Английский язык для горных инженеров-механиков. Учебное пособие

fashion to a milling machine. The sharer usually of about 150 KW power, pulls itself along a static chain stretching the length of the coal face. However this method of haulage is now being phased out and the sharers are now pulling themselves along using the rack and pinion method, which reduces the potential danger of injury due to breaking or whipping chains.

The sharer then cuts back and forth along the face line extracting a section of coal 560 mm wide and 1 to 3 meters high, depending on the coal thickness.

In an attempt to speed up production, sharers have been produced with two cutting drums and more powerful motors. This, of course, brings problems with associated equipment which has to be re-designed. To further increase production many coal faces have two sharers and some have three.

The Armoured Flexible Conveyor

The armoured flexible conveyor is an essential part of any modern coal face. The AFC is an ali-steel-trough-like structure, running the length of the coal face and strong enough the carry the massive weight of the modern power loader, which slides along the top of the trough.

Two chains within the trough pull steel flights or paddles, which in turn drag the coal to the end of the trough, where it is turned at right-angles and is discharged onto another AFC, the stage loader. This is a turn deliver onto a belt conveyor and the coal then starts its journey to the mine shaft.

The AFC has the advantage that it suits the power loader and can easily carry the heavy load of one of these machines. The coal can pass under the travelling power loader in the trough of the AFC and this can be promptly “snaked” close behind the power loader, enabling the powered supports to be advanced only a few minutes after the coal has been cleared by the power loader.

II.2. Answer the following questions.

1.What operations does the power loader perform during its run?

2.What is the most common power loader used in long-wall mining?

3.What is the drum fitted with?

4.What reduces the potential danger of injury due to breaking or whipping chains?

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5. What section of coal does the shearer extract during one phase of its

run?

6.What changes in the construction of the loader increase the productivity?

7.What is AFC?

8.What is the advantage of the AFC?

9.Where does the power loader slide?

II.3. Find out the paragraph which describes the advancing of the cut coal.

II.4. Find out the paragraph speaking on the advantages of the

AFC.

II.5. Try to describe the combined work of the power loader and AFC in some sentences.

III

III.1. Read the text and give the main idea of each paragraph in one or two short sentences.

TEXT С. Rapid Excavation

Rapid excavation is the concept of replacing the intermittent operations of rock breakage and materials handling in mining with a system of continuous extraction.

Figure 3 illustrates schematically the principle and components of rapid excavation, with a TBM (tunnel-boring machine, also called a mole), in which breakage, handling, support and ventilation are attempted simultaneously.

The term rapid excavation was coined in the 1960s to convey the concept of continuous, high-speed mining or tunnelling. It received acceptance and remains the ultimate goal of those who speak to maximize the

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performance of the entire extraction system. Applicable to surface and underground mining, rapid excavation is applied mainly to the subsurface. While the entire operating cycle is involved, the element of rock breakage lies at the heart of rapid excavation.

In terms of application, two types have become popular, the continuous miner for coal and soft rock and the boring machine for soft to medium-hard rock (the latter is more closely identified with rapid excavation). Continuous mining machines are widely used for both development and exploitation in room and pillar and long-wall mining. Boring machines in soft-and hard-rock mining find application mainly for development, in tunnels and drifts (TBM), raises (raise-boring machines–RBM ), and shafts (shaft-boring machine–SBM ).

Historically, continuous excavating machines have been in existence for a good many years, preceding the invention of dynamite (in 1867). The first such machine, a TBM, appears to have originated in Italy in 1846; it utilized percussive-blow energy to produce a slot around the face. TBMs were used in the earliest attempts to tunnel under the English Channel, starting in 1865; most of them used drag-bit or disk cutters. Modern rockboring machines were developed in the 1950s.

Progress in rapid excavation can be measured by several performance parameters: (1) hardness of the rock penetrated, (2) time percentage of machine availability, (3) diversity of application, (4) rate of advance, and (5) cost of advance. In all respects, rapid excavation has made gains.

One of the major deterrents to applying rapid excavation in underground mining is the rather massive dimensions of the boring machine plus the trailing gear. The TBM aione in Fig.3 is about 50 ft (15m) in length, which is not excessive compared with a continuous miner, typically 35 ft (10 m) long. But the addition of the usual trailing gear for tunneling comprised of haulage, ventilation, and ground-control equipment, can bring the length of the entire system to over 450 ft (135 m). Application of TBM, other than continuous miners, to exploitation is largely experimental because of size and mobility constraints. More compact horizontal (TBM) equipment for hard rock using the partial-face design is under development.

III.2. Answer the following questions.

1. What does the term “rapid excavation” mean?

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2.What operations are executed simultaneously by a mole?

3.What is the goal of rapid excavation?

4.Where is rapid excavation applied mainly?

5.What kinds of machines are the most popular in performing rapid excavation?

6.When were the first TBM used?

7.What is one of the major deterrents to applying rapid excavation in underground mining?

8.Why is application of TBM largely experimental?

9.What performance parameters are considered to measure the progress in rapid excavation?

10.May the aspect of massive dimensions be considered as an advantage of a boring machine?

