Galvanic method

The galvanic method is used to apply coatings from complex sulfite solutions of trivalent chromium. Additives of some elements, in particular manganese (according to K.N. Pimenova), make it possible to increase the hardness and corrosion resistance of iron-chromium deposits. From the point of view of manufacturability, galvanic deposition in mass production is cumbersome, multi-operational, and requires careful observance of labor protection and safety conditions. Coatings have insufficient adhesion to the base, crack when deformed. For thick coatings on structural steels, the process is much more complicated and requires the use of special electrolytes, salts, suspensions, followed by annealing, pressing and coating with other metals.

Figure 1.1 shows a diagram of the galvanic coating method.

Fig.1.1

Cladding method

The cladding method is mainly used to obtain protective coatings on rolled products. There are several varieties of this method of obtaining coatings: pouring, joint plastic deformation, surfacing or electric welding. In the 60s, a method of explosion welding was developed, the essence of which is as follows. The plate of the cladding material is placed at a certain angle to the surface to be coated, an auxiliary plate is placed on the plate with explosive. After the explosion, a strong connection is formed under the action of significant pressure, tangential movement and due to the cleaning of the surfaces to be joined from oxide films.

Metalization methods

Metallization methods are common in obtaining coatings from Fe-Cr alloys. Depending on the method of melting the material, electric arc, flame, and plasma spraying are distinguished.

Arc plating

The essence of the method of electric arc metallization is heating (before melting) with an electric arc in a sprayer of converging wires. Drops of molten metal are then blown away by the gas flow towards the substrate. Metal coating of the surface, as a rule, is carried out in several passes. The most commonly used coating is aluminum, zinc.

Figure 1.2 shows a diagram of the operation of the metallizer.

Fig.1.2

Guides are installed in the electric metallizer, through which two sprayed wires are continuously fed. An electric arc is excited between the ends of these wires. In the central part of the electrometallizer there is a nozzle through which compressed air is supplied.

A jet of compressed air detaches particles of molten metal from the electrode wires and carries them to the surface to be sprayed. The electrometallizer can operate both on direct and alternating current. When using alternating current, the arc burns unstable and is accompanied by a lot of noise. At direct current, the nature of the work is stable, the sprayed material has a fine-grained structure, and the spraying performance is high. Therefore, at present, direct electric current sources are used for arc deposition.

For spraying, a wire with a diameter of 0.8 is usually used; 1.0; 1.6 and 2.0 mm. The metallization layer is applied to the open surfaces of the structures, if possible, the direction of the jet of molten metal at an angle of 45 to 90°. The surface intended for metallization must be prepared, cleaned of dirt, oils, rust. Surface preparation for metallization is carried out by shot-blasting (sandblasting). Surfaces to be treated must be free of burrs, sharp edges, welding spatter, and flux residues. Degrease before surface treatment. To ensure adhesion (and accordingly High Quality metallization coating) the time between preparation and spraying operations should not exceed 2 hours. To reduce thermal internal stresses, the metallization process should be carried out with interruptions between individual passes, avoiding overheating of the metallized surface.

The development of modern engineering and technology makes it possible to protect metal structures, structures, products and various parts from the effects of precipitation, aggressive environments and increase their service life several times. One of effective ways protection of metals from corrosion is spray metallization (flame, electric arc). The process of metallization has been known for a long time, and since the 50s of the last century, it has been widely used for anticorrosion protection of metal structures. This is a proven and proven technology for corrosion protection, restoration of worn and damaged surfaces of steel structures and products. The spray metallization process consists in the continuous melting of metal, spraying it into tiny particles and applying it to a specially prepared surface.

Getting on the metallized surface, the particles are deformed, piled on top of each other and form a metallization coating of a layered structure.

Fig.1.3

Metallization followed by painting, used to protect steel structures, is called combined coatings, which are two-layer systems, the lower layer of which is obtained by metallization, and the upper one by applying a paint coating. The service life of combined coatings due to synergy is significantly greater than the sum of the service lives of each layer separately, therefore they should be used for long-term corrosion protection of steel structures that will be used in medium and highly aggressive environments inside buildings, outdoors and under sheds, as well as in liquid organic and inorganic media.

