Impeller fabrication

Fig. 1.61 Erosion-corrosion. Impeller fabricated from Cu-10Sn-2Zn alloy used for pumping a slurry containing 5-10% H2SO4 after six months service. The blades of the impeller were extensively corroded. Note the directional form of the attack...

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... 

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

The biggest use of plastics is for piping sheets are also used for lining vessels and for fabricated ducting and fan casings. Mouldings are used for small items such as, pump impellers, valve parts and pipe fittings. 

Wear is the removal of surface material by one of three mechanisms erosion, abrasion, or cavitation. Erosion is the removal of a polymer s surface by abrasive materials carried in a fluid medium. We see this type of wear in plastic pipes used to transport waterborne slurries of minerals in mining operations and in vacuum transfer pipes used to convey powders in a stream of air. Abrasion is the result of two surfaces sliding against each other. We commonly observe abrasion of polymers in the fabrics of our clothes and upholstery. Cavitative wear is caused by voids in a liquid medium collapsing against a surface. It is essentially an impact process. Cavitation is a relatively uncommon cause of wear in polymers. Pump impellers are one of the few applications where polymers must resist this type of wear. 

Unless otherwise approved by the purchaser, impellers shall be of the fully enclosed type and constructed as single piece castings. Fabricated impellers require the purchaser s specific approval. 

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 ... 

Impellers shall be single-piece castings, forgings or fabrications. 

NOTE Impellers made as forgings or fabrications have machined waterways, w hich may offer improved performance for low suction specific speed designs. 

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