Page 117 - Improving Machinery Reliability

Machinery Reliability Audits and Reviews 89

(3-1)
W

where p = lubricant viscosity, Ib-sec/in.*
N = rotor speed, Hz
D = bearing diameter, in.
L = bearing length, in.
R = bearing radius, in.
W = bearing load, lbs
C = radial machined clearance, in.

Several pa~ers~-~ discuss various types of bearings and their stiffness and damp-
ing characteristics. Table 3-1 gives a typical set of bearing calculations for a 5 shoe,
load on the pad, tilting pad bearing. The dimensionless coefficients and the actual
stiffness and damping values are shown versus speed and eccentricity ratio.
The normal procedure in a design audit is to calculate the bearing characteristics
for the range of expected clearances, preload and oil temperatures. The maximum

Table 3-1
Bearing Coefficients for Tilting Pad Bearing
5-Shoe Tilting Pad Bearing

Load on pad UD = .42 Preload = .444
Arc length = 52.00" Pivot ang. = 54.00" Offset = -540
Dimensionless Tilting Pad Bearing Coefficients

ECC. Sommerfeld Kxx KYY cxx CYY Torque
(dim) (dim) (dim) (dim) (dim) (dim) (dim)
~ ~
.05 3.96E+00 3 1.352 31.641 34.475 34.677 25.157
.10 I .96E+00 15.657 16.264 17.144 17.564 25.246
.I5 1.27E+00 10.398 11.355 11.311 1 1.966 25.397
.20 9.25E-01 7.740 9.084 8.350 9.257 25.613
.25 7.09E-01 6.113 7.889 6.530 7.707 25.900
.30 5.60E-01 4.996 7.254 5.227 6.744 26.265
.35 4.49E-01 4.162 6.964 4.343 6.120 26.720
.40 3.628-0 1 3.503 6.9 18 3.607 5.714 27.279
.45 2.92E-01 2.956 7.072 3.002 5.461 27.963
so ?!.34E-01 2.486 7.409 2.489 5.320 28.803
.55 1.85E-01 2.072 7.935 2,045 5.269 29.842
.60 1.44E-01 I .70 1 8.678 1.653 5.291 31.144
.65 I .10E-01 1.366 9.695 1.307 5.375 32.813
.70 8.04E-02 1.062 1 1.089 1.000 5.502 35.020
.75 5.63E-02 ,789 13.046 .73 I 5.659 38.078
.80 3.688-02 ,548 15.901 .500 5.875 42.625
.85 2.17E-02 ,344 20.595 .3 10 6.233 50.248
.90 1.08E-02 .I83 30.649 ,162 7.020 66.733

(table continued on next page)