| 摘要 |
<p>PERCUSSION HAMMER DRILL WITH UPPER END COCKING SPRING A percussion hammer drill stem has a reciprocally movable internal hammer which forms a large part of its mass. A single precompressed cocking spring is positioned around the upper end of the hammer and supports it within a bore of a casing. When the drill stem is dropped in drilling operations, the spring is restricted against downward movement, but the hammer moves a short distance after an initial impact to provide a follow up impact. During this movement the spring is compressed further to absorb some of the kinetic energy built up by the hammer during its drop. The spring is located away from a debris chamber at the lower end of the hammer where dust and debris tends to accumulate from the internal impacts between the hammer and the casing.</p> |
