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Canada's “Rock to Road”
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Processing system overview Cewe’s Pipeline Road sand & gravel operations By Andy Bateman, Engineering Editor The centrally-located clarifier and belt press at Jack Cewe Ltd.’s Pipeline Road site is part of a comprehensive aggregate processing operation that includes separate wash plant and crushing circuits as well as a stationary hot mix asphalt plant. Wash plant circuit The production process for the aggregate wash plant begins at the 9.1 m face, where a Hough 555 loads two Volvo A25C 6x6 dump trucks on primary haul. From time to time, a loader is sent up to the upper levels of the pit face, where it loosens and casts out material to the active face below. The loaded trucks discharge into a 7,6 m 3 feed hopper with grizzly bars and belt feeder, feeding a series of eight field conveyors, each 38 m long x 914 mm wide, conveying pit run to a second similar feeder known as the front feeder. This layout provides flexible loading from different pit faces and the feeders may be run singly or in tandem. A Volvo A25 6x6 articulated hauler dumps feed material from the pit face at the primary crusher. Downstream of the two feeders, pit run is conveyed to a 6x20 inclined single-deck Simplicity scalping screen, which divides material at 44 mm. Oversize goes to the crushing circuit while undersize goes to the washed plant tower. Here, two stacked 6x16 screens size the material utilising rubber screens. The upper screen, a Telsmith Specmaker triple-deck unit, cuts material at 22, 14 and 9 mm sizes. Under-size passing the 9 mm screen falls on to the lower 6x16 screen deck, a Telsmith single-deck Vibro King with a 7 mm screen. The product range from this set up includes 44 mm minus granular, 19 mm minus round stone and 9.5 mm round stone in addition to bird’s eye stone (14 mm x 9 mm) and 9 mm minus sand. The latter is further processed in a Vamco 1.82 m x 6.1 m single sand screw from where sand is stockpiled. Overflow from the screw is pumped by a 6x8x18 cyclone pump to a hydrocyclone tower, where the underflow from pair of hydrocyclones produce a fine sand. Their overflow, containing predominantly minus 200 mesh fines, drops into a tub and from there is pumped to the clarifier, again by a 6x8x18 pump. Crushing circuit Like the wash plant circuit, the crushing circuit is fed with a Hough 555 loader and a pair of Volvo A25C 6x6 haulers. It is fed from a stockpile of 762 mm minus material, drawn from a number of locations in the pit. Material is dumped into the first of two 4x20 feeders that supplies a Hewitt-Robbins 30x48 jaw crusher, reducing the feed to 203 mm minus. A series of four conveyors then convey material to a grizzly hopper. Here, oversize discharges into a second smaller jaw crusher, a Cedarapids 25x40, reducing the material stream from 203 mm minus to 101 mm minus. Material is then conveyed to a Simplicity 6x20 double-deck screen, the first of the crushing plant screens. This Simplicity unit has a urethane top deck with 50 mm openings and a wire cloth with 14 mm openings in the bottom position. Material retained on the top deck is crushed by a Symons 4-1/4 cone crusher, while material retained on the lower deck bypasses the cone and is recombined with the cone product. This stream is conveyed to a second screen above a set of three product bins, while material passing the bottom deck (14 mm minus) drops conveyed directly into the product bins. The screen is a Nordberg 6x20 triple-deck unit carrying 38 mm, 20 mm and 14 mm screen cloths. Material retained on both the upper and middle decks (20 mm plus) is crushed in a Nordberg 1560 Omnicone, and from there conveyed to a Hewitt-Robbins 6x16 triple-deck screen fitted with 20 mm, 16 mm and 3 mm cloths for further sizing. Granular base sizes produced by the crushing circuit include 50 mm minus highway granular base, 19 mm minus highway granular base and 19 mm minus municipal granular base. The two 19 mm granular products vary slightly in their grading curve, particularly in allowable fines con-tent; highway base specifications set an upper limit of 5 per cent passing the 200 mesh sieve, while the municipal base has a 8 per cent limit on material passing the same sieve. As general manager George Turi explained, continuing reductions in the allowable fines content in these base materials were a factor in the company’s decision to invest in the clarifier and belt press set up. Additional products from the circuit include 14 mm minus feedstock for the pitbased Madson 5000-lb asphalt batch plant, as well as the occasional production of 25 mm minus granular base, 19 mm clear and 16 mm x 3 mm pipe bedding. Finished product is stockpiled by conveyors serving the product bins, with the Volvo truck fleet hauling product to other stockpiles as necessary. The company’s shipping loader fleet includes two Caterpillar 980G’s, with one loader normally assigned to each plant.
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