Grasstree delivers black gold with Controlled Start Transmission

Longwall coal clearance is carried to the surface via a series of belt conveyors, elevating the coal more than 250m over a 6 kilometre track. Two main trunk conveyors which can deliver up to 6000tph are designed around Dodge CST (Controlled Start Transmission) technology, and are engineered to easily cater for the 4500tph longwall capacity plus development unit output.
The Dodge CST is a patented 2-in-1 drive that combines a planetary gear reducer and hydro-viscous clutch specifically engineered to deliver and synchronise power and to control acceleration of high-inertia loads such as long-haul conveyors.
There are more than 2000 CST units in operation around the world with about 180 of these in Australia. CSTs have a proven track record on conveyors up to 10 kilometres in length in coal, gold, iron ore and copper mines, cement and power generation as well as port facilities. Clutch-only versions are also highly effective for braking in decline application.
The first of the Grasstree trunk conveyors GCV006, delivers the coal over 1600m with a climb of 60 metres. This conveyor uses an 1800mm belt normally operating at 4.28m/sec for a capacity of 6,000tph. The conveyor is driven by three 630K CST drives mounted at the head, two driving the main pulley and one driving the secondary pulley. This conveyor also incorporates a tripper drive utilising another CST 630K, and there are provisions for an additional 2 tripper units as the belt is lengthened.
During mine development, a 1000 tonne underground bin was constructed in an excavated cavity between trunk conveyor GCV006 and GCV005. This smooths the flow of coal through the conveyor system, and provides additional production flexibility and prevents the need for total shut-down during short delays in production or clearance.
A vibrating feeder delivers a controlled flow of coal from the bin onto trunk conveyor GCV005 which has a length of 2500 metres and a climb of 80 metres. Using a 1600mm steel cored belt operating at 4.3m/sec, this conveyor is conservatively rated at 4,500tph. Conveyor GCV005 is driven by four 550kW/3.3kV, 4 pole Reliance motors which are direct coupled to 630K CST drives. These are in-turn direct coupled on each side of the primary pulley and secondary pulley in a horizontally opposed arrangement.
For easy transport in and out of the mine shafts, Grasstree has arranged the motors, CST drives and hydraulic circulating pumps neatly on skid platforms. Cooling units are on separate skids and placed to suit the available space and air flow requirements.
Bill Laing, Baldor’s field service engineer - mining, has had many years of experience with CST drives and provides front-line support to the mines.
He said, “CST technology has proven to be very reliable and robust. Generally all that is required is periodic oil sampling checks, and oil and filter changes when required, and that just translates into more availability production time.”
The efficient incorporation of helical and planetary reduction gears and the hydro-viscous clutch (which is on the output side of the CST drive) results in a low overall height and a compact footprint, provides very high torque density, and allows efficient and easily controlled synchronising and load sharing of all drives. These are highly desirable features, particularly in underground applications where height and space are always minimal. Motors are started under no-load, reducing electrical delivery problems and mechanical stress on all components. A PLC controller (which can synchronise up to four drives) provides an appropriate S-curve start-up ramp via managed hydraulic pressure to the clutch pack. Mine-wide connectivity is delivered via DH+ datahighway, ethernet or other popular proprietary links. The CST clutch technology has proven easier to balance than alternatives and is very forgiving on shock loads and surges, which are a major concern for conveyor failure.
There are 14 CST models ranging in torque capacity from 280,000 in-lb to 2.5 million in-lb and motor capacities up to 3MW, and both parallel and right angle configurations to cater for all conveyor types, lengths and capacities.
For more information contact tel: 1300 BALDOR or visit: www.baldor.com.au