Page 93 - Steam Turbines Design, Applications, and Rerating

74 Chapter Three

loaded side), so that the hydrodynamic forces and thereby the frictional
forces decrease on this side.
A thrust bearing can be monitored satisfactorily only by temperature
sensors (thermocouple, resistance thermometer) near the babbitt lining
in the area of highest oil film temperatures. A thermometer in the oil
discharge of the thrust bearing cannot indicate overheating of a bearing
pad, because the additional friction heat generated by the endangered
pad is so small in relation to the total friction heat of the thrust bearing
that temperature rise in the early stages of incipient bearing failure is
not likely to be detected. A thermometer in the oil discharge can only
monitor the bulk oil supply temperature of the thrust bearing.
Finally, some remarks on the application of thrust bearings in tur-
bines: Well-engineered thrust bearings are often simple and robust and
may incorporate a minimum of moving parts. The best proof of this
statement is seen in Fig. 3.26a and b, which compare conventional
rocking pivot tilt-pad bearings with the KMC flexure pivot configura-
tions. Where the former types create a converging wedge through rock-
ing motion of the pad pivot support, the latter form a wedge through
flexure of the post support while eliminating the pivot wear and high-
contact stresses. The same principles are embodied in the combination
radial/thrust flexure pivot tilt-pad bearing depicted in Fig. 3.27.

(a)

(b)
Figure 3.26 (a) Conventional rocking pivot tilt-pad radial bearing and
modern flexure pivot™ tilt-pad principles; (b) conventional tilt-pad
thrust bearing and modern flexure pivot™ tilt-pad principles. (KMC,
Inc., West Greenwich, R.I.)