Backing Bearings
Backing Bearings
Backing Bearings
Fig. 2
Dynamic measurement of an assembled backing bearing
Advantage: optimized running accuracy
SKFs advanced manufacturing processes enable tighter running
accuracy tolerances. Higher running accuracy means better, more even
support of the intermediate and work rolls during operation to provide
a more consistent, high quality rolled product.
Advantage: close section height
Using computer controlled measuring, sorting and assembly proced-
ures, the section height tolerance can be kept within narrow limits.
To do this, all inner and outer rings are measured individually and
matched with rollers of the appropriate size. The assembled bearings
are then dynamically checked ( fig. 2) and sorted according to their
actual running accuracy. This process controls the maximum deviation
of the section height of all SKF backing bearings to within 5 m, even
during operation.
3
Advantage: increased load carrying capacity
To obtain optimum load distribution and the lowest stress levels within
a bearing, SKF uses a quasi-logarithmic profile both in the roller/race-
way contact surfaces as well as on the outside surface of the outer ring
( fig. 3).
The logarithmic profile of the roller/raceway contact surfaces maxi-
mizes the contact area, enabling the bearing to accommodate heavy
static and dynamic loads. The effective load carrying capacity of the
backing bearing is also enhanced by the logarithmic profile of the out-
side support surface.
Advantage: improved wear-resistance
All SKF backing bearings are produced from ultra-clean bearing steel
and the steel is subjected to a unique bainitic heat treatment process.
This process provides a surface hardness in excess of 58 HRC while
maintaining good ductility of the rings.
The improved surface structure enables the lubricant film to be built
up reliably. This also contributes to a reduction in wear.
Advantage: improved resistance against cracking
Backing bearings are typically not susceptible to cold welding to the
intermediate rolls, and there is little risk of heat cracks occurring in the
side faces of the bearing where they make contact with the thrust
washers. Compressive stresses at the raceway surface resulting from
the bainitic heat treatment ( fig. 4) make the rings tougher and
and more resistant to cracking. Increased ductility also means that the
bearing is better able to withstand the over-rolling of contaminants.
Advantage: extended service life
Improved wear resistance resulting from the ultra clean steel and opti-
mized heat treatment process used to make SKF backing bearings can
significantly extend their service life. The logarithmic profile of the out-
er ring also improves service life as it maintains a favourable distribu-
tion of load and stresses within the bearing.
Should wear tracks appear on the backing bearings, the SKF
Remanufacturing Services ( page 8) can help. Remanufacturing can
return the bearings to a like-new condition, to fully exploit the life of
the bearing.
The application
Backing bearings have been specially developed for use on the backing
bearing shafts of cluster (Sendzimir) mills. Several bearings are
arranged on a stationary support shaft. The thick-walled outer rings
are in direct contact with the intermediate rolls and finally support the
work rolls.
The rolling forces are transmitted to the housing via the backing
bearings, support shafts and saddles.
Uniform load distribution of the roll force on each backing bearing
depends on its dimensional accuracy.
SKF backing bearings are excellent at providing such support.
Fig. 3
Logarithmic contact profile and stress distribution
Fig. 4
Internal stress condition after bainitic heat
treatment
tension compression
5mm
1mm 15
10
20
Backing bearings for cluster mills
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The product range
Backing bearings for cluster mills are manufactured in various
sizes and designs for support shaft diameters ranging from 70 to 180
mm; the outside diameters range from 160 to 406 mm.
The product tables on the following pages show the standard
assortment. For other sizes, check SKF for availability.
Bearing data general
Dimensions
Backing bearings are tailored products and have dimensions that are
not standardized either internationally or nationally. The standard
assortment of SKF backing bearings shown on pages 6 and 7 covers
the most common sizes used in cluster mills.
Tolerances
The inner rings are produced with a running accuracy that is better
than P4. The running accuracy of the outer rings is better than SP
(Special Precision). For cluster mills the section height of all backing
bearings on one support shaft must be as close as possible. Therefore,
the bearings are graded into section height groups ( table 1) and
are marked accordingly.
The position of the maximum wall thickness of the rings is marked
on one side of the inner and outer rings with an arrow. Two more
markings can be found on the outer ring side face: to the left of the
arrow the serial number of the bearing is marked and to the right of
the arrow the section height group is marked ( fig. 5).
Table 1
Section Section height
height group tolerance
measured
dynamically
m
A or 4 0 to 5
B or 2 5 to 10
C or 0 10 to 15
Material
SKF backing bearings belonging to the standard assortment are pro-
duced from extremely clean bearing steel and are bainite hardened.
Load carrying ability
The basic load ratings quoted in the tables take into consideration fac-
tors arising from the support of the outer rings by the intermediate
rolls.
However, for reasons of strength and deformation of the outer ring,
the value of the maximum permissible radial force F
r
should not be
exceeded.
The permissible static load acting on a backing bearing should not
exceed the value of F
0r
or C
0
, whichever is smaller.
Lubrication
Depending on the design and application, backing bearings can be
lubricated with
grease
oil
an oil/air mixture
the lubricant used for rolling.
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