Shafts are made from alloy steel forgings, finished by grinding or honing to produce the required finish. Special requirements are detailed in API 617 for balancing and concentricity during rotor assembly. Impellers are normally mounted on the shaft with a shrink fit with or without a key, depending on the particular manufacturer and compressor frame size. Most manufacturers use shaft sleeves to both locate impellers and provide protection for the shaft in the event of contact with internal labyrinth seals.
Special attention must be given to minimizing mechanical and electrical runout at the shaft area observed by proximity probes. See the General Machinery Manual for more information on mechanical/electrical mount.