Dust Screws

A row of dust screws runs underneath the bag filter at Kandos Cement Works, collecting the dust caught by the filter bags above and feeding it back into the cement stream. Each screw is housed in a steel trough roughly half a metre across, with a hinged inspection lid and a row of bolted access plates along the length. The drive motors sit at one end on small concrete pedestals, coupled to the screw shafts through reduction gearboxes. The whole assembly is bracketed off the floor at chest height. A pale grey crust of cement dust covers the upper surfaces of the troughs and the supporting steelwork. Light from the high windows of the bay catches the row of motors and pools on the floor below.

Dust screws are an unglamorous but essential part of any cement-handling circuit. The plant's bag filters collect cement dust from the extraction air, and the dust drops out of the filter housings into the screws below, which then carry it laterally to a discharge point where it rejoins the cement stream. The system runs continuously while the plant is operating. At Kandos the dust screws ran across the operational life of the cement mills and bag filters they served. The works closed in September 2011 after 95 years of cement production. Cement Australia's reasons cited at closure were dated, inefficient technology and high fixed costs, and the considerable distance from the Sydney market. The screws have not moved since.