During metallization, the adhesion of particles to the base occurs due to surface roughness and under the action of molecular forces and is mainly mechanical in nature. In some cases, metallization is the only and indispensable way to protect structures from corrosion and destruction. Metallization coatings can be applied both in the factory and at the assembly site.

The main anti-corrosion materials applied by metallization to steel structures and products are zinc, aluminum and their alloys. Zinc coatings are corrosion resistant in sea water and marine atmosphere. The greatest influence on the corrosion rate of zinc in the industrial atmosphere of industrial cities is the content of sulfur oxides in it, as well as other substances (for example, chlorine and hydrochloric acid vapors) that form hygroscopic compounds with zinc.

Aluminum in its own way chemical properties it is very active, but in the presence of oxidizing agents it is covered with a protective film, which sharply reduces its chemical activity. The corrosion resistance of aluminum depends on the conditions under which corrosion occurs. In a heavily polluted atmosphere, aluminum corrodes many times faster than in clean air. Aluminum is resistant to hot and soft water.

Zinc and aluminum alloys (Zn/Al 15, Zn/Al 5) create coatings resistant to any atmosphere, which is explained by the rapid filling of pores with zinc corrosion products. The contact of aluminum with zinc is safe, since the electrode potential of zinc is more negative than aluminum, therefore, zinc, dissolving, electrochemically protects aluminum.

Aluminum coatings are also widely used to protect iron and steel against gas corrosion. Zinc and aluminum form a dense layer of corrosion products, much larger in volume than the metal from which they were formed. A zinc coating that has been in water for a long time is covered with a dense layer of carbonate oxide or zinc hydroxide, the pores are clogged with corrosion products. Such a coating significantly increases corrosion resistance over time.

Fig.1.4

Anti-corrosion coatings are applied mainly metallization wire-type devices (plants for applying powder materials are used less frequently).

The principle of operation of wire-type metallization devices is based on the fact that metal in the form of a wire is continuously fed into the device, where it is melted by a gas flame or electric arc, and then sprayed with compressed air into the smallest particles that are applied to the surface.

The main reasons for the use of metallization coatings are:

1. high anti-corrosion resistance of metallization coatings;

2. no deformation of products;

3. mobility of metallizing installations and the possibility of applying protective coatings in the field;

4. high adhesive strength of metallization coatings (in comparison with paint coatings);

5. high plastic characteristics of metallization coatings;

6. high process productivity and the possibility of significant

7. reducing the time spent on spraying. For example, at a current of 750 A

it is possible to spray a steel coating with a productivity of 36 kg/h, which is several times higher than the productivity of flame spraying.

Compared to flame spraying, metallization makes it possible to obtain more durable coatings that are better connected to the substrate. When using wires from two different metals as electrodes, it is possible to obtain a coating from their alloy. The operating costs of the electric metallizer are quite small. When spraying a coating by spraying two electrodes from dissimilar materials, it is desirable to use such electrometallizers that would allow separate adjustment of the feed rate of each electrode. The main disadvantages of metallization are:

1. high porosity (up to 20%);

2. significant loss of metal during spraying. To increase the density and reduce the permeability of coatings, various impregnations are used that are resistant to aggressive media, as well as coloring;

3. overheating and oxidation of the sprayed material at low feed rates of the sprayed wire;

4. a large amount of heat released during the burning of the arc leads to a significant burnout of the alloying elements included in

5. sprayed alloy (for example, the carbon content in the coating material is reduced by 40-60%, and silicon and manganese by 10-15%). This must be taken into account and a wire containing an increased amount of alloying elements should be used for sputtering.

Metallization is the process of applying coatings with a thickness of tenths of a millimeter by means of electric arc or high-frequency heating of the metal.

Unlike the method plasma spraying in the method of electric arc metallization (EDM), the arc column is brought to minimum size, and the metal of the wire, melted by the arc, is sprayed by a gas flow directed along the wire.

Execution technique.

