Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
BORING
Online EncyclopediaEncyclopedia Home :: BLA-BOS
del.icio.us it!
|
BORING . The operations of deep boring are resorted to for ascertaining the nature, thickness and extent of the various 252 See also:geological formations underlying the See also:surface of the See also:earth. Among the purposes for which boring is specifically employed are: (I) prospecting or searching for See also:mineral deposits; (2) sinking See also:petroleum, natural See also:gas, artesian or See also:salt See also:wells; (3) determining the See also:depth below the surface of See also:bed-See also:rock or other See also:firm substratum, together with the See also:character of the overlying materials, preparatory to See also:mining or See also:civil See also:engineering operations; (4) carrying on geological or other scientific explorations. Prospecting by boring is practised most successfully in the See also:case of mineral deposits of large See also:area, which are nearly See also:horizontal, or at least not highly inclined; e.g. deposits of See also:coal, See also:iron, See also:lead and salt. Wide, See also:flat beds of such minerals may be pierced at any desired number of points. The depth at which each hole enters the See also:deposit and the thickness of the mineral itself are readily ascertained, so that a See also:map may be constructed with some degree of accuracy. Samples of the mineral are also secured, furnishing data as to the value of the deposit. While boring is sometimes adopted for prospecting irregular and steeply inclined mineral deposits of small area, the results are obviously less trustworthy than under the conditions named above, and may be actually misleading unless a large number of holes are bored. Incident-ally, See also:bore-holes See also:supply See also:information as to the character and depth of the valueless depositions of earth or rock overlying the mineral deposit. Such data assist in deciding upon the appropriate method for, and in estimating the cost of, sinking shafts or See also:driving tunnels for the development and exploitation of the deposit. In sinking petroleum wells, boring serves not only for discovering the oil-bearing strata but also for extracting the oil. This See also:industry has become of See also:great importance in many parts of the See also:United States, in See also:southern See also:Russia and elsewhere. Rock salt deposits are sometimes worked through bore-holes, by introducing See also:water and pumping out the See also:solution of brine for further treatment. The sinking of artesian wells is another application of boring. They are often hundreds, and sometimes thousands, of feet in depth. A well in St See also: Earth augers comprise See also:spiral and pod augers. The See also:ordinary spiral See also:auger resembles the See also:wood auger commonly used by carpenters. It is attached to the See also:rod or See also:stem by a socket See also:joint, successive sections of rod being added as the hole is deepened. The auger is rotated by means of horizontal levers, clamped to the rod—by See also:hand for holes of small See also:diameter (2 to 6 in.), the larger sizes (8 to 16 in.) by See also:horse See also:power. Clayey, cohesive soils, containing few stones, are readily bored; stony ground with difficulty. The operation of the auger is intermittent. After a few revolutions it is raised and emptied, the See also:soil clinging between the spirals. Depths to 50 or 6o ft. are usually bored by hand ; deeper holes by horse power. For sandy, non-cohesive soils, the auger may be encircled by a See also:close-fitting See also:sheet-iron See also:cylinder to prevent the soil from falling out.
Pod augers generally vary in diameter from 8 to 20 in. A See also:common See also:form (fig. I) consists of two curved iron plates, one attached to the rod rigidly, the other by See also:hinge and See also: By being turned through a few revolutions the pod is filled, and is then raised and emptied. For boring in sandy soils, the open sides are closed by hinged plates. Fig. 2 shows another type of pod auger. For holes of large diameter earth augers are handled with the aid of a See also:light See also:derrick. 2. Drive pipes are widely used, both for testing the depth and character of soft material overlying solid rock and as a necessary preliminary to rock boring, when some thickness of surface soil must first be passed through. In its simplest form the drive See also:pipe consists of one or more lengths of wrought iron pipe, open at both ends and from z in. to 6 in. diameter. When of small See also:size the pipe is driven by a heavy See also:hammer; for deep and large holes, a light See also:pile-See also:driver becomes necessary. The See also:lower end of the pipe is provided with an See also:annular See also:steel See also:shoe; the upper end has a drivehead for receiving the blows of the hammer. Successive lengths are screwed on as required. For shallow holes the pipe is cleaned out by a " bailer " or " See also:sand-See also:pump "—a cylinder 4 to 6 ft. long, with a See also:valve in the lower end. It is lowered at intervals, filled by being dashed up and down, and then raised and emptied. If, after reaching some depth, the See also:external frictional resistance prevents the pipe from sinking farther, another pipe of small diameter may be inserted and the driving continued. Drive pipes are often sunk by applying weights at the surface and slowly rotating by a See also:lever. Two pipes are then used, one inside the other. Water is pumped down the inner pipe, thus loosening the soil, raising the debris and in- creasing the See also:speed of driving. The " driven well " for water supply is an See also:adaptation of the drive pipe and put down in the same way. 3. Drill and Rods.