Mechanical excavation of hard rocks using conventional tools is not yet viable from both the technical and economic point of view due to the poor performance of the equipment in terms of excavation rate and specific energy as well as to the high wear rate of the mechanical instrument if the rock is also abrasive. A new opportunity is opened by the development of tools with special design coated with a layer of polycrystalline diamond. However they are very delicate to handle because of the fragility to impact of the active tip which is also sensitive to the high-temperature heat generated by the contact with the rock. The assistance of a water jet in front of the tool is the only way for efficient cooling as well as for supporting the mechanical action in the initiation and propagation of fractures. Linear grooving experiments have been carried out at the Waterjet Laboratory of the University of Cagliari in the frame of a bilateral programme involving the National Research Council of Italy and the Academy of Science of Czech Republic. Data of forces and displacement as a function of time have been recorded and processed by means of a computer in order to monitor the tool performance in real time. Tests have been carried out on two rock samples with different toughness by varying the vertical load (pushing force) and the features of the water jet (pressure and flowrate). Performance has been evaluated in terms of specific energy (mechanical and hydraulic) and wear has been assessed with high-resolution optical fibre microscopy. The paper describes the laboratory set-up used for the tests and illustrates the results obtained outlining the prospects of the technology.
展开▼
