Separated Surface Down-the-Hole Drilling

The working principle of a down-the-hole (DH) drill is similar to that of a conventional rotary rock drill, but it has its unique features. The DH drill separates the impact mechanism (impactor) and places it at the bottom of the hole. Regardless of the drilling depth, the drill bit is directly mounted on the impactor, eliminating the need to transmit impact energy through the drill rod, thus reducing energy loss.

Specifically, during operation, the pressure regulating mechanism continuously advances the drill string while maintaining contact between the drill bit and the rock at the bottom of the hole. The rotary mechanism drives the drill string to rotate. Under the action of compressed air, the piston of the impactor at the front of the drill rod continuously impacts the drill bit, energizing it to penetrate the hole and generate an impact force that compresses the rock. Simultaneously, the rotation of the drill string avoids repeated impacts on the same chisel mark and generates a shearing force that scrapes the rock. Under the combined action of impact and shearing forces, the rock is crushed and sheared. Compressed air travels through the hollow drill rod to the bottom of the hole, blowing rock debris out of the annular space between the drill rod and the hole wall, thus forming a blast hole.