| 摘要 |
A rotary crane having a telescopic mast with a liftable upper portion and a boom pivotally mounted at the end of that portion. The boom includes an end hinged element, a hinged tip and an intermediate member between the end element and the tip. Each portion of the boom is of a triangular shape and has two lower chords and one upper chord interconnected by rods. The boom is foldable and expandable by a rope system which includes boom supporting ropes and a boom folding rope. The end hinged element is connected to the intermediate member by a shackle having an oblong opening into which a pin is inserted to pivotally connect the end element to the intermediate member.
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