Hanson customises Metroliner for underground operations

Building material company, Hanson, has created a concrete agitator specifically designed for the most extreme underground conditions.

The Mack Metroliners, three in total, operate at the Fosterville Gold Mine, an all-underground mine that runs 24 x 7, 28 kilometres northeast of Bendigo in Victoria.

To prevent the mine shafts collapsing, the miners spray high-density, rapid-drying shotcrete onto the walls and ceiling.

Hanson’s Concrete Plant Manager, Matthew Bray was charged with solving the problem of getting the concrete down into the mine.

“It’s a harsh, incredibly dusty environment that often turns to mud and slurry the moment it is exposed to water from the water carts or mining machines,” said Bray.

“The temperature down the bottom can get up to 50 degrees centigrade. Truck filters clog up quickly which compound into a vast array of truck faults,” he said.

Hanson installed all heavy-duty fittings on the Mack Metroliners, including extra layers of paint and rust-proofing, large custom external trays and a single conveyor guard over the drive wheels with additional bracing to handle the bumpy and steep conditions.

The single guard gives Hanson more room to change the tyres out, according to Bray, as they go through about ten tyres a month.

“The single guard allows us to mount larger external trays on top, which hold the chutes and some custom wheel chocks we’ve had manufactured,” he explained.

“When the floor is underwater conventional chocks can float away, and if we’re on an extreme gradient they can slip. Having these handy around the truck gives us a bit of reassurance and prevents the truck sliding.”

Bray and his team worked closely with Mack’s engineers to customise all aspects of the Metroliners, using an agile development process that saw them making changes on the fly as new truck data came to hand from the mine.

A part of this process involves keeping the trucks slow enough to stay in control.

The track is a steep and narrow tunnel that reaches a 7-to-1 gradient in places.

“Slowing the truck down enough on the descent is a major safety issue, especially when the roads are wet,” said Bray.

“If the driver sits on the air-brakes all the way down the compressor can’t keep up and you risk running out of air and not being able to stop. Besides the obvious potential damage caused to the truck, sliding into the tunnel wall could also cause large safety and structural concerns, so this was a large challenge we worked with Mack to engineer out.”

To get around this problem, Hanson imposed a speed limiter of 30 km/h on the engine, installed a transmission retarder to reduce the need for braking, and lowered the diff ratio so the retarder cuts in earlier than usual at low speeds.

Interior view of Hanson’s underground Mack Metroliner agitator.

“Ideally, we want the drivers to be able to get down there without using the brakes much at all,” explained Bray.

In this regard the retarder is crucial as it functions as the control mechanism on the descent, especially when roads are slippery, which is often.

“The drivers are super-excited about it, they’ve had the experience of hubs overheating from riding the brakes and the seals blowing, and we’re confident this approach will solve that.”

In the confined space of the tunnels there’s very little room to traverse, so Hanson went with a single-steer model Metroliner and added a four-way camera system so the driver can see all around the vehicle.

Rollover protection was added on the top in case Hanson had to modify it.

It’s been fully-enclosed with all the bolts removed along the top to make it smooth.

“We wouldn’t be popular if we ripped the air ventilator bags along the roof of the tunnel,” joked Bray.

Designing and engineering trucks locally in Australia gives Mack the flexibility to create fully customised trucks for unique tasks.

“Pushing the boundaries to drive application excellence is a very strong pillar of the brand and something we’re very proud of,” said Tom Chapman, Mack Trucks Vice President.

“Partnering with Hanson to trailblaze safety and technology advances for the Fosterville Gold Mine project is a great example of this. It’s a real testament to what can be achieved with a strong business partnership where there is a commitment to mutual progress and success.”

The three new Metroliners are expected to enter service within a month or so and will run continuously 24 x 7.

“We’ve got 13 drivers doing 12-hour days 7 days a week, with a week off, then the same schedule at night,” said Bray.

“The trucks never stop, they do two or more trips each per shift, and it’s a three-hour round trip down and back. We service them every 400 hours, and we change every filter every time.”

With a schedule like that, avoiding stoppages is key, but if a truck is forced to stop for any reason, Hanson have developed a reliable way to put the concrete ‘to sleep’.

“If we have a delay we don’t want the concrete to set in the bowl, so we pump chemicals in there to prevent that, but we’ve found that that the conditions are so harsh the pumps just keep breaking down, so we’ve configured the Metroliner’s compressor as the pump instead.”

Hanson is looking to run the mining Metroliners for at least five years according to Bray.

“The Mack driver trainers are coming down to help our drivers get the most out of them. It’s a complete package, and Mack really pulled out all the stops to build exactly what we were after.”

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