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Port Machinery School Series - Gantry Crane
2025-08-18
Introduction to Portal Crane
A Portal Crane is a typical rotary jib - type crane that runs on rails. It gets its name because its appearance resembles a gate.
Portal cranes are widely used in cargo loading and unloading at ports and docks, construction and installation in shipyards, and construction projects of large - scale hydropower stations.
Portal cranes have developed along with the growth of the port industry. In 1890, a Fixed, non - luffing, rotatable jib - type crane was first installed on a running semi - portal that spans over a narrow dock, becoming an early semi - portal crane for port use. As the width of docks increased, portal and semi - portal cranes developed side by side, and the luffing jib and horizontal luffing system were commonly adopted.
After World War II, port - used portal cranes developed rapidly. To facilitate the parallel operation of multiple cranes on the same ship, the rotating column type portal crane (where the rotating part is connected to the column) or the rolling bearing type slewing support device (where the rotating part is connected to the portal via large bearings) was generally adopted to reduce the tail diameter of the rotating part. A portal structure that reduces the dock coverage area (the projection of the portal main body on the ground) was also used. During the development process, portal cranes were gradually extended to shipyards and hydropower station construction sites with operating conditions similar to those of ports.
Commonly known as "portal cranes", they refer to the cranes traditionally used at the front of port docks. On the gate - shaped base that runs along the ground rails, a rotatable jib frame is installed, which has four coordinated working mechanisms: hoisting, slewing, luffing, and traveling. Trains or other vehicles can pass under the portal, enabling ship - to - shore and transshipment operations.
Portal cranes have advantages such as an attractive appearance, safe and reliable operation, advanced performance, easy maintenance, and durability. They are widely used in loading and unloading operations at major port docks. They are an ideal model for multi - cargo - type docks in comprehensive ports and are also the most numerous main - type equipment at major bulk cargo and comprehensive docks at present.
High Adaptability to Cargo Types
Except for specialized liquid bulk docks for loading and unloading oil products, liquefied gas, etc., portal cranes are basically suitable for all cargoes handled at docks, such as iron ore, grains, coal, bauxite, cement, timber, steel plates, oversized items, ship outfitting, bagged solid chemicals, general cargo, containers, etc. Moreover, this model can be flexibly applied to both loading and unloading operations. The advantage of the diversity of applicable operation types of portal cranes is not only reflected in the multi - functionality of a single berth but also becomes more obvious in large - scale ports when dock loading and unloading equipment needs to be renovated, upgraded, or relocated due to factors such as dock planning and changes in market routes.
Economy of Portal Cranes
The economy of portal cranes is mainly reflected in the following aspects: Among the fixed loading and unloading equipment at the dock front, the construction cost of portal cranes is much lower than that of large - scale specialized ship loading and unloading equipment such as ship unloaders. The advantages of its equipment cost are mainly reflected in the following aspects:
1. In terms of basic design and technology, the model design is mature and economical, and the market competition is sufficient. In addition to several large domestic main engine manufacturers having independent design and innovation capabilities, there are also professional universities and design consulting companies as supplements for the design of portal cranes. Whether adopting the "turnkey" general contracting form or separate bidding and procurement for design and manufacturing, the design part can achieve optimization in both design fees and reasonable economy in the domestic market, and the design cost actually accounts for only about 3% of the total equipment contract price.
2. Compared with specialized dock - front unloading equipment such as ship unloaders, portal cranes have relatively lower speed and duty cycle. In terms of component selection, currently, except for key components such as bearings and some electronic control components, most components can be domesticated or manufactured domestically by imported brands. The large - scale localization of components not only directly reduces the procurement cost of new machine components but also greatly improves the quality assurance and timeliness of spare parts for equipment after - sales service, and also significantly enhances the economy of equipment later - stage maintenance. Moreover, from the perspective of the whole - process control of the project, due to component localization, the construction period is greatly shortened, and the capital turnover rate is accelerated, which is beneficial to both buyers and sellers. With the large - scale application of portal cranes in shipyards, docks, logistics centers, etc. in recent years, the market for portal crane accessories is constantly expanding, attracting a group of powerful upstream and downstream manufacturers of port machinery equipment to invest in the research and development of domestic accessories. Great breakthroughs have been made in key components of portal cranes such as reducers, brakes, electronic control hardware and systems, container spreaders, and grabs, and they have been maturely applied on a large scale.
