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Operator's instructions
7. Drilling
High coupling sleeve temperature
NOTE: The coupling sleeve temperature should not exceed 120ºC (248ºF)
1. Excessive coupling sleeve temperature is indicated by:
a. Measuring with a thermometer
b. Oil dripping from the rock drill vaporises on the coupling sleeve
c. The coupling sleeve changes colour
2. Depending on the layers of the rock, temperature can vary even within a small
area. High coupling sleeve temperature is usually due to a poor relationship
between drill feed pressure, percussion pressure and rotation pressure. The follow-
ing solutions are recommended to reduce coupling sleeve temperature.
a. Check the condition of the drill bit. An over drilled bit gives less torque in the
coupling sleeve.
Grind the drill bit.
b. Change to a drill bit with ballistic buttons.
c. If the rock is too hard for ballistic bits, then...
reduce rotation speed as much as possible without causing the drill string to
rotate jerkily
check the drill feed pressure and set it to the recommended value
Reduce percussion pressure to below the basic setting (5-10 bar). A reasonable
reduction in penetration rate must be accepted.
Difficulties in loosening the coupling sleeve
The best method of loosening the coupling sleeve is to "drill" the last few centimetres
without feed pressure and rotation, leaving percussion active for a few seconds to
break loose the coupling sleeve.
Hole deflection
1. Try to drill with as low a drill feed pressure as possible
2. Check the condition of the drill bit
3. Drill the first drill steel with reduced drilling for at least half of the drill steel in
order to minimise hole deflection at the
start of the hole.
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