RU2547374C1 - Chromating composition for treating zinc-plated steel - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: chromating composition for treating zinc-plated steel contains, g/l: hexavalent chromium ions 3.744-6.318, trivalent chromium ions 0.01-0.09, phosphate ions 13.60-22.95, thiocarbonic acid diamide 0.10-0.12 and water. The ratio of hexavalent chromium ions to phosphate ions in the solution is 0.275.

EFFECT: with minimum content of components, the chromating composition provides high corrosion resistance of zinc-plated steel, is environmentally friendly owing to optimum content of hexavalent chromium ions.

1 tbl, 4 ex

Description

The invention relates to the protection of metals from corrosion, in particular to chromating of galvanized steel, and can be used in metallurgy and mechanical engineering.

A known composition for processing described in patent No. P-39432 "Solutions for chromatization" (1)

The composition contains, g / l:

10-100 - chromic acid;

1-21 - Cr ³⁺ ions;

0.1-4 - phosphate ions;

0,1-4 - fluorozirconate ions

Moreover, the ratio of the mass fractions of chromium (VI) and chromium (111) is from 1.5: 1 to 5: 1, the ratio of the mass fractions of chromic acid and fluorozirconate ions is from 5: 1 to 100: 1 and the ratio of the mass fractions of phosphate ions and ions fluorozirconate is from 0.5: 1 to 2: 1.

The closest in technical essence to the claimed chromate composition is a chromate composition described in patent RU 2425911 C1 "Chroma composition for processing a galvanized surface" (2), containing, g / l:

51.0-90.0 CrO ₃ ions

1.0-1.5 Cr ³⁺ ions

102.0-120.0 phosphate ions

0.1-4.0 fluorozirconate ions

3.0-6.0 ammonium polyacrylate

As CrO ₃ ions, a spent chromium-containing electrolyte solution is used for chromium plating of piston rings with a CrO ₃ content _of 200-300 g / l.

As phosphate ions, extraction phosphoric acid with a concentration of 72% is used, and 40% hexafluorozirconic acid is used as fluorozirconate ions.

The disadvantages of this composition is the high content of environmentally harmful Cr ⁶⁺ , multicomponent and the complexity of the manufacture of the composition.

The aim of this invention is to develop a chromating composition providing high corrosion resistance of galvanized steel with a minimum content of Cr ⁶⁺ ions, the optimal number of components and ease of manufacture of the composition.

The problem is achieved in that the chromating of galvanized steel is carried out by a chromating composition containing, g / l: Cr ⁶⁺ ions 3,744-6,318, Cr ³⁺ ions 0,01-0,09, P ₂ O ₅ ions 13,60-22, 95, thiocarbonate diamide 0.10-0.12, water the rest, and the ratio of Cr ⁶⁺ ions to P ₂ O ₅ ions is 0.275.

The use of this composition provides high corrosion resistance of galvanized steel during processing by the high-speed method for 3 seconds, meets modern environmental requirements - it contains the optimum Cr ⁶⁺ content.

In accordance with the hygienic standards GN 2.2.5.1313-03 “Maximum permissible concentrations (MPC) of harmful substances in the air of the working zone“ Ministry of Health of the Russian Federation ”: - MPC of chromic acid (in terms of Cr ⁶⁺ ) 0.03 / 0.01 mg / m ³ .

In accordance with the hygienic standards GN 2.1.5.1315-03 “Maximum permissible concentrations (MPC) of chemicals in the water of water bodies of drinking and cultural and domestic water use“ Ministry of Health of the Russian Federation ”: - MPC value Cr ⁶⁺ 0.05 mg / l .

Orthophosphoric acid with a concentration of 85% is used as P ₂ O ₅ ions.

The essence of the invention is illustrated by the following examples.

Example 1

Samples of galvanized steel are treated at a temperature of from 20 to 40 ° C for 1-3 seconds by immersion in the following content, g / l:

Cr ⁶⁺ ions; 3.744;

Cr ³⁺ ions; 0.01;

P ₂ O ₅ ions 13.60;

thiocarbonate diamide 0.10;

water the rest.

Moreover, the ratio of Cr ⁶⁺ ions to P ₂ O ₅ ions is 0.275.

To prepare this composition, 1000 ml of water are poured into a 1000 ml container with a pre-installed mixing device, 90.0 g of chromic anhydride are poured, stirred for 10-15 minutes, 276.0 g of phosphoric acid are added, mixed for 10-15 minutes, 0 is added , 10 g of diamide thiocarbonic acid, stirred for 10 minutes and add the remaining amount of water to 133.9 ml to a total weight of 1 kg Then 80 g of the prepared composition is dissolved in 920 ml of demineralized water. Stirred for 10-15 minutes.

After applying a chromating coating in this composition, its excess is removed by squeezing gummed rollers and dried at a temperature of 100-120 ° C.

