Page 101 - Steam Turbines Design, Applications, and Rerating
P. 101
82 Chapter Four
Figure 4.1 Built-up rotor. At lower operating speeds, turbines are
often supplied with built-up rotors in which the disks are shrunk
and keyed to the forged alloy steel shaft. Disks are profiled to keep
stresses at a minimum. (Elliott Company, Jeannette, Pa.)
Purchaser approval is required for built-up rotors when blade tip veloci-
ties exceed 825 ft./sec. at maximum continuous speed or when stage inlet
temperature exceeds 825°F.
Design conservatism relates to pitch diameter, operating speed, and
steam temperature.
4.2 Pitch Diameter and Speed
A commonly used industry rule-of-thumb to determine if built-up con-
struction is suitable for a particular application is when the product of
r/min and pitch diameter does not exceed 160,000. This is easily kept in
Figure 4.2 Solid turbine rotor. Wheels (disks) and shaft are
machined from a single, integral forging. (Dresser-Rand Company,
Wellsville, N.Y.)
