In March 2005, Crushing & Mining Equipment (CME) made the first prototypes of what it says are the largest self-tensioning motorbases ever built.
The units were installed on a 325kW cone crusher motor at a prominent WA iron ore mine, and with the belt drive design capacity at over 700kW it needed very high belt tension.
Prior to installing the Rosta motorbases, the crushers were driven by a fixed motor on conventional slide rails. Belt changes often took between four and five hours to complete, and needed regular re-tensioning after installation.
With the motorbases installed, belt changes are completed in about 15 minutes. Adjustment is by an impact gun attached to a single, central jacking screw and there is no need to realign pulleys once the initial installation is complete.
CME manager for Rosta products Steve Davidson tells Australian Mining that although the Rosta self-tensioning motorbases are an additional capital expense, they can often pay for themselves within a very short time.
“Shutting down the crushing circuit on any mine can result in substantial losses in production, especially where this occurs as a result of an unexpected failure,” Davidson says.
“Because the motorbases are designed to automatically compensate for belt stretch, the mine can maintain the required belt tension with minimal ongoing maintenance and costly shutdowns. The belts don’t slip, so they last longer,” Davidson says.
Because of the size of the motor and the critical importance of the crusher, the customer asked that the motorbase lock rigidly in case the Rosta unit was unable to handle the extreme loading experienced.
When it was first installed the Rosta unit was locked, but then later the motorbase was operated with the Rosta unit free, which enabled it to pre-tension the belts.
“A completely unexpected benefit experienced at the mine was a significant decrease in maximum power draw when the Rosta unit was released,” Davidson says.
“On top of that, there seems to be a visible smoothing of power consumption, which allows the crushers to operate at higher tonnage rates,” he says.
During heavy overloads due to crusher bogging, the motorbase allowed the motor to deflect towards the crusher, which let the motor maintain adequate belt tension with no visible belt slip.
To protect the motor and operator, the motorbases have built-in safety features. In the event of a belt failure, the motor is protected from damage by heavy-duty rubber impact pads.
Limiting the motor travel to within safe limits enhances operator safety. The Rosta unit is disengaged from use when lifting the motor and in the event of a mechanical failure an emergency safety overload chain protects the operator.
Following the success of these installations, and subsequent smaller units at other sites, CME is now extending its range of motorbases to include drives up to 750kW.