Are auto repair companies profitable

Gas dynamic spraying. "cold" spraying of metal coatings. The process of spraying high and low pressure

The process of gas dynamic spraying is the fixation of metal particles on metal, glass, ceramic or concrete products at the time of the collision of the gas powder sweep with the outer surface of the substrate. This occurs due to the preliminary acceleration of these particles in the nozzle for supersonic dispersion of particles, while the temperature of the accelerated metal particles does not exceed their melting temperature. The metal layer, which is deposited on the product using the dynamic cold gas spraying process, differs in its high-quality adhesion to the surface of the substrate and is resistant to mechanical damage.

History of the discovery of the phenomenon and facts discovered experimentally

The fact that, in order to form a metal coating on a substrate surface, it is not necessary to bring metal particles to or near their melting state, as is normally done using standard spraying techniques, was recognized by Russian scientists in the late 20th century discovered. The results of a series of experiments carried out by scientists from the Russian Academy of Sciences showed that spraying surfaces can also be achieved by heating solid metal particles to a temperature much lower than their melting point.

In addition, the following important facts were recorded during the experiments:

  • the main parameter in the technology of dynamic cold gas spraying, on which the quality of the adhesion depends, is the rate of acceleration of the gas-powder mixture. This parameter affects the degree of adhesion of the spray to the surface to which it is applied, as well as the properties of the spray layer such as porosity and mechanical strength. At a speed of solid particles above 500-600 m / s, erosion processes are converted into a permanent coating layer.
  • empirically, a critical limit of the particle flow was found at which a metal layer does not form for any duration of exposure of the gas powder flow to the substrate;
  • if the powder consumption exceeds a critical value, a strong and reliable adhesion of particles on the sprayed surface occurs and a dense spray layer is formed.
  • of the total volume of solid particles dispersed by supersonic flow, only a small amount forms a surface spray layer. Most of the particles are sprayed and cannot gain a foothold on the treated surface. Accordingly, the amount of metal particles deposited and fixed on the product depends directly on the volume of powder material consumed;
  • the surface of the substrate is slightly heated during the formation of the deposition layer. The temperature of the surface, which is streamlined by the gas flow, and of the substrate that is being sprayed gas-dynamically, differ by approximately 45 degrees from one another.

Types of cold gas dynamic spray and their advantages

Cold gas dynamic spraying has two types:

  1. High pressure spraying with helium, nitrogen or a gas mixture. The consumption of powder material is 4.5-13.5 kg / h.
  2. Cold gas dynamic low pressure spraying with compressed air. The amount of powder consumed is in the range from 0.3 to 3 kg / h.

Both types of spray have their advantages and disadvantages:

  • when using high pressure in the technological process, the coating is better preserved, although the size of the solid particles of the metal powder can vary from 5 to 50 micrometers, and not within 5 to 30 micrometers, as in the compressed air technology;
  • the technological process of low pressure spraying uses smaller equipment, the cost of which is significantly lower than that used for high pressure spraying.

The process of spraying high and low pressure

During high pressure cold spray, the gas is heated and combined with solid particles of the powder material. This gas-powder mixture enters a supersonic nozzle, accelerates there to a supersonic speed and is directed at a pressure of 7 to 40 bar onto the surface of the product on which a metal coating has to be formed.

Cold spraying with compressed air differs technologically from the high pressure spraying process in that the main processes take place directly in the nozzle in order to accelerate the particles to supersonic speed: the gas is heated directly in it and the powder enters the nozzle perpendicular to the gas flow. In addition, when using the low-pressure spray process, powders are used in which, in addition to metal particles, ceramic particles are also present. Such additives improve the surface condition of the product to be sprayed and increase the quality of the adhesion of materials. In addition, the ceramic particles continue to clean the walls and nozzle exit as the mixture flows through the equipment.

Scope of cold gas dynamic spray

Cold gas dynamic coating is used to solve the following problems:

  • restoration of metal parts that were prone to chips, cracks, abrasion and other mechanical damage;
  • coating of metal products by spraying in order to improve their anti-corrosion and thermal conductivity properties;
  • protection of the contact surfaces of metal cable lugs.

Candidates in physical and mathematical sciences O. KLYUYEV and A. KASHIRIN.

