RU2233915C1 - Method of creation of a protective decorative coating - Google Patents

Abstract

FIELD: galvanotechnics.

SUBSTANCE: the invention presents a method of creation of a protective decorative coating and is dealt with the area of galvanotechnics and may be used for deposition of corrosion-resistant wear-proof coatings with the decorative appearance. The method of creation of a protective decorative coating includes a sequential deposition on a surface of an item by the galvanic method of an inner layer and an outer chromium layer. The inner layer is deposited as a zinc layer of 1-5 microns thick and outer chromium layer of 0.1-1 micron thick. At that deposition of the both layers is exercised in electrolytes with addition of brighteners. Technical result: the invention allows to decrease consumption of materials and the cost price of items; at that the coating provides reliable protection of items against corrosion, against mechanical damages and has the decorative properties kept at a continuous exploitation.

EFFECT: the invention allows to decrease consumption of materials and the cost price of items, ensures reliable protection against corrosion and mechanical damages.

Description

The invention relates to the field of electroplating and can be used in any industries for applying corrosion-resistant, wear-resistant coatings having a decorative appearance.

From the prior art there is known a method of creating an anti-corrosion coating (RF patent N 2145647, CL C 25 D 5/18, 1998).

This method includes placing in an electrolytic solution with Zn or Cr ions electrodes, one of which is a coated product, and passing unipolar positive current pulses through the electrolyte. As a result of this, a single-layer zinc or chrome coating is formed on the product.

The disadvantage of this method is that a single-layer zinc coating can easily be subjected to mechanical damage (Zn is a soft metal, its hardness on the MOOS scale is 2.5 units), which leads to a rapid loss of the decorative appearance of the coating. Loss of decorative effect also occurs when this coating contacts an aggressive environment (water spray, sweaty hands, soap suds).

A single-layer chrome coating is cracked, so on its own it cannot reliably protect the surface from corrosion, which is its significant drawback.

A known method of producing a two-layer protective coating, in which the nickel coating is 5-7 μm thick, then copper, 20-25 μm thick, and then heat treatment is carried out in three stages (RF patent No. 2066715, class C 25 D 5/50, 1994).

The disadvantage of this method is the high consumption of expensive, strategically important nickel material, because in order for this coating to be non-porous, it must be thick enough.

Heat treatment requires additional energy and time.

The cost of such a coating is high, so it cannot be widely used.

Closest to the proposed is a method of creating a protective decorative coating, comprising sequential application of the inner layer and the outer chrome layer to the surface of the product (RF patent No. 2080423, class C 25 D 5/14, 1995).

This coating provides neither reliable electrochemical protection against corrosion, as the sublayer (milk chrome) is opaque, nor decorative.

The creation of such a coating is a lengthy process, since the current yield of a chrome bath is 8-16%. So, for example, to obtain a coating with a thickness of 1 μm, with a current density of 10 A / dm ² , 9-17 minutes are required. To create the same zinc coating takes 0.3 minutes, because current efficiency in a zinc bath is 100%.

In addition, as a rule, the chrome coating is uneven in thickness. On the protruding parts, its thickness is 8-10 times more than average. To create a uniform chrome coating requires special complex fixtures, chrome is a very expensive material.

In accordance with the foregoing, tasks are set that are simultaneously aimed at:

- the creation of a wear-resistant coating that provides reliable electrochemical protection of steel products from corrosion due to the use of zinc (Zn is an anode coating with respect to steel) from mechanical damage due to the use of chromium (chromium hardness according to the MEP scale is 9 units);

- providing protective and decorative properties that are preserved during the long-term operation of products prepared both from steel and from non-ferrous metals (copper and its alloys);

- reducing material consumption by reducing the thickness of the coating;

- reduction of energy consumption, energy and cost of the product.

This problem is solved by the fact that in the method of creating a protective decorative coating, which involves sequentially coating the surface of the product with the galvanic method of the inner layer and the outer chrome layer, the inner layer is applied in the form of a zinc coating with a thickness of 1-5 microns, and an outer chrome layer with a thickness of 0.1- 1 μm, while the deposition of both layers is carried out in electrolytes with bright-forming additives.

The introduction of brightening agents into zinc electrolyte provides the coating with additional density, which increases its corrosion resistance. In addition, the introduction of brighteners into the substrate (zinc layer) eliminates the operation of polishing the layer before applying the second chromium layer, which reduces the labor required to create a coating.

The introduction of brighteners into the chromium electrolyte allows us to expand the parameters of the deposition of brilliant sediments.

The method is as follows.

The coated product is pre-cleaned of fat and oxide contaminants. The compositions of the cleaning solutions depend on the condition of the surface being treated and the material from which this product is made. Then the product is thoroughly washed with running water and placed in a bath with an electrolyte, which includes, for example, g / l:

Zinc oxide 10

Sodium hydroxide 150

Glitter 2-5

The zinc coating is carried out at a temperature of 15-55 ° C, a current density of 0.5-15 A / DM ² . Zinc precipitation can be carried out with current reversal, pulsed currents or in a stationary mode. The thickness of the deposited zinc coating is 1-5 microns. Then the product is washed from the electrolyte and chromium plated. The composition of the electrolyte may be, for example, such a g / l:

Chrome Anhydrite 80-400

Sulfuric acid 0.8-4

Brightening Additives 2-20

The area for obtaining brilliant precipitates with satisfactory scattering power for the chromium coating is limited both in the concentration of the components and in the mode of the process.

Brightening additives allow you to expand the process parameters. Chrome plating is carried out in the following mode: electrolyte temperature of 20-60 ° C, current density of 7-50 A / dm ² , deposition rate of 0.2-0.7 μm / min. The chromium layer is applied with a thickness of 0.1-1 microns. Next, the product is washed with running water and dried.

Using this method will create a coating that provides reliable electrochemical protection of products from corrosion, from mechanical damage; to provide the coating with the necessary decorative properties, preserved during long-term operation, to reduce material consumption and the cost of the product.

Claims (1)

A method of creating a protective decorative coating, comprising sequentially coating the surface of the product with the galvanic method of the inner layer and the outer chrome layer, characterized in that the inner layer is applied in the form of a zinc coating with a thickness of 1-5 microns, and an outer chrome layer with a thickness of 0.1-1 microns, while the application of both layers is carried out in electrolytes with bright-forming additives.