Vocabulary

rack – рейка

lever – рычаг

pump – насос

reciprocating – возвратно-поступательный

valve – клапан

piston – поршень

chamber – камера

cone – конический

clutch – сцепление

to engage – соединять

to disengage – разъединять

band brake – ленточный тормоз

rack and pinion jack – домкрат с механизмом реечной передачи

ram – плунжер

winch – лебёдка

hoist – подъёмник, таль

assembling – сборка

ratchet gear – храповая передача

to release – отпускать, освобождать

trolley – тележка

roller chain – роликовая цепь

reduction gear – передача через редуктор

rest – опора

lever – рычаг

hook casing – кожух крюка

sheave – шкив

ЗАДАНИЯ К ТЕКСТУ:

1. Прочтите и переведите текст, пользуясь словарём.

2. Ответьте на вопросы:

1.Whatisajack?2.What jacks do you know? 3. How does a rack-and-pinion jack operate? 4.What is a handling capacity of hydraulic jacks? 5.How does a hydraulic jack operate? 6. Where are jacks used? 7. What is a hoist? 8. What hoists do you know? 9. How does a traveling electric hoist operate?

TOWER CRANES

(Part 1)

Tower cranes are of predominant use in construction practice. They are used to lift materials, parts and whole structures onto the buildings being erected, to install separate elements and for loading and unloading operations.

These cranes are classified by:

(a) the load moment: 4, 16, 25, 40, 60, 100, 160 and 250 ton-meters. The load moment is the product of the weight being lifted by the outreach (work arm);

(b) the number of working movements: three movements (hoisting, slewing, traveling), or four movements (the same plus luffing or jibbing).

(c) the design of the revolving structure: with an upper or lower revolving head;

(d) the arrangement of the counterweight: at the top or at the bottom.

The tower crane is made up essentially of a support, tower, revolving structure, boom, counterweight and controls.

The support carries the traveling mechanism.

The tower carries the operator's cab and some of the mechanisms. It is designed as a latticed steel framework or is made of large-diameter steel tubes.

The operating members consist of the boom, a hoisting pulley and a load handling attachment, usually a hook. Counterweight compensates for the weight of the boom and part of the weight of the load being lifted by the crane.

Vocabulary

to jib - поворачиваться

counterweight - противовес

frame - рама

tapered - конический

to ship - поставлять

inclination - наклон

support - опора

tower - башня

boom - стрела

load handling attachment – грузозахватный орган

hook - крюк

gantry - козлы

ЗАДАНИЯ К ТЕКСТУ:

1. Прочтите и переведите текст, пользуясь словарём.

2. Ответьте на вопросы:

1. Where are tower cranes used? 2. What are the cranes used for? 3. What are tower cranes provided with? 4. How are tower cranes classified? 5. What does a tower crane consist of? 6. What is a support of tower cranes like? 7. What does the support carry? 8. What does the tower carry? 9. What are the operating members of tower cranes? 10. What weight does counterweight compensate?

TOWER CRANES

(Part 2)

The first group includes cranes with the turntable and the counterweight mounted at the top. The stationary tower is a metal framework consisting of several sections. The rigid sup­port is made in the form of gantry on traveling wheels. When this crane has to be shipped from site to site it is split into separate large units and is then assembled again at the new site. The operator's cab is built into the middle of the tower.

The development of prefabricated reinforced-concrete structures and large-size panels gave a powerful stimulus to the production of new mobile tower cranes with a highly maneuverable boom. The winding gear provides for a horizontal movement of the load as the boom changes its angle of inclination, thus facilitating the placement of the load. The load winch is equipped with a mechanism ensuring that the load is smoothly set at a low speed, an extremely valuable feature in erecting elements of prefabricated structures of buildings and bridges.

In cranes of this group all mechanisms and the counterweight are arranged at the bottom, on the turntable, which revolves together with the tower. This improves the crane sta­bility, and simplifies its assembly and dismantling. The revolving gear takes the form of a ring resting on a supporting frame where it joins the turntable.

The running gear of certain cranes enables them to travel round curves on the runway. This becomes necessary when the crane is used to erect buildings of a complicated configuration.

To facilitate passage round sharp curves provision is made for a third rail laid between the main runway rails, which is bent and rises slightly above them. The crane, provided with a fifth wheel which runs on the third rail, goes round the curve on three wheels. A new and simpler device is a system of wheels mounted on hinge-jointed angle brackets.

Tower and other rotary jib cranes (crawler- and truck-mounted, etc.) should be so designed as to circumvent the hazard of being tipped over by an excessive load or an excessive load moment. Since the weight of the structures that have to be raised at con­struction sites is difficult to estimate beforehand, automatic devices are used for this purpose. The most widespread device is a load or height stop. With an electric drive, a switch is opened when the stop acts and the electric motor is turned off. The stop is mounted at the end of boom. The end of rope of the pulley system is secured by clamp to rod with calibrated spring.

When the weight of the load exceeds the safe limit the spring will be compressed, the rod and arm will go down, the end of the lever will press on small weight and open the contacts of switch. This will stop the motor of the hoisting mechanism. If the hook casing reaches the upper limit, lug will raise weight and slop the motor.

Sometimes stops of this kind are mounted on tower and other rotary cranes whose outreach changes when the boom is being raised. They automatically change the safe load-lifting capacity while keeping the load moment constant, making it possible to increase the weight of the load at a smaller outreach.