A sticky situation

With drier surface deposits exhausted, miners in the Pilbara region of northern Western Australia increasingly excavate below the water table, where the moisture content of ore rapidly hits the so-called "sticky threshold" of between four and 12 percent. Sticky ores clog up machinery and block chutes, bringing processing to a halt while maintenance takes place. At worst, clumps of ore fall down the chute, and uneven loading causes tracking issues and premature wear of conveyor belts.

When ore turns to glue
Trelleborg's Flexi-Guard chute-lining system has been helping mining companies handle this issue for over a decade.

"The headache for a mine operator is that they've got to shut the area down, make it safe, get a team in there to debug the chutes. It's a mundane, repetitive, unnecessary task," says Keith Jones, Business Development Manager for Trelleborg’s mining solutions. "Essentially, our Flexi-Guard eliminates quite a bit of downtime, and within the mining space, there's a lot of value that you can attach to that," he continues.

Flexi-Guard acts like a live wall-lining system, its rubber fingers oscillating under the impact of the ores tumbling through the underflow chutes. These fluttering molded rubber fingers prevent hang-ups, where fragmented ore becomes lodged, preventing further flow of material, from developing and ensuring that ore travels through a chute and out of a discharge opening.

Trelleborg has now developed an upgraded and improved design which simplifies the installation and maintenance of both the fingers and the hanger used to attach them to chute walls. The new design is a radical change from the original system, using a cantilever type locking mechanism with an interlock fit at the top and bottom of the hanger.

"You push the finger into the hanger, push it down and it snap locks into position," Jones explains. "You don't have to do anything else. Essentially, once the hangar is attached to internal chute walls, it becomes a boltless, toolless system for plant operators to maintain."

From bolts to clicks 
The first generation of Flexi-Guard was a significant improvement on earlier solutions, which required the erection of scaffolding on the outside of the chute during routine maintenance and replacement. Fingers had to be bolted through chute walls from the inside with a team outside, working at heights, attaching and fixing nuts to secure the fingers. 

Trelleborg’s innovation was to integrate the fixing mechanism into a hangar. It was a radical approach, and it did not take mine maintenance personnel very long to adopt this two-component solution. The hangar is a one-time, fit-and-forget item, either welded or bolted to the chute wall via existing chute drill patterns. Once the hangar is installed, it is protected by rubber fingers inserted into it.  

The result was no more external scaffolding and working at heights, less manpower and time required to replace worn rubber fingers, with all work performed from inside the chute.  

The approach has served Trelleborg and its customer base well for over a decade. Trelleborg felt, however, that there was room for improvement. 

"Although it was a relatively easy process, installers still had to align integrally molded indexed tabs in the back of a rubber finger and then align these tabs with slots in the hangar to get it right. This involved tools," says Jones. "What we have come up with now is a true toolless system. It’s just a case of shove-in, push down, click, and go, to install the finger. Then to remove it, it’s push up and pull up. It’s as simple as that”. 

The company has applied for patents for the locking mechanism in Australia and internationally, covering the design of both the hanger and the rubber finger.  

Rubber for harsh conditions 
This second-generation rubber finger is molded from the same blend of natural rubber as the first – one that has been optimized over many years. It needs to handle both abrasion from ore particles and rubber fatigue from the constant flexing and flutter of the Flexi-Guard finger.    

While natural rubber is resistant to fine particle abrasion, particle size distributions in the bulk ore streams can range from 0.075 to 25 millimeters. This means that the natural rubber needs to be reinforced and strengthened with additives to deal with larger particles in the ore stream. The trick is balancing resistance to fine particle abrasion, coarser particle impact abrasion and fatigue. At the same time, the material needs to keep its rebound resiliency and elastic properties, so the rubber finger can oscillate and flutter under the bulk ore stream. 

Trelleborg's rubber chemists have refined the blend to produce the optimal balance of rubber mechanical properties. The result is a robust, durable, self-cleaning, live wall chute lining system with excellent service life, which promotes the flow of problematic moist sticky ores through screening plants.   

The next generation Flexi-Guard will be installed for the first time in a trial at a mineral processing plant operated by one of Trelleborg’s customers by the end of March 2026. While installing a complete set of second-generation hangers and fingers into a chute will require it to be shut down for several hours, this trial will involve a more limited installation with only the bottom 10 rows of the chute upgraded. As the new design is interchangeable with the existing one, there is no obstacle to using both generations of the Flexi-Guard product simultaneously in the same chute.  

Beyond iron ore 
Flexi-Guard enjoys a significant market share in the Australian iron ore market, and Trelleborg hopes to maintain or even extend this as it rolls out the new generation design. The company is also looking at developing the use of the product with other mining customers where sticky ore can be a problem.  

"It's not specific to iron ore, it's specific to the problem of processing moist sticky ore that exists in a lot of mineral processing flowsheets screening and extracting – copper, gold, bauxite - you name it,” Jones says. “We've tried not to be as narrow this time in our marketing to open up for new applications."  

Geographically, the obvious next step is Brazil, which comes second after Australia in iron ore production. Trelleborg is, however, looking elsewhere, not least in Sweden, where the company has both its history and headquarters, and which has the biggest iron ore production in Europe. "We've a superb product here that functions exceptionally well in mineral processing circuits in Australia. There’s no reason to suggest that this product will not deliver and create value for other mineral processing plants around the world. We’ve just got to find them as we continue to grow and expand,” concludes Jones.  

Writer: Richard Orange
Photos: Trelleborg