10
B� Breaking the driver-chuck joint using the bit
removal tool
If the driver-chuck joint is very tight, the special
bit-removal tool should be used to break the joint.
Important: Never use a sledge-hammer on down-
the-hole hammers�
• Place the bit-removal tool in the drill steel support.
N�B� Looking from behind the feed beam, make sure
that the shaft of the bit-removal tool is touching the
left-hand edge of the feed beam.
• Carefully run the bit down into the bit removal tool.
• Slowly start up the impact mechanism of the ham
-
mer.
• Stop the impact mechanism as soon as the
driver-chuck joint “cracks”.
• Unscrew the driver chuck by rotating the COP hammer to the
LEFT (anti-clockwise).
Dirt in the hammer
Stoppages and breakdowns caused by dirt in the percussion
mechanism are practically inevitable with all rock drills, and DTH
hammers are no exception. However, it should be remembered
that, while DTH hammers are no more sensitive to dirt than top-
hammers, there is obviously a greater risk of dirt ingress in down-
the-hole drilling, especially during pipe jointing. Any dirt that
enters the drill pipes goes straight into the percussion mechanism.
To ensure reliable operation of the hammer, every effort should
therefore be made to prevent dirt from entering the drill pipes. The
following rules should be observed:
• Always keep drill pipes clean. Always store or stack drill pipes
in such a way that the risk of dirt ingress is minimized. Do not let
the thread ends rest on grit or mud. Use thread covers wherever
practicable.
• Always keep the open thread end of the drill pipe covered during
jointing, and remove the cover just before the pipe is coupled up.
• Before coupling up, check that the drill pipe is clean around the
threads and on the inside. If in doubt, blow clean the pipe.
Remember to cover the pipe end that is already in the hole.
• If threads are dirty, they should be cleaned using a strong bristle
brush or a cloth.
N�B� Always clean away from the hole in the pipe. Do NOT let
grit fall into the hole in the pipe. After cleaning, always coat the
threads with Atlas Copco thread grease before jointing.
• Take extra care during jointing operations when drilling in abra
-
sive rock formations, since the ingress of quartz particles into the
hammer will cause heavy wear.
• When drilling holes in water-bearing rock, never leave the ham
-
mer at the hole bottom with the air supply switched off. If drilling
is to be suspended temporarily, always pull up the hammer by at
least two pipe lengths.
• Clean around the driver chuck before changing the drill bit. Make
sure the shank of the new drill bit is clean.
• Keep the hammer clean and plug both ends when not in use.
Change worn or damaged parts in good time.
All Secoroc COP down-the-hole hammers
contain a check valve that is designed to trap a
quantity of air inside the hammer when the air
supply is switched off. In most conditions, this
prevents the ingress of water and dirt into the
hammer during jointing operations. The check
valve A and O-ring B must be fault-free when
drilling in water-bearing formations. When
drilling deep holes in rock with a high water
inflow, however, it is possible that some
seepage of water into the front of the hammer will take place
during jointing. Since only very small particles of dirt would be
able to penetrate the hammer in this way, the threat to the hammer
is not serious.
The sealing efficiency of the check valve
can be checked by pouring a small
quantity of lubricant through the top sub
of the hammer, with the hammer held
vertical. If the lubricant passes through
the checkvalve, then the valve spring
and/or valve seal is worn or damaged
and should be replaced immediately.
Other instructions
Wear to the driver chuck and hammer
cylinder
Since the driver chuck and hammer
cylinder are “sand-blasted” continuously
by large volumes of abrasive cuttings
during drilling, they eventually be come
worn out. The areas adjacent to the
cuttings grooves in the drill bit will be
subjected to the most wear. To prevent
uneven wear of the hammer cylinder,
therefore, the driver chuck and bit should
be marked as shown in figure, before the
chuck is lifted off the bit.
When fitting the driver chuck back on to
the drill bit after grinding or replacing a
drill bit, its radial location on the bit
shank should be advanced by one spline
section. This will give a more even
distribution of wear on the driver chuck
and hammer cylinder.
If the driver chuck is exposed to exceptionnally heavy wear, e.g.
when drilling in rock formations with a high quartz content (gran
-
ite, quartzite etc.), it may be necessary to turn the driver chuck by
more than one spline section in order to prevent the driver chuck
and hammer cylinder from wearing out too quickly. As a rule, the
cuttings grooves in the bit should always be pointing towards the
part of the driver chuck that is least worn.
Since the hammer cylinder has three thread inlets, the part of the
driver chuck that is worn the most can be located against the part
of the hammer that is worn the least.
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