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A hydraulic rockbreaker for the mining industry

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dc.contributor.author Frangakis TJ en
dc.date.accessioned 2016-09-22T11:26:44Z
dc.date.available 2016-09-22T11:26:44Z
dc.date.submitted 1997 en
dc.identifier.uri http://hdl.handle.net/20.500.11892/121872
dc.description.abstract The aim of this research was to develop a non-explosive (continuous) mining device in order to improve mine profitability. The specific mechanism under consideration is one which fractures rock through the application of liquid pressure pulses into drilled holes. A critical survey of the literature indicated that in order to multiply fracture rock a peak pressure of approximately 250 MPa is required, with a rise time of about 0.5 ms. Computer modelling was used to evaluate several ideas, on this basis the most effective was found to be a "kinetic energy" concept which employs air for energy storage and a mtoving piston as the energy transfer medium. A system based on this principle was computationally optimised and a full-scale machine was designed, built and tested. It utilises a double diaphragm mechanism to abruptly pressurise the back of an 80 kg piston of diameter 200 mm. Once the piston has accelerated (in air) to its maximum velocity, it impacts with a further thin diaphragm enclosing water in a simulated "hole" comprising a thick-walled steel cylinder of internal dimensions 40 mm diameter x 1000 mm deep. An LVDT was used to monitor the piston displacement, while a pressure transducer tracked the hole pressurisation. Tests were conducted over a range of gas precharge pressures, between 1.3 MPA and 9.2 MPa. Measurements (liquid pressure, piston displacement, piston velocity variations with time; energy transfer efficiency) and predictions generally corroborated satisfactorily, validating the effectiveness of the computer model as a practical design tool. Peak pressures in excess of 300 MPa were achieved in the liquid section, with associated rise times of about 0.7 ms using a maximum gas precharge pressure of 9.2 MPA. Comparisons between measured and theoretical maximum liquid pressures showed a variance of only 5%, while discrepancies in piston displacment and velocity were between 5% and 15%, ascribed to air pressure build-up ahead of the moving piston, leakage of water from the nozzle section, air contained in the nozzle, and deflection of the connecting rod between the piston and displacement transducer. Overall energy transfer efficiencies (from expansion of the compressed gas to compression of the liquid in the test section) varied in the range 70% to 80%. In conclusion; the research validated the basic concept that large pressures for fracturing rock could be rapidly and efficiently generated through the impact of a moving mass on a column of water filling a hole. However, successful implementation of the concept would depend on designing a practical valving system to replace the diaphragms used in the laboratory facility. en
dc.language English en
dc.title A hydraulic rockbreaker for the mining industry en
dc.type Masters degree en
dc.description.degree MSc(Eng) en

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