Drilling(redirected from Drilling and threading)
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the process of construction of a mining installation of cylindrical shape, such as a hole, blasthole, or mine shaft, by crushing the rock at the mine face. As a rule, drilling is carried on within the earth’s crust; less frequently, within artificial materials (concrete, asphalt, and others). In a number of cases drilling involves the shoring-up of hole walls (mainly for deep holes) by means of tubular casings, with the injection of cement suspension into the annular gap between the casings and the hole walls.
The field of application of drilling is varied: it includes searching and prospecting for minerals; the study of rock characteristics; the extraction of liquid, gaseous, and solid (by leaching and melting) minerals through working holes; the conducting of blasting operations; the excavation of solid minerals; the artificial securing of rock (by freezing, bituminizing, cementing, and other methods); the draining of flooded mineral deposits and swampy areas; the exposure of deposits; the laying of underground communications equipment; and the construction of pile foundations.
The yearly volume of drilling is enormous: in the USSR alone during 1967 the drilling of deep holes for petroleum and gas totaled approximately 12 million m, of which 5.8 million m was for prospecting holes; more than 20 million m of blast and seismic-prospecting holes and 10-12 million m of structure-exploratory holes were also drilled.
Classification of drilling methods. According to the manner in which the rock is crushed, drilling methods are divided into the mechanical method, in which the drilling tool acts directly on the rock to break it down; and the nonmechanical method, in which crushing occurs without direct contact between the rock and the source of the action upon it (thermal, explosive, and so on). Mechanical drilling methods are subdivided into rotary and percussion methods. (There are also rotary-percussion and percussion-rotary methods.)
In rotary drilling the rock is crushed by turning a tool that is pressed against the drill face. Depending on the hardness of the rock, the rock-breaking drilling tool utilized in rotary drilling may be of the cutting type, a diamond drilling tool, or a shot bit (which crushes rock by means of shot). The percussion methods of drilling are subdivided into percussion or percussion-rotary drilling (with hammer drills, including submersible types; also churn drilling and rod-boring), in which the tool rotates between strokes on the face; percussion-rotary drilling (with submersible pneumatic and hydraulic strikers; also hammer drilling with independent rotation, and so on), in which the strokes are delivered by a continuously rotating tool; and rotary-percussion drilling, in which a rock-breaking drilling tool under high axial pressure is in constant contact with the rock and crushes it owing to the rotary motion at the face and to periodically applied strokes. The rock at the drill face is crushed either over the entire area (continuous-face drilling) or in a ring-shaped space with the extraction of the core (core drilling). The products of the crushing operation are removed periodically by a slush pump or continuously by screw conveyers, by spiral rods, or by supplying gas, liquid, or drilling mud to the face.
Drilling is sometimes subdivided according to the type of drilling tool (auger, rod, diamond, or cutter drilling), the type of drilling machine (hammer, pneumatic-percussion, or turbine), or the method of driving the hole (directional, multiple, and so on). The technical facilities for drilling consist mainly of drilling machines (drilling rigs) and a rock-crushing tool. Among the nonmechanical drilling methods, wide use is made of thermal drilling for blastholes in quartz-bearing rocks, and efforts are being made to introduce explosive drilling.
Drilling was developed and became specialized in connection with three fundamental areas of technology: the deepest holes (several meters) are drilled for petroleum and gas; shallower holes (hundreds of meters), in prospecting and exploring for solid minerals; and holes and blastholes are drilled to depths from several to dozens of meters for the placement of explosives (chiefly in mining and construction).
Drilling petroleum and gas wells. The first holes in the world were drilled by hand (12-15 cm in diameter and up to 900 m deep) in China over 2,000 years ago to extract brines. The drilling tool (a bit and bamboo rods) was lowered into the hole on cables 1-4 cm thick, which were spun from rattan.