Through two channels, two wires (1.5-3.2 mm in diameter) are continuously fed into the burners, between the ends of which an arc is excited and the wire is melted. The molten metal is picked up by a jet of compressed air flowing from the central nozzle of the electric metallizer, and in a finely molten form is transferred to the surface of the base material. Spraying and transportation of the molten metal are usually carried out with compressed air, and when sprayed with corrosion-resistant steel and aluminum alloys use nitrogen.

The feed rate is set depending on the arc burning mode in order to maintain a certain gap between the electrodes for stable arc burning.

Typical values ​​of EDM operation parameters: voltage 24...35 V, current

75.. .200 A, productivity 30.300 g/min, compressed air pressure 5 atm.

With arc spraying at direct current, the process proceeds stably, providing a coating layer with a fine-grained structure at a high process productivity (Figure 1.8).

To implement the process of applying protective coatings by electric arc metallization, a number of equipment and devices have been developed and are commercially produced. So, for example, NPO Remdetal has developed a universal electric arc metallizer EDM-3 (Fig. 1.2.), Which can be used both in manual and machine versions. It consists of the metallizer itself 5, control panel 1 and wire cassettes 2. The torque from the adjustable electric drive in the control panel is transmitted by means of a flexible drive shaft 6 (2 m long) and the metallizer feed roller mechanism.

The wire from the coils is pulled through two flexible hoses 4 to the metallizer. The control panel and wire cassettes are mounted on a stand 3 and can be rotated around an axis.

The small weight of the metallizer (1.8 kg), flexible connection with the control panel, as well as the possibility of turning the cassette and the control panel in a horizontal plane create conditions for its convenient use.

Another design of the EM-6 electric arc metallizer for coating application provides for its mounting on a caliper lathe. Between the metallizer and the sprayed shaft, a funnel made of sheet steel is installed (Fig. 1.3.), The inner surface of which was covered with a protective layer of powdered graphite paste and liquid sodium or potassium glass. The device made it possible to increase the efficiency of using the sprayed metal by 10...15%.

In the spraying system of the metallizer, a conical air-spraying nozzle was used, which made it possible to reduce the opening angle of the spray cone, increase the energy of the spray jet and spray at an air pressure of 0.45-0.50 MPa.

Advantages.

The advantages of this method are high productivity, reaching 50 kg/h. This method also provides the maximum energy efficiency values. spraying and spraying. Due to the large values ​​of the enthalpy of the sprayed particles, high-quality coatings with sufficient adhesion and cohesion and low porosity, more durable coatings compared to flame spraying, can be obtained.

Flaws.

The disadvantages include the danger of overheating and oxidation of the sprayed material at low feed rates of the melted wire. Therefore, the often deposited metal is saturated with oxygen and nitrogen, and also contains significant amount oxides.

For example, when spraying carbon steel (0.14% carbon), the coating contains 10.5% oxides and 1.5% nitrides.

In addition, a large amount of heat leads to a significant burnout of the alloying elements included in the sprayed alloy, i.e., a change in the chemical composition of the coating is observed.

The use of only wire for deposition limits the possibilities of the method. In addition, the hygienic characteristic of the air in the working area during arc metallization with flux-cored wire is determined by chemical composition solid component of the aerosol (TSCA) and the performance of general ventilation. Air pollution with TSCA metal dust is relatively high, which determines the need to equip the equipment with a cleaning system.

In recent years, the need for electric arc metallization has increased. Arc plating(EDM) has wide possibilities in comparison with all known methods of applying metal coatings. With EDM, you can restore details machines of a wide range in various industries and Agriculture, to provide long-term aluminum and zinc diffusion aggregates of sugar factories, pipes, tanks and other metal structures, to obtain coatings from pseudo-alloys, for example, from aluminum and steel, copper and steel, bronze and steel, as well as decorative coatings with non-ferrous metals (copper, bronze, brass , aluminum).

A schematic diagram of arc metallization is shown in fig. Through two channels in the burner, two wires are continuously fed, between the ends of which an arc is excited and the wire is melted. The molten metal is picked up by a jet of compressed air flowing out of the central nozzle electrometallizer, and in a finely atomized form is transferred to the surface of the base material. Spraying and conveying the molten metal is usually done with compressed air, although nitrogen is used for spraying 308 stainless steel and aluminum alloys. At arc spraying at direct current, the process proceeds stably, providing a coating layer with a fine-grained structure at high process productivity. Therefore, at present, direct current sources with a voltage stabilizer or sources with a slightly increasing characteristic are used for arc spraying.

