Monday 16th Dec, 2019

Grasberg’s choice of ceramic lagging system

Inferior technologies, heavy rainfall and heavy-duty usage had resulted in ceramic/rubber bond failure and other damage.
Inferior technologies, heavy rainfall and heavy-duty usage had resulted in ceramic/rubber bond failure and other damage.

Indonesian miner PT Freeport approached Sandvik and Elastotec for a rubber-backed ceramic lagging with better performance than the miner had previously used at its Grasberg copper/gold mine in Papua.

The Grasberg open pit mine is the largest gold mine and the third largest copper mine in the world.

Operated by PT Freeport Indonesia, the Grasberg mine employs 30,000 people and produces in excess of 600,000 tonnes of copper concentrate, along with 55 tonnes of gold and 170 tonnes of silver by-product each year, per annum.

With the open pit heading to be exhausted in 2017, PT Freeport Indonesia is undergoing a planned transition to full underground production. Two massive underground mines are in construction – Deep Mill Level Zone (DMLZ) and Grasberg Block Cave (GBC)

There are currently more than 150 separate conveyor systems that support the open pit mining operation at Grasberg.

The underground mining phase is expected to equal or exceed current production levels, and the design of the DMLZ and GBC conveyor systems requires more than 30 conveyors, ranging in length from just 20m to 2.1km.

PT Freeport consulted some of the industry’s top engineers in an effort to develop a low-ongoing-maintenance conveyor system, which it decided was optimal due to the underground, confined space the conveyors will operate in.

The design of some of the larger conveyor pulley systems is in excess of 30 tonnes, making removal of a pulley for relagging both time-consuming and potentially problematic.

In order to obtain the necessary coefficient of friction for the large drive loadings, as well as to provide the life needed between pulley changes, the pulleys needed to be ceramic-lined.

The operating conditions for the conveyors are difficult, with high rainfall (200-400mm each month) resulting in very wet conditions, leading to issues in the past with corrosion and lagging/tile adhesion.

PT Freeport considered a number of scenarios in the design phase.

Direct-bonded ceramic lagging was rejected given the likely excess belt wear it would cause. PT Freeport had previously experienced problems using traditional cold-bonded rubber-backed ceramic lagging, including: delaminating of cold-bonded ceramic lagging due to high tensions run on these conveyors and inadequate bond strength between the rubber backing and steel pulley shell; tile loss due to the ceramic/rubber bond failure; tile cracking leading to tile loss; and bond failure at the edge of the pulleys and at the joints between the ceramic lagging strips due to water ingress and corrosion.

So the miner approached bulk handling supplier Sandvik, with a brief outlining its need for a rubber-backed ceramic lagging with better performance than what had previously been used.

Sandvik Mining Systems tackled the issue by taking advantage of its ongoing relationship with pulley lagging and ceramic wear panel producer Elastotec.

Sandvik and Elastotec have been working collaboratively on the development of an improved ceramic lagging system, dubbed the hot vulcanised ceramic lagging (HVCL) system.

 

Sandvik/Elastotec HVCL installed on a large pulley at PT Freeport’s Grasberg mine in the Indonesian province of Papua.
Sandvik/Elastotec HVCL installed on a large pulley at PT Freeport’s Grasberg mine in the Indonesian province of Papua.

The HVCL system’s hot vulcanised bonding layer is designed to provide a 100% rubber tear bond between the ceramic lagging and the pulley shell.

Importantly, the collaborators pointed out to ABHR, there are no joints between the strips, with the hot vulcanising process forming an impervious barrier at these points. This prevents water ingress and the resulting pulley shell corrosion.

The HVCL achieves rubber-to-pulley shell adhesion levels above 20 N/mm, resulting in superior bond strength and increased durability, Sandvik and Elastotec said.

The improvements in the ceramic/rubber adhesion provide a rubber tear bond that exceeds 6.0 Mpa and is also well suited to the region’s wet conditions, another significant factor in extending the service life of the pulleys, according to the suppliers.

The thickness of the rubber backing on the HVCL was set at 15mm to provide sufficient flexibility in the tiles to minimise the chance of belt cover wear.

PT Freeport chose the HVCL system for all new DMLZ/GBC ceramic lagged pulleys. Sandvik and Elastotec say that the HVCL system is now standard for all new pulleys on site.

Contacts: www.mining.sandvik.com

www.elastotec.com.au