Seismic events can lead to rockbursts in mines and can result in injury or death to mining personnel. The Dynamic Prop Tester was designed to test hydraulic props, which are used in mines to mitigate the effects of rock bursts by absorbing energy and hence reducing rockburst damage. A prop consists of two telescoping steel cylinders which are extended by hydraulic pressure, which in turn is generated by a hydraulic pump powered by air.
The test machine was built and commissioned by Gauteng Metrology Services, a company that manufactures special testing machines and refurbishes and upgrades all makes of test equipment. The client was Elbroc Mining, a manufacturer of non-sacrificial and sacrificial mine props.
Harsh environments
Rapid yielding hydraulic props were introduced into the South African mining industry in 1970. These props rapidly gained popularity on mines which were experiencing rockbursts. Expansion and deepening of mining activities, combined with the need to meet operational and safety requirements, has resulted in increased demand for these props.
Developed by Elbroc, these sophisticated patented hydraulic props are now used in many South African gold mines. They meet CSIR and Chamber of Mine Research Organisation (COMRO) guidelines for the safety of hydraulic stope support and are designed to slow yield at 20 tons and rapid yield at 40 tons, with a travel capacity of 300 mm to 500 mm, which enables them to withstand seismic events. They are used in stopes up to four kilometres underground, where conditions include a typical roof movement of up to 35 mm in 24 hours. This requires a high level of engineering and component quality. Following manufacture, performance characteristics are verified through batch testing, where they are exposed to both slow yield and rapid yield of up to 3 ms-1.
CSIR and Comro specifications
The Dynamic Prop Tester was first required to compress the prop at 30 mm/min for a displacement of 100 mm. Once the prop reached a static load of 200 kN (20 ton) and had completed the displacement required, the dynamic test phase was triggered. This phase compressed the prop at a rate of 3 m/s for a displacement of between 100 and 200 mm. This released the relief valve on the prop, which had to attain a peak force of 500 kN (50 ton). Once this was completed, the machine had to go back to static testing (100 mm displacement at 30 mm/min).
A machine to meet the challenge
To meet these stringent demands the test machine had to have a variable static speed of 0–120 mm/min and a dynamic capability of 3 m/s. The data acquisition system was capable of a sample rate of 49 kHz. The machine frame capacity was rated for 100 ton maximum for safety reasons.
Specially developed software
Gauteng Metrology Services developed the interface electronics and software in-house to process the data, generate real-time graphs and print out a report on the performance of each prop against the required test specifications.
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