CARB® toroidal roller bearings – a revolutionary ... - Acorn Bearings

1 Product information 2 Recommendations 3 Product data
Page ............. 3 Radial location Page ............. 37
Design of bearing arrangements
Two bearings are generally required to
support, guide and locate a shaft in
the radial and axial directions. To do
this, one bearing is designated the
locating bearing and the other is the
non-locating bearing.
In traditional self-aligning bearing
systems, the locating bearing locates
the shaft axially in its housing while
the non-locating bearing typically
moves in its housing to accommodate
axial expansion of the shaft.
With the new SKF self-aligning
bearing system, a CARB toroidal roller
bearing is used in the non-locating
position and either a spherical roller
bearing (➔ fig 1 ) or a self-aligning
ball bearing (➔ fig 2 ) is used in the
locating position. Because a CARB
bearing can accommodate axial
expansion internally like a cylindrical
roller bearing, it prevents internally
induced axial forces from occuring that
would otherwise that would otherwise
be present if the bearing had to slide
on its seating in the housing. This ability
to accommodate internal axial forces
allows the bearing rings to be axially
located on the shaft and in the housing.
Radial location
To take advantage of the very high load
carrying capacity and full life potential of
a toroidal roller bearing, the bearing
rings must be fully supported around
their whole circumference and across
the full width of the outer ring.
Selecting the proper fit
To locate a shaft radially, most applications
require an interference fit between
the bearing rings and their seatings.
However, if easy mounting and dismounting
are required, the outer ring
will have a looser fit.
Recommendations for suitable shaft
diameter and housing bore tolerances
for CARB toroidal roller bearings are
given in tables 1 , 2 and 3 . These
recommendations apply to solid steel
shafts and housings made from cast
iron or steel.
Generally, CARB toroidal roller bearings
follow the fit recommendations
for spherical roller bearings on shafts
and in housings. However, a spherical
roller bearing on the non-locating side
must be axially free, which requires a
loose housing fit – this is not necessary
for bearing arrangements using a CARB
toroidal roller bearing. CARB bearings
(and locating spherical roller bearings)
can therefore utilise the advantages of
tight outer ring fits if mounting and
dismounting allow this, but for normal,
stationary outer ring load it is not necessary.
For example a K7 fit is applied to
bearings in the split housing for a fan
with an unbalanced fan rotor and a P7
fit applied to a non-split housing.
Bearings with a tapered bore are
mounted either directly on a tapered
journal or on an adapter or a withdrawal
sleeve on cylindrical shaft seatings.
The fit of the inner ring in these
cases depends on how far the ring is
driven up the tapered seating.
Accuracy of associated components
The accuracy of the cylindrical seatings
on the shaft and in the housing bore
should correspond to that of the bearing.
For CARB toroidal roller bearings
the shaft seating should be tolerance
grade 6 and the housing seating grade
7. For an adapter or withdrawal sleeve,
wider diameter tolerances can be
SKF self-aligning bearing system with a spherical roller
bearing at the locating side and a CARB toroidal roller bearing
at the non-locating side
SKF self-aligning bearing system with a self-aligning ball
bearing at the locating side and a CARB toroidal roller bearing
at the non-locating side
Fig 1
Fig 2
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