Compressors impeller fabrication

Figure 5-34. A fabricated centrifugal compressor impeller. Courtesy ofA-C Compressor Corporatiofi ...

Impeller Fabrication Centrifugal-compressor impellers are either shrouded or unshrouded. Open, shrouded impellers that are mainly used in single-stage applications are made by investmentcasting techniques or by three-dimensional milling. Such impellers are used, in most cases, for the high-pressure-ratio stages. The... 

Impeller Problems The high-speed rotation of the impeller of a centrifngal compressor imparts the vital aerodynamic velocity to the flow within the gas path. The buffeting effects of the gas flow can canse fatigue failures in the conventional fabricated shrouded impeller due to vibration-induced alternating stresses. These may be of the following types ... 

Materials of Construction. The principal materials of construction are ferrous throughout, but different grades are used for the different components. Casings usually are in cast iron or cast steel, and impellers may be in the same materials or in fabricated steel. Early designs of centrifugal compressors used riveted assembly for impellers castings or welded construetions are preferred today. Shafts usually are of carbon steel with hardened or stainless steel sleeves at points where erosion is likely. The selection of materials for smaller components that may be subject to friction is particularly important because of the danger of comlnistion. 

The compressor usually is of cast iron (perhaps with high nickel and molybdenum contents). The impeller may be ductile iron with an alloy steel shaft. There is usually a shaft sleeve fabricated from a more resistant alloy. 

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