Operation method of passivation treatment

According to the material of stainless steel and the severity of scale, it can be diluted with stock solution or water at the ratio of 1: 1 ~ 4 before use. Austenitic stainless steel with low ferrite, martensite and nickel content (such as 420, 430, 200, 20 1, 202, 300, 30 1, etc. ), and austenitic stainless steels with high nickel content (such as 304, 32 1, 3 16, etc. ) Generally, it is used at room temperature or heated to 50-60 degrees, and soaked for 3-20 minutes or longer (the specific time and temperature are determined by the user according to his own trial situation) until the surface dirt is completely removed and becomes uniform silvery white, forming a uniform and dense passivation film. After treatment, take it out and rinse it with clear water, preferably with alkaline water or lime water for neutralization.

Passivation treatment: the process of forming trivalent or hexavalent chromium layer on metal surface with chromate solution, which is called passivation, also called chromizing. It is mostly used to treat aluminum, magnesium and their alloys, and it can also form chromizing layer on steel, but it is rarely used alone, and it is often used in combination with phosphating to close the pores of phosphating layer and passivate exposed steel in phosphating layer, so as to inhibit the corrosion of residual phosphating accelerator and further increase the protective ability. Passivation is generally done with potassium dichromate solution (2-4g/L, sometimes with 1-2g phosphoric acid), soaked at 80-90 degrees Celsius for 2-3 minutes, and then washed with water.

In the process of etching stainless steel, we often encounter the yellowing of products, so passivation process is needed here to deal with it.

Composition and working conditions of 1) primary passivation solution

Composition and conditions: Bleaching after color passivation The composition was bleached after conditional color passivation.

Concentration and temperature of liquid and temperature

Chromic acid 250 ~ 300 g/L, sulfuric acid10 ~ 20 ml/L, 24 ~ 30 ml/L.

30~40ml/l15 ~ 20ml/l temperature 30 ~ 40 degrees room temperature.

2) Composition and working conditions of secondary printing solution: If nitrilotriacetic acid-zinc ammonium chloride is used for secondary passivation, the passivation film will be uniform in color, bright in color, fine in film, good in adhesion between film and galvanized layer, and better in corrosion resistance than primary passivation.

Composition and conditions of secondary passivation solution: tank A and tank B.

The mass concentration of chromic anhydride/g L- 1 1 70 ~ 200 40 ~ 50.

Sulfuric acid volume fraction/ml. L- 1 6~7 2

Nitric acid volume fraction/ml. L- 1 7~8 5~6

The mass concentration of ferrous sulfate/g L- 1 8~ 10 6~7.

Zinc powder mass concentration/g L- 1 1~2 6~8

Room temperature room temperature room temperature

Time/sec 20~40 20~30

After passivation in tank A, it is directly put into tank B without cleaning, and the passivation solution in tank B is sometimes diluted for use.