Corrosion Causes And Protective Measures Of Steel Fasteners

Fastener connection is a common part of aircraft, and also an important connecting part of aircraft, which can also be called an aircraft navigation symbol. After the disassembly of aircraft fasteners, corrosion products can penetrate into the fastener holes and cause corrosion of the hole walls and fasteners. Since steel fastener areas that are often disassembled are prone to corrosion, what are the main causes of corrosion of steel fasteners? What would happen if the steel fasteners were protected against corrosion?

Xinchi Fasteners as a professional fastener supplier, based on years of understanding of the fastener industry, would be glad to share the relevant knowledge with you.

Analysis of main causes of corrosion of steel fasteners

1) The corrosion resistance of the surface treatment layer of fasteners is poor.

It was found that corrosion occurred mainly in steel fasteners with a diameter of 8 mm or less. This part of the fastener bolts and gaskets in the domestic mainly use galvanized surface treatment, galvanized layer in the Marine environment does not only have poor corrosion resistance but also easy to falls off after disassembly.

2) The fastener hole wall is not protected.

In aircraft manufacturing, if the fastener hole wall is not specially protected, the corrosion of the substrate will be directly caused after the corrosive medium is immersed.

3) Failure of the surface paint layer.

After the disassembly of the fastening connection structure, the coating at the fastener hole and the joint surface is broken. If no effective protective measures are taken during the reinstallation, the corrosive medium can directly penetrate into the fastener hole and the joint surface, leading to the corrosion of the fastener and the hole wall and expanding from the tight firmware hole to the body structure.

Therefore, for the corrosion protection of the steel fastener connection area which is often disassembled, the work should be carried out from three aspects: the improvement of fastener surface treatment, the protection of the fastener hole wall, and the improvement of the assembly process.

Corrosion protection measures for steel fasteners

Based on the analysis of the corrosion causes of steel fasteners which are often disassembled and assembled, and referring to the corrosion protection design and repair experience of aircraft at home and abroad, the corrosion protection measures are formulated.

1) Improve the surface treatment process of fasteners.

According to the test results, the corrosion resistance of cadmium plating in the marine environment is obviously better than that of the galvanizing process, so the washers and bolts originally used in galvanizing passivation process are changed to cadmium plating passivation process for surface treatment.

2) Fastener hole wall surface protection.

For the fastener hole wall of aluminum alloy structure without surface treatment, alodine is used for surface treatment, and then coated with a layer of anti-corrosion primer; Apply a phosphating primer to steel structural fastener hole walls that have not been surface treated.

3) Wet assembly of fasteners.

After the primer of the fastener hole wall is cured, the fastener is wetly and assembled with grease. Using grease assembly can not only play a sealing role, preventing the medium from leaking into the gap, and the fastener disassembly is convenient, which is convenient for field construction.

4) Spray corrosion inhibitor.

After the fasteners are assembled, a layer of soft film water displacement corrosion inhibitor is sprayed on the surface of the fastening connection area. Corrosion inhibitor is an important means of corrosion prevention and control. With good permeability and water displacement, it can quickly penetrate into the inside of the cracks of aircraft structures, displace the water inside the cracks and on the metal surface to the outside, and isolate the metal from the water. At the same time, a protective film is deposited on the metal surface, which can effectively delay the corrosion of metal materials.

Conclusion:

1) Comprehensive protection measures for surface protection and assembly seal can effectively solve the corrosion problem of steel fastening connection areas often disassembled and assembled, which can be popularized and applied in aircraft manufacturing and maintenance.

2) Protective measures such as painting the fastener hole wall and spraying corrosion inhibitor after assembly can be used for reference in the corrosion protection design and repair of other connecting structures.

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