Percussion an overview ScienceDirect Topics
The percussion or churn drill digs a vertical hole using the principle of a freely falling chisel bit hanging by a cable to which percussive motion is imparted by power units The power units work by manual lift and drop compressed air and electrically driven winches A tungsten carbide bit fitted in a hammer is lifted a few meters up and allowed to drop Fig 7 1 to hit the bottom of the hole