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FIELD

The present invention relates to a galvanized steel wire, in particular, it relates to a high corrosion resistance coating treatment method of hot galvanized steel wire. A metallic metallurgical art.

Background technique

Zinc surface of galvanized steel by easily oxidized in air, poor corrosion resistance. Prone to white rust after a short period galvanizing surface, prone to red rust after a long time. Effect of quality of its appearance and corrosion resistance. For this reason, after the foreign-plated galvanized steel wire after completion of the stretching, a liquid-impregnated with an aqueous solution of hexavalent chromium and acidified (anhydrous chromic acid: sulfuric acid = 1:2.5:5:1:: nitric acid) in , then placing the air, and finally dried by heating, the hot galvanized steel surface hexavalent chromic acid rapidly form a dense film.

The reaction mechanism for the formation of hexavalent chromic acid coating: hot dipping galvanized steel, zinc dissolved in the solution acidified to hexavalent chromium, chromic acid reduction to produce the acid aqueous trivalent chromium compound as a main component in the surface coating of zinc precipitate, chromate coating formation. Reaction the following steps: 1) dissolution reaction of zinc: 2) chromic acid reduction reaction: 3) After this reaction, the galvanized layer surface PH value rise, precipitation of chromium acidified water:

4) Water is then acidified with chromium chromate and then reacting:

5) water with an acid to generate an acid group hexavalent mesh structure: 6) after hot air drying, shrinking film hexavalent chromic acid reaction, the precipitated zinc surface, forming the anticorrosive film.

Hexavalent chromic acid oxidation barrier film may be formed in contact with the layer of pure zinc oxyntomodulin to protect zinc, then there is enough iron to form zinc to protect the steel substrate potential, thereby further improving the corrosion resistance of galvanized steel wire, but also has excellent conductivity and coating with self-healing capabilities. However, due to the carcinogenic hexavalent chromium, hexavalent chromium acid film, and was banned around the world.

SUMMARY

Object of the present invention is to overcome the above disadvantages, there is provided a can enhance the corrosion resistance of galvanized steel wire, and a regeneration performance of the film, nor carcinogenic high corrosion resistance hot dip galvanized steel wire coating treatment method.

Object of the present invention is implemented as follows: A high-corrosion coating treatment method of hot galvanized steel, which is characterized in that it is hot dip galvanized steel wire after drawing the line after the end of the plate, washed with water, immersed in dilute nitric acid after washing with water, with aqueous chromic acid chemical conversion solution as the impregnation solution dipping 30-60 seconds, and then placed in the air, and finally dried by heating 50-60 deg.] C, the hot galvanized steel surface rapidly form a dense free trivalent chromate coating film, the chromic acid anodizing solution is a mixture of chromium trichloride with nitric acid, both the volume ratio is: chromium trichloride: nitric acid = 0.8 to 1.2, and a control aqueous chromic acid chemical conversion solution of at a concentration of 100-150 mg / l.

The present invention employs a mixture of chromium trichloride with nitric acid as the chemical conversion solution to promote formation of a dense hot galvanized steel surface oxide film chromic acid, chromic acid oxidation barrier film may be formed in contact with the layer of pure zinc oxyntomodulin to protect zinc, in turn, have sufficient protective potential of zinc and iron to form steel substrate, thereby further improving the corrosion resistance of galvanized steel, but also has excellent conductivity. Chromic acid and the oxide film is not carcinogenic, and in accordance with international standards SGS ROS instructions.

BRIEF DESCRIPTION

FIG chromate free coating structure 1 in FIG trivalent present invention.

Trivalent chromate FIG. 2 of the present invention changes the charge following FIG.

FIG ligand chromic acid conversion in FIG. 3 of the present invention.

Chromic acid, and hydroxide polynuclear misprinted wrong vitro hydroxide present invention. FIG. 4 is reacted FIG.

Detailed ways

The present invention provides a high corrosion resistance coating treatment method of hot galvanized steel, which is galvanized steel wire after drawing the line after the end of plating, after washing with water, dipping in dilute nitric acid, washed with trivalent chromated into the liquid immersion liquid impregnation solution as 30-60 seconds, and then placed in the air, and finally dried by heating 50-60 deg.] C, the hot galvanized steel surface rapidly form a dense coating of trivalent chromium free, trivalent chromium chemical conversion of the fluid is chromium trichloride with nitric acid mixture, the volume ratio of the two is: chromium trichloride: nitric acid = 0.8 to 1.2, and continually adding to the impregnating solution in chromic acid chemical conversion solution of chromic acid in order to control concentration of the aqueous solution into 100-150 ml / liter.

The present invention is a trivalent chromate coating film is formed as the reaction mechanism: free chromate film configuration 1) a trivalent: chromic acid type electron configuration of d (2) sp (3), is formed having six water molecules compound misalignment (FIG. 1).

2) trivalent chromate There are several variations of charge (Figure 2): [Cr (H2O) 6] (3 +) [Cr (H2O) 5X] (2+) [Cr (H2O) 4X2] ( +) [Cr (H2O) 3X3] [Cr (H2O) 2X4] (- 1) [Cr (H2O) X5] (- 2) [CrX6] (- 3) 3) chromic acid conversion ligand: ligand chromate water molecules and hydroxyl groups on the acid releases water keys, chromic two adjacent atoms combine to form polynuclear wrong, this is the conversion of water polynuclear acid group (FIG. 3).

4) These chromic hydroxide and polynuclear misprinted hydroxide reacts with the wrong vitro, the release of water, chromic acid misprinted increase, reducing the charge, the final acidified water and chromic acid chromium compound precipitates on the surface of the zinc, free chromate film is formed (FIG. 4).

The present invention is free trivalent chromate coating properties: 1, the galvanized surface of the chromate film, dehydration condensation shrinkage after drying, to form an aqueous hair corrosion resistant coating, the film thickness of chromate film is in the order of: Bright < black=""> The drying temperature of 40-50 deg.] C, corrosion resistance of the coating film is preferably, the drying temperature exceeds 70 ℃, coating corrosion resistance decreased sharply.

2, where the film is exposed to physical damage zinc chromate film can be regenerated, which is a unique characteristic of the chromate film.

3, the trivalent and hexavalent chromium free chromic acid coating film, having the same corrosion resistance. Galvanized steel wire heat treatment performed after coating JIS Z2371 salt spray test results are as follows:

Such weak aqueous coating heat at 120 ℃ ~ 150 ℃, loses crystal water film, corrosion resistance decreases.