The arc can be powered by AC or DC. When using direct current, the arc burns continuously and steadily, therefore, compared with alternating current, the melting process is more stable, high dispersion of the particles of the applied metal and the density of the coatings they create are ensured.

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Arc plating

The essence of the process lies in the fact that the sprayed metal is melted by an electric arc, sprayed into particles of 10–100 µm, and transferred to the surface to be restored by a gas jet.

Rice. 4.49. Scheme of electric arc metallization: 1 - sprayed surface; 2 - guide tips; 3 - air nozzle; 4 - feed rollers; 5 - wire; 6 - gas.

An electric arc is excited between two electrode wires 5, which are isolated from one another and are uniformly fed by roller mechanisms 4 at a speed of 0.6-1.5 m/min through guide tips 2. If the wires are made of different materials, then the coating material is their alloy. The distance from the nozzle to the part is 80-100 mm.

At the same time, compressed air or an inert gas at a pressure of 0.4-0.6 MPa enters the arc zone through the air nozzle 3, which sprays the molten metal and transfers it to the surface of the part 1. High speed of movement of metal particles (120-300 m / s) and an insignificant flight time, calculated in thousandths of a second, cause at the moment of impact on the part their plastic deformation, filling the pores of the surface of the part with particles, adhesion of particles between themselves and with the part, as a result of which a continuous coating is formed on it. By successive layering of metal particles, it is possible to obtain a coating with a thickness of more than 10 mm (usually 1.0–1.5 mm for refractory and 2.5–3.0 mm for low-melting materials).

The arc can be powered by AC or DC. When using direct current, the arc burns continuously and steadily, therefore, compared with alternating current, the melting process is more stable, high dispersion of the particles of the applied metal and the density of the coatings they create are ensured.

For electric arc spraying, electric metallizers are used: machine tools EM-6, MES-1, EM-12, EM-15 (with a significant amount of restoration work), which are usually mounted on lathes or special equipment, or manual (portable) EM-3, REM-ZA, EM-9, EM-10 (with a small amount of work).

The filler material for metallization, depending on the purpose of the coating, is usually an electrode wire (steel, copper, brass, bronze, aluminum, etc.) (Table 4.8) with a diameter of 1-2 mm. To obtain anti-friction coatings, a bimetallic lead-aluminum wire with a mass ratio of these metals of 1:1 is used.

The wire should be smooth, clean and soft. Rigid steel wire is annealed at a temperature of 800-850°C, followed by slow cooling together with the furnace. To reduce the rigidity of the wire made of copper and its alloys, heating to 550–600°C is necessary, followed by cooling in water.

The main advantages of electric arc metallization are high productivity compared to other methods (up to 50 kg of sprayed material per hour) and simple technological equipment.

Its disadvantages include significant (up to 20%) burnout of alloying elements and increased oxidation of the metal. To eliminate these shortcomings, in justified cases, instead of compressed air, natural gas or hydrocarbon fuel combustion products are used to spray molten metal, excluding the interaction of metal particles with air (activated metallization method). In this case, due to the carburization and hardening of the metal particles, the hardness of the sprayed layer increases.

Table 4.8

Electrode wire material for various coatings

High frequency metallization

This method is based on the melting of the filler material by induction heating with a high frequency current (200-300 kHz) and spraying the molten metal with a jet of compressed air. Carbon steel wire and rods 3–6 mm in diameter are used as filler material. Coatings are applied by high-frequency metallizers MVCh-1, MVCh-2, etc.

The filler material 6 is melted in the inductor 4 of the metallizer, which is connected to a high frequency current generator. The filler material is continuously fed by rollers 7 through the guide bushing 8 and, due to the presence of the concentrator 3, melts over a short length. Compressed air coming from channel 5 to the melting zone sprays the molten material and transfers its particles in the form of a gas-metal jet 2 to the sprayed surface 1.

Rice. 4.50. Scheme of deposition by the high-frequency method: 1 - sprayed surface; 2 - gas-metal jet; 3 - current concentrator; 4 - inductor; 5 - air channel; b - wire; 7 - feed rollers; 8 - guide sleeve

Compared to electric arc, high-frequency metallization reduces the burnout of alloying elements and coating porosity, and also increases the productivity of the process.

Coatings deposited by high-frequency metallization, due to favorable melting conditions of the filler material, have better structure and physical and mechanical properties than with other methods, except for plasma metallization. These advantages are due, in particular, to the fact that the burnout of the main chemical elements is reduced by 4–6 times, the saturation of the coating with oxides is reduced by 2–3 times, and this increases the adhesion strength and reduces the consumption of filler material. The disadvantage of this metallization method is the need for more complex technological equipment.

