SU775188A1 - Solution for anodized treatment of steel parts - Google Patents

Description

one

The invention relates to the preparation of the surface of metal products before electroplating, in particular, to electrochemical passivation of the surface of steel parts before applying copper and brass coatings in the pyrophosphate electrolyte.

Electrochemical passivation of steel parts is known before electrolytic copper plating in a 3- or 10% solution of nitric acid or in a boiling solution (135-143 ° C) containing 600 g / l sodium hydroxide and 150 g / l sodium nitrite 1.

However, the solution of nitric acid is aggressive, the detail in it is heavily poisoned, which leads to a change in its size. Adhesion to the base (adhesion) after treatment in this solution is 1 and 8 bends for brass and copper coatings (by bending with bending), respectively.

The use of a boiling solution containing a high concentration of caustic soda is dangerous in operation, and in addition, the subsequent long-term washing of parts from alkali is necessary.

Closest to the invention is the solution for anodic treatment (decapitation) of steel parts before electroplating (copper plating).

5 in a pyrophosphate electrolyte) containing an alkali metal oirophosphate, for example sodium 2.

However, the use of sodium pyrophosphate requires the use of a high current density (5-6 A / dm), which is difficult to achieve when processing the bell and drum type detreated in the baths. Duration of treatment (0.5-1.0 min),

15, when working with a large number of parts, does not provide satisfactory passivation of the inner surface of complexly shaped parts, as a result of which the coating is peeling in the recess areas, adhesion to the base is 5 and 7 bends for brass and copper, respectively.

The purpose of the invention is to increase the adhesion of coatings with the base.

This is achieved by the fact that the solution additionally contains potassium acid phosphate and potassium sulfate, and as the pyrophosphate of the alkali metal-potassium pyrophosphate acid in the following ratio of components, r / jti

Potassium pyrofodofrnokisly ---- 140 1BOKALI acid phosphate 10-20 Potassium sulfate 40-50 Passivation is recommended to be maintained at pH 9-10.5 and 20-EPA, anodic current density 0.8-1.0 A / dm for 20- 30 min.

The solution is prepared by separately dissolving the constituents in water. The resulting solutions are drained into the working bath and the volume is brought to the desired level with water. The acidity of the solution is adjusted. With 10% sulfuric acid or 10% caustic potash, a thin passive film is formed on the surface of the parts and a surface potential equal to or more than -0.12 V is created, which eliminates contact deposition of copper on the surface of steel parts in electrolytes, for example copper plating or brassing having a pH of 9.8, resulting in a better adhesion of the coatings to the substrate. The adhesion strength of the coatings With the base is checked during the manufacturing of the parts, since the parts coated with brass undergo the deformation during the manufacturing of the parts during the fourfold drawing operations.

In addition, the adhesion strength is checked by using the details on the press. Peeling of the brass coating does not occur.

The parts coated with copper are subjected to heat treatment during their manufacture, and in case of unsatisfactory adhesion during the heat treatment process, swelling (bubbles) appears on the surface of the parts. g When processing the parts before coating in the proposed solution during heat treatment, no detachment of the copper coating is observed.

The adhesion of copper and brass to the steel base is 9-10 bends. (Uncoated parts withstand 13 bends before breakage).

The introduction of potassium sulphate into the pre-growth solution of potassium increases its electrical conductivity, so that 0 ensures the passivation of the surface of complexly shaped parts, and the voltage on the bath decreases.

The introduction of acidic 5 phosphoric acid into the potassium solution allows the pH of the solution to be kept constant and, consequently, the required potential of the surface (equal to or more than -12 V) is obtained for a long time of solution operation, and one or two-substituted potassium phosphate is indifferently introduced.

The results are shown in the table.

140

10 20 15 20 20 20 8 160 150 160 160 160 130

25 20 170 160

20 30 25

sp

Claims (1)

30 15 30 20 30 As can be seen from the table, a more positive potential (-0.12 V) is also obtained at lower and higher concentrations of the components in solution 1 and higher values of pH and current density. However, despite this, a lower concentration of components is impractical because it causes more frequent adjustment of the solution. Higher concentration, pH, and current density should not be applied for economic reasons. Thus, the steel passaged in the proposed solution to a potential of –0.12 V can be successfully coated with copper or brass in pyrophosphate electrolytes at pH values of 8.5–9.8, due to the fact that the passive film under these conditions impedes exchange for 30-40 minutes even with the condition of mixing parts in the drum or bell. In addition, the proposed solution has a composition similar to that of pyrophosphate electrolytes, used to apply coatings of copper and its alloys, which makes it possible to unify the technological process as a whole and prevents the introduction of foreign chemical catches into the coating bath. A solution for anodic treatment of steel parts before electroplating, containing pyrophosphate "Christmas tree, the difference is that, in order to increase the adhesion of coatings with the base, it additionally contains potassium acid phosphate and potassium sulfate, and as the alkali metal pyrophosphate - potassium pyrophosphoric acid in the following ratio of components, g / l: Kyoshchy pyrophosphate140-160 Potassium acid phosphate 10-20 Hydrogen sulfate 40-50 Sources of information taken into account during examination 1. Kadaner L.I. Uniformity of electroplated coatings, Kharkov, Kharkov University Press, 1960, p. 370-373. , .P yav. and others. Handbook for zayshtno-decorative coatings m. MgL, -Mashgiz, 1951, p. 140.