Page 233 - Rollingbearings

Bearing interfaces
Operating temperature and
The next higher viscosity grade, ISO VG 100, would give κ = 2,5. But
this would result in the NU 311 ECP bearing having κ > 4, which, dur-
ing cold starts in particular, would give unwanted high κ values. speed
2. Contamination factor, η
c
Given:

• contamination conditions are typical (i.e. open bearings, no iltering, Determine whether a detailed thermal analysis is required (Thermal
wear particles and ingress from surrounding environment) equilibrium, page 131) by checking that:
• d = 95 mm
m
• the rotational speed is less than 50% of the bearing limiting speed:
then, using table 6, page 105, η = 0,2 – This is true for the non-locating support.
c
– For the locating support, it is 56%, which is just slightly above the
Given: limit. That is, for a pair of single row angular contact ball bear-
P = 2 × 3,2 = 6,4 kN ings, the limiting speed is reduced by 20% (Permissible speed,
u
P = 11,52 kN (Basic rating life) page 402), and so 3 000/(0,8 × 6 700) = 0,56.
• the load ratio C/P > 10:
then η P /P = 0,2 × 6,4/11,52 = 0,11 – This is true for the locating and non-locating supports.
c u
• there is no pronounced external heat input:
3. Life modiication factor a SKF – The pump is located in an environment where the ambient tem-
Given: perature is 20 to 30 °C (70 to 85 °F).
κ = 1,8 – The pump medium is at ambient temperature, so no additional
η P /P = 0,11 heat lows to the bearings.
c
u
7312 BECBP are SKF Explorer bearings
Therefore, no further thermal analysis is needed.
then, using diagram 9, page 96, a SKF = 5
Given:
L 10h = 17 400 h Bearing interfaces

then L 10mh = 5 × 17 400 = 87 000 h

Conclusion

The pair of 7312 BECBP SKF Explorer bearings are of a suitable size. Because the loads on the bearings will be greater, as a result of the
modiication to the pump, you should check the bearing seat toler-
ances to make sure the bearings are mounted with adequate its.
Given the standard steel shaft and cast iron housing, the bearing
Lubrication loads, speeds and temperatures, which are all within standard condi-
tions, you can apply Seat tolerances for standard conditions,
page 148.

Shaft tolerances
The pump has an oil bath. This is typical of process pumps, because
of their requirement for long service intervals. In this pump, for sim- You can ind shaft tolerances for seats for radial ball bearings in
plicity, the locating and the non-locating support bearings are lubri- table 5, page 148, and for radial roller bearings in table 6,
cated by the same oil bath. page 149.
As determined in previous steps, κ is 1,8 for the pair of angular
contact ball bearings and 2,8 for the cylindrical roller bearing, and so
the viscosity grade of the selected oil is adequate.
C.3 Centrifugal pump

231