Analysis Of Multi-plating Technology On The Surface Of Drill Bolt

With the leap-forward development of various mechanical equipment, in the process of processing shaped parts, some parts of the drilling bolt technology require two or more surface treatments in different parts of the same part due to functional requirements.

Because the surface treatment of this special-shaped part involves multiple different plating species, the processing steps are complicated, difficult, and quality problems are prone to occur. The main problem to be solved during processing is how to avoid the rework caused by the destruction of the plating layer of the previous process during the next process. Therefore, in order to process multiple surface treatments on the same part, we must first determine the processing order according to the performance of the coating and the difficulty of protection, and then carefully design the insulation protection tooling and loading tooling of each process.

Processing special-shaped parts-drilling bolts must solve the conflict between the various plating on the surface

Since this part needs three surface treatments of chrome plating, cadmium plating and bluish plating, in order to avoid destroying the previous plating layer when processing the next plating type, it is necessary to combine the characteristics of each plating layer and the processing difficulties, and test the protection as a whole during processing The degree of difficulty in order to arrange the processing order of the three plating species reasonably.

1.1 Chrome plating

Chromium is a silver-white metal with a slight sky blue. The chromium layer can be quickly passivated in the atmosphere, forming a dense oxide layer on its surface: it can resist many chemical media corrosion, has excellent corrosion resistance in various environments, and high hardness (Vickers hardness can reach 800 ~ 1100HV) and good wear resistance. Therefore, chromium is widely used as a protective decorative coating and a functional raw coating.

1.2 Cadmium plating

Cadmium is a gray shiny soft metal with good plasticity and is easy to forge and roll. The pot layer is resistant to alkali and nitric acid, and dissolves slowly in dilute sulfuric acid and dilute hydrochloric acid. In the ocean and high-temperature atmospheric environment, the cadmium coating is an anodic coating, which has good corrosion resistance, especially the passivated cadmium coating, which can withstand the salt spray test for 360 h. Protective layer.

1.3 Bluish

Blueing is to heat steel in air or directly immerse it in a concentrated oxidizing solution to form an extremely thin oxide film on its surface. The development of steel parts can be carried out in the molten salt of sodium nitrite and sodium nitrate, or in hot air with high temperature and hot steam above 500% C. The composition of the solution, the processing temperature and the processing time of the development monitoring vary according to the material of the parts. The composition of the bluish film is magnetic iron oxide, the thickness is 0.5 ~ 1.5um, and the color is related to the material composition and process conditions. The blueing film alone has poor corrosion resistance, but after saponification, sealing or oil immersion, the corrosion resistance and friction resistance are improved.

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