What is the blackening treatment of metal surface?

The surface treatment of steel parts generally includes alkaline oxidation and acidic oxidation. Acid oxidation is also called "bluing". The purpose is to form an oxide film on the metal surface to prevent the metal surface from being corroded. Acid oxidation, also known as "phosphating treatment" (adopted by most military enterprises in the world), has better wear resistance and corrosion resistance than bluing. The oxide film formed on the surface of steel products after "bluing" treatment is mainly composed of ferroferric oxide. Black, blue or dark black.

First, alkaline oxidation of "blue" liquid medicine

1. Formula (available in chemical stores):?

Sodium nitrate 50 ~ 100g, sodium hydroxide 600 ~ 700g?

Sodium nitrite 100 ~ 200g water 1000g?

2. Preparation method: after weighing according to the formula, the ingredients are added in turn under the condition of stirring, dissolved and evenly mixed. I use an abandoned iron drum.

3. Process:

(1) The metal surface must be cleaned, dried and degreased before it can be treated as "hair basket". It is suggested to brush with washing powder water, and then soak with 1: 100 dilute hydrochloric acid 1-5 minutes to remove oil and impurities.

(2) Put the parts to be processed into an iron drum and "cook" with the solution for about 1 hour.

(3) After the metal turns blue, it is best to rinse it with hot soapy water for a few minutes, and then rinse it with cold water. Then, rinse it with hot water and blow it. Finally, the surface is coated with engine oil for sealing protection.

Second, the acid oxidation method "phosphating treatment" liquid medicine

1. Formula (available in chemical stores):?

Phosphate 3 ~ 10g, calcium nitrate 80 ~ 10g?

Manganese peroxide 10 ~ 15g water 1000g?

2. The preparation method and process are the same as alkaline bluing.