| Abstrakt: |
The aim of the research was to develop a scaled experimental model of a Clamshell mucker and assess its performance over a range of operating parameters, including bucket closure angular velocity, bucket starting height (translating into increased depth of penetration and bucket fill), bucket angle of attack, and location of the bucket relative to a boundary wall. An experimental rig was developed consisting of a 1/6th scale model opposed bucket arrangement which was actuated by means of hydraulic cylinders. The digging performance was assessed in two materials: a mixture of hard plastic spheres (of diameters 19 and 25 mm), and 13 mm decomposed granite stone aggregate. Flow visualisation tests conducted in the plastic spheres and stone aggregate revealed that particles move initially downwards ahead of the bucket jaws before rising to the interior of the buckets. Tests conducted in decomposed granite revealed that force chains developed between the particles which resisted the motion of the buckets. The force chains resulted in local peaks in the bucket torques. The peak torque required to scoop material was found to increase with increasing depth of penetration, was not affected significantly by angular velocity of the buckets (although the number of local peaks associated with force chains decreased), bucket torque was found to increase in the presence of a smooth boundary within one particle width of the buckets, and was not significantly affected by different angles of penetration. An initial estimate of the energy required to fill the buckets indicated that the least amount of energy was required for lower bucket angular velocities. However, at low angular velocities there was a propensity for bucket stall due to the wedging of particles. [ABSTRACT FROM AUTHOR] |
