Enhancing the Drilling Potential of Polycrystalline

Work on the development of mechanical tools to remove rock has, for a number of years, been restricted by the increasing wear rates of conventional carbide bits. Performance can be increased by using diamond coated tools, but in their initial application these give penetration rates of equivalent level to those of existing tools. For drilling to be made more economic, penetration rates in harder rock must be significantly improved - a problem with conventional tools, and an area in which PDC equipment has yet to be validated. By examining the damage pattern under PDC tools it can be shown that the damage can be divided into two zones, one of intense rock crushing and one where the rock is severely cracked but not liberated. Where the loading of the tool can be increased (a benefit of the use of the diamond coating) then a crushed zone of greater than twice the penetration depth is created. When this material is removed by the short pulse of a high pressure jet stream, then the penetration rate of the combination can, thus, be more than doubled. The results from laboratory tests with a suite of rocks, ranging from sandstone to quartzite and basalt are discussed both using static and dynamic impact loading. A preliminary novel design for a rock drilling bit is proposed and discussed