A General Semi-Theoretical Model for Conical Picks

Theoretical explanation of rock cutting mechanism with a conical pick is a very difficult task due to inherent complexities in the cutting action. Furthermore, previous studies evidently showed that theoretical models have difficulties on estimating the cutting force accurately. The empiricism seems as the only option for proposing a general force estimation equation with considering the strength of rock, the geometry of tool and the geometry of cutting action. Based on this context, a detailed analysis of conical pick cutting mechanism was performed to demonstrate challenges of the theoretical explanation. Afterwards, present conical pick cutting data, which have been published so far, were compiled including 165 cutting test results of 47 different materials including rocks, ores, coals and artificial rocks with considering the brittleness (sigma(c)/sigma(t)) of the materials. As an initial step, a general trend between the cutting force and the rock strength was explored. Afterwards, a theoretical rake angle function which had been, formerly, proposed for chisel picks was assigned to explain the trend between the cutting force and the rake angle. Furthermore, a back-clearance angle correction function was assigned to the model to reflect the actual cutting conditions. Besides, a universal ratio of maximum cutting force to mean cutting force (k) was investigated through the entire data by considering the probability distribution of experimental results. As a result of this effort, it was discovered that k = 2.45 for conical picks and k is independent of tool geometry and rock properties. The final versions of the proposed models were utilized to compare the estimated and the experimental cutting force. The results from these comparisons have led to a conclusion that the models successfully estimate the cutting force and capture the overall trend between the cutting force and the cutting depth. From a practical standpoint, proposed models might be used for computation of the torque and the power requirements of partial-face excavation machines such as roadheaders which are widely employed in mining and tunnelling practices.