Abstract:
A rotary impeller assembly is for a fluid machine and includes a support member having an outer surface and blades connected to the support member. Each blade includes first and second integral portions, the blade first portion having a first thickness and being spaced from the base surface and the blade second portion is disposed against the support member outer surface and has a second thickness. The second thickness is substantially greater than the first thickness such that the blade has greater stiffness proximal to the support and a lesser stiffness generally distal from the support. Preferably, the blades are connected with the support welds between each blade sidewall and the support member. Further, each blade first portion is sized such that the blade first thickness is maintained in a significant area of the blade spaced from the weld(s) so as to allow blade flexure away from the weld.

Description:
[0001]     This application is a continuation of co-pending application Ser. No. 10/741,945, filed Dec. 19, 2003, the content of which is incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     The present invention relates to a method of welding and an assembly formed by the method.  
         [0003]     Welding methods are often very critical when an assembly if formed by welding two or more components together. For example, an important consideration in connection with rotary machines including compressors, turbines, refrigeration and gas liquefaction units, and the like, is the design of the impellers since they substantially affect the performance of the machine. A typical radial flow impeller includes a plurality of angularly-spaced blades extending from a central support member, such as a hub or a shroud. However, the blades are often welded to the support member in a manner that results in significant steady state and alternating stresses within the weld joint, and a reduction in fatigue resistance.  
         [0004]     Therefore, what is needed is welding technique that eliminates, or at least significantly reduces, the above problems. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIGS. 1-3  are sectional views of an impeller depicting three manufacturing steps according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0006]     Referring to  FIG. 1 , the welding technique according to an embodiment of the present invention will be described, for the purpose of example, in connection with welding an impeller blade  10  that extends perpendicular to, and radially from, a support member  12 , which, for the purpose of example, is in the form of a hub or shroud. The blade  10  and the member  12  form a portion of an impeller assembly used in a rotary machines (not shown) such as a compressor, turbine, refrigeration and gas liquefaction unit, and the like. Although not shown in the drawing, it is understood that additional blades, which can include splitter blades and blades similar or identical to the blade  10 , also extend from the member  12  in an angularly-spaced relation to the blade  10 . The blade  10  is connected to the outer surface of the member along one edge of the blade in a manner to be described.  
         [0007]     The thickness, or width, of a major portion of the blade  10 , as viewed in  FIG. 1 , is represented by T 1 . However, the thickness of the blade  10  increases from the thickness T 1  to an increased thickness represented by T 2  at an area of the blade spaced from, and in a direction towards, the member  12 . As a result, the opposite side walls of the blade  10  have two gradually tapered, or flared, portions  10   a  and  10   b , respectively, extending from the portion of the blade having the thickness Ti to the portion of the blade having the thickness T 2 . The thickness T 2  extends from the lower portions of the tapered portions  10   a  and  10   b  to the edge of the blade connected to the member  12 .  
         [0008]      FIG. 1  depicts a first manufacturing step in the preparation of the blade  10  in accordance with an embodiment of the invention, which includes forming of the blade with the thicknesses T 1  and T 2  and the tapered portions  10   a  and  10   b , and  FIG. 2  depicts a second step. In particular, two welds  14   a  and  14   b  are made at the corners between the two side walls of the blade and the corresponding surfaces of the member  12 . The welds  14   a  and  14   b  extend along the respective walls of the blade  10  from just below the lower portions of the tapered portions  10   a  and  10   b , as viewed in the drawing, to the member  12  and along the corresponding walls of the latter member. The welds  14   a  and  14   b  can be in the form of any conventional welds such as a full or partial penetrating fillet welds, or the like.  
         [0009]     The final welded assembly is shown in  FIG. 3  after an additional manufacturing step. In particular, two concave toes  10   c  and  10   d  are formed into the opposite side walls of the blade  10  and into the welds  14   a  and  14   b . The toes  10   c  and  10   d  can be formed in any conventional manner such as by cutting, grinding or by a resolidification welding step. The toes  10   c  and  10   d  extend from the area of the blade  10  having the thickness T 2  just above the welds  14   a  and  14   b , respectively, (often referred to as the “heat affected zone”) into the upper portions of the welds. As an example, approximately one half of each toe  10   c  and  10   d  extends in the latter area of the blade and the remaining half of each toe extends into the weld. The thickness of the blade  10  as a result of the forming of the toes  10   c  and  10   d  is represented by T 3 . Thus, a generous radius at the weld toes  10   c  and  10   d  is permitted without compromising the thickness T 3 .  
         [0010]     As an example of the above dimensions, it will be assumed that the thickness T 1  is approximately 0.46 inch, and the thickness T 2  is approximately 0.52 inch. Thus each wall of the blade would be 0.03 inch greater in the area having the thickness T 2  when compared to the walls in the area having the thickness T 1 . Each toe  10   c  and  10   d  is formed in that portion of the blade having the increased thickness T 2 , and each toe is formed to a depth of approximately 0.03. Therefore, the thickness T 3  of the blade  10  at the toes  10   c  and  10   d,  is equal to the thickness T 2  (0.52 inch) reduced by 0.06 inch to a value of 0.46 which is approximately equal to the thickness T 1 . Thus, the toes  10   c  and  10   d  are formed without undercutting, or reducing, the thickness T 1 .  