Plasma plating

This is a progressive method of coating, in which the melting and transfer of material to the surface to be restored is carried out by a plasma jet. Plasma is a highly ionized state of gas, when the concentration of electrons and negative ions is equal to the concentration of positively charged ions. A plasma jet is obtained by passing a plasma-forming gas through an electric arc when it is powered by a direct current source with a voltage of 80-100 V.

The transition of a gas to an ionized state and its decay into atoms is accompanied by the absorption of a significant amount of energy, which is released during plasma cooling as a result of its interaction with the environment and the sprayed part. This causes a high temperature of the plasma jet, which depends on the current strength, type and flow rate of the gas. As a plasma gas, argon or nitrogen is usually used, and less often hydrogen or helium. When using argon, the plasma temperature is 15000-30000°C, and nitrogen - 10000-15000°C. When choosing a gas, it should be taken into account that nitrogen is cheaper and less scarce than argon, but in order to ignite an electric arc in it, a much higher voltage is required, which leads to increased requirements for electrical safety. Therefore, sometimes when igniting the arc, argon is used, for which the voltage of excitation and arc burning is less, and in the process of deposition, nitrogen is used.

The coating is formed due to the fact that the applied material entering the plasma jet is melted and transferred by a hot gas flow to the surface of the part. The flight speed of metal particles is 150–200 m/s at a distance from the nozzle to the surface of the part of 50–80 mm. Due to the higher temperature of the applied material and the higher flight speed, the strength of the connection between the plasma coating and the part is higher than with other plating methods.

High temperature and high power compared to other heat sources is the main difference and advantage of plasma metallization, which provides a significant increase in process productivity, the ability to melt and apply any heat-resistant and wear-resistant materials, including hard alloys and composite materials, as well as oxides, borides, nitrides and etc., in various combinations. Thanks to this, it is possible to form multilayer coatings with different properties (wear-resistant, well run-in, heat-resistant, etc.). The highest quality coatings are obtained by using self-fluxing surfacing materials.

The density, structure, and physical and mechanical properties of plasma coatings depend on the applied material, fineness, temperature, and collision velocity of the transferred particles with the part to be restored. The last two parameters are provided by controlling the plasma jet. The properties of plasma coatings increase significantly during their subsequent reflow. Such coatings are effective at shock and high contact loads.

The principle of operation and the device of the plasma torch is illustrated in Fig. 4.51. The plasma jet is obtained by passing the plasma-forming gas 7 through an electric arc created between the tungsten cathode 2 and the copper anode 4 when a current source is connected to them.

The cathode and anode are separated by insulator 3 and are continuously cooled by liquid b (preferably distilled water). The anode is made in the form of a nozzle, the design of which provides compression and a certain direction of the plasma jet. Compression is also facilitated by the electromagnetic field that arises around the jet. Therefore, the ionized plasma-forming gas exits the plasma torch nozzle in the form of a jet of small cross section, which ensures a high concentration of thermal energy.

Rice. 4.51. Scheme of the plasma spraying process: 1 - powder dispenser; 2 - cathode; 3 - insulating gasket; 4 - anode; 5 - carrier gas; 6 - coolant; 7 - plasma gas

The applied materials are used in the form of granular powders with a particle size of 50-200 microns, cords or wire. The powder can be fed into the plasma jet together with the plasma-forming gas or from the dispenser 1 by the transport gas 5 (nitrogen) into the gas burner nozzle, and the wire or cord is introduced into the plasma jet below the plasma burner nozzle. Before use, the powder should be dried and calcined to reduce porosity and increase the adhesion of the coating to the part.

Protection of the plasma jet and the molten metal particles contained in it from interaction with air can be carried out by an inert gas flow, which should cover the plasma jet. For this, an additional nozzle is provided in the plasma torch concentrically to the main one, through which an inert gas is supplied. Thanks to it, oxidation, nitriding and decarburization of the sprayed material are excluded.

In the considered example, the power source is connected to the electrodes of the plasma torch (closed connection), so the electric arc serves only to create a plasma jet. When using the applied material in the form of a wire, the power source can also be connected to it. In this case, in addition to the plasma jet, a plasma arc is formed, which also participates in the melting of the rod, due to which the power of the plasma torch increases significantly.

