The level of wire rope technology used in mine hoisting applications has a significant effect on the overall efficiency of the hoisting system. Steel wire ropes are used essentially for transmitting tensile forces. The main characteristics which make them so well suited to this function are flexibility and their strength in terms of both mass and diameter. Various rope constructions also possess other characteristics in varying combinations, such as resistance to abrasion, to repeated bending, to shock loading and to lateral pressure.
Underground mines access is only possible through a series of vertical, or incline shafts and during its lifetime, an underground mine may sink many surface and sub-surface shafts to access the ore. Ideally, a mine shaft can be almost any shape although cost dictates that it is either rectangular or circular.
Function of steel wire ropes
To date, the only method that has been devised to transport workers, equipment and rock in a shaft is some form of conveyance running in steel guides that stretch the length of the shaft from surface to the bottom. The hoisting of broken ore to surface is normally conducted in one or more dedicated compartments. These compartments are equipped with a special type of conveyance designed to convey rock known as skips- with capacities up to 20T. Steel wire ropes are currently the only practicable method of suspending and moving a conveyance between operating levels in the shaft and surface. A conveyance is then suspended from one end of the steel wire rope, with the other end attached to the winding engine drum.
It also goes without saying that since mines are continuously increasing in depth, wire ropes safety is of utmost importance. So much so that back in 1904, the government of South Africa made it mandatory for mines to cut samples from the ʻfront endʼ of the winding rope at six month intervals and send to the Government Mechanical Laboratory for destructive tensile testing. This was after a winding rope broke in a shaft at the Robinson Deep mine in Johannesburg causing the deaths of 46 miners in the same year.
Over time, wire rope technology evolved to deliver larger diameter ropes with higher breaking forces, able to cater for increasing mining depths and heavier payloads. As a result, rope technology and industry needs outgrew the capacity of the 500T machine and it was replaced by the 1 000T (10MN) machine in 1973. Further advances in rope technology eventually resulted in this machine being replaced by a 15MN, commissioned in 1989 and still in use today.