Drilling rotary percussion drills

Luiz, F.P. Franca. 2011. A bit-rock interaction model for rotary-percussive drilling. IntemationalJoumal of Rock Mechanics Mining Sciences 48 827-835. 

Rotary percussion drills are designed for rapid drilling in rock (Fig. 7.8). The rock is subjected to rapid high-speed impacts while the bit rotates, which brings about compression and shear... 

Rotary percussive drilling with crawler-mounted machines... 

The drill bit, operating by rotary percussive action, shatters the rock, and the cuttings are removed from the hole by air issuing from the bit. 

Clay intercalations, sand inclusions or soft moist limestone strata are forced aside by the rotary percussive drill bit and remain sticking to the wall of the borehole, so that a proper sample of such material is not obtained. Nor is it possible to get information on the presence of any cavities in the rock. The most serious drawback of rotary percussive drilling, however, is that it offers no possibility of sampling the rock as such and thus forming a reliable picture of the occurrence of limestone in the deposit under investigation. 

After the bedrock is exposed and clean, the next procedure is drilling. The productivity of large rotary and percussion drilling rigs is such that these rigs have largely replaced lower capacity well ddUs. 

Air Hammer. This is a special downhole drilling tool for controlling severe deviation problems and for drilling very hard formations. The air hammer is an air percussion hammer system that operates from compressed air and the rotary motion of the drill siring. 

Another way to categorize pneumatic devices is as either portable or rock drills. Portable devices include buffers, drills, screwdrivers, wrenches, and paint mixers. This category is powered by a rotary-vane type of air motor. Rock drills or percussion hammers are composed of high-carbon steels. In this type, the compressed air drives a piston down onto a loosely held drill inside a cylinder. 

Similar considerations are applicable to percussive rotary drilling with crawler-mounted machines of the type used for the drilling of blastholes. This method is unsuitable for deposits consisting of loose-textured or soil-type deposits. 

There is no doubt that the fully automatic one-man-operated rotary drill requires more skill on the part of the operator, and also more servicing, than does the percussive rotary drill powered with compressed air and mounted on crawler tracks. These machines are of relatively low weight. With a suitable compressor in tow, a machine of this kind can move about under its own power even on difficult terrain. The drill guide mast can be tilted and swivelled in all directions, so that a wide variety of drilling duties can be performed. These machines are the preferred type in small and medium-size quarries and in cases where highly skilled operating personnel are unavailable. 

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