Methods for preventing discoloration of stamping parts after bright tin plating

Generally, when electroplating Ningbo stamping parts, the following treatment will be done to prevent discoloration after bright tin plating.
Before tin plating and drying of stamping parts, it is necessary to remove the film in 10% phosphoric acid solution, and then clean it with hot and cold water for many times, which is a very important step.
If not, it is easy to wash the tin plate on the surface of the tin plate by stirring the tin plate for three times. Finally, the workpiece is immersed in sodium phosphate diluent at about 50 ℃, and then it can be cleaned three times, and the copper substrate is pre plated.
Neutralization and passivation should be carried out after electroplating to neutralize the residual acid and form a protective film on the tin surface. In electroplating plant, the coating metal or other insoluble materials are used as anode, and the workpiece to be plated is used as cathode. The cation of coating metal is reduced to form coating on the surface of the workpiece to be plated. In order to eliminate the interference of other cations and make the coating uniform and firm, it is necessary to use the solution containing metal cations as plating solution to keep the concentration of metal cations unchanged. General alkaline phosphates are used for neutralization. After neutralization, it is washed into the passivation process. The passivation solution was dichromate at 6080 ℃ for 2 min, and an oxide film was formed on the surface of tin.
To prevent the tin coating from turning yellow, it is necessary to pay attention to poor cleaning after electroplating, excessive current density and high bath temperature.
The passivation of the coating is effective for discoloration, but it must be cleaned.
A protective film is formed on the surface of precision stamping parts by impregnating stearic acid solution.