Page 235 - Rollingbearings

Bearing execution
Results:

NU 311 ECP Pair of 7312 BECBP

d m 87,5 mm 95 mm
–11 μm –11 μm
Δr temp

4. Operating clearance

NU 311 ECP Pair of 7312 BECBP

min /avg /max –13 / 30 / 55 μm –27 / 17 / 4 μm

For a cylindrical roller bearing, negative clearance (i.e. preload) is
generally not recommended.
Pairs of angular contact ball bearings should have an average
operating clearance close to zero (ranging between small clearance
and light preload), particularly when the pairs are loaded predom-
inantly axially. A small range is required to:
• limit preload – to limit friction (increased friction results in higher
temperatures, and therefore reduced viscosity and reduced bear-
ing life)
• limit clearance – to avoid ball skidding

This manual calculation does not consider smoothing of the mating
surfaces, nor elastic delection under load, nor the probability of
extreme values occurring at the same time.
Analysis using more advanced SKF software gives operating clear-
ance results:
NU 311 ECP Pair of 7312 BECBP

min /avg /max 3 / 34 / 59 µm –10 / 11 / 24 µm

These results indicate that Normal internal clearance is suitable.

Cage selection

Given the estimated operating temperature of 85 °C (185 °F) (i.e. the
higher temperature of the two bearing supports), a speed of well
below the limiting speed, and considering availability and price, the
standard rolling element guided polyamide cages are conirmed as
adequate
For historical reasons, in some geographical areas, brass cages are
preferred for angular contact ball bearings These are available as
standard from SKF This also applies to the cylindrical roller bearings
C.3 Centrifugal pump

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