Quarry Southern Africa July 2018 | Page 28

WINNING
All photos by Kal Tire
Most quarry fines are produced during the crushing , milling , and size classification of quarried rock to produce single-size aggregate .
material , such as quartzite or dolerite , will produce fewer fines compared to a fine-grained material such as limestone or dolomite . To produce less blasting-related fines , the blasting method can be adapted to produce larger fragmentation , but this would require a trade-off study between the costs of blasting and crushing . A reduction in blasting costs may be offset by increased crushing-related cost or vice versa .
Rocks that contain a high percentage of flaky material , such as mica , have the effect of gradually blinding the screen , reducing the overall efficiency of the screen and product quality . In both crushing and screening , it is advisable to keep the moisture content less than five per cent .
The type of impact applied in a vertical shaft impact crusher can also influence the production of fines . Rock-on-rock
Oversize pieces of rock will slow the loading process and may exceed the maximum screen size set for the primary crusher , leading to reduced efficiency .
26 _ QUARRY SA | JULY / AUGUST 2018