement ribs. In this manner, the cover plate can be produced in a more accurate shape and a sonotrode can be evenly placed on the cover plate to create ultrasonic vibrations and to apply this vibrational energy to a solid. Because the ribs are a component of the cover plate, the adjacent areas automatically serve as locating surfaces, particularly if these areas are not melted for geometric reasons. To this end, the ribs are significantly narrower at their base than the pump blades at their upper surfaces opposite the ribs. 
         [0007]    In further embodiments of the present invention, a provision is that two locating surfaces, which extend to both sides of the ribs, are provided in the cover plate. In this manner, the pump blades can be supported on the cover plate. Even better support is ensured when the locating zones connecting in the longitudinal direction of the ribs also serve as support zones. The ribs are completely surrounded by support surfaces/support zones in this manner. This leads to a defined geometric allocation between the base plate and the cover plate. 
         [0008]    In a second embodiment of the invention, the ribs are each arranged in a groove-like recess in the cover plate. The recess serves as an additional reinforcement element and primarily as a joining aid. The width of the recess here is significantly larger than the width of the ribs so that some play remains. 
         [0009]    In a refinement of the second embodiment, a recess-like groove extends along the ribs between the locating surfaces and the ribs. These grooves serve to concentrate the ultrasonic energy on the weld point even better. In order to increase the strength of the welded connection and accelerate the melting process, an impeller blade is provided instead of two parallel extending ribs. 
         [0010]    Ultrasonic welding can also lead to the formation of particles, which is why it is beneficial for the groove-like recess to be designed only 0.1 mm to 0.4 mm wider than the pump blades. In this manner, particularly larger particles remain caught within the recess. 
         [0011]    A further provision is that the recess becomes narrower as the depth increases, and the pump blades taper at their ends facing toward the cover plate. This causes the gap between the pump blades and the recess to narrow and the resulting particles are additionally caught and partially melted and firmly bonded together. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS 
         [0012]    The invention is better understood by reading the following detailed description of the preferred embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which: 
           [0013]      FIG. 1  shows a partial sectional view of a first embodiment of the invention; 
           [0014]      FIG. 2  shows a partial sectional view of a second embodiment of the invention; 
           [0015]      FIG. 3  shows a partial sectional view of a first variation of the second embodiment of the invention; 
           [0016]      FIG. 4  shows a partial sectional view of a second variation of the second embodiment of the invention; 
           [0017]      FIG. 5  shows a view of a cover plate of a centrifugal pump impeller; 
           [0018]      FIG. 6  shows a view of a base plate of the centrifugal pump impeller; 
           [0019]      FIG. 7  shows a first assembly position between the base plate and the cover plate; 
           [0020]      FIG. 8  shows a second assembly position between the base plate and the cover plate; 
           [0021]      FIG. 9  shows an enlarged section of  FIG. 7 ; 
           [0022]      FIG. 10  shows an enlarged section of  FIG. 8 ; 
           [0023]      FIG. 11  shows a partial sectional view through a pin; 
           [0024]      FIG. 12  shows the top view of the assembled centrifugal pump impeller; and 
           [0025]      FIG. 13  shows a three-dimensional representation of the assembled centrifugal pump impeller. 
