Mill lining optimization increases wear life by 36% at TISCO

Yuanjiacun Iron Mine, founded by Taiyuan Iron and Steel Group (TISCO) and located in Lanxian, Lvliang City, Shanxi province of China, has geological reserves of 1.25 billion tons, making it the largest open-pit metallurgical mine in Asia. In fact, the ore properties of the mine belong to the Anshan type sedimentary metamorphic type magnetic hematite mixed lean iron ore. It has not been developed on a large scale since its discovery in 1958 due to its special ore properties: a mix of many types of ores, high hardness, complex composition, finely disseminated iron material, and difficulty in grinding and separation.

The iron ore concentration plant of Yuanjiacun Iron Mine began operating in 2012 with the installation of 3 10.37x5.49m Metso SAG mills. Because the special ore properties result in a short service life and frequent breakage of the lining, the SAG mills used to shut down. During the first three years in operation, the mine tested a variety of mill linings from several manufacturers; ultimately, it realized that the quality and service life requirements would need more than just improvements to the mill lining material or production process – the design of the lining would also have to be considered.

“There are presently many mills of a similar size in operation in China. I have visited and surveyed many mines, and most of them are using mill linings that are of low quality. We tried to use the linings that perform well in other large mines, but the results did not meet our requirements,” explains Bai Zhijun, Chief of Mineral Processing, Yuanjiacun Iron Mine.

Extended service life and easier to schedule maintenance

Metso introduced metallic mill linings to the Chinese market in 2015. TISCO believed that the Metso optimization solution could prevent breakage. During the first four sets of feed head liner testing, liner breakage was effectively avoided. Meanwhile, in close cooperation with TISCO, Metso collected data on site and communicated with TISCO in an effort to further optimize the feed head liners. The improved feed head liners were installed in August 2015.

“So far, we have used 19 sets of Metso feed head liners. The service life is now extended to 65 days from 60 days and, most importantly, no breakage. This will make it easier for us to schedule maintenance,” Mr. Bai adds.

“Metso’s feed head liners have a long service life and are stable for more than 60 days. The service life of other brand liners varies between 58-60 days, without the possibility to make improvements. Under the same circumstances, the Metso liners are more stable,” says Li Jinjun, Chief of Machinery and Power Department, Yuanjiacun Iron Mine.

Optimized shell lining results in less liner wear and improved grinding efficiency

Based on the successful results of the feed head liners, TISCO and Metso decided to work together to optimize the shell lining. “I have strong confidence in Metso’s engineering capability,” says Mr. Bai. “They follow up on the wear profile every time a lining is changed, and they carefully listen to our needs and problems. Every proposed modification is communicated with us to ensure that our requirements are met as much as possible. Production is arranged only after approval by TISCO.”

For the shell lining optimization solution submitted to TISCO at the beginning of 2016, Zhang Tiebin, the product support manager for Metso mill lining, explained: “Metso optimizes the charge motion of the material in the SAG mill by changing the lifting angle and height of the shell lining. This way, the direct media-to-liner impact can be reduced to minimize liner wear and improve grinding efficiency. In the design process, we take into full consideration the types of feed materials, mill speed, maintenance plan, safety, impact and material selection etc. Metso has improved the material properties, such as hardness and thickness, so that its hardness and toughness correspond to the working conditions. As a result, we have improved the resistance to breakage and increased the service life of the shell lining.”

“I have seen Metso’s simulation software. It is obvious that the face angle of the lifter is of great importance in securing an optimal charge motion. It determines the design. The technology to make the ideal shape and profile of the liners is unique to Metso,” Mr. Bai expresses his appreciation of Metso’s optimization capability.

From the installation of the first shell lining in July 2016 to the third set currently in operation, optimization of the shell lining has never stopped. TISCO has measured that the service life of the shell lining has increased from 70 days to 75 days. “Our requirement for mill linings is stable quality and easy replacement to ensure efficient maintenance,” says Mr. Bai. “Another advantage of the Metso mill lining is the easy disassembly, no matter how high the hardness or the thickness. This is due to its low and almost negligible impact deformation.”

“Frankly, Metso is the only one with such design capabilities,” says Li Jinjun.

Targeting 89.91% uptime

“Our current target is to ensure that the linings are not breaking and to then steadily increase the service life. Our uptime was 87.6% in 2016. Our requirement for uptime depends on the needs of the market. Our target is 89.91% this year. To achieve this goal, the quality of the lining is one factor, but production organization, failure rate control and repair time reduction, etc are also closely linked. For example, we can reduce maintenance frequency and duration by replacing the grate and shell lining simultaneously. The increased wear life of the shell lining from 70 to 75 days without breakage has been a big factor in the higher uptime. If the wear life is kept stable, we will use a half set of shell lining less per year.

In order to help the customer to achieve these goals, Metso continued in-depth studies to further optimize the SAG mill linings. At the end of September 2016, Metso provided a grate optimization solution. The new type of grate has changed the sectional shape of the discharge opening to prevent blockage caused by small grinding media. Furthermore, it is designed so that the shell lining and the grates can be replaced at the same time.

Mr. Bai pointed out: “The performance of the Metso grate is now stable. But the replaced grates are very thick and have too much waste.” Zhang Yumei, the services sales manager of Metso China, acknowledged this and responded by saying: “Metso’s goal is to ensure our customer’s production. Therefore, a safe design with no breakage is the primary factor. We will carry out rigorous research and verification according to TISCO’s requirements and steadily promote the optimization in order to achieve continuous improvements.”

Metso’s innovative mill lining optimization design has reached staged achievement at TISCO by stages. The performance of the lining is stable, and the average wear life is extended by 36%, which effectively reduces the unexpected downtime and thereby ensures that the maintenance and repair work keeps pace with the plan and contributes a lot to a higher uptime.

Mr. Bai concludes by saying, “We are all satisfied with Metso’s mill linings. We believe in Metso’s design and look forward to the next optimization results. At the same time, we are extremely appreciative of Metso’s efforts. Only Metso has been able to give us such advancements in the mill lining.”

About TISCO Taiyuan Iron and Steel is a super iron and steel giant in China, as well as the world’s largest producer of stainless steel. It operates five self-owned mines and has rich experience in mining and mineral processing with advanced mining equipment and strong technical strength. In 2013, under the severe situation with the global steel market, TISCO produced 9.98 million tons of steel and achieved sales of 146 billion yuan with a profit of 0.5 billion yuan, ranking it among the leaders in the industry.

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