Fig. 13. Ransomes and Rapier w2000 walking dragline stripping overburden at phosphate mine in Jordan

The largest models are the 498 t O&K RH300, one of which has been operating in the UK, since 1979, and the Soviet BC-20 of similar weight which was put on test in the USSR around the same time. P&H has promoted a comparable 2200 model but one has not yet been made. In the next size group-over sixty units of the Demag H241, now weighing up to 280 t and introduced in 1978, were shipped during the first five years of production. At the new Quintette coal mine in British Columbia, eight H241 machines will be employed by 1986. Since the Marion 3560 appeared in 1982, units have commenced operating in the USA and Canada. Testing of the Soviet EG-12 began in 1978 at the Kedrovoye coal mine in the Kuzbas area.

Although most machines are diesel powered - Cummins, G M Detroit, Deitz, Caterpillar and Komatsu engines are used - electric power is being offered increasingly as an alternative. A Demag H241 electric backhoe at a coal mine in the Witbank area of the Transvasl in South Africa is particularly interesting. It has a power pack consisting of a 300 kW diesel engine, hydraulic pumps and an oil tank, mounted on a wheeled chassis which can be hooked behind the machine. Hoses transmit hydraulic power to the H241's drive motors on long distance moves to regain the mobility an electric powered excavator loses when its power comes via a trailing cable.

Modular construction is employed for large hydraulic excavators as well as draglines. Despite the size of the Marion 3560 its modular form makes it possible to assemble in only five days. This machine also exhibits features found on other models of hydraulic mining excavators. The operator's cab is fully insulated with thermostatically controlled heating and air conditioning: radio and tape deck are included as standard fittings. An announce panel alerts the driver to potential problems through an electrical sensing system which monitors twenty-three functions.

Modern computer technology has now been applied to this type of excavator: both the Komatsu PC1500-1 and Mitsubishi MS1600, for example, have onboard microcomputers. The computer on the PC1500-1 controls an energy saving system, and that fitted by Mitsubishi makes possible intricate digging and loading operations by the driver using a single lever at any one time.

The Poclain Servodyn system retrieves energy when the boom is raised, correctly positions the bucket between loading and discharging, levels the bucket during forward movement at ground level when required, allows the bucket to follow floor contours without jolting, and retracts the boom so that the bucket clears the rock pile. The Variodyn variable flow hydraulic circuit allows independent and simultaneous operation of all functions (fig 14).

Fig. 14. Shows the rh120c introduced in 1933 as an intermediate size between the rh75 and rh300, incorporating “Tripower" geometry

The TriPower system of kinematics for shovel equipment employs a pair of solid links, working through bell cranks and interconnected with the boom and bucket rams, to provide parallel bucket action when crowding at the face and lifting to dump position. Increased digging power throughout the digging arc is achieved without increased energy consumption, and a machine weighing relatively little compared to its perfor­mance results in lower operating costs. A float position on the boom cylinders reduces bucket wear as well as undercarriage tipping, with automatic and rapid return to the digging position minimizing cycle time. The TriMatic system for backhoe equipment employs a two-piece boom and related hydraulics. This evens out pressure levels during lifting, and at close reach increases both digging and loading heights while giving greater machine stability.

No doubt even larger and more sophisticated hydraulic excavators will be employed at surface mines in the near future. There are indications that Hitachi and Коmatsu are amongst manufacturers that intend to introduce larger machines; proposals for a 500-600 t hydraulic excavator jointly sponsored in Japan are believed to be under active consideration. In 1981 Hitachi gave an indication of one form of highly innovative excavator that could be created when it demonstrated the concept of the UH999. This large hydraulic mining excavator would have a rotating bucket and telesco­ping dipper arm allowing dual use as a shovel or backhoe without changing equipment. Its cab could be moved hydraulically to improve vision and the crawler could be extended for increased stability (Fig. 15).

Fig. 15. Shows the росlain 350 CK that was first shown in 1982 and has since proved very successful at many tough mining and quarrying sites

UNIT 3

DRAGING

PRE-READING

Exercise 1.

