Crane Development origin: history. Rotating mechanism for allowing the sale of 30 tons crane jib rotation is determined by the drive means and the rotary bearing device. Metal structure is the skeleton of a crane 30 tons crane manufacturers, the main carrier such as bridge, boom and mast can be a box-shaped structure or truss structure, but also for the web structure, and some can be used as a steel support beam. Crane main performance parameters indicators: starting weight. Lifting capacity: nominal weight of the crane can lift the material along with the spreader or attachment can be divided into the sum (such as grab, electromagnetic sucker, balance beam and other quality effective starting weight: Effective from the weight of the crane can lift the net quality materials.