The first holes drilled in Russia date to the ninth century A.D. and were for the extraction of common salt (Staraia Russa). Salt mines were subsequently developed in Balakhna (12th century) and in Solikamsk (16th century). Rod-tool drilling has long been used in Russian salt mines. To avoid rust, the drill rods were made of wood; the walls of the holes were shored up with wooden pipes. In a 17th-century manuscript, “An Account of How to Set About Making a New Pipe in a New Place” (Izvestiia imp. arkheologicheskogo ob-va, 1868, vol. 6, sec. 1, issue 3, pp. 238-255), the methods of this period are described in detail. The first drilled well supported by pipes was drilled for water in 1126 in the province of Artois (France); since then deep wells that yield water under pressure have been called artesian wells.
The development of drilling methods and technology in Russia began in the 19th century because of the necessity of supplying large cities with drinking water. The Artesian Well Society, which drilled four wells to depths of 36-189 m, was formed in Odessa in 1831. During 1831 and 1832 wells were drilled in St. Petersburg (on the Vyborg side); in 1833 in Tsarskoe Selo, Simferopol’, and Kerch; in 1834 in Tambov, Kazan, and Evpatoriia; and in 1836 in Astrakhan’. In 1844 the first well for artesian water was driven in Kiev. The first artesian well in Moscow was drilled in 1876 on Iauzskii Boulevard to a depth of 458 m. The first hole drilled in the USA was for the extraction of brine near Charleston, West Virginia (1806).
Vigorous progress in drilling began with the development of petroleum extraction. The first petroleum well was drilled accidentally in the USA in 1826 near Burkesville, Kentucky, while prospecting for brine. The first well for petroleum was established in 1859 by the American E. L. Drake near Titusville, Pennsylvania. On Aug. 29, 1859, petroleum was found at a depth of 71 ft (about 20 m), thus initiating the petroleum industry in the USA. The first well for petroleum in Russia was drilled during 1864 near Anapa (Northern Caucasus).
Technical advances in drilling were made during the 19th century when the German engineer Oeynhausen (1834) proposed the use of so-called shears (a shifting pair of links in rod drilling). The idea of dropping a bit attached to rods led to the invention in France by Kind (1844) and Fabian (1849) of the freely falling tool (the “free-fall”). This was known as the German procedure. In 1846 the French engineer Fauvelle published a report on a new method of clearing drill holes with streams of water circulated from a pump on the surface through a hollow rod. The first successful test of wash-boring was made by Fauvelle in Perpignan (France).
In 1859, G. D. Romanovskii was the first to mechanize drilling operations, using a steam engine to drill a hole near Podol’sk. The first steam engines appeared in 1873 in the oil fields of Baku, and in ten years they had replaced horse power almost everywhere. In the first stage of drilling petroleum wells the percussion method (rod boring, cable drilling, and rapid percussion drilling with flushing of the face) was developed. Rotary drilling for petroleum using bladed bits and flushing with a drilling mud was adopted in the late 1880’s in New Orleans, Louisiana. Rotary wash-boring was first used in Russia at Groznyi to drive a petroleum well down to 345 m (1902). In Surakhany (Baku), on the grounds of the Kokorev factory, a well was started in 1901 for extracting gas. A year later, gas that was utilized to heat the factory was obtained from a depth of 207 m. In 1901 at the Baku petroleum fields the first electric motors made an appearance as a substitute for steam engines in drilling. A hole with a solid face was driven in 1907 using rotary continuous-face drilling and flushing with drilling mud.
The use of an automatic machine for controlling the tool feed in rotary drilling was first proposed in 1924 by Heald (USA). During the early 1920’s a method of directional rotary drilling with small-diameter drill bits, in which the bore hole was subsequently enlarged, was developed in the USA.
As early as the 1870’s there were proposals to create face motors—that is, to locate the motor directly above the drill bit at the bottom of the drill hole. The creation of a face motor was the concern of outstanding specialists in many countries who based designs on the power obtained from a hydraulic flow and later from electrical energy. In 1873 the American engineer H. G. Cross patented a tool with a single-stage hydraulic turbine for drilling holes. In 1883, G. Westinghouse (USA) designed a turbine face motor. These inventions were not put into practice, and the problem was considered to be insoluble. In 1890 the Baku engineer K. G. Simchenko patented a rotary hydraulic face motor. In the early 1900’s the Polish engineer Wolski designed a rapid percussion hydraulic face motor (the so-called Wolski ram), which was used in the industry and became the prototype of modern hydraulic hammers.
