Page 226 - Rollingbearings

Bearing size (step 2) 2. Life modiication factor, a SKF
To determine the life modiication factor for radial ball bearings,
diagram 9, page 96 is used, with:
• P = 0,55 kN
From the conclusions in Bearing size, page 223, the minimum load • κ = 1
needs to be checked and, now the lubrication has been selected, the • P = 0,655 kN
u
SKF rating life can be veriied. • η = 0,6
c
The contamination factor is chosen based on table 6, page 105.
Minimum load • SKF 6207-2RSH/WT is an SKF Explorer bearing.

Using the minimum load equation from Loads, page 254, the mini- With η P /P = 0,7 and using diagram 9, page 96, the a SKF of about
c u
mum load, F , is given by: 50 is much greater than 1, so the SKF rating life is far above the
rm
required life.
q ν n w2/3 q d w 2
m
rm r < 1 000 z < 100 z Conclusion
F = k ––––– ——
The bearing SKF 6207-2RSH/WT is adequate in terms of fatigue
where: life.
k = 0,025
r
ν = 210 mm 2 /s
When determining the minimum load, to cover all critical oper-
ating conditions, use the highest oil viscosity that might occur.
This will be at the lowest temperature, which is 20 °C (70 °F).
Base oil viscosity of WT grease at 40 °C (105 °F) is 70 mm 2 /s ≈
ISO VG 68. Estimated from diagram 13, page 100, or calcu-
lated with the SKF Bearing Calculator
(skf.com/bearingcalculator), for WT grease ν = 210 mm 2 /s at
20 °C (70 °F).
d = (d+D)/2 = (35+72)/2 = 53,5 mm
m

Therefore:
F = 0,44 kN < 0,55 kN, so the bearing 6207-2RSH/WT is
rm
adequate.

SKF rating life

L 10mh = a SKF 10h
L
Because P < P , fatigue is not a factor (Fatigue load limit, P ,
u
u
page 104). However, it is useful to verify the lubrication condition
(viscosity ratio) and life modiication factor.
1. Lubrication condition – the viscosity ratio, κ

κ = ν/ν
1
The following are used:
• ν is determined from diagram 14, page 101
1
• with d = 53,5 and n = 2 450 r/min, ν is close to 12 mm 2 /s
C.2 Rope sheave For WT, the base oil viscosity at 90 °C (195 °F) can be estimated from
m
1
diagram 13, page 100, or calculated with the SKF Bearing Calculator
(skf.com/bearingcalculator) and is 12 mm 2 /s.

Viscosity ratio, κ = 12/12 = 1

224