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:: Three-part Skega Mill Lining helps keep Lisheen Mine at Full Production
Metso Minerals has worked closely with Anglo American to develop grinding mill linings that can be replaced without halting the Lisheen mine’s production of zinc and lead concentrates.
The resulting design provides optimum performance while enabling the Skega linings to be quickly replaced during scheduled shutdowns. The grinding mill’s feed, central and discharge sections are each fitted in separate months during the mine’s normal maintenance periods.
Splitting the relining into three shorter parts avoids the need for any special closures that would halt the output of lead and zinc concentrates. “We’ve got to the stage where the lining downtime isn’t impacting on production," says Lisheen Mine Surface Engineer Jack Smith.
The Lisheen mine is near the village of Moyne in County Tipperary, Ireland. It opened in 1999 and produces some 300,000t of zinc concentrates and 40,000t of lead concentrates every year. Material is crushed underground then stockpiled in a “teepee”-shaped building before being conveyed to the semi-autogenous grinding (SAG) mill.
On entering the mill the material has a nominal size of 150mm; by the time it leaves it is just 0.4mm. Further processing takes place in a ball mill - also fitted with Skega linings - before the pulverised slurry is fed into the floatation process that extracts the zinc and lead concentrates.
Up to 250t of ore is fed into the SAG mill every hour and the lining system has to be robust enough to withstand at least nine months of this hard use without replacement. When the time comes for a new lining, it must be fitted without disrupting the relentless production process.
Jack Smith particularly favours the use of steel and rubber Poly-Met linings for SAG mills, rather than just steel. “Steel is very difficult and time-consuming to change," he says. With Poly-Met, replacement is more straightforward and the weights can be handled more easily.
The lining is also fully inspected in situ every month during the downtime. Wear is recorded and Metso produces drawings to illustrate the change from month to month. According to Metso Minerals (UK) Sales Manager Dave White, the company makes regular visits taking measurements of the linings.
“Metso Minerals provides active support for the Lisheen Mine," says Dave White adding, “The co-operation between us is reciprocated with the mine carrying out tests for Metso." Four lifters with a new composition are for example, currently awaiting installation so that Metso can evaluate their performance.
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