Rock to Road

Equipment Pits & Quarries
Oldie but Goodie


July 28, 2008
By Andy Bateman


Topics

As part of its vertically integrated aggregates and roadbuilding business, Guelph, Ont.-based Cox Construction Ltd. offers contract crushing, utilising a number of portable spreads. One of these spreads has now been in service for more than twenty years, is still in mostly original condition and continues to deliver for its owner.

As part of its vertically integrated aggregates and roadbuilding business, Guelph, Ont.-based Cox Construction Ltd. offers contract crushing, utilising a number of portable spreads. One of these spreads has now been in service for more than twenty years, is still in mostly original condition and continues to deliver for its owner.

Aggregates & Roadbuilding recently saw the plant in a quarry application where it was producing Granular A base material and a clear sized drainage stone from unabrasive dolomitic limestone. Plant foreman Paul Tolton explains that this has been typical duty for the plant. By any measure, Tolton is well qualified to comment on this plant’s operation, having been its principal operator since it went into service back in 1987!


In production, shot rock was fed to the plant by two wheel loaders, Caterpillar 980G and 980H units, feeding both sides of a 15-tonne capacity feed hopper. Any material in the shot rock already smaller than 100 mm passed through a grizzly and bypassed the primary crusher while larger material was crushed to 127 mm minus by the Cedarapids 32×42 primary jaw. Primary crusher run was conveyed to a 6×16 ElJay screen fitted, for this application, with 52 mm and 24 mm opening screen cloths on the top and middle decks respectively, with the bottom deck open. Material passing both screens was stockpiled as Granular A base material. At the same time, plus 52 mm material retained on the top deck was conveyed to a 1.37 m Cedarapids/ElJay Rollercone Classic cone crusher fitted with a standard head. The 32 mm minus product from this crusher fell onto a common belt also passing underneath a second 1.37 m Cedarapids/ElJay Rollercone Classic cone crusher fitted instead with a fine head. Material from both crushers was conveyed to the plant’s second screen, a 6×20 El Jay triple-deck screen, fitted with 32 mm, 24 mm and 6.3 mm screen cloths on the top, middle and bottom decks, respectively. Plus 32 mm material retained on the top deck of this screen was conveyed to the standard head cone, while material passing the top deck and retained on the middle deck (minus 32 mm plus 24 mm) was conveyed to the fine head crusher. Material passing the screen’s middle deck and retained on the bottom deck, minus 24 mm plus 6.3 mm, was stockpiled as clear sized drainage stone, while minus 6.3 mm material passing the bottom deck joined material from the 6x 16 screen going to the Granular A stockpile. The plant was operating with a crew of four, consisting of operator, two feed loaders and a ground man. Average reported production rate in the configuration seen was 350 tonnes/h.


In Tolton’s view, daily plant inspections and regular servicing are two essential elements of extended equipment life, both fixed and mobile. For instance, full services are completed on the crushers every 750 hours and every 750 hours on the wheel loaders with the aid of bypass filtration. Company president Regan Cox explains that these services are coordinated so that they are completed at the same time to maximise overall plant uptime. The extended service interval also means only one shutdown is necessary every 750 hours instead of the three that would be necessary on 250-hour service cycles. For Cox, this approach makes good environmental sense as well as good business sense; extended service intervals means less virgin oil consumed and therefore less waste oil produced.


For the whole crushing spread, plant life is further boosted by a regular overhaul. Most winters, the plant goes into Cox’s Guelph shop where any significant repair work or process flow alteration is completed to minimise unscheduled downtime the following season. Once the plant is back in service, Tolton stresses the importance of keeping a close eye on items such as wear plate, conveyor belting and bearings to prevent minor problems from developing into much bigger headaches. Good housekeeping plays a valuable role in this process to keep platforms, catwalks and work areas clear, with the added safety benefit of reduced trip and stumble hazards.

Tolton notes that the plant’s entire throughput, in excess of ten million tonnes, has passed through the primary jaw crusher which, apart from a frame repair last year, has processed all of that material uneventfully. In addition, the crusher’s original set of jaw dies lasted over ten years (including turns), reflecting the plant’s duty in limestone that significantly less abrasive than, for instance, the granite of the Canadian Shield.


Asked to estimate the plant’s total accumulative operating hours, Tolton points to the engine that has powered the plant’s 800kW generator since new. "Whenever I’ve been here, that engine has been running, so the total hours on that engine are probably similar to the hours I’ve spent operating this plant." The hour meter on the Caterpillar 3512 diesel engine records an impressive 31,000 total hours and itself underscores Tolton’s point about the value of regular servicing. A recommended top engine overhaul was completed at approximately 25,000 hours, but that aside, the engine is all original and has delivered continuous service from its in service date to the present.


According to the processing plant’s manufacturer, Cedarapids, design and construction also play a role in performance and longevity. The nitrogen-over-hydraulic tramp iron relief system on the two roller cone crushers is said to pass large uncrushable objects that would jam or stall other crushers. In addition, the massive base frame is said to direct compression forces to the product, greatly reducing energy losses due to structural deflection found in other shaft type cones. The crusher’s roller bearings are over designed to provide a very long service life, while weight and crushing stresses are spread over two radial and two thrust bearings such that the pressure in any one area is reduced. The literature adds that Rollercone Classics run cooler than other cones due to less internal friction, as evidenced by their reduced oil requirement compared to other designs. The Rollercone has two oil systems to provide adequate lubrication, with an external bearing pre-lube pump for start up and an internal pinion shaft driven pump for operation. All of the oil is self-contained in the crusher base, so that no external cooling tanks are necessary, while the tightly sealed system is said to reduce the chance of contamination by water and grit. n


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