A dense protective film is formed on the surface of the spring, which usually adopts oxidation treatment and phosphating treatment. Phosphating treatment places the spring in a phosphate solution containing manganese, iron, and zinc to form a layer insoluble in water on the metal surface The method of phosphate film is called phosphating.
The appearance of the phosphating film is dark gray, gray or black gray, without luster. The thickness of the phosphating film is generally 5~20μm. The phosphating film is relatively stable under general atmospheric conditions, and its corrosion resistance is 6~ 24 times.
Phosphating film has a microscopic pore structure and has good adsorption capacity for paints and oils. Therefore, phosphating is often used in conjunction with coating methods such as painting. After phosphating, dichromate filling, oil immersion or coating Lacquer can further improve its corrosion resistance.
phosphating film is relatively stable in animal oil, vegetable oil, mineral oil, and also relatively stable in some organic solutions (such as benzene, toluene).
The phosphating film can withstand high temperatures of 400~500°C. Therefore, some springs that work at high temperatures, such as the springs of the projectile launch part, are often phosphated.
It is best to use sandblasting before phosphating the spring. After sandblasting, it should not be left for too long, and phosphating should be carried out immediately. If there is no sandblasting equipment, chemical degreasing and pickling methods can also be used to remove oil stains.
The spring produces a large amount of hydrogen during the phosphating process, so the spring after phosphating has hydrogen embrittlement. For the spring of the key part, it should be dehydrogenated after phosphating.