DOUBLE-PIPE DRILLING TOOLS

摘要

PURPOSE: A boring device for a double tube is provided to reduce costs of ring bits by expanding an excavation area by pilot bits and reducing an excavation area by the ring bits. CONSTITUTION: A boring device for a double tube is composed as follows. Engaging convex parts(11) for transferring rotation are formed on the inner surface of a ring of a ring bit(2). The front end of a pilot bit(3) has multiple front convex parts(15) protruded to the side of a circular part. Multiple carbide tips are arranged on the surface of the circular part. Engaging parts for transferring a strike come into contact with the engaging convex parts for transferring rotation.