Company representative Tom Tsoumbris said the crawler-mounted Pack Mule was a more effective and reliable mover of longwall roof supports to and from a face area — where the Mule Haul had proven its worth as an installation tool — than conventional rubber-tyred vehicles.

Earlier this year at the Newlands mine in central Queensland a Pack Mule was used to cart 30 tonne powered supports to a new face during a two-week longwall move. While mine management was initially concerned the crawler-mounted vehicle would be too slow compared with rubber-tyred units it proved superior in its handling of boggy, watery roadway conditions outbye of the new face line.

“The worse affected area was about 200-300m outbye, where for about 30-40m there was a swilly with water and slurry up to 700mm deep,” Tsoumbris said.

“The area was holding the water and slurry for during the whole longwall relocation, but the Petitto Pack Mule had no problem whatsoever tramming through the area. The only problem experienced was on a few occasions when the engine overheated due to the radiator getting blocked with slurry. A quick washdown of the stainless steel radiator was all that was needed.”

Tsoumbris said the depth of the slurry encountered by the Pack Mule may also have contributed to several hose failures on the push/pull ram arrangement used to pull the support on board, or push it off when unloading. “Early indications suggest the hose reeler seized up with slurry,” he said.

Manual correction of the slack hose was used as a temporary fix, but AMS has since replaced the slack hose arrangement with a new hose reel arrangement it says has fixed the problem.

The Pack Mule is being presented as a solution to the problems being faced by longwall mines using bigger and heavier powered shields. Designed to carry 2m-wide supports it is said to exert a floor pressure of only 28psi while carrying a 40t load. This is up to five times lower than rubber-tyred vehicles. According to Tsoumbris, the Pack Mule can travel at 5kmph on incline grades of up to 1:4 with a 40t load.

“Most mine operators were adamant the machine had to be at least as fast, and preferably faster, than the current rubber wheeled carriers available,” he said.

“Petitto carried out a worldwide search for crawler track options which would allow such speeds, but they found that it is highly impractical to move heavy loads on undulating roadways at these speeds.

“The shock loading would have a catastrophic effect on reliability. The failure rates on rubber wheel carriers tend to substantiate this finding.”

Newlands is again using the Pack Mule in its latest longwall relocation. The mine has also issued AMS a letter of intent to use the machine for two further longwall moves scheduled to occur by mid-2002.