3. Economy in transportation and installation: Due to its relatively small self - weight and low overall height, the currently mature transportation and installation modes for portal cranes in China all adopt large - piece or scattered - piece transportation schemes. Although this increases costs in terms of on - site final assembly and floating crane coordination compared to large - scale equipment such as ship unloaders, the transportation ship type can be miniaturized as much as possible, and there are significant savings in lashing labor and materials, and the risk of the equipment landing is minimized, making it relatively more economical.
Characteristics of Portal Cranes
- High - speed working mechanisms: The working mechanisms have relatively high movement speeds. The hoisting speed can reach 70m/min, and the luffing speed can reach 55m/min. The rated lifting capacity range is very wide, generally from 5 - 100 tons. For portal cranes used in shipbuilding, the lifting capacity range is even larger, currently reaching 150 - 300 tons.
- High efficiency: It can work 22 hours a day, and the hourly efficiency is also very high, generally reaching more than 100 tons per hour.
- Three - dimensional structure: The structure is three - dimensional, not occupying much dock and yard area. With a tall portal and a long - distance cantilever, it has a large lifting height and working range, meeting the requirements of mechanized loading and unloading and transshipment of ships and vehicles at port docks, as well as making full use of the site.
- High cost of construction: It requires a large amount of steel, with a self - weight generally ranging from 500T - 1000T. A large power supply is needed, and the common power supply is 10kV/50Hz. Generally, the wheel pressure is relatively large. For example, for a 40T/45M crane, the wheel pressure is generally ≤300KN, requiring a solid foundation. There are also many auxiliary equipment, such as substations and cables.
Classification of Portal Cranes
Portal cranes can be classified into the following types according to different structural types:
1. Classified by portal structure type
Portal cranes can be divided into full - portal cranes, semi - portal cranes, and portal cranes with hoppers.
- Semi - portal cranes do not have a complete portal. Their two running rails are not on the same horizontal plane; one is laid on the ground, and the other is laid on a warehouse or a specially - built trestle.
- Portal cranes with hoppers, commonly known as "hopper - equipped portal cranes", have their own cargo conveying devices. They combine the functions of portal cranes, ship loaders, and ship unloaders. Compared with traditional portal cranes, they have advantages such as high automation, strong professionalism, high loading and unloading efficiency, easy operation, low energy consumption, and low environmental pollution. They can greatly improve the loading and unloading efficiency of bulk cargo at ports and reduce port loading and unloading costs.
Currently, dock loading and unloading is constantly developing from general - purpose docks to specialized docks, greatly improving dock loading and unloading efficiency. However, in the face of the market for multiple loading and unloading cargo types, the single - cargo - type adaptability of specialized dock loading and unloading machinery has caused obvious defects in dock loading and unloading, and the emergence of hopper - equipped portal cranes has made up for these defects.
Hopper - equipped portal cranes are specialized equipment for bulk cargo loading and unloading at specialized docks, with a relatively high degree of automation. Their dock rail gauge is only 10.5 meters, while the dock rail gauge of ship unloaders is as high as more than 16 meters. In addition, the portal structure of hopper - equipped portal cranes is compact, the equipment volume is small, the occupied dock area is small, the failure rate is low, and the performance is superior. Moreover, they have the rotatable function of portal cranes, can handle general cargo loading and unloading, and increase the diversity of cargo types for users' dock loading and unloading. Because they can load and unload different types of bulk cargo and general cargo, and have strong adaptability to loading and unloading cargo types at docks and high versatility, they are very popular among owners in port equipment procurement. In recent years, the demand for hopper - equipped portal cranes in the port machinery market has been continuously increasing.
For loading and unloading docks using hopper - equipped portal cranes, compared with ordinary dock portal crane loading and unloading, the traditional bulk cargo loading and unloading process is optimized. In the past, bulk cargo was unloaded from ships to docks by portal cranes and then transferred to the yard by dump trucks for stacking. Now, hopper - equipped portal cranes directly transfer bulk cargo to the dock belt conveyor through the on - board belt and then to the rear - yard yard, reducing transshipment in the middle, which not only improves efficiency but also reduces energy consumption. Users have found through comparison that the loading and unloading efficiency of the bulk cargo loading and unloading process using hopper - equipped portal cranes is more than three times that of the traditional process. The belt - conveyed bulk cargo greatly reduces cargo spillage, avoiding losses for cargo owners. The dust removal device of the hopper and the fully - sealed setting of the belt conveyor also greatly improve dock environmental protection. Through the belt flow detection equipment, the bulk cargo flow can be accurately mastered, further improving the scientific management of the dock.
