Portal Cranes - Main Performance Parameters of Quay Container Cranes

1. Lifting Capacity The lifting capacity of port hoisting machinery—specifically quay container cranes—is conventionally the sum of the rated lifting capacity and the weight of the spreader. That is, the rated lifting capacity does not include the container spreader. Therefore, the rated lifting capacity is generally determined by the maximum gross weight of the containers being lifted; for the international standard 40ft container, its maximum gross weight is taken as 30.5t. Currently, quay container cranes worldwide commonly use telescopic spreaders, which generally weigh approximately 10t. With continuous structural improvements, the weight of some telescopic spreaders has been reduced to 8-8.5t. Statistics show that over 70% of the various quay container cranes currently in use worldwide have a lifting capacity of 40.5t or 37.5t.

Port hoisting machinery – quayside container cranes have undergone four generations of upgrades: the first generation of quay cranes could lift 30.5 tons of cargo, with a lifting height of 18 to 20 meters and an extension of 28 meters over the sea, using an electric motor generator; the second generation could lift 35.5 tons of cargo, with a lifting height of 25 meters and an extension of 40 meters over the sea, using a thyristor DC speed control system; the third generation could lift 50 tons of cargo, reach a height of 32 meters, and extend 50 meters over the sea, using an intelligent AC frequency converter drive control system; the fourth generation could lift 70 tons of cargo, reach a height of 42 meters, and extend 70 meters over the sea, using an intelligent AC frequency converter drive device.

2. Dimensional Parameters

These include lifting height, outboard reach, inboard reach, track gauge, base distance, and gantry clearance height.

The lifting height should be determined based on the ship's depth, draft, tidal range, and container loading conditions. It should be able to load and unload three layers of containers and stack them up to four layers high under light load and high water levels; and be able to lift the bottom layer of containers at the bottom of the hold under full load and low water levels.

The outboard reach refers to the maximum horizontal distance between the centerline of the sea-side rails of the quay container crane and the vertical centerline of the spreader. It is determined based on the ship's beam and considers the ability to lift the top layer of containers on the outer deck even when the ship is tilted outwards by 3°, with four layers of containers stacked on the deck.

The inboard reach refers to the maximum horizontal distance between the centerline of the land-side rails of the quay container crane and the vertical centerline of the spreader. To ensure efficient ship loading and unloading, the inboard reach can act as a buffer when horizontal handling machinery at the quay edge cannot handle the loads in time. Furthermore, considering the crane's need to lift hatch covers into the inner reach range and the different power supply methods on the landside of the crane, the inner reach range is set at 7–11 m.

The track gauge should be determined to ensure sufficient crane stability and account for the impact of track gauge variations on crane wheel pressure. Simultaneously, the loading and unloading processes at the quayhead must be considered. Typically, it is required that three rows of containers be temporarily stacked within the crane's track gauge range, allowing straddle carriers free access to move these containers. Container loading and unloading generally does not involve direct transshipment between rail and ship, so the dimensional requirements for the laid railway line can be disregarded. In summary, a track gauge of 16 m can be used, and 26 m for broad gauge.

The gantry clearance height depends on the external height of the mobile handling machinery passing under the gantry, primarily considering the passage of straddle carriers while allowing a safety clearance of 0.8–1 m. For a straddle carrier carrying two layers of containers stacked three layers high (approximately 9 m), the gantry clearance height can be set at 10 m.

The base distance refers to the distance between the center lines of the two main supports on the same track. The space within the door frame should be large enough to allow a 40ft container to pass through. Considering the large hatch cover (14m x 14m) and the potential swaying of the container during loading and unloading, a certain gap must be left on both sides; therefore, the effective width within the door frame should be approximately 16m.

3. Working Speed

The selection of working speed should meet the requirements of loading and unloading productivity and the working speed of each mechanism should be reasonably allocated. Increasing the lifting and trolley running speed is of great significance for shortening the loading and unloading cycle time, but the speed allocation should be matched with the capacity specifications of the motor as much as possible, and the mechanical and electrical equipment parts should be made as universal as possible to facilitate maintenance and replacement. In addition, the increase of crane working speed will increase the sway of the spreader. Therefore, corresponding technical measures such as anti-sway should be considered at the same time, otherwise the effect will be poor. Working speed of each mechanism of quay container crane:

(1) Lifting speed: Usually, two speeds are designed: full load and no load. Moreover, the no load lifting speed is more than twice that of the full load speed. For example, the full load lifting speed of ordinary quay container crane is 35-40 m/min, and the no load is 70-90 m/min; the high speed type has a full load lifting speed of 50 m/min and a no load of 120 m/min. The corresponding productivity of high speed quay container crane is 30-35 TEUs per hour. Qingdao Port in Shandong has set a new world record of 52.1 TEUs/hour.

(2) Trolley Travel Speed: The trolley travel distance of a quay container crane is generally around 40m, and the trolley travel time accounts for about 25% of the total work cycle time. Therefore, increasing the trolley travel speed is significant for shortening the work cycle time and improving productivity. However, increasing the trolley travel speed will increase the swaying of the spreader and the fatigue of the operator, so an effective anti-sway device is necessary. The trolley travel speed of a standard quay container crane is 120-125m/min, and that of a high-speed crane is about 150m/min. Depending on actual usage, a spreader anti-sway device must be installed when the trolley travel speed is above 140m/min.

(3) Trolley Travel Speed: The purpose of moving the trolley is to adjust the working position; therefore, a high trolley travel speed is not required, generally 25-45m/min is sufficient.

(4) Boom Pitch Time: Boom pitch is a non-working operation. When a container ship docks at the quay and leaves after loading and unloading, the quay container crane needs to raise the boom to allow the ship to pass. A typical pitching work cycle, i.e., boom raising and lowering, is 8-10 m/min.