Collaring; Feed And Rotation; Feed Force; Rotation Speed - Atlas Copco SECOROC COP 34 Manual

DANGER
When drilling on soft or unstable ground, great care must be taken
because the fl ushing air from the hammer can erode the material around
the drill hole, and so undermine the ground beneath the drill rig. This can
pose a great danger to personnel and risk damaging the equipment.
CAUTION
Always wear ear protectors during drilling.

Collaring

Feed the hammer downward until the drill bit is
the collaring point.
Start rotation to the right at low speed (creeping).
Feed the hammer on to the rock using minimal feed force, so that
the bit is pressed into the hammer, and into the impact position.
Start collaring the hole with reduced impact and feed, until the bit
has entered the rock.
Open the impact mechanism control fully and adjust the rotation
and feed so that the hammer drills smoothly and steadily.

Feed and rotation

With holes of relatively shallow depth, the setting of feed and rotation
is usually a simple matter in DTH drilling, since the hammers are
comparatively insen sitive to small variations in the "normal" fl ow and
pressure settings. The settings can be regarded as correct when
the drill string turns evenly without jerks or jamming, and a steady
penetration rate is obtained.

Feed force

When drilling with COP DTH-hammers, the feed force should be high
enough to keep the shank of the drill bit pressed into the hammer
during drilling.
Feed force – recommendations
Feed force
Feed force at 16 bar
COP 34
Ø 100 mm

Rotation speed

– recommendations (r/min) 45 – 90
6
a b o u t 5 c m f r o m
COP 34 COP 44 COP 54
4–13 kN 5–15 kN 6–17 kN
6 kN 10 kN 12 kN
COP 44 COP 54
Ø 115 mm Ø 140 mm
40 – 80 35 – 70
Too low a feed force will give easy rotation, excessive vibra-
tion and reduced penetration. The resultant refl ex shock waves can
damage the rotation unit and feed beam.
Too high a feed force causes the rotation to jam (either erratically
or completely) and can subject the drill string to severe bending
stresses. It can also damage the rotation unit and feed beam.
The feed force often needs to be corrected during drilling, depending
on the rock formation and the weight of the drill string, which obviously
varies with the hole depth.
A rough guide to drill pipe weights for different sizes of DTH-hammer
are given in the table below:
Pipe dimension
76 mm
89 mm
102 mm
114 mm
127 mm
140 mm
Bit diameter, rock formation, hole depth and available rotation torque
will have a considerable infl uence on the setting of the feed force.
What is important is that the feed force is adjusted to give steady
penetration and a constant, even rotation speed with no jamming
(see table).
N.B. It is important that the feed force be adapted to suit the weight
of the drill string. When drilling deep holes, this requires control facili-
ties for "negative feeding", a so-called "holdback" function .
Rotation speed
In hard rock the rotation speed for COP hammers should be set
between 20-90 r/min, depending on the hammer size and bit diameter
(the larger the bit diameter, the slower the speed). The upper limit
generally produces the best penetration rate. In very abrasive rock
formations, however, the rotation speed should be reduced to avoid
excessive wear of the drill bit. When drilling in softer rock or with high
air pressure (above 18 bar) in non-abrasive formations, higher rotation
COP 64.2/64.3 COP 84.2L COP 84
7–20 kN 7–20 kN 10–30 kN
14 kN 14 kN 22 kN
COP 64.2/64.3 COP 84.2L COP 84
Ø 165 mm Ø 203 mm Ø 219 mm
30 – 60 25 – 40 20 – 40
Approx. weight
9 kg/m
15 kg/m
18 kg/m
20 kg/m
23 kg/m
34 kg/m
speed may be used. The follow-
ing should be noted:
Too high a rotation speed will
cause increased wear to the
drill bit, hammer and drill pipes.
Stresses to the feed and rota-
tion unit will also increase.
Too low a rotation speed
results in a poor drilling output
and uneven operation.