Mill ball charging systems have undergone little change during the past two decades. Most operations utilize a locomotive/ball car combination to load and haul charges from the ball storage bin to the mill charging boxes or, alternatively, transport charges to the charging boxes by means of a ball bucket handled by bridge crane.
The grinding section at Island Copper is a semi-autogenous, two-stage circuit comprising six 9.75 m diameter by 4.27 m primary mills with 6000 HP drives and three 5.03 m diameter by 6.71 m secondary mills with 3000 HP drives.
Components of the ball handling system are:
- Ball storage hopper with vane feeder and drive.
- Conveyor flight No. 1 to transfer point inside the mill building.
- Transfer point and operator station.
Conveyor flight No. 2 from transfer point to the charging stations.
- Nine ball charging stations on conveyor flight No. 2 to serve the nine mills.
- Nine ball launders to accept balls from the belt unloading stations and convey to the mill feed chutes.
- Control system.
At the charging station the top strand of the belt rides from the transition idlers onto a flat steel plate set at the same elevation as the last transition idler in front of the station. Belt hold-down rolls are provided at each corner of the flat plate to stabilize transit of the belt through the station.