Roller Mils are directly driven bevel-wheel planetary gears or bevel cylindrical gear units. The gear unit represents an almost integral component of the mill. The output flange of the gear unit is rigidly connected with the grinding table. In addition to transmitting the torque ,the gear unit also has capability to take up the reaction forces from the the griding force of the mil’s rollers. Hydro dynamically or hydrostatically lubricated thrust bearing being mounted in the upper housing parts of the gear unit absorb the grinding force which is then transferred though the housing into mill’s foundation. This growing number of roller mills in operation as well as the increasing specific need and demand of gear transmission feature.
| Spec |
Detail |
| Features |
Bevel Planetary Gear box with horizontal input and vertically flanged output shaft with inbuilt thrust bearings |
| Advantages |
Compact design suitable for high power transmission and capable of withstanding high loads due to grinding rollers |
| Technical Specifications |
B1PV 80 to B1PV 200 |
| Product Application |
Vertical Roller Mills for grinding in Coal, Raw and Cement |
| Range |
B1PV 80 to B1PV 200, Power up to 2,000 kw |
The growing number of roller mills in operation as well as the increasing specific need and demand of gear transmission features such as:
- High power transmission capability of the mill
- Favourable efficiency
- Low-noise
- Lower space requirements
- Low weight
- High availability
Contrary to the bevel cylindrical gearboxes used in the past, the bevel planetary gear units in particular stand out with the following advantages:
- Package-type, space saving design, thus lower weight by dividing power onto several planetary gears.
- More favorable efficiency as a portion of the power in the planetary stage is transmitted without losses as coupling power.
- Lower noise level, as only a part of the power in the planetary stage is transmitted by the gear teeth. More-over, the high-speed bevel gear stage is located centrally within the gear unit, a fact contributing to additional noise damping.
- Direct transmission of the grinding forces from the mill into the foundation over a circular symmetric housing with nearly the same stiffness.
- Arrangement of the axial bearing pads directly above the housing wall, so that partial deformation of the axial bearing due to axial forces coming from the mill are avoided.
- Higher precision of manufacturing quality owing to the circular symmetric shape of the housing.
- The compact design automatically necessitates a smaller, and thus more simpler foundation plate.
- Particularly easy to assemble and disassemble, not only because pressure plates and gears can easily be dis-mounted, but also because there is no need to seal the joint surfaces as is required for split housings.
Further developments and improvements following the extensive experience gained over the years with the operation of many gear units ensure the high reliability of bevel planetary gear units B1PV.
The comparison of the above sketches shows that the bevel planetary gear unit has much smaller dimensions, yet with the same power transmission capabilities.
Construction of the Bevel Wheel-Planetary Gear Unit B1PV
Input Stage
Drive is accomplished over a bevel gear stage with horizontally arranged input shaft. The bevel pinion shaft (1) and the bevel gear shaft (2) are mounted on anti-friction roller bearings.
The paired taper roller bearings take up the axial thrust coming from the bevel gear stage.
Planetary Stage
The torque is transmitted by a gear coupling (3) from the bevel gear shaft (2) to the central sun pinion (4) of the planetary stage. The uniform distribution of the torque on three planet gears (5) is ensured by the freely adjusting sun pinion (4) and by the planet gears (5) which are supported on spherical roller bearings.
As an additional degree of freedom the planet carrier (6) will not be supported by bearings in case of gearboxes from size B1PV 140 onwards. In this case, a gear coupling connects the planet carrier with the thrust plate (8) on the output side. For gearboxes up to the size B1PV 125 (Fig. 2) the planet carrier (6) is connected with the thrust plate (8) by the shrink fit. Here, the planet carrier is radially guided over the upper anti-friction roller bearing. The central annulus (9) of the planetary stage is firmly held with the housing in both cases.
Output
The output of the gear unit is effected over a pressure plate (8) that is firmly connected with the grinding table by means of bolts. The vertically directed grinding forces induced from the mill are directly led over various slide bearing pads (10) and across the housing wall into the foundation. Additional radial forces out of the grinding process will be absorbed by slide bearings for gearboxes as of size 140, and by roller bearings for smaller gearboxes up to the size 125.
Axial Thrust Bearing
The optimum design and construction of the axial thrust bearing ensures high operational safety. Here, the circular symmetric slide bearing pads proved very great success. The axial thrust bearing is rated on the basis of the required lubrication film and of sufficient security as a function of geometry of the circular pads, load, circumferential speed and oil viscosity.
The Hydrodynamically Lubricated Axial Thrust Bearing
Hydrodynamically lubricated thrust bearings are used for small and medium grinding forces, whereby the main motor will drive the mill with unloaded or raised grinding rolls to operating speed (Fig. 1 ).
Hydrodynamically & Hydrostatically Lubricated Axial Thrust Bearing
Thrust bearings continuously lubricated hydrodynamically and, in addition, hydrostatically, are used for medium up to high grinding forces, where the mill with unloads grinding rolls is slowly accelerated by an auxiliary drive.
The Fully Hydrostatically Lubricated Axial Thrust Bearing
Fully hydrostatically lubricated axial thrust bearings are used for mills with very high grinding forces and for nearly all starting conditions. (Fig. 2)