As reported in this column last April, Caterpillar announced plans to build a mechanical-drive haul truck sized to match the capacity of existing and anticipated large mining shovels. The company recently released more details on the yet-to-be-built 360-ton-capacity vehicle. That announcement, although unrelated, follows the commissioning of O&K's first 55-cu-yd RH400 hydraulic shovel, designed to load 240-ton and larger haul trucks.

The new Cat 797 will be a two-axle, mechanical-drive haul truck rated at 360 tons payload capacity. The power system will have a gross rating of 3,400 hp. A seven-speed electronically controlled transmission will move the 1.2 million-lb machine at a top speed of 40 mph. Loading height of the bed will be 22.7 ft.

With a maximum dumping height of 40 ft, O&K's new RH400 is easily capable of loading the 797. The 1.8 million-lb shovel can be powered by two, water-cooled Cummins diesel engines with total output of 3,400 hp or by two electric motors. Both ground-level crowd force and breakout force are rated at 471,930 lb. The hydraulic system requires a total oil volume of 3,450 gallons and achieves pressures as high as 4,350 psi for the attachment and 5,220 psi for travel. Top speed is 1.37 mph.

An optional operator's amenity cab extension serves as an on-board lunchroom and includes clothes lockers, microwave, water dispenser, coffee maker, toaster oven and refrigerator.

Neither of these giant machines are likely to turn up at an aggregate operation in the foreseeable future. But it's reasonable to expect that some of the technology incorporated into their design will in some way help improve the productivity and reliability of smaller mining equipment.

In early November 1997, a German limestone quarry began operating a 4,400-tph, semi-mobile primary crushing plant manufactured by Krupp Fordertechnik. The plant features two gyratory crushers, each with a 54-in. feed opening and 75-in. cone diameter. The total plant weighs about 3,100 tons.

Within the plant, two identical crusher stations are arranged in parallel about 100 ft apart. Each station has a 385-ton dump hopper underlain by an 8-ft-wide apron conveyor that feeds material to a roller screen, which removes minus 6-in. rock. A water spray also washes off sand and clay contaminants.

The gyratory crushers reduce the limestone to a minus 7-in. size. Crusher discharge passes to a vibrating trough and then to a transfer conveyor belt that transports the material to a 4,600-ft-long central belt conveyor linking the crusher stations with the limestone-washing plant.

The minus 6-in. material that passed through the roller screens is further separated on a double-deck, linear-vibrating screen before being transferred to the washing plant.

A service unit installed between the crusher stations contains a crane for performing maintenance on the facility.

Design and manufacture of the crushing plant took 17 months; on-site construction required seven months, Krupp said.

Krupp said it built the world's largest semi-mobile crushing plant in 1989 for an open-pit copper mine in Chile. That plant processes 11,000 tph of overburden.