During my years in the crane industry, I have discovered that one of the most vexing issues for customers is overhead gantry crane selection. Many of my customers and friends are extremely confused when it comes to crane selection. Especially when multiple suppliers are quoting, the quoted models may be different, and they cannot choose the most cost-effective solution. To solve this problem, the simple differences between gantry cranes and how to select them are briefly explained.
The overhead gantry crane is a variant of the bridge crane and is mainly used for loading and unloading outdoor cargo yards, material yards, and bulk cargo. Its metal structure is like a door-shaped frame, with two legs installed under the main beam, which can walk directly on the track on the ground. Both ends of the main beam can have outstretched cantilever beams.
Structurally, it consists of a mast, a trolley operating mechanism, a lifting trolley, and electrical parts.
Some gantry cranes only have outriggers on one side, and the other side is supported on the factory building or trestle, which is called a semi-gantry crane.
To expand the operating range of the crane, the main beam can extend beyond the outriggers to one or both sides to form a cantilever. A lifting trolley with a boom can also be used to expand the crane’s operating range through the pitching and rotation of the boom.
The single main girder gantry crane has a simple structure, is easy to manufacture and install, and has a small mass. The main girder is mostly a deflection box frame structure. Compared with double main girder gantry crane, the overall stiffness is weaker.
Single girder gantry crane door legs are available in L-type and C-type. The L-type is easy to manufacture and install, has good stress resistance, and has a small mass. However, the space for lifting goods to pass through the legs is relatively small. The C-shaped legs are made in an inclined or curved shape to create a larger lateral space so that goods can pass through the legs smoothly.
Double main girder gantry cranes have strong load-bearing capacity, large spans, good overall stability, and many varieties. However, compared with single main girder gantry cranes with the same lifting capacity, their own mass is larger, and the cost is higher. According to the different main beam structures, it can be divided into two forms: box beam and truss. Generally, box-shaped structures are used.
① Truss Gantry Crane
The structural form welded by angle steel or I-beam has the advantages of low cost, light weight and good wind resistance. However, due to the large number of welding points and the defects of the truss itself, the truss beam also has shortcomings such as large deflection, low stiffness, relatively low reliability, and the need for frequent detection of welding points. It is suitable for sites with lower safety requirements and smaller lifting capacity.
② Box Gantry Crane
Steel plates are welded into a box structure, which has the characteristics of high safety and high stiffness. Mainly used for large-tonnage and ultra-large-tonnage gantry cranes. Box beams also have the disadvantages of high cost, heavy weight, and poor wind resistance.
③ Honeycomb beam
Generally referred to as “isosceles triangle honeycomb beam”, the end face of the main beam is triangular, there are honeycomb holes on the oblique webs on both sides, and there are chords on the upper and lower parts. Honeycomb beams absorb the characteristics of truss beams and box beams. Compared with truss beams, they have greater stiffness, smaller deflection, and higher reliability. However, due to the use of steel plate welding, the self-weight, and cost are slightly higher than that of truss beams. It is suitable for sites or beam sites with frequent use or heavy lifting capacity. Since this beam type is a patented product, there are fewer manufacturers.
Generally speaking, if the lifting capacity is below 50t, the span is within 35m, and there are no special usage requirements, the single main beam type should be selected. If you require a large door leg width, a high working speed, or if you often lift heavy or long items, you should select a double-girder gantry crane.
The span of a rail mounted gantry crane is an important factor affecting the quality of the crane itself. During selection, the span should be minimized as much as possible on the premise of meeting the equipment usage conditions and complying with the span series standards.
① It can meet the stability requirements of the mast along the direction of the crane track.
② The overall dimensions of the cargo must be able to pass through the flat steel frame of the outriggers smoothly.
③ Pay attention to make the wheelbase B and the span S have a certain proportional relationship.
During work, a certain space should be left between the external dimensions of the gantry crane and the cargo and transport vehicle passages in the yard to facilitate loading and unloading operations. When loading and unloading general transport vehicles within the span, they should maintain a distance of more than 0.7m from the door legs. When the spreader is not working, there should be a distance of more than 0.5m from the transport vehicle. When the goods pass through the door legs, there should be a distance of more than 0.5m.
If you have any inquiry about overhead gantry cranes, please feel free to contact us.
