An Experimental Study of Cutting Performances of Worn Picks

Abstract

The best means to assess rock cuttability and efficiency of cutting process for using mechanical excavation is specific energy (SE), measured in full-scale rock cutting test. This is especially true for the application of roadheaders, often fitted with drag-type cutting tools. Radial picks or drag bits are changed during the operation as they reach a certain amount of wear and become blunt. In this study, full-scale cutting tests in different sedimentary rock types with bits having various degree of wear were used to evaluate the influence of bit wear on cutting forces and specific energy. The relationship between the amount of wear as represented by the size of the wear flats at the tip of the bit, and cutting forces as well as specific energy was examined. The influence of various rock properties such as mineral content, uniaxial compressive strength, tensile strength, indentation index, shore hardness, Schmidt hammer hardness, and density with required SE of cutting using different levels of tool wear was also studied. The preliminary analysis of the data shows that the mean cutting forces increase 2-3 times and SE by 4-5 times when cutting with 4 mm wear flat as compared to cutting with new or sharp wedge shape bits. The grain size distribution of the muck for cutting different rock types and different level of bit wear was analyzed and discussed. The best fit prediction models for SE based on statistical analysis of laboratory test results are introduced. The model can be used for estimating the performance of mechanical excavators using radial tools, especially roadheaders, continuous miners and longwall drum shearers.