Modern Mining May 2015

CRUSHING, SCREENING AND MILLING

Massive scalping screen engineered for tonnage

Engineering vibrating screens and feeders requires an in-depth understanding of the nature of the application. Gunter Vogel, Chairman of Joest South Africa, says that it is critical with screens and feeders to ensure that forces are directed through sections of the structure and components that are sufficiently strong to handle them.

I n addition, he emphasises that it is impor- tant to ensure that for screens and feed- ers the centrifugal forces generated are directed evenly along the designed drive angle, near or through the centre of grav- ity. “This ensures that the machines run sym- metrically along the longitudinal axis. In this way the material will be carried across the feed deck of the screen or feeder in a steady and even motion, providing effective screening,” he says. Kenny Mayhew-Ridgers, General Manager Engineering at Joest South Africa, states that screens should not be merely an add-on in a processing plant flowsheet. It is critical that these sometimes very large items of equipment are integrated during the design stages of the project and that all aspects of downstream and upstream processes are factored in to guarantee fit-for-purpose screens. “This is the only way to ensure that a screen is engineered for the required tonnage,” he adds. Scalping or run-of-mine screens are typi- cally the first step in screening Run-Of-Mine (ROM) material in the extractive metallurgical

Kenny Mayhew-Ridgers, General Manager Engineering at Joest South Africa. process on a mine. These machines are often required to separate large boulders from vast amounts of smaller material for recrushing. Joest South Africa produced its first scalp- ing screens during the 1970s and has built a substantial footprint of scalping screens throughout Africa, with the majority of the mines in the Northern Cape operating with some or all types of Joest screens. The biggest scalping screen manufactured to date by Joest South Africa is 3,7 m by 10,2 m and is driven by three of the largest exciter gearboxes which generate a centrifugal force of in excess of 2 MN (meganewton). “Due to be installed on an iron ore mine, this ROM screen may not be Joest South Africa’s largest screen in terms of its dimensions, but it is certainly the heavi- est, weighing in at over 50 tons,” says Mayhew-Ridgers. Joest South Africa received this sig- nificant order to re-engineer, manufacture and commission what is one of the largest screens ever produced to date for a mine in the Northern Cape. The scalping screen is required to handle variable ore condi- tions with a continuous feed load of a maximum of 6 000 t/h plus a 15 % higher surge capacity. Mayhew-Ridgers points out that the feed material from the mine is supplied

Joest scalping or run-of- mine screens are typically the first step in screening ROMmaterial in the extractive metallurgical process on a mine.

feature

60  MODERN MINING  May 2015