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Factors Affecting .hrust-Bearing .esign
The principal function of a thrust bearing is to resist the thrust unbalance developed within the working elements of a turbomachine and to maintain the rotor position within tolerable limits.
After an accurate analysis has been made of the thrustload， the thrust bearing should be sized to support this load in the most efficient method possible. Many tests have proven that thrust bearings are limited in load capacity by the strength of the babbitt surface in the high load and tempera-ture zone of the bearing. In normal steel-backed babbitted tilting-pad thrustbearings， this capacity is limited to between 250 and 500 psi (17 and 35 Bar) average pressure. It is the temperature accumulation at the surface and pad crowning that cause this limit.
The thrust-carrying capacity can be greatly improved by maintaining pad flatness and by removing heat from the loaded zone. By the use of

Figure 13-16.Severity charts: (a)displacement， (b)velocity，
Figure continued on next page

Figure 13-16. (continued). Severity chart: (c) acceleration.

Figure 13-17. Comparison of thrust-bearing types. Figure 13-1.. .arious types of thrust bearings.

Figure 13-19. Thrust-bearing temperature characteristics.
high thermal conductivity backing materials with proper thickness andproper support， the maximum continuous thrust limit can be increased to 1000 psi or more. This new limit can be used to increase either the factor of safety and improve the surge capacity of a given size bearing or reduce the thrust bearing size and consequently the losses generated for a given load.
Since the higher thermal conductivity material (copper or bronze) is a much better bearing material than theconventional steel backing， it is possible to reduce the babbitt thickness to .010..030 of an inch (.254. .762 mm). Embedded thermocouples and RT.s will signal distress in the bearing if properly positioned. Temperature monitoring systems have beenfound to be more accurate than axial position indicators， which tend to have linearity problems at high temperatures.
In a change from steel-backing to copper-backing a different set of tem-perature limiting criteria should be used. Figure 13-19 shows a typical set of curves for the two backing materials. This chart also shows that drain oil temperature is a poor indicator of bearing operating conditions because there is very little change in drain oil temperature from low load to failure load.
.hrust-Bearing Po.er .oss
The power consumed by various thrust bearing types is an important consideration in any system. Power losses must be accurately predicted so that turbine efficiency can be computed and the oil supply system properly designed.
Figure 13-20 shows the typical power consumption in thrust bearings as a function of unit speed. The total power loss is usually about 0.8.1.0% of the total rated power of the unit. New vectored lube bearings that are being tested show preliminary figures of reducing the power loss by as much as 30%.
Seals
Seals are very important and often critical components in turbomachinery， especially on high-pressure and high-speed equipment. This chapter covers the principal sealing systems used between the rotor and stator elements of turbomachinery. They fall into two main categories: (1) noncontactingseals， and (2) face seals.
Since these seals are an integral part of the rotor system， they affect thedynamic operating characteristics of the machine; for instance， both the
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SHAFT SPEED – RPM×10–3
stiffness and damping factors will be changed by seal geometry and pres-sures.Hence， these effects must be carefully evaluated and factored in during the design of the seal system.
.oncontacting Seals
These seals are used extensively in high-speed turbomachinery and have good mechanical reliability. They are not positive sealing. There are two types of noncontacting seals (or clearance seals): labyrinth seals and ring seals.
　
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本文鏈接地址：燃氣渦輪工程手冊 Gas Turbine Engineering Handbook 2(87)