M&C refurb of massive mill motor at Freda Rebecca mine in Zimbabwe

The largest AC electric motor operating in Zimbabwe drives a reduction mill, and this synchronous motor was recently refurbished by leading rotating machinery repairer, Marthinusen & Coutts, a division of ACTOM. Estimated to be around 30 years old, the 2,150 kW synchronous mill motor, which was in operation at Freda Rebecca gold mine, suffered a catastrophic failure caused by its age and metal fatigue. The main hub of the electrical rotor component had sheared off.

Following preliminary repair work undertaken by the mine, Marthinusen & Coutts was called to site by the mine to investigate further and to provide a long term world class solution. A full assessment undertaken by the Marthinusen & Coutts team resulted in the motor being brought back to the division’s facility in South Africa.

It was decided, following negotiations with the mine, to do a design modification instead of replacing the hub. Richard Botton, Divisional CEO of Marthinusen & Coutts, explains that this option was chosen as it would save costs and reduce the lead time without sacrificing the performance of the refurbished motor.

“Our team’s extensive experience and understanding of large rotating machinery enabled us to offer an alternative to the mine that would ensure optimum reliability going forward. One of the solutions was to use the existing rotor superstructure with a bolt-on hub on the motor,” Botton says. In addition, 18 main pole coils were replaced; these were manufactured by Marthinusen & Coutts at its ISO 9001 accredited facility in Cleveland, Gauteng.

A complete rewind of the stator was necessary due to the extensive damage caused during the failure at the mine. Fortunately, the mine store had a spare set of coils, manufactured 20 years ago, and these were rewound at Marthinusen & Coutts in South Africa. A compete upgrade and modification to the sleeve bearings also brought these back to OEM specifications.

“The ability to implement enhancements during the repair of critical electrical rotating machinery such as this motor is a major advantage to the mine as it allows for the latest technology and enhancements to be included in the final product solution,” Botton says. The scope of work included the on-site commissioning of the motor which was facilitated by the Marthinusen & Coutts Zimbabwe operation with technical support from the division’s centre of excellence in Johannesburg.

Through the level of skills and expertise that reside within this leading rotating machinery service provider, Marthinusen & Coutts, a division of ACTOM (Pty) Ltd, has established a strong reference base and reputation for this.