Development and principle of operation
Roller presses, also referred to as cylinder crushers or horizontal mills, were developed in the mid-eighties. They consume considerably less energy than is required for traditional size reduction processes. Machines are currently being developed which will even surpass the throughput of 1000 t per hour generally obtained today. In this connection, FAG maintains a dialogue with all roller press manufacturers of importance.
Roller presses are used for coarse grinding, hybrid grinding and fine grinding. Coarse grinding produces grain sizes of up to 20 mm, fine grinding up to 0.04 mm. Typical grinding stocks include raw material of cement, cement clinker, foundry sand, coal and ores as well as other mineral materials.
One of two rolls which are synchronously driven in counterrotation is hydraulically adjusted against the other one. Under high pressure the roller press causes the formation of cracks in the material charged. Misalignments caused by the grinding process are compensated via the adjustment mechanism of the hydraulically preloaded roller. Depending on the requirements, the rollers feature either a level or a shaped surface.
Due to their high load carrying capacity, spherical roller bearings (fig. 8) or multi-row cylindrical roller bearings (fig. 9) are preferably used to support the rollers in roller presses.
Spherical roller bearings transmit high radial loads, and axial guiding forces. Moreover, they compensate tiltings resulting from a shaft deflection or from misalignments from one spread to the other.
The spherical roller bearing at the drive end is designed as a locating bearing whereas that at the operator end is a floating bearing.
Alternatively, the high radial loads can be accommodated by multi-row cylindrical roller bearings of a special design. The axial loads are accommodated by spherical roller thrust bearing pairs.
The machine manufacturer must make the chocks (housings) self-aligning so that the limiting values of the admissible contact pressure in the raceway/roller contact areas of the cylindrical roller bearings are not exceeded.
By providing narrow tolerances for the roller boundary circle diameter and the raceway diameter of the inner rings, an even load distribution over all roller rows of the cylindrical roller bearing is achieved. When new roller presses are developed FAG designs the bearing arrangements together with the machine manufacturer.