Talking about the four types of hot-dip galvanized fasteners

The first type, electro-galvanized

Electro-galvanization is the most common surface treatment method and process technology in the manufacture of fastener products.

The electro-galvanized layer is a typical anodic coating, mainly used to improve the corrosion resistance of the substrate. Because of its thin coating thickness, it is mainly used for surface anti-corrosion protection under general environmental conditions.

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

Electro-galvanized surface treatment method and process technology, low cost, stable and reliable process, and convenient to use. However, hydrogen embrittlement is very easy to occur, so the hydrogen removal treatment should be carried out in time after electrogalvanization. In addition, it has poor acid and alkali resistance, short anti-corrosion time, and low process environmental protection.

The second type, powder sherardizing (Guide: Four major inspections for special quality of fasteners)

Powder sherardizing uses a zinc immersion agent as the source of zinc, and generates zinc by heating, and the inter-diffusion of iron atoms results in a surface treatment process for the zinc-dipping layer (zinc-iron alloy layer) on the surface of the steel.

The main component of powder sherardizing is pure zinc powder, which is added with appropriate filler materials such as alumina, refractory clay and ammonium chloride.

The most prominent feature of powder sherardizing is not an external 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 sherardized layer is far better than that of 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 down 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.

The third type, mechanical galvanizing

Mechanical galvanizing is the use of impact media (such as glass balls) to impact the surface of steel parts in the presence of zinc powder, dispersants, accelerators, and liquid media (usually water). A surface treatment process is required to form a galvanized layer on the surface of the piece.

The mechanical galvanizing layer is a kind of anti-corrosion coating formed by a process completely different from electro-galvanizing 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 will collide with the parts with the rotation of the drum to generate mechanical impact force, and the zinc powder will collide and deposit on the surface of the part. , So as to form a coating with the basic physical characteristics of metallic zinc.

Process characteristics: The galvanizing process of the mechanical galvanizing process does not produce hydrogen embrittlement hazard to high-strength steel.

Process defect: The thickness of the zinc layer is uneven; the zinc layer is not as smooth and bright as the electroplated layer.

The fourth type, hot dip galvanizing

Hot-dip galvanizing is usually also called hot-dip galvanizing

Hot-dip galvanizing is a process and method that takes pre-processed steel parts into molten zinc to form zinc and (or) zinc-iron alloy coatings on their surfaces to obtain metal coatings.

The application of hot-dip galvanizing is extremely wide, such as hot-dip galvanized highway traffic barriers (highway corrugated beam steel guardrail fastener connection pair), pipelines and hot-dip galvanized fastenings that are widely used in power transmission Pieces and other fasteners, etc.

The service life of hot-dip galvanizing is not only related to the process itself, but also directly related to the adhesion of the galvanized layer.

The hot-dip galvanized layer has good coverage and protection ability, and its ability to resist atmospheric corrosion is better than electro-galvanized.

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