SKF - Rolling Bearings

Bearing specifics
The initial internal clearance referred to as
Normal implies that a suitable operating
clearance can be obtained if the recommended
shaft and housing fits are realized during
mounting and operating conditions are normal.
Where operating and mounting
conditions differ from normal, for example,
when interference fits are used for both bearing
rings or considerable temperature differences
prevail, bearings with greater or smaller
internal clearance than Normal are required.
In these cases, SKF recommends checking residual
(radial) clearance in the bearing after it
has been mounted.
Bearings with an internal clearance other
than Normal are identified by the suffixes C1
to C5 († table 16).
The clearance values for the various bearing
types are listed in the relevant product chapters
and are valid for unmounted bearings. For
paired (universally matchable) single row angular
contact ball bearings and tapered roller
bearings, double row angular contact ball
bearings and four-point contact ball bearings,
values for the axial internal clearance are listed
instead of radial clearance, as the axial clearance
is of greater importance for these bearing
types.
For additional information about clearance
or preload, refer to Selecting internal clearance
or preload († page 212).
Materials for rolling bearings
The materials from which bearing components
are made, determine, to a large extent, the
performance and reliability of the bearing. For
the bearing rings and rolling elements, typical
considerations include hardness for load carrying
capacity, fatigue resistance in the rolling
contact area, under clean or contaminated
lubrication conditions, and the dimensional
stability of the bearing components. For the
cage, considerations include friction, strain,
inertial forces, and in some cases, the chemical
action of certain lubricant additives, solvents,
coolants and refrigerants. The relative importance
of these considerations can be affected
by other operational parameters including
moisture, elevated temperatures, shock loads
or a combination of these and other conditions.
Rolling bearings with integral contact seals
can also have a considerable impact on the
performance and reliability of the bearings.
Their materials must be able to resist heat,
chemicals and oxidation. Bearings that are
capped on both sides normally are lubricated
for life. For detailed information about lubrication
and lubricants, refer to Lubrication
(† page 239).
SKF has the competence and facilities to
provide a variety of materials, processes and
coatings. Therefore, SKF application engineers
can assist in selecting materials that can provide
superior performance for a particular
application.
Supplementary designation for internal clearance
Table 16
Suffix
Internal clearance
C1
C2
CN
C3
C4
C5
Smaller than C2
Smaller than Normal
Normal, only used together with an additional
letter that identifies a reduced or displaced
clearance range.
Greater than Normal
Greater than C3
Greater than C4
150