Overlay borehole drilling rig - has independent rotary drives for inner and outer tubes on feed assembly

摘要

A drilling tool is fitted at the end of an inner tubular rod linkage unit, running inside an outer one and turned by a rotary drive, in a drilling assembly for overlay drilling. An independent second rotary drive unit (13) turns the outer linkage system. The two drive units (13,21) are mounted on a power driven forward thrust assembly (27). The drilling tool is of the full-bore type. The forward thrust assembly may have two mutually displaceable parts, each carrying one drive unit. A percussion device (22) striking the inner linkage system may be mounted to the rear of this one's drive unit.