The boom of a truck crane is the most important part of the crane. The crane uses the pulley block at the top of the boom to support the hoisting wire rope to hang heavy objects, and changes the lifting height and working radius by changing the length and inclination of the boom. Although the function of the boom is to hang and carry objects, the performance and efficiency of the crane are very different with different boom structures and technologies.

First, the boom structure of truck crane

The boom of a truck crane usually includes a main arm and an auxiliary arm. There are two main types of main arms of truck cranes, one is a truss structure arm welded by profiles and pipes, and the other is a box structure arm with various sections. With the development of truck crane, the main boom of truck crane is mostly box structure, and only a few are truss structure.

The function of the auxiliary arm of the truck crane is to connect the auxiliary arm to the end of the main arm when the height of the main arm can not meet the needs, so as to achieve the purpose of lifting objects upwards. The auxiliary arm can only lift light objects. Generally, there is only one auxiliary arm, and there are more than two folding auxiliary arms or telescopic auxiliary arms, among which the folding truss structure auxiliary arm is the most common.

Second, the crane boom telescopic principle

(a) crane boom telescopic form has the following kinds:

1, sequential telescopic mechanism-each section of the telescopic arm is telescopic in a certain order.

2. Synchronous telescopic mechanism-each arm of the telescopic arm expands and contracts at the same relative speed.

3, independent telescopic mechanism-each arm can independently telescopic mechanism.

4. Combined telescopic mechanism-When the telescopic arm has more than three sections, any two telescopic modes listed above can be used for telescopic at the same time.

(2) According to the technical points of telescopic mechanism, truck crane can be divided into pin-free full hydraulic telescopic mechanism and automatic bolt telescopic mechanism.

1, pin-free full hydraulic telescopic mechanism, easy to change the arm length, various types of working arm length, and strong practicability. The disadvantage is self-weight, which has a great influence on the stability of the whole machine.

There are different combinations of pin-free full hydraulic telescopic mechanism, which can be multi-hydraulic cylinders plus primary rope row, single hydraulic cylinder or multi-hydraulic cylinders plus secondary rope row.

The characteristic of multi-hydraulic cylinders plus one-stage rope row is that the last telescopic arm adopts wire rope to expand and contract, and other telescopic arms adopt multi-stage cylinders or multiple single-stage cylinders or multi-stage cylinders and single-stage cylinder liners to expand and contract directly with the cylinders. Therefore, the cross-section of the last telescopic arm changes greatly, while the cross-section of other arm segments changes little.

Schematic diagram of multi-hydraulic cylinders plus one-stage rope arrangement

1- basic arm; 2- 2 arms; 3- 3 arms; 4- 4 arms; 5- master cylinder; 6- secondary oil cylinder; 7- 3 cylinder

The characteristic of single hydraulic cylinder or multi-hydraulic cylinder plus two-stage rope row is that single cylinder or double cylinder plus two-stage rope row can realize the expansion and contraction of four or five arms. This telescopic method is the most advanced in China, but it is very difficult to solve the problem of telescopic boom with more than five sections.

Schematic diagram of two-stage rope arrangement with single hydraulic cylinder

1, 7- guide pulley; Double boom wire rope; 3, 4, 6- Fixed rope clamp; 5- Telescopic boom wire rope; 8, 9- Oil cylinder fixing rope; 10- Balance pulley

Schematic diagram of the main arm of the two-stage rope arrangement with five-arm double hydraulic cylinders

2. The automatic pin telescopic mechanism adopts the electronic technology of single cylinder, cylinder pin interlocking with arm pin and accurate length measurement. Its advantages are light weight, minimal influence on the stability of the whole machine, fast expansion and contraction speed, small change in the cross section of the boom and good lifting rigidity, but it is technically difficult, costly and has few types of boom lengths. (sequentially expanding and contracting from the inside out)

Telescopic structure diagram of boom of single-cylinder bolt crane

The automatic latch telescopic mechanism has interlocking cylindrical pins and arm pins, the cylindrical pins are designed on both sides of the boom and the arm pins are designed on the upper plane of the boom. Its advantages are simple structure and strong self-locking, but its disadvantage is that it is laborious to pull out the arm pin with large deformation, and it needs to be stretched back and forth to pull it out.

Knowing the boom structure and telescopic principle of truck crane, we can understand the key points of truck crane performance. Users can choose their own truck crane products according to their specific work needs when purchasing.