HAMMER DRILL, perforator (EN: hammer drill; DE: Bohrhammer; FR: marteau perforateur; ES: taladro de percusion; RU: бурильный молоток) is the machine of the striking action for the drilling of the blastholes (less often of the boreholes). The modern hammer drill represents by itself the machine of the hammer type, within which the piston-striker, which is performing the advancing-retreating movements, performs the strikes onto the shank of the rotating borer with the drill crown, which is fixated onto the borer.
The borer rotates intermittently during the retreating (less often during the advancing) movement of the piston, with the help of the helical pair with the ratchet mechanism, or continuously with the help of the motor with the gearbox, which is built into the hammer drill. For the cleaning of the bottomhole, they deliver the water or air through the axial channel (with the diameter of 6-7 millimetres) of the drill rod and of the piston-striker (the central flushing), or through the coupling with the seal, which is placed onto the shank of the borer (the lateral flushing). The specific energy of the single strike of the hammer drill amounts to 10-15 joules per 1 centimetre of the diameter of the blasthole. According to the frequency of the strikes, they distinguish the hammer drills with the decreased (up to 1000 strikes per minute), normal (1600-2000 strikes per minute), and increased (2500 strikes per minute) frequency. There are distributed the hammer drills with the increased energy of the single strike and with the normal frequency. They use the high frequency hammer drills, because of the excessive level of the noise (up to 120 decibels) and of the vibration, only in case of their installation onto the drill carriages with the remote control.
They distinguish the following hammer drills: manual, or portable, with the mass of 10-30 kilograms, for the drilling of the blastholes with the depth of up to 3 metres, with the diameter of up to 46 millimetres (during the work, they hold these hammer drills using the hands, or install them onto the pneumatic supports); the columnar hammer drills with the mass of 50-70 kilograms (the depth of the blastholes and boreholes is up to 25 metres, the diameter is up to 85 millimetres), which are installed onto the columns (less often), or onto the manipulators of the drill carriages; the telescopic hammer drills with the mass of 40-50 kilograms, for the drilling of the blastholes and boreholes (the depth is up to 15 metres, the diameter is up to 85 millimetres), which are directed upwards. The advancement of the columnar hammer drills with the determined axial force (up to 6000 newtons) onto the bottomhole is performed by the automatic advancers of the screw, rope, or piston types. They install onto the drill carriages the automatic advancers with the long stroke, which are performing the continuous advancement of the hammer drill along the length of 3-4 metres. The telescopic hammer drill comprises the hammer drill proper, and the telescopic advancing device in the form of the extendable rod with the piston (the length of the advancement is up to 650 millimetres, the force is up to 1600 newtons). There are most distributed the pneumatic hammer drills, less often there are used the hydraulic, gasoline-powered, and electric hammer drills. The pneumatic hammer drills are powered by the compressed air (the pressure is 0.5-0.6 megapascals; abroad, there are being developed the powerful hammer drills with the pressure of up to 1.5-2.0 megapascals). The consumption of the air (cubic metres per minute) for the manual hammer drills is 2.5-3.5; for the telescopic hammer drills is 3.5-5.5; for the columnar hammer drills is 9-13; the striking power (kilowatts) is 1.6-2.1; 1.9-3.7; 4-5 respectively; the torque (joules) is 12-18; 20-29; 175-245. With the increasing of the striking power of the hammer drill, and of the torque, there increase the rapidity, depth, and diameter for the drilling of the blastholes and boreholes.
With the increasing of the strength of the rocks, the speed of the drilling decreases from 1-2 to 0.15-0.2 metres per minute. Since the end of the 1970-ies, there are increasing the quantities of the drilling by the hydraulic hammer drills, which have the greater mass (than the pneumatic hammer drills), the specific energy of the strike of 20-30 joules per 1 centimetre of the diameter of the borer, the torque of up to 250 joules, and are powered by the oil with the pressure of up to 30 megapascals. They install the hydraulic hammer drills onto the self-propelled drill carriages for the drilling of the blastholes with the diameter of more than 44 millimetres.
During the work of the hammer drill, there emerge the noises and vibrations, for the decreasing of which they use the protective devices (the spring-loaded vibration-protected handles, the gloves with the polyvinyl chloride plastic inserts, the mufflers and plugs, the acoustic earmuffs).
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