The fastener connection is a common part on the aircraft, and it is also an important connecting part of the aircraft, and it can also be called the navigation mark of the aircraft. After the aircraft fasteners are disassembled, corrosion products can penetrate into the holes of the fasteners, causing corrosion of the hole walls and fasteners. The area of steel fasteners that are often disassembled and assembled is extremely prone to corrosion. What are the main reasons for the corrosion of steel fasteners? What if anti-corrosion protection measures are taken for steel fasteners?
1. Analysis of main reasons for corrosion of steel fasteners
Figure 1 Corrosion of fasteners after disassembly
1) The surface treatment layer of the fastener has poor corrosion resistance. After inspection, it was found that corrosion occurred mainly on steel fasteners with a diameter of 8 mm or less. The bolts and gaskets of this part of fasteners are mainly galvanized for surface treatment in China. The galvanized layer not only has poor corrosion resistance in marine environments, but also tends to fall off after disassembly and assembly.
2) The walls of the fastener holes are not protected. In aircraft manufacturing, if the fastener hole wall is not protected by special surface protection, the corrosive medium will directly cause the corrosion of the substrate.
3) The surface paint layer fails. After the fastening connection structure is disassembled, the coating at the fastener hole and the joint surface breaks. If effective supplementary protective measures are not taken when reinstalling, the corrosive medium can directly penetrate into the fastener hole and the joint surface, resulting in The fasteners and hole walls are corroded, and expand from the fastener holes to the body structure.
Therefore, for the corrosion protection of the connection area of steel fasteners that are often disassembled, work should be carried out from three aspects: the improvement of the surface treatment of the fasteners, the protection of the hole walls of the fasteners, and the improvement of the assembly process.
2. Corrosion protection measures for steel fasteners
Based on the analysis of the regional corrosion causes of steel fasteners that are often disassembled and assembled, and referring to the experience of aircraft corrosion protection design and repair at home and abroad, a corrosion protection measure plan is formulated.
1) Improve the surface treatment process of fasteners. According to the test results, the corrosion resistance of cadmium plating is significantly better than that of galvanized process in marine environment, so the washers and bolts that used galvanized passivation process were changed to cadmium plated passivation process for surface treatment.
2) Surface protection of the fastener hole wall. For the hole wall of the aluminum alloy structure fastener without surface treatment, use Alodin for surface treatment, and then apply a layer of anti-corrosion primer; for the hole wall of the steel structure fastener without surface treatment, apply a layer of phosphorus Primer.
3) Wet assembly of fasteners. After the fastener hole wall primer has cured, the fasteners are wet-assembled with grease. Grease assembly can not only play a sealing role to prevent the medium from penetrating into the gap, but also the fasteners are easy to disassemble, 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 fastened connection area. Corrosion inhibitors are an important means of corrosion prevention and control. They have good permeability and water displacement, and can quickly penetrate into the gaps in the aircraft structure, displacing the moisture in the gaps and metal surfaces to the outside, and isolating the metal from the moisture. At the same time, a protective film is deposited on the metal surface to effectively delay the corrosion of metal materials.
in conclusion:
1) By taking comprehensive protective measures for surface protection and assembly sealing, it can effectively solve the corrosion problem of steel fastening connection areas that are often disassembled and assembled, and can be popularized and applied in aircraft manufacturing and maintenance.
2) Protective measures such as painting the walls of fastener holes and supplementary spraying of corrosion inhibitors after assembly can be used for reference in the corrosion protection design and repair of other connection structures.