—This method has long been used in See also:Europe and else- where for deep boring. In the United States it is rarely employed for depths greater than 200 or 300 ft. The usual form of cutting See also:tool or drill is shown in fig. 3. The iron rods are from I to FIG. 3. 2 in. square, in long lengths with Drill See also:Bit. See also:screw See also:joints (fig. 4). Wooden rods are occasionally used. For shallow holes (50 to 75 ft.) the See also:work is done by hand, one or two See also:cross-bars being clamped to the rod. The men alternately raise and drop the drill, meanwhile slowly walking around and around to rotate the bit and so keep the hole true. The cuttings are cleaned out by a bailer, as for drive pipes. In boring by hand, the See also:practical limit of depth is soon reached, on See also:account of the increasing See also:weight of the rods. For going deeper a " See also:spring-See also:pole " may be used. This is a tapering pole, say 30 ft. long and 5 or 6 in. diameter at the small end. It rests in an inclined position on a fulcrum set about to ft. from the See also:butt, the latter being firmly fixed. The rods are suspended from the end of the pole, which ex-tends at a height of several feet over the mouth of the hole. With the aid of the spring of the pole the strokes are produced by a slight effort on the See also:part of the driller. See also:Average speeds of 6 to lo ft. per lo See also:hours are easily made, to depths of 200 to 250 ft. For deep boring the rod system requires a more elaborate plant. The rods are suspended from a heavy " walking See also:beam " or lever, usually oscillated by a steam See also:engine. By means of a screw-feed See also:device, the rods, which are rotated slightly after every stroke, are gradually fed down as the hole is deepened, length after length being added. A tall derrick carries the sheaves and ropes by which the rods and tools are manipulated. The drill bit cannot be attached rigidly to the rods as in shallow boring, because the momentum of the heavy moving parts, transmitted directly to the bit as the See also:blow is struck, would cause excessive vibration and breakage. It becomes neces- sary, FIG. 5. therefore, to introduce a sliding-See also:link joint be- tween the rods and bit. One form of link is shown sliding Link. in fig. 5. On striking its blow, the bit comes to See also:rest, while the rods continue to descend to the end of the stroke, the upper member of the link sliding down upon the lower. Then, on the up stroke the lower link, with the bit, is raised for delivering another blow. For large holes the striking weight is, say, 800 to moo lb, length of stroke 21 to 5 ft., and speed from 20 to 30 strokes per See also:minute. Pod Auger. Rod Joint. By using the sliding link the cross-See also:section and weight of the rods may be greatly reduced, the only See also:strain being that of tension. To deliver a See also:sharp, effective blow, however, the rods must drop with a See also:quick stroke, which brings a heavy strain upon the operating machinery. For overcoming this difficulty, various " See also:free-falling tools " have been devised. By these the bit is allowed to fall by gravity; the rod follows on its measured down stroke, and picks up the bit. Free-falling tools are of two classes: (I) those by which the bit is released automatically; (2) those operated by a sudden twist imparted to the rod by the drillman. One of the best known of the first class is the See also:Kind free-fall (fig. 6). The shank of the bit is gripped and released by the jaws J,J, worked through a toggle joint by movements of the disk D. 
When the rod begins its down-See also: A heavy See also:bar (auger stem) is generally inserted between the jars and bit, for increasing the force of the blow. The weight of another bar above the jars (sinker-bar) keeps the rope taut. The length of stroke and feed are regulated by the " See also:temper-screw " (fig. 7), a feed device resembling that used for rod-boring. Clamped to it is the drill rope, which is let out at intervals, as the hole is deepened. The bits usually range from 3 to 8 in. diameter, the speed of boring being generally between 20 and 40 ft. per 24 hours, according to the kind of rock. A great variety of See also:special " fishing tools " are made, for use in case of breakage of parts in the hole or other See also:accident. 5. See also:Diamond Drill.—The methods described above are capable of boring holes vertically down-ward only. By the diamond drill, holes can be bored in any direction, from vertically downward to vertically upward. It has the further ad-vantage of making an annular hole from which is obtained a core, furnishing a practically complete cross-section of the strata penetrated; the thickness and character of each stratum are shown, together with its depth below the surface. Thus, the diamond drill is peculiarly well adapted for prospecting mineral deposits from which samples are desired. The first practical application of diamonds for drilling in rock was made in 1863 by See also:Professor See also:Rudolph Leschot, a civil engineer of See also:Paris. The apparatus consists essentially of a See also:line of hollow rods, coupled by screw joints, an annular steel bit or See also:crown, set with diamonds, being attached to the lower end. By means of a small engine on the surface the rods are rapidly rotated and fed down automatically as the hole is deepened. The speed of rotation is from 300 to 800 revolut;ons per minute, depending on the character of the rock and diameter of the bit. While boring a stream of water is forced down the hollow rods by a pump, passing back to the surface through the annular space between the rods and the walls of the drill hole. The cuttings are thus carried to the surface, leaving the bottom of the hole clean and unobstructed. For recovering the core and inspecting the bit and