The world’s first practical turbodrill was patented by M. A. Kapeliushnikov, S. M. Volokh, and N. A. Kornev (1922) and was used two years later for drilling in Surakhany. This turbodrill was designed on the basis of a single-stage turbine and a multistage planetary reduction gear. Turbodrills of this design were used in drilling oil wells until 1934. From 1935 to 1939, P. P. Shumilov, R. A. Ioannesian, E. I. Tagiev, and M. T. Gusman developed and patented a more advanced design for a multistage turbodrill without reduction gears; as a result, the turbine method of drilling became the main method in the USSR. Turbine drilling is being improved by the development of sectional turbodrills having a lower speed of rotation and higher torque.
A cable electrical drill was patented in 1899 in Russia. Industrial tests of an electrical drill (with an armature for sensing the torque moment) that was lowered into the drill hole on a cable were made in the USA in the 1930’s. In 1936 the USSR’s first design for an electrical drill with a reduction gear was developed by Kvitner and N. V. Aleksandrov, and in 1938 an electrical drill in which the bit was rotated by a submersible electric motor was created by A. P. Ostrovskii and N. V. Aleksandrov. The first well was drilled with an electrical drill in Baku in 1940.
In 1951-52, according to a proposal made by A. A. Minin, A. A. Pogarskii, and K. A. Chefranov, an electrical drill with sign-variable rotation to damp the torque moment was used for the first time in drilling an oil well; the drill was lowered on a flexible electric cable. Electrical-drill design in the USSR was substantially improved in the late 1960’s—reliability was increased and the current conductor was improved.
Directional drilling dates from 1894, when S. G. Voislav drove a water well by this means near Briansk. The successful sinking of wells in the Bay of Il’ich (Baku) according to the proposal of R. A. Ioannesian, P. P. Shumilov, E. I. Tagiev, and M. T. Gusman, which used turbine-controlled directional drilling, marked the introduction of directional turbine drilling, which has become the principal method of directional drilling in the USSR and has become commonplace abroad. With this method, a group of up to 20 holes can be drilled from one base (multiple drilling) on broken topography and in the case of marine deposits. A fundamental theory for continuous directional controlled turbine drilling with a stationary string of drill pipes was developed in the USSR from 1938 to 1941. This method became the principal one for drilling directional holes both in the USSR and abroad.
In 1941, N. S. Timofeev proposed the use of so-called multiface drilling.
In 1897 the first offshore drilling was carried out in the Pacific Ocean off Summerland Island (California, USA). The first marine hole was drilled by the rotary method during 1924 and 1925 in the USSR near the Bay of Il’ich on an artificial islet; it produced petroleum at a depth of 461 m. In 1934, on Artem Island in the Caspian Sea, N. S. Timofeev carried out multiple drilling for several holes from a common platform, and in 1935 he built the first metal platform for offshore drilling. Since the 1950’s offshore drilling has been used to extract petroleum and gas from the ocean floor. Platforms that float drilling equipment by means of submersible pontoons and special drilling ships with methods for dynamic stabilization of the drilling equipment when operating at great depths have been developed.
The principal drilling method in the USSR (1970) for petroleum and gas uses turbodrills (76 percent of the footage of holes drilled), 1.5 percent of the footage is accomplished with electrical drills, and the rest by means of rotary drilling. In the USA rotary drilling is the most common; toward the end of the 1960’s turbodrills began to be used for controlled directional holes. In the countries of Western Europe turbodrills are used for directional drilling and for drilling vertical holes using diamond bits. The speed and depth of drilling for petroleum and gas increased substantially during the 1960’s. Thus, for example, in Tataria holes were drilled with a bit 214 mm in diameter to a depth of 1,800 m in an average of 12-14 days; the record in this area is 8-9 days. Between 1963 and 1969 the average depth of operating petroleum and gas wells in the USSR increased from 1,627 to 1,710 m. The deepest holes in the world, 7-8 km, were drilled during the 1960’s in the USA. In the USSR near Baku a hole was drilled to a depth of 6.7 km, and in the Caspian lowlands (near Aralsor), to a depth of 6.8 km. These holes were sunk to explore for petroleum and gas. Ultradeep drilling operations to study the crust and upper mantle of the earth are being carried on in accord with the international program entitled “The Upper Mantle of the Earth.” According to this program, there are plans to drill a number of holes as deep as 15 km in five regions in the USSR. The first such hole was started on the Baltic Shield in 1970. This hole is being sunk by the turbine drilling method.
