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CONSTRUCTION OF TURBINES | Up
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SUMMARY |
Figure 5-8.—Typical sliding surface bearing.
applications use casings made of carbon molyb-
denum steel. For turbine casings used on
submarines, a percentage of chrome stainless steel
is used, which is more resistant to steam erosion
than carbon steel. Each casing has a steam chest
to receive the incoming high-pressure steam. This
steam chest delivers the steam to the first set of
nozzles or blades.
Nozzles
The primary function of the nozzles is to
convert the thermal energy of steam into kinetic
energy. The secondary function of the nozzles is
to direct the steam against the blades.
Rotors
Rotors (forged wheels and shaft) are manu-
factured from steel alloys. The primary purpose
of a turbine rotor is to carry the moving blades
that convert the steam’s kinetic energy to rotating
mechanical energy.
Bearings
The rotor of every turbine must be positioned
radially and axially by bearings. Radial bearings
carry and support the weight of the rotor and
maintain the correct radial clearance between the
rotor and casing.
Axial (thrust) bearings limit the fore-and-aft
travel of the rotor. Thrust bearings take care of
Figure 5-9.—Labyrinth packing gland.
any axial thrust, which may develop on a turbine
rotor and hold the turbine rotor within definite
axial positions.
All main turbines and most auxiliary units
have a bearing at each end of the rotor. Bearings
are generally classified as sliding surface (sleeve
and thrust) or as rolling contact (antifriction ball
or roller bearings). Figure 5-8 shows a typical
sliding surface bearing.
Shaft Packing Glands
Shaft packing glands prevent the leaking of
steam out of or air into the turbine casing where
the turbine rotor shaft extends through the
turbine casing. Labyrinth and carbon rings are
two types of packing. They are used either
separately or in combination.
Labyrinth packing (fig. 5-9) consists of rows
of metallic strips or fins. The strips fasten to the
gland liner so there is a small space between the
strips and the shaft. As the steam from the
turbine casing leaks through the small space
between the packing strips and the shaft, steam
pressure gradually reduces.
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