Rubber manufacturing company Multotec Rubber, in conjunction with extractive metallurgy company Multotec Zambia, has relined two mills with its heavy-duty (HD) MultoMet liners for a customer in the Zambian Copperbelt, significantly reducing mill downtime, says Multotec Rubber MD Spike Taylor.

“This[comes] as a result of the significant improvement in the liner life, compared to the manganese grid liners used previously,” Taylor says, noting that MultoMet liners last seven to nine months, compared with manganese liners’ two-month life span.

He explains that the HD MultoMet liners can withstand the harsh operating environment of a grinding mill, as the proprietary chromium-molybdenum (CrMo) alloy cast steel insert absorbs greater impact.

“It also offers superior abrasion resistance. The castings for the lifter bars can further be designed to accommodate a range of milling process specifications, which gives Multotec Rubber the necessary flexibility to cater for diverse customer requirements,” Taylor says.

He notes that the Zambian customer’s mill circuit required five relines a year, which resulted in a total loss in production time of 25 to 30 days. In addition, the manganese grid liners only lasted two months, mainly as a result of the fact that the steel castings from the local foundry had cracks and uneven moulding.

“This not only made the liners difficult to install, but the liners failed to fit properly as well,” Taylor points out.

Further, significant gaps between the liners resulted in excessive wash behind the liners, which damaged the shell severely, while the poor fit led to even more downtime, as the rubber backing had to be removed and renewed with every reline.

Taylor adds that the relining process was also slow, owing to the dimensions and weight of the individual grid liners and manganese peens and flows, which meant that the worn liners often had to be cut out with a cutting torch. As a result, it took five to six days to reline the semiautogenous grinding (SAG) mills and ball mills simultaneously.

Service Approach
“We embarked on a multifaceted approach to supplying the liners,” Taylor says, noting that Multotec Rubber’s comminution product manager visited the site twice to assess the grinding circuit and to carry out mass balance measurements.

The customer was also advised on feed-size change recommendations, best practice for the addition of grinding media and the granulometry of the ore if the SAG and ball mills ran in parallel, as well as on sump-level control.

Once the measurements had been taken and the necessary quotes supplied, the installation of the HD MultoMet liners was carried out jointly by Multotec Rubber and Multotec Zambia.

“Such was the success of the project that both mills were relined simultaneously in a record 60 hours, as opposed to five days for the manganese grid liners,” Taylor highlights.

The HD MultoMet liners are easier to handle and can be fitted with far less effort and manpower, Taylor says. In addition, the quality and fit of the liners mean that no difficulty is encountered during the relining process itself.

“The liners are [also] much more cost-effective [and] also improve the final product quality.”

Taylor explains that this is because the HD MultoMet lifter bars provide a designed trajectory. This ensures correct impact of the grinding media on the toe of the charge while the grid liners simply drag the charge across the surface owing to the protruding grinding balls.

“The rubber grate plates are far more effective in eliminating blinding, which guarantees a good mill throughput,” Taylor says.

In addition to carrying out mill relines, Multotec Zambia is also able to conduct regular inspections and thereby advise its customers of any potential problems.

Taylor notes that, for this customer, in particular, the company was able to improve the liner fixing arrangements by simply increasing the bolt specifications. It was also able to increase the grate life from four to seven months by adding a Hardox insert as an integral lifter bar in the centre of the grates.

“Our next step is to record the profile measurements and data on our Hawkeye predictive maintenance software,” Taylor says.