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Flat Thrust Plate Bearing Design Equation and Calculator

Machine Design Applications
Bearing Engineering and Design

Flat Thrust Plate Bearing Design Equation and Calculator: Fluid thrust bearings contain a number of sector-shaped pads, arranged in a circle around the shaft, and which are free to pivot. These create wedge-shaped regions of oil inside the bearing between the pads and a rotating disk, which support the applied thrust and eliminate metal-on-metal contact. Although each bearing section is wedge shaped, as shown below right, for the purposes of design calculation, it is considered to be a rectangle with a length b equal to the circumferential length along the pitch line of the section being considered, and a width a equal to the difference in the external and internal radii.

Typical Thrust Plate
Typical Thrust Plate

Basic Element of thrust bearing

Basic Element of thrust bearing
Basic Element of thrust bearing

Preview: Flat Thrust Plate Bearing Design Calculator

Thrust Bearing Typical Loads
Surface
Loads
Lbs/in2
Max Loads
Lbs/in2
Parallel surface
< 75
< 150
Step Surface
200
500
Tapered Land Surface
200
500
Tilting Pad Surface
200
500

Reproduced with permission from Wilcock and Booser, Bearing Design and Applications, McGraw-Hill Book Co., Copyright © 1957.


External diameter formula:

D2 = ( ( 4 W ) / ( ( π Kg p ) + D12 )1/2

Where:

W = applied load, pounds
Kg = fraction of circumference occupied by pads; usually, 0.8
p = bearing unit load, psi


Radial pad width, given in inches

a = (1/2) ( D2 - D1 )


Pitch line circumference, given in inches

B = π ( D2 - a )


Number of bearing pads, i. Assume that the oil groove width, s is minimum

i = B / ( a + s ) = nearest even number

i as the nearest even number to that calculated.


Length of bearing pad given in inches

b = [ B - ( i s ) ] / i


Actual unit load, given in psi

p = W / ( i a b)


Pitch line velocity, given in fpm

U = ( B N ) / 12

where, N - rpm


Friction power loss, given in HP

Pf = i a b M

M = Horsepower Loss per in2 derived from:

Friction power loss, M, vs. peripheral speed, U — thrust bearings.chart


Oil flow required, given in gpm

Q = ( 42.4 Pf ) / ( c Δt )

where:

c = Specific heat of oil in Btu/gal/°F
Δt = temperature rise °F


Film flow, given in gpm

Qf = [ ( 1.5 ) ( 105 ) i V h3 ps ] / Z2

Where:

V = effective width-to-length ratio for one pad, a/b
Z2 = oil viscosity at outlet temperature
h = film thickness
Note: Because h cannot be calculated, use h = 0.002 inch.


Required flow per. chamfer, given in gpm

Qc = Q / i


Kinetic energy correction factor ξ derived from chart using values Z2l and Qc

Kinetic energy correction factor chart


Uncorrected flow per chamfer, given in gpm

Qoc = Qc / ξ


Depth of chamfer, given in inches

g = [ ( Qoc l Z2 ) / ( 4.74 x 104 ps ) ]1/4


Flat plate thrust bearing example design.*
Flat plate thrust bearing example design.

Notation:

a = radial width of pad, inches
b = circumferential length of pad at pitch line, inches
b2 = pad step length
B = circumference of pitch circle, inches
c = specific heat of oil, Btu/gal/°F
D = diameter, inches
e = depth of step, inch
f = coefficient of friction
g = depth of 45° chamfer, inches
h = film thickness, inch
i = number of pads
J = power loss coefficient
K = film thickness factor
Kg = fraction of circumference occupied by the pads; usually, 0.8
l = length of chamfer, inches
M = horsepower per square inch
N = revolutions per minute
O = operating number
p = bearing unit load, psi
ps = oil-supply pressure, psi
Pf = friction horsepower
Q = total flow, gpm
Qc = required flow per chamfer, gpm
Qoc = uncorrected required flow per chamfer, gpm
QF = film flow, gpm
s = oil-groove width
∆t = temperature rise, °F
U = velocity, feet per minute
V = effective width-to-length ratio for one pad
W = applied load, pounds
Yg = oil-flow factor
Yl = leakage factor
YS = shape factor
Z = viscosity, centipoises
α = dimensionless film-thickness factor
δ = taper
ξ = kinetic energy correction factor

References:

  • Machinery's Handbook, 29th Edition
  • Understanding Journal Bearings, Malcolm E. Leader, P.E. Applied Machinery Dynamics Co.
  • Theory and Practice of Lubrication for Engineers by Dudley D. Fuller, Wiley and Sons, 1984, ISBN 0- 471-04703-1
  • Bearing Design and Application by Donald F. Wilcock and E. Richard Booser, McGraw Hill, 1957, 195, LC number 56-9641
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