Modern plasma surfacing installations have electronic systems for regulating process parameters, equipped with manipulators and robots. This increases the productivity and quality of the deposition process, improves the working conditions of the maintenance personnel.

Flame metallization

The gas-flame coating method consists in melting the applied material with a high-temperature flame, spraying and transferring metal particles to the previously prepared surface of the part with a jet of compressed air or an inert gas. The flame temperature of combustible gases mixed with oxygen is in the range of 2000-3200 °C. For gas-flame metallization, materials are used in the form of wire, powders and cords. The cords consist of a powdered filler sheathed in a material that burns out completely in a gas flame.

The melting of metal is carried out by a reducing flame, which makes it possible, in comparison with electric arc metallization, to reduce the burnout of alloying elements and the decarburization of the material, and thereby improve the quality of the coating. The advantage of gas-flame metallization is also a relatively small oxidation of the metal when it is sprayed into small particles, which provides a higher density and strength of the coating. The disadvantage of this method is the low productivity of deposition (2-4 kg of metal per hour) and the higher cost of surfacing materials.

Depending on the purpose of the part, its material and operating conditions, various methods of gas-flame metallization are used during restoration.

Flame spraying from bar materials. Filler wire 3 is melted by a flame 7 of a mixture of combustible gas (acetylene or propane-butane) with oxygen, which are fed into the mixing chamber 1 through channels 5 and 2, respectively. Compressed air or an inert gas enters through channel 6, which sprays the molten metal in the form of saturated particles jet metal 8 and transfers them to the sprayed surface 9.

Burners can be manual and machine. Wire burners use wire with a diameter of 1.5 to 5.0 mm.

Rice. 4.52. Scheme of metallization with wire material; 1 - mixing chamber; 2 - oxygen supply channel; 3 - wire; 4 - guide; 5 - acetylene supply channel; 6 - air channel; 7 - flame; 8 - gas metal jet; 9 - sprayed surface

Flame spraying of powder materials. This metallization method has gained wide acceptance due to the fact that the use of powdered materials provides additional advantages. These include:

– high flexibility of the process, which is expressed in the possibility of applying coatings to products of various dimensions;

– no restrictions on combinations of coating materials and parts, which allows you to restore parts of a wider range and purpose;

- less influence of the coating process on the properties of the material of the part, etc.

Worn seating surfaces of shafts and body parts are subjected to flame spraying.

Depending on the purpose and material of the part to be restored, the conditions of its operation, the requirements for the coating and its additional processing, flame coating methods are used.: without reflow and with reflow, which can be performed both during the deposition process and after it. (See table.)

Depending on the spraying method used, appropriate powder materials are used (see table).

Flame spraying without subsequent reflowis used to restore undeformed parts with wear up to 2.0 mm and a preserved structure of the base metal, which are not subjected to shocks, alternating loads and high-temperature heating during operation. The part is preheated with a burner with an excess of acetylene to prevent surface oxidation. Steel parts are heated to 50-100 °C, bronze and brass - up to 300 °C.

Spraying without flashing is carried out in two stages: first, a sublayer is applied (PT-NA-01 powder), and then the main layer (PT-19N-01 powder or others). The main layer is applied in several passes, while the coating thickness should not exceed 2.0 mm per side. Shaped and flat parts are sprayed manually, and parts of the “shaft” type are sprayed manually or on mechanized installations with automatic supply of the metallizer.

Reflow is necessary for metallization coatings operating under shock loads, since, due to the low adhesion strength to the base metal, unmelted coatings can crack and peel off. The coatings to be reflowed must contain materials that wet the surface of the part well and have the property of self-fluxing, such as nickel-based powder alloys.

The liquid phase formed during the melting of the coating contributes to the intensification of diffusion processes between it and the metal of the part. As a result, the adhesion strength, toughness, wear resistance and density of the coating material are increased. For reflow, various heat sources are used (oxy-acetylene flame, plasma arc, high-frequency currents, laser beam, furnaces with a protective-reducing atmosphere, etc.). The melting temperature should not exceed 1100 °C. Reflow technology should exclude overheating and peeling of the coating. After reflow, the part is cooled together with a suitably heated furnace.

Spraying followed by reflowit is used to restore parts of the "shaft" type with a coating thickness of up to 2.5 mm. Reflow is performed immediately after spraying. The sprayed area is heated until the coating melts, as a result of which it acquires a shiny surface. The hardness of melted coatings depends on the brand of powder. They are resistant to corrosion, abrasive wear, high temperatures and can be used for parts operating under alternating and contact loads.

