Vishnu Pillay, Director of CSIR Mining Technology, explains that as depths increase, along with the demand for bigger and heavier payloads, rope testing is an increasingly important part of mine safety. CSIR Mining Technology currently runs one of only two hoist rope testing facilities approved by the Department of Minerals and Energy (DME) in South Africa, at its Cottesloe laboratory in Johannesburg.
"The records of the DME show more than 1 000 registered mines in South Africa, of which an estimated 135 are underground operations," says Pillay. "The CSIR's own rope database reflects more than 1 150 hoist ropes in use, illustrating the responsibility that rests with our laboratory to provide mine engineers with accurate test data and results."
The statutory testing of mine hoist ropes was introduced following the failure of a winding rope in No. 2 shaft, Robinson Deep, on 25 April 1904. This accident caused the death of over 40 men and led to the immediate introduction of a government regulation that stipulated the periodic removal of a section of head rope adjacent to the skip, to be tested at the Government Mechanical Laboratory of the Department of Mines.
The Department of Mines relinquished control over the Government Mechanical Laboratory in 1964, when it was taken over by the CSIR and incorporated into its National Mechanical Engineering Research Institute. This laboratory now forms part of CSIR Mining Technology and continues to conduct statutory tests on mine hoist ropes and provide related mechanical testing services.
Hoist rope FACT FILE
- South African mines hoist about 350 000 people up and down mine shafts each day.
- The same mines hoist about 10 million tons of ore every month.
- DME regulations stipulate that rope installed on licensed winders must be tested every six months.
- CSIR Mining Technology's hoisting and mechanical testing laboratory tests between 2 000 and 3 000 ropes every year, including hoist ropes, scraper ropes, dragline ropes and ropes for marine applications.
- The biggest sample the centre has ever tested is a 143 mm diameter dragline, which was locally manufactured and is being used in Australia.
- The biggest steel wire rope used in South Africa is 63 mm in diameter, and weighs 17 kg a metre. At a depth of more than 2 000 m, the weight of this rope alone - without any skips or cages attached - is some 34 tons.
- Although mines sometimes experience winding accidents, they are rarely due to rope failure. Rope testing allows mines to predict and prevent such failure. Testing also keeps costs down, as it helps mines to avoid premature replacement of expensive steel wire rope.
- Statutory testing is only required on ropes attached to licensed winders.
- CSIR Mining Technology maintains the largest database of rope tests in Africa, to ensure the traceability of all test specimens.
CSIR Mining Technology's Cottesloe testing facility
The largest tensile test machine in use at Cottesloe is a 15 MN MFL machine that was commissioned in 1988. In addition to the testing of mine hoist ropes, the MFL machine is able to accommodate large diameter wire ropes (~160 mm) as used in the oil drilling, bridge and shipping industries. The capacity of the 15 MN machine also caters for tensile tests on conveyor belts up to 1.2 m wide and large-link chains, such as those used on coal mine draglines.
The hoist rope tests evaluate a rope's absolute breaking force, mechanical properties, modes of wire and strand failure, extent of corrosive and abrasive damage, and the state of lubrication. If the results of the test show that the rope does not conform to the code of practice (SABS 0293, 1996), then the recommendation is that the rope be discarded.
The majority of ropes, however, reach this condition only following several years of service. The results of the test, a graphical history thereof and subsequent visual examination of the test specimen, are recorded on a test certificate supplied to the mine.
The smallest diameter hoist rope that CSIR Mining Technology tests is about 16 mm in diameter, and the largest is currently 63 mm. In terms of hoist ropes, the predominant size ranges between 30-50 mm in diameter. The test machine, however, is able to test ropes up to 155 mm in diameter.
In addition to the testing of mine hoist ropes, CSIR Mining Technology offers a range of other mechanical tests including tensile, proof and compression tests of a broad range of mining and industrial products.
- a 4 448 kN Mohr and Federhaff tensile test machine with a 25 m bed;
- an 8 896 kN Mohr and Federhaff compression test machine; a feature of this compression test machine is the "daylight" opening of 4.5 m, permitting the testing of full-scale mine support systems such as packs and elongates; and
- three Amsler universal testing machines, with capacities of 100 kN, 500 kN and 1 000 kN.
Andrew Peake (Head: Mining, Engineering, Technology and Laboratories) at CSIR Mining Technology, tel 011-853-4550, email miningtek@CSIR.co.za, website www.CSIR.co.za/miningtek