Atlas Copco SECOROC COP 54 Manuel - Sayfa 4

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1. Technical Data

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.

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.