The boom structure is a trolley luffing horizontal boom, which is divided into single lifting point, double lifting point and hammer trolley luffing horizontal boom, in which the boom and the balance arm are integrated. Single lifting point is statically indeterminate, and double lifting points are statically indeterminate. The luffing horizontal boom of hammer trolley is installed at the top of the tower, which looks like a hammer, and the tower body looks like a hammer handle without a spire, so it is also called flat head type. Flat head makes the structure simpler, more conducive to stress, reduce self-weight, simplify the structure and so on. The horn of the car mostly adopts regular triangle section.
Tower structure, also known as tower, is the main body of tower crane structure. At present, tower cranes all adopt square section, and the section dimensions are widely used:1.2m×1.2m× 1.4m× 1.4m, 1.6m× 1.6m, 2.0m× 2. The common dimensions of standard section of tower body are 2.5m and 3m. The most commonly used connection methods of tower standard section are cover plate bolt connection and sleeve bolt connection, followed by socket pin connection and plug plate pin connection. Standard section includes integral tower standard section and assembly tower standard section. The latter has high processing precision and great manufacturing difficulty, but it occupies a small area and has low cost. The tower section must be provided with ladders for drivers and mechanics to get up and down. The width of the ladder should not be less than 500mm, the step distance should not be greater than 300mm, and a retainer should be set every 500mm. When the height of the ladder exceeds 10m, the ladder should be transferred in sections, and a rest platform should be added at the transfer point.
The function of the tower tip is to bear the upper load from the drawstring of the boom and the drawstring of the balance arm, and transmit it directly to the tower structure through the rotary tower, turntable, bearing seat and other structural components. The top of jack-up tower has truncated cone column, forward or backward truncated cone column, herringbone frame and diagonal support frame.
All top-swing tower cranes need to be equipped with balance weights, whose function is to support the balance weights, so as to form the balance torque required by the design in the opposite direction to the lifting torque. In addition to the counterweight, a lifting mechanism is often installed at its tail. The hoisting mechanism is placed at the end of the balance arm together with the counterweight, which can play the role of partial counterweight, increase the distance between the rope drum and the guide wheel of the tower tip, facilitate the winding of the wire rope and avoid rope disorder. The size of the counterweight is inversely proportional to the length of the balance arm, and the length of the balance arm is proportional to the length of the boom. The amount of balancing weight is considerable, generally, light tower cranes need at least 3 ~ 4t, and heavy tower cranes need nearly 30t. The balance weight can be cast iron or reinforced concrete: the former has high processing cost but small windward area; The latter is large in volume and windward, which is not conducive to stability, but simple and economical, so it is generally used. The usual practice is to prefabricate the counterweight into 2 ~ 3 specifications, the width and thickness are the same, but the height is adjusted to match the boom with different lengths. There are many kinds of lifting parts used in each tower crane, among which the number of wire ropes is the largest, with strict technical requirements and complex specifications. According to different functions, wire ropes for tower cranes include: lifting wire ropes, luffing wire ropes, boom ropes, balance arm ropes, trolley traction ropes, etc. Wire rope is characterized by high strength, uniform strength, light weight, bearing vibration load, high elasticity, winding in a circle, high-speed balanced movement and no noise. After being worn, its skin will produce many burrs, which are easy to be found and disposed of in time. Steel wire rope is usually twisted into strands by thin steel wire with a diameter of 0.3 ~ 0.4 mm, and then twisted into rope by strands. The tower crane adopts alternating torsion, which is characterized by not being easy to loosen and twist. As far as the cross-sectional shape of strands is concerned, multi-strand untwisted steel wire rope is the most suitable for tower crane in high-rise building construction. This kind of wire rope is composed of two layers of strands, and the twisting directions of the two layers of strands are opposite. They are twisted by the principle of rotating moment balance, and the free end does not twist when it is stressed. Generally, the safety factor of hoisting wire rope and luffing wire rope of tower crane is 5 ~ 6, the safety factor of trolley traction rope and boom pull rope is 3, and the safety factor of hoisting wire rope of tower crane elevator shall not be less than 10. The safety factor of wire rope is an indispensable safety reserve factor, and the maximum allowable safety load of wire rope shall not be increased without authorization by virtue of this safety reserve surface. Because of the importance of wire rope, it is necessary to strengthen the regular and comprehensive inspection of wire rope and store it in a warehouse with closed and dry ground and wooden floor or asphalt concrete floor to avoid corrosion. Don't damage the surface when loading and unloading, and erect it when stacking. The systematic lubrication of wire rope can improve its service life.
The luffing trolley is an important part of the horizontal arm tower crane. The whole luffing trolley consists of frame structure, steel wire rope, pulley, traveling wheel, guide wheel, steel wire rope supporting wheel, steel wire rope anti-falling roller, trolley traction rope tensioner and broken rope protector. For the super-long horizontal boom (more than 50 meters in length), one side of the luffing trolley is attached with a maintenance basket, which can carry maintenance personnel to various maintenance points for maintenance. After the operation, the trolley drives back to the root of the boom, unhooking the hanging basket from the luffing trolley and fixing it at the special support on the boom structure.
Other components include pulleys, slewing bearings, hooks and brakes. The main electrical equipment of tower crane includes:
Cable reel-central slip ring;
Motor;
Electrical appliances that operate motors, such as controllers, main controllers, contactors and relays.
