5
Getting started
In order to get optimal drilling the impact, feed and rotation must
harmonize. Start off by setting the percussion pressure on the
compressor. Secondly, set the rotation speed. Thirdly, set the feed
force. Adjust your settings continuously. The goal is to have the
drill string rotate evenly without jerks or jamming, and a steady
penetration rate.
The impact depends on the percussion pressure. The higher the
percussion pressure, the faster and the harder the impact you will
get.
Recommended settings
The pressure depends on the depth and the type of rock that the
operator is about to drill.
Depth
With modern compressors that provide pressures up to 35 bar,
the impact energy is initially too high. If the operator were to use
maximal pressure the equipment would be damaged. Therefore,
the operator normally uses a lower pressure down to depths of
70–100 metres (by then you will have a counteracting pressure of
2–4 bar).
The illustration shows the principled correlation between
percussion pressure and rock hardness.
Safety: Preparations
•
Take care when handling the
hammer, it is very heavy. The
hammer and its internal
components are heavy and
difficult to handle, especially in
the case of the larger hammers.
•
When you lift the hammer using mechanical lifting equip-
ment, sling the hammer as shown in the figure. Alternative-
ly, a lifting-eye coupling can be screwed on to the backhead.
WARNING
•
Always check the condition of drill string components. Bent
or worn pipes can cause damage and excessive wear to the
hammer and rig
.
CAUTION
Operation
Pre-Torque
Simply put, it is the amount or force applied to the back-head and
chuck to lock by compression internal components of the ham-
mer. Each threaded part will be individual torqued tight, with rig,
or hydraulic bench before operating!
A common practice in the field is to use the rotary head, which
can never supply enough torque for the specification need to keep
internal parts tight.
Golden rule: torque threaded joints between (40.5-54 kN-m / 750-
1,000 lbf-in) per inch or hammer dia.
Example: 5"/127 mm DTH hammer
5 x 750 - 1,000 ft�lbs = 3750 - 5000 lbs�in
127 mm x 40�5 - 54 Nm = 5143�5 - 6858 Nm
Example: 8"/203 mm DTH hammer
8 x 750 - 1,000 ft�lbs = 6,000 - 8,000 lbs�in
203 x 40�5 - 54 Nm = 81349 - 10962 Nm
The four basic parameters of percussive drilling are impact, feed,
rotation and flushing. In the following sections we will take a look
at how you can adjust your settings to achieve best possible drill
-
ing results.
To Next Page
Loading...
Need help?
General