Arc plating has the following advantages. The use of powerful electrometallization installations (electric arc metallizer,) can significantly increase the productivity of the process and reduce time costs. For example, at a current of 750 A, you can spray steel coating with a capacity of 36 kg / h, and with a current of 500 A - zinc coating with a capacity of 1.2 kg / min, which is several times higher than the performance of flame spraying.

Among the disadvantages of arc spraying is the danger of overheating and oxidation of the sprayed material at low feed rates of the sprayed wire. In addition, a large amount of heat released during arc burning leads to a significant burnout of the alloying elements that make up the sprayed material (for example, the carbon content in the coating material is reduced by 40-60%, and silicon and manganese - by 10-15%) .

When applying a coating layer on the surface of a part, heating it to 50 - 70 ° C does not cause any structural changes in the metal of the part, i.e. its mechanical properties are preserved, which makes it possible to apply a coating layer on any materials: metal, plastic, wood, rubber etc. Metallization provides a high hardness of the sprayed layer, which contributes to an increase in the service life of the restored parts. A wide variety of metals are dusted. For example, spraying can be used bimetallic wire made of aluminum and lead, which allows not only to replace expensive tin babbits and bronzes, but also to significantly increase the service life of bearings.

However, applying metallization, it must be taken into account that the metallized layer deposited on the surface of the part does not increase its strength. Therefore, metallization should not be used to restore parts with a weakened section. When restoring parts under the action of dynamic loads, as well as parts operating under friction without lubricants, it is necessary to know that the adhesion of the sprayed layer to the base metal of the part is insufficient.

Receipt quality coatings is possible only with strict observance of the regimes and careful preparation of the surfaces of parts undergoing metallization.

When preparing the surface of parts for metallization, individual operations are performed in the following sequence: parts are cleaned of dirt, films, oxides, grease stains, moisture and corrosion products; perform pre-treatment by cutting the surface to give it the correct geometric shape; get on the surfaces of parts the roughness necessary to hold the deposited metal layer; provide protection for adjacent surfaces of parts that are not subject to metallization.

Surfaces of parts to be metallization, cleaned of dirt in washing machines, brushes, washed in gasoline or solvents, heated in ovens with a gas burner or blowtorch flame. By cutting, the geometric shape of the part is corrected and the dimensions of the part are brought to sizes at which it is possible to apply coatings of a given thickness. At the ends of the cylindrical surfaces, beads are left and locks are machined in the form of annular grooves, which protect the coating from destruction.

The required roughness on the surface of the parts to be metallized is obtained by the following methods. On the surface of a thermally untreated round part on a screw-cutting lathe, "torn" thread with a cutter installed with a large overhang below the axis of the part by 3 - 6 mm. The vibration of the cutter results in a rough surface with burrs. The thread is cut at a cutting speed of 8 - 10 m / min (without cooling) in one pass of the cutter to a depth of 0.6 - 0.8 mm. The thread pitch is 0.9 - 1.3 mm, and for viscous and soft materials - 1.1 -1.3 mm. Threads are not cut on fillets. To exit the cutter during threading and eliminate chipping of the coating at the end of the part, annular grooves are made, the depth of which should be 0.2–0.3 mm greater than the depth of the thread. In some cases, the annular grooves are replaced by rough turning, leaving beads 1–2 mm wide. In table. 31 shows some modes when cutting a torn thread.

Often threading is replaced by a more productive process - thread rolling. In this case, the strength of the bond between the base metal and the coating deteriorates somewhat.

The performance of spraying with electric devices depends on the material used. If the spraying mode is chosen correctly, then with a coating thickness of 0.5 - 0.7 mm, the surface layer is heated to 70 ° C; with a coating thickness of 2–3 mm or more, the temperature of this layer reaches 100–150 °C. Heating can cause high voltages. To reduce the heating of the part, the coating is applied in thin layers in separate sections. So, when spraying shaft necks with a diameter of 150 mm and a significant length of these necks, a surface of no more than 800 - 1000 mm 2 is sprayed in one pass.

