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Friction, lubrication and wear in higher kinematic pairs 247
following equation
n
where n is the cam shaft speed [r.p.m.], 5 = (^ 0 alO ) lubricant parameter
and b — 2r^ — l , where / is the distance from the nose tip to the shaft axis,
and r l is the nose radius.
Figure 6.7
where r is the follower radius and <j = ^]a\ +a\ is the composite roughness;
where 0*1,2 is the root mean square (r.m.s.) surface roughness of surfaces 1
and 2 in /im. If the arithmetic average K a (also known as c.l.a.) is available,
multiply by 1.3 to convert to r.m.s.
In general, the value of A in cam systems is well below one. In this regime,
elastohydrodynamic lubrication is not very effective and we must rely
heavily on surface film or boundary lubrication to protect the surfaces
against scuffing and excessive wear.
References to Chapter 6 1. F. F. Ling. Surface Mechanics. New York: Wiley, 1973.
2. A. W. Crook. The lubrication of rollers, I. Phil. Trans., A250 (1958), 18-34.
3. A. W. Crook. The lubrication of rollers, II and III. Phil. Trans., A254 (1961),
141-50.
4. A. W. Crook. The lubrication of rollers, IV. Phil. Trans., A255 (1963), 261-9.
5. B. Jacobson. On the lubrication of heavily loaded cylindrical surfaces consider-
ing surface deformations and solidification of the lubricant. Trans. ASME, J.
Lub. Technoi, 95 (1973), 176-84.
6. D. Dowson and G. R. Higginson. Elastohydrodynamic Lubrication. New York:
Pergamon Press, 1966.