III.3. Examine Figure 3 carefully and try to speak on the

components of a TBM.

Fig3 TBM

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SUPPLEMENTARY READING

UNIT I

EARLY MINING METHODS

Only seams lying near the surface would be worked in the early days of coal-mining. At first the coal was got by the open-cast working. Where the coal was deposited too deep for open-cast working, tunnels were driven from the outcrop to the seam.

Where possible these tunnels were driven on a slight rising gradient to allow drainage as no pumps were then available. The coal was carried along the underground road ways to the surface on the back of women, boys and girls known as bearers. Where the coal was more or less flat but lay at a depth too great for opencast working, shallow pits were sunk. These shallow pits were sunk to the coal seam and then were widened to remove as much coal as possible without supporting the roof. Then the pit was abandoned, and another one sunk nearly.

The coal was still carried by the bearers along the adits and up the shafts until about the middle of the 14th century, when windless or jack rolls, similar to those used for winding water from wells, were introduced for hosting the coal up the shafts in baskets; this method of winding was employed until the 19th century. The coal was got by wooden picks tipped with iron and by iron wedges.

For the sinking of shafts and driving of levels or tunnels in rock, fires were lighted in contact with the rock or stone to be broken, and these fires were extinguished and the rock cooled by water, thus causing it to split.

Little progress was made in mining methods for several centuries largely owing to lack of tools and equipment, and the miners or pit men who were more or less serfs.

About the middle of the 17th century horses were employed for winding coal from mine shafts.

With deeper and somewhat more extensive area of working around the shafts difficulties of ventilation and drainage arose.

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MINING METHODS

Traditional mining methods of exploitation fall into two broad categories based on locale: surface or underground. Surface mining includes mechanical excavation methods such as open pit and open cast and aqueous excavation methods such as placer and solution mining.

Underground mining is usually classified into three classes or methods, including unsupported (e.g. room and pillar, sublevel stoping), supported (e.g. cut and fill, stull stoping), and caving (e.g., longwall, block caving).

Surface mining. Surface mining is the predominant exploitation method used world wide. In open pit mining, (mechanical extraction methods), a thick deposit is generally mined in benches or steps; a relatively thin deposit may be mined from a single face, as in quarrying, augering, or open cast mining. Any overburden must be removed by a stripping process before or during mining, except in open cast mining where overburden is removed and mineral (usually coal) recovered in successive operations. Open pit or open cast mining is usually used to exploit a deposit near the earth surface being preferably large in extent, and uniform in value. It necessitates a large capital investment but generally results in high productivity, low operating cost, and good safety conditions.

The aqueous extraction methods are uniquely reliant on water or another liquid during mining and processing. Placer mining is used to exploit mineral deposits that are loosely consolidated, such as sand or gravel, and contain a valuable heavy mineral in a free state. Gold, diamonds, platinum and tin commonly occur in placer form.

Hydraulicking utilizes a high-pressure stream of water that is directed against an exposed placer bank, thereby undercutting it and causing it to crumble. Dredging accomplishes extraction of the ore minerals mechanically or hydraulically from floating vessels. In both placer methods the valuable mineral constituent, generally heavier than the waste material, is removed from a water-base slurry by concentration. Solution mining includes both borehole methods, and solvent leaching.

Underground Mining. Underground methods unsupported, supported and caving are differentiated by the type of wall and roof supports used, the configuration of production openings, and the direction in which mining

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operations progress. The unsupported methods of mining are used to extract mineral deposits that are roughly tabular, flat or steeply dipping, and generally in contact with strong wall rock. Room and pillar mining is adaptable for regular, flat-lying deposits; support of the roof is provided by natural pillars of coal or ore that are left standing in a systematic pattern, and rooms are cut from access entries to provide working faces. When it is necessary additional support is supplied by roof logs or timbers. Stope and pillar mining is a similar method used in noncoal mines where thicker, more irregular ore bodies occur. In shrinkage stoping mining progresses upward with slabs of ore being broken along the length of the stope. The broken ore is allowed to accumulate in the stope to provide a working platform for the miner and is thereafter withdrawn through chutes into haulage drifts on the level below. Sublevel stoping differs from shrinkage by providing several working benches aligned vertically, and mining progresses horizontally. Long blastholes are drilled into the ore in a parallel of fanlike design to fracture the rock. Shrinkage stoping is more suitable than sublevel stoping for stronger ore and weaker wall rock.

Since they provide support to the wall rock, supporting stoping methods are often used in mines having weak structure. Cut-and-fill stoping is employed for dipping tabular deposits. As the mining progresses upward, waste backfill is placed in the stope to provide support for the walls. The ore is moved to chutes or orepasses mechanically, and the waste is usually distributed hydraulically. Square set stoping also involves backfilling however it relies mainly on timber sets to support the walls during mining. These timber sets are assembled in a continuous supporting structure to form hollow prisms that are subsequently filled with waste material. Stull stoping is a supported method using timber or rock bolts in narrow, tabular pitching ore bodies.

