Page 231 - Rollingbearings

Bearing size, non-locating support
Bearing size, non-locating
• for the locating support – a pair of universally matchable single
row angular contact ball bearings, 7312 BECBP, arranged
back-to-back: support
– max. radial load: F = 1,45kN
r
– max. axial load: F = 11,5 kN
a
– estimated operating temperature: T = 85 °C (185 °F)
Following pump industry standards, the basic rating life L 10h should The given operating conditions, and the effects of rolling contact
be at least 16 000 h at maximum load conditions. fatigue, indicate that bearing size should be determined using the
basic rating life and SKF rating life.
Product data for NU 311 ECP is on page 522.

Bearing type and Basic rating life

arrangement ⎛ 10 6 w ⎛ C w p
⎝ 60 n ⎠ ⎝ P ⎠
L 10h = J J J

From Loads, page 509, P = F . Therefore, the load ratio
r
A cylindrical roller bearing is used as the non-locating support and a C/P = 156/3,29 = 47
pair of universally matchable single row angular contact ball bearings
are used as the locating support. 3,33
⎛ 10 6 w ⎛ 156 w
The cylindrical roller bearing, of type NU, is used for the following L 10h = J J J J J J > 1 000 000 h
⎝ 60 × 3 000 ⎠ ⎝ 3,29 ⎠
reasons:
• It can accommodate, within itself, thermal expansion of the shaft. The bearing is oversized.
• The inner ring is separable from the outer ring, with rollers and
cage – this simpliies assembly of the pump and the use of inter- SKF rating life
ference its on both inner and outer ring.
L
L 10mh = a SKF 10h
For the pair of universally matchable single row angular contact ball
bearings: 1. Lubrication condition – the viscosity ratio, κ

• Ball bearings with a 40° angle are well suited to accommodate κ = ν/ν
1
high axial loads and medium to high speeds.
• The bearings are arranged back-to-back, with the inner rings Given:
clamped and mounted with an interference it to the shaft. oil viscosity grade = ISO VG 68
Because the clearance of the pair is controlled by clamping the operating temperature = 70 °C (160 °F)
inner rings, the outer rings can be positioned in the housing
between a shoulder and a cover, without the need for precise then, using diagram 13, page 100, ν = 20 mm 2 /s
clamping.
Given:
Both bearing housing seats are machined in one clamping position, n = 3 000 r/min
which guarantees good alignment. Misalignment is less than 2 min- d = 0,5 (55 + 120) = 87,5 mm
m
utes of arc, which is within the acceptable misalignment limits for the
angular contact ball bearing pair and cylindrical roller bearing. then, using diagram 14, page 101, ν = 7 mm 2 /s
1
Conclusion Therefore, κ = 20/7 = 2,8

The current selection of bearing type and arrangement is adequate 2. Contamination factor, η
c
C.3 Centrifugal pump
for this application. Given:
• contamination conditions are typical (i.e. open bearings, no ilter-
ing, wear particles and ingress from surrounding environment)
• d = 87,5 mm
m
then, using table 6, page 105, η = 0,2
c

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