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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 sectorshaped pads, arranged in a circle around the shaft, and which are free to pivot. These create wedgeshaped regions of oil inside the bearing between the pads and a rotating disk, which support the applied thrust and eliminate metalonmetal 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
Basic Element of thrust bearing
Preview: Flat Thrust Plate Bearing Design Calculator
Thrust Bearing Typical Loads


Surface

Loads
Lbs/in^{2} 
Max Loads
Lbs/in^{2} 
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, McGrawHill Book Co., Copyright © 1957.
External diameter formula:
D_{2} = ( ( 4 W ) / ( ( π K_{g} p ) + D_{1}^{2} )^{1/2}
Where:
W = applied load, pounds
K_{g} = fraction of circumference occupied by pads; usually, 0.8
p = bearing unit load, psi
Radial pad width, given in inches
a = (1/2) ( D_{2}  D_{1} )
Pitch line circumference, given in inches
B = π ( D_{2}  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
P_{f} = i a b M
M = Horsepower Loss per in^{2} derived from:
Friction power loss, M, vs. peripheral speed, U — thrust bearings.chart
Oil flow required, given in gpm
Q = ( 42.4 P_{f} ) / ( c Δt )
where:
c = Specific heat of oil in Btu/gal/°F
Δt = temperature rise °F
Film flow, given in gpm
Q_{f} = [ ( 1.5 ) ( 10^{5} ) i V h^{3} p_{s} ] / Z_{2}
Where:
V = effective widthtolength ratio for one pad, a/b
Z_{2} = 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
Q_{c} = Q / i
Kinetic energy correction factor ξ derived from chart using values Z_{2}l and Q_{c}
Kinetic energy correction factor chart
Uncorrected flow per chamfer, given in gpm
Q^{o}_{c} = Q_{c} / ξ
Depth of chamfer, given in inches
g = [ ( Q^{o}_{c} l Z_{2} ) / ( 4.74 x 10^{4} p_{s} ) ]^{1/4}
Flat plate thrust bearing example design.
Notation:
a = radial width of pad, inches
b = circumferential length of pad at pitch line, inches
b_{2} = 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
K_{g} = 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
p_{s} = oilsupply pressure, psi
P_{f} = friction horsepower
Q = total flow, gpm
Q_{c} = required flow per chamfer, gpm
Q^{o}_{c} = uncorrected required flow per chamfer, gpm
Q_{F} = film flow, gpm
s = oilgroove width
∆t = temperature rise, °F
U = velocity, feet per minute
V = effective widthtolength ratio for one pad
W = applied load, pounds
Y_{g} = oilflow factor
Y_{l} = leakage factor
Y_{S} = shape factor
Z = viscosity, centipoises
α = dimensionless filmthickness 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 471047031
 Bearing Design and Application by Donald F. Wilcock and E. Richard Booser, McGraw Hill, 1957, 195, LC number 569641