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Phosphating and Dacromet process of fasteners


Phosphating is a process of forming a phosphate chemical conversion film by chemical and electrochemical reactions. The formed phosphate conversion film is called a phosphate film. The thickness of the film is generally 10-15 microns, and the friction coefficient is about 0.05.

The main purpose of phosphating is: to provide protection to the base metal and prevent the metal from being corroded to a certain extent; for primer before painting to improve the adhesion and anti-corrosion ability of the paint film; to reduce friction in the metal cold processing Use for lubrication.

Phosphating process category:

According to different performances, it can be divided into: rust removal and phosphating process, wear-resistant film reduction lubricating phosphating process, and pre-paint phosphating process.

According to the phosphate coating system, it is divided into: zinc series, zinc calcium series, zinc manganese series, iron series, and amorphous iron series.

According to the treatment temperature, it can be divided into: normal temperature phosphating (no heating), low temperature phosphating (25-45℃), medium temperature phosphating (60-70℃), high temperature phosphating (>80℃)

crafting process:

Degreasing and rust removal → water washing → surface adjustment activation-phosphating → water washing-chromate treatment-drying-grease coating

Phosphating applications in the industrial field:


Dacromet is the transliteration and abbreviation of DACROMET, abbreviated as Dacromet, Dacromet, and Dirkron. Named as zinc-chromium coating in China, it is a new type of anti-corrosion coating with zinc powder, aluminum powder, chromic acid and deionized water as the main components. It has extremely high corrosion resistance, a clean production process and a high-tech that is in the embryonic stage in China, and is known as a new process with epoch-making significance in the international surface treatment industry. This process can replace iron and steel electroplating zinc, cadmium, zinc-based alloy, hot-dip galvanizing, hot-spraying zinc, and mechanical galvanizing.

Process flow:

Organic solvent degreasing-rust removal / shot blasting-dip coating / spraying-drying-pre-coating-sintering-cooling-inspection-packaging


Compared with the traditional electroplating process, Dacromet is a kind of "green" electroplating. Its advantages are as follows:

1) Super corrosion resistance

2) No hydrogen embrittlement

3) High heat resistance

4) Good adhesion and recoating performance

5) Good permeability

6) No pollution and pollution


1) Dacromet contains chromium ions which are harmful to the environment and human body, especially hexavalent chromium ions have carcinogenic effects.

2) Dacromet's sintering temperature is higher, the time is longer, and the energy consumption is large.

3) Dacromet's surface hardness is not high, wear resistance is not good, and Dacromet coated products are not suitable for contact and connection with copper, magnesium, nickel and stainless steel parts, because they will produce contact corrosion. Affect the surface quality and corrosion resistance of the product.

4) The surface color of Dacromet coating is single, only silver white and silver gray, which is not suitable for the needs of individualized automobile development.

5) The conductivity of Dacromet coating is not very good, so it is not suitable for conductive connection parts, such as electrical grounding bolts.


Blackening is a common method of chemical surface treatment. The principle is to produce an oxide film (ferric oxide) with a thickness of 0.6 to 0.8 microns on the metal surface to isolate the air and achieve the purpose of rust prevention. Blackening treatment can be used when the appearance requirements are not high. The surface blackening treatment of steel parts is also called blue.

Commonly used methods for blackening treatment include traditional alkaline heating blackening and late normal temperature blackening. But the blackening process at room temperature is not very effective for low carbon steel.

Alkaline blackening is subdivided, and there is a difference between blackening once and blackening twice. The main components of blackening liquor are sodium hydroxide and sodium nitrite. The temperature required for darkening is relatively large, and a good surface can be obtained between 135-155°C, but the time required is somewhat lengthy.

crafting process:

Rack cleaning-alkaline water degreasing-washing-pickling-boiling water washing-oxidation blackening-washing-saponification-washing-drying-soaking hot oil-oil control-inspection- Warehousing