The role of various components in the plating solution

1. Zinc oxide
The content of zinc plays an important role in the performance of the plating solution and the quality of the coating. If the zinc content is too high, although the current efficiency is improved, the dispersion ability and deep plating ability are correspondingly reduced, and the coating on complex parts with sharp edges will be rough and have negative and positive surfaces; The content is low, the cathodic polarization increases, and the dispersion ability is good, but the deposition speed is slow. Usually, the hanging plating content is 10-12g/L, and the rolling plating content is 8-10g/L.
2. Sodium hydroxide
The main function is to synthesize stable zinc salts by complexing with zinc ions, and to enable the anode to dissolve normally and perform complexation and conductivity functions. But generally, the content should not be too high, as too high will cause the coating to be rough, showing blue-grey spots, and the passivation film will not be bright; It should not be too low, as it will make the zinc anode easy to passivate. It is necessary to contain an appropriate excess of sodium hydroxide to stabilize the plating solution. Regularly analyze the content of zinc and sodium hydroxide during production, and maintain a certain proportion of sodium hydroxide and zinc. Generally, the ratio of sodium hydroxide to zinc (mass ratio) should be controlled to be 10:1 for hanging plating; Roll plating control sodium hydroxide to zinc (mass ratio)=12:1.
3. Additives
In the past, triethanolamine (also known as trihydroxyethylamine, represented by TEA) was used as an auxiliary complexing agent in the old process. Hexamethylenetetramine (also known as H promoter) had a similar effect to triethanolamine, which could improve the dispersion ability of the plating solution, enhance the luster of the coating, and promote fine crystallization; Triethanolamine is a non conductive viscous liquid that increases the resistance of the plating solution, reduces the deposition rate, and deteriorates the bright layer of the coating when the content is too low. Brighteners include glycerol, gelatin, anisaldehyde, etc. Glycerol has a certain effect on improving brightness when combined with colloids in alkaline zinc plating, but compared with DE, DPE, and other additives used domestically, there is a certain gap in their application. Glycerin and other substances are rarely used.