Production of aggregates

Where does gravel come from Mines – rivers, banks, quarries Rivers – use dragline to mine gravel from river Banks – veins of gravel run thru a sand pit. Gravel mined by front end loader Quarries – rock blasted from walls of quarry, loaded on trucks and crushed Most gravel needs to be crushed

Rock Crusher –Reduce gravel to a smaller size –T 7-1 –F 7-1, 7-2 –Limemill – makes lime –Crusher output depends on crusher size and type, crusher settings, feed size, crusher speed, & other operating conditions F 7-3 –T 7-2 – T 7-3 specs –Primary crusher – first crusher in series –Secondary & tertiary crushers

Feeders and Screens Feeders supply gravel to crusher –Apron – hopper box over plate feeder F 7-4 –Reciprocating plate –Vibratory –Belt – uses hopper to feed belt –Grizzly – used over hoppers to remove oversize material – series of bars

Feeders and Screens Screens –Separate aggregate by size for storage, blending, recrushing –Rotating, vibrating (horizontal, inclined) –Usually in a deck of 2 or more screens F7-5 –Scalping screen removes oversized materials –Capacity based on Screen size, screen opening size, slope of screen, position in deck, amount of oversize and half size material, material conditions, shape, weight. F 7-6, Ex 7-1

Crushing Cycle F 7-7 Ex 7-2

Washing & Belt conveyor Need to wash aggregate before and after crushing Scrubber drums – inclined revolving drum with fins and spray nozzles Wet screens – screens with spray nozzles overhead Log washers – revolving auger paddles in a tub of water Sand Dehydrators – rotating augers in an inclined trough Clarifying tank – takes water & fines and clarifies water –Belt conveyor – major piece of equip in quarry – carries aggregate from place to place –Radial stacker – conveyor on a pivot to rotate