Hoisting Machinery – Introduction to Rubber-Tired Container Portal Cranes

Hoisting machinery --- rubber-tired container portal cranes, also known as yard cranes or RTGs, are specialized machines used for stacking container cargo.They consist of a gantry frame, power transmission system, hoisting mechanism, trolley traveling mechanism, auxiliary trolley traveling mechanism, and telescopic spreader. They are equipped with telescopic spreaders capable of lifting 20-foot and 40-foot containers. Yard crane spreaders typically use fixed guide plates. Mechanical anti-sway devices are installed to reduce spreader sway. For easy container handling, a small-angle slewing device is provided. The traveling trolley equipped with the container spreader travels along the main beam track for container loading, unloading, and stacking operations. The rubber-tired traveling mechanism allows the crane to move within the yard and make 90° right-angle turns, enabling flexible operation from one yard to another.

Generally, the standard span for yard cranes is 23.47 meters (six rows plus aisles), but non-standard spans are also available. The lifting height is sufficient to lift a 40-foot-long, 9’6” high container, traversing four (or five to six) stacked containers.

Hoisting machinery—Tire-mounted container gantry cranes—can be classified by drive method into diesel-electric and diesel-hydraulic types.

The diesel-electric system uses a diesel engine to drive a DC generator, which in turn drives a DC motor, which in turn powers various mechanisms, employing digital frequency conversion speed control. In recent years, AC frequency conversion speed control systems and AC squirrel-cage motor drives have begun to be used, as these are popular due to the simplicity and ease of maintenance of the motors.

The diesel-hydraulic system uses a diesel engine to drive a hydraulic system, which in turn drives a hydraulic motor, which powers various mechanisms. This system offers good acceleration performance and a lighter power unit, but it is prone to oil leaks and requires more complex maintenance, resulting in less common use. Yard cranes utilize AC or DC speed control systems, providing excellent speed regulation and constant power control, and can automatically adjust lifting speeds based on the weight of the containers.

In recent years, due to increasingly stringent environmental and energy consumption requirements, various ports, terminals, and yards have converted their RTGs from diesel generator sets to electric power, replacing traditional diesel generator power with a combination of shore power and diesel generators, adding a separate power supply system to the RTG. When the RTG is performing normal stacking operations in the yard, the diesel generator set is shut down to reduce emissions, and the power supply selection switch is switched to shore power. When the RTG needs to be moved, the shore power is disconnected, and the power supply is switched to the diesel generator set to provide power for the trolley drive.