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Raise drill tackles first African project

CUTTING FEATS The Redbore 100 can cut holes of up to 8 m in diameter to depths of up to 1 km through solid rock

AFRICAN DEBUT The Redbore 100 has met the Synclinorium vent shaft project’s target rates, with Redpath on track to meet the projected completion date in July

24th March 2017

By: Tasneem Bulbulia

Senior Contributing Editor Online

     

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The Redbore 100, “the crown jewel” of Redpath Mining’s series of raise drills, is undertaking its inaugural African project, in Zambia, extols Redpath Mining Africa raiseboring manager Johan Davel.

“One of the most powerful, largest- capacity, proven raise drills ever manufactured” is in operation at Zambian-registered copper miner Mopani Copper Mines’ Synclinorium vent shaft project, Davel tells Mining Weekly.

He states that the Redbore 100 has met the project’s target rates, with Redpath on track to meet the projected completion date in July.

The Redbore 100 is being used to drill a 1 170-m-deep, 6.1-m-diameter ventilation shaft in two sections of about 700 m and 470 m each. The ventilation shaft project uses a combination of conventional raiseboring and blind sink methods to provide sufficient ventilation to the bottom of the mine.

With the Redbore 100 having drilled similar holes in Canada and Australia, Davel says securing a project for the raise drill in Africa “was a major win for our African business”.

Redpath has been able to grow its footprint in the African market, despite the global economic downturn, he says, adding that the company regards the continent as the perfect location to base Redpath’s flagship raise drill machine.

Redpath Mining Africa raiseboring projects manager Werner Schwartz says, while similar machines to the Redbore 100 are in operation in Africa, the drill offers a more efficient and cost-effective solution, owing to its low-profile and compact design.

Similar raise drills are 11 m high when extended, while the Redbore 100 is 7.6 m high. This height reduction ensures substantial savings on operational space and development cost, states Schwartz. Moreover, as the equipment is easily dismantled, it is quicker and, therefore, cheaper to transport to and from underground sites; ultimately, ensuring safer and more efficient equipment mobilisation.

When compared with standard machines in the industry of a similar capacity, Schwartz notes that the machine also uses about 30% less power. This enables significant cost savings in terms of electricity, which is especially beneficial in Africa.

Machinery at Work

Davel explains that the raiseboring process involves placing the Redbore 100 on the upper level of the two levels that need to be connected. A small-diameter pilot hole is drilled to the level required. Once the drill has broken through to the target level, the bit is removed.

The cutting tool or ‘reamer’ is then attached to the drill string and raised back towards the machine while it is pulled and rotated against the rock face. The drill cuttings from the reamer head fall to the floor of the lower level, where they are removed. The finished raise has smooth walls, negating the need for rock bolting or other forms of ground support.

Davel says the drilling method used by the Redbore 100 is faster, cleaner and more cost effective than traditional drill-and-blast methods. It cuts holes of up to 8 m in diameter to depths of up to 1 km through solid rock using hydraulically driven cylinders with more than 15 500 kN of thrust.

He explains that as the bit descends, 2.1-m-long drill sections are added to push the drill bit further into the earth. Each of the 345 individual sections feature a unique thread design to withstand the torque and thrust they are exposed to.

Davel notes that high make-up torque is put out by the machine to fully join and lock the individual drill rod sections together. This is critical to ensure a safe and efficient operation.

Pilot holes can easily deflect as a result of geological features within the rock formation. “It is, therefore, essential that this machine’s immense power is precisely managed, as a deviation of just 1% will result in a 10 m inaccuracy over 1 000 m,” cautions Davel.

Schwartz avers that, as companies continue to mine deeper to exploit new ore reserves, it is important that production costs are limited, within reason, to ensure profitability.

“Technology such as our Redbore 100 plays a big role in infrastructure development in a cost-effective manner,” he concludes.

Edited by Tracy Hancock
Creamer Media Contributing Editor

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