Caving methods are varied and versatile and involve caving the ore and/or overlying rock. Longwall mining is a caving method particularly adapted to thin seams, usually coal at some depth. In this method, a face of considerable length (a “long” wall) is maintained and as the mining progresses, the overlying strata are coved, thus promoting the breakage of the coal itself. A different method, sublevel caving, is employed for a dipping tabular or massive deposit. As mining progresses downward alternate slices

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of ore are mined out, and the intervening layers or ore are recovered by caving. The overlying rock is also subsequently caved. Block caving is a remarkable, large-scale, mass production method that is highly productive, low-cost, and ideal for massive deposits that must be mined underground. A large block of ore, several hundred feet (meters) to a side is undercut and thereby caved. As the block fragments and collapses, the ore is drawn off through chutes or loading points into haulage drifts. Block caving is adaptable to weak or moderately strong ore and rock bodies.

UNIT II

POWER SOURCE

Mining machinery is very commonly powered by compressed air but electricity is also widely used and is often the basic source. Compressed air has the advantages of simplicity of transmission and safety under wet conditions. It is especially advantageous underground as an aid to ventilation. Machines powered by compressed air can be easily designed to accommodate on surface as well as underground. Large central compressors and extensive pipeline distribution systems are common, especially at underground mines.

Electric power, purchased from public sources or locally generated at a large central station is common in open-pit and strip mines and dredging operations. Underground coal and saline-mineral mines often use electric power production machinery, but in other underground mines electricity is normally used only for pumps and transportation systems in relatively dry or permanent locations. Direct-current (dc) devices are dominant because of simplicity of speed and power control, but alternating-current (ac) apparatus is becoming common. Mobile equipment is often either battery or cable-reel (having a spring-loaded reel of extension power cable mounted on the machine) type. Processing machines are almost exclusively powered by individual electric motor.

Diesel engines are popular for generating small quantities of electric power in remote areas and for transporting units.

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Underground ventilation is essential as well as waste scrubbers, chemical oxidizers, and other accessories to aid the removal of noxious and irritant exhaust gases. Hydraulic (oil) control and driving mechanisms are widely used for these purposes. Transfer of power by wire rope is common, especially for main vertical transportation.

UNIT III

NEW LARGE BLASTHOLE RIG

The Halifax Tool Co. (Southward. Halifax West Yorkshire HX3 England. Phone (0422)–53441 Telex 51416) earlier this year showed a new large blasthole drilling rig at a granite quarry in Leicestershire, England. The TR75-35 from Halco’s* 1170 series is the latest in an extensive range of blasthole drilling rigs produced by the company.

This new rig is fully hydraulic with a gross weight of 3 It and is capable of drilling 5–7 in. blast holes at very high penetration rates. Halco claims drilling rates of up to 140-160 ft/h using the very high-pressure down- the-whole hammers which the company has developed. The TR 75-35 will replace the three existing smaller Halco rigs and is expected to produce 2.5- 2.7 Mt/y of rock.

A key feature of the unit is a slew mechanism which permits 360° rotations of the drill rig on the tracks. This minimizes maneuvering between holes, reduces non-productive time and provides easier access in difficult areas. The powerful track drives have continuous infinitely variable speed control, while good stability with the mast raised, and this improves hole-to- hole times and machine utilization.

The mast uses 25 ft drill rods and is designed with hydraulic ram and chain feed. Angie drilling up to 25° from the vertical can be achieved, with the mast hydraulically clamped at the angle selected. Whilst drilling, the rig is supported by three jacks. A drill pipe handle is provided, holding one or two 25 ft long drill pipes.

The rig is powered by a single 445hp diesel engine which has fueffl consumption at a maximum continuous power of 18.3 gal/h. An integral two-

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stage screw-type compressor provides high-pressure air, 750 ft /min at 350 lb/in to drive the down-the-hole hammer and to remove the rock chippings. Both engine and compressor are fitted with separate large-capacity, dry-type, two-stage air cleaners; full dust collection is provided by a hydraulically driven dust collector unit.

The operator’s cab has been designed to provide a good working environment; it is sound-insulated, air-conditioned with tinted glass, and a stereo radio is provided. The controls have been laid out ergonomically in order to reduce fatigue and improve safety. All major hydraulic components arc outside the cab to ensure that hydraulic noise and pollution are avoided.

The layout of the main chassis components has been designed to facilitate servicing, so access is good to all parts of the deck and the engine (pumps/compressor) can be fitted with canopies if required, to reduce noise and to protect the important components.

The unit is also available in rotary form for open pit mining or for medium-to soft ground conditions.

* Halco–name of a firm.

UNIT IV

LONGWALL FACES

The potash seam is worked using a specially designed double-drum, shearer built in *MDPA's central workshop. These machines are indirectional in operation hauling themselves along the face by a capstan working on a chain anchored at the face-ends. The machine cuts the ore as it works the face from one tail gate to the main (conveyer) gate, and returns idle.

The lower drum is the leading drum cutting the bottom part of the seam with its picks working upwards. Ideally, the machine is adjusted so that the lower drum cuts just to the underside of a relatively hard central anhydrite band which like all the other subbeds in the seam, is remarkably persistent throughout the deposit. The upper drum slightly behind the lower works the

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