Bridge cranes come in a variety of configurations and are all “custom” to some extent. In simple terms, a bridge crane is a lifting device, riding on an elevated structure, which provides movement of material in three axes. The vertical movement is by the hoist, the lateral movement is by the trolley and the longitudinal movement is by the bridge. The operation of the crane can be manual or powered, and can be controlled by a push button pendant, radio remote controls or can be fully automated.
Other variables in crane design include:
Single girder vs. double girder: Single girder cranes are the most cost effective configuration. Double girder cranes typically provide the best hook height out of the available space.
Standard beams vs. box beams: Standard beams are commercially rolled sections that are readily available from your local steel service center. These are appropriate for use for many applications and can be reinforced to carry greater loads. When the combination of crane span and crane capacity exceeds what even a reinforced standard beam can handle, box girders built from steel plates are the answer. By varying the height, width and material thickness, box girders can be designed for use at long spans and high capacities.
Wire rope hoists vs. chain hoists: Electric chain hoists are a good choice below five tons and are frequently used for work station and jib crane applications. Chain hoists tend to be less expensive, simple to maintain but as the capacity increases, the speeds decrease due to the simplistic gear box design. Wire rope hoists are the standard in all higher capacity applications. They are available in a wide variety of speeds and lengths of lift as well as being rated for different duty cycles.
Packaged hoists vs. built up hoists: Packaged hoists are mass produced by a number of different hoist manufacturers. They are a popular choice in Class “C” and some Class “D” applications as they are massed produced, the popular models tend to be available from stock for quick delivery. Built up hoists are custom to each application, but are the correct solution in high duty cycle applications, severe environments or where longer lifts and faster speeds are needed.
Speed: each function can be single speed, two speed or variable speed. Adjustable frequency drives are almost an industry standard for the trolley and bridge function of the crane. They provide smooth acceleration and deceleration which gives the operator the ability to precisely locate the load. Many manufacturers have standardized on two speeds for hoists. Variable speed on the hoist is available and in some applications it is absolutely necessary.