1. The spring is blackened
(1) Spring blackening process
Alkaline chemical oxidation treatment to blacken is to put the processed qualified spring into a concentrated alkali solution 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 the 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.
Degreasing——(Removing Copper)——→Pickling——→Cleaning——→Oxidation (or Secondary Oxidation)——→Cleaning——→Hot Water Cleaning——→Saponification——→Change Oil in Water Soaking Film Device ——→Warehousing.
Requirements for each process
No. Name Formula and Technical Requirements Remarks
1 Degreasing 1. Chemical degreasing NaoH100～150g/L+Na2CO320-27g/L heated to boiling point, add a small amount of waste acid and iron in the drum
2. Wash the oil with gasoline or diesel.
3. Use sandblasting or shot blasting to remove oil and rust
4. The quenched and tempered spring can be used to remove oil and rust from a rolling barrel
Second, for copper removal, 250～300 g/l of chromic acid + 80～100 g/l of ammonium sulfate can be omitted when there is no copper.
Soak in water for 1 to 2 minutes, then rinse in clean water
3. Pickling Use 30% industrial hydrochloric acid to soak for 1 to 2 minutes to remove oil and rust. The pickling time should not be too long
Four cleaning After cleaning, neutralize in the weak alkali tank to prevent acid from being carried into the oxidation tank
Five oxidation Sodium hydroxide 650～700 g/L + sodium nitrite 100～150 g/L, heating to 140～144℃, keeping for 30～60 minutes NaoH: NaNO2=5～8:1
Six cleaning, rinse in running water after oxidation
Seven hot water cleaning Hot water 90～100℃, cleaning for 1～2 minutes
8. Saponification 10～20% industrial soap flakes or triethyl oleic acid soap, heating at 50～60℃ for 1～2 minutes, the temperature should not be too high
Ten oiling, MS-1 water film replacement anti-rust oil
(2) Blackening process operating procedures
(Ⅰ) Turn on the power supply after work every day to heat the tank liquid to boiling point, and remove the iron oxide (precipitate) in the tank;
(Ⅱ) After removing the sediment, add about 0.5kg of yellow blood salt (potassium ferrocyanide);
(Ⅲ) Add a certain amount of sodium nitrite according to the technical requirements of the blackening process (in accordance with 5-8:1);
(Ⅳ) Use a thermometer to measure the humidity of the blackened bath liquid to ensure that the bath temperature is 140～144℃. If the temperature is too high, add water and control the heating power supply;
(Ⅴ) Before turning black, the spring must be fully pickled and cleaned, and the tension spring must be framed vertically for easy cleaning;
(VI) When it turns black, the technical requirements must be strictly implemented, the oil residue on the liquid level must be removed in time, and the tank liquid must be refilled in time;
(Ⅶ) After blackening, the spring must be spray-washed with high-pressure water and washed with boiling water, and the saponification temperature should be controlled at 50～60℃;
(Ⅷ) The spring is framed and put into storage after draining excess oil. The iron frame with the spring down must be sprayed with high-pressure water before being reused.
(Ⅸ) When leaving get off work, add a certain amount of sodium hydroxide (in accordance with 5-8:1) into the oxidation tank and turn off the power. Clean up and clean the work site to keep the site tidy;
Matters needing attention in the operation of blackening process
(I) If yellow frost is found on the oxidized workpiece, it indicates that the bath temperature is too high and the moisture is too little.
(Ⅱ) The oxidized workpiece is not black, but gray, because the bath temperature is too low or sodium nitrite is lacking.
(Ⅲ) Sodium hydroxide should be added if the boiling point of the oxidation tank is below 140℃.
(IV) The saponification tank should always be replenished with soap flakes or triethyl oleic acid soap to maintain a certain concentration.
(Ⅴ) The oxide film of silicon-containing steel is allowed to be brown or brown-black;
(Ⅵ) The self-checking of the quality of blackening of the workpiece should be carried out before the spring oiling process. The 2% copper sulfate solution immersion method for 30 seconds is qualified without copper precipitation.
3% copper sulfate spot test. Put a drop of copper sulfate or 2% copper sulfate on the workpiece for corrosion test. The workpiece is completely immersed in the copper sulfate solution. After 30 seconds, the oxide film does not change color by naked eye observation. Both the spot test and the erosion test are carried out before the workpiece is oiled, and the finished product should be sampled with wine to remove the oil stains. The blackened and oxidized workpiece will not rust within one year under normal storage.