Protection devices, such as automatic fuses, overcurrent relays and limit switches.
Control and switching appliances in main circuit and auxiliary circuit, such as buttons, switches and meters.
Belonging to auxiliary electrical equipment are: lighting, signal lights, electric bells, etc. The main components in the hydraulic system of tower crane are hydraulic pump, hydraulic cylinder, control element, oil pipe and pipe joint, oil tank and hydraulic oil filter.
Hydraulic pump and hydraulic motor are the most complicated components in the hydraulic system. Oil is sucked by the hydraulic pump and delivered to the hydraulic cylinder or motor through the pipeline, so that the hydraulic cylinder or motor can work normally. Hydraulic pump can be regarded as hydraulic pressure and heart, and it is the energy source of hydraulic pressure. The hydraulic pumps used in the hydraulic jacking system of domestic tower cranes are mostly CB-G gear pumps, CB is not the code name of gears, Heglon G is the fixed axial clearance, and the working pressure is 12. 5 ~ 16 MPa.
Hydraulic cylinder is the executive component of hydraulic system. Functionally, both hydraulic cylinder and hydraulic motor are conversion devices that convert the pressure energy of working oil flow into mechanical energy. The difference is that the hydraulic motor is used for rotary motion, while the hydraulic pressure is used for linear motion.
The whole process of hydraulic jacking is:
Move the balance weight so that the tower is not affected by the moment, the boom is in place, the orientation is the same as that of the entrance track and locked, and a standard section of the tower is hoisted and placed on the shuttle bus;
Jack-up;
The positioning pin is positioned and locked, the piston rod is lifted, and an introduction space is formed in the jacket;
Introduction of standard section;
Bring out the standard section and launch car ferry;
Put the standard section in place and install the connecting bolts;
Gently jack up, pull out the positioning lock, and connect the transition section with the connected tower. Safety device is one of the essential key equipment of tower crane, which is divided into: limit switch (limiter); Overload fuse (overload power-off device); Buffer stop device; Anti-dropping device for steel wire rope; Anemometer; Emergency safety switch; Security protection of audio signal.
Limit switches have the following functions: hook travel limit switch, rotary limit switch, trolley travel limit switch and cart travel limit switch. When the jack-up tower crane reaches its free height, it must be attached to the building structure through anchorage to improve its stability coefficient and maintain its lifting capacity. The attachment level is related to the total height of the construction floor, the structure of tower crane and tower body, and the free height of tower body. Generally speaking, it is enough to set two kinds of anchoring inks. Attention should be paid to the selection of attachment points on buildings: the distance between two attachment and reinforcement points should be appropriate; The fixed point should be set at the corner of T-wall and external wall; For frame structures, the attachment points should be distributed near the root of the column; Arranged near the floor, convenient for force transmission and installation.
In order to ensure the safe use and long service life of tower crane, it must be lubricated, troubleshooting, regular maintenance and parts overhaul.
General situation of foreign development
The tower crane really developed after World War II. After the war, all countries are faced with the arduous task of rebuilding their homes, and the huge engineering quantity urgently needs a large number of tower cranes with good performance. It has been more than 50 years since the tower crane showed its talents in construction engineering and gradually became an important branch of construction machinery, during which it has experienced a tortuous and complicated development stage. At the end of 1970s, due to various reasons, foreign tower crane manufacturing industry fell into a trough, many small and medium-sized factories closed down or changed production, and only a few large factories were able to maintain. It was not until the late 1980s that it gradually recovered. The recovery year is 1994, and the country with the best recovery momentum is Germany. According to relevant data, in the 1970s, when the tower crane manufacturing industry was at its peak, there were 48,500 tower cranes in West Germany, but in the 1980s, the total number was reduced to 1/3. In recent years, with the merger of East and West Germany, the scale of infrastructure has expanded, and the output of tower cranes has increased. There are nearly 40,000 tower cranes, half of which are less than five years old.
Today, the most prosperous areas in the world tower crane market are Eastern Europe and the Asia-Pacific region (especially Southeast Asia). The famous manufacturers active in the tower crane market are Liebherr, Pena and Wolff in Germany, Potam and BPR in France, Potam-Simma, Comedil, Nauva, EDILMAC in Italy, Comanza in Spain, Betrox in Finland, KRφLL in Denmark and Favco in Australia. In order to occupy more shares in the international tower crane market, these big manufacturers must pay attention to summing up experience, carefully analyze market trends, and strive to update and develop products. [3], foreign tower crane new product development generally has the following characteristics:
⑴ More and more manufacturers begin to pay attention to the development of tower cranes in economical cities and expand them into series products.
⑵ Among the new tower crane products abroad, some novel light and medium-sized folding tower cranes are quite noticeable.
(3) According to the relevant regulations of urban construction authorities in some countries, in order to prevent the boom of tower crane from running in a narrow space and avoid the boom colliding with adjacent buildings, the self-lifting tower crane with movable arm must be used in the construction of urban high-rise buildings.
(4) After a long period of development, the crawler horizontal arm tower crane came out as a new product.
5] Frequency conversion speed regulation system has been popularized and applied in new tower crane products abroad.
[6] High-tech has been applied to tower cranes.
At one time, no matter whether the tower crane rotates upward or downward, it attached great importance to the plane design and space treatment of the cab.