VI. Retell the information of the text.

TEXT V

Dragline Excavator

Fig. 6.5Dragline Excavator

I. Read and translate the text using the words given below:

A dragline excavator (Fig. 6.5) is a piece of heavy equipment used in civil engineering and surface mining.

Draglines fall into two broad categories: those that are based on standard, lifting cranes and the heavy units which have to be built on-site. Most crawler cranes with an added winch drum on the front can act as a dragline. For example, this video shows a crane-type Linkbelt dragline in operation. These units (like other cranes) are designed to be dismantled and transported over the road on flatbed trailers. Draglines used in civil engineering are almost always of this smaller, crane type. These are used for road, port construction, pond and canal dredging, and as pile driving rigs. These types are built by crane manufacturers such as Linkbelt and Hyster.

The much larger type which is built on site is commonly used in strip-mining operations to remove overburden above coal and more recently for tar-sand mining. The largest heavy draglines are among the largest mobile land machines ever built. The smallest and most common of the heavy type weigh around 2,000 tons while the largest today weigh around 8,350 tons.

A dragline bucket system consists of a large bucket which is suspended from a boom (a large truss-like structure) with wire ropes. The bucket is maneuvered by means of a number of ropes and chains. The hoist rope, powered by large diesel or electric motors, supports the bucket and hoist-coupler assembly from the boom. The dragrope is used to draw the bucket assembly horizontally. By skillful maneuver of the hoist and the dragropes the bucket is controlled for various operations.

In a typical cycle of excavation, the bucket is positioned above the material to be excavated. The bucket is then lowered and the dragrope is then drawn so that the bucket is dragged along the surface of the material. The bucket is then lifted by using the hoist rope. A swing operation is then performed to move the bucket to the place where the material is to be dumped. The dragrope is then released causing the bucket to tilt and empty. This is called a dump operation.

On crane-type draglines, the bucket can also be 'thrown' by winding up to the jib and then releasing a clutch on the drag cable. This would then swing the bucket like a pendulum. Once the bucket had passed the vertical, the hoist cable would be released thus throwing the bucket. On smaller draglines, a skilled operator could make the bucket land about one-half the length of the jib further away than if it had just been dropped. On larger draglines, this is not a common practice.

Draglines have different cutting sequences. The first is the side cast method using offset benches; this involves throwing the overburden sideways onto blasted material to make a bench. The second is a key pass. This pass cuts a key at the toe of the new high wall and also shifts the bench further towards the low-wall. This may also require a chop pass if the wall is blocky. A chop pass involves the bucket being dropped down onto an angled high wall to scale the surface. The next sequence is the slowest operation, the blocks pass. However, this pass moves most of the material. It involves using the key to access to bottom of the material to lift it up to spoil or to an elevated bench level. The final cut if required is a pull back, pulling material back further to the low-wall side.

The primary limitations of draglines are their boom height and boom length, which limits where the dragline can dump the waste material. Another primary limitation is their dig depth, which is limited by the length of rope the dragline can utilize. Inherent with their construction, a dragline is most efficient excavating material below the level of their base. While a dragline can dig above itself, it does so inefficiently and is not suitable to load piled up material (as a rope shovel or wheel loader can).

Despite their limitations, and their extremely high capital cost, draglines remain popular with many mines, due to their reliability, and extremely low waste removal cost.

II. Learn the vocabulary to the text:

Draglineexcavator – канатно-ковшовый экскаватор

On-site – местный, локальный, непосредственно на месте

Winchdrum – барабан буровой лебёдки

Tobedismantled – разбираться, убираться, демонтироваться

Flatbedtrailer – прицеп-площадка

Rig – приспособление, устройство, буровая платформа, навесное оборудование

Tarsand – смоляной песок, нефтеносный песок

Hoistrope – подъёмный трос, грузоподъёмный канат

Tobedumped – быть сброшенным, сваленным, опрокинутым

Totilt – наклонять, опрокидывать, опорожнять

Dumpoperation – разгрузка, отвальные работы

Jib – стрела подъёмного крана, укосина крана

Pendulum – отвес, прокладка между противовесами подъёмного крана

Blastedmaterial – разрушенный, повреждённый материал

Tobeblocky – быть глыбистым (о структуре почвы)

Inherent – присущий, свойственный, внутренний, собственный

Piledupmaterial – накопленный, выброшенный материал

Ropeshovel – подвесной ковш экскаватора, канатный экскаватор

Dragrope – урез, ваер

III. Give the English equivalents to the following word combinations:

Тяжёлое оборудование, обширная категория, в действии, гражданское строительство, строительство порта, дноуглубительные работы каналов и прудов, производители кранов, поверхность материала, тем не менее, ограничение, глубина копки, длина каната, чрезвычайно высокая стоимость, подъёмный кран, гусеничный кран, открытая разработка месторождений, зажимное устройство, тяговой канат драглайна, последовательность рубок, откос, очищать поверхность, возвратный канат, колёсный одноковшовый погрузчик, уборка мусор.

IV. Give the Russian equivalents to the following word combinations:

To remove overburden, truss-like structure, hoist-coupler assembly, offset bench, key pass, toe, low-wall, chop pass, to be based on, heavy units, mobile land machine, wire rope, skillful maneuver, typical cycle of excavation, drag cable, common practice, side cast method, to be suitable, to remain popular.

V. Answer the following questions using the information from the text:

1. What is a dragline excavator?

2. Can you describe two categories of draglines?

3. What does a dragline bucket system comprise?

4. How is the bucket maneuvered?

5. What is powered by large diesel or electric motors?

6. Do you know the function of the dragrope?

7. Where is the bucket installed?

8. Describe the process of a dump operation.

9. Enumerate the types of cutting sequences of draglines.

10. Draglines have some limitations, don’t they?

11. Are draglines popular in mining?