Updating a 108-year-old mine winch

Bringing 19th century mining machinery up to 21st century safety standards is not easy, but the challenge has been met with electronic technology.

Yielding almost 700 tonnes of gold to date, Bendigo's goldfields have made Victoria rich. Industry sprang up in the town and Bendigo manufacturer, A Roberts and Sons built steam-driven mine winders to haul men and ore from the shafts.

"Rated at a safe working load of 3000 kg, the winder speeds cages as deep as 412 metres through the shaft at up to a 3 metres per second. Aside from a direct conversion from steam to compressed air, the operation of the winder is unchanged."

Today, the Central Deborah mine is no longer a working shaft, but an A Roberts and Sons mine winder dating from 1896 is still kept busy delivering equipment and bringing up ore samples while providing an emergency egress. On a quiet day, says winder driver Karl Penrose, 70 to 80 visitors see the winder in operation, but during the Easter peak, tours run every 15 minutes.

Rated at a safe working load of 3000 kg, the winder speeds cages as deep as 412 metres through the shaft at up to 3 metres per second. Aside from a direct conversion from steam to compressed air, the operation of the winder is unchanged.

The air, at between 50 and 100 psi, is fed onto the 45 cm diameter piston ends and the winder goes to work, lifting one cage while lowering its counterbalanced pair. Separate cables are wound around two massive winding drums, which can be operated independently using a simple dog clutch.

The winder's safety requirements were many and, while there had not been any accidents at Central Deborah, the consequences of an incident could be serious.

The first hazard to be addressed was the possibility of slack cable. Cages risked becoming wedged in the shaft, allowing the cable to slacken and add weight to the top of the cage. Slack cable is difficult for the driver to detect quickly and has the potential to see the cage plummet when released unexpectedly. To prevent open gates causing jams, the slack rope system incorporates limit switches on the cage gate, which must be shut before the winder is activated.

The safety system also includes speed monitoring. When the normal speed is exceeded by more than 3 per cent, an alarm sounds and valves vent air to provide partial braking. When the speed reaches 10 per cent beyond normal, full braking is automatically applied and the system is locked down electronically.

As well as speed, maximum limits apply to depth. The mine is flooded at level 15 and limit switches signal the Pilz safety control system to shut the winder down once level 10 is breached. Similarly, 'overwinding' or sending the cages too high is prevented by limit switches that are monitored by the Pilz system.

A ground level access gate to the cage is monitored by an interlock safety switch that prevents the winder operating unless the area is secure, ensuring the safety of the surface personnel.

Finally, a 'dead man' switch on the throttle control and two emergency stop buttons are fitted at Karl's side, covering all unforeseen contingencies in the operation of this century-old manual machine.

All of the 14 inputs and outputs are managed by Pilz PNOZPlus expandable failsafe safety relays. These relays then control fail to safe solenoids on the air system to the winder. The relays require the driver to reset the system once a failure has been detected and will refuse to restart while a failure persists.

Despite all the new safeguards, Karl Penrose says the mine winder feels little different.

"The safety equipment hasn't affected the way it drives at all, but it is nice to know how safe it is, I must say."