The portal structure of hopper - equipped portal cranes is complex, with many electronic control programs. Compared with portal cranes, their design includes additional telescopic beam mechanisms, conveyor systems, and hopper systems, while having all the functions of commonly - used port portal cranes. For manufacturers, this not only increases the technological content but also significantly increases the production difficulty, thus becoming a benchmark to test the design level and production capacity of port machinery manufacturers.
Nanjing Port Machinery has continuously launched new - type hopper - equipped portal crane products in recent years, aiming at different dock loading and unloading needs of users, learning from the advantages of various loading and unloading equipment, and through discussions with academies, users, and port machinery experts. Years of manufacturing experience have established Nanjing Port Machinery's advanced technology and manufacturing level in the hopper - equipped portal crane manufacturing industry. Aiming at the different specific gravities of wood chips, soybeans, and coal bulk cargo, the engineering designers of Nanjing Port Machinery have designed, with their own patents, different portal structures, hopper structures, and unloading systems, and different hoppers and hopper openings for different materials, ensuring the fluidity of different materials, avoiding material accumulation, spillage, and arching, and improving loading and unloading production efficiency.
Nanjing Port Machinery has successfully manufactured two 16 - ton hopper - equipped portal cranes for loading and unloading soybeans and three 16 - ton ones for loading and unloading wood chips for Rizhao Port, Shandong; three hopper - equipped portal cranes for loading and unloading coal for Haikou Power Plant, Hainan; four 16 - ton hopper - equipped portal cranes for Ningbo Port; two 16 - ton hopper - equipped portal cranes for Oji Paper, Japan; and six 28 - ton wood chip hopper - equipped portal cranes for Asia Pacific Resources International Holdings Ltd., Singapore. The six 28 - ton wood chip hopper - equipped portal cranes for Asia Pacific Resources International Holdings Ltd., Singapore are large - scale customized hopper - equipped portal cranes. Whether in terms of mechanical performance, equipment lifting capacity, or loading and unloading efficiency, they have reached the world - leading level. Through hopper tests and grab tests, they fully meet the technical requirements of users for wood chip loading and unloading. Equipped with the largest - capacity grab in China and a 2.4 - meter conveyor belt, which is a precedent in China, the hourly loading and unloading volume of 1800 cubic meters almost reaches the loading and unloading efficiency of equivalent ship unloaders.
2. Classified by jib structure type
Portal cranes can be divided into two types: four - link combined jib portal cranes and single - jib portal cranes. The four - link combined jib portal cranes are further divided into traditional four - link portal cranes and double - four - link portal cranes. The double - four - link portal crane is designed to meet the needs of lifting containers. To prevent container tilting and rotation during lifting, a small four - link device is added to the traditional four - link jib, enabling stable lifting and loading/unloading operations of containers and facilitating the switching of various spreaders. The biggest advantage of the four - link portal crane is that the net height under the jib is relatively large, so under a certain lifting height requirement, the total height of the crane is relatively low, but the structure is complex and the weight is large. In contrast, the single - jib crane is the opposite. Currently, most domestic applications use four - link combined jib cranes.
Taking Nanjing Port Machinery's MQ5039 double - four - link portal crane as an example:
This four - link multi - purpose portal crane is based on the design of conventional portal cranes, with a small four - link device added to the jib, enabling stable lifting and loading/unloading operations of container spreaders. This product can easily switch between loading and unloading different cargo types such as bulk cargo, general cargo, and containers, while maintaining high loading and unloading efficiency. It is suitable for multi - cargo - type dock operations, especially for non - specialized docks. After being put on the market, this multi - purpose portal crane has been highly praised by users.
The main features of this crane are that the jib system adopts a double - four - link system. In the hook and grab working conditions of the conventional four - link portal crane, the double - four - link setting can smoothly complete the container rotating spreader operation. Within the 39 - meter range, it can perform 50 - ton hook operations, 40 - ton grab operations, and 40 - ton container spreader operations. The hoisting, luffing, slewing, and traveling mechanisms all adopt AC frequency conversion speed regulation.
