SKF - Rolling Bearings

Radial location of bearings
Radial location of bearings
If the load carrying ability of a bearing is to be
fully exploited, its rings or washers should be
fully supported around their complete circumference
and across the entire width of the
raceway. The support, which should be firm
and even, can be provided by a cylindrical or
tapered seat or, for thrust bearing washers, by
a flat (plane) support surface. This means that
bearing seats should be manufactured to adequate
tolerance classes and uninterrupted by
grooves, holes or other features. In addition,
the bearing rings should be reliably secured to
prevent them from turning on or turning in
their seats under load.
In general, satisfactory radial location and
adequate support can only be obtained when
the rings are mounted with an appropriate degree
of interference († Bearing clearance,
page 213 and Bearing preload, page 214).
Inadequately or incorrectly secured bearing
rings generally can cause damage to the bearing
system. However, when axial displacement
(as with a non-locating bearing) or easy
mounting and dismounting are required, an
interference fit cannot always be used. In
cases where a loose fit is required, special
precautions are necessary to limit the inevitable
wear from creep (turning). This can be
done, for example, by surface hardening the
bearing seat and abutments, lubricating
mating surfaces via special lubrication
grooves, or providing locating slots in the
bearing ring side faces to accommodate
keys or other holding devices († fig 12,
page 499).
Selecting fits
When selecting fits, the information provided
in this section should be considered, together
with the general guidelines in the section
thereafter.
1. Conditions of rotation
Conditions of rotation refer to the bearing ring
being considered relative to the direction of
the load († table 1, page 166). Essentially,
there are three different conditions:
• rotating load
• stationary load
• direction of load indeterminate
Rotating loads pertain if either the ring or the
direction of the applied load is stationary while
the other rotates. Heavy loads that do not rotate
but oscillate, such as loads acting on connecting
rod bearings, are generally considered
to be rotating loads. A bearing ring subjected
to a rotating load creeps on its seat if mounted
with a too loose fit, and leads to wear and/or
fretting corrosion of the contact surfaces. To
prevent this, an adequate interference fit between
the rotating ring and its seat must be
used. The degree of interference is dictated by
the operating conditions († points 2 and 4
below).
Stationary loads pertain if either both the
bearing ring and the direction of the applied
load are stationary or both are rotating at the
same speed. Under these conditions, a bearing
ring normally does not turn on its seat. Therefore,
the ring does not need to have an interference
fit, unless it is required for other reasons.
Direction of load indeterminate refers to
variable external loads, shock loads, vibrations
and unbalanced loads in high-speed applications.
These give rise to changes in the direction
of load, which cannot be accurately described.
When the direction of load is indeterminate
and particularly where heavy loads are involved,
SKF recommends an interference fit
for both rings. For the inner ring, the recommended
fit for a rotating load is normally used.
However, when the outer ring must be free to
move axially in the housing, and the load is not
heavy, a somewhat looser fit than that recommended
for a rotating load can be used.
F
165