​Spring blackening process
Alkaline chemical oxidation treatment to blacken is to put the processed qualified spring into a solution containing concentrated alkali and heat it to obtain a thin and dense oxide film on the surface of the spring, which has an anti-corrosion effect.

In the heated solution of the spring, iron ions (ferrous compounds) are produced due to alkali corrosion on the surface of the spring. The addition of oxidizing agent-sodium nitrite in the alkali can change the oxidation process and form a dense oxide film on the surface of the spring (4 Ferric oxide). This oxide film is mainly composed of magnetic iron oxide, and the generation time of the oxide film is 30-60 minutes. If the time is extended, the thickness of the oxide film cannot be increased.

1. Process:

Degreasing—(removing copper)—pickling—cleaning—oxidation (or secondary oxidation)—cleaning—hot water cleaning—saponification—oil change in water-soaked membrane device—stored in storage.

2. Requirements for each process

(1) Degreasing

Chemically degreasing NaoH100～150g/L+Na2CO320-27g/L heated to boiling point, add a small amount of waste acid and iron in a rolling drum.

Use gasoline or diesel to wash the oil.

Use sandblasting or shot blasting to remove oil and rust.

The quenched and tempered spring can be used to remove oil and rust from a roller barrel.

(2) Remove copper

Chromic acid 250～300g/L + ammonium sulfate 80～100g/L, this process can be omitted when there is no copper.

Soak in water for 1 to 2 minutes, and then rinse in clean water.

(3) Pickling

Soak in 30% industrial hydrochloric acid for 1 to 2 minutes to remove oil and rust. The pickling time should not be too long.

(4) Clean, neutralize in a weak alkali tank after cleaning to prevent acid from being carried into the oxidation tank.

(5) Oxidation

Sodium hydroxide 650-700 g/liter + sodium nitrite 100-150 g/liter is heated to 140-144°C, kept for 30-60 minutes, NaOH:NaNO2=5-8:1.

Disc spring blackening treatment process
(6) Wash, rinse in running water after oxidation.

(7) Hot water cleaning, hot water 90～100℃, cleaning for 1～2 minutes.

(8) Saponification

Heating 10-20% industrial soap flakes or triethyl oleic acid soap at 50-60°C for 1 to 2 minutes, and the temperature should not be too high.

(9) Oiling, immersing MS-1 water film to replace rust preventive oil

(10) Storage