INTRODUCTION

Text I. CLASSIFICATION OF CRANES

Materials handling plays an important part in industrial life. Modern enterprises would not function without cranes. The function of a crane is to hoist or lower a load suspended from its jib. The type and size of cranes best suited for a specific operation are influenced by the following factors:

(1). The nature of the work on which it is to operate,

(2). The weight of load it has to handle.

In cranes every possible source of energy has been applied to drive them. The earliest cranes were all hand-operated. Then came steam, high-pressure water, compressed air, electricity, petrol, etc. Thus we might classify cranes broadly into band-ope­rated cranes, hydraulic, pneumatic, electric cranes and so on.

Some cranes are tied to one spot and so are known as fixed cranes. Others can go almost everywhere, having unlimited mobili­ty. Some are mounted on wheels, others have chain tracks suitable for travelling over rough ground. There are also floating cranes for use in rivers and docks. Thus on the mobility basis of classi­fication we have (I) Fixed, (2) Revolving, (3) Travelling, (4) Floating, (5) Locomotive cranes and others.

Again cranes of various classes may be identified by their conventional names as (I) Derrick, (2) Jib, (3) Overhead travel­ler, (4) Portal, (5) Gantry, (6) Caterpillar cranes and so on.

Part I. Overhead travelling cranes

Text 2. GENERAL ARRANGEMENT

For regular inside work the overhead traveller excells all other forms of crane. In its simplest form an overhead traveller consists of a bridge mounted on an elevated track. The bridge is provided with the mechanism necessary for giving to the load a to-and-fro motion. Upon the bridge there is a mechanism for giv­ing to the load an up-and-down motion and side-to-side motion.

The load depends from a trolley which runs backwards and forwards on a track.

Each motion, namely lifting, traversing and travelling, has its own motor. Cranes of small capacity have, therefore, three motors. Of these two are usually mounted on the trolley. Cranes of large capacity are usually provided with an auxiliary lifting mechanism. The capacity of the auxiliary hoist is much smaller than that of the main lifting mechanism (20 to 25 per cent). But it operates at a correspondingly higher speed (4 to 5 times).

In another group of cranes two trolleys are provided. They may run on a common track, or each trolley may have its own track so that either trolley can traverse the span independent of the position of the other.

Text 3*. ADVANTAGES OF THE OVERHEAD TRAVELLING CRANE

The overhead travelling crane is able to serve a large area while itself occupying no floor-space. It has a high degree of mobility and speed of handling even heavy loads. It has the abi­lity to lift the maximum load at any point within its service area. They require a minimum of headroom and permit complete freedom of movement.

The overhead travelling crane is readily adaptable to many different methods of handling, e.g., for grabbing, for handling bulk loads by skip, for magnetic lifting of ferrous scrap or for special duties.

Text 4*. TYPES OF OVERHEAD TRAVELLING CRANES

There are more forms of this type of crane than any other. Overhead travelling cranes vary in design from single girder cranes to two-girder cranes.

There may be hand-power or power-operated overhead cranes. They may also be of the cab-controlled type when the crane is controlled from the operator's cabin; or they may be of the floor controlled type when the crane is controlled from the floor, or from the ground.

Lastly, overhead travellers may also be classified according to their gripping devices into those equipped with a hook, a mag­net, or a grab.

Text 5**. GANTRY CRANES

In general construction, the gantry crane is similar to the electric overhead travelling crane. It consists of a horizontal bridge carries at a considerable hight above the ground on run­ways. The runways are supported by A-shaped frames at the ends. The whole structure may be fixed (fixed gantry) or capable of moving (travelling gantry).

Generally there is a trolley, carrying a hoist, running on the bridge. But instead we may have a derrick, a jib crane, etc.

If the bridge overhangs one end-support we have a single-cantilever gantry. If the bridge overhangs both end-supports we have a double-cantilever gentry. The cantilever ends are often unequal in length. The load may run either from end to end or entirely outside the supports, which are then relatively close together.

A single motor is often used for operating all motions of the crane.

Speeds of certain gantry cranes, of 5- to 10-ton capacity and 200-ft. to 250 ft. span, are:

Lifting full load, 100 to 300 ft. per min.

Travelling with full load, 300 to 900 ft. per min.

