Metso reported that it has been working in close collaboration with two technological partners over the past three years to develop a new mill drive solution for large SAG and ball mills, and after exhaustive design research followed by fabrication, installation and continuous full-scale testing, it is ready to introduce the new QdX4 mill drive system.
With the new QdX4 mill drive system, Metso has converted a dual system into a quad system that equally distributes input power from two load-sharing motors into four pinions.
Until now, gear-driven solutions for large SAG and ball mills have been limited to 18 MW. In the past, grinding mills operating between 18 MW and 28 MW required a large electrical wrap-around motor, known as a Gearless Mill Drive (GMD). The QdX4 system has been developed as an alternative to GMDs. According to Metso, the new system was tested for more than 3 million cycles at 28 MW (2 x 14 MW) with an input speed of 320 rpm, proving the torque splitting system arrangement.
“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,” said Frank Tozlu, product manager–large grinding mills, at Metso Minerals’ facility in York, Pennsylvania, USA.
The QdX4 mill drive system provides the next step in the evolution of mechanical mill drive architecture, according to the company. The progression from a single- to a dual-pinion arrangement has been a way to transmit twice as much power in the past. Metso said it has converted the dual system into a quad system that equally distributes input power from two load-sharing motors into four pinions. With this architecture, the system is capable of delivering up to 32 MW in horizontal mill comminution.
Metso said the system has features that help customers achieve both time and cost efficiencies from an equipment point of view and in terms of 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 QdX4 system also reduces the need for massive reinforced foundations and requirements for large installed crane capacities.
The Metso system uses traditional engineering load distribution calculations for sizing standard baseplates and hold-down anchor bolts, similar to that associated with dual-pinion drive arrangements. The system is claimed 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 are no requirements for large brakes and foundation brake piers or the need for extended feed and discharge mill flanges, allowing a better optimized design of the rotating structure. The company asserts that, 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 system clearly stands as an alternative option for operating SAG and ball mills greater than 18 MW.
The system also is designed to save time and money when it comes to 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.