Page 94 - Steam Turbines--Design, Applications, and Rerating by Heinz-Bloch, Murari-Singh

Bearings for Mechanical Drive Turbines 75

Figure 3.27 Combination radial thrust flexure pivot tilt-pad bear-
ings. (KMC, Inc., West Greenwich, R.I.)

In many reaction turbines, the bearing housing is supported on
adjusting elements in a pedestal that, in turn, is rigidly bolted to the
concrete foundation. It is connected to the turbine merely by two thrust
rods. With thermal expansion of the turbine outer casing, the bearing
housing is shifted on the pedestal. It is guided so that it will slide with-
out cocking or twisting. The outer casing itself is supported by its
brackets on the pedestal. Any deflection of the turbine outer casing
does not affect the position of the bearing housing.
For this type of mounting, thrust bearings with self-equalizing tilt-
ing pads (e.g., Kingsbury), are not required. However, for turbine
designs where the bearing housing is affected by casing thermal
expansion, or where compensation is achieved by bending of “wobble-
plates,” Kingsbury thrust bearings represent a better solution. Figure
3.28 depicts a Kingsbury bearing which accommodates considerable
misalignment. This type of bearing is often found on impulse turbines
and centrifugal compressors.

3.4 Active Magnetic Bearings
Active magnetic bearings (AMBs) are frictionless, unlubricated bear-
ings that levitate moving machinery parts in an electromagnetic field.
They are able to support large loads at speeds well beyond the range of
conventional bearings with no wear and virtually no vibration. As of
mid-1994, a few dozen major turbomachines (up to 7000 hp/approxi-
mately 5000 kW) and several hundred canned motor pumps and simi-