Koepe rope-up procedure successfully completed at the Bakubung mine

South Africa’s first locally designed and built mobile rope-handling system, engineered for installing both head and tail ropes onto a four-rope Koepe friction winder, was successfully used at Wesizwe Platinum’s Bakubung mine, in the North West.

The system was designed and manufactured by Tech Edge Group, based in Johannesburg, in conjunction with lead consulting engineers for the project WorleyParsons.

“Eighty tons of steel wire ropes were handled during the process. Stringent design parameters and standards had to be adhered to in order to ensure that the roping-up process was completed safely and timeously,” Tech Edge MD Bannister Erasmus tells Mining Weekly.

Safety is always the number one priority in such a critical project, any failure by the equipment would have had disastrous effects, as well as significant delays.

“The equipment is adequately designed to meet and exceed the necessary design requirement to ensure a successful rope-up of the Koepe winder,” Erasmus states.

He explains that the friction winch and associated equipment met the requirements set out by WorleyParsons, which was contracted to build the mine infrastructure and awarded Tech Edge the tender. The two companies started discussions and preliminary designs for the friction winch in mid-2015.

Erasmus says, from the initial design phase to the final delivery of the friction winch, two years had passed. The friction winch system was completed in February 2017 and was delivered to the mine later in the year, with the full roping-up of the winder completed in October 2017.

The total cost of the friction winch is well below the average costs paid by the mining industry. Erasmus states that the cost of the friction winch was reduced mostly by “value engineering”, using South African parts, manufacturers, fabricators and suppliers. However, the electrical control system, which includes the programmable logic controller and variable-speed drive was bought from international control system company Schneider Electric.

Challenging Installations
Maintaining friction between the drums and ropes was challenging as the head ropes have a coefficient friction level of 0.25, whereas the tail ropes have a coefficient friction level of only 0.09, says Erasmus.

“The tail ropes proved to be most challenging as they are of the double lubricated type and the friction built-up design on the friction winch had to cater for the low frictional coefficient.”

Erasmus points out that the transportation of the friction winch also posed some problems, as the trailer on which it is mounted is not roadworthy.

“Originally, the plan was to simply tow the trailer with a truck and deliver it to the mine. Although the trailer was built to be roadworthy, it was never subjected to the necessary road tests. “This challenge was solved by devising a solution with transportation service company Transcor.”

This led the company having to hire a trailer capable of carrying up to 100 t to transport the friction winch to the Bakubung mine.

Further, it had to be ensured that, well before the trailer arrived at the mine, the foundation anchor points were accurately positioned for interfacing with the trailer. Erasmus highlights that this mechanical interface is critical.

“The foundation blocks are relatively large, owing to the load that has to be handled. Because of problems we have had previously, in terms of the mechanical and civil structures not interfacing correctly, we decided to manufacture cast-in frames. “These frames were fabricated by us and handed to the civil contractors to form part of the foundation, enabling us to know the exact measurements and that they are correct,” Erasmus explains.

This approach worked exceptionally well, he says, adding that, once the friction winch was delivered to the mine, the installation process required no unforeseen modifications to the friction winch trailer.