Traversing with full load, 500 to 1200 ft. per min.

A type of drive used on many of the largest gantry cranes consists of motors geared direct to the truck axles.

Gantry cranes are made with a span up to 200 ft. or more. Gantry cranes are used for outdoor services where overhead run­ways would be very expensive. They are widely used in railroad storage yards and at docks for handling ore, coal, cement, etc.

Text 6.

Прочтите текст и ответьте на следующие вопросы:

1. Каковы габаритные размеры крана "Голиаф"?

2. Какова грузоподъемность этого крана?

3. Какова конструкция крана?

4. Где расположена и что собой представляет кабина машиниста?

5. Как и с какой скоростью осуществляется движение крана?

6. Что является уникальной особенностью крана "Голиаф"?

Время на чтение - 4 минуты.

Text 6. THE GOLIATH CRANE

The overall dimensions (габаритные размеры) of this crane are 400 ft. (140 m) wide and 3I6 ft. (96 m) high, with a hight from rail tracks (рельсы) to the underside (нижняя часть) of the bridge girders of 230 ft. (70)m). Its safe working load (допустимая рабочая нагрузка) is 840 tons distributed (распределять) between three lifting hooks while under test loading it has lifted 1 050 tons.

Basically the crane consists of the pier leg (жесткая опора), the sheer leg (гибкая опора в виде двуноги), the crane bridge girders and the two lifting trolleys. The pier leg is of box construction and contains a stairway (лестница) to the bridge girders and a four-man lift which operates at a speed of 0,5 m/sec for a height of about 180 ft. (54.4 m).

The crane bridge is also of box gider design and rigidly (жёстко) connected on one side to the pier leg and on the other side it bears against (опираться на) the sheer leg. The trolleys can traverse the whole length of the bridge girder, the lower trolley passing beneath (под) the upper trolley. The heights of the two trolleys are upper 31 ft. 1 1/2 in (9.5 m) and lower 14 ft. in (4.32 m). The upper trolley has two hoists (механизм подъёма), each of 300 tons capacity, which are arranged symmetrically to the bridge centre, and an auxiliary hoist of 15 tons capacity. The lover trolley has a hoist of 15 tons capacity.

In addition to lifting gear (подъемный механизм), the upper trolley also carries the driver's cabin, this being attached to an outrigger (кронштейн) mounted on the upper trolley in order to afford all-round vision (обеспечить полный обзор) for the driver who is in telephonic communication with a number of points on the crane itself, and in radio communication with the ground. All windows in the driver's cab are of the opening type, the front windows being fitted with integral heating elements for de-icing (удаление льда). a 15-ton maintenance slewing crane (поворотный кран для профилактических и ремонтных работ) is arranged on top of the pier leg, and can directly lift compo­nents out of the trolleys and the machinery room and lower these to the ground. The radius and lifting capacity of this crane is suitable for the heaviest machinery components.

The Goliath crane runs on a 800 m track. Its load weight of approximately 4 000 tons is taken on 64 special anti-friction bearing (подшипник) mounted wheels, each of 35 1/2 in (902 mm) diameter. Twelve identical driving motors are fitted - 6 to each leg - so arranged to provide direct driving to 36 of the wheels.

In operation the crane moves along the track at a speed of about 100 ft. (30 m) per minute, although this can be increased to 150 ft. (450 m) per minute for loads of 100 tone or lees. Special devices ensure that the legs move at identical speeds, thus pre­venting slewing (перекашивание).

A unique feature ot the crane is that it is powered by elect­ricity generated within the crane itself. This generating plant is installed in the top section of the pier log and consists of the following: two 1 485 hp 750 rev/min main diesel engines, each driving two 365 kW 600 v dc (постоянный ток) generators directly coupled (соединять), and one 90 kw 600 v dc and one 45 kW 300 v dc generators.

The two 365 kW generators supply power for the main hoisting movements, while the smaller generators supply power for the up-per trolley and lower trolley cross travel motors respectively (соответственно). (From Shipbuilding & Marine International).

Text 7.

Прочтите текст 7. Расскажите о преимуществах однобалочной кон­струкции мостовых кранов и прокомментируйте все имеющиеся в тексте цифровые данные. Время на чтение - 2 минуты.

Text 7.SINGLE-GIRDER BRIDGE CRANES