Modern Mining May 2015



MODERN MINING



May 2015

CRUSHING, SCREENING

AND MILLING

feature

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

Massive

scalping screen

engineered for tonnage

Joest scalping or run-of-

mine screens are typically

the first step in screening

ROMmaterial in the

extractive metallurgical

process on a mine.

Kenny Mayhew-Ridgers, General Manager Engineering at

Joest South Africa.

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.

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