School of Earth Sciences - Theses

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Start date: 1980 × End date: 1999 × Type: Masters Research thesis × Subject: diamond bits ×

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    Investigations into diamond drilling and rock drillability: microscale and fullscale impregnated bits
    Siribumrungsukha, Boonsom ( 1980)
    Drill bits having cutting edges formed of a matrix of sintered metal powder impregnated with diamond bort (the so called "impregnated" diamond bits) have the potential to greatly increase the economy of diamond drilling, due to low production costs and long bit life resulting from reconditioning of the cutting edges. However, little detailed research into the performance of impregnated bits has been conducted, and the capacity to predict their field behaviour is limited. As a contribution to the knowledge of impregnated bit performance, this project has studied basic relationships between thrust, rotational speed and the penetration of diamond bits into rock, with particular attention paid to the development of techniques suitable for laboratory testing using miniature impregnated bits. A conventional bench drill and a radial arm drill were modified and instrumented to enable operating conditions to be controlled and drilling parameters to be measured and monitored, for microscale and fullscale drilling using impregnated drill bits. Bit performance and drilling characteristics were studied for four rock types, and rock drillability studies were carried out on seven rock types. Statistical relationships between penetration rate, specific energy, torque and drilling distance that were determined enable projection of drilling data from a standard "sharp" condition. A wear measuring device was developed to assess matrix wear of the impregnated microbits. Reconditioning was done by drilling medium-strength, abrasive Stawell sandstone. Initial penetration rate increases linearly with increases in thrust and/or rotational speed, but only within a limited range, depending on rock type and the other operating parameters. Matrix contact with the rock surface, "clogging" of the diamonds, time-dependency, and strength of diamonds and the diamond-matrix bond play important roles in these phenomena. Comparison of rock drillability between that of microscale and fullscale bits shows a straight-line relationship indicating the possibility to predict drilling performance in the field. Uniaxial compressive strength, tensile strength, and Sklerograf hardness can be used as a preliminary, but not reliable guide, to predict drillability. Petrographic characteristics and the relative scale of diamond size to grain size of minerals affect rock drillability.