Hot Dip Plating Process

The so-called hot dip plating is to dip a base metal in the molten state of another low melting point metal, forming a metal protective film on its surface.

According to the different pretreatment methods of hot dip plating, the process can be divided into solvent method and protective gas method:

Solvent hot dip plating

This is the most commonly used hot-dip plating method. Before hot-dip plating, a coating aid is applied to the clean metal surface to prevent oxidation of the steel.

After dipping into the bath, the coating can be decomposed rapidly, and play a role of removing the oxide on the surface of the base metal, reducing the surface tension of the molten metal, so as to improve the quality of the coating.

The basic technological process of solvent method is divided into four basic technological stages: surface treatment before plating, assisted plating, hot dip plating and post plating. The process is as follows: alkaline washing of pre-plating parts - acid washing - water washing - hydrochloric acid treatment - water washing - flux treatment - drying - hot dip plating - post plating - products. Solvent treatment is an important part of the process, which is the key step to improve the quality of coating and prevent leakage.

Its functions are as follows:

(1) Can remove the pre-plated parts after pickling in the air and oxidized to generate a small amount of oxide, improve the adhesion of the coating to the matrix material;

(2) Remove iron salts not completely pickled off on the surface of pre-plated parts;

(3) remove oxides from the surface of the molten metal;

(4) Reduce the surface tension of the molten metal surface, and promote the surface of iron to be wet by the molten metal.

Solvent method is intermittent operation, plating various shapes and different sizes of iron and steel parts, can also make each process line linkage, plating coated coils of wire and so on.

Protective atmosphere reduction hot dip plating (typical production process is Sendzimir method), the surface pretreatment of steel in Sendzimir method is completed in an oxidation furnace and a reduction furnace in sequence.

In the reduction furnace, the oxide on the steel surface is reduced by hydrogen by heating with high temperature radiation. After proper cooling, the steel is introduced into the leaching solution.

The main process is as follows:

(1) the base material is sent to the heating furnace of the oxidation atmosphere, at 400~500℃ to carbonize the oil and dirt on the surface of the steel, or into the form of easy to remove in the following steps;

(2) The steel is sent to the reducing furnace, and the oxide remaining on the surface of the steel is reduced at 800~850℃;

(3) Under the protection of reducing atmosphere, the treated steel is directly sent to the molten dipping solution of aluminum or aluminum alloy for plating.