Friction
Kinematic replenishment/starvation
reduction factor
For oil-air, oil jet, low level oil bath lubrication
(i.e. oil level H lower than the centre of the
lowest rolling element) and grease lubrication
methods, continuous over-rolling displaces
excess lubricant from the raceways. In applications
where viscosity or speeds are high,
the lubricant may not have sufficient time to
replenish the raceways, causing a “kinematic
starvation” effect. Kinematic starvation
reduces the thickness of the hydrodynamic
film (decreasing k value, page 241) and rolling
friction.
For the type of lubrication methods described
above, the kinematic replenishment/starvation
reduction factor can be estimated using
frs = 1
e Krs n n (d + D)
Kz
2 (D – d)
where
frs = kinematic replenishment/starvation
reduction factor
e = base of natural logarithm ≈ 2,718
Krs = replenishment/starvation constant:
• for low level oil bath and oil jet
lubrication † 3 ¥ 10–8
• for grease and oil-air lubrication
† 6 ¥ 10–8
KZ = bearing type related geometric
constant († table 5, page 112)
n = actual operating viscosity of the oil or the
base oil of the grease [mm2/s]
n = rotational speed [r/min]
d = bearing bore diameter [mm]
D = bearing outside diameter [mm]