Page 183 - Tribology in Machine Design

Friction, lubrication and wear in lower kinematic pairs 169

Table 4.3. Coefficient of friction for various face materials at
6
PV = 3.5xl0 Pam/s
Sliding material
Coefficient of
rotating stationary friction

carbon-graphite cast iron
(resin filled) ceramic 0.07
tungsten carbide

silicon carbide 0.02
silicon carbide 0.015
(converted carbon)
silicon carbide tungsten carbide 0.02
silicon carbide converted carbon 0.05

silicon carbide 0.02
tungsten carbide 0.08

Table 4.3 by introducing lubrication grooves or hydropads on the circular
flat face of one of the sealing rings. In most cases a slight increase in leakage
is usually experienced. As there is no standardized PV test that is used
universally throughout the industry, individual test procedures will differ.

4.15.8. Analytical models of wear
Each wear process is unique, but there are a few basic measurements that
allow the consideration of wear as a fundamental process. These are the
amount of volumetric wear, W, the material hardness, H, the applied load,
L, and the sliding distance, d. These relationships are expressed as the wear
coefficient, K

By making a few simple algebraic changes to this basic relationship it can be
modified to enable the use of PV data from seal tests. With sliding distance,
d, being expressed as velocity x time, that is d = Vt, load L as the familiar
pressure relationship of load over area, P = L/A, and linear wear, h, as
volumetric wear over contact area, h = W/A, the wear coefficient becomes

or

Expressing each of the factors in the appropriate dimensional units will
yield a dimensionless wear coefficient, K. Since several hardness scales are