| 摘要 |
<p>The device of the invention comprises a lower concave housing (15) suitable to receive and to hold the upper end (12a) of an element (12) to be screwed or unscrewed into the drill stem in the drill hole; the concave housing (15) forms a conical surface (16) divergent in a downward and outward direction. A plurality of blocks (17) slides along said conical surface, each of said blocks has an outside sliding surface (18), parallel and cooperating with the conical surface (16) and an inside surface (19) suitable to engage the element (12) to be held. The blocks (17) are mounted in order to slide along the conical surface (16) and said blocks can have two alternative configurations: a first free configuration, with the locking device (10) in its lifted position, wherein the blocks are pushed by elastic means (24) towards the lower, outside portion of the conical surface (16), and a second locking configuration, with the locking device (10) positioned on the element (12) to be held, wherein the blocks (17) are radially clamped against the upper end (12a) of said element (12). <IMAGE></p> |
