Maintenance under the mill
Major maintenance of conventional VRM drives involves the removal of drive motor, coupling guard, coupling and gear unit from under the mill. After maintenance, the motor has to be realigned.
COPE opens a new horizon in the maintenance of compact gear drives under VRMs: If one drive is inoperable, the operator has four options:
- disconnection of the motor and letting it idle until the operational requirements allow its removal
- quick drive disengagement where the drive unit remains passively in the gear unit and is just radially moved to disengage
- removal of the drive unit and operation with less motors
- replacement of the drive unit.
In any case, the gear unit is left under the mill which can continue operating at close to nominal load as one motor just represents 12.5 % (8 motors) to 17 % (6 motors) of the total installed power.
Through the grinding table of the LM, the central sun gear and the coupling between the two stages are accessible.
This way, more than 50 % of the geared components and more than 70% of the bearings are accessible without requiring a major stop, on-site work by gear specialists and shaft alignment. For conventional drives, this figure is around 10 % for both the geared components and the bearings. This is a big step forward in maintainability.
All bearings which are not easily accessible are fatigue-proof sleeve bearings. Gears (except the driving pinion) and couplings are designed in a way that their back flank can become the load flank – i.e. COPE is the first large size drive with the “spares built in”.