The main trend in improvements in drilling for petroleum and gas in the USSR has been the creation of turbodrill designs that increase the rate of sinking for a bit run (the total operating time of a bit in the hole until it is raised to the surface). In 1970 turbodrills without reducing gears were designed, which made it possible to achieve optimum drilling conditions using rolling cutter bits in the most efficient speed range (150-400 rpm) and to utilize a bit with a pressure drop at the nozzles of up to 10 meganewtons per sq m (MN/m2)—100 atmospheres—instead of 1-1.5 MN/m2 (10-15 atmospheres). Turbodrills with a high rate of rotation (800-1,000 rpm) were designed for drilling with diamond bits, which produced a severalfold increase in the working rate and mechanical drilling speed per bit run. New designs were developed for the bottom of the drill string so that it is possible to drill under complex geological conditions with minimal distortion of the shaft. Work is being done on the chemical treatment of drilling muds in order to facilitate the drilling process and increase its safety. Turbines have been designed with a sloping pressure line, making it possible to obtain information regarding the operating conditions of the turbodrill at the bottom of the hole and to automate the drilling process.
Prospecting and exploring for solid minerals. The development of exploratory drilling is associated with the invention by the Swiss clockmaker G. Leschot (1862) of the diamond drill, which consisted of a hollow steel cylinder studded with diamonds and attached to a hollow metal rod (through which water was passed for flushing the bottom). The first efficient drilling equipment with a diamond tool was designed by the French engineer Perret and attracted attention at the Paris World’s Fair (1867), which was the beginning of the spread of diamond drilling in Europe and America. In 1850 a number of exploratory holes were sunk for coal in Russia.
In 1871 and in 1872, near Bakhmut and Slaviansk, the first exploratory holes in Russia for rock salt were drilled to depths of 90 and 120 m. The improvement of exploratory drilling in Russia at the end of the 19th century is associated with the name of Voislav, who in 1885 invented and in 1897 obtained a patent for a drill for driving large-diameter holes by hand. The Voislav drill had an expander that could increase the diameter of the holes, which reached a depth of 22 m. In 1898, Voislav, together with L. Kulesh, obtained a patent for an original machine for diamond drilling and developed a new method of inserting diamonds in a crown bit so that the use of smaller diamonds became possible. In America in 1899 the engineer Davis proposed shot drilling. During World War I the use of hard alloys (called wolomite), which had been suggested by the German engineer Loman, was initiated for drilling. Later these alloys were used for drilling exploratory holes in the area of the Kursk Magnetic Anomaly (1923).
Radical changes in drilling technology in Russia occurred after the Great October Revolution. Beginning in 1923, drilling with hard alloys, as well as shot drilling (1924-25), were adopted in Russia; the production of domestic hard alloys was begun in 1929. In 1927 shot was successfully used by V. M. Kreiter and B. I. Vozdvizhenskii for core drilling. During 1925 and 1926 production of churn drills of the Keystone type (and later of the Empire type) for gold prospecting was begun at the Sormovskii factory. Several years later, N. I. Kulichikhin developed the first domestic churn drills (UA-75-150). In 1928 and 1929 the production of rotary core drilling rigs was set up at the Izhora factory (Leningrad), the Vorovskii Plant (Sverdlovsk), and others. At that time the KA-300 and KA-500 rigs were mainly used for core drilling down to 500 m. During the postwar years (beginning with 1947) the geological prospecting service was completely re-equipped with technological apparatus: drill pipes, casings, and core barrels were improved; new rigs with a lever-differential feed (ZIV-75 and ZIV-150) were created; new multispeed rig designs with hydraulic feeds (ZIF-300, ZIF-650, ZIF-1200, VITR-2000, and others), which could drill holes to depths of 300-2,000 m, were developed; a series of self-propelled drilling rigs has been created; and means for automating and mechanizing labor-consuming processes, along with new designs for the rock-crushing tool, have been developed.