Coating hardness can be controlled by the selection of the starting material or the cooling mode during the coating process.

As stated earlier, technological process Coating varies depending on the shape of the part. Parts with flat surfaces are usually coated by hand. In some cases, metal-cutting machines are used to apply the sprayed material. When spraying coatings on flat parts, a number of difficulties arise, which are primarily the result of the appearance of residual tensile stresses that tend to tear the coating from the part. With a layer thickness of more than 0.3 mm, separation of the coating at the ends of flat surfaces is possible.

To prevent chipping or chipping of the coating along the outer perimeter of a flat surface, special grooves.

The preparation of flat parts for coating consists in cutting "torn" grooves on planers or creating a rough, rough surface by electrical means. On the surfaces of small flat parts, they are cut on turning or carousel machines"Ragged" grooves in the form of an Archimedean spiral. On planers, cut-off cutters with a rounded blade can cut parallel grooves and roll the tops of the grooves. Rolled surfaces are sandblasted. The grooves must be perpendicular to the direction of the load.

With a coating thickness of more than 0.5 mm, the preparation of the part consists in cutting grooves in the form of a dovetail with a step of 2 - 3 mm or in installing studs (in a checkerboard pattern) with a notch of the gaps with a chisel.

Details complex shape to seal cracks, shells and flat parts, sandblasting is used with dry quartz sand with a particle size of 1.5 - 2 mm.

In some cases, rough surfaces are obtained by winding a wire with a diameter of 0.5 - 1.6 mm cleaned of scale on the part in increments of two to five wire diameters. The wound wire is fixed by welding, after which sandblasting is carried out.

To obtain a high quality coating, the sprayed metal jet is directed perpendicular to the workpiece and the distance from the metallizer nozzle to the product (part) is kept within 150–200 mm. First, the metal is applied to parts of the part with sharp transitions, corners, fillets, ledges, and then the entire surface is metallized, increasing the metal evenly. The required dimensions, quality of finish and the correct geometric shape of the surfaces coated with sprayed metal are obtained during the final machining.

Works on the restoration of worn parts by metallization are associated with pollution of the surrounding air by dust and vapors of the sprayed metal, the action of an electric arc, as well as the noise emitted by the apparatus. In accordance with the requirements of labor protection, when using a metallizing plant, ventilation must be installed in a workshop or a closed room. In the conditions of commonly used standard metallizing equipment, this ventilation consists of a system of local exhausts, which must be installed at each workplace (sandblast cabinet, cabin, lathe). Based on the experience of operating metallizing installations, the air velocity in the plane is assumed to be at least 1 - 1.2 m / s, and in the cross section of an open horizontal umbrella at a lathe, at least 4 m / s. The air exhausted from the sandblasting cabinet must be cleaned from dust in dust collectors installed outdoors or in cyclones. In addition, the room for the metallization plant of the enterprise must be equipped in winter with a supply ventilation system with heating of the air supplied to the room. To protect your eyes from the action of ultraviolet rays, you must use glasses with dark lenses.

The process of electric arc metallization has been known for a long time, and since the 50s of the last century, it has been widely used for anticorrosion protection of metal structures. In electric arc plating, an indirect electric arc is used, which burns between two current-carrying wires. Molten drops of electrode metal are sprayed in the direction of the workpiece by a stream of compressed air or shielding gas. As the wire melts, it is fed into the electric arc burning zone by two pairs of feed rollers. The process diagram is shown in rice. 3.5.

The melting of the electrodes occurs mainly due to the energy released by the arc in the area of ​​the near-electrode spots. The mass-average temperature of the liquid metal sprayed by the gas jet is in the range from the melting point to the boiling point. Such a significant heating of the filler material leads to significant losses of alloying elements due to waste. A stable sputtering process corresponds to arc burning modes without short circuits, which is ensured by the presence of a dynamic balance between the average melting rate and the electrode feed rate.

