Engineering success impacts on coal haulage costs

STARTING with an innovative redesign of the wagons for coal haulers some 10 years ago, Brisbane-based engineering company Chaseling McGiffin and its joint venture manufacturing partner ADE Products have earned a reputation for delivering mine-site specific coal haulage solutions.
Engineering success impacts on coal haulage costs Engineering success impacts on coal haulage costs Engineering success impacts on coal haulage costs Engineering success impacts on coal haulage costs Engineering success impacts on coal haulage costs

Chaseling Mcgiffin's oil cooled conveyor brake for underground conveyors.

Staff Reporter

The company has now designed two large pieces of mobile plant which have the potential to deliver major cost benefits to mines. These are a rigid bottom-dump coal hauler and an innovative swing wheel low-loader, to replace traditional low-loaders (more on these later).

The company’s genesis as a designer of equipment goes back to the late 1980s when Chaseling McGiffin was called in to help with ongoing structural problems in coal haul wagon bodies in Queensland’s coalfields, particularly with the hitches and bodywork cracking. The company identified the problems and designed new haulers, using technology such as finite element modelling to identify areas of high stress.

To increase fatigue resistance, for instance, the company promoted the use of steel castings in critical areas to replace complicated welding joints. The slight initial cost premium for tooling paid off quickly in simplifying fabrication and the castings have proved fatigue free in operation.

The initial design was a 220t hauler, for the Caterpillar 784 prime mover, followed by a 160t hauler designed for the Caterpillar 776 prime mover. Nineteen of the larger machines and six of the smaller units have been constructed, with the oldest exceeding 60,000 hours of operation to date.

Another major success for Chaseling McGiffin was the development of booster drives for haulers at the Moura mine in Queensland. Sharply dipping seams and complex geology make it difficult for haulers to negotiate the sharp inclines out of the pit.

“The weakness with articulated haulers is they don’t have enough of their weight on the driving wheels,” said Arthur Chaseling. “Inevitably some of the weight is dragging along on the non-powered trailing axle so they won’t climb hills like a rear dump will.”

The company set out to solve the problem by fitting a booster drive to the haulers, which has made a major difference to the mine’s ability to haul coal. This involved fitting a second engine on the deck of the prime mover and powering the trailer axle via a hydrostatic drive.

Chaseling McGiffin has conducted performance evaluations on Moura’s boosted and unboosted machines with boosted machines showing improvements in the transmission lives and final drives of 4 or 5 times over their unboosted counterparts. In addition, the mine’s operating envelope has increased because the boosted haulers can operate in the rain and slippery conditions.

Following on from the design of towed coal haul trailers, power-assist systems for trailers and a host of other projects, Chaseling McGiffin turned to the design on a rigid bottom-dump coal hauler.

“By that stage we’d come to the conclusion that the proper way to haul was to start with a clean sheet of paper and design from scratch a vehicle specifically for hauling coal,” recalled Chaseling

Described as a self-propelled hopper this vehicle is simpler and lighter than an articulated hauler, with considerable cost savings in both purchase price and running costs, according to Daniel Reid one of Chaseling McGiffin’s design engineers.

“The current design has a payload of 220 tonnes, but preliminary design has also been carried out on 160 tonne and 300-tonne vehicles. Apart from a more favourable tyre configuration for high-speed running than rear-dump coal haulers, these vehicles have the advantage that they are low enough to be loaded by wheel loaders, which are much more mobile than the hydraulic and rope shovels required to load high coal bodies on rear-dump trucks,” Reid said.

The idea is not a new one – the Kress Corporation produced something similar in the past. What is different are some key features in the design that overcome the operational problems experienced by earlier hopper configurations.

The AC drive system uses a single electric drive motor connected to the differential, with the engine and generator fitted above the rear axle. Using a single motor significantly reduces the cost of the electronics required to control the vehicle.

The radiator is fitted at the front of the vehicle in dust-free air, and is mounted in an inclined position to keep it clear of the tyre-changing area. The AC electric drive also allows a simple and light electric retardation system to be used in place of the oil-cooled brakes and hydraulic system required on a mechanical-drive truck.

The vehicle has been designed with many components common to existing mining vehicles, which means parts are an off-the-shelf purchase.

“Our vehicle can carry the same payload [as comparable vehicles] with 50t less tare weight. We believe they could be up to a third cheaper to run.”

Initial discussions are underway with an equipment manufacturer and other investors to investigate building a prototype.

The company has also tackled the redesign of traditional low loaders, a large vehicle used to move large pieces of equipment around mine sites, typically supported by a multitude of small tyres fitted under a platform. Problems including heavy tyre and axle damage make these high maintenance cost items. Low loaders are also incapable of negotiating negative grades.

Chaseling McGiffin has developed an alternative to these which addresses the issues of severe tyre scrub and limited braking capability. Their design replaced the numerous wheels with one set of 3.5m diameter wheels and a pair of axle assemblies from large mining trucks.

The company, which believes its design will significantly reduce the operating costs of this type of equipment, is presently tendering to produce one of the loaders for a metal mine.

In the underground coal mining sector the company’s most recent success has been the development of an oil cooled conveyor brake, particularly for downhill geometry where high torque and heat dissipation are essential requirements. Multi-caliper dry disk brakes are the usual configuration in this application but are unsuitable for use in underground coal mines because they operate at high temperature. Chaseling McGiffin replaced these with a standard Caterpillar truck brake. The CAT-769D wheel hub brake was modified to suit a torque-arm mounting on a conveyor pulley.

The first brake was installed in 1999 and has required minimal maintenance.

In almost 15,500 hours this brake has only cost about 15-20 hours downtime. Pressure switch failures on the cooling circuit were resolved by replacing them with transducers, a couple of trips from limit switches required adjustment to account for pad wear, and one pump change have been the only problems with the powerpack. The brake itself has caused no trouble at all.

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