How To Prevent Corrosion Of Hoisting Machinery?

How to Prevent Corrosion of Hoisting Machinery?

In recent years, with the development of my country's engineering construction, hoisting machinery has become more and more widely used in modern production such as ships, aerospace, electric power, base materials, metallurgy, bridges and railways.
 

The increase in the number of cranes has brought opportunities for manufacturing companies, but also many challenges. According to authoritative statistics, while the number of cranes is increasing year by year, the number of cranes that are dismantled and scrapped each year also increases significantly, and more than 80% of the cranes are scrapped because of the corrosion failure of their metal structures.
 

Due to the high frequency of use of lifting machinery and the relatively harsh working environment, they are often placed in the open air or in a humid and corrosive environment. The protective paint layer on the surface of the crane often loses its protective function due to damage, causing the metal structure to be corroded.
 

There have been two incidents of gantry cranes due to severe corrosion of the main stress-bearing components, and the use unit violated regulations and forcibly overloaded them, resulting in damage to the metal structure and accidents involving machine crashes and fatalities. Taking the United States, a developed country, as an example, according to statistics, more than 50 people are killed in crane accidents every year. The corrosion of metal structure materials of lifting machinery not only easily leads to safety accidents, but also causes huge waste of metal materials.
 

Article 3.9 of GB6067.1-2010 "Safety Regulations for Hoisting Machinery Part 1: General Rules" clearly stipulates that when the main stress-bearing components of the crane are corroded, inspection and measurement should be carried out.

When the corrosion of the section of the main force-bearing member reaches 10% of the design thickness, if it cannot be repaired, it should be scrapped.

It can be seen that in harsh environments, how to improve the corrosion resistance of the metal structure of the crane and reduce the energy consumption of the crane is an urgent problem to be solved.

Corrosion behavior and cause analysis of metal structure of hoisting machinery

The main beam and other main parts of the crane are mainly made of ordinary carbon steel Q235, and the important load-bearing components of the crane metal structure are stipulated to use Q235B, Q235C, and Q235D. For the general metal structure of the crane, when the design temperature is not When it is lower than -25℃, it is allowed to use boiling steel Q235F.

For ordinary carbon steel corrosion forms can be divided into uniform corrosion, hole corrosion and intergranular corrosion. Uniform corrosion is less harmful. Since metal components have a certain cross-sectional size, slight uniform corrosion generally does not significantly reduce the mechanical properties of the metal. But for the box-shaped metal structure (box-shaped beam, box-shaped outrigger, box-shaped arm, etc.) ACCIDENT.
 

Pore corrosion and intergranular corrosion are corrosions that occur on a localized scale in a metal body. These two kinds of corrosion will reduce the effective cross-sectional area of the component and make the parts prone to sudden fracture. These two kinds of corrosion behavior are more harmful.
 

Studies have shown that intergranular corrosion is mainly caused by the residual stress inside the material or the stress imposed by the outside, which leads to the combined action of stress, strain and corrosion on the material and leads to damage. This kind of corrosion leads to extremely serious consequences of damage and failure of the metal structure.
 

The corrosion mechanism of metal structure of hoisting machinery is mainly chemical corrosion and electrochemical corrosion.
 

Chemical corrosion refers to the destruction of materials caused by direct pure chemical corrosion between materials and non-conductive media, while electrochemical corrosion is the most common and important type of corrosion of metal materials through electrochemical reactions. Under normal circumstances, the steel structure of hoisting machinery generally generates rust on the surface. But in the case of high temperature, the steel structure is easy to form oxide scale. In addition, steel is prone to react with gas at high temperature, and the gas generated escapes from the surface of the steel, and a decarburization layer is formed on the surface of the steel structure, which affects the performance of the lifting machinery.
 

In a harsh environment, it is easy to meet the three conditions necessary for electrochemical corrosion: the existence of a potential difference, an electrolyte solution, and contact. As long as the above three conditions are met at the same time, electrochemical corrosion can be formed, thereby destroying the metal structure of the lifting machinery.

Analysis of protection methods for metal structures of hoisting machinery

At present, the anti-corrosion methods of crane metal structures mainly include metal structure surface coating method and sacrificial anode protection method.
 

The sacrificial anode protection method usually adds fillers (such as zinc) that are more active than steel to the paint. Through the electrochemical principle, the sacrificial anode can protect the metal structure from corrosion. Although this method does not require an external power source, it is harmful to corrosion. The quality of the coating is extremely high, and non-ferrous metals will be consumed at the same time, and the anode needs to be replaced regularly, which is costly and complicated.
 

Surface coating methods are mainly divided into two types: corrosion-resistant metal covering method and non-metal covering method. Corrosion-resistant metal covering methods generally include electroplating method, cladding method, hot-dip method, permeation plating method, spraying method, etc. The process requirements of these methods High, high cost, suitable for small workpieces, but for large-scale lifting machinery that has been put into practical use, it is beyond the reach of the above methods, so it has not been widely used.
 

The non-metal covering method is to apply basic anti-rust paint on the metal surface. This method is low in cost and easy to operate, and is widely used in crane anti-corrosion. However, a single paint film cannot completely prevent moisture and oxygen from penetrating to the metal surface, which may cause aging and damage. In addition, the gap in the process of painting may also cause the paint to not play a good long-term effective protection.