International Journal of Advance Research In Science And Engineering http://www.ijarse.com
IJARSE, Vol. No.4, Special Issue (01), March 2015 ISSN-2319-8354(E)
1680 |
P a g e
Fig. 4
Pivoted pad bearings
Fig. 5
Illustration of tilting pad bearing and terminology
Tilting-pad bearings have the great advantage over fixed incline bearings that
the pad convergence ratio
K =
- 1
le
te
h
h
is a function of
the position of the pivot only, where
,
l e
t e
h
h
are the
oil film thickness at the
leading edge and trailing edge respectively. K is independent of the operating conditions (when thermal effects
and side leakage are negligible). The load carrying capacity depends strongly on K and
fixed incline bearings
therefore do not work well under varying operating conditions. This problem was solved by the introduction of
the pivot-pad bearing. A schematic illustration of a tilting-pad thrust bearing is seen in figure 5.
Michell’s construction was based on a line pivot not allowing for radial pivoting. Kingsbury used a
spherical
pivot, which allows the bearing-pad to tilt in all directions to compensate for misalignment between the pad and
the rotor. Due to this additional advantage of Kingsbury’s design the spherically
pivoted bearing is in more
widespread used.
The present day bearing designs are very similar to the original design. In figure 6, some examples of modern
tilting-pad thrust bearings are shown. To enhance the performance some modifications of the design have been
introduced over the years. Leveling systems have been introduced to ensure equal loads on all pads.
In large
bearings crowning of the pads due to thermal gradients between the oil film side and the backside of the pads
may constitute a problem due to a negative influence on the oil film thickness distribution. In order to reduce
thermal crowning circular supports, internal cooling of the pads or sandwich constructions has been introduced
by bearing designers.
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