         [0011]     According to another example, it will be assumed that the thickness T 1  is approximately 0.46 inch, and the thickness T 2  is approximately 0.52 inch, as in the previous example. In this case, each toe  10   c  and  10   d  would extend to a maximum depth of 0.025 inch, to form a thickness T 3 . Since portions of the toes  10   c  and  10   d  are formed in that portion of the blade having the increased thickness T 2 , the thickness T 3  is equal to the thickness T 2  (0.52 inch) reduced by 0.05 inch to a value of 0.47 which is slightly greater that the thickness T 1 . Thus, the toes  10   c  and  10   d  are formed without undercutting, or reducing, the thickness T 1 .  
         [0012]     It is emphasized that the dimensions of the thicknesses T 1 , T 2 , and T 3 , as well as the depth of the toes  10   c  and  10   d , as set forth above, are only for the purpose of example and that they can vary within the scope of the invention.  
         [0013]     It can be appreciated that the blade  10  can be positioned relative to the member  12  with the lower edge of the blade engaging a corresponding surface of the member as viewed in the drawings at any stage of the above sequence of steps, and that the blade is shown so positioned relative to the member in all three figures for the convenience of presentation. Also, it is understood that the depth, or length, of the toes  10   c  and  10   d  and the welds  14   a  and  14   b  can extend for the entire length of the blade  10 .  
         [0014]     It is understood that toes can also be made in the surfaces of the member  12  adjacent the welds  14   a  and  14   b , and that the thickness of the member  12  can be increased accordingly to accommodate the latter toes without undercutting the member  12  in the same manner as discussed above in connection with the member  10 .  
         [0015]     As a result of the above, the weld joints have extra material for stress reduction, yet the relative low thickness T 1  can be maintained in a significant area of the blade  10  spaced from the welds  14   a  and  14   b , which thickness is ideal from a design standpoint to allow flexure away from the welds that reduces bending stress and overall aerodynamic blockage, and permits operation at a higher centrifugal speed. Levels of stresses on the weld joing, such as bending stress, tensile stress, local stress concentration, as well as alternating and mean stress levels, are thus reduced along with susceptibility to quench, heat treatment, and overspeed (proof testing) cracking. Also, increased fatigue resistance and the lives of the weld joints and subsequently the overall assembly is achieved. Still further, grinding tolerances and flexibility are increased without degrading weld joint performance, and relative large shot size can be used when shot preening for more fatigue resistance. The relative small thickness T 1  is maintained in a significant area of the blade  10  spaced from the welds  14   a  and  14   b , which thickness is ideal from a design standpoint to allow flexure away from the joint that reduces overall joint stress and reduces overall aerodynamic blockage.  
         [0016]     The above technique allows improved sensitivity and flaw identification using non-destructive inspection techniques such as wet or dry magnetic particle or dye penetrant techniques. Overall, this technique also allows the analysis effort for fatigue and other failure mechanisms to move away from a fracture mechanics approach towards a continuum approach for a welded structure.  
       Variations  
       [0017]     It is understood that variations may be made in the above without departing from the scope of the invention. Examples of the variations are as follows:  
         [0018]     1. The above embodiment is not limited to the welding of a blade to a support member, but is equally applicable to the welding of other types of components to form a welded assembly.  
         [0019]     2. The above embodiment is not limited to joining two members at a 90-degree angle but rather the angle between the members can vary from a relatively large acute angle to a relatively large obtuse angle.  
         [0020]     3. The sequence of at least some the manufacturing steps shown in  FIGS. 1-3  can be changed.  
         [0021]     4. The above-mentioned specific dimensions of the members discussed above, including the dimensions of the thicknesses T 1 , T 2 , and T 3  as well as the radii of the toes  10   c  and  10   d  can be varied within the scope of the invention.  
         [0022]     5. Spatial references, such as “side”, “edge”, “radial”, “angular” “perpendicular” “below”, etc., are for the purpose of illustration only and do not limit the specific spatial orientation of the structure described above.  
         [0023]     6. A weld toe, of the above type, can be formed in only one side wall of the blade.  
         [0024]     7. The shape of the blade  10  at both thicknesses T 1  and T 2  can vary and, for example, could take an “hourglass” shape in which the width of the blade is variable along its length in a directions towards the member.  
         [0025]     8. The shape of the welds  14   a  and  14   b  can be different than illustrated in the drawings, and, as such, could have different convexity or shaped hypotenuse.  
         [0026]     9. Toes, similar to the toes  10   c  and  10   d  could be formed in the support member  12  and welds  14   a  and  14   b  in the same manner as described above in connection with the blade  10 , in which case the corresponding dimensions of the support member  12  would be modified, such as widened, to accommodate the toes.  
         [0027]     10. The welds and the toes discussed above can be made in only one wall of the blade  10  rather than in the opposed walls as shown.  
         [0028]     11. The relative portions of each weld and the blade that are reduced during the formation of the weld toes  10   c  and  10   d  can vary.  
         [0029]     12. The above welds and toes have been shown, for the purpose of example in connection with the side walls or edges of the blade  12 , and it is understood that they could also be applied to the leading (front) and trailing (rear) walls or edges.  
         [0030]     Although only one exemplary embodiment has have been described in detail above, those skilled in the art will readily appreciate that many other variations and modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of this invention. Accordingly, all such variations and modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.