After exhaustive design research that concluded with the build, installation and continuous full-scale testing operation, Metso has introduced the Metso QdX4 mill drive system.

This system was tested for over 3 million cycles at 28MW (2 x 14MW) with an input speed of 320 rpm, proving the torque splitting system arrangement.

Metso explained that in the past, grinding mills operating between 18MW and 28MW required a large electrical wrap-around motor, known as a gearless mill drive (GMD). The Metso QdX4 mill drive system is an alternative option to the GMD. Until now, the gear-driven solution for large SAG and ball mills was limited to 18MW.

Frank Tozlu, product manager of large grinding mills at the Metso Minerals grinding headquarters in York, Pennsylvania, US, said: “Traditionally, the mining industry has been somewhat reluctant to change, but change has occurred nonetheless and the industry is now encouraging innovations to operate in a more efficient way. Our goal was to design a robust, reliable, cost-effective, high-powered mechanical solution without compromising the high design standards we are all used to seeing in our customers' specifications.”

He added: “SAG and ball mill specifications have been developed over many decades and we are still developing them today. We must continue to look at advancing innovative ideas through our standards and practices when expanding upon transmittable mechanical power.”

Metso stated that the QdX4 mill drive system provides the next step in the evolution of mechanical mill drive architecture. The progression from a single- to a dual-pinion arrangement has been a way to transmit twice as much power in the past. The company has simply rearranged the dual system into a quad system that equally divides input power from two load-sharing motors into four pinions. With this architecture, the Metso QdX4 mill drive is capable of delivering up to 32MW in horizontal mill comminution.

Time and cost efficiencies 

The Metso QdX4 mill drive system has many features that help customers achieve both time and cost efficiencies from an equipment point of view and in terms of the overall costs in a large-scale project.

For example, two installed QdX4 drive units weigh less than one GMD quarter section - this significantly reduces transportation cost, delivery time, equipment handling, and site preparation. The Metso QdX4 mill drive system reduces the need for massive reinforced foundation volumes and the requirement for customers to install large crane capacities.

Similarly, there is no need for extensive, costly, time-consuming dynamic system analysis studies that, in the end, essentially verify the integrity of the GMD stator. 

The Metso QdX4 mill drive system uses traditional engineering load distribution calculations for sizing standard baseplates and hold-down anchor bolts, very similar to that seen with dual-pinion drive arrangements. The Metso Qdx4 mill drive system is estimated to take less than one-third the time to install when compared to a GMD system and can be mounted and aligned by trained on-site personnel. There is no requirement for large brakes and foundation brake piers or the need for extended feed and discharge mill flanges, allowing a better optimised design of the rotating structure.

With the installation of two high-powered single motors equipped with load-sharing variable speed drives, frozen charge protection, inching and creep capabilities, and standard cooling, the Metso QdX4 mill drive system is an alternative option for operating large SAG and ball mills greater than 18MW.

The Metso QdX4 mill drive system can also save the user time and money when it comes to reliability and maintenance in terms of gear/pinion lubrication. Two dedicated lubrication units are provided, one for the internal transmission gearing and one for the closed loop mill gear and pinion interface. Minimising the complexities related to mill installation, operation, and maintenance activities maximises mill availability and can increase overall profitability for customers.