Ball Mill Outlet

The discharge end of a ball mill at Ashio Copper Mine drops the milled ore into a covered chute that runs down to the next stage of the processing line. The outlet itself is a riveted-steel housing bolted to the end of the mill drum, with a grate insert to separate the steel balls from the ground ore. Ore residue has built up around the housing in pale grey crusts, hardened where moisture has worked into the seams. The frame supporting the housing carries the marks of years of work: paint worn back to bare metal at the grip points, splattered with grease around the bearing housings. A short ladder gives access to the outlet for maintenance. The light here is low, falling through the milling-area windows in flat panels.

The ball mill outlet is where the rotating drum's product passed into the rest of the flotation circuit. Operators monitored the outlet for blockages and for changes in ore consistency, since either could shut the mill down within minutes. At Ashio the mills ran almost continuously for decades under the Furukawa modernisation that began in 1877. The Excavation Department closed in 1973. The mills stopped at the same time. The outlet has been still since, the residue cooling into the cement-like crust that holds the seams together more reliably than the original fasteners.