TourTour Spiral groove thrust bearing
Calculation nominal operating conditions
 Load F N
 Bearing diameter D=2R 10-3 m
 Film thickness h0   (h0/R > 510-5 ) 10-6 m
 Viscosity   (default air lubrication) 10-6 Pas

 groove depth h2  (default δopt.=h0/h2=0.37) 10-6 m
 λ=ri /ro
 groove angle α deg.
 number of grooves k
 δ =h0/h2
 H
 g1
 C2
 F'
 g2
 '
 angular velocity ω(F, h0) rad/s
 revolutions per minute rpm
 friction coefficient
 friction torque Nm
 power loss Watt
First step in thrust spiral groove bearing design may be to minimize the rotational speed at which full film lubrication begins. For this the optimal non dimensional load is aimed at minimum film thickness h0, where h0 is based on machining accuracy.

The optimum value for the non dimensional load F' is a function of α, k, λ and δ (Figure 9.22). A combination of these parameters which are much used in practice is calculated with eq.9.54 and is filled in as default.

S.g.b.'s operate with air lubrication as well with oil or grease. The grooves are usually etched in the smooth finished surface (photo etch-mask on the right). The grooves have a shape such that the angle between the tangent to the groove and the local velocity vector (wxr) has at all times the value a (construction).

From the numerical example above it follows that if a grooved disc of 150 mm diameter is placed on a smooth one and rotated in the right direction, a rotational speed of 1 revolution per second will be enough to separate the discs by a layer of air about 12 micron thick, which will then support the weight of 1 kg. The friction losses then are 0.0025 W.

Next step in spiral groove bearing design, after that the bearing geometry is optimized, is to compute the bearing parameters at nominal operating conditions. For this step compute the angular velocity with trial value for h0.

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