Abstract
Content
1. Introduction
In modern industry, a large proportion of all lifting and transport mechanisms occupy cranes. Various functions are assigned to them: transportation of various products, movement of raw materials, installation and repair of equipment.
The tower crane contains elastic mechanical links, due to which low-frequency elastic vibrations occur during the robot, which adversely affects the durability and strength of the mechanisms. Swinging of the load occurs when starting, braking, turning the crane, as well as when lifting and lowering the load. Oscillations increase the time of the technological cycle and make it almost impossible to precisely stop the working body, which is necessary for cranes performing precise installation operations. In some cases, fluctuations can lead to a collision of cargo with objects in the vicinity of the transported objects. Oscillations do not fade for a long time due to weak air resistance and channel stiffness. Therefore, it is necessary to take measures to damp the oscillations.
The aim of the work is to review the design and principle of operation of the tower crane, as well as the study of methods for damping oscillations of the load.
1. Overview of construction
A tower crane is a rotary crane [1] (fig. 1) with an arrow 2 fixed in the upper part of the tower 6. The crane’s mechanisms are controlled by the driver from the cab 4. The load is lifted when assistance of the cargo winch 10, the cargo rope and the hook suspension 1, necessary for grabbing objects.
The crane performs movements such as: lowering, lifting cargo, moving and turning, changing departure.
The change of departure is carried out by changing the angle of the boom with the help of the jib pulley 7 and the boom lifting mechanism 9 (Fig. 1a), or by moving the trolley 17 (Fig. 1b).
The crane moves on the construction site with the help of a rail chassis on steel running wheels driven by the mechanism of movement along crane tracks. For the connection of the swivel and fixed parts of the crane, there is a turntable 13, which provides both the transfer of loads from the turning part of the crane to the not turning chassis 15, and the rotation of the turning part relative to the not turning [2] .
Cranes are classified by:
1) Tower type
- with swivel tower (fig. 1a);
- with fixed tower (Fig. 1b).
A slewing bearing in cranes with a fixed tower is located at the top of the tower. The rotary part consists of the boom 2, the swivel head 3, the counterweight console 19, the counterweight 8 and the load lifting mechanism 10.
In cranes with a swinging tower, a turntable is placed at the bottom of the tower. The turning part includes an arrow 2, a tower with a tip and a strut 5, a turntable 12 with mechanisms for raising the boom 9 and load 10, as well as counterbalance plates.
2) Variable arrow type
- with lifting boom (fig. 1a);
- with beam boom (rice 1.b).
In cranes with a lifting boom, the load is suspended from the end of the boom. The change of departure is carried out by turning the boom relative to the support hinge. Such cranes are simpler in construction, but less accurate.
In cranes with a beam boom, the load is suspended from the load trolley, which moves as the departure changes along the guide beams of the boom. This type of cranes provides a more accurate position of the cargo in space.
Figure 1 - Tower Crane
а) – with swivel tower and boom; b) - with a fixed turret and a beam boom; 1 - hook suspension; 2 - arrow; 3 - tip; 4 - cab; 5 - strut; 6 - the tower; 7 - jib pulley; 8 - counterweight; 9 - boom lifting mechanism; 10 - load lifting mechanism; 11 - rotation mechanism; 12 - turntable; 13 - rotary support; 14 - ballast; 15 - chassis frame; 16 - trolley; 17 - trolley; 18 - trolley movement mechanism; 19 - counterweight console.
Findings
1. Tower cranes occupy a large share, in industry, among transport lifting mechanisms;
2. Elastic vibrations adversely affect the design, metal fatigue appears, the device becomes unusable faster;
3. Vibration damping reduces the load and weight of the boom on 5%.
List of sources
- Башенный кран [Электронный ресурс]. – Режим доступа: https://ru.wikipedia.org/wiki/
- Проектирование башенного крана.
- Технические характеристики и выбор грузоподъемных кранов [Электронный ресурс]. – Режим доступа: https://rep.bntu.by/bitstream/handle/data/6504/
- Лекции Демпфирование и его характеристики. Экспериментальные методы определения характеристик демпфирования [Электронный ресурс]. – Режим доступа: https://gigabaza.ru/doc/177712.html
- Предохранительное устройство для стрелы крана [Электронный ресурс]. – Режим доступа: http://www.findpatent.ru/patent/