A mechanical grab utilizes a drive to control the opening and closing of its jaws, allowing it to grab and release bulk materials, such as scrap steel, coal, and ore. Its core structure includes:
Jaws: The gripping components, designed with 4 to 8 jaws, feature a curved shape to accommodate different materials (e.g., a one-sixth spherical structure).
Pin/link mechanism: Connects the jaws and transmits the driving force.
Drive system: Provides the opening and closing force, available in three types: hydraulic, electric, and mechanical.
Control system: Regulates the jaws' trajectory and force, integrating sensors and a PLC for automation.
Drive System Classification and Principles of Grabs
Hydraulic Drive of Grabs
Principle:
A hydraulic cylinder drives the jaws open and close, while a solenoid valve controls the oil circuit. When closed, the cylinder piston moves upward, closing the jaws. When open, the oil circuit opens, causing the jaws to open under their weight.
Advantages:
High gripping force (10-20 times greater than mechanical drive) and capable of gripping non-magnetic materials.
Stepless speed regulation, stable operation, and support for unloading at any height.
Electric Drive
Principle:
The motor drives the claw movement through a gear/connecting rod mechanism, while the PLC controls precise positioning (e.g., laser ranging, encoder feedback).
Advantages:
High efficiency, low energy consumption, and support for automated control (e.g., 3D radar scanning, anti-sway systems).
Integrated remote monitoring and fault self-diagnosis functions.
Mechanical Linkage of Mechanical Grabs
Principles of Mechanical Grabs:
Driven by external force from a rope or connecting rod, a single-rope grab utilizes a single wire rope to alternate between open and closed positions.
Features:
Simple structure but low efficiency, requiring manual assistance for opening (like a single-rope grab).
Suitable for light-duty operations (such as small-volume bulk cargo loading and unloading at ports).
Claw Design and Maintenance
Claw Design Details
Number and Layout:
Adjustable from 4 to 8 jaws. The six-jaw grab utilizes a uniformly distributed linkage mechanism to ensure even force distribution.
Asynchronous opening and closing (such as the multi-jaw grabs used by the Shanghai Port Timber Handling Company) accommodate materials of varying sizes.
Material and Reinforcement of Mechanical Grabs:
The jaws' curved surfaces utilize cast steel with wear-resistant tines. Externally welded box-shaped reinforcements and horizontal ribs enhance rigidity and gripping force.
Key areas (such as the pulley rollers) should be regularly greased to prevent sticking.
