On a longwall the focus on drum technology tends to be on its loadability and the system (armoured face conveyor) capacity, rather than on maximum cutting efficiency, machine stability, fines/size of product and whole of life cost.
"Longwall operators are more aimed at total performance of the system than peak cutting performance. You can have a drum set for peak cutting performance and then you can't convey the coal," said Bill Furniss, engineering manager development product, Joy Mining Machinery.
Furniss said that typically on a longwall there was less focus on optimum performance of cutting than on optimising conveying of the drum to match the AFC/coal clearance system.
On a continuous miner, however, the requirement of the drum is quite different. For one, the drum doesn't have a dual function. Rather, the aim is for the coal to come off the face as quickly as possible with maximum material size while maintaining stability of the miner.
Unlike a shearer, a continuous miner is not captive or tracked and the action of the cutter has a dramatic effect on the machine's stability and its ability to perform. “In fact, get it wrong and the miner can get a mind of its own and dance all over the place without cutting a thing,” Furniss said.
Joy has a long history of monitoring CM cutter head performance related to machine optimisation, probably one of the reasons that OEM-fitted drums remain in service for the life of a Joy continuous miner.
The power rating of a shearer drum and a CM drum also makes for an interesting comparison. CM drums are usually rated at 350kW, while each of the two shearer drums could be rated at up to 525kW.
The wide head continuous miner cutting a 5m entry has approximately 80 picks on the drum utilising the total 350kW, while the average longwall drum has 45 picks with a drive motor rating of 525kW -- some 275% more motor power per pick.
A significant portion of the power in a shearer drum is utilised in scrolling or loading the cut material onto the AFC. This additional power can also "mask" inefficiency in the cutter design.
On the maintenance side of shearer drums, Joy argues that while its drums are more expensive upfront, the costs over the life of the machine are lower. As Joy engineering director Brad Neilson put it: "Our drums are built like a brick outhouse."
Furniss said he was not aware of a lot of work being done on drum maintenance costs, in particular on tonne per dollar of pick.