Example 2

Samples of galvanized steel are treated at a temperature of from 20 to 40 ° C for 1-3 seconds by immersion in the following content, g / l:

Cr ⁶⁺ ions 6.318;

Cr ³⁺ ions 0.09;

P ₂ O ₅ ions 22.95;

thiocarbonate diamide 0.12;

water the rest.

Moreover, the ratio of Cr ⁶⁺ ions to P ₂ O ₅ ions is 0.275.

To prepare this composition, 1000 ml of water are poured into a 1000 ml container with a pre-installed mixing device, 130.0 g of chromic anhydride are poured, stirred for 10-15 minutes, 357.2 g of phosphoric acid are added, mixed for 10-15 minutes, 0 is added , 12 g of diamide thiocarbonic acid, stirred for 10 minutes and add the remaining amount of water 12.68 ml to a total weight of 1 kg Then 135 g of the prepared composition is dissolved in 865 ml of demineralized water. Stirred for 10-15 minutes.

After applying a chromating coating in this composition, its excess is removed by squeezing gummed rollers and dried at a temperature of 100-120 ° C.

Example 3

Samples of galvanized steel are treated at a temperature of from 20 to 40 ° C for 1-3 seconds by immersion in the following content, g / l:

Cr ⁶⁺ ions 5.031;

Cr ³⁺ ions 0.050;

P ₂ O ₅ ions 18.275;

thiocarbonate diamide 0.11;

water the rest.

Moreover, the ratio of Cr ⁶⁺ ions to P ₂ O ₅ ions is 0.275.

To prepare this composition, 500 ml of water are poured into a 1000 ml container with a pre-installed stirring device, 110.0 g of chromic anhydride are poured, stirred for 10-15 minutes, 316.6 g of phosphoric acid are added, mixed for 10-15 minutes, 0 is added. 11 g of thiocarbonate, stirred for 10 min and add the remaining amount of water 73.29 ml to a total weight of 1 kg Next, 107.5 g of the prepared composition is dissolved in 892.5 ml of demineralized water. Stirred for 10-15 minutes.

After applying a chromating coating in this composition, its excess is removed by squeezing gummed rollers and dried at a temperature of 100-120 ° C.

The processing of galvanized steel in the inventive chromating composition can be carried out by immersion, spraying, rolls.

Tests of the invention were carried out on samples of hot-rolled galvanized steel.

Example 4 (prototype)

Samples of galvanized steel with a size of 150 × 200 mm were processed by spraying at room temperature for 1-3 seconds as part of the following contents:

90.0 g / l CrO ₃ ions;

1.5 g / l of Cr ³⁺ ions;

120.0 g / l phosphate ions;

4 g / l fluorozirconate ions;

6.0 g / l ammonium polyacrylate.

To prepare the composition, 360 g of spent chromium-containing electrolyte with a CrO ₃ content _of 250 g / l, 172 g of extraction phosphoric acid and 448 g of water were mixed. The mixture was stirred and heated to 70 ° C. Then, without stopping stirring, 4.5 g of phosphinic acid was added as a reducing agent in order to partially restore hexavalent chromium to trivalent chromium to obtain 1.5 g / l of Cr ³⁺ ions. After an hour (the end of the reduction reaction), 10 g of hexafluorozirconic acid and 6.0 g of ammonium polyacrylate were added to the solution. The mixture was stirred until the components were completely dissolved. Before use, the chromatating composition was cooled to room temperature.

After coating, the excess chromating composition was removed by rollers and the samples were dried at a temperature of 100-120 ° C.

After 24 hours of exposure, samples of galvanized steel with a chromating coating are subjected to corrosion tests, which are assessed by the area of damage to the surface of galvanized steel with white rust.

Corrosion resistance tests are carried out in a salt spray chamber according to GOST 9.308-85 in terms of: corrosion initiation (first points), hour; test completion, hour; the proportion of the affected surface,%.

The results of corrosion tests of these compositions are shown in the table

Table 1 Formulation Examples White rust test,
% defeat The beginning of corrosion, hour Test completion, hour The proportion of the affected surface,% one 39 148 82.3 2 41 150 79.4 3 40 147 81.8 four 35 96 87.4

From the above examples it is seen that the use of the inventive chromating composition provides high corrosion resistance of galvanized steel during processing by the high-speed method for 3 seconds.

Literature

1. Patent No. R-39432 "Solutions for chromatization."

2. Patent RU 2425911 C1.

Claims (1)

The composition for chromating galvanized steel, containing hexavalent chromium ions, trivalent chromium ions, phosphate ions and diamide thiocarbonic acid in the following components, g / l:
Cr ⁶ ions 3,744-6,318 Cr ³⁺ ions 0.01-0.09 P ₂ O ₅ ions 13.60-22.95 diamide thiocarbonate 0.10-0.12 water rest,
moreover, the ratio of hexavalent chromium ions to phosphate ions is 0.275.