Page 287 - Cam Design Handbook

THB9 9/19/03 7:26 PM Page 275

CAM MATERIALS AND LUBRICATION 275

(a) Hertzian conditions.

(b) Elastohydrodynamic conditions.
FIGURE 9.11. Grubin’s model of elastohydrodynamic contact.
From Zaretsky (1997).

h 0 = lubricant absolute viscosity (atmospheric pressure) 1bf - s/in 2
a¢= pressure-viscosity coefficient of fluid, psi -1
and

1 1 1
= + (9.17)
R R R
x 1 x x 2
when
= radii of bodies 1 and 2in rolling direction, in
R x 1 ,R x 2
2
E ¢ = (9.18)
(
(1 - v 1 2 ) E 1 +- v1 2 2 ) E 2
where
E 1, E 2 = elastic modulii for bodies 1 and 2, psi
n 1, n 2 = Poisson’s ratios of bodies 1 and 2, psi
6
2
For typical steels, E¢= 33 ¥ 10 lb/in and for mineral oils, a typical value of a¢= 1/5 ¥
-4
2
10 in /lb. Thus for mineral oils, lubricated rolling elements G = 5000.