Although the electroplating tin plating solutions are different, the electroplating tin plating process flow is basically the same, which is divided into pre-treatment, electroplating tin plating, softening melting, passivation, and application of anti rust oil and other process stages.
pretreatment
Pre treatment generally includes two processes: alkali washing and acid washing, with the aim of removing organic oil and oxide film on the surface of low carbon steel to expose fresh steel surface and prepare for subsequent electroplating.
The widely used alkaline washing solution is generally a composite solution composed of NaOH, alkaline phosphate, silicate, and surfactant, which can effectively remove oil stains on the surface of strip steel.
For several different plating solution systems, sulfuric acid solution is basically used for chemical pickling, while the fluoroboric acid electroplating tin plating process uses hydrochloric acid solution. During pickling, cathodic anodic electrolysis treatment is used to remove the surface oxide film and activate the substrate.
Electrodeposition
The Florentine tin plating method uses main salts, with strict concentration ranges for both and. In addition, the plating solution must also contain free acids and additives, each of which plays a different role and has corresponding requirements for concentration control.
Soft melting
Soft melting refers to heating a steel plate above the melting point of tin (232 ℃), so that the melted tin coating eliminates micropores and appears glossy under the smoothing effect; Simultaneously, intermetallic compounds are generated between the tin plating layer and the iron substrate, further increasing the adhesion of the coating. According to the heating method, soft melting can be divided into resistance soft melting, induction soft melting, and resistance induction combined soft melting. [2]
Post processing
Including two process stages: passivation and oil coating treatment. Passivation treatment can increase the corrosion resistance, sulfur resistance, and painting performance of tinplate, and prevent the growth of tin oxides during storage and sulfide corrosion during tin plate canning. Passivation often uses sodium dichromate solution, and there are two treatment methods: chemical passivation and electrochemical passivation.