Quarry Processes And Equipment
While each quarry has its own specialized equipment, crushed stone, gravel, and sand quarries utilize similar processes. Heavy digging equipment like the front end loader can move over 50 cubic yards of material per scoop; drag lines can scoop more than 100 cubic yards (around 120 tons) of material per load. Considering 1 cubic yard of 3/8" pea gravel can cover a 50 sq.ft.area 6 inches deep, that single drag line scoop could move enough material to cover nearly 5000 sq.ft.! In order to move that much aggregate to various processing stations efficiently, conveyor belts and auger screw systems can transport over 5000 tons of material per hour from the mechanized excavation equipment. Powerful jaw, impact, and cone crushers can reduce the size of the feed belt raw material to the desired size range in minutes while imparting a fractured, coarse texture to the aggregates. This texture can be important for applications requiring good particle to particle contact, such as structural road beds.
Automated screen decks sort the output of either raw material or crushed feeds into prescreened gravel sizes, sand, and dust. This is a typical bottleneck in quarry operations, as accurate and efficient screening is a function of the raw material feed consistency (particle size distribution, density, foreign materials, and moisture content), how much oversize material is present, the desired screening efficiency, and the geometry of the screens. For example, overloading a screen by placing more material per square foot than can be sifted in a given amount of time will clog the openings and result in inconsistent sizing and excess overflow. Constant flow wash screens can further refine crushed and/or mined aggregates by washing off dirt, clay, and organic matter leaving behind clean, well sized gravels and sands. These products would typically be used for landscaping, asphalt pavements, drain beds, and other applications which cannot tolerate the presence of clays and silts. By utilizing settling ponds and deflocculants this wash water can be recycled many times, conserving a precious natural resource.
By operating these processes continuously stockpiles of commonly specified products can be created to provide almost instantaneous access to these construction materials in an efficient, timely manner. Location is also less critical as products can be loaded into rail cars and bottom dump truck and trailers to transport them to distant locations.