When the first metal tools appeared, it turned out that they were strong and durable, and very often they were spoiled under the influence of moisture. Over time, people created mechanisms and machines, and the more perfect they got, the more difficult the conditions had to be for their metal parts. Vibrations and changing loads, enormous temperatures, radiation, aggressive chemical environments - this is not a complete list of the "tests" to which they are subjected. Over time, people have learned to protect metal from corrosion, wear and tear, and other phenomena that shorten the life of parts. In fact, there are two approaches to providing such protection: either alloying elements are added to the base metal that give the alloy the desired properties, or a protective coating is applied to the surface. The operating conditions of machine parts determine the properties that coatings should have. The technologies for their application are diverse: there are common and relatively simple ones, there are very thin technologies that allow you to create coatings with unique properties. And restless engineers keep inventing new coatings and finding ways to preserve them. The fate of these inventions can be happy if the coating far surpasses its predecessors in useful properties, or if the technology achieves a significant economic effect. The development of the Obninsk physicists combined these two conditions.

Metal particles that fly at enormous speed when they hit the substrate are welded to it, and ceramic particles seal the coating (a); Stuck ceramic particles (b) are visible on the thin section of the metal layer.

Scheme (above) and general view (below) of the device for spraying metal coatings.

With the device it is possible to apply coatings in any room and even in the field.

A vacuum zone is created behind the critical section of the nozzle, into which powder is sucked. Thanks to this phenomenon, the design of the feeder has been simplified.

Errors in case details (left) and spray result (right): a - crack in an automatic transmission; b - cavity in the cylinder head.

Instruments covered with a copper or aluminum layer can be used in areas at risk of fire: if they are hit against metal objects, they will not give off a spark.

TEMPERATURE PLUS SPEED

Of the methods of surface metallization in modern technology, the most commonly used are electrodeposition and melt immersion. Vacuum deposition, vapor deposition, etc. are used less often. The development of Obninsk physicists comes closest to gas thermal metallization, when the deposited metal is melted, sprayed onto the smallest droplets and transferred to a substrate with a stream of gas.

Metal is melted by gas torches, electric arcs, low temperature plasma, inductors, and even explosives. Accordingly, metallization processes are referred to as flame spraying, arc and high frequency metallization, plasma and detonation gas spraying.

In flame spraying, a metal rod, wire or powder is melted and sprayed into the flame of a burner that works with a mixture of oxygen and a combustible gas. With arc metallization, the material is melted by an electric arc. In both cases, metal droplets move with an air stream onto the sprayed substrate. Plasma spraying uses a plasma jet consisting of different types of plasma matrons to heat and spray the material. The detonation gas spray occurs as a result of an explosion that accelerates metal particles to enormous speeds.

In all cases, particles of the sprayed material receive two types of energy: thermal - from the heat source and kinetic - from the gas flow. These two types of energy are involved in the formation of the coating and determine its properties and structure. The kinetic energy of particles (with the exception of the detonation gas method) is low compared to thermal, and the nature of their connection with the substrate and with each other is determined by thermal processes: melting, crystallization, diffusion, phase changes, etc. Coatings are usually characterized by good Adhesion to the subsurface (adhesion) and unfortunately a poor uniformity, since the variation of the parameters over the gas flow cross-section is large.

The coatings produced by thermal processes have a number of disadvantages. This includes high porosity first of all, unless, of course, the goal is to make the coating specifically porous, as is the case with some details of radio tubes. In addition, high internal stresses arise in the coating due to the rapid cooling of the metal on the surface of the substrate. The workpiece inevitably heats up, and if it has a complex shape it can "lead". Finally, the use of flammable gases and high temperatures in the work area make it difficult to take measures to ensure the safety of personnel.

The detonation gas method is slightly different. In the event of an explosion, the particle velocity reaches 1000-2000 m / s.Therefore, the main factor that determines the quality of the coating becomes its kinetic energy. Coatings are characterized by high adhesion and low porosity, but explosion processes are extremely difficult to control and it is almost impossible to guarantee the stability of the result.

SPEED PLUS TEMPERATURE

The desire to develop more advanced technologies has long arisen. The engineers aimed to preserve the advantages of traditional technologies and eliminate their shortcomings. The direction of the search was more or less obvious: first, coatings should be formed mainly due to the kinetic energy of metal particles (particles should not be allowed to melt: this prevents heating of the part and oxidation of the substrate and coating particles), and second, the Particles do not collect at high speed due to the explosion energy, as in the detonation gas method, but in a stream of pressurized gas. This method was called gas dynamic.

The first calculations and experiments have shown that it is possible to produce coatings with quite satisfactory properties in this way if helium is used as the working gas. This choice was explained by the fact that the gas flow rate in a supersonic nozzle is proportional to the speed of sound in the corresponding gas. In light gases (hydrogen was not considered due to its explosiveness) the speed of sound is much higher than in nitrogen or air. It would be helium, which accelerates metal particles to high speeds and