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Sublevels were required to have the access to the fan

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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) ⇓ ELECTRIC ⇓ Soft rocks ⇓ ⇓ PNEUMATIC ⇓ Medium-hard to hard rocks ⇓ HYDRAULIC ⇓ Medium-hard to 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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