       
    
    
       [0026]    Note: The reference numbers with index alpha characters and the corresponding reference numbers without index characters refer to details with the same name in the drawings and the drawing description. This reflects use in another embodiment or the prior art, and/or the detail is a variant. The reference number list contains only reference numbers without index characters for the sake of simplicity. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
         [0028]      FIG. 1  shows a partial sectional view of a first embodiment of a centrifugal pump impeller  1   a , having a base plate  2   a  and a cover plate  3   a , wherein the base plate  2   a  is a single piece with pump blades  4   a  having a trapezoidal cross-section and the cover blade  3   a  is a single piece with protruding ribs  5   a  (one of which is visible). The base plate  2   a , the cover plate  3   a , and the pump blades  4   a  define a liquid channel, through which a conveyed medium, such as a coolant, can be conveyed. The ribs  5   a  protrude from the cover plate surface such that locating surfaces  7   a  emerge laterally from the ribs  5   a , with which an upper surface  10   a  of the pump blade  4   a  can make contact during and/or after a welding process. The minimum width d 1  of the pump blades  4   a , which is deemed present at the upper surface  10   a , is significantly greater than the maximum width d 2  of the ribs  5   a . The ribs  5   a  are also characterized as energy directors. The width of the ribs  5   a  reduces in the direction of the pump blades  4   a  and form, as illustrated, a reverse triangular roof shape. If a sonotrode is placed on the cover plate  3   a  and the cover plate  3   a  is placed into ultrasonic oscillation, the oscillation energy is concentrated onto the points of the ribs. They heat up and start to soften. The adjoining areas of the upper surface  10   a  of the pump blades  4   a  are melted. In doing so, both parts to be joined together are moved toward one another such that a gap  11   a  maintained by the ribs  5   a  closes and a close connection of the adjoining material areas is formed. This process is continued until the upper surface  10   a  of the pump blades  4   a  makes contact with the locating areas  7   a  of the cover plate. In doing so, excess material of the ribs  5   a  may be displaced into the gap  11   a.    
         [0029]      FIG. 2  shows a second embodiment of the centrifugal pump impeller  1   b  having a base plate  2   b  and a cover plate  3   b . The base plate  2   b  is formed identically to  FIG. 1 . The cover plate  3   b  has longitudinal recesses  9   b , which correspond to the pump blades  4   b  of the base plate  2   b . Within the recesses  9   b , ribs  5   b  protrude from the base of the recess  9   b , but do not reach the surface  13   b  of the cover plate  3   b . In this manner, the recesses  9   b  enable a pre-centering of the base plate  2   b  and the cover plate  3   b  while interacting with the pump blades  4   b . The pre-centering here is not carried out by the ribs  5   b  but rather by sidewalls  14   b  of the recesses and by the pump blades  4   b . Furthermore, the recesses  9   b  and the ribs  5   b  may improve the inherent stability of the cover plate  3   b . The base  12   b  of the recess  9   b  simultaneously forms the locating surface  7   b.    
         [0030]      FIG. 3  shows a first variant of the second embodiment of the centrifugal pump impeller  1   c  having a base plate  2   c  and a cover plate  3   c . The base plate  2   c  corresponds to the embodiment of  FIGS. 1 and 2 . The cover plate  3   c  has a recess  9   c  similar to  FIG. 2 . There are two recess-like grooves  8   c , which border a rib  5   c  laterally, within the recess  9   c.    
         [0031]      FIG. 4  shows a second variant of the second embodiment of the centrifugal pump impeller  1   d  having a base plate  2   d  and a cover plate  3   d . The base plate  2   d  corresponds to the embodiment of  FIGS. 1, 2, and 3 . The cover plate  3   d  has a recess  9   d  similar to  FIGS. 2 and 3 . There are two ribs  5   d , which are bordered by a clearance  15   d , within the recess  9   d . The base  12   d  of the recess  9   d  forms the locating surfaces  7   d , which border an axial feed during the welding process. The second rib improves the mechanical strength of the connection between the base plate  2   d  and the cover plate  3   d.    
         [0032]      FIG. 5  shows a cover plate  3   b  of the second embodiment according to  FIG. 2 , shown from the side to be welded. The cover plate  3   b  has a central opening  16   b , through which the medium to be conveyed can flow. The cover plate  3   b  has a disc shape in its projected image and has seven recesses  9   b . One rib  5   b  protrudes from each recess  9   b . The length of the ribs  5   b  is significantly shorter than the length of the recesses  9   b . The ribs  5   b  are less than half the length of the recesses  9   b  and extend from a peripheral area toward the inside in the shape of a spiral. This results in locating zones  23   b , which enable a reliable and precise alignment of the parts to be joined, on both sides of the ribs  5   b  in their longitudinal direction. Additional locating surfaces  7   b  on the side of the ribs  5   b  (reference numbers only indicated on one rib) enhance this effect and result in a defined smooth locating surface. The recesses  9   b  correspond to pump blades  4   b  as shown in  FIG. 6 . Two recesses  9   b  additionally have mortises  17   b , which serve assembly in the correct angular position and a torsionally resistant connection. A notch  22   b  enables the optical detection and positionally correct alignment of the cover plate  3   b  during assembly. 
