Refresher course Cranes for overhead handling
Here's a rundown on basic types of industrial cranes and their applications for overhead lifting in the plant and warehouse.
By Ray Kulwiec -- Modern Materials Handling, 7/1/1998
The top-running, overhead traveling bridge crane has long been a workhorse in industry. Usually it provides the overall heavy lifting capability in a plant, and overall coverage of the main operations floor of the facility. Over the years, for the sake of efficiency and productivity, an entire "supporting cast" or family of secondary cranes has evolved to complement the work of the big bridge crane, in specific work areas of the plant. Such cranes include jibs, gantries, and in recent years a European import, the work station crane. This article covers the various types of cranes and their applications.Gantry crane is a bridge crane using a horizontal bridge beam that is supported at each end. One- or two-leg versions are available, with provision for the legs to travel along rails.
The single-leg version uses a wall-mounted, fixed rail for one end of the bridge, and a vertical leg at the other end. The double-leg type uses a vertical leg at each end of the bridge, traveling on floor-mounted rails. In either case, a trolley or hoist may be suspended from the bridge beam.
Bridge crane provides six degrees of motion for the load being handled. The "bridge" consists of one or more girders that span the distance between two runway beams that in some cases extend the length of the building. The bridge travels along the runway on wheeled carriages called end trucks, that are mounted to each bridge end. Finally, the hoist body is mounted atop the bridge, or suspended from it. The hoist travels along the bridge on a trolley.
Top-running, double-girder bridge crane provides the greatest headroom or lifting height, because the hoist trolley travels on rails mounted atop the bridge girders. This unit also generally carries the highest load capacity, ranging to 100 tons.
Single-girder, top-running crane has a bridge consisting of just one beam. The bridge travels on a rail atop the runway, but the hoist trolley rides on the lower flange of the bridge girder.
Single-girder underhung crane has bridge end trucks running on lower flanges of runway beams.
Double-girder underhung crane has hoist mounted above the bridge, so it provides a little more headroom, or lifting height, than the single-girder version.
Stacker crane is a variation of a bridge crane (usually double-girder) that involves suspending a mast from the trolley instead of a hoist. The mast may be rotating, rigid or telescoping, and may be equipped with forks for handling pallets or heavy metal coils. In so doing, it can allow a clear, unobstructed floor operation-or, conversely, can move loads readily over floor obstructions.
Jib crane consists of a horizontal beam that pivots around a vertical axis. A trolley and hoist may be suspended from the beam. Jibs have three degrees of freedom-vertical, radial, and rotary. However, they cannot reach into corners. Typical applications include localized activity, as in a machine shop.
Floor-mounted unit has a column that is free to rotate, and can swing 360 deg. When the jib is mounted to a column that rotates about pivots in the floor and roof, a full 360 deg rotation also is available. Wall-mounted jib is usually supported from an existing building structure, and can swing 180 deg. Conventional floor- or pit-mounted jib also has 180 deg swing, but when pivots are offset from the column, a swing of up to 270 deg is possible. Finally, wall-traveling or "walking-wall" type has its beam cantilevered from two horizontal tracks mounted one above the other on building columns.
Work-station crane provides a lighter-duty, stand-alone version of the traditional overhead traveling bridge crane. The unit serves specific work areas in a plant, in contrast to the top-running bridge crane that serves the entire length of a facility. And, it provides a larger work envelope in a given area than does a localized jib crane. Some light-duty versions made of aluminum provide ergonomic benefits as well.
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