Internationally, there has been a growing trend (тенденция) towards the single-girder design for bridge cranes.
The single-girder crane has considerable advantages over the two-girder model. Here are some of them:
a) much lower input of material (зд.: расход) with favourable effect on the price (стоимость);
b) small height and less overhanging (выступающий, выходящий за пределы) dimensions enable use in limited space;
c) small deadweight (собственный вес) of the crane helps to cut back (сократить) cost for crane track and foundations;
d) Modern shape meets highest demands (отвечать требованиям) and compares favourably with other models on world markets;
e) maintenance is easy and cheap;
f) assemblies (узел) are unitized (унифицированный) for inter-changeability (взаимозаменяемость);
g) the crane is highly adjustable to most various conditions.
To meet the demands of manufacturers the Takraf group (GDR) has developed a power-driven single-girder crane. These single-girder bridge cranes are available as a system series, with spans between 4.0 m and 24.0 m. The maximum hoisting height is 12 m.
The crane bridge is an all-welded (цельносварной) design. The travelling wheels of the crane are standardized and, therefore, easily exchangeable (взаимозаменяемый). Travelling speeds are 63 m/min or 31.5 m/min. Overload-protected (снабженный ограничителям грузоподъемности) electric hoists are used for hoisting.
Trolley track speeds are 20 m/min or 25 a/min. The movements of floor-controlled cranes are regulated from a control panel. For cab-controlled cranes a push-button panel (панель с кнопочным управлением) is provided in а roomy (просторный) all-glass, convenient operato's cab. (From Monthly Technical Review).
Part II. Tower cranes
Text 8*. TOWER CRANES
Tower cranes are widely used in construction practice. They are employed for lifting materials onto the buildings being erected, for loading and unloading operations.
A tower crane consists essentially of a support, a tower, a revolving structure, a boom, a counterweight, and controls.
The operating members consist of the boom, a hoisting pulley and a load handling attachment, usually a hook. The counterweight compensates for the weight of the boom and part of the weight of the load being lifted by the crane.
The counterweight may be mounted at the top of the stationary tower. Some cranes of this type have a trolley travelling along the boom which makes it much easier to set precisely in the required place.
Text 9.
Прочтите текст 9 и ответьте на следующие вопросы:
Каковы достоинства самомонтирующегося крана?
Как самомонтирующийся кран доставляется на место работы?
Прокомментируйте следующие параметры: 20 минут, 3 часа, 7 киловатт, 38 киловатт, 18 метров, 32 метра, 45 метров, 3 тонны.
Время на чтение - 2 минуты
Text 9. SELF-ERECTING CRANES (САМОМОНТИРУЮЩИЕСЯ КРАНЫ)
Self-erecting cranes consist of a straight jib set (устанавливать) at right angles (прямой угол) from a vertical tower.
A self-erecting crane will arrive on site as a compact unit. It is either towed (буксировать) behind a truck (грузовик), carried on a low loader (зд.: трайлер, платформа), or transported as a semi-trailer (полуприцеп). No additional transportation is required for jibs or tower sections, because everything can be carried on the base unit. Many models will even carry their own ballast weights.
When in position it will, without any outside (извне, внешний) mechanical help, erect its own tower, load its own ballast and erect its own jib. The time to do this will depend on the model but can be anything from 20 minutes to three hours, at the end of each time the machine is totally (полностью) ready for work.
The majority of these cranes are electrically operated, either from an outside power source, or from a generator carried on the machine itself. Total motor output (максимальная мощность) can vary from 7 to 38 kW.
Height under hook could vary from 18 m on the smaller models to more than 32 m for the larger machines. Working radius can be as much as 45 m. Maximum capacity will depend on working radius, but a middle range crane can easily achieve 3 tonnes, with a considerable increase in a performance for the larger models.
(From Materials Handling News)