         [0033]      FIG. 6  shows a base plate  2   b  with pump blades  4   b  and pins  6   b . The pins  6   b  are used for access into the mortises  17   b  of  FIG. 5 . An inner ring  18   b  extends from the drawing plane in the center of the base plate  2   b . The inner ring  18   b  is a single piece with the base plate  2   b  and adjoins a ring-shaped inflow area of the conveyed medium into the centrifugal pump impeller. A notch  24   b  at the edge of the base plate  2   b  enables the optical detection and positionally correct alignment of the base plate  2   b  during assembly. 
         [0034]      FIG. 7  shows a sectional view through the centrifugal pump impeller  1   b  with the base plate  2   b  and the cover plate  3   b  of the second embodiment. The representation shows the base plate  2   b  and the cover plate  3   b  in a first assembly position, wherein there is an space between the parts to be joined, particularly the pump blades  4   b  and the ribs  5   b.    
         [0035]      FIG. 8  shows the same arrangement as  FIG. 7 , wherein the base plate  2   b  and the cover plate  3   b  are shown in a second assembly position, in which the pump blades  4   b  and the ribs  5   b  make contact and the welding process is initiated. Furthermore,  FIGS. 7 and 8  show the opening  16   b , the inner ring  18   b , an outer ring  21   b , a bushing mount  19   b , and a brass bushing  20   b . The bushing  20   b  is used to press onto a permanent magnetic rotor. The brass bushing  20   b  is injection-molded into the base plate  2   b  for this purpose. 
         [0036]      FIG. 9  shows an enlarged section A of  FIG. 7  in the connection area, with the base plate  2   b , the cover plate  3   b , a pump blade  4   b , and a rib  5   b , wherein the pump blade  4   b  has an space with respect to the rib  5   b.    
         [0037]      FIG. 10  shows an enlarged section B of  FIG. 8  in the connection area, with the base plate  2   b , the cover plate  3   b , a pump blade  4   b , and a rib  5   b , wherein the pump blade  4   b  and the rib  5   b  are making contact with one another. 
         [0038]      FIG. 11  shows a sectional view through a pin  6   b  as a one-piece component of the base plate  2   b  in the assembled state. The pin  6   b  penetrates into the mortise  17   b  of the cover plate  3   b.    
         [0039]      FIG. 12  shows a top view of the assembled centrifugal pump impeller  1   b , with the base plate  2   b , the cover plate  3   b , the pin  6   b , the mortises  17   b , the inner ring  18   b , and the outer ring  21   b . The cover plate  3   b  has a notch  22   b , which is used for optical detection of the angular position during assembly. 
         [0040]      FIG. 13  shows a three-dimensional representation of the assembled centrifugal pump impeller  1   b , with the base plate  2   b , the cover plate  3   b , the pin  6   b , the mortises  17   b , the blades  4   b , the inner ring  18   b , the outer ring  21   b , and the notch  22   b.    
         [0041]    It is to be understood that the present invention is not limited to the illustrated embodiments described herein. Various types and styles of user interfaces may be used in accordance with the present invention without limitation. Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Centrifugal pump impeller 
           2  Base plate 
           3  Cover plate 
           4  Pump blade 
           5  Rib 
           6  Pin 
           7  Locating surface 
           8  Groove 
           9  Recess 
           10  Upper surface 
           11  Gap 
           12  Base 
           13  Surface 
           14  Sidewall 
           15  Clearance 
           16  Opening 
           17  Mortise 
           18  Inner ring 
           19  Bushing mount 
           20  Brass bushing 
           21  Outer ring 
           22  Notch 
           23  Locating zone 
           24  Notch