The owner of a large cement plant and adjacent quarry in the southeastern United States needed a new, custom, easy-to-relocate portable impact crusher and 700-ft. highly mobile conveyor to work in conjunction with an existing stationary crusher and permanent overland conveyor with a highly sophisticated chemical analyzer installed on it.
The quarry features two similar but chemically different types of limestone. It is necessary to feed the proper blend of these stones to the cement plant. With only one crusher, blending the limestone mix dictated by the analyzer was cumbersome. So much of one type of stone would be fed into the crusher, then so much of the other. But two crushers – with each handling a different type of limestone and automatically feeding the conveyor as directed by the chemical analyzer – would make the job easier, faster and more precise.
Making it Work
To meet operational specifics, Grasan designed a wheel-mounted, electric-motor-powered crushing plant with the feed hopper on the “hitch” end and a discharge conveyor on the “tail” end. A tow dolly installed at the fifth wheel hitch allows the plant to be moved with a front-end loader. The plant utilizes a Hazemag APPH hydraulically controlled horizontal primary impactor for increased crusher capacity, smoother operation and more uniform products.
Six individually controlled hydraulic leveling legs (two front, two middle, two rear) make the crusher plant quick and easy to tear down and set up as needed for moving. Unlike hydraulic jacks, which provide support only until braces or blocks are put in place for operation, the hydraulic legs provide total operational support without the need for braces, blocks or other devices. Each leg has its own raise-lower control for precise leveling and 324-sq. in. footpad for stable footing, even on soft ground.
The new crushing plant’s discharge conveyor feeds a radial stacking conveyor that feeds a surge bin. Level controls in the surge bin control the feed rate of the grizzly feeder on the new crushing plant. The surge bin, with its variable speed drive, meters the tonnage determined by the analyzer onto the 700-ft. conveyor.
Simultaneously, the existing crusher, with its own variable speed drive, feeds the 700-ft. conveyor at a rate also determined by the chemical analyzer. Improved mix control comes from being able to feed both materials – one from each crusher – onto the conveyor at the same time with their respective rates determined by the chemical analyzer.
Grasan developed a design for the moveable 700-ft. conveyor by engineering 40-ft. modules, made of heavy steel channel frames that snap together using self-aligning joints, with a single box-frame support leg on the end of each module. This design facilitates an easy tear down and reassembly setup procedure. The modules can be moved with a front-end loader.
Since the crushing plant is about a half-mile from the cement plant, the system utilizes a 4,160-volt power supply to keep the power cable to a reasonable size for portability and economy. Grasan, in conjunction with the cement plant electrical engineer, developed a modular control station with transformer and switch gear. The control station is skid-mounted for easy towing.