Wire plasma atomizer for surfacing. Plasma welding is an effective way to protect metal parts. The main features of metal surfacing using plasma technology

Plasma surfacing methods are currently widely used. In plasma surfacing (PN), plasma is used as a heating source, which is a substance in a highly ionized state. 1 cm 3 of plasma contains 10 9 - 10 10 and more charged particles. Plasma is formed in almost any arc discharge. The main method of obtaining plasma for technological purposes is the passage of a gas jet through an electric arc located in a narrow copper channel. At the same time, due to the lack of the possibility of expanding the arc column, the number of elastic and inelastic collisions of charged particles increases, i.e., the degree of ionization increases, the density and voltage of the arc increase, which causes an increase in temperature to 10,000 - 15,000 ° C.

The presence of a stabilizing water-cooled nozzle channel in plasma torches is the main difference from conventional torches used in shielding gas welding with a non-consumable electrode.

When hardening and restoring parts, depending on their shape and working conditions, several types of plasma surfacing are used, which differ in the type of filler metal, the method of its supply to the hardened surface, and the electrical circuits for connecting the plasma torch.

In plasma surfacing, two types of compressed arc are used in relation to the welded part: direct and indirect action. In both cases, ignition of the plasma torch arc and the implementation of the surfacing process are performed in a combined way: first, an indirect arc is excited between the anode and cathode of the plasma torch using an oscillator.

Arc of direct action is formed when a low-ampere (40 - 60 A) indirect arc comes into contact with a current-carrying part. Materials can be fed into the arc zone: neutral or current-carrying wire, two wires (Fig. 8.8), powder, powder simultaneously with the wire.

Indirect arc method lies in the fact that a direct arc is formed between the pilot arc and the current-carrying wire, the continuation of which is an indirect independent arc in relation to the electrically neutral part.

High productivity (up to 30 kg / h) is provided by plasma surfacing with the supply of two consumable electrodes 1 (Fig. 8.8) into the bath, connected in series to the power source and heated almost to the melting temperature. Shielding gas is supplied through nozzle 2.

Universal method of plasma surfacing - surfacing with blowing powder into the arc(fig.8.9). The burner has three nozzles: 3 - for the formation of a plasma jet, 4 - for supplying the filler powder, 5 - for supplying a protective gas. One current source serves to ignite the arc with an oscillator 2 between the electrode and the nozzle, and the other current source forms a plasma arc of direct action, which melts the surface of the product and melts the powder supplied from the hopper 6 by a gas flow. By changing the current of both arcs with devices 1, it is possible to control the amount of heat used to melt the base metal and the filler powder and, consequently, the proportion of metal in the deposited layer.

Rice. 8.9. Plasma powder surfacing

The increase in the productivity of the plasma surfacing process largely depends on the efficiency of heating the powder in the arc. The temperature that the powder particles acquire in the arc is determined by the intensity and duration of heating, which depend on the plasma parameters, the conditions for introducing the powder into the arc, and the technical parameters of the surfacing process. The greatest influence on the heating of the powder is exerted by the arc current, particle size, and the distance between the plasma torch and the anode.

The main advantages of the PN method: high quality of weld metal; small depth of penetration of the base metal with high adhesion strength; the possibility of surfacing thin layers; high production culture.

The main disadvantages of PN: relatively low performance; the need for sophisticated equipment.

The technological process of applying coatings during melting of both filler material (rods, wires, tubes, rods, tapes, powders) and the surface layer of the deposited metal surface. Depending on the type of heating source, surfacing can be carried out using the heat of a gas flame (gas-flame), electric arc (electric arc in a protective gas environment, submerged arc, etc.), molten slag (electroslag), concentrated energy sources - compressed arc (plasma), laser beam (laser) and other methods.

Purpose

Production of parts with wear and corrosion-resistant surface properties, as well as restoration of the dimensions of worn and defective parts operating under high dynamic, cyclic loads or subject to intense wear.

Choice of method

The choice and use of a specific surfacing method is determined by the production conditions, the number, shape and dimensions of the welded parts, the permissible mixing of the deposited and base metal, technical and economic indicators, as well as the amount of wear. The choice of the type of coating material is made in accordance with the operating conditions of the parts. As a filler material in surfacing parts, in many cases, the most effective use of powders, which are manufacturable and provide a wide range of chemical and phase composition of the coating.

