P&N High Temperature Bearings
P&N specialises in the Design and Manufacturing of Bearings for Strand Guiding Rolls. In every segment of bow casting machines there are different bearing requirements. P&N provides a different solution for every requirement.
The Strand Guiding directly below the mould and segment 0 or 1 works with Split Rolls. This means that there are many rolls running on one journal. Depending on the strand width, the P&N design has two or three rolls mounted on one journal. The design solution with one continuous roll is not possible because there would be too much deflection because of the required low roll diameter.
|Drawing 1 (at the bottom of the page) shows that every roll is
guided by two moveable bearings. By using two moveable bearings, the roll can be shifted
freely in an axial direction - we call this a swimming roll.Temperature-related length
expansions of the roll casing caused by contact with the red hot strand do not damage the
bearing. The spiral inner bushings are mounted solidly on the journal. Meanwhile, the
other bearing parts like Roller cages spiral outer bushes and side rings are mounted
inside the roll. The Strand Guiding Roll can therefore move freely in an axial direction
with the roller cage which is guided by two side rings.
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.
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