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U bolt:different types of surface treatment


According to the method of galvanizing and the different requirements of customers, the more commonly used galvanizing processes for U-shaped bolts include electrogalvanizing, powder galvanizing, mechanical galvanizing, and hot-dip galvanizing. Let's analyze each method below. Pros and cons

1. Electro-galvanized

Electro-galvanizing is a very common surface treatment method and process technology in the production of fastener products. The electro-galvanizing layer is a typical anodic coating, which is mainly used to improve the corrosion resistance of the substrate. Because of its thin coating thickness, Mainly used for surface corrosion protection under general environmental conditions.

After chromate passivation treatment, its anti-corrosion performance is greatly improved, and the excellent electro-galvanized layer can be used for neutral outdoor protection. However, the corrosion resistance is relatively poor in the harsh industrial atmosphere and coastal climate.

The surface treatment method and process technology of electro-galvanizing have low cost, stable and reliable process, and convenient to use, but hydrogen embrittlement is very easy to occur. Therefore, dehydrogenation treatment should be carried out in time after electro-galvanization. In addition, the acid and alkali resistance is poor, and the anti-corrosion time is short. Process environmental protection is low.

2. Powder sherardizing

Powder sherardizing uses zinc dipping agent as the source of zinc, and generates zinc by heating, and the inter-diffusion of iron atoms results in the surface treatment process of zinc dipping layer (zinc-iron alloy layer) on the surface of steel. The main components of powder sherardizing are Pure zinc powder, adding appropriate amount of filler materials such as alumina, refractory clay and ammonium chloride.

The most prominent feature of powder sherardizing is not an attached coating, but the base metal and the infiltrating layer form an organic whole, so the combination is very strong. The hardness and corrosion resistance of the powder sherardizing layer are far better than the electrogalvanized layer. The powder sherardizing process is to bury the surface-treated workpiece in a sealed container filled with powder sherardizer, heat it to below the melting point of zinc, keep it for a certain period of time, and then cool it to room temperature with the furnace.

The most prominent feature of powder sherardizing is uniform infiltration layer, no ammonia embrittlement, and almost no deformation. It is especially suitable for the surface anti-corrosion treatment process of nuts, bolts and other fasteners and small hardware products, workpieces with complex shapes and powder metallurgy products.

3. Mechanical galvanizing

Mechanical galvanizing is the use of an impact medium (such as glass balls) in the presence of zinc powder, dispersant, accelerator, liquid medium (usually water) and other substances to impact the surface of steel parts, and form on the surface of the parts. Surface treatment process for galvanized layer.

The mechanical galvanizing layer is a kind of anti-corrosion coating formed by a process completely different from electrogalvanizing and hot-dip galvanizing. Process characteristics: production operation under room temperature conditions, through the rotation of the plating cylinder of the loaded parts, the impact medium in the cylinder follows The rotation of the drum and the collision of the parts produce mechanical impact force, and the zinc powder is deposited on the surface of the part to form a coating with the basic physical characteristics of metallic zinc. Process characteristics: the galvanizing process of the mechanical galvanizing process is effective for high-strength steel Does not produce hydrogen embrittlement hazards, process defects: the thickness of the zinc layer is uneven; the zinc layer is not as smooth and bright as the electroplated layer.

4. Hot dip galvanizing

Hot-dip galvanizing is the process and method of taking pre-treated steel parts into molten zinc to form zinc and (or) zinc-iron alloy coatings on the surface to obtain a metal coating. Hot-dip galvanizing applications The surface is extremely wide, such as hot-dip galvanized highway traffic barriers (highway corrugated beam steel guardrail fastener connection pair), pipelines, and hot-dip galvanized fasteners and other fasteners that are widely used in power transmission.

The service life of hot-dip galvanizing work is not only related to the process itself, but also directly related to the adhesion of the galvanized layer. The hot-dip galvanizing layer has a good coverage and protection ability, and its ability to resist atmospheric corrosion is better than that of electro-galvanized.

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