Marthinusen & Coutts (M&C), a division of ACTOM (Pty) Ltd, has successfully installed stator windings for two massive gearless mill drive (GMD) motors for a ball grinding mill (AG) and a semi-autogenous grinding mill (SAG) in Northern Zambia, completing the installations in record time.
The two mills recently repaired by Marthinusen & Coutts in Northern Zambia are among the largest in Africa, with the SAG mill having a diameter of 12.5 m, a length of 6.5 m and an installed power rating of 18 MW. This mill is designed to grind 2,450 t/h or 20 million tonnes per annum. The ball mill is driven by a 16 MW, 64-pole, 4,000-volt motor with 480 slots, while the SAG mill’s 18 MW, 4,000 V motor has 88-poles with 648 slots.
The motors are so large that they are transported in quartered sections and then assembled on site using some of the largest mobile cranes available. Each quadrant weighs about 65 tonnes, and the total motor dimensions are 20×3, with a stator ID of 12.6 m.
Each joint has seven large, uninsulated, overhung, ‘flexible’ coils that help manage the pitch, while the remaining coils are standard resin-rich diamond-type coils, each weighing 44 kg.
Since the mill drives are exposed to the weather, special precautions must be taken to protect the windings from all elements and prevent moisture and dirt from entering. Custom-designed equipment and tools are necessary for installation tasks.
Led by M&C CEO Richard Botton, M&C assembled a team of 10 to 14 specialists to undertake various functions and tasks, ensuring the installation was carried out to the highest standard. Throughout the process, M&C implemented quality control measures, carefully checking each stage of the repair work to ensure compliance with industry standards.
M&C conducted a series of inspections and operational checks to ensure the mill was operating properly. As part of the comprehensive testing protocol, the team monitored parameters including electrical currents, temperatures and mechanical responses.
The SAG and Ball mill motors were installed successfully within a record time of 31 and 28 days, respectively.
M&C has once again demonstrated its ability to deliver superior on-site engineering services to complete large projects such as these, ensuring the mill was commissioned and operational in the shortest possible time.