Rice. 3.5
1 - wire electrodes; 2 - feed rollers; 3 - insulators; 4 - blower tube; 5 - detail

In this mode, at the end of the electrodes, the molten metal is first accumulated, and then it is sprayed with a gas stream. Along with the periodic ejection of portions of metal from the interelectrode gap during metallization, there is also a continuous jet runoff of overheated metal from the surface of the electrodes. The sizes of sprayed particles during electric arc metallization are approximately 100 μm, which corresponds to a particle mass of 1.4 x 10-9 kg. The maximum particle size, with rare exceptions, does not exceed 200 microns. The metal that has left the electrodes continues to be crushed under the influence of the gas-dynamic forces of the air jet. Moreover, this dispersion largely depends both on the pressure of the transporting gas and on the properties of the molten metal, including its overheating.

Electric arc plating is carried out at a pressure of compressed air or shielding gas of 0.5-0.6 MPa. The current strength during electric arc metallization varies within:

• from 35 to 100 A for low-melting metals (aluminum and zinc);
• from 70 to 200 A for steels and alloys based on iron and copper.

The voltage varies from 20 to 35 V. Productivity when spraying zinc is up to 32 kg/h, aluminum - up to 9 kg/h.

The speed of movement of metal particles in the gas flow ranges from 120 to 300 m/s. This determines the short duration of their transfer to the surface of the part (the flight time is thousandths of a second) and significant kinetic energy, which at the moment of impact with the surface of the part turns into heat and causes additional heating of the contact zone. The impact at the moment of contact with the surface of the part causes the compaction of the metallized layer and reduces its porosity to 10-20%.

Arc metallization can produce layers in a wide range of thicknesses from 10 µm to 1.5 mm for refractory metals and 3.0 mm for fusible metals. The productivity of electric arc metallization is 3-20 kg/h.

The metallized layer can be applied to the outer and inner surfaces of structures at an angle of molten metal spraying relative to the part surface from 45° to 90°. To obtain a high quality coating, the jet of sprayed metal is directed perpendicular to the workpiece and the distance from the metallizer nozzle to the product (part) is kept no more than 150-200 mm. In table. 3.4 presents data on the effect of spray distance on the characteristics of the metallized layer.

Table 3.4. Physico-mechanical properties of the coating at different distances of metallization.

In order to increase the efficiency of coating with an electric arc, it is intensified by blowing with a gas flow, applying electromagnetic fields to it, or using discharges with a very high current density on the electrodes. A high current density is obtained by reducing the cross section of the electrodes or by using high-current discharges. Compaction of metallized layers is provided by combining the process of spraying and shot blasting. The shot is guided in such a way that its impacts cause plastic deformation of the freshly deposited layer.

The surface intended for plating must be free of dirt, oils, rust. Surface preparation is most often done by shot blasting (sandblasting). Degrease before surface treatment. To ensure satisfactory adhesion, the time between preparation and metallization operations should not exceed 2 hours. To reduce thermal internal stresses, the metallization process should be carried out with interruptions between individual passes, avoiding overheating of the metallized surface.

First, the metal is applied to parts of the part with sharp transitions, corners, fillets, ledges, and then the entire surface is metallized, increasing the metal evenly. The required dimensions, quality of finish and the correct geometric shape of the surfaces coated with sprayed metal are obtained during the final machining.

Metallization followed by painting is used to protect steel structures, referred to as combined coatings. The service life of combined coatings due to synergy is significantly greater than the sum of the service lives of each layer separately, therefore they should be used for long-term corrosion protection of steel structures that will be used in medium and highly aggressive environments inside buildings, outdoors and under sheds, as well as in liquid organic and inorganic media. Coatings obtained by electric arc metallization are used to protect steel structures and reinforced concrete supports of bridges, fuel tanks, pipelines, equipment used in heating networks, oil and chemical industries.

Filler materials

The choice of material for coating depends on the operating conditions and the main wear processes occurring on the surfaces. The main type of filler material is a continuous wire electrode. Both solid wires and powder wires with a diameter of 1.0 to 2.5 mm are used. The wire feed speed varies from 220 to 850 m/h.

