Measurement and Modelling of Vibration Characteristics of a Mining Skip During Unloading
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Arc gate skips can carry larger payloads compared to other designs due to the superior safety of the arc gate design, however these skips experience large amplitude vertical oscillations during unloading. Data were collected from a salt mine with arc gate skips in operation to observe and gather information on the system. Full scale computational simulations were developed to theoretically characterise and analyse the full scale system. A small scale experimental apparatus was designed and fabricated to perform experiments, and complementary small scale computational simulations were also developed. The analysis of every unloading cycle in the mine site data revealed the peak amplitude of the oscillations and damping constant varied considerably between unloading cycles, while the primary oscillation frequency remained relatively constant between cycles. Each unloading cycle was categorised according to the six characteristic shapes observed in the oscillations. Two cycles from each category were selected for further analysis. The small scale experiments investigated the level of influence of the angle of the exit chute walls and floor, the number of internal stiffener bands, grain size distributions, and moisture content of the ore. The experiments showed that an increase in ambient humidity and possible increase in moisture content of the ore caused the greatest increase in the oscillation amplitude, followed by the angle of the exit chute walls and floor with the optimum angle being 5° to 10° steeper than the current angles. The stiffener band experiments revealed that removing all the stiffener bands gave the largest reduction in the oscillation amplitude. Finer grain ore was found to reduce the oscillation amplitude, although it had the least significant effect in comparison to the other variables. The full and small scale simulations confirmed that, when compared to the raw data from the mine and the control experiments, the system was best modelled as a single degree of freedom mass-spring-damper system with a linearly decreasing mass. The high speed camera experiments revealed the stiffener bands created a plug effect with the ore close to the walls, causing ore-on-ore friction, whereas without stiffener bands the ore flowed together, resulting in ore-on-aluminium friction.