1. There different kinds of mining. Can you name some of them?

2. What do ore mining procedures depend on?

Exercise 2. Match the words and their synonyms:

utility refer to specific reclamation impact environment

influence restoration relate surroundings usefulness definite, particular

READING

Exercise 3. Read the text and learn more about ore mining.

Text 1. What Is Ore Mining?

Globally, there exist five major kinds of mining: oil and gas, coal, nonmetallic mineral quarrying and ore mining. Oil and gas mining is the largest mining operation in the world, as this operation produces major sources of global energy. Ore mining extracts metals. Since the earth's metal minerals are nonrenewable, ore mines have finite utility.

Ore mining technically encompasses any kind of mining in the "ores," or insides of the earth. However, ore mining commonly refers to the mining of metal. Ore mining targets base metals, including copper, lead, nickel and zinc. Ore mining also targets non-base metals, including iron and aluminum.

Ore mining is different from other kinds of mining (oil, gas and coal) in that the removal of minerals is not intended for fuel or energy. Ore mining removes metallic minerals from the earth to produce different metals. Mined metals are treated with chemicals and heat to convert them into the metals used for all kinds of products, from kitchen appliances to aircraft carriers.

Ore mining procedures depend upon the specific operation, as different regions have different technological capacities, regulations and resources. However, the major phases that most ore mining operations follow include exploration, mine development, extraction of the ore, ore beneficiation, storage, transportation, mine closure and reclamation of the land. There are two kinds of extraction - underground and surface. Surface mining occurs in an open pit.

Ore mining, much like oil, gas and coal mining, negatively impacts the environment. Ore mining generates solid waste, which causes pollution, in various phases of mining operations, especially in the extraction, storage and transportation of mined metals. The waste to ore ratio, known as the "overburden," is slightly less for surface mining than underground. Ore mines that are highly sulfuric also cause pollution through drainage, as there is much run-off of high concentrations of dissolved heavy metals. (http://www.ehow.com/info_8686940_ore-mining.html)

COMPREHENSION CHECK

Exercise 4. Are the statements true or false? Correct the false statement using the facts from text1.

1. The earth's metal minerals are renewable.

2. Ore mining commonly refers to the mining of metal.

3. There are many kinds of extraction.

4. Ore mining negatively impacts the environment.

VOCABULARY

dredging - драгирование

thawing – оттайка

frozen – замерзший

muck - отбитая неубранная порода, почва

creek - бухта, залив, устье реки

giant – гидромонитор

lumber – строевой лес, пиломатериал

hull – понтон, каркас, корпус

floating - плавучий

trommel screen - барабанный грохот

pond - пруд, отстойник, водоем

to percolate – просачиваться, дренировать

barrel - барабан

to curtail - сокращать, укорачивать

outlet - выход

a riffle - перегородка

perforated steel plates - перфориро­ванные стальные пластины

clean-up - очистить

to grind - измельчать

to flush off – смывать

staker - укладчик

to take up – снять, поднять

the content - содержимое

gold bricks – слитки золота

Exercise 5. Find the meaning of the word combinations in the dictionary and try to remember them:

dredging industry; methods of thawing; frozen gravel; barren frozen "muck"; to overlay the gold-bearing gravel; amount of "muck"; volume of "dredging section"; to determine gold con­tent; payable value; width and course of the dredge path; creek gravels; hill and bench gravels; thawed ground; decomposed vegetable matter; underlying gravel and overlying silt; to wash (flush off) the muck run-off; to set up a hydraulic giant; wastage of water; erection of a dredge; outlet; tailing piles; riffles.

Exercise 6. According to suffixes define the part of speech of the words below.

development; recent; thawing; frozen; layer; depth; payable; calculation; width; equipment; commencement; hydraulic; pressure; lumber; muck; creek; hull, barrel, riffle, directly, effective, usually, available.

READING

Exercise 7. Read the text below looking for the main ideas concerning development of dredging.