Bit Changing; Process Instructions - Atlas Copco Secoroc QLX Series Operator Instructions Manual

can sometimes require very heavy levels of water injection.
These applications are unique in that they can either be
drilled totally dry or totally wet....not in between. Marginal
fluid injection results in making a tacky mud which sticks to
the drill rods and hole wall and hinders hole cleaning. The
correct level of fluid injection thins the paste so it will be
cleared from the hole.

Bit changing

Removing the drill bit
Bit removal can be one of the most dangerous and frustrating
tasks associated with the drilling operation. However, with the
proper tools and techniques it should require no more than a few
minutes to remove a bit. The following lists pointers which will
be beneficial in helping you remove a bit quickly, safely and with
reduced risk to damaging DTH hammer parts and components:
1. Use sharp tong jaws. Worn or rolled over tong jaws increase
the jaw pressure and make the wrench more prone to
damaging the hammer case. Many Atlas Copco hammer cases
are case hardened which means sharp jaws are needed to grip
through the hardened case.
2. Grip the casing in the proper location. Gripping over the
threads can make thread loosening extremely difficult.
Example; as the wrench tightens it exerts an inward force
which can pinch the threads if they are under the wrench jaw.
This only increases the torque needed to uncouple the thread.
Also, do not grip the casing in an area where the bore is not
supported by either the piston or bearing. Gripping over an
unsupported area can distort the bore. The following table
and figure shows the recommended locations for wrenches.
CHAIN WRENCH POSITIONS
Hammer model Minimum distance
from chuck to
lower jaw
QLX 35 4.7 in. (119 mm)
QLX 40 5.5 in. (139 mm)
QLX 50/55 6.5 in. (165 mm)
QLX 60/65 6.5 in. (165 mm)
QLX 100 9 in. (228 mm)
Bottom
of jaw
Minimum
distance
QLX 35 minimum distance from bottom of chuck to bottom of
jaw / 4.7 in. (119 mm). Maximum distance from bottom of chuck
to top of jaw / 8.5 in. (216 mm)
QLX 40 minimum distance from from bottom of chuck to bottom
of jaw / 5.5 in. (139 mm) Maximum distance from bottom of
chuck to top of jaw / 13.5 in. (342 mm)
QLX 50/55 minimum distance from bottom of chuck to bottom of
Maximum dis-
tance from chuck
to upper jaw
8.5 in. (216 mm)
13.5 in. (342 mm)
12.5 in. (318 mm)
13 in. (330 mm)
20 in. (508 mm)
Top of jaw
Maximum
distance
jaw / 6.5 in. (165 mm). Maximum distance from bottom of chuck
to top of jaw / 12.5 in. (318 mm)
QLX 60/65 minimum distance from bottom of chuck to bottom of
jaw / 6.5 in. (165 mm). Maximum distance from bottom of chuck
to top of jaw / 13 in. (330 mm)
QLX 100 minimum distance from bottom of chuck to bottom of
jaw / 9 in. (228 mm). Maximum distance from bottom of chuck to
top of jaw / 20 in. (508 mm)
3. Insure the bit fits properly within the bit basket. An improper
fit may result in the bit slipping from the basket.
4. Never weld or hammer on the casing to loosen it. Many
casings are case hardened for extended service life. The hard
casing surface can be cracked by welding or impacting with a
sledge hammer. If a chuck or backhead is difficult to loosen,
repeatedly tapping the casing at the thread location with a
brass bar or hammer while torque is applied may help loosen
the joint.
WARNING
Insure chain wrenches or tongs are rated for
the torque applied. The flying parts of chain
wrenches can cause injury or death when they
break!
Removing the bit with percussion only
If a chuck is difficult to loosen it´s sometimes helpful to use low-
pressure percussion assisted with reverse rotation to free the
thread. The following lists the process and cautionary
notes:
CAUTION
Wear eye protection as the hammer will be cycling above
ground. Insure that all drill string joints are tight. Watch
other string Joints to insure they do not loosen before
the chuck. If they do loosen, stop the process

Process instructions

1. Place a piece of relatively hard polyurethane or conveyor
belting in the bit break-out basket to absorb shock.
2. Remove all drill pipe so only the DTH hammer and required
adapters are attached to the rotary head.
3. Bring the drill in contact with the bit basket with a relatively
light feed.
4. Bring the hammer pressure up to roughly 150 psig (10.3 bar).
5. See if the joint has loosened on its own after about 10 seconds
of cycling.
6. If the joint has not loosened, ´Bump´ the rotation in reverse at a
slow speed while the drill cycles until the joint has loosened.
7. Stop as soon as the chuck loosens, grease and air will be
noticed coming from the loosened joint.
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