General; Application (Drill Rigs); Technical Description - Atlas Copco SECOROC COP 34 Manual

General

The down-the-hole hammer is a percussion hammer drill. As the
name implies, the hammer works down the hole at the end of the drill
string, where the impact piston strikes the drill bit directly.
Compressed air is led to the hammer via the rotation spindle and drill
pipes. Exhaust air from the hammer is discharged through holes in the
drill bit and used to fl ush clean the drill hole. Rotation is provided by a
rotation unit on the feed beam and transmitted to the hammer via the
drill pipes. The drill pipes are threaded so that the drill string can be
extended as drilling progresses and the hole becomes deeper. Feed
force is also transmitted to the hammer via the rotation unit and drill
pipes. One of the main advantages of DTH hammers is that the drilling
rate is not affected very much by the length or depth of the drill hole.
DTH hammers are very productive and have many applications in the
mining, quarrying, civil-engineer ing and water-well drilling industries.

Application (drill rigs)

A=Drill pipe B=Down-the-hole hammer
C=Drill bit D=Rotation unit
E=Feed F=Drill rig
Secoroc COP down-the-hole hammers are designed for use on DTH
or ITH drill rigs. They can also be used on rotary and auger type
drill rigs, provided that such rigs meet the specifi cations for DTH
applications. The main demands on the drill rig are as follows:
It should be equipped with
a rotation unit that has a var-
iable rotation speed of 0–90
r/min and a rotation torque of
750–3000 Nm (75–300 kpm).
Naturally, the torque demand
for a recommended rotation
speed will depend on the
hammer size and bit diameter.
A variable feed force of
3–43 kN (300–4300 kp) for
shallow holes (less for deeper
holes, bearing in mind the
weight of the drill string). Obvi-
ously, the feed must be strong
enough to pull the hammer
and drill string out of the
drill hole. This is an especially
important consideration when
drilling deep holes. The weight
of the drill string varies
between 9 and 34 kg/m,
depending on the pipe- and bit
diameters.

Technical description

The Secoroc COP down-the-hole hammer and drill bit operate at the
bottom of the hole as a unit.
COP hammers have a long cylinder D, which houses a check valve
B, compression ring C (COP 34/44/54/84) or disc spring unit (COP
64.2/64.3/84.2L), impact piston F, control tube E, bit bushing G
(COP 34/64.2/64.3), stop ring H and drill-bit shank J. The back end
of the cylinder is closed by a threaded top sub A. The top sub has
a male thread for connection to the drill pipes, and is provided with
wrench fl ats.
A driver chuck K threads into the front end of the cylinder. The splined
union between the driver chuck K and bit shank J transmits rotation to
the drill bit. The front end of the driver chuck transmits feed force to the
drill bit. The split stop ring H limits axial movement of the drill bit. The
check valve B prevents water from entering the ham mer through the
driver chuck when the compressed air supply is shut off.
When feed force is applied, the drill bit is pushed into the hammer
and pressed against the front of the driver chuck. The impact piston
strikes the shank of the drill bit directly. The passage of compressed
air through the hammer is directed by the piston and control tube, both
of which have regulating ducts. A built-in damping chamber cushions
the piston return stroke and increases the impact frequency.
After the compressed air has imparted most of its pressure energy
to the piston, it is led as exhaust air through the foot valve L into the
central gallery in the drill bit. The exhaust air then emerges as fl ushing
air through holes in the drill bit head. This gives effi cient transportation
of cuttings out of the drill hole.
4
When the hammer is lifted off the bottom of the hole, the piston drops
into the air blowing position. This disengages percussion and gives
air blowing only, i.e. a large volume of air fl ows straight through the
hammer and drill bit. During drilling, air blowing starts if the drill bit
loses contact with the bottom of the hole. The hammer starts operating
again as soon as the bit is pressed back against the driver chuck. Air
blowing is used when powerful fl ushing of the drill hole is required, and
in certain diffi cult drilling conditions.
In diffi cult drilling conditions, extra fl ushing can be obtained by chang-
ing the valve M in the top sub. This might be desirable, e.g. when there
is a large infl ux of water into the hole, when there is a big difference
between the diameter of the drill bit and the diameter of the drill pipes,
or when penetration rates are abnormally high.
Friction between the drill pipes and the hole wall can sometimes
reduce the pen etration rate. This can often be counteracted by
increasing the air pressure to give more impact power and faster
penetration.
Together with Atlas Copco ODEX equipment, COP hammers are used
for simultaneous drilling-and-casing through overburden. When used
with Secoroc precision drilling equipment, COP hammers are capable
of drilling long, straight holes.
A
M
B
C
D
E
F
L
G
H
J
K