| 摘要 |
<p>A percussion rock drill comprising a drill string having in combination a drill rod, a drilling bit threaded on the end of said drill rod, and at least one ridged reinforcing drill string guiding sleeve sleeved on and bonded to the drill rod with the first sleeve located immediately next to the drilling bit. The sleeve has an outer cylindrical surface having a diameter substantially the same as but not larger than the diameter of a hole that the bit would cut under operation of the rock drill. The sleeve preferably has cuttings guiding passageways in its periphery which preferably are helically fluted.</p> |
