The down-the-hole hammer drill is a pneumatically operated bottom-hole drill that efficiently combines the hitting action, similar to that of cable tool drilling, with the turning action of rotary drilling. The pneumatic drill can be used on any standard rotary rig with an integral or auxiliary air compressor of sufficient capacity. It is used for fast and economical drilling of medium to extremely hard formations. Fast penetration results from the air piston blows transmitted directly to the bit, so practically no energy is wasted in chewing up cuttings. A straight hole is assured by short, rapid blows that minimize the effect of dipping and broken formations. Down-the-hole hammer drilling is by far the fastest method of penetration in hard rock material. The bit is turned slowly (10 to 15 RPM) by the same method that rotates the drill bit in the mud or air drilling operation.
Air Hammer with Casing (Overburden System)
The methods of drilling with casing treatment at same time are two typical method. One is overburden system and the other is Dual Rotation System.
This method is using overburden bit, odex bit or tubex bit and so on. The kinds of bit is just different the design. However, they achieve same result.
Tricon bit Drilling with Mud
In the rotary method of drilling, action is accomplished by rotating a drill pipe by means of a power driven rotary table or hydraulic powered top head drive, with a bit attached to the bottom of the pipe. The bit cuts and breaks up the material as it penetrates the formation. Drilling fluid for mud is pumped through the rotating drill pipe and through holes in the bit. This fluid swirls in the bottom of the hole picking up material broken by the bit, then flows upward in the space outside the drill pipe, carrying the cuttings to the ground surface and clearing the hole. The greater the fluid flow the faster the drilling. The drill pipe and bit move downward deepening the hole as the operation proceeds. At the surface, drilling mud flows into a ditch to a settling pit where the cuttings settle to the bottom. From the settling pit the fluid overflows into another pit from which it is picked up through the suction hose of the mud pump and re - circulated through the drill pipe. In the rotary drilling method the casing pipe is not introduced until after the drilling operations are completed. The walls of the hole are held in place by the pressure of the mud pump against the sides of the hole.