Advantages

• application of coatings of considerable thickness;
• no restrictions on the size of the surfaces to be deposited;
• obtaining the required dimensions of the parts to be restored by applying a material of the same composition as the base metal;
• use not only to restore the dimensions of worn and defective parts, but also to repair products by healing defects (shells, pores, cracks);
• low heat input into the base metal during plasma surfacing;
• repeated carrying out of the recovery process and, consequently, high maintainability of the welded parts;
• high performance;
• relative simplicity and small size of the equipment, ease of automation of the process.

Flaws

• the possibility of changing the properties of the deposited coating due to the transition of elements of the base metal into it;
• change in the chemical composition of the base and deposited metal due to oxidation and burnout of alloying elements in the near-weld zone;
• the occurrence of increased deformations due to thermal effects;
• the formation of large tensile stresses in the surface layer of the part, reaching 500 MPa and a decrease in fatigue resistance characteristics;
• the possibility of structural changes in the base metal, in particular, the formation of a coarse-grained structure, new brittle phases;
• the possibility of cracks in the deposited metal and the heat-affected zone and, as a result, a limited choice of combinations of the base and deposited metals;
• the presence of large allowances for machining, leading to significant losses of the deposited metal and an increase in the labor intensity of machining the deposited layer;
• requirements for the preferential location of the deposited surface in the lower position;
• the use in some cases of preheating and slow cooling of the deposited product, which increases the complexity and duration of the process;
• the difficulty of surfacing small products of complex shape.

Plasma welding

Plasma production technologies are those that use the impact of plasma (the fourth state of aggregation of matter) on various materials in order to manufacture, maintain, repair and / or operate products. During plasma surfacing, the part and filler material are heated by electric arc plasma, which is generated by a direct arc compressed by a compressed plasma nozzle and plasma gas or an indirect arc burning between the electrode and the plasma nozzle (between the electrode and filler wire) or by two arcs simultaneously.

Plasma-powder surfacing

In plasma-powder surfacing, both a process using a single direct arc and a two-arc PTA process (plasma transferred arc) are used, where a direct arc is operating simultaneously, burning between the electrode and the workpiece, and an indirect arc, burning between the electrode and the plasma nozzle (Fig. 1). Due to the fact that traditionally the process of applying coatings using an indirect arc is called plasma spraying, and using a direct arc - plasma surfacing, the PTA process is called plasma surfacing-spraying.

The process of plasma surfacing-spraying can be characterized as a method of applying powder coatings with a thickness of 0.5-4.0 mm with controlled heat input into the powder and the product by a plasma torch with two burning arcs of direct and indirect action. The indirect (pilot, standby) arc is used to melt the filler powder, and the main arc is used to melt the surface layer of the part and maintain the required temperature of the powder on the part. Separate regulation of the parameters of the main and indirect arc ensures efficient melting of the powder with minimal heating of the workpiece surface.

The main advantages of plasma surfacing-spraying:

• minimal thermal impact on the base metal;
• minimal mixing of base and deposited metal;
• high utilization rate of filler material;
• minor allowances for machining;
• minimal deformation of the deposited part;
• uniformity of the deposited layer height;
• high process stability.

In table. 1 shows the distinctive characteristics of plasma surfacing-spraying from the closest analogues. Thus, coatings applied by plasma surfacing using a direct arc provide excessive melting of the base metal and its mixing with filler material, and coatings applied by plasma spraying are not non-porous and are limited to a thickness of about 1 mm (beyond which cracking is possible due to high internal stresses). ).

Table 1. Main properties of coatings applied by plasma methods

The view of plasma torches for the process of plasma surfacing-spraying is shown in fig. 2.

Rice. 2. Plasmatrons for plasma surfacing-spraying

Comparative characteristics of all production plasma technologies are given in Table. 2 (the positive aspects of the processes are highlighted in gray cells, and the greatest advantages are marked in bold), and in Fig. 3 shows options for their use.

Table 2. Characteristics of plasma technologies

Plasma cladding is most commonly used for coating automotive and marine engine valves, various extruders and screws, fittings and other parts. The economic efficiency of plasma surfacing is determined by an increase in the durability of the deposited parts while reducing the consumption of powder materials used, the cost of processing them, and saving gas.