Solid wires are mainly used to create coatings on surfaces for fixed landings (from low-carbon steels Sv-08, Sv-10GA) and mobile joints (from high-carbon steels Np-50, Np-85 and alloyed steels Np-30X13, Np-40X13, Np-60X3V10F). To obtain coatings with high hardness, flux-cored wires are used.

Highly alloyed iron-based wires (Sv-08Kh18N8G2B, Sv-07Kh18N9TYu, Sv-06Kh19N9T, Sv-07Kh19N10B, Sv-08Kh19N10G2B, Sv-06Kh19N10M3T), as well as wires from non-ferrous metals (nickel, zinc, copper, etc.) are used to create anti-corrosion coatings. .).

The main non-ferrous anti-corrosion materials applied by the method of electric arc metallization on steel structures and products are zinc, aluminum and their alloys. Zinc coatings are corrosion resistant in sea water and marine atmosphere. The greatest influence on the corrosion rate of zinc in the industrial atmosphere of industrial cities is the content of sulfur oxides in it, as well as other substances (for example, chlorine and hydrochloric acid vapors) that form hygroscopic compounds with zinc.

Arc plating A coating process that uses electricity to heat/melt the wire material. A direct current of different polarity is supplied to two consumable wires, due to which the arc is ignited, the wires are melted, and the separated particles of materials are transferred by a stream of compressed air to the spraying surface.
The use of direct current makes it possible to stabilize the arc discharge and carefully control the deposition parameters.

Rice. one. Arc plating

Peculiarities
Electric arc metallization is characterized by excellent, in comparison with other technologies, performance, high efficiency. In addition, equipment for electric arc metallization is characterized by ease of use, unpretentiousness of use, low requirements for the connection infrastructure, which allows it to be used both in a workshop with stationary lines of electricity and compressed air, and in conditions outside the workshop, where it is sufficient to additionally use widely used industrial compressors and generators.
Materials for electric arc metallization are produced in the form of wires, including powder ones.
Electric arc metallization involves the use electrical energy to melt the material. The absence of an open flame and combustion, as such, allows the use of electric arc plating in enclosed spaces. Widely known is the use of electric arc plating for spraying the internal surfaces of tanks for the storage and transportation of food and oil products, ballast tanks; it is allowed to use metallization inside ventilated mines, etc.
The range of materials used is limited by the obligatory presence of conductive elements in the supplied material. Electric arc plating is not applicable for the deposition of polymer, ceramic and other non-conductive materials.

Application
The most common use of arc metallization is the deposition of low-melting materials (Zn, Al, their alloys). Coating systems based on zinc, aluminum, alloys based on them, as well as the addition of magnesium, titanium and other elements, are characterized by a low electrochemical potential, which allows them to be used to protect structural steels from corrosion.
Such coatings prevent corrosion not only by isolating steel surfaces from corrosive attack. environment as paint materials. The electrode potential, which is negative with respect to steel, galvanically protects the surface from corrosion even in the event of local damage to the coating. In addition, when using such coatings, in principle, the development of under-film corrosion is impossible, which very often occurs when using paints and varnishes.
Another significant advantage of metallization coatings is the high adhesion of metal coatings. Moreover, over time, adhesion only increases due to the mutual diffusion of metals, while any paintwork sooner or later loses adhesion and peels off due to the fundamental heterogeneity of materials.

Fig.2. Application of an anti-corrosion coating on the zone of variable wettability of an offshore platform.

In addition to anti-corrosion coatings, electric arc plating can be used to apply wear-resistant coatings.
The use of specially designed flux-cored wires implies a three-stage process of coating formation: first, the sheath of the flux-cored wire is melted from the energy of the metallizer, melting is an endothermic reaction; The heat released during the melting of the shell melts the charge mixture that fills the cord material.
Electric arc plating, in contrast to the widely used high-speed spraying for wear-resistant coatings, has greater productivity and mobility, which makes it an excellent alternative for creating wear-resistant coatings, while EDM coatings are much cheaper, however distinctive feature from HVOF coatings is high porosity, which can in some cases lead to corrosion, as well as a lower level of adhesion.