Published in September 2007 Australian Longwall Magazine

Centennial’s Mandalong mine has entered a new phase of its evolution, widening its longwall face and introducing new equipment late last year. With the first 150m wide block done and dusted, and having commenced the second 150m wide block, the mine is well on its way to achieving an average of 5 million tonnes per annum through to 2012.

Located 40km south of Newcastle, Mandalong’s history can be traced back to 1982 when extraction near workings was carried out at the Cooranbong bord and pillar operation. Although there was some early longwall experience, it was not until after Centennial bought the mine in 2002 that a large capital injection was pumped into Mandalong, enabling the longwall to commence in January 2005.

The old workings at Cooranbong are now used as underground access for the dedicated conveyor from Mandalong which then connects overland to the Eraring Power Station. The workings also serve as an alternative escape route. The mine also has underground roadways and a drift connecting to the surface infrastructure of overland conveyors to supply directly to Delta’s Vales Point Power Station.

While the mine’s employees enjoy the proximity to the central coast and Hunter Valley vineyards, it also means the operation is in a highly populated area, requiring it to be on its toes when it comes to community relations. This awareness has been reflected in the original width of longwall blocks – a compromise to minimise subsidence.

After extracting four panels at the conservative 115m wide with “nil to low” impact, Mandalong has proved to the local community that it can minimise subsidence impacts, and has given the community confidence to expand the face width to 150m.

“The community expected impacts that just have not eventuated. Now the community have become more positive and are confident that we are going to do what we say we are going to do,” mine manager John Turner said.

The face expansion kicked in June last year with the first wider panel finishing in December and Longwall 6 commencing in February this year. The wider panels have allowed the longwall team an extra 35m of straight cutting which has increased productivity – and increased production time means the mine can hit its production targets.

“The major benefit we have seen from the wider blocks is a lot more consistent tonnes from all crews. We are constantly looking at ways to improve our cut rates and the availability of the system,” Turner said.

To increase Mandalong’s exposure to the export market, Centennial is currently exploring a number of options. These options may include a new haul road to facilitate access to the existing preparation plant at Newstan or a rail loop.

With a face expansion comes new equipment – namely an additional 21 Joy two-leg 1050t capacity shields and pans. The shields include face sprags to help with slabbing.

A tailgate drive was also purchased, as the shorter 115m face did not require one. The tailgate drive was installed at the same time as the face extension.

“The new interface between the new drive and the tailgate supports was a major concern at the time and these were set up and a surface trial conducted to look for any clashes in the equipment,” Turner said.

“The face side of the equipment did not change as our original tailgate drive was designed to allow for a transfer box to be mounted and then a drive to be fitted – so there was no need for us to set the shearer up on the face to look for clashes.

“Another cause for concern was the software change from a HCU to a CCU [single to double unit] and the new software for the tailgate drive integrating with our existing software. This created some headaches during the commissioning stage, but with the assistance of Joy and the mine’s electrical tradespeople this problem was sorted.”

The major challenges of the wider face, Turner said, have all been successfully worked through.

“The major challenges were integrating the new equipment with the old, and steering the face up through a 1:8.5 grade also presented us with a few problems. We had to get used to operating with the tailgate drive module instead of an idler,” he said, adding that the importance of maintaining a good horizon had also been highlighted.

Currently the Joy 7LS6 shearer takes 35 minutes to traverse the face using a uni-di cutting pattern. Rated at 1760kW, the machine incorporates 750kW ranging arms, twin 110kW AC haulage and ultratec 2000 face haulage.

According to longwall superintendent Scott Ashbourne, a good day on the wall produces 20,000t, with the September 2007 quarter producing a record 1.409Mt. While the longwall is currently above plan, development is “just in time”, said Turner. Keeping development ahead of the longwall is a constant challenge for the mine with its high development to extraction ratio due to the narrow longwall blocks.

Existing equipment on the face includes “one of the most powerful AFCs around”, with 2MW of power. A 42mm x 146mm Parsons Xtra chain is used.

Ampcontrol supplies the electrical package for the mine and the pump stations have been supplied by UK company Repower Mining International (RMI).

A 3x105m pillar Macquarie Manufacturing monorail with materials handling system is also used.

In late 2007 Mandalong purchased a Joy 7LS shearer which will be delivered in September 2008 in time for Longwall 7 and will serve as a second shearer. The arrival of the shearer at Mandalong is part of Centennial’s plan to have two shearers at each mine, which Centennial general manager of Operations North Steve Bracken says is an important part in reducing move times across all the group’s operations and giving the OEM more time to overhaul the machine. This in turn grants the OEM more control over quality and costs the mine less.

Part of Mandalong’s new equipment list is interlinked with the operation’s sister mine, Newstan. Newstan is currently on its last block – which is being mined in two parts due to a geological structure in the middle of the panel. According to Bracken, Newstan will finish up in September this year and will be put onto care and maintenance.

While one mine dies, it will give new life to another – Mandalong – in the form of equipment and manpower. Part of the Newstan workforce moved to Mandalong, allowing manning levels to be brought up to planned levels for the operation.

The first piece of equipment to arrive at Mandalong was a ...click here to read on.