The use of tower cranes requires high safety. The loss of its failure is not a two-point problem. Therefore, tower-lifting structures and parts have certain requirements for safety. We are here to introduce the application of high-strength bolts in tower cranes.
High-strength bolts are an important part of the tower crane's connection. In addition to guaranteeing its design and manufacturing quality, its proper use is also crucial. Therefore, users must attach importance to seamless steel pipes in procurement, installation, and use.
The high-strength bolts used on the tower body are generally 10.9. The 20kNm compact tower crane can use 8.8-grade high-strength bolts. Tower body high-strength bolting force generally has two kinds, one is to bear tensile force, and the other is to withstand shear force. The former is widely used on tower cranes and has the advantages of simple manufacture, economical reliability, and easy disassembly and assembly.
1. Pre-tightening force calculation of high-strength bolts Pre-tightening force is an important indicator to ensure the quality of bolt connection. It comprehensively reflects the installation quality of bolts, nuts and washers. Currently, the connection form of high-strength bolts in China is classified into friction type and pressure type, and friction type is generally adopted.
In the design, when the bolt length is more than 15 times of the diameter, the reduction of the connection carrying capacity is generally considered. Insufficient or excessive pre-tightening force during fastening is unfavorable for bearing and leads to early effectiveness of bolts. In recent years, it has been proposed to take into account the complex force of the tower crane, the modular design, versatility and mass production of the design. it is good.
The tower body high-strength bolts are usually tightened by the torque method and tightened in the elastic region. Pre-tightening torque value can be calculated by the following formula: T=KFd
In the formula, K———dispersion coefficient, 0.18～0.21 for general machining surface without lubrication
F———Preload of high-strength bolts (N)
d———nominal diameter of thread (mm)
2. Manufacturing of high-strength bolts 2.1 Process For the production of large-diameter (>M22) bolts of 10.9 or above, most of the domestic companies currently use two kinds of technologies:
1 Blank-hot forging, roughing, heat treatment, quenching, quenching, finishing rolling;
2 rough a hot forging a roughing a heat treatment a fine car rolling forming a quenching.
For process reasons, medium-carbon alloy structural steels are generally used for 10.9 high-strength bolt materials. After practice and research, low-carbon alloy structural steels can also be applied to high-strength bolts of grade 10.9 and have broad prospects for development.
2.2 The production of high-strength bolts is manufactured in the same batch. Each connection consists of 1 bolt, 1 nut and 2 washers. It must be supplied in accordance with the guaranteed torque factor. At the same time, the manufacturer shall provide product quality inspection reports in batches. book.
3) Installation of high-strength bolts for the tower body 1) Before installing the tower, conduct a comprehensive inspection of the high-strength bolts, check whether the specifications, grade marks, check bolts, nuts, and washers are damaged. After confirming the correctness, apply the bolts on the nut bearing surface and the threaded portion. A small amount of lubricating oil to reduce the friction coefficient to ensure the preload force and torque value.
2) When bolts, nuts, and washers are used in combination, bolts of class 8.8 are generally not allowed to use spring washers to prevent loosening, bolts of grade 8.8 or higher are not allowed to use spring washers to prevent looseness, and flat washers must be used. The tower body high-strength bolts must be double nuts to prevent looseness. The small tower crane tower body generally uses a high-strength nut and an ordinary nut. The high-strength nut should be placed in the bolt end lock.
3) There are two types of bolts for the tower body, one is to insert the bolts from top to bottom, and the other is to interpenetrate from bottom to top, and the stress condition is the same. In the case of ensuring the thread and pre-tightening force, the following advantages are interspersed from top to bottom; the bolt screw thread is not easily damaged by a falling object at high altitude, and the screw thread faces downward so that the rust proof effect is good, even if the nut is loosened, the bolt will not fall off.
For the use of high-strength bolts in tower cranes and related safety considerations, we have carried out detailed analysis and use instructions above. We hope relevant personnel will pay attention to the use of high-strength bolts to ensure the safety of operations. .
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