| 摘要 |
PROBLEM TO BE SOLVED: To rationalize the constitution of a top guide having a prevention mechanism preventing a kelly bar from being raised therealong. SOLUTION: The diameter of a hole 29 in a lower surface plate 23 of the top guide 21 is formed into such a dimension as allowing only a last-stage kelly bar 35 of a multistage expansion type kelly bar 31 to pass through. When upper kelly bars 33 and 34 are raised along with the last-stage kelly bar in winding up a wire rope, the upper ends of the upper kelly bars abut on the lower surface to prevent the raising and are stopped. This constitution can dispense with a stopper plate and its welding works so as to eliminate any possibility of falling of the stopper plate, which is different from a conventional top guide wherein a stopper plate is welded in the hole to prevent the kelly bar from raised therealong. COPYRIGHT: (C)2004,JPO
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