- The rail gauge of this crane is 22 meters, and the distance from the slewing center to the sea - side rail gauge is 4.75m. The difference in wheel pressure between the sea and land sides is large. To prevent rail gnawing, a traveling deviation correction device is added to the design, so that the traveling mechanisms on the two rails maintain the same speed, avoiding rail gnawing during use.
- Since this crane has a container operation condition, considering the safety of container operations, two sets of hoisting braking devices for the high - speed and low - speed shafts are set in the hoisting mechanism. One set is used for normal hoisting braking, and the other set is used for safety braking during emergency braking. This braking device is installed on the flange of the hoisting drum.
- The double - four - link jib system is the main feature of this crane. During container loading and unloading operations, by changing the winding method of the steel wire rope, the four steel wire ropes suspended with the spreader are arranged in a trapezoid, which can greatly reduce the rotation of the container during loading and unloading. At the same time, to prevent the container from tilting during loading and unloading, the front compensation rod in the small four - link is always designed to be in the 45 - degree position, ensuring that the length and relative position of the four steel wire ropes remain unchanged at different luffing positions, improving the stability of the container and solving the problem of large shaking of containers during loading and unloading by conventional portal cranes. In addition, considering the replacement of steel wire ropes when using different spreaders during use, a working platform is set in the middle of the jib, which can safely, quickly, and conveniently adjust the winding method of the steel wire ropes to meet the needs of different working conditions.
- When using portal cranes for container loading and unloading, due to the slewing movement of the portal crane, conventional portal cranes require manual assistance for positioning during container loading and unloading, which limits production efficiency. However, this crane adopts a rotating spreader, so that the spreader can always be parallel to the dock during the slewing process of the portal crane, and the container spreader can be automatically positioned, greatly improving the loading and unloading efficiency.
- This product also adopts a full - set energy feedback control system, feeding back the potential energy of hoisting and the energy of slewing braking to the power grid. At the same time, the application of reactors and filters suppresses high - order harmonics to the maximum extent, achieving the purpose of cleaning the power grid. For safe and efficient use, the electronic control design adopts setting control of hoisting height, luffing amplitude, and slewing angle, reducing the labor intensity of the driver and improving work efficiency.
After being put into operation, the hourly container loading and unloading volume of this product reaches 22 boxes, close to the efficiency of container quay cranes. But most importantly, it has good safety performance, reducing potential safety hazards during operation. At the same time, the hourly unloading volume of bulk cargo grabs reaches 580 tons, truly realizing the multi - purpose of portal cranes, providing a new choice for port users in the selection of front - dock equipment.
3. With the structural type of the supporting device for the rotation of the upper rotating part relative to the lower running part as the main symbol.
Portal cranes can be divided into rotating column type portal cranes, fixed column type portal cranes, turntable type portal cranes and large bearing type portal cranes. The turntable type portal crane has a complex structure and is difficult to process and manufacture, so it is rarely used at present; the rotating column type and fixed column type have good overall stability and are commonly used forms at present, among which the rotating column type is the most widely used; the large bearing type has a novel structure, few components, light weight and broad development prospects.
Classification according to different uses and occasions
Portal cranes can be divided into three types: port - used portal cranes, shipbuilding - used portal cranes and construction - used portal cranes. In addition, according to different loading and unloading purposes of the port, they can be divided into general - purpose portal cranes and special - purpose portal cranes. General - purpose portal cranes are used in general cargo terminals, with hooks or grab spreaders. Special - purpose portal cranes are used in special terminals or for a single type of cargo, such as lifting coal, grain, etc. In addition to hooks and grab spreaders, they are also equipped with specially functional equipment. For example, the portal crane with a hopper is specially equipped with a hopper, a belt conveyor and other equipment.
Portal cranes can be divided into three types: port - used portal cranes, shipbuilding - used portal cranes and construction - used portal cranes. In addition, according to different loading and unloading purposes of the port, they can be divided into general - purpose portal cranes and special - purpose portal cranes. General - purpose portal cranes are used in general cargo terminals, with hooks or grab spreaders. Special - purpose portal cranes are used in special terminals or for a single type of cargo, such as lifting coal, grain, etc. In addition to hooks and grab spreaders, they are also equipped with specially functional equipment. For example, the portal crane with a hopper is specially equipped with a hopper, a belt conveyor and other equipment.
(1) Portal cranes for loading and unloading: mainly used in ports and open storage yards, for loading and unloading with grabs or hooks. The lifting capacity generally does not exceed 50 tons and does not change with the amplitude. The working speed is relatively high, so productivity is often an important indicator.
