How to carry out blackening and phosphating quality inspection

Appearance inspection: silicon-containing spring posts are reddish brown, and other spring steels are black. The oxide film should be uniform and dense, without spots, flowers on the surface or red and dark deposits attached. Corrosion resistance inspection: wash the surface of the spring with alcohol or gasoline and dry it, soak it in a 2% copper sulfate solution for 30s, and wash it in water after taking it out. There should be no red spots on the surface.
The appearance of the phosphating film should be uniform, without blooming, and the surface should be gray or dark red. There are two methods for checking the corrosion resistance.

(1) The composition of the test solution of the copper sulfate solution spot method is as follows:

0.5N CuSO4 solution 40ml

10% NaCl solution 20ml

0.1 HCL solution 0.8ml

After the three solutions are mixed, drop them on the surface of the spring cleaned with alcohol, and record the time when the red spots appear. The normal phosphating film can be maintained for at least 1 min.

(2) Salt water soaking method: Soak the phosphated spring in a 3% salt solution for 15 minutes, take it out and rinse it with water, and place it in the air to dry for 30 minutes. If there is no yellow rust, it is qualified.