The boom assembly is one of the main load-bearing components of the crane. The front end of the boom assembly bears the force of heavy objects, and the rear end of the boom assembly bears the reaction force of the column and the luffing cylinder; the main body of the boom assembly is composed of The multi-section telescopic boom structure is composed of a telescopic oil cylinder or a cylinder + wire rope pulley mechanism between each section to achieve multi-stage expansion and contraction to achieve the purpose of changing the working range or height of the crane; in the design of the straight-boom telescopic truck-mounted crane In China, the design of the boom assembly has always been the top priority.

 There are two common types of boom expansion and contraction: multi-stage hydraulic cylinder step-by-step expansion and simultaneous expansion and contraction of a telescopic hydraulic cylinder + wire rope pulley mechanism. Extendable boom telescopic mechanism; multi-stage hydraulic cylinder sequential telescopic structure has two ways: external and internal hydraulic cylinders. The external maintenance is convenient but the appearance is poor, and the cylinder is easy to be damaged. The internal beauty is beautiful but the maintenance is difficult. The structure has the advantage of large expansion and contraction strength, but the cost is relatively high, the sequence of actions is disordered, and there are many faults such as oil leakage. The second boom and other booms that extend before the work position remain unchanged for a long time, which may cause material fatigue and bend. In addition to the early products, its application has become less and less; the synchronous telescopic structure of the telescopic oil cylinder + wire rope pulley mechanism has the advantages of fast action, low cost, less failure, and the continuous change of the working position of each arm. The large telescopic cylinder bore can also make up for the shortcomings of insufficient telescopic force.

There are many ways of synchronous telescopic wire rope pulleys, and the habits used by each factory are different. They also have multiple forms of wire rope outside and wire rope inside or inside and outside. The inside type is beautiful in appearance and the boom height is small, but there are many failures. Maintenance and repair are difficult, and the jib of the boom caused by the excessively long wire rope length and elasticity is too flashy and not suitable for China’s national conditions; the external structure is relatively solid and durable, but no matter which structure it is, it is designed It should be considered that the length of the wire rope of the boom assembly should be as short as possible, and the number of wire ropes should be as small as possible. The direction of the wire rope should be as simple as possible, with less round-trip bending. When designing, the pulling force of each wire rope should be correctly calculated, and the appropriate size of the wire rope diameter should be selected according to the force and the due safety factor, and then the pulley diameter should be calculated according to the wire rope diameter, and the selection of the bearing model should be determined according to the relevant According to industry standards, the safety factor of the telescopic steel wire rope should be no less than 4, and the diameter of the telescopic pulley should be no less than 12 times the rope diameter. At present, the synchronous telescopic structure of the wire rope pulley is being adopted by more and more crane boom assembly factories; and the winch telescopic Due to the small expansion force, low safety factor and inconvenient layout, the structure can only be applied to some low-end products.