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42b it is unbeatable in difficult drilling conditions

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Unformatted text preview: e on the rock and cracks off the chips (fig. 4.2(b)). It is unbeatable in difficult drilling conditions, as it gives high productivity and good penetration rates in such conditions.1 In surface mines and civil construction sites 90–165 mm (3.5 -6.5 ) hole diameters is the usual range.1 4.5.4 AUGUR DRILL The augur drill (fig. 4.2(c)) is the simplest type of rotary drill in which a hallow-stem augur is rotated into the ground without mud or flushing. The continuous-flight augurs convey the cuttings continuously to the surface. This also works on the rotary cutting principle. 4.5.5 ROTARY ABRASIVE DRILLING (THIS HAS BEEN DEALT IN CHAPTER 3) Figure 4.2(f) provides a guideline for the application of various types of rock drills, working on the different principles, for rocks of different compressive strength. 4.6 ROCK DRILL CLASSIFICATION1,3,4,5,7 In order to meet the variety of conditions encountered in rock drilling several distinct types of drills have been developed with the passage of time as illustrated in figures 4.5 and 4.6. In general, rock drills may be classified as either hand held or mounted, as illustrated by a line diagram shown in figure 4.4. The hand held drills include an electric drill (fig. 4.5(a)), jackhammer (fig. 4.5(b)), jackdrills or jacklegs (fig. 4.5(c)) and stoper (fig. 4.5(d)). The mounted drills are known as ‘drifters’ (fig. 4.6(a)). Table 4.1,4 shows that each type of pneumatic drill is available in several sizes from different manufacturers and the range of parameters within which they can operate. © 2005 by Taylor & Francis Group, LLC 66 SURFACE AND UNDERGROUND EXCAVATIONS ROCK DRILLS’ MOUNTING ⇓ ⇓ Handhold ⇓ Pusherleg ⇓ Column & bar ⇓ Rig ⇓ Carriage ⇓ Jackhammer ⇓ Jackleg, stoper, parallel feed ⇓ Drifter ⇓ Drifter ⇓ Drifter, DTH General drilling, shaft sinking Tunneling, raising Drilling parallel holes & fans Ring & fan drilling Tunneling, drilling rings, fans & parallel holes. Figure 4.4 Rock drills classification based on their mountings. 300 Face drilling (b) Drilling m/hr. (a) 200 Hydraulic multi-boom jumbos 150–300 m/hour; II generation Automatic computer assisted (d) Pneumatic/Hydraulic Multi-boom jumbos. 50–150 m/hour; I generation 100 Swedish pusher leg drills - a great break-through 1900 300 2000 Surface bench drilling (e) Hole dia. mm 1950 (c) 200 For benches above 10 m, hole dia. 100 mm and more. DTH, rotary drills For benches above 5 m, hole dia 51 to 100 mm. Top hammer drills 100 Bench height up to 5 m with integral steels hole dia. 30–40 mm 1900 1950 2000 Figure 4.5 Historical review of rock drilling technology. Top: Development of rock drills jackleg to fully automatic multi-boom hydraulic jumbos. Bottom: Sinkers to DTH, Rotary and Top-hammer drills. Right top: Sinker/jack hammer; bottom; jackleg drill; right-most: Stoper for drilling in up-ward direction. (Courtesy: Atlas Copco)1 The jackhammers or sinkers are used for general mine utility (services such as: pinholes, anchor holes, pop holes), and shaft or winze sinking purposes. They can be classified according to their weight as light, medium or heavy duty. The weight ranges from 7 to 30 kg. © 2005 by Taylor & Francis Group, LLC Energy consumption (H.P.) DRILLING 67 Feed motor 225 200 175 Hydraulic energy Pneumatic rig Rotation motor 150 Pneumatic energy 125 Diesel engine 100 75 Hydraulic rig 50 Centralized and clamp 0 80 90 100 110 120 130 140 150 Drilling diameter (mm) Down-the-hole diameter (a) Energy consumption for hydraulic drills as per hole diameter Propulsion motors (b) A typical down-the-hole (DTH) drill Figure 4.6 Comparison hydraulic and pneumatic power. Table 4.1 Rock drills’ specifications, in general.4 Weight or cylinder bore diameter Hole Air diameter consump. Impact range, Cfm# H.P mm Hole depth range, m Use Maintenance General utility Gene...
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