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.