The scheme of gas-powder spraying without reflow is shown in fig. 4.53.

Rice. 4.53. Scheme of flame spraying of powder material using a carrier gas: 1 - a mixture of oxygen with a combustible gas; 2 - carrier gas; 3 - sprayed powder; 4 - nozzle; 5 - torch; 6 - coating; 7 - substrate

Spraying with simultaneous reflow(gas-powder surfacing) is used to restore parts with local wear up to 3-5 mm, operating under alternating and shock loads, made of cast iron, structural, corrosion-resistant steels, and other materials.

The basis of the installation for spraying powder coatings with simultaneous flashing is a typical welding torch, supplemented by a device for feeding the powder into a gas flame. Spraying installations differ in the degree of mechanization (manual and machine), power (very low, low, medium and high power), powder supply method (injector and non-injector).

The technological process of restoring parts with flame coating generally includes the following operations:

— preheating of the part to be restored up to 200–250 °С;

- application of a sublayer as the basis for applying the main layers;

- application of the main coating layer with the necessary physical and mechanical properties;

– mechanical processing of the applied layer and control of the coating.

Ceteris paribus, the preheating of the part and the application of the sublayer affect the adhesion strength of the coating to the base metal. It also depends on the method of preparing the surface for spraying, the use of thermoregulating powders, the effective power of the flame, the method and parameters of the spraying process, the presence of surface-active additives in the coating material, the equipment used, and other factors.

Processing of sprayed coatings with hardness up to 40HRC is carried out by cutting with carbide tools and tools made of superhard materials. Turning is recommended to be performed in the following sequence: chamfering at the edges of the coating; turning the applied layer from the middle of the coating to the ends of the part until the unevenness of the applied layer is eliminated or final processing of the restored surface with the required accuracy and roughness.

Processing of sprayed surfaces is also carried out by grinding on appropriate machines (cylindrical grinding, inside grinding, surface grinding). In this case, it is mandatory to use a coolant, for example, a 2-3% solution of soda ash. Grinding is carried out immediately after coating or after preliminary turning. Grinding of sprayed coatings with hardness up to 60HRC is carried out with silicon carbide or white electrocorundum wheels, and with a hardness of more than 60HRC - with diamond wheels.

Spray coating by detonation method

The metallization process in this type of deposition is carried out due to the energy released during detonation - the process of chemical transformation of the explosive, which occurs in a very thin layer and propagates through the explosive in the form of a special type of flame at supersonic speed (in gas mixtures 1000-3500 m / s ).

In metallization installations, a mixture of oxygen and acetylene is used as an explosive, the detonation of which is a type of combustion of gaseous fuel. The potential energy of the gas mixture released in this case creates a shock wave and maintains a high temperature (over 5000 °C) and pressure (several tens of GPa) in it. The source of detonation is usually the thermal effect on the gas mixture (electric spark).

The powder materials entering the detonation zone are heated to temperatures above 3500°C and move along with the detonation products at a high speed, which at the exit from the barrel is 800–900 m/s. Thus, the coating material is ejected by the blast wave onto the treated surface at supersonic speed.

In practice, detonation coatings are formed due to the energy of periodically generated explosions of a mixture of oxygen and acetylene. The installation (gun) for detonation spraying (Fig. 4.57) contains: a combustion chamber made together with a water-cooled barrel 5; ignition device (electric candle) 2 with power source 3; oxygen and acetylene supply device 1, powder dispenser 4.

Rice. 4.57. Scheme of installation for spraying by the detonation method: 1 - device for supplying a mixture of gases; 2 - electric candle; 3 - power supply; 4 - powder dispenser; 5 - trunk; 6 - substrate; 7 - detail; 8 - coating; 9 - powder

Sprayed item 6 is installed at a distance of 70-150 mm from the edge of the barrel. During the coating process, the following sequentially occur: supply of oxygen and acetylene to the combustion chamber; supply from the dispenser in a nitrogen flow of a certain amount of sprayed powder; ignition by an electric spark of a mixture of oxygen and acetylene; combustion of the gas mixture, shot of powder from the barrel in the direction of the sprayed surface. Powder and gases are fed into the gun barrel automatically. The protection of gas valves from the action of an explosion and the cleaning of the barrel from combustion products is ensured by the supply of nitrogen into it.