In 1935 the Soviet engineer V. N. Komarov proposed a percussion-rotary drilling rig, for which a theoretical basis was subsequently developed by E. F. Epshtein. In 1939 drilling by means of submersible pneumatic hammers was developed, and since 1940 rotary drilling, in which the rock is conveyed out of the holes by a screw (auger drilling), has been adopted. This is used on a large scale for geophysical work, engineering-geological prospecting, drilling for water, and other operations in soft rock. In the USSR the technology of pumpless drilling, in which the entire core is discharged in unstable rock, has been developed, and shot-drilling technology has been radically improved (by S. A. Volkov). The diamond rock-crushing tool has been used more extensively since the discovery of diamond fields in Yakutia, and since 1962 synthetic diamonds have become commonplace. The Soviet scientists F. A. Shamshev, I. A. Utkin, B. I. Vozdvizhenskii, and S. A. Volkov have played a large role in the improvement of diamond drilling technology.
The average monthly drilling rate for exploratory holes in the Donbas was 265 m (1956); in the Krivoi Rog Basin, 360 m (1956), and in the Kursk Magnetic Anomaly, 600 m (1965). In exploring steep ore-bearing bodies where it is necessary to have several holes in order to traverse the body at different levels, controlled directional multiface drilling is used in order to shorten the holes; this is achieved by diverting devices that are set in the hole at various depths.
Prospecting drilling is carried out chiefly by means of rotary equipment, which accounts for 80 percent (1970) of the footage drilled (50 percent of the drilling is with a hard alloy tool, 20 percent with a diamond tool, and 10 percent with shot); percussion-rotary, auger, vibration, and other types are used to a more limited extent.
Work in the field of prospecting drilling has been directed toward the preservation of cores taken from great depths and the development of apparatus and reliable methods for rock sampling. The improvement of the techniques and technology of prospecting drilling for solid minerals has been directed toward the replacement of shot drilling by diamond drilling, the introduction of hydraulic percussion drilling and coreless drilling using side-drilling coring tools, the further improvement of the technical facilities and technology of drilling, the development of new methods of crushing rock in drilling, and the automation of all production processes.
Drilling of blastholés. Machine drilling of blastholes instead of manual drilling, which was used until the early 1800’s for crushing hard rocks with explosives, began to be used during the late 1700’s when the first machines for drilling horizontal blastholes were invented. In 1683 the mechanic G. Gutman proposed machine drilling. In 1803 the Austrian engineer Hainsching, and in 1813 the English mechanical engineer Trevithick, made improvements on the drilling machines then being manufactured. In 1849, Couch (USA) obtained one of the first patents on a steam drilling machine. In 1852, Colladon (Switzerland) proposed a drilling machine that operated on compressed air. When driving the Mont Cenis tunnel in 1861, Sommeiller first used piston drills for blastholes, thus permitting a sharp reduction in the time required for the construction of the tunnel. During the late 1800’s hammer drills appeared and rapidly supplanted the less productive piston variety. High-frequency and rotary-percussion drilling machines (1950’s), adjustment and feed accessories (pneumatic supports and manipulators; automatic feeders), and mobile drilling rigs, which provided maximum mechanization of the drill operator’s work, were subsequently developed. The products of the crushing process in drilling were removed by flushing. Light- and heavy-duty electric and pneumatic drills and high-quality drill tools that allowed the driving of blastholes into rocks of medium hardness were created. In 1965 in the Kuznetsk Basin and in 1968 in Kirghizia, electrically and hydraulically driven drilling assemblies with electrohydraulic gear were used for driving blast-holes by the rotary and rotary-percussion methods.