Rice. 3. Plasma welding process

Link to books and articles

• Sosnin N.A., Ermakov S.A., Topolyansky P.A. Plasma technologies. Guide for engineers. Publishing house of the Polytechnic University. St. Petersburg: 2013. - 406 p.
• Topolyansky P.A., Topolyansky A.P. Progressive coating technologies - surfacing, spraying, deposition. Rhythm: Repair. Innovation. Technology. Modernization. 2011, No. 1 (59). - pp. 28-33
• Ermakov S.A., Topolyansky P.A., Sosnin N.A. Evaluation of the quality of the plasma surfacing process. Welding and diagnostics. 2015. No. 3. - C. 17-19
• Ermakov S.A., Topolyansky P.A., Sosnin N.A. Optimization of plasma powder surfacing with a two-arc plasma torch. Repair. Recovery. Modernization. 2014. No. 2. - S. 19-25

Plasma-powder surfacing (Plasma transfer Arc, PTA)

Plasma is a highly ionized gas heated to a high temperature, reaching a temperature of +10 ... 18 thousand C. A plasma jet is formed in special burners - plasma torches. The cathode is a non-consumable tungsten electrode. A jet of plasma gas with a flow rate of up to 15,000 m/s captures and delivers the powder to the surface of the part.

Advantages of plasma-powder surfacing:

1. High concentration of thermal power.
2. Minimum heat affected zone width, no leash.
3. The thickness of the deposited layer is from 0.1 mm to several mm.
4. Surfacing of various wear-resistant materials on a steel part.
5. Plasma hardening of the product surface.
6. Slight mixing of the deposited material with the base.

JSC "Plakart" has significant experience in plasma-powder surfacing solutions. This method of applying a wear-resistant coating ensures high quality and uniformity of the deposited metal.

Applications:

• Protection against corrosion and wear of parts of shut-off and shut-off and control valves: valves for the shipbuilding and chemical industries, power valves, oil and gas valves. Trouble-free operation of welded parts of shut-off valves for more than 10 years. Wear-resistant fittings (saddle, gates, rods) for the mining industry.
• Hardening by wear-resistant coatings of highly loaded parts (neck rings and valves, etc.)

After plasma-powder surfacing, the parts withstand the influence of aggressive chemical environments, elevated temperatures, and retain high strength characteristics.

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Manual arc surfacing with stick electrodes

The most versatile method, suitable for surfacing parts of various shapes, can be performed in all spatial positions. Alloying of the deposited metal is carried out through the electrode rod and/or through the coating.

For surfacing, electrodes with a diameter of 3-6 mm are used (with a thickness of the deposited layer of less than 1.5 mm, electrodes with a diameter of 3 mm are used, with a larger one, with a diameter of 4-6 mm).

To ensure minimal penetration of the base metal with sufficient arc stability, the current density should be 11-12 A/mm 2 .

The main advantages of the method:

• versatility and flexibility when performing a variety of surfacing work;
• simplicity and availability of equipment and technology;

The main disadvantages of the method:

• poor performance;
• difficult working conditions;
• inconstancy of the quality of the deposited layer;
• large penetration of the base metal.

Semi-automatic and automatic arc surfacing

For surfacing, all the main methods of mechanized arc welding are used - submerged arc welding, self-shielded wires and tapes, and in a shielding gas environment. The most widely used is submerged arc surfacing with a single wire or strip (cold-rolled, flux-cored, sintered). To increase productivity, multi-arc or multi-electrode surfacing is used. Alloying of the deposited metal is carried out, as a rule, through the electrode material; alloying fluxes are rarely used. Arc surfacing with self-shielding flux-cored wires and strips has become widespread. Arc stabilization, alloying and protection of the molten metal from nitrogen and oxygen in the air is provided by the components of the core of the electrode material.

Arc surfacing in shielding gases is used relatively rarely. CO2, argon, helium, nitrogen or mixtures of these gases are used as shielding gases.

Due to the large penetration of the base metal during arc surfacing, the required composition of the deposited metal can be obtained only in a 3–5 mm layer.

The main advantages of the method:

• universality;
• high performance;
• the possibility of obtaining deposited metal of almost any alloying system.

Main disadvantage:

• large penetration of the base metal, especially when surfacing with wires.

Electroslag surfacing (ESHN)

ESP is based on the use of heat released when an electric current passes through a slag bath.

