LASER-MECHANICAL DRILLING OF SILICA-BEARING MATERIALS Russian patent published in 2014 - IPC E21B7/14 E21C37/18 

FIELD: mining.

SUBSTANCE: laser radiation is fed to bore face is delivered via quartz optical 0.2-1 mm dia fibre. Optical fibre is locked in pipe along the drilling tool inner space axis. Note here that radiating end of optical finer is spaced from ribbed bit cutters end surface for h≤d₀/[2tg(arcsinNA)], where d₀ is ribbed bit cavity diameter, NA is optical fibre numerical aperture. Protective gas flow is forced in circular gap between optical finer surface and pipe inner surface towards the face. Said face is irradiated with laser beam with radiation sport at face surface of diameter smaller than that of ribbed bit OD by (0.6÷2)Δ, where Δ=(20÷35)/q is depth of thermally weakened material layer (cm), q=P(l-R)(l-ρ) is absorbed laser radiation density (W/cm²), P is power density of incident laser radiation (W/cm²), R is the factor of reflection from material surface, ρ is heat loses from radiation from heated material. For this, prior to irradiation drill tool end surface is set at L=[D-d₀-(0.6÷2)Δ]/[2tg(arcsinNA)] from face surface, where D is ribbed bit OD. Drilling is conducted in intermittent manner. In every cycle, face surface is irradiated for t=(45000÷130000)/q² (s), for face surface heating to material fusion and boiling temperature. Then, face surface is cooled by coolant for 1-15 s at heat exchange factor of 300÷5000 W/m²·deg. Then, drill tool is displaced towards the face till the contact therewith by ribbed bit end cutters. Lengthwise forces are applied to mechanically crush said thermally weakened material to depth Δ with simultaneous forced removal of slime from face zone. Thereafter drill toll is shifted from face surface for distance L. Drill cycles are reiterated unless preset bore depth is reached.

EFFECT: higher efficiency of drilling.

5 cl, 7 dwg