The described cycle is usually repeated at a frequency of 3-4 Hz, which can be increased to 15 Hz or more. With each explosion, the coating is applied to a limited area of ​​the surface, so a continuous coating is formed by moving the part relative to the gun. The coating is formed from completely melted powder particles or from a mixture of melted or unmelted particles. The high speed at the moment of impact and the high temperature in the interaction zone cause welding of the powder on the surface of the part. Despite the high temperature of the detonation products and powder particles, the coated part is heated to a temperature of no more than 200 °C.

Unlike flame and plasma methods, detonation coatings are formed at higher particle velocities and the presence of larger unmelted powder particles. The first layer of the coating has practically no pores (porosity is less than 0.5%), and the individual pores formed in it decrease in volume or disappear during the formation of subsequent layers.

Detonation coatings also have high adhesive strength (up to 20 GPa) with the base metal. This is due to the fact that, despite the low overall temperature of the surface layer of the part (200–250 °C), the temperature at individual points of contact between the applied and base metals reaches the melting temperature of steel. Therefore, fusion and mixing of these metals occurs with the formation of a strong connection.

Detonation methods spray powders of pure metals - N i , Al, Mo, oxides, carbides, nitrides, etc. The thickness of detonation coatings is usually 40–220 μm. Thinner coatings have poor wear resistance. The coating consists of three zones: the transition zone 5–30 µm thick determines the adhesion strength of the coating to the substrate; the main zone, the thickness of which, depending on the purpose of the coating, is 30–150 µm; a surface zone 10–40 µm thick, which is usually removed during processing.

The technological process of detonation coating includes preparation of the sprayed surface and powder; coating application and quality control; mechanical processing and quality control of coatings after mechanical processing.

To form a strong bond between the materials of the part and the coating, it is recommended to apply an intermediate layer - a substrate. It is necessary in case of weak adhesion between the coating and the material of the part, when the values ​​of the coefficients of thermal expansion of the materials of the coating and the part differ significantly, and if the part operates under conditions of variable temperatures. The thickness of the intermediate layer is 0.05–0.15 mm. For its application, powders of nichrome, molybdenum, nickel-aluminum alloys, steel 12X18H9, etc. are used. Surface areas of parts that are not coated are covered with screens made of thin sheets of metal.

The spraying distance is set depending on the material, the dimensions and shapes of the part, the material and the required coating thickness within 50–200 mm. The required coating thickness is obtained by multiple repetitions of deposition cycles. The displacement of the part between two cycles should not exceed 0.5 of the hole diameter in the barrel.

Properties of thermal coatings

Interacting with atmospheric oxygen, metal particles are oxidized. The resulting oxide film separates them and prevents the formation of strong metallic bonds between the particles and the base and among themselves. Due to the significant amount of oxides and slag inclusions, the coating has an inhomogeneous,porous structure. Usually the density is 80-97%. Coatings from A l 2 O 3 and Zr0 2 have a porosity of 10-15%. Nickel-based self-fluxing alloy coatings may have a porosity of less than 2%.

The metal coating is enough fragile with low tensile strength and low fatigue strength of the sprayed material (tensile strength for steels is on average 10–12 MPa). Therefore, the coating does not increase the strength of the part, butits fatigue strengtheven decreases, which is associated, in particular, with the formation of additional stress concentrators on the surface of the part during its preparation for metallization. In this regard, metallization should not be used to restore parts with a low margin of safety.

The coating is characterized relativelyweak bonding strengthwith the base metal and particles between themselves, since without the use of a special additional effect, it is determined by the molecular forces of the interaction of the areas in contact with each other and by the purely mechanical adhesion of the sprayed particles to the surface irregularities of the part. Only at some local points can individual particles be welded to the metal of the part. Therefore, for example, the adhesion strength of the coating (MPa) during electroplating is 10–25, with gas flame - 12–28, with plasma up to 40. In this regard, plating is not used to restore parts operating at high shear stress (gear teeth, cams etc.), subjected to shock loads, as well as small surfaces that perceive significant loads (thread, grooves, etc.).

Special methods for increasing the adhesion of the coating to the base include: preheating the part to a temperature of 200–300 °C, applying an intermediate layer (sublayer) of low-melting or low-melting materials, and melting the coating.

Spray Coatingswork well for compression. For example, the compressive strength of a steel coating is 800–1200 MPa, which is higher than that of cast iron.

Hardness of the metallized layer is usually higher than the hardness of the original metal due to the hardening of the deposited material during the metallization process, hardening of the transferred metal particles upon impact on the surface, and the presence of oxide films in the formed layer.

