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Surface treatment of fasteners

Fasteners, as connecting and fixing components, are widely used in various fields such as automobiles, machinery, electronics, etc. During use, fasteners need to withstand various environmental and mechanical forces, so surface treatment technology is particularly important. Through surface treatment, the corrosion resistance, wear resistance, aesthetics, and other properties of fasteners can be improved, extending their service life. This article will provide a detailed introduction to several common surface treatment methods for fasteners, such as galvanizing, phosphating, blackening, chrome plating, and Dacromet, and explore how to choose the most suitable surface treatment method in different application scenarios.

Galvanized

Galvanizing is a common anti-corrosion treatment method, which can effectively prevent corrosion by forming a layer of zinc on the surface of fasteners. There are various ways of galvanizing, including hot-dip galvanizing, electroplating galvanizing, etc.

Hot dip galvanizing is the process of immersing fasteners in molten zinc to form a zinc and/or zinc iron alloy coating. This type of coating has a relatively thick thickness and is not easy to control, but it has good corrosion resistance and is commonly used for fasteners in outdoor and harsh environments, such as steel pipe towers, angle steel towers, etc. The long service life of hot-dip galvanized workpieces is directly related to the adhesion of the galvanized layer. In addition, hot-dip galvanizing process also has the advantages of high reliability, comprehensive protection, low processing cost, and time-saving and labor-saving.

Electrogalvanizing is the process of depositing zinc ions on the surface of fasteners through electric current. Electrogalvanizing has low cost, stable and reliable process, and is convenient to use, but its anti-corrosion performance is average and it is prone to hydrogen embrittlement. Therefore, hydrogen removal treatment should be carried out promptly after galvanizing.

Phosphating

Phosphating is a chemical reaction that forms a phosphate chemical conversion film, also known as a phosphating film, on the surface of fasteners through chemical and electrochemical reactions. Phosphating film has the functions of wear resistance and prevention of electrochemical corrosion, and is a commonly used method for surface treatment of fasteners.

Phosphating is divided into zinc based phosphating and manganese based phosphating. Zinc based phosphating has better lubrication performance, while manganese based phosphating has stronger corrosion resistance and wear resistance. Phosphating is suitable for the connection of some important components, such as engine connecting rod bolts, nuts, etc. The torque preload consistency of the phosphated fasteners is excellent, ensuring that the expected tightening requirements are met during assembly. In addition, the use of phosphating for high-strength bolts can also avoid hydrogen embrittlement problems.

Blackening

Blackening, also known as boiling black or bluing, is a common method of chemical surface treatment. By immersing the workpiece in a highly oxidizing chemical solution, a beautiful, dense, and rust resistant black iron oxide film is formed on the surface.

The blackening process has the advantages of low cost and easy operation, but its corrosion resistance is generally average. The consistency between torque and preload force of fasteners after blackening is poor. If it needs to be improved, grease can be applied to the internal threads during assembly before screwing. Blackening treatment is commonly used for fasteners in high cleanliness and sealed environments such as engines and transmissions.

Chrome plating

Chromium plating is a common surface treatment method for fasteners. By coating a layer of chromium on the surface of the fastener, its glossiness and aesthetics can be effectively improved, while also enhancing its corrosion resistance. Fasteners treated with chrome plating can maintain good performance in humid and corrosive environments, making them particularly suitable for outdoor and harsh environments.

Chromium plating has the advantages of high hardness, good wear resistance, and strong corrosion resistance, but the cost is relatively high. In addition, hydrogen embrittlement is also prone to occur during the chrome plating process, and dehydrogenation treatment measures need to be taken. Therefore, chrome plating is commonly used for fasteners that require high aesthetic and corrosion resistance.

dacromet 

Dakro is a new type of anti-corrosion coating mainly composed of zinc powder, aluminum powder, chromic acid, and deionized water. Dakro technology has become the preferred solution for surface treatment of high-strength fasteners due to its excellent corrosion resistance, hydrogen free brittleness, high heat resistance, good adhesion and recoating performance.

The anti-corrosion performance of fasteners treated with Dacromet far exceeds traditional galvanizing process, and salt spray testing shows that its performance can reach more than 20 times that of galvanizing. In addition, Dacromet also has advantages such as hydrogen free brittleness, high heat resistance, and good permeability. However, the surface hardness of the Dacromet coating is not high, and its wear resistance is relatively poor; The single color limits its application in personalized needs; Poor conductivity, not suitable for parts used for conductive connections.

Dakro technology, due to its excellent anti-corrosion performance, was first widely used in fields with high anti-corrosion requirements such as military equipment. In recent years, with the continuous development of technology, Dacromet has gradually been widely used in the civilian field.

conclusion

When choosing a surface treatment method for fasteners, multiple factors need to be considered comprehensively. Firstly, it is necessary to consider the usage environment and working conditions of the fasteners to determine the required corrosion resistance and wear resistance requirements. Secondly, the aesthetic requirements of fasteners should be considered to meet the overall appearance and quality requirements of the product. Finally, it is necessary to consider cost factors and choose the most cost-effective surface treatment method.

Galvanized fasteners are suitable for outdoor and harsh environments; Phosphating is suitable for connecting some important components; Blackening is commonly used for fasteners in high cleanliness and sealed environments; Chromium plating is suitable for fasteners with high requirements for aesthetics and corrosion resistance; Dacromet is suitable for high-strength fasteners with high anti-corrosion requirements. In practical applications, a balance should be made between specific needs and cost considerations to achieve the best surface treatment effect.