Blackening process of spring

Blackening process of spring:
Alkaline chemical oxidation treatment blackening is to heat the qualified spring processed in concentrated alkali solution to obtain a thin and dense oxide film on the surface of spring, which has anti-corrosion effect
In the heated solution, the spring produces iron ions (ferrous compounds) due to the corrosion of alkali on the spring surface. The oxidation process can be changed by adding the oxidant sodium nitrite into the alkali, and a dense oxide film (ferric oxide) is formed on the spring surface. The oxide film is mainly composed of magnetic iron oxide, and the formation time of the oxide film is 30 ~ 60 minutes, The thickness of oxide film can not be increased
Process:
Deoiling – (copper removal) – acid pickling → cleaning → oxidation (or secondary oxidation) – → cleaning → hot water cleaning → saponification → oil change of immersion membrane unit → storage
Requirements of each process
Serial number, name, formula and technical requirements
Chemical deoiling naoh100 ~ 150g / L + na2co320-27g / L, heat to boiling point, add a small amount of waste acid and ferric chloride into the barrel
2. Wash the oil with gasoline or diesel oil
3. Remove oil and rust by sandblasting or shot peening
4. The quenched and tempered spring can be used to remove oil and rust
2. Chromic acid 250 ~ 300 g / L + ammonium sulfate 80 ~ 100 g / L for copper removal, this process can be omitted without copper
Soak in water for 1-2 minutes, then wash in clean water
Three acid washing with 30% industrial hydrochloric acid for 1 ~ 2 minutes to remove oil and rust, pickling time should not be too long
IV. neutralize in weak alkali tank after cleaning to prevent acid from entering oxidation tank
Sodium hydroxide pentoxide 650 ~ 700 g / L + sodium nitrite 100 ~ 150 g / L, heated to 140 ~ 144 ℃, holding for 30 ~ 60 minutes, NaOH: NaNO2 = 5 ~ 8:1
6. Wash in flowing water after oxidation
7. Hot water cleaning, hot water 90 ~ 100 ℃, cleaning for 1 ~ 2 minutes
8 saponified 10 ~ 20% industrial soap or triethyloleic acid soap heated at 50 ~ 60 ℃ for 1 ~ 2 minutes should not be too high
Replacing antirust oil with MS-1 water film immersed in oil
11. Warehousing
(2) Operation procedures for blackening process
(I) after going to work every day, turn on the power supply to heat the bath liquid to boiling point, and remove the iron oxide (sediment) in the tank;
(II) remove the sediment and add about 0.5kg of yellow blood salt (potassium ferrocyanide);
(III) add a certain amount of sodium nitrite (5 ~ 8:1) according to the technical requirements of blackening process;
(IV) measure the humidity of blackening bath liquid with thermometer to ensure the temperature of bath liquid is 140 ~ 144 ℃. If the temperature is too high, add water and control the heating power supply;
(V) before blackening, the spring must be fully pickled and cleaned, and the tension spring must be vertically framed for easy cleaning;
(VI) in case of blackening, the process and technical requirements must be strictly implemented, the oil residue on the liquid level should be removed in time, and the tank liquid should be replenished in time;
(VII) after blackening, the spring must be sprayed with high pressure water and cleaned with boiling water. The saponification temperature should be controlled at 50 ~ 60 ℃;
(VIII) after excessive oil is drained, the spring is framed and put into storage. The iron frame with spring removed must be sprayed with high-pressure water and reused
(IX) when off duty, add a certain amount of sodium hydroxide (5 ~ 8:1) into the oxidation tank, turn off the power supply, clean and clean the working site, and keep the site clean and tidy;
Precautions for blackening process operation:
(I) if yellow frosting is found on the oxidized workpiece, it indicates that the bath liquid temperature is too high and the water content is too low
(II) the oxidized workpieces are not black and gray, but the bath solution temperature is too low or the sodium nitrite is deficient
(III) when the boiling point of oxidation tank is below 140 ℃, sodium hydroxide should be added
(IV) the saponification tank should be supplemented with soap or triethyloleic 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 inspection of blackening quality of the workpiece should be carried out before the oiling process of the spring. If copper does not precipitate after 30 seconds immersion in 2% copper sulfate solution, it is qualified
Drop test of 3% copper sulfate. The corrosion test of copper sulfate or 2% copper sulfate was carried out on the workpiece. The workpiece was completely immersed in the copper sulfate solution, and the oxidation film did not change color after 30 seconds. Both the spot test and the corrosion test were conducted before the workpiece was oiled. The oil stain should be removed with alcohol before the finished product sampling inspection. The blackened and oxidized workpiece will not rust within one year after normal storage