Sunday 7th Mar, 2021

Improving uptime with new mill lining solutions

One of Sweden’s largest open-air copper mines has adopted a milling solution that minimises components and maximises uptime.

One of Sweden’s largest open-air copper mines has adopted a milling solution that minimises components and maximises uptime.

At Boliden Aitik, an open-air copper mine in Gällivare, Sweden, the mill determines the pace of the entire maintenance process.

Most maintenance shutdowns are planned according to a schedule set for the reline of the mill, meaning that if a reline can be done faster, the entire process will be too.

Establishing as much uptime as possible is critical for the mine, especially as it aims to grind 45 million tonnes in 2020.

For years, Boliden has had a Life Cycle Services (LCS) cost-per-tonne agreement with industrial machinery company Metso for mill linings and additional services. Kjell-Arne Johansson, Senior Technical Supervisor Concentrator at Boliden, believes this has helped improve the mine’s products and services.

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“Our cost-per-tonne agreement for mill linings makes development beneficial both for us and Metso. The agreement strengthens our cooperation, as we challenge and drive the development together,” Johansson says.

Boliden Aitik is a world leader when measured by tonnes produced per employee hour. It has around 100 employees working at the concentrator with about three to four employees in the maintenance department focusing on mill linings.

That number would have been higher if mill lining expertise and service had not been part of the LCS agreement, according to Malin Ömalm, Maintenance Engineer at Boliden. 

“We have regular follow-up and performance improvement meetings. Weekly reconciliations, technical meetings and steering committee meetings all contribute to control, knowledge transfer and development,” Ömalm says. 

Megaliner for a new era

Boliden Aitik was one of the first in the world to install the Metso Megaliner. Today, its primary AG mills feature Megaliner mill liners on the shell and feed-end head. 

“Megaliner represents a new era and there is no going back. We haven’t had any problems since we started using Megaliner. The design and the wear life have fulfilled our expectations, and we have been able to significantly improve the reline time while also improving safety,” Johansson says.

Because the mill determined the maintenance schedule for the entire process, minimising downtime is essential. Each hour that can be saved puts pressure on the areas in the process to also improve. This includes the maintenance schedule (wear life) as well as the length of maintenance shutdown (reline).

“We want the mill to be up and running for as long as possible, and when the liners are worn out, they need to be changed as quickly as possible. Some six to seven years ago, we used to have six maintenance shutdowns per year. Today we have a balanced wear life and just two to three shutdowns per year,” Johansson.  

In addition to the mill lining solution, Metso is also focused on other methods of assisting Aitik to improve its shutdown times. Shutdown optimisation services, such as time and motion analysis studies, mill relining simulations and special tooling, all play a part in reducing downtime. One of the goals of the LCS contract is to find the best way to bring all of these elements together to deliver the best overall result for the mine.

Per Sundström, Product Support Manager at Metso, says it is always looking for new ways to improve uptime.

“We like the challenge and the trust. It makes us want to continue to pursue improvements in both mill linings and services,” Sundström says.

“When we started, the mill was a bottleneck, but the development has been continuous; today we are pushing all other areas towards fewer and shorter maintenance shutdowns. Mill availability right now is around 98 per cent, and our team keeps improving the design of the lining and tools. That means even less downtime in the future.”

Raising the bar

Another of Boliden Aitik’s targets for 2020 is to further reduce downtime. A new technology that Metso is testing to make this possible is the Megaliner for discharge systems.

The Megaliner for discharge systems minimises the number of components necessary for installation by integrating dischargers, grates and filling segments, reducing the number of liner components by up to 70 per cent. Reline time has been improved, as the liner has fewer attachment points.

Removing the bolts, which are attached from the outside of the mill, also helps cut down on downtime. Traditional long bolts that go through the grate, pulp lifter and the mill discharge head are not used, eliminating the need for recoilless hammers.

“I see lot of potential in the Megaliner for discharge system,” Johansson says.

“First of all, it is favourable from a safety point of view. And it will increase uptime, as there are fewer parts to handle and the bolts are attached from the outside of the mill. We estimate a time savings of up to 30 hours per reline – that’s a lot of money.

“The time savings will also mean that we will be less dependent on critical equipment, such as the liner handler and recoilless hammers. This is the equipment that must work during a maintenance break, and days can be lost if they break down.”

The company expects the test installation at Boliden Aitik will enable a 50 per cent faster reline of the discharge end in the semi-autonomous grinding mill.