Walking Dragline

Overview

A walking dragline is among the largest mobile land machines ever built, a multi-thousand-tonne electric excavator used in surface coal and oil-sand mines to strip the overburden lying above the seam. Rather than load trucks, it casts spoil directly from the cut to a dump area beside it, so a single machine can move enormous volumes at very low cost per cubic metre. The whole upper structure swings on a central tub, and the machine relocates by literally walking on a pair of hydraulic shoes.

The digging tool is a Dragline Bucket of tens of cubic metres, slung from wire ropes with no rigid arm. Two rope systems do the work: drag ropes pull the bucket toward the machine to fill it, and hoist ropes lift it clear for the swing. Because the bucket hangs free, a dragline is a forgiving, high-volume digger but a coarse one, it strips bulk material, leaving precise grading to other equipment.

How it works

A dig cycle has four moves: cast the bucket out, drag it back through the bank to fill, hoist and swing to the spoil side, then dump. The Drag Machinery and Hoist Machinery each wind their ropes on a large grooved drum driven by twin DC Mill Motor units through a heavy Reduction Gearbox; a band brake on each drum holds the loaded bucket between moves. The ropes run out over the Boom & Mast, whose lattice boom is held up by suspension ropes off the mast and turns the hoist ropes down to the bucket at the boom-point sheaves.

Swinging the loaded bucket to the dump is done by several Swing Drive Unit units spaced around the Walking Mechanism roller circle; their pinions walk the upperworks around the swing rack on the tub. Moving the machine between dig positions uses the same walking mechanism: eccentric cams driven through the propel gearing lower the Walking Mechanism shoes, which lift and shift the tub one step at a time, then set it back down to dig.

All of this is powered and controlled from the deck. The Electric House & Power takes the incoming utility feed through a transformer into motor-generator sets and drive cabinets that supply smoothly variable current to every main motor. The operator runs the cycle from the Operator Cab on master controllers, while the Control System enforces interlocks, watches rope loads, and logs production.