| 摘要 |
A rock drilling apparatus has a noise reducing drill rod cover which comprises a pair of elongated strips, each of which, when in an extended condition in the longitudinal direction thereof, form part-cylindrical members which matingly engage the other strip to form a generally cylindrical cover around the drill rod. Spool means is provided, preferably in the area of the centralizer, to selectively roll the elongated strips thereon, the strips being flattened when rolled onto the spool means. The elongated strips are rolled onto simultaneously driven spools, and comprise either metallic strips, metallic strips covered with rubber on one or both surfaces thereof, or elastic strips having spaced metallic inserts embedded therein. |
