Spring blackening process

Alkaline chemical oxidation treatment for blackening refers to heating the processed qualified spring in a solution containing concentrated alkali to obtain a thin and dense oxide film on the surface of the spring, which has an anti-corrosion effect.

In a heated solution, the spring corrodes its surface with alkali, producing iron ions (ferrous compounds). Adding an oxidizing agent - sodium nitrite - to the alkali can alter the oxidation process and generate a dense oxide film (ferric oxide) on the surface of the spring. This type of oxide film is mainly composed of magnetic iron oxide, and the formation time of the oxide film is 30-60 minutes. If the time is extended further, the thickness of the oxide film cannot be increased.

1. Process:

Oil removal - (copper removal) - acid washing - cleaning - oxidation (or secondary oxidation) - cleaning - hot water cleaning - saponification - oil change of immersion membrane device - storage.

2. Requirements for each process

(1) Degreasing

1. Chemical degreasing NaoH100-150 g/L+Na2CO320-27 g/L, heat to boiling point, and add a small amount of waste acid and iron to the rolling drum

2. Wash the oil with gasoline or diesel.

3. Use sandblasting or shot blasting to remove oil and rust

4. Springs that have been quenched and tempered can be degreased and rusted using a rolling barrel

(2) Copper removal

When using 250-300 g/L chromic acid and 80-100 g/L ammonium sulfate without copper, this process can be omitted

Soak in water for 1-2 minutes, then rinse in clean water

(3) Pickling

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

(4) Clean and neutralize in a weak alkaline tank to prevent acid from entering the oxidation tank

(5) Oxidation

Sodium hydroxide 650-700 g/L+sodium nitrite 100-150 g/L, heat to 140-144 ℃, hold for 30-60 minutes NaOH: NaNO2=5-8:1

(6) Wash, oxidize and rinse in flowing clean water

(7) Hot water cleaning, hot water at 90-100 ℃, cleaning for 1-2 minutes

(8) Saponification

10-20% industrial soap or triethyloleic acid soap should be heated at 50-60 ℃ for 1-2 minutes, and the temperature should not be too high

(9) Oil and immerse in MS-1 water film to replace rust prevention oil

(10) Warehousing

Blackening process operating procedures

(1) After starting work every day, turn on the power to heat the tank liquid to the boiling point and remove the iron oxide (sediment) from the tank;

(2) After removing the sediment, add about 0.5kg of yellow blood salt (potassium ferrocyanide)

(3) Add a certain amount of sodium nitrite (in compliance with 5-8:1) according to the requirements of the blackening process technology;

(4) Measure the humidity of the blackened tank liquid with a thermometer to ensure a temperature of 140-144 ℃. If the temperature is too high, add water and control the heating power supply;

(5) Before turning black, the spring must be thoroughly pickled and cleaned, and the tension spring must be vertically framed for easy cleaning;

(6) When blackening occurs, the process and technical requirements must be strictly followed. The oil residue on the liquid surface should be promptly removed, and the tank liquid should be replenished in a timely manner;

(7) After blackening, the spring must be sprayed and washed with high-pressure water, and then cleaned with boiling water. The saponification temperature should be controlled between 50-60 ℃;

(8) After draining excess oil, the spring is framed and stored in the warehouse. The iron frame with the spring removed must be washed with high-pressure water before reuse;

(9) At the end of the workday, add a certain amount of sodium hydroxide (in compliance with 5-8:1) to the oxidation tank, turn off the power, clean and tidy the work site, and keep the site tidy.