Emphasising that no two mill liner applications are identical, Sam Hearn of Multotec says that their DEM software results in very specific refinements in the liner design for each customer. A detailed understanding of the operating conditions of larger semi-autogenous grinding (SAG) mills is vital to ensure that the final solution delivers optimal results.
“Our strong analysis capabilities in the design process, including discrete element analysis (DEM) and finite element analysis (FEA), allow us to continuously evolve the application of our composite liners,” Sam adds. “We use DEM software to simulate the interaction between the mill charge and the liners, and to evaluate liner profile over the life of the liner.
“The DEM analysis considers a range of variables such as the ore’s bond work index, its specific gravity, the size of the grinding media, the mill speed and the slurry density,” he explains. “Sophisticated simulation capability allows us to accurately model the performance and wear of our mill liners. This includes predicting the liners’ wear life, to avoid unscheduled downtime and to extend the time between replacements.”
Steel and rubber
He notes that the traditional use of steel liners in large SAG mills presents a number of challenges. For instance, there may be bending stress inside the steel liner due to inexact fitting on the mill’s curved surface, and the higher rigidity of steel compared with rubber makes it less than optimal for absorbing the energy of rock material inside the mill.
“This is where our composite liners come into their own,” he contends. “These innovative liners combine the impact resistance of Hardox 500 steel inserts and the absorption capacity of our specially formulated wear-resistant rubber compound. Through the simulation, the structural integrity of the liners can be verified, while the geometric layout of the liners can be optimised.”
The composite liners are locally manufactured at Multotec’s extensive facility in Spartan, Gauteng, in an advanced process that includes its unique submerged cutting technique to preserve the surface hardness of the liners.
Following the design and manufacturing process, the company conducts field trials to compare to the relative performance of composite liners and steel liners. “We are confident that, given our product improvement processes and simulation ability, the wear-life of our liners will achieve and often exceed expectations,” Sam concludes.