Design and optimization of abrasive slurry feed system, control circuit and jet drilling tool for mining applications,

This dissertation focused on an investigation of small diameter hole drilling using abrasive slurry jet (ASJ) technology. The existing ASJ feed systems were reviewed and found inadequate to satisfy the requirements of an ASJ drill. A novel feed system was designed which improved on existing systems by resolving problems with the inability to perform stop/start operations and ensure precise metering of abrasive feed. This system met standards of consistency and evenness of feed required for machining aircraft component parts for Air Force Research Laboratory (AFRL). Theoretical and experimental analysis of the power of an ASJ stream yielded valuable design information that was then included in drilling tool design. The concept of introducing a swirl component in the nozzle before accelerating the slurry stream was used to design a Dispersed Abrasive Slurry jet (DASjet) nozzle. The influences of abrasive feed rate and pressure on the hole depth and diameter were studied. The effect of variation of the swirl angle on performance was found and an optimal angle identified. Material removal rates in air and under hole backpressure were determined. The loss in drilling performance when the drill operates against backpressure was overcome initially by the introduction of an air sheath around the jet. The cutting fluid and air shroud were then replaced with supercritical carbon dioxide. Supercritical CO₂ was shown to be a superior fluid medium to form the slurry jet because of the phase change which occurs at the nozzle orifice. Laboratory experiments conducted to validate this change successfully showed that this tool could drill holes to larger than two-inches in diameter, without nozzle rotation, and at rates of penetration of up to 400 ft/hour. As a result a novel drilling tool has been created for use in microhole drilling --Abstract, page iii