Around the turn of the 20th century, specialists tried to devise an electric hammer drill. In 1879 the German inventor W. Siemens made an unsuccessful attempt to use electrical current to operate a blast-hole drilling machine for blasting operations. In 1885 the American inventor G. Westinghouse repeated this attempt.
The first holes drilled with heavy drilling hammers were used instead of bore holes for breaking out ore in the early 1930’s in the underground mines of the Apatit combine at Krivoi Rog. The construction of machines for underground drilling began in this period. In the mid-1930’s a method of rod boring of blast holes was introduced, which made possible a technical revolution in working thick ore deposits. In 1935, A. A. Miniailo designed a rotary drilling machine with cutting tools up to 150 mm in diameter for drilling in soft rock. During the late 1930’s multiple hammer drilling in deep holes was introduced in the Krivoi Rod mines. In 1938, A. K. Sidorenko proposed drilling with submersible hammers inside the hole. In 1949 and 1950 tests of drilling machines with submersible pneumatic strikers (the pneumatic hammer is rotated from the surface by means of drill rods) were made in underground mines of the USSR. In 1954 the Novosibirsk Mining Institute and the Kuznetsk Metallurgical Combine created a production model of the BA-100 drilling machine, the first in which an air-water mixture served as the actuating medium (energy system). The spent mixture provides simple and reliable dust suppression during drilling. The universal introduction of the high-productivity BA-100 machines in mines has made it possible to extend a progressive system of developing deposits by breaking out the ore with deep blastholes. This machine was the starting point for the creation in the USSR of a series of drilling machines (including the semiautomatic NKR-100 machine in 1959) for the pneumatic percussion drilling of holes 85-100 mm in diameter to a depth of 50 m, which during the 1950’s and 1960’s accounted for over 50 percent of the volume of the ore broken out. Since the 1960’s this method has been introduced into practice for both prospecting and working deep holes. Machines for drilling holes by means of rolling cutter bits—one of which (type BSh-145) is manufactured serially—were developed and put into use in the underground Altai mines in the USSR beginning in 1950. Rotary-percussion drilling machines mounted on mobile drilling rigs, as well as drilling machines with high-powered drill hammers and independent tool rotation, were developed during the 1960’s for underground drilling of holes 60-70 mm in diameter.
The drilling of holes for blasting operations in open-cut mines was first used in Russia for iron-ore enterprises in the Urals in 1908. Churn drilling rigs for blastholes in open-cut mines were used for the first time in the USA during the early 1900’s. In the USSR the use of this method began during the 1930’s, and until the 1960’s it has been the principal method for holes from 150 to 300 mm in diameter through rocks of above-average hardness. Churn drilling rigs for open-cut mines were produced by the Sverdlovsk Metallist factory in 1932. The rotary drilling of holes by means of cutting tools with removal of the fines by means of screw conveyers has been utilized in the USSR since 1939. The first rotary drilling machine (with a screw conveyer and a caterpillar drive) was produced in the Urals for the Bogoslovskii open-cut mine) in 1943. During 1956 and 1957 work began on the rolling cutter bit drilling of blastholes in open-cut mines. A combination percussion-rolling cutter bit drilling tool that could be used on rotary drilling machines with pneumatic scavenging of the holes was proposed in 1958. In 1959 production was started on flame (thermal) drilling machines (types SBO-1 and SBO-2) for hard quartz-bearing rocks. The rocks in this case are crushed through the rapid heating of the surface at the face by jets of gas that emerge from burners at a temperature of 2000° C and a velocity of about 2,000 m/sec. During the 1960’s a standard series of rolling cutter machines (types 2SBSh-200, SBSh-250, and SBSh-320) was developed for drilling blastholes 200-300 mm in diameter down to 30 m. The productivity of the machines is 20-70 m per shift. Efforts to create combined thermomechanical methods of crushing are promising.
The drilling of blastholes in open-cut mines in the USSR (1970) is accomplished mainly by the rolling cutter method (about 70 percent of the hole footage); auger drilling is common (about 20 percent), and 10 percent of the hole footage is drilled by other methods (pneumatic-hammer, thermal, and churn drilling). The drilling speed has increased considerably: the production per shift of a rolling cutter machine when driving holes 250 mm in diameter through hard rock (limestone, dolomite, and such) is 40-60 m. In working underground coal deposits the most common drilling methods use hammer drills and electric drills, and in ore deposits, hammer drills, submersible pneumatic strikers, and rolling cutter rigs are used.