(2) Portal cranes for shipbuilding: mainly used in shipyards, floating docks and outfitting sites for hoisting work such as hull splicing and equipment outfitting, with hooks as spreaders. The maximum lifting capacity is 300 tons, and the lifting capacity decreases accordingly when the amplitude is large. There are multiple lifting speeds, and the lifting speed can be increased when the lifting weight is light. Some working mechanisms are also equipped with micro - motion devices to meet the installation requirements. Those with a high portal can adapt to the requirements of large lifting height and large amplitude operations, but their working speed is low and the operation productivity is not high.
(3) Portal cranes for construction and installation: mainly used in hydropower stations for dam pouring, equipment and prefabricated parts hoisting, etc., generally with hooks. The lifting capacity and working speed are generally between the first two types of cranes. It has the characteristics of good overall assembly, disassembly and transportation performance, large lowering depth of the spreader, and good adaptability to temporary work and work on trestles.
Structure of Portal Crane
The portal crane is generally composed of the following parts:
Structural Part
Including jib system, A - frame, rotating platform, driver's cab, portal frame, etc.
Mechanism Part
Including hoisting mechanism, luffing mechanism, slewing mechanism, and traveling mechanism.
Electrical Part
The crane is usually powered by a cable reel or a trench sliding wire and adopts direct electric drive. Only when the power supply cannot be solved, composite drive devices such as steam power generation or diesel power generation are considered. The electrical part generally includes wires and cables, central collector rings, motors, transformers, resistors, control cabinets, consoles, lighting, etc.
Safety Device Part
Including limit devices, overload limiters, buffers, wind - resistant and anti - sliding devices, etc. For large - scale portal cranes where the height of the driver's cab and machine room platform exceeds 20m, an auxiliary simple elevator should be considered for installation.
The slewing mechanism of the crane is installed on the base of the portal crane, and the portal - shaped base is actually the load - bearing part of the crane. There is a traveling mechanism under the portal - shaped base, which can move on the rails set on the ground. The jib of the hoisting mechanism and the luffing mechanism are also installed on the slewing mechanism. The four mechanisms work together to complete the installation of equipment or hull sections, or the loading and unloading of goods.
Trains and vehicles can pass under the portal - shaped base. According to needs, it should be determined during construction whether one, two or three trains can pass. When one, two or three trains pass, the gauge of the portal crane is 6m, 10.5m and 15m respectively. Portal cranes are usually powered by an external power grid through flexible cables, and the large mechanisms are generally driven by three - phase induction motors respectively.
Portal cranes have hoisting, slewing, luffing and traveling mechanisms. The first three mechanisms are installed on the rotating part and participate in the operation in each cycle. The rotating part is also equipped with a tiltable single jib or combined jib and a driver's cab. The traveling mechanism is installed at the lower part of the portal to adjust the working position of the crane. Portal cranes with hoppers are also equipped with additional equipment such as telescopic funnels and belt conveyors to improve the productivity of the portal crane when loading and unloading bulk materials with grabs. In addition to electrical protection devices, safety devices such as lifting weight or lifting torque limiters and crane rail clamps are also installed.
Portal Crane System
The control system of portal cranes generally adopts AC frequency conversion speed regulation and PLC control, and can be equipped with an intelligent "status monitoring and control system". At present, many docks are also carrying out the unmanned control transformation system of portal cranes and have achieved some results.
Most of the portal crane mechanism systems adopt horizontal luffing systems.
(1) The centers of gravity of the heavy object and the jib system have almost no vertical displacement during the luffing process. One of the methods is to add a movable counterweight to balance the lifting and lowering of the combined center of gravity when the jib system is luffed. This method is convenient in arrangement, reliable in operation and widely used. The second method is to rely on the mechanical characteristics of the jib system to ensure that the movement track of the combined center of gravity is close to the horizontal line during luffing, without a movable counterweight.
(2) The hoisted heavy object moves along a nearly horizontal track during the luffing process, and the compensation method and the combined jib method can be adopted. The compensation method is to automatically retract and release the corresponding hoisting rope during the luffing process through a special rope storage system to compensate for the vertical displacement of the spreader caused by the lifting and lowering of the jib. The combined jib method relies on the mechanical characteristics of the combined jib to ensure that the jib end moves close to the horizontal during luffing. Both methods are widely used.