However, his wear resistanceis not related to hardness and in dry friction it can be 2-3 times less than that of the metal of the part; therefore, metallized coatings cannot be used in matings operating without lubrication or with periodically supplied lubrication. However, in the presence of lubrication, metallized coatings provide a lower coefficient of friction in mating and greater wear resistance of parts. This is due to the fact that, due to the porosity, the metallized layer absorbs oil up to 9% of its volume. Thus, the effect of self-lubrication of the coating is observed. With insufficient lubrication or with a temporary cessation of lubrication, seizing occurs much later compared to a non-metallized surface. Plasma coatings made of refractory materials have significant wear resistance, which is due to their physical and mechanical properties.

Under conditions of abrasive wear, coatings made of self-fluxing alloys based on nickel and A l 2 O 3

In particular, the wear resistance of coatings made of self-fluxing nickel-based alloys (SNHS) is 3.5–4.6 times higher than the wear resistance of hardened steel 45. Coatings made of tin-lead-copper pseudo-alloys have good antifriction properties for plain bearings.

To create corrosion-resistant coatings, aluminum, zinc, copper, chromium-nickel, and other alloys are usually used. Due to the porosity of the coatings, their thickness should not be less than 0.2 mm for zinc; 0.23 mm - for aluminum; 0.18 mm for copper; 0.6-1.0 mm for stainless steel.

Baking Powder Coatings

baking - this is the process of obtaining a metal coating on the surface of a part, including applying a layer of powder to it and heating them to a temperature that ensures sintering of the powder material and the formation of a strong diffusion bond with the part. This method is based on the technological methods of powder metallurgy.

To obtain a durable layer on the surface of the part that has reliable adhesion to the base, it is necessary to activate the surface of the part, the powder, or both components. The most accessible and effective are the followingtypes of activation: chemical, thermal (accelerated heating and the introduction of additives that reduce the melting point at the points of contact between the powder and the part), power (creating a reliable contact between the powder and the part).

At chemical activationactive additives are introduced into the charge, usually in the form of a dispersed powder (boron, silicon, phosphorus, nickel, etc.), evenly distributed in the applied powder. They reduce metal oxidation and destroy oxide films.

Thermal activationconsists in accelerated heating in order to activate diffusion processes and create for a short time in local zones a temperature exceeding the melting point. In this case, to reduce the temperature of the appearance of the liquid phase, additives are used (as a rule, together with chemical activation), which form a low-melting eutectic. The most efficient and technologically advanced is heating in the inductor by high-frequency currents. Due to the short duration of heating up to the temperature providing sintering, the oxidation of the powder and the part is reduced, which eliminates the need for protective-reducing media or vacuum.

Force activationnecessary in cases where without proper adhesion of powder particles to each other and to the surface of the part it is impossible to create the conditions necessary for baking. Force activation promotes an increase in the density of the coating and significantly accelerates the diffusion processes between the powder particles and the part. In practice, for force activation, the following are used: static application of a load with simultaneous heating, sintering with the application of vibrations, pressure using centrifugal forces.

Simultaneous application of chemical, thermal and force activation makes it possible to obtain the highest quality coatings.

Electrocontact baking. In practice, the method of electrocontact sintering with force activation is usually used. The coating process in this case is carried out as follows. A powder is fed onto the surface of the part, which is pressed against it by an electrode (usually a roller one) of a contact welding machine. Under the action of electric current pulses, the powder is heated to a temperature of 0.9–0.95 of its melting point. Heating occurs due to the energy released during the passage of electric current through active resistance, which is formed by contacts between powder particles, the surface of the part and the electrode.

Under the action of pressure from the side of the electrode, the plastic particles of the powder are deformed, sintered between themselves and the surface of the part. The coating is formed as a result of a non-diffusion process of setting and diffusion processes of sintering and welding.

The sintering process is provided with the following parameters: current strength up to 30 kA, voltage 1–6 V, current pulse duration 0.01–0.1 s, pressure on the powder up to 100 MPa.

The electrocontact sintering method, having high productivity and low energy intensity, ensures the strength of adhesion of the applied powder layer to the part of 150–200 MPa, creates a small heat-affected zone in the part, does not require the use of a protective atmosphere, is not accompanied by light emission and gas evolution. Alloyed powders are used to give the coating the necessary indicators of porosity, hardness and wear resistance.

To disadvantages This method should be attributed to the instability of the properties of the coating along the length of the part with the traditional (cylindrical) shape of the electrode (roller), which is due to uneven heating of the powder within its width. If under the middle part of the roller, where the pressure exerted on the powder is maximum, it can be overheated to melt, then under the extreme sections the heating temperature may be insufficient for high-quality baking, which may cause the applied layer to chip during operation.

