hopper quary crane mostly run along the crane track on the ground or on the building to carry out lifting and loading and unloading operations. The crane with a "" shaped portal is called a semi-portal crane, and one side of its running track is located on the ground, and the other side is located on the building above the ground.
Introduction to the device
Gantry cranes are developed with the development of the port industry. In 1890, for the first time, a fixed rotatable jib type crane with an invariable amplitude was installed on a running semi-gantry crane that spanned the narrow pier, becoming an early port semi-gantry crane. With the increase of the width of the wharf, portal and semi-portal cranes have been developed in parallel, and pitching booms and horizontal luffing systems are commonly used. After the Second World War, the port portal crane developed rapidly to facilitate multiple cranes to work in parallel with the same ship, and the rotating column type portal crane (Fig. 1 [Rotating column portal crane]) that is connected to the column body is widely adopted, or the rolling bearing type support slewing device that the rotating part is connected to the portal by a large bearing to reduce the tail diameter of the rotating part, and the portal structure that reduces the dock cover surface (the projection of the door seat body to the ground) is adopted. In the process of development, portal cranes are also gradually promoted and applied to slipways and hydropower station construction sites with similar operating conditions to ports.
It can be divided into 3 categories according to the application:
(1) Gantry crane for loading and unloading: mainly used in ports and open-air stockpiles, loading and unloading with grab buckets or hooks. The lifting capacity is generally not more than 25 tons, and does not change with the amplitude. The speed of work is high, so productivity is often an important indicator.
(2) Portal crane for shipbuilding: mainly used for slipway, floating dock and outfitting site, for hull splicing, equipment outfitting and other hoisting work, using the hook as a spreader. The maximum lifting capacity is up to 300 tons, and the lifting capacity is reduced accordingly when the amplitude is large. There are multiple lifting speeds, which can increase the lifting speed when the lifting weight is light. Some working mechanisms are also equipped with micro-moving devices to meet the installation requirements. The height of the door seat is large, which can adapt to the requirements of large lifting height and large operation, but the working speed is low, and the operation productivity is not high.
(3) Gantry crane for construction and installation: mainly used in hydropower stations for dam irrigation, equipment and prefabricated parts hoisting, etc., generally with hooks. The lifting capacity and working speed are generally between the first two types of cranes. It has the characteristics of good transportability of the whole machine assembly and disassembly, large depth of spreader dropping, and good adaptability to temporary work and work on the trestle.
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The portal crane has lifting, slewing, luffing and running mechanisms, and the first three mechanisms are installed on the rotating part, and they participate in the operation in each cycle. The rotating part is also equipped with a tilting single boom or a combined boom and a cab that can be tilted. The running mechanism is installed in the lower part of the portal seat to adjust the working position of the crane, and the gantry crane with bucket (Fig. 2 [gantry crane with bucket]) is also equipped with additional equipment such as telescopic funnel and belt conveyor to improve the productivity of the gantry crane when loading and unloading bulk materials with a grab. In addition to the electrical protection device, it is also equipped with safety devices such as lifting capacity or lifting moment limiter, crane rail clamp and so on.
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Most portal cranes use horizontal luffing systems.
(1) The center of gravity of the weight and the boom system has almost no vertical displacement during the luffing process. One of its methods is to balance the lifting change of the synthetic center of gravity when the boom system pitches by adding a movable counterweight, and this method is more convenient to arrange, and the work is also more reliable, and is widely used. The second method is to rely on the mechanical characteristics of the boom system to ensure that the movement trajectory of the synthetic center of gravity is close to the horizontal line during luffing, and there is no active counterweight.
(2) The hoisted heavy object moves along the trajectory close to the horizontal line in the process of luffing, and the compensation method and the combined boom method can be adopted. The compensation method is to automatically retract and release the corresponding lifting rope in the process of luffing through the special rope storage system to compensate for the vertical displacement of the spreader caused by the lifting of the boom. The combined boom method relies on the mechanical characteristics of the combined boom to ensure that the arm end moves close to horizontal in the process of luffing. Both methods are widely used.
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