The development of the mining industry will require a two-to four-fold productivity increase. The improvement of mechanical drilling methods and the search for new methods are necessary to reach this goal. Drilling machines can be improved by increasing the load parameters on the tool and by mechanizing and automating auxiliary operations. The development of vibration drills is promising. Explosive drilling, which consists in the continuous working of the face of a hole with small explosive charges injected into the flow of the flushing agent (air or liquid) either as capsules (capsule or cartridge explosive drilling) or as a continuous jet (jet explosive drilling), has been developed. The capsule charges have a streamlined shape and are safe to handle, since the combination of nonexplosive liquid components and the production of the explosive substance occur directly at the face. Solid explosives require high-velocity shocks (not less than 80 m/sec) in order to explode. In jet explosive drilling, an explosive mixture in the form of a flat liquid charge is produced directly at the face from a fuel and an oxidizer; it is triggered by a eutectic mixture of potassium and sodium, which is injected at a regular rate. The productivity of drilling holes can be increased by a factor of 2-5 with explosive drilling, especially in hard rocks.
Work is being done on the design of apparatus that produces a pulsed jet that is periodically shot from a nozzle against the face of the hole in order to perform so-called hydraulic pulse drilling, as well as on electrical pulse machines, in which the rock is broken down by means of a powerful electric discharge.
The mechanized drilling of vertical mine workings with large cross sections (over 3.5 m in diameter)—mine shafts—is of considerable interest.
Advances in the development of effective drilling facilities and methods are based on studies of the physicomechanical properties of the rocks to be broken down and the crushing mechanism in various drilling methods and conditions. In the USSR fundamental work is proceeding on the study and determination of the basic physical characteristics of rocks in order to evaluate the effectiveness of the major rock-crushing processes used for drilling.
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R. A. IOANNESIAN, N. I. KULICHIKHIN, and B. N. KUTUZOV
(1) In metalworking, the process of making through holes and blind holes in solid material. Drilling is done on drilling machines, lathes, turret lathes, boring machines, and multiple-spindle drilling machines; power-driven hand drills are also used. Drilling produces holes in the fourth and fifth precision classes. Higher grade holes are obtained after subsequent boring, countersinking, or reaming.
In drilling, the principal motion is rotary, and the feed motion is linear. On drilling machines the drill is both rotated and fed; on other machines the drill is fed into rotating work.
The cutting process in drilling is determined by the cutting speed v and the feed rate s. The theoretical cutting speed is the peripheral speed of the lip farthest removed from the drill axis: v = πDn/1,000 m per min, where D is the diameter of the drill across the margins in millimeters and n is the drill rotation speed in rpm. The permissible cutting speed during drilling v = CvDxv/Tmsyv m per min, where Cv is a coefficient dependent on the material being worked, the configuration of the cutting edge, the material from which the drill is made, and other operating factors (such as cooling and depth of drilling), T is the life of the drill (the period of operation before normal loss of sharpness occurs) in minutes, and m is an index of relative drill life. The feed, that is, the linear displacement of the drilling during each of its rotations in mm per revolution, is determined according to the formula s = CsD0.6 mm per revolution, where Cs is a coefficient dependent on the mechanical properties of the material being worked and engineering factors.
Drilling efficiency is characterized by the machining time per piece: Tp = L/ns min, where L is the length of travel of the drill in mm in the direction of feed.
D. L. IUDIN
(2) In woodworking, the process of making through holes in solid wood or wood materials by means of a drill. In Soviet usage such processes as the making of grooves and mortises are classified under the heading of drilling. The precision of the hole diameters is of the second or third class; hole depths are of third or fourth class. Drill speeds range from 3,000 to 12,000 rpm, with feed rates of 0.1–0.5 mm/revolution for hard materials and 0.7–2.2 mm/revolution for soft materials.
V. S. RYBALKO