Over the past 15 years the drive power installed in mining equipment has doubled, with production now reaching 5100-plus tonnes per hour.
Despite the huge increase in cutting rates, face conveyor service life has been tripled through the use of controlled start transmission drives and advances in line pan, machine frame, chain and sprocket design.
As longwall cut and load speeds increase, face conveyors have to keep pace. This means longer, more powerful conveyors with greater drive power, resulting in thicker chains and larger chain sprockets.
Wear can be a major problem, as uncontrolled wear leads to high-cost maintenance and effort, and unplanned longwall downtime due to chain failure.
Bucyrus tackled the problem by developing flat chains; however, early designs still suffered from the standard wear patterns. This was the result of surface pressures of 2000N/mm2 between the chain and the chain sprocket.
Despite the use of high-strength steel and hardened chain pockets, some working panels could not be completed without replacement of both chain and chain sprocket.
Tackling the problem again, Bucyrus resolved one approach was to increase the contact surface, thus reducing surface pressure and wear. This led to the development of the Power Chain.
The chain is produced through hot-forming of chain links, combining the use of round-steel and forged elements, or rolled profiles and forged elements.
Power Chain’s vertical link has a 42mm-diameter and is rolled to form a semicircular cross-section, thus offering greater link surface area.
The horizontal links are forged, with a 42-mm link surface area. The leading edge – normally round in a conventional chain – is flat, which Bucyrus says offers a larger contact surface area for drive sprocket. The central area for securing the flight bar has a key that engages a slot on the flight bar.
The OEM says the design almost halves surface pressure at contact points.
Bucyrus is currently developing a Power Chain suitable for up to 3 x 1800kW (3 x 2412hp), with tests having been completed in November 2007.
Power Chains are currently being prepared for several installations in Australia and the US.