Page 107 - The Tribology Handbook

A18 Hvdrostatic beari nas

DESIGN OF HYDROSTATIC JOURNAL BEARINGS
The geometry and nomenclature of a cylindrical journal Table 18.1 Dimensionless stiffness (for
bearing with n pads are illustrated in Fig. 18.13. Forjournal a journal bearing with n pads)
bearings the optimum value of design pressure ratio is
fi = 0.5 as for other hydrostatic bearings. Other values Constant
of fl will reduce the minimum film thickness and may reduce Capillary Orijice Po.,
the maximum load. The following equations form a basis
for safe design of journal bearings with any number of 3.82 8 (1 -8) 7.658 (1 -8) 3.82 8
-
recesses and the three principal forms of flow control (refer 4 1+Y (1-8) 2--8+2Y (1-8) 1 +Y
to Fig. 18.13 and Table 18.1).
4.128 (1 -B) 8.25 8 (1 -8) 4.258
Load : W = p r-Ae.
where Wis a load factor which normally varies from 5 1 +0.69 y (1 -8) 2-8-t 1.38Y (1 -8) 1 +0.69Y
T -_ .
0.30 to 0.6 a better guide is = - 4.30 8 (1 -8) 8.608 (1 -8) 4.308
2 2-84-Y (1-8)
x = dimensionless stiffness parameter from Table 18.1 6 1+0.5y(l-8) 1+0.5y
2 = value of for capillary control and fi = 0.5,
A, = D (L-a).
Pf 41
Concentric stiffness: A = -
c
where C = h, = radial clearance.

Flow-rate :
- nD
where B=-
6an
is the flow factor for one of the n recesses.
n a (L-a) Fig. 18.13. Typical hydrostatic journal bearing
Y=
nDb
is a ircumferential flow factor. If the dimension ‘6’ is too
small the value y will be large and the bearing will be un- Previous Paragraph heded ‘Plane Hydrostatic pad
stable. Design’. Values of viscosity and clearance should be
The recommended geometry for a journal bearing (see selected So that:
Fig. 18.13).
L L ZD Pr
a=- 4, _- D-l, b=-
4n where X = rotational speed in revlsec
Journal bearings which operate at speed should be = [(total area) -3 (recess area)]/D2
optimised for minimum power dissipation and low tern- R~~~~~ depth = 20 radial clearance. ~~~i~~~ tem-
perature rise for the same reasons as given under the perature rise may be calculated as for plane pads.

A18.5