Unformatted text preview: , the principal application
of these drills is in the primary blasthole drilling. Prior to the advent of these drills,
extensive development work was required in the stopes before the production drilling
could be started. Sublevels were required to have the access to the fan or ring drills
to the stopes; which in turn amounts more development work. To utilize a DTH drill
only top heading and draw points are necessary.
Various configurations of DTH drills are available. The basic energy source for this
drill is compressed air but other functions are powered either by the compressed air or
by air powered hydraulic power pack. The pneumatic rigs utilize several basic air
motors and conventional feed systems and they are more familiar. The hydraulic systems are better with respect to the speed, force and accuracy, and becoming common
for underground applications. The DTH drills are mounted either on crawler track
fig (4.6) or rubber tyre vehicle and the tramming power is provided either by the © 2005 by Taylor & Francis Group, LLC 70 SURFACE AND UNDERGROUND EXCAVATIONS pneumatic or hydraulic motors. Mostly, these drills are towed to the working spots
by other vehicles. A spindle in the rotary head that is mounted on the feed rotates the
drill rods and the drill. The torque is supplied either by pneumatic or hydraulic motors.
The rotation speed is variable and it ranges from 0 to 50 rpm. A DTH drill consists of
a replaceable shell or jacket, containing a piston that oscillates back and forth to strike
directly on the shank end of the bit. Most DTH drills are without valve, using ports to
control the movement of the piston. The exhaust air is ported through the bit, providing the flushing air that cleans the face and conveys the cuttings to the collar of the
hole. Based on the required hole size, these drills are available in various sizes. The
usual compressed air pressure to operate these drills is upto 250 psi (1725 kPa).
The common sizes of the bits used with these drills are 102 to 165 mm diameters. Flat
faced button bit is very common bit that is mostly used but drop center, X and cross
bits could also be used.
The type of drills (described above) used on jumbos include percussive drills,
rotary drills, rotary percussive drill and auger drills. Applications of these drill jumbos
during the stoping operations in underground metal mining operations have been illustrated in figure 16.33(b) and their selection is usually governed by the rock strength. 4.6.7 ROOF BOLTING JUMBOS
These jumbos are meant for roof bolting. In some designs of multi boom jumbos one
or two booms are exclusively meant for rock bolting so that along with the face
drilling rock bolting of the immediate roof can be undertaken. 4.7 MOTIVE POWER OF ROCK DRILLS
In addition to the above-mentioned basis, there are several other ways to classify the
rock drills. Depending upon the motive power they can be classified as pneumatic,
electrical and hydraulic rock drills, as illustrated in figure 4.7. 4.7.1 ELECTRIC DRILLS
These are used for the rotary drilling of the shot holes (fig. 4.5(a)). These can be hand
and column mounted. Handhold drills are suitable for drilling in soft rocks having
weight: 15–25 kg; motor rating 1–1.5 kw; and rotation speed 300–900 rpm. Column
mounted drills can be used for the blast-hole drilling and for the core drilling, e.g. diamond drills for exploration and prospecting purposes.
ROCK DRILLS’ MOTIVE POWER (ENERGY)
Soft rocks ⇓
hard rocks ⇓
hard rocks Figure 4.7 Rock drills’ classification based on their motive power. © 2005 by Taylor & Francis Group, LLC DRILLING 71 4.7.2 PNEUMATIC DRILLS
These are the most commonly used drills in metal and non-metal mines, and tunnels...
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- The Land, Taylor & Francis Group