Why is the screw / nut to decontinate? What is the black processing?

The surface of the steel parts is black and treated, and it is also known as blue. The principle is to rapidly oxidize the surface of the steel article to form a dense oxide film protective layer. Decorative treatment now commonly used methods have traditional alkaline heating and white, which is more late.

Normal temperature hanging black processing process, mainly completed by the following process steps:

Clean：
2. Sense: The workpiece must be completely immersed in the degrease liquid; the degreased concentration pH 12-14, the treatment time is 10-30 min, and each time 3-5 minutes is jitter, the liquid concentration is lower than pH12 to supplement the degreasing powder;
3. Wash;
4. Sour: Acid washing liquid concentration pH 2-4, treatment time 5-10 min;
5. Water washing;
6. Black: Pool concentration pH 2.5-3.5, treatment time 10-12min;
7. Wash;
8. Blow dry;
9. Oil.

The advantages of black treatment are:
1. Black security is not electrified, and 100% electricity is required to use electricity.
2. Improve the effectiveness: 1-2 minutes.
3. The black cost is low, the equipment is simple, the operation is convenient; the black time is strictly controlled.
4. Process adaptability: Solve the problem of ductile iron can't be black. Black in force and rust.