The uneven heating of the powder in this case is due to its flowability, due to which the density of the powder layer and, consequently, its electrical resistance across the width of the roller are variable. To stabilize the heating of the powder along the width of the roller, its outer contact surface is made concave.

The sintering method developed at INDMASH NASB is increasingly used in industry, in which force activation is carried out by centrifugal forces, and the powder and the part are heated by the inductive method during the sintering process.

A significant advantage of this sintering method is that due to the action of centrifugal forces on each powder particle, high-quality coating formation is ensured simultaneously along the entire length of the part surface. In addition, due to the combination of heating and coating molding in time, this sintering process is characterized by high productivity with minimal oxidation of the surface of the part and powder.

By induction centrifugal sintering, antifriction and wear-resistant coatings are applied to the inner, outer and end surfaces of cylindrical parts in a wide range of diameters. For this, special centrifugal installations are used. The part is usually rotated around a horizontal axis with an external inductor, which makes it possible to obtain a uniform coating thickness along the length of the part and to apply coatings in holes of small diameter.

According to a typical technological process of centrifugal induction sintering, a “sleeve” type part is placed in a protective steel shell in the hole, a mixture of powder and flux is poured into the hole, the hole is closed from both ends of the part with non-stick gaskets and covers.

The device assembled in this way is fixed on the spindle of the centrifugal installation, having previously provided the necessary positioning relative to the inductor. Then the spindle is rotated and the power supply circuit of the inductor is turned on. The heating temperature of the part is controlled by an appropriate system.

After sintering the powder material and sintering the coating, the inductor is turned off, while maintaining the rotation of the spindle. Rotation is stopped when the part is cooled to 350-600 °C, after which the device is removed from the installation and cooled to natural temperature. The resulting coating is processed to the required size.

Metallizer electric arc - a set of equipment for arc metallization of surfaces of parts and equipment in order to protect against corrosion and restore wear by spraying metal coatings. Aluminum, zinc, steel and their alloys are used for work. The resulting coating has increased wear-resistant, anti-corrosion properties.

We offer the following metallizers:

Set of equipment for electric arc metallization TSZP-LD/U2 300

Purpose of the set of equipment for electric arc metallization TSZP-LD/U2 300:

The main purpose is the application of anti-corrosion coatings on large surfaces: bridges, metal structures, apparatuses, tanks, GPA exhaust shafts, chimneys. With this kit, it is possible to carry out aluminizing and galvanizing of structures after installation. The installation is characterized by performance, high reliability, ease of configuration. It is widely used in Russia and abroad to protect structures from corrosion in sea and fresh water and in the atmosphere. The installation design includes a power supply unit, a remote block of push-motors with a control system and a burner. Use is possible both in the workshop and in the field

Complete set of equipment for electric arc metallization TSZP-LD/U2 300:

• Manual gun LD/U2 with open and closed nozzle system
• Wire spraying is carried out by compressed air
• Adjustable for diameter 1.6, 2.0 and 2.5 mm
• Hose set LD/U2 300 A, 3.5 m long, complete with fittings
• Supply hose LD/U2, 8 m long, with quick-release connection on one side
• Tool kit for maintenance of a set of equipment
• Documentation in Russian
• Wire feeder

Specifications:

Purpose of the equipment set:

The main purpose is the automated deposition of protective metal coatings on particularly complex surfaces of parts and equipment. It features a large set of settings, ease of use and ease of learning to work. In addition, it can be used as part of automated complexes.

The TSZP group of companies supplies installations and complexes, equipping them with Kuka and ABB industrial robots, manipulators, rotators, soundproof chambers, exhaust and flow ventilation systems and air filters. In addition, we provide maintenance, supply of spare parts and commissioning of coating systems. You can always contact us for qualified assistance.

Complete set of equipment for electric arc metallization TSZP SPARK 400:

Specifications:

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 methods of 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 fits (from low-carbon steels Sv-08, Sv-10GA) and mobile joints (from high-carbon steels Np-50, Np-85 and alloyed steels Np-30Kh13, Np-40Kh13, 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 spray 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 plating involves the use of 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 the corrosive effects of the environment, like paints and varnishes. 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, but a distinctive feature from HVOF coatings is high porosity, which can in some cases lead to corrosion, as well as a lower level of adhesion.