diamonds, the rods are raised at every 3 to 8 ft. of depth. This is done by a small See also:drum and rope, operated by the driving engine. Diamond drills of See also:standard designs (fig. 8) bore holes from 1194 to 24 in. diameter, yielding cores of t to I; in. diameter, and are capable of reaching depths of a few See also:hundred to 4000 ft. or more. They re-See also:quire from 8 to 30 See also:boiler horse-power. Large See also:machines will bore shallower holes up to 6, 9 or even 12 in. diameter. For operating in underground workings of mines, small and compact machines are sometimes mounted on columns (fig. 9). They bore t 4 to Ike in. holes to depths of 300 to 400 ft., cores being to I in. diameter. Hand-power drills are also built. In the See also:South See also:African goldfields several diamond drill holes from 4500 to 5200 ft. deep have been successfully bored. Rates of advance for core-drilling to moderate depths range usually from 2 to 3 ft. per See also:hour, including ordinary delays,though in favourable rock much higher speeds are often attained. In deep holes the speeds diminish, because of time consumed in raising and lowering the rods. If no core is desired a " solid bit " is used. The drilling then proceeds faster, as it is only necessary to raise the rods occasionally, for examining the See also:condition of the bit. The driving engine has two inclined cylin- FIG. Io. ders, coupled to a See also:crank-shaft, by which, Diamond Drill Bit. through gearing, the drill-rod is rotated. The rods are wrought iron or steel tubes, in 5 to 10 ft. lengths. For producing the feed two devices are employed, the See also:differential screw and See also:hydraulic cylinder. For the differential feed (fig. 9) the engine has a hollow See also:left-hand threaded screw-shaft, to which the rods are coupled. This shaft is driven by a spline and See also:bevel gearing and is supported by a threaded feed-See also:nut, carried in the lower bearing. Geared to the screw-shaft is a light See also:counter-shaft. By properly proportioning the number of See also:teeth in the system of See also:gear-wheels, the feed-nut is caused to revolve a little faster than the screw-shaft, so that the drill-rod is fed downward a small fraction of an See also:inch for each revolution. To vary the See also:rate of feed, as suitable for different rocks, three pairs of gears with different ratios of teeth are provided. The screw-shaft and gearing are carried by a swivel-See also:head, which can be rotated in a See also:vertical See also:plane, for boring holes at an See also:angle. The hydraulic feed is an improvement on the above, in that the rate of feed is See also:independent of the rotative speed of the rods and can be adjusted with the utmost nicety. There are either one or two feed cylinders, supplied with water from the pump. The rod, while rotating freely, is supported by the feed cylinder See also:piston and caused to move slowly downward by allowing the water to pass from the lower to the upper part of the cylinder. A valve regulates the passage of the water and hence the rate of feed. The bit (fig. to and fig. 11, B) is of soft FIG. II. steel, set with six to eight or more diamonds, CoreLifter and See also:Barrel. according to its diameter. The diamonds, usually from IZ to 21 carats in size, are carefully set in the bit, projecting but slightly from its surface. Two kinds of diamonds are used, ' carbons " and " borts." The carbons are opaque, dark Temper Screw. in See also:colour, tougher than the brilliant, and have no cleavage planes. They are therefore suitable for drilling in hard rock. Borts are rough, imperfect brilliants, and are best used for the softer rocks. As the bit wears, the stones must be reset from time to time. The See also:wear of carbons in a well-set bit is small, though extremely variable. Above the bit are the core-lifter and core-barrel. The core-lifter (fig. A) is a device for gripping and breaking off the core and raising it to the surface. The barrel, 3 to io ft. long, fits closely in the hole and is often spirally grooved for the passage of the water and debris. It serves partly as a See also:guide, tending to keep the hole straight, partly for holding and protecting the core. Diamond drills do not work satisfactorily in broken, fissured rock, as the carbons are liable to be injured, loosened or torn from their settings. In these circumstances, and for soft rocks, the diamond bit may be replaced by a steel toothed bit. Another apparatus for core-drilling is the See also:Davis Calyx drill. For hard rock it has an annular bit, accompanied by a quantity of chilled steel shot; for soft rock, a toothed bit is used. Diamond drill holes are rarely straight, and usually deviate considerably from the direction in which they are started. Very deep holes have been found to vary as much as 45° and even 6o° from their true direction. This is due to the fact that the rods do not See also:fit closely in the hole and therefore See also:bend. It is also likely to occur in drilling through inclined strata, specially when of different degrees of hardness. By using a long and closely fitting core-barrel the liability to deviation is reduced, but cannot be wholly prevented. Holes which are nearly horizontal always deflect upward, because the sag of the rods tilts up See also:tire bit. Diamond drill holes should there-fore always be surveyed. This is done by lowering into the hole See also:instruments for observing at a number of successive points the direction and degree of deviation.' If accurately surveyed a crooked hole may be quite as useful as a straight one. Additional information and CommentsThere are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML. Site content, images, and layout Copyright © 2006 - Net Industries, worldwide. |
|
|
[back] BORIC ACID |
[next] BORIS FEDOROVICH GODUNOV |