If the crane is dismantled it has to be inspected and tested at its final destination. This increases costs, and conditions at the final location may not be the best for an accurate and safe job.
Alternatively, the crane has to be assembled and reassembled before loading on board ship. This requires a careful study to determine the best way to arrange cranes on deck for economy by reducing unused space. With conventional gantry cranes there is still a lot of unused space even with the best loading pattern, and due to the need for lashing down of the loads, this usually cannot be used for other cargo, even if logistical considerations allow it. The result is a high freighting element of the final cost of each crane.
Movable portal mount
The new design for a gantry crane is intended to minimise these transportation problems of existing designs, and includes two portals supporting an extended superstructure (4 in Fig 1) extended horizontally. This carries the load lifting unit, or hoist. The first portal (2) can be physically associated with the superstructure by an interposed movable block (7), which, in one configuration is spaced away from the second portal (3) and, in another configuration, close up to the second portal.
Such an arrangement will allow more cranes to be loaded on a ship, reducing freight costs, but without prejudicing any controls and tests conducted prior to shipment.
Ways and means
As shown in Fig 1, the two or more substantially vertical portals of the RTG crane support a horizontally extended superstructure (4). Two or more tracks are mounted on the superstructure along which a sliding load lifting unit or hoist is carried. On the bottom ends of the portals there are tyred, steered wheels (6) which can be motorised.
The first portal can be associated to the superstructure by interposing movable blocking. In this configuration the crane is fully operative for lifting and lowering loads by means of the hoisting unit (5). When the first portal (2) is in close-up configuration to the second portal, the size of the crane on the ground is compact to be easily transportable on a ship.
In a first embodiment of the invention (Figs 1 and 2), the superstructure forms one rigid body. In the spaced configuration the upper end of the first portal is associated to the first end (4a) of the superstructure. In the close-up configuration the portal is associated around the centre position of the superstructure. The upper end of the second portal is firmly and irremovably connected to the second end (4b) of the superstructure.
The first movable blocking (7) comprises a joining element (8) associated to the upper end of the first portal and connectable to two flanges (9) on the superstructure at the location of both the spaced and close-up configurations. As an aid, the first end of the superstructure is also equipped with a connection element (10), such as a substantial eyelet, which can be attached to an external supporting point during transfer movement of the first portal between spaced and close-up configurations. This supporting point may be an auxiliary crane that balances the second portal and superstructure as the first portal is moved.
Part 12 is a means of moving the first portal comprising a sliding element (13) made up of a temporary supporting trolley of the first portal made to slide along horizontal guides on the superstructure. These may be the same tracks that carry the hoisting unit, or separate from them, mounted at the bottom of the superstructure.
The means of sliding also keeps the first portal balanced on its wheels, which, during transfer between configurations, have their rotational axes orthogonal to the longitudinal directional of the superstructure to enable them the roll along the ground. Propulsion to transfer the first portal can come from the thrust of the lifting trolley normally used for load handling or from motorised wheels.
Alternatively, the movement can come from the component 12 at first portal being connected to a rope hoist or similar. This can be integral to the crane, fixed or removable, or external and mounted on another machine.
In Fig 2, the first movable blocking means includes one or more shoring bars (14). In the close-up configuration, these can be positioned obliquely between the cantilevered part of the superstructure and the first portal to provide greater structural stability.
In this embodiment the crane is operated for transport as follows. The crane is assembled before loading on the ship for testing and inspection with the first portal in spaced configuration. Before loading onto the ship (N), the first portal is moved into the close-up configuration with constraining element (10) attached to an adjacent crane, the first portal connected to the temporary supporting trolley, and the joining element (8) disconnected from the connecting flange (9).
The first portal is transferred and fixed in the close-up position using the joining element (8) and other connecting flange. The shoring bars can then be connected and the crane, in close-up configuration, loaded on the ship as in Fig 2.
The reduced floor space required by the crane in close-up configuration means that two cranes can be placed side by side on the ship’s deck, compared to only one in the spaced configuration. So, double the number of cranes can be transported on a ship of the same tonnage.
At the destination, the crane is made operational by moving the first portal into the spaced configuration.
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