Summary:
All you need to know about Quayside container crane
The main structure of shore container cranes
Classification of shore container cranes
The quayside container crane, also known as the shore bridge or bridge crane, is a specialized crane for loading and unloading container ships at the forefront of container terminals. It mainly uses specialized container lifting equipment to complete container loading and unloading operations. To adapt to the loading and unloading of heavy cargo on individual container ships, some shore container cranes are equipped with heavy cargo hooks, while a few port shore container cranes have both container and grab loading and unloading functions.
The shore container crane consists of a gantry consisting of two front and rear door frames and pull rods, as well as a bridge supported on the gantry. The traveling trolley lifts the container along the tracks on the bridge using specialized lifting tools for loading and unloading operations. The gantry can walk along a track parallel to the shoreline to adjust the operation position and align with the box position. In order to facilitate the docking and departure of ships from the dock, the part of the bridge that extends outside the dock can be tilted. For high-speed shore container cranes, there is also a suspension anti roll device installed.
The main structure of shore container cranes
Lifting mechanism
Bridge type grab ship unloaders are usually operated at full load, but the load variation of the lifting mechanism of shore container cranes is significant. Due to the current cargo capacity of containers generally only being 50% to 60% of the rated cargo capacity, for example, if the rated lifting capacity of a crane is designed to be 30.5t, when lifting a 20ft container, even if the maximum total weight is used, it only reaches 67% of the rated lifting capacity of the crane.
In order to improve loading and unloading efficiency, it is required that the lifting speed varies with the size of the load. If the lifting speed of the rated load is constant, it is required that when the lifting load is less than the rated load, the lifting speed should increase inversely. Generally, the no-load speed is twice or even 2.5 times the heavy-duty speed.
Car operation and anti roll mechanism
The traveling distance and speed of the container crane’s trolley are relatively long. When the trolley starts and brakes, the cargo will sway in the direction of the trolley’s movement. The higher the speed of the car, the more severe the sway, which affects loading and unloading efficiency and operational safety. Therefore, it is necessary to install anti roll devices.
Crane operating mechanism
When loading and unloading container ships, due to the need to frequently move the crane to align with the container positions on the ship, it is not necessary to collide with adjacent containers or the superstructure of the ship. Therefore, the crane operating mechanism is required to have good speed regulation, micro motion, and braking performance, so DC electric motor drive is usually used.
Drive and power supply methods
To meet the working requirements of shore container cranes and achieve good speed regulation performance, a DC stepless speed regulation system is generally adopted, and each mechanism is driven by a DC motor.
There are three power supply methods for DC power: the first is the AC motor DC generator method, which is more commonly used and works more reliably. The power supply voltage is basically not affected by grid voltage fluctuations and is relatively stable. The disadvantage is that the unit is heavy, expensive, and noisy. The second type is the thyristor rectification method, which has high electrical efficiency, good speed regulation performance, light weight of the unit, small footprint, and convenient maintenance.
However, it requires a large power grid capacity and small voltage fluctuations. In addition, there is a high requirement for the technical level of maintenance. The third type is the power supply method of diesel engine DC generator, which is not affected by external power sources and improves the maneuverability of container cranes. It is particularly suitable for docks with inconvenient power supply and can save investment in power supply facilities. However, this type of unit has high noise, complex maintenance of diesel engines, and is not suitable for the current strict environmental policies.
Classification of shore container cranes
Classified by the structural type of the main beam
Single box type
This type of box shaped structural main beam only has one box shaped beam, and most of the small cars installed on it place the lifting mechanism. Of course, there are also a small number of self-propelled cars that can operate on the track of the main beam.
There are two forms of its cross-section, one is rectangular and the other is trapezoidal. In general, the main beam with a rectangular cross-section is equipped with a trolley running track on the upper part of the main beam.
The main beam with a trapezoidal cross-section has its trolley running track configured at the lower part of the main beam. The main beam structure with a rectangular cross-section has good resistance to bending and twisting, but the smoothness of the car’s operation is poor. The main beam of the trapezoidal structure has better rigidity for the trolley.
Double box type
The double box type structural main beam has two box type beams. The crossbeam connects two box beams together. Usually, the flat honing frame is placed between the crossbeam and the main beam to enhance the structural stiffness of the beam.
The main advantages of the double box structure main beam are: small lateral windward area, lower total height of the shore container crane, stable center of gravity, smooth operation of the trolley, ability to withstand strong loads, and good rigidity.
Combination type of plate beam and truss
This combination form has typical structures where two welded composite I-beams are applied on both sides, a planar truss is configured in the upper and lower horizontal planes, and a truss or frame is configured in the vertical plane.
trusses
The main beam of this type of structure is lightweight, but the overall structural size is large, the manufacturing cost is high, and the maintenance cost is high. It is rarely used in general.
There are various ways to classify shore container cranes. According to the number of containers lifted in a single lift, there are single box shore container cranes and double box shore container cranes; According to the type of crane gantry, there are H-type gantry shore container cranes and A-type gantry shore container cranes.
The most commonly used classification is based on the structural type of the crane trolley
Full rope trolley shore container crane
The lifting mechanism and the trolley operating mechanism are both arranged in the machine room on a fixed bridge, and the shore container crane is pulled by ropes to operate the trolley.
Half rope trolley shore container crane
The trolley operating mechanism is arranged on the trolley, and the lifting mechanism is arranged on the shore container crane in a fixed machine room.
Self propelled trolley shore container crane
A shore container crane with both the lifting mechanism and the trolley operating mechanism installed on the trolley.
Among the three types mentioned above, the semi rope traction trolley type is the most commonly used. Due to its convenient control, it eliminates the need for steel wire ropes pulled by small cars, greatly reducing maintenance workload and lowering loading and unloading costs.
The self-propelled trolley type steel wire rope has the least amount, but the overall weight of the machine is relatively large. Moreover, due to the increasing power of the lifting motor, it requires a large cross-section of mobile cables for power supply, which is very difficult and costly, so it is less commonly used. The weight of a full rope traction car is the lightest, but the steel wire rope is the longest and difficult to maintain. It is only considered for use when the dock allows for a smaller load.
Classification based on height restrictions of shore bridges
Pitch type
Working in windy conditions, the main beam tilts upwards at a 45 degree angle, keeping the highest point unchanged. Its clearance height is as long as the main beam can be lower than the high-rise buildings on the ship.
Telescopic
The main beam of this type of shore bridge can freely expand and retract, and there is a driving device inside. During operation, the main beam of the shore bridge extends towards the sea side; When not in operation, the main beam can be extended to the land side. This type of shore bridge is mainly used in situations where the clearance height is very strict.
Bending type
The front main beam of this type of shore bridge can be bent. When carrying out loading and unloading operations, the main beam is placed in a horizontal position and its upward position presents a bending form.