Although tin electroplating solutions are different, the technological process of tin electroplating is basically the same, which can be divided into pretreatment, tin electroplating, soft melting, passivation and anti-rust oil coating. [1]

Before processing

The pretreatment generally consists of alkaline and pickling processes to remove the organic oil and oxide film from the surface of low carbon steel to expose the fresh steel surface for subsequent electroplating.

The widely used alkaline lotion is generally NaOH, alkaline phosphate and silicate as well as surfactant compound solution, which can effectively remove oil stains on the surface of strip steel.

Tin plating

For several different plating solution systems, the acid solution is basically sulfuric acid solution for chemical pickling, and fluoroboric acid type tin electroplating process using hydrochloric acid solution, pickling using cathode-anodic electrolysis treatment, in order to remove the surface of the oxide film, activation matrix.

electrodeposition

Flostein tin plating method used

Main salt, among them

and

There are strict ranges of concentrations. In addition, the plating solution must also contain free acids and additives, which play different roles and have corresponding requirements for concentration control.

Soft melting

Soft melting is to heat the steel plate to the melting point of tin (232℃) above, so that the molten tin coating in smooth action to eliminate the micro-hole, appear luster; At the same time, it is formed between tin plating layer and iron matrix

Intermetallic compound to further increase the coating adhesion. According to the heating method, the melting can be divided into resistance melting, induction melting and resistance-induction combined melting. [2]

post-processing

It includes two process sections, passivation and oil coating. The passivation treatment can increase the corrosion resistance, sulfur resistance and paint resistance of tin plate, and prevent the growth of tin oxide during storage and sulfide corrosion in tin plate tin making process. The passivation mainly USES sodium dichromate solution, and the treatment methods include chemical passivation and electrochemical passivation.