Electric arc metallization is a procedure of layer-by-layer deposition of metal of small thickness on heated products. In this case, the height of the electric arc is minimal, and the molten wire is dissipated by the gas flow directed along the axis of the filler material. The technology was developed back in the 1950s and is widely used to protect structures for various purposes from corrosion.

To perform metallization, an indirect electric arc is used, burning between conductive wire elements. The electrode metal, heated to a droplet state, is sprayed onto the workpiece with a stream of protective gas or compressed air. As the additives melt, they simultaneously enter the arc region by two pairs of rollers.

Anticorrosion protection by the method of metallization is characterized by:

• low energy consumption;
• high productivity and consumption efficiency of the sprayed additive;
• the possibility of creating a coating with a thickness of up to 15 mm without limiting the size of parts;
• small temperature effect on the base material of the processed products;
• reliability, ease of maintenance of equipment;
• the possibility of full or partial automation of the process, the creation of production lines.

Metallization using an electric arc also has disadvantages:

• limited range of filler material;
• the content in the coating of a large number of oxides that reduce impact strength;
• insufficiently high adhesion strength with the base material;
• high porosity of the layers, which prevents the continuous operation of products in corrosive environments without additional protection.

Metal processing technology

The flow of melted filler wires with a cross section of 1.5–2 mm is made through the holes in the burner. An electric arc is excited between the filler rods, which causes them to melt.

Compressed air comes out of a nozzle located in the middle of the metallization device, picking up small molten metal drops and transferring them to the surface to be treated.

Compressed air is usually used to atomize and transfer the melt. If stainless steel or aluminum alloys are used as filler material for arc coating, then nitrogen is used.

The intensity of the flow of the diluted additive during electric arc plating is selected in accordance with the required arc mode, which affects the distance between the wire elements.

Electric arc metallizers have the following standard modes of operation:

• voltage - 24-35 V;
• current strength - 75–200 A;
• supply air pressure - 0.5 MPa;
• production of devices - 30–300 g / min.

The process of electric arc metallization is stable at direct current, allows you to create deposition with a fine-grained structure.

The figure shows the main elements of the metallizer:

• 1 - nozzles;
• 2 – point of injection of filler material;
• 3 – compressed air outlet point.

The surface to be metallized is preliminarily cleaned of oils, dirt, and corrosion centers. The preparation of large products is carried out using sand or shot blasting after preliminary degreasing.

To increase adhesion, the time period between the end of the preparatory work and the implementation of the electric arc coating should be no more than 120 minutes.

To minimize thermal stresses and prevent overheating of products, layer-by-layer metallization is carried out with interruptions for cooling and coating formation.

The metal is first applied to parts of the product in places of sharp transitions, fillets, corners, ledges or ledges. Then, the main areas are metallized, provided that the additive is applied uniformly in one or several passes.

The required form, dimensions and shapes of the product are obtained after electric arc spraying during the final processing.

Filler materials

A wire rod of continuous length is preferably used as filler material. Additives are supplied in two types:

• solid section;
• powder.

The flow rate is assigned 220–850 m/h.

To create a protective layer of metal elements with their subsequent landing or with a fixed connection, a solid wire thread is used. To create surfaces of increased hardness during electric arc metallization, powder rods should be used.

Highly alloyed iron-based filler materials and non-ferrous metal wires are used to form anti-corrosion layers.

Aluminum, zinc and compounds based on them are most often used for application by electric arc metallization.

The additive from the coils comes through two flexible hoses to the metallizer. The cassettes and the remote control are located on the pedestal 3 and can be turned along the vertical axis.

The electric arc apparatus for metallization EDM-3 has a low weight (1.8 kg), and the possibility of turning the cassette and the control unit horizontally makes it convenient for use.

An electric arc apparatus of a different design, EM-6, is to be installed on the support of a lathe, on the shaft of which the sprayed part is mounted. A steel funnel is attached between the metallizer and the product. Powdered graphite, liquid potassium or sodium glass is applied to its surface. Thanks to this solution, the efficiency of using filler material increases by 10–15%.

The spraying system of the electric arc apparatus has been modernized by installing a cone-shaped air nozzle. This makes it possible to reduce the opening angle of the cone, increase the energy of the spray flow and apply layers under a pressure of 0.45–0.5 MPa.

Structural elements of the electric arc device for metallization EM-6:

1. Metallizer.
2. Conical nozzle.
3. The item to be processed.
4. Cartridge.
5. A device used to move the machine support along with the arc metallizer in the longitudinal direction.