RU2004620C1 - Process of zinc diffusion plating over steel articles with oxidized surfaces - Google Patents

Description

serves as a catalyst in the reduction of iron oxides. When wetting the processed products with aqueous solutions of bases with a concentration of less than 5% or acidic solutions with a concentration of less than 0.1%, the generated hydrogen is not enough to increase the reduction ability of the powder until the iron oxides are completely reduced on the surface of the products and to obtain a high-quality coating of uniform and predetermined thickness, and wetting of the processed products with aqueous solutions of bases with a concentration of more than 15% and acidic solutions with a concentration of more than 3% is impractical, because already wetting the workpieces with aqueous solutions of bases with a concentration of 15% and acidic solutions with a concentration of 3% is sufficient to completely restore iron oxides and obtain a uniform coating with a given thickness; in addition, a further increase in the content of base or acid in the electrolyte solution will result in a more expensive process.

It should be noted that the environmental friendliness of the method is enhanced by the absence of environmentally harmful effluents resulting from washing products after degreasing and pickling. In addition, the proposed method for applying a diffusion zinc coating allows to increase the corrosion resistance of steel products with an oxidized surface.

To carry out the proposed method for applying a diffusion zinc coating to steel products with an oxidized surface, electrolyte solutions, for example, aqueous solutions of NaOH, HCI and HNOa, are preliminarily prepared.

The compositions of the tested electrolyte solutions are shown in the table.

EXAMPLE 1. Hardware (bolts, nuts) made of steel 45 with an oxidized surface, traces of copper and coolant immediately before being introduced into the coating zone containing the saturating mixture, are moistened in an aqueous solution of NaOH (GOST 4328-77) (compositions tested solutions are given in the table) for 0.5 min. Then, the processed hardware is introduced into the coating zone, the zone is sealed by any known method, for example, by a fusible closure, and the surface of the products is diffusion saturated at (460 ± 10) ° C and (500 ± 10) ° C for 120 minutes. The thickness of the coating formed on the processed hardware is shown in the table.

EXAMPLE 2. Hardware (bolts, nuts) made of steel 45 with an oxidized surface, traces of oil and coolant immediately before being introduced into the coating zone containing a saturating mixture, 5 are wetted in an aqueous HCI solution (GOST 3118-77 ) (the compositions of the tested solutions are given in the table) for 0.5 min. The rest is as in example 1.

0 Example Z. According to example 1, but moistened in an aqueous solution of HMO3 (GOST 4461-67).

Example 4. For comparison, a diffusion zinc coating on hardware (bolts, nuts) of steel 45 with an oxidized surface 5 and traces of oil was applied by the prototype method. The steel surface of the hardware is cleaned from oxides and oil. To do this, first sequentially degrease the surface in a solution containing caustic soda (GOST 4328-77) in an amount of 1 wt.%, Trisodium phosphate (TU 6-09-03-384-74 (- May 2.5.%, Soda ash (GOST 4530 -76) - 2.5 wt.%, Liquid glass (TU 6-09-01-154-73) - 0.5

5 wt.%, For 5 minutes Then the hardware is washed in cold and hot water for 1 min and subjected to etching in an aqueous solution of hydrochloric and sulfuric acids, and hydrochloric acid is taken in an amount of 3.8

0 wt.%, And sulfuric in the amount of 1.8 wt.%. Etching was carried out at 70 ° C for 3 minutes. After pickling, the hardware is again washed in cold and hot water for 1 minute. Then, the processed products are introduced into the coating zone, the zone is sealed with any known method, for example, by a fusible closure, and the surface of the products is diffused saturated under conditions similar to Example 1. The thickness of the coating formed on the processed metal products is also shown in the table.

After coating the hardware, 5 hardware was tested for corrosion for 60 days. when completely immersed in a solution of 3% sodium chloride containing 0.1% hydrogen peroxide (conditions simulating corrosion 0 in seawater). The test results are also shown in the table.

As can be seen from the above examples and the table, the proposed method of applying a diffusion zinc coating on 5 steel products with an oxidized surface allows to reduce the complexity of the method by replacing the operation of cleaning the surface of steel products with an oxidized surface by the operation of wetting them with an electrolyte solution

composition which can be carried out 18-20 times faster.

The corrosion resistance of the coating obtained by the proposed method is 1.5-2 times higher than the corrosion resistance of the coating obtained by the prototype method. The thickness of the coating of hardware in this case, obtained by the proposed method, is 10-15 microns greater than the thickness of the coating obtained by the prototype method. This is because an increase in the reducing ability of a saturating mixture is also accompanied by an increase in its saturating ability.

When using the proposed method, iron-zinc phases Ј and g / with a high zinc content are formed on the surface of the products in comparison with the prototype, which leads to an increase in the protective and protective properties of the coating.

(56) Proskurin E.V. IDR, Galvanizing / Reference. - M.: Metallurgists, 1988, her. 417-420.

Table continuation

Claims (1)

The claims METHOD FOR APPLYING DIFFUSION ZINC COATING TO STEEL PRODUCTS WITH OXIDIZED SURFACE, including surface pretreatment and diffusion galvanizing in powder saturating mixture, characterized in that, in order to reduce the complexity of the process while increasing the environmental friendliness of the method, as a preliminary treatment of the surface, it is wetted with either a 5-15% aqueous solution of the base, or 1 0.1-3.0% ;. | 0 aqueous solution of acid.