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a floating ore-concentration installation with equipment designed for the working of submerged mineral deposits and for the extraction of valuable components with a
|Table 1. Main technical features of Soviet-produced multiple-scoop dredges (1970)|
|Irkutsk Heavy Machinery Plant||Perm’ Machine-building Plant|
|Scoop capacity (liters)...............||80||150||250||600||380||400|
|Underwater excavation depth (m)...............||6||9||12||50||30||17|
|Average productivity (m3/hr)...............||100||180||320||500||400||450|
|Rated power of electric motors (kW)...............||392||800||1,082||7,300||2,110||2,494|
|Structural weight (tons)...............||386||912||1,373||10,331||3,252||2,594|
|Displacement under operating conditiosn (tons)...............||410||990||1,460||10,854||3,480||2,865|
specific gravity exceeding 3 (gold, platinum, tin, diamonds, and so on). Dredges are used mainly in working alluvial and eluvial-deluvial placers, as well as offshore and coastal placers, with the exception of boulder varieties, which are strongly cemented by rocks and viscous clays.
Dredges are divided into two categories, continental and seagoing. The former (for working placers on land), as a rule, are mounted on a flat-bottomed pontoon (ship), which ensures normal flotation and operation on a closed body of water, in accordance with the requirements of the River Register of the RSFSR. Seagoing dredges are designed for working placer and sedimentary deposits lying in offshore waters and in deep-water areas of large lakes, seas, and oceans. These dredges generally are mounted on self-propelled or towed keel ships (less frequently flat-bottomed vessels), ensuring normal flotation and operation in the open sea under storm conditions, in accordance with the requirements of the Marine Register. Dredges are equipped with washing and concentrating equipment that is mounted on the ship, or they operate on an “extraction-concentration” scheme, sending ore to shore-based or floating concentration installations for processing.
Seagoing and continental dredges are distinguished according to their type of power (electric, diesel-electric, diesel, and steam), their means of propulsion (cable-pile or cable-anchor systems), their maximum possible depth of working or extraction (shallow—to 6 m, medium—to 18 m, deep—to 50 m, and extradeep—over 50 m), and the operating principle of the extraction apparatus. This apparatus may be of the scoop type (single-scoop, with a power-shovel scoop, a grab bucket, or a bucket dragline; and multiple-scoop, with an interrupted or continuous scoop chain). Scoop capacities are classified as low (to 100 liters), medium (to 250 liters), and high (over 250 liters). Pneumatic-suction and hydraulic extraction equipment consists of suction dredges with or without mechanical or hydraulic scarifiers and jet, airlift, and suction dredges with deep-well pumps.
The area of use of dredges is determined by the depths at which minerals are worked. In working continental placers, there is widespread use of electric (less frequently diesel and steam), multiple-scoop dredges with continuous and interrupted scoop chains (capacity 50-600 liters) and closed concentration cycles; seagoing dredges use one-scoop hydraulicand pneumatic-suction devices. Seagoing dredges differ structurally from continental varieties in terms of maneuvering and transport-dumping equipment (the absence of pile supports and stacker conveyer). In the open sea, navigation and maneuvering of the dredge along the face of mineral deposits is accomplished by means of a cable-anchor device.
A multiple-scoop dredge consists of a floating vessel, generally in the form of a welded all-metal flat-bottomed pontoon on which are located the massive trusses of the hull (the superstructure), which are rigidly fastened to it, and the above-deck structure, as well as the forward and rear towers, scooping and maneuvering devices, and concentrating equipment.
In Russia small-capacity one-scoop dredges known as pakhari (plowmen) were used by prospectors to mine gold from small channel-lag placers. The first multiple-scoop dredge with mechanized steam-engine drive was built in New Zealand in 1870. In Russia the first multiple-scoop dredge, which was re-equipped from a dredging shovel bought in Holland, was set up in 1893 in the Kudacha River valley at the Amur Rozhdestvenskii mine. The first Russian dredges were produced in 1900 at the Nev’ianskii Plant in the Urals. The largest increase in dredge construction took place in the 1930’s and 1940’s, when the operating fleets of foreign countries numbered nearly 400 high-capacity dredges. The Krasnyi Putilovets plant (now the Kirov Plant in Leningrad) was a pioneer in Soviet dredge construction. From 1926 to 1930 it produced electric dredges with scoop capacities of 210 and 380 liters. Foreign imports of dredges were ended as a consequence of such production. In 1931 the Irkutsk Heavy Machinery Plant manufactured the first dredges with scoop capacities of 150 liters. In 1969 the Irkutsk plant manufactured the world’s largest electric dredge, with scoop capacities of 600 liters and a maximum excavation depth of 50 m below the surface of the water. Soviet dredge-construction enterprises are mass-producing electric dredges of several types and sizes (see Table 1).
In most foreign countries, because of the exhaustion of the supplies of continental placers, operating dredges are commonly transferred from one mineral deposit to another (South America). New dredges, intended basically to process tin-bearing placers (Malaysia and Indonesia), and coastal-offshore diamond-bearing placers (West Africa), are being manufactured in small quantities.
The USSR, which has the most powerful and largest dredge fleet in the world, has great achievements to its credit in dredge construction and is a pacesetter for world technology and science in this field.
A new development in dredge construction consists of equipping maneuvering devices with independent hoists and gears that are designed to perform one specific technical operation. As a rule, these hoists are electrically interlocked and centrally controlled, which ensures rhythmic operation of the dredge. Under optimum conditions for ore concentration on dredges, high degrees of extraction are achieved (from sand, 93.8-98.6 percent of heavy metals and 89.5-95.6 percent of light minerals). The development of dredge construction is proceeding in the direction of maximum standardization of dredge units and assemblies. Dredges are being equipped with the latest high-production apparatus, including efficient systems of variable electric drive and means of automated control, monitoring, and remote inspection of technological processes, electronic control devices, computers, industrial television, and sound fixing and radiogeodetic installations.
REFERENCESSviridov, A. P. Dragi i dragirovanie. Moscow, 1952.
Shorokhov, S. M. Razrabotka rossypnykh mestorozhdenii i osnovy proektirovaniia. Moscow, 1963.
Leshkov, V. G. Spravochnik drazhnika. Moscow, 1968.
Leshkov, V. G. Sovremennaia tekhnika i tekhnologiia drazhnykh rabot. Moscow, 1971.
Mero, J. Mineral’nye bogatstva okeana. Moscow, 1969. (Translated from English.)
V. G. LESHKOV