The Four-link portal crane is a mobile slewing crane commonly found in ports and large industrial sites. It is used for the efficient and precise loading, unloading, and handling of heavy materials. Through a four-link system composed of the boom, jib boom, and backstay-working in coordination with the luffing mechanism-the hook can move in an approximately horizontal path during luffing (radius change), significantly improving handling efficiency. Combined with the portal structure, hoisting, slewing, and traveling mechanisms, it forms a classic port handling machine capable of operating in three-dimensional space.
I. Core Mechanism and Working Principle
Its core is a system of four rigid members connected by hinges:
Main Components: Boom, jib boom, backstay, and a fixed support on the upper frame (or A-frame).
Working Principle: When the drive pushes the boom to luff up or down, the geometric constraints and linkage of the four members force the head of the jib boom (the hook point) to follow a pre-designed, nearly horizontal trajectory.
II. Main Structural Features
Portal Structure: The lower section features a tall frame (portal) under which rail vehicles or other equipment can pass, enabling non-interfering, three-dimensional operation between ground and aerial tasks.
Hoisting Mechanism: The core is a winch system consisting of a high-power motor, high-speed/low-speed brakes, a reducer, a drum, wire rope, and pulley blocks. Its function is to provide vertical lifting power for the main hook, typically with multiple speed settings (fast for light loads, slow for heavy loads).
Luffing Mechanism: The power system that drives the four-link boom system to pitch. Typically driven by a motor, it uses a reducer to drive a rack or wire rope/hydraulic cylinder to push/pull the boom's base for luffing. Its function is to change the hook's working radius. Its special design ensures minimal hook height fluctuation during luffing, achieving near-horizontal movement.
Slewing Mechanism: The mechanism that drives the slewing platform to rotate 360 degrees relative to the portal. It usually employs multiple motors driving through vertical reducers to power pinions, which mesh with a large-diameter slewing bearing gear ring fixed to the portal. Its function is to provide circumferential coverage for the hook's working position.
Traveling (Gantry) Mechanism: The mechanism that drives the entire crane to move longitudinally along ground rails. Multiple sets of driven and idler bogies are installed under the portal legs, with wheels driven by motors via reducers. Its function is to extend the crane's longitudinal working range. It is equipped with complete anti-wind and anti-slip devices (e.g., rail clamps, anchor devices).
III. Core Operational Capabilities
The crane integrates three motions, enabling the hook to efficiently cover a vast three-dimensional workspace:
Luffing: The hook can move forward/backward while maintaining a nearly constant height during operation.
Slewing: The hook can rotate around the crane's center.
Traveling: The entire machine can move longitudinally along tracks, expanding its operational range.
IV. Typical Application Scenarios
Due to its high efficiency and large working range, it is primarily used for continuous bulk material handling at fixed points:
Ports and Terminals: For loading/unloading bulk cargo (coal, ore, grain) and general cargo (breakbulk).
Large Infrastructure and Industrial Sites: Such as shipyards for handling hull sections, thermal power plants for coal stacking/reclaiming, and hydropower stations for equipment installation.
In summary, it is a heavy-duty lifting device installed atop a vehicle-passable portal. It utilizes an ingenious four-link mechanical system to achieve horizontal hook movement during luffing, specifically designed for high-efficiency, continuous point-to-point handling.
As a professional crane manufacturer in China, YuFei Crane is a comprehensive industrial enterprise that integrates the entire process of material handling equipment, including design, production, sales, installation, and service.
With over 3,000 employees, YuFei Crane has more than 500 management and technical personnel, including over 100 senior engineers. Our factory covers an area of more than 200,000 square meters.
YuFei Crane operates with a first-class quality assurance system, a comprehensive and rigorous management system, robust production capacity, and advanced inspection methods to ensure the high quality of both products and output.
If you have any questions about four-link portal Cranes, please feel free to contact us at any time.