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Impeller Fabrication

 Impeller Fabrication

  • Centrifugal-compressor impellers are either shrouded or unshrouded. Open, shrouded impellers that are mainly used in single-stage applications are made by investment casting techniques or by three-dimensional milling. Such impellers are used, in most cases, for the high-pressure ratio stages.
  • The shrouded impeller is commonly used in the process compressor because of its low-pressure ratio stages. The low tip stresses in this application make it a feasible design.
  • several fabrication techniques. The most common type of construction is seen in A and B where the blades are fillet-welded to the hub and shroud. In B the welds are full penetration.
  • The the disadvantage in this type of construction is the obstruction of the aerodynamic passage. In C, the blades
  • are partially machined with the covers and then butt-welded down the middle.
  • For backward lean-angled blades, this technique has not been very successful, and there has been difficulty in achieving a smooth contour around the leading edge.
  • D illustrates a slot-welding technique and is used where blade-passage height is too small (or the backward lean-angle too high) to permit conventional fillet welding. In E, an electron-beam technique is still in its infancy, and work needs to be done to perfect it.
  • Its major disadvantage is that electron-beam welds should preferably be stressed in tension but, for the configuration of E, they are in shear.
  • The configurations of G through J use rivets. Where the rivet heads protrude into the passage, aerodynamic performance is reduced.

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