Liners and their associated lifter profiles have two main functions. The first is to provide wear protection for the mill shell. The second is to provide lift to the charge for the required size reduction. Though generally accepted that liner design and wear has an impact on milling performance; it has been difficult to quantify the influence of wear in a production environment as the effects of other key performance factors alongside changes in the feed mask the effects of a dynamic liner profile. Adding to the difficulty of quantifying the effect of liner profile on mill performance is the fact that detailed measurements of mill liner profiles were both impractical and infrequent in the past.
It has been found that through the use of rigorous grinding surveys at various times throughout the liner life, 3D laser scanning of the mill internals, JKSimMet modelling and statistical analysis of historical production data; the effect of liner wear on mill performance can be quantified and the new-found insights can be used for mill optimisation throughout the liner life.
An increase in throughput of 10.5% over the liner life was observed for the mill studied. The separate effects of liner wear were also decoupled, showing that the increase in throughput due to liner wear can be further divided into the following components;
• Increase in grate aperture, 5.3%,
• Increase in mill diameter, 3.2 %, and
• Change in liner profile, 2.0.
JKSimMet modelling showed distinctly different breakage rates for new and worn liners. This result highlights the need to adjust mill control and process parameters depending on the stage of liner life. It was also found that through statistical analysis of production data that it typically requires a two week period of wear for a statistically significant change in throughput to occur. This equates to approximately 20 mm of wear on the lifter (5% of original thickness and 7% of original height.).
A model has been provided to calculate actual charge mass and percentage mill filling. This model addresses the current limitations of using a load cell reading, when the significant loss in liner mass due to wear is not taken into account. An improved approach to liner design and reline schedule to maximise mill performance whilst retaining an acceptable liner life has also been outlined.