Galvanic coating. Technology of electroplating. Electroplating

Galvanic coating is a method of coating one metal with some other by electrolysis. This procedure is carried out using traditional immersion methods. After preliminary preparation, the printed circuit boards are loaded into a galvanic bath, which is a dielectric capacitor filled with an electrolyte and equipped with anodes (they can be soluble and insoluble), as well as a device for maintaining the temperature and stirring the solution.

Processing boards

The transmission of a direct current leads to the fact that uncovered by a protective mask and connected to the electrode sections of the board are covered with a layer of nickel or gold of a certain thickness. The correct arrangement of the anodes ensures that the thickness of the coating will be approximately uniform.

Gilding of printed circuit boards is usually performed using a two-stage process. First they are immersed in a bath, where nickel is applied by galvanic method. At the same time, a high current density is used, thanks to which a layer of nickel, whose thickness is 0.05-0.1 μm, is deposited from the acid solution. Due to this, a strong adhesion of nickel and copper is provided, which allows to reduce the porosity of the coating, as well as to prevent the penetration of copper into the gold layer. After washing, the products are usually moved to the gilding bath, where the gold layer is increased to 0.5 μm from the electrolyte.

Electroplating and decoration

Already in ancient times there was a decorative decoration of artistic metals. Modern production assumes that galvanic treatment will be used to impart some special properties of the metal surface. Protective coatings of precious metals can be obtained by depositing metals from saline solutions under the influence of electric current. Thanks to such coatings, it is possible to preserve the color and shine of jewelry for a long time. They not only prevent darkening of products, but also have an excellent polishing effect. For example, galvanic coating with gold or silver allows you to retain the color and shine of the jewelry for a long time.

There are several different versions of this process, each of which involves the use of a particular metal:

- chrome plating;

- copper plating;

- galvanizing;

- nickel plating;

- tin-bismuth coating;

- chemical oxidation;

- chemical passivation;

- anodizing;

- Electropolishing.

Chromium plating

This is the diffuse saturation of the steel surface with chromium or the deposition of a layer of matter from the electrolyte on the part by the action of an electric current. In this case the electroplating is oriented to protection against corrosion, it is used for decoration or for increasing the degree of hardness of the surface. Chromium in the industry can be used for decoration. In this case, the main purpose of the procedure is to give the metal surface a beautiful effective shine. The part must be polished before applying chromium.

Coating properties

The hard chrome coating is characterized by heat resistance, high degree of wear resistance, poor wettability, low coefficient of friction, and also low ductility. In addition, the surface receives such properties as frictional stability, the ability to withstand the distribution load, and also the disadvantage associated with the ease of destruction under the action of concentrated impact loads. Galvanic coating in the form of milk chromium has a low degree of wear resistance and hardness, low porosity. The surface is protected against corrosion, while retaining an attractive decorative appearance.

Using chromium in the industry

The main purpose with which it is used in industry is to impart details such properties as increased wear resistance, increased resistance to corrosion, and reduced friction. Due to this process, steel becomes stronger, does not undergo gas corrosion, and also does not break down in sea and ordinary water, nitric acid. Galvanic coating of this type leads to the fact that surface defects become only more significant, which requires subsequent processing, since in this case there is no alignment effect.

Copper

The use of copper coatings is important in cases where it is required to increase the electrical conductivity, and also they are used as an intermediate layer on steel products before the chrome, nickel or other coating is applied. So it is possible to provide better adhesion, as well as increase the protective ability. Electroplating with copper is usually not used as a stand alone or decorative. Due to the fact that this metal is able to prevent the formation of sparks, the product can be used in the oil and gas industry.

Application of copper plating

This process is used for coating copper from steel products or steel wire. Often, this type of coating is used to protect individual parts of steel products from cement, and the treatment is then subjected to those areas that are further treated with cutting.

Galvanic coatings of metals in this case are often used in the oil and gas industry to avoid the formation of sparks, in the electric power industry for the subsequent application of multilayer coatings for protection and decoration, in the production of printed circuit boards, for improving soldering, and for many other purposes. The surface acquires a color from light pink to dark red. Shades are usually not standardized.

Zinc plating

One of the most common methods for the protection of metal products is zinc coating. Usually it is used for processing a variety of alloyed or carbon steel grades. The application of galvanic coatings of this type is quite in demand for the protection of articles made of wire and fasteners. Getting to a moist environment, the zinc surface acts as an anode, due to which oxidative reactions are slowed down, and the base metal is thus protected against negative environmental factors.

Electroplating of this type can only be used after the metal products have been treated in a special way. To do this, they should be cleaned of rust, scale, and lubricating-cooling technical equipment. When the galvanizing process is completed, the product must be clarified, that is, it is etched with a weak solution of nitric acid, and then passivation is carried out. So not only is it possible to increase the resistance of galvanized products to negative factors, but also to make them more decorative, that is, to give shine and a certain shade. The technology of galvanic coatings in this case assumes a thickness of the zinc layer from 6 μm to 1.5 mm.

Nickel plating

Protection of metal products can be carried out using a variety of technologies. One of the most popular and common at the moment is nickel plating. Such popularity is explained by the chemical properties of nickel. It has a high degree of resistance to corrosion in an aqueous medium, and nickel oxide prevents subsequent oxidation of the metal. In addition, nickel is weakly affected by salts, acids and alkalis, with the exception of nitric acid. For example, galvanic coating thickness of 0.125 mm reliably protects against most industrial gases, characterized by increased aggressiveness. It is very important and such a moment: almost all metals can be nickel-plated, so this method can be used for additional processing of products.

The use of nickel plating is appropriate for solving a number of problems:

- protection of metal products;

- use as a decorative coating;

- Formation of a preliminary layer, which will be subjected to further processing;

- restoration of parts and assemblies.

The coating is characterized by increased wear resistance and hardness and is recommended for parts that work in friction, especially in the absence of any lubricant, is used to protect against corrosion, and to ensure high-quality soldering of low-temperature solders, all of which is prescribed in GOST. Galvanic coatings have increased brittleness, therefore it is not recommended to flare and bend the parts that have undergone nickel plating. It is recommended to use it for difficult-to-profiled parts. After the heat treatment at 400 ° C, the coating acquires maximum hardness.

Tin-Bismuth

The tin coating is resistant to sulfur compounds, so it is recommended for parts that are in contact with rubber and plastics. Among its properties can be called excellent adhesion to the base metal, elasticity, the ability to bend, stretch, stamping, flaring, press fit, and good retention when screwing. The freshly deposited tin coating is well solderable.

conclusions

Galvanic coating allows improving conductive characteristics of parts, giving them excellent electrical insulation properties, as well as protecting against the effects of various substances. In addition, this method makes it possible to obtain excellent surfaces having a mirror image, as well as imitating the coating with enamel. It is difficult to overestimate the importance of electroplating in modern production, as the development of technology has made the process more perfect.