Faced with a challenge of large rocks in the run-of-mine (ROM) feed regularly damaging main support structures, chutes and grizzly feeder a diamond mine in Botswana reached out to Weba Chute Systems to custom design an innovative solution to overcome this costly challenge, which included major safety hazards.
According to Hilton Buys, regional manager at Weba Chute Systems, the mine’s existing chutes at the ROM section were cracking and breaking under the barrage of heavy kimberlite rocks measuring up to a metre in diameter.
“Even the robust grizzly feeder could not withstand the impact of these rocks, which were free-falling about two metres from an apron feeder before contact,” says Buys. “Apart from the costs incurred by this damage, the transfer points were posing a significant safety hazard to mine employees.”
The solution – designed and manufactured at Weba Chute Systems’ Wadeville facility – was a special four-tonne swing door in a discharge chute, feeding from the apron feeder to the grizzly. The heavy, fabricated door is strong enough to withstand the impact while absorbing the energy of the falling rocks before allowing them to drop onto the loading section of the grizzly. The feed can then move in a more controlled manner over the grizzly into the crusher below.
“The key principle was for the door not to give way easily, thereby reducing the velocity and momentum of the large chunks,” he says.
There was also a design requirement to accommodate the movement of smaller rocks. This was dealt with through the addition of a second door, to also ease these rocks onto the grizzly to ensure a more gradual feed into the crusher feed chute. The success of the design, which is based on the Weba Chute Systems principle of controlled flow, has been demonstrated in the chute’s ability to operate with very little maintenance, he says. The only components needing regular attention are chute lips and swing door rails.
“We also included some specific design elements in the crusher feed chute, by installing impact rubbers,” says Buys. “Any rocks that may diverge from the main flow stream will then strike this rubber, minimising the vibration and impact on the body of the chute and are still able to drop gently into the crusher.”
Following on the success of this design, the solution was repeated at other customers’ sites, including mines in the Northern Cape which experienced similar challenges.