The temperature transition through the strand on the roll casing causes an
increase of the roll diameter and consequently of the bearing bore. The spiral outer bush
is fitted with pretension to the outside and expands proportionately without losing
contact with the expanding bore. The bearing clearance increases accordingly.
Advantages of Spiral Bush Bearings
1. The bearings are manufactured from spring steel. Spring
steel has an annealing temperature of 350° and is therefore less temperature sensitive
than Ball Bearing Steel (100Cr6) which has an annealing temperature of 180ºC. At
temperature loads above the annealing temperature, materials undergo extreme loss of
hardness. Spring steel is therefore better suited at high temperatures.
2. The Spiral Bushings have pretension whereby an easy mounting is
possible. With the help of two hook spanners, the inner bushes (journal bushings) can be
fitted on every suitable point. The bushings then adhere because of internal tension.
Using drawn materials with a tolerance field h9 or even h11 for the journal is common
practise and expensive machining on the journals can therefore fall away.
3. The bearings are sturdy and are insensitive to dirt, scale,
water and also hydrofluoric acid (which forms when casting powder mixes with water). The
thin-walled spiral bushings leave a large space for rolling elements with large diameters
which can roll over dirt and other foreign bodies and press particles into the coil gap of
the spiral bushings. This keeps the running trail of the bearing free.
3. The special advantage of the spiral bushing bearings is that
the roll jackets can be used many times. Once the roll jacket on the outer surface has
been worn out bent due to the temperature influence, it is then possible to re-machine
these roll jackets. The bearing seating bores also have to be reworked. In these cases,
only the spiral outer bushings and not the complete bearings must exchanged. All the other
bearing parts are used again. The reworking of the bearing bores happens in stages of 1mm
steps in diameter. One increases, for example, a bore of 105mm to 106mm, and fits in the
spiral outer bush with a larger wall thickness. As this can be repeated up to a diameter
of 110mm, the roller jackets can be reworked up to six times and an equivalent often
brought into action. This means a substantial cost saving especially as all the other
bearing parts may also be re-used up to six times.
In the down sections (Drawing 2) of slab casters
there are continuous rolls with proportionately larger roll diameters. Often, a centre
support through a split and water-cooled bearing is chosen. These bearings are custom
designed and produced. P&N offer the bearings as well as the bearing housings. These
rolls are also bound by one fixed and a number of moveable bearings. P&N offer an
alternative to the common use of spherical roller bearings: a cylindrical roller bearing
which is self-aligning due to a spherically-shaped outer ring. These bearings offer an
advantage in that roll deflection and mounting inaccuracies can be tolerated and, at the
same time, a smooth axial shifting of the roll inside the moveable bearing is facilitated.
The roll pivot with inner bushing can be shifted smoothly between the inner bush and
rolling elements because the bearing play occurs exactly at this point. The outer
measurements of these bearing are the same as the measurements of spherical roller
bearings. Consequently, these P&N Self-Aligning Cylindrical Roller Bearings are
interchangeable with spherical roller bearings.