The main schemes of electroslag surfacing are shown in fig. 25.2.

Rice. 25.2. Schemes of electroslag surfacing:
a - a flat surface in a vertical position: b - a fixed electrode of large cross section; in - a cylindrical part with wires; g - electrode-pipe; e - granular filler material: e - composite alloy; g - composite electrode; h - a flat surface in an inclined position; and - liquid filler metal; k - horizontal surface with forced formation; l - two electrode tapes with free formation; 1 - base metal: 2 - electrode; 3 - mold; 4 - deposited metal; 5 - dispenser; 6 - crucible; 7 - flux

ESP can be produced in a horizontal, vertical or inclined position, as a rule, with the forced formation of a deposited layer. Surfacing on a horizontal surface can be done with both forced and free formation.

The main advantages of the method:

• high stability of the process in a wide range of current densities (from 0.2 to 300 A/mm 2), which makes it possible to use both electrode wire with a diameter of less than 2 mm and large-section electrodes (> 35000 mm 2) for surfacing;
• productivity reaching hundreds of kilograms of deposited metal per hour;
• the possibility of surfacing in one pass layers of large thickness;
• the possibility of surfacing steels and alloys with an increased tendency to cracking;
• the ability to give the deposited metal the required shape, to combine surfacing with electroslag welding and casting, on which butt-slag surfacing is based.

The main disadvantages of the method:

• high heat input of the process, which causes overheating of the base metal in the HAZ;
• the complexity and uniqueness of the equipment;
• the impossibility of obtaining layers of small thickness (except for the method of ESHN with tapes);

Plasma welding (PN)

PN is based on the use of a plasma arc as a source of welding heating. As a rule, PN is performed by direct current of direct or reverse polarity. The welded product can be neutral (plasma jet surfacing) or, which is the case in the vast majority of cases, included in the electrical circuit of the arc power source (plasma arc surfacing). PN has a relatively low productivity (4-10 kg / h), but due to the minimum penetration of the base metal, it allows to obtain the required properties of the deposited metal already in the first layer and thereby reduce the amount of surfacing work.

There are several PN schemes (Fig. 25.3), but the most widely used is plasma-powder surfacing - the most versatile method, since powders can be made from almost any alloy suitable for surfacing.

Rice. 25.3. Plasma surfacing schemes:
a - a plasma jet with a current-carrying filler wire; b - plasma jet with a neutral filler wire; c - combined (double) arc with one wire; g - the same, with two wires; d - hot wires; e - consumable electrode; g - with internal supply of powder into the arc; e - with external supply of powder into the arc; 1 - protective nozzle; 2 - plasma torch nozzle; 3 - protective gas; 4 - plasma gas; 5 - electrode; 6 - filler wire; 7 - product; 5 - indirect arc power supply; I - direct arc power supply; 10 - transformer; II - consumable electrode arc power supply; 12 - powder: 13 - carbide powder

The main advantages of the PN method:

• high quality of weld metal;
• small depth of penetration of the base metal with high adhesion strength;
• high production culture.

The main disadvantages of PN:

• relatively low performance;
• the need for sophisticated equipment.

Induction surfacing (IN)

IN is a high-performance, easy-to-mechanize and automate process, especially effective in mass production. In industry, two main variants of induction surfacing are used: using a solid filler material (powder charge, chips, cast rings, etc.) melted by the inductor directly on the surface being deposited, and liquid filler metal, which is melted separately and poured onto the surface heated by the inductor welded part.

The main advantages of the IN method:

• small depth of penetration of the base metal;
• the possibility of surfacing thin layers;
• high efficiency in mass production.

The main disadvantages of IN:

• low efficiency of the process;
• overheating of the base metal;
• the need to use for surfacing only those materials that have a melting temperature below the melting temperature of the base metal.

Laser (light) surfacing (LN)

Three LN methods are used: melting of pre-applied pastes; melting of the sprayed layers; surfacing with the supply of filler powder to the flashing zone.

The productivity of laser powder surfacing reaches 5 kg/h. The required compositions and properties of the deposited metal can be obtained already in the first layer of small thickness, which is important from the point of view of the consumption of materials and the costs of surfacing and subsequent processing.

The main advantages of the method:

• low and controlled penetration with high bond strength;
• the possibility of obtaining thin deposited layers (<0,3 мм);
• small deformations of the welded parts;
• the possibility of surfacing hard-to-reach surfaces;
• the possibility of supplying laser radiation to several workplaces, which reduces the time for equipment readjustment.

The main disadvantages of the method:

• low productivity;
• low efficiency of the process;
• the need for complex, expensive equipment.

Electron beam surfacing (ELN)

With ELN, the electron beam makes it possible to separately control the heating and melting of the base and filler materials, as well as to minimize their mixing.

Surfacing is carried out with the addition of solid or flux-cored wire. Since surfacing is carried out in a vacuum, the flux-cored wire charge can consist of only alloying components.

The main advantages of the method:

• the possibility of surfacing layers of small thickness.

The main disadvantages of the method:

• complexity and high cost of equipment;
• the need for biological protection of personnel.

Gas welding (GN)

With GN, the metal is heated and melted by a flame of gas burned in a mixture with oxygen in special burners. As a fuel gas, acetylene or its substitutes are most often used: propane-butane mixture, natural gas, hydrogen, and other gases. GN is known with the addition of rods or with doubled powder into a gas flame.

The main advantages of the method:

• low penetration of the base metal;
• universality and flexibility of technology;
• the possibility of surfacing layers of small thickness. The main disadvantages of the method:
• low process productivity;
• instability of the quality of the deposited layer.

Furnace hardfacing of composite alloys

The method of furnace surfacing of especially wear-resistant composite alloys is based on the impregnation of a layer of hard refractory particles (carbides) with a binder alloy under autovacuum heating conditions.

As a wear-resistant component of a composite alloy, granulation relit 0.4-2.5 mm or crushed waste of sintered hard alloys of the WC-Co type is most often used. A commonly used binder alloy contains about 20% Mn, 20% Ni and 60% Cu.

Furnace surfacing of composite alloys is mainly used in ferrous metallurgy to increase the durability of blast furnace cones, equalizing valves and other parts operating under conditions of intense wear.

The main advantage of the method:

• the possibility of surfacing unique products of complex shape.

The main disadvantages of the method:

• the need to manufacture metal-intensive equipment, which, after the end of the process, is removed into scrap metal;
• long duration of preparatory operations.

Volchenko V.N. "Welding and welded materials".

One of the main methods for increasing the reliability and service life of glass moulds, valves, valves is plasma surfacing (Plasma transfer Arc, PTA).

Using the method of plasma-powder surfacing can significantly improve the quality of the welded parts, increase productivity and impart special properties to the surface being deposited.

The choice towards the PTA method by the largest manufacturers and consumers of valves, mold sets for glass production, valves - confirms the benefits of using the plasma-powder surfacing method, since the resulting deposited layer with improved properties can significantly increase the service life of parts and assemblies, extend the overhaul intervals and reduce costs for major and current repairs.

Plasma surfacing machines KSK are designed for surfacing of parts from rings and valves to fine glass molds and parts of valves.

• Increasing competitiveness: the methods we offer are used by all leading foreign manufacturers of fittings, glass, valves, rolls.
• Increase in overhaul cycles: the service life of parts increases from 3 to 10 times.
• Reducing downtime: reducing the number of stops, and, accordingly, less time for debugging equipment to reach the desired mode.

Professional hardfacing equipment

Metsol LLC presents to the attention of potential customers automatic plasma surfacing installations from the Czech manufacturer KSK. The equipment is designed for surfacing of sealing and working surfaces, including glass molds, valve seats, valve rings, surfacing of internal diameters. The design of plasma torches is suitable for products of various shapes and surfacing methods. The developers offer 7 types of plasma torches, which guarantee effective cooling of the installation even at maximum operation. In the course of work adjustment of settings of welding programs by the operator through the touch screen on the panel of the panel is allowed. This allows you to reduce the percentage of rejects in test samples.

Qualitative approach

One of the activities of Metsol LLC is the supply, installation and commissioning of a plasma surfacing installation in Yekaterinburg for customers. Experienced specialists effectively solve production problems at a high professional level. The service department has modern knowledge in the field of welding technologies and metalworking. Having decided to buy an automatic plasma surfacing installation, you will receive:

• Increasing competitiveness at the level of leading foreign manufacturers of fittings, glass, valves, rolls.
• Increase in overhaul intervals: the service life of parts increases from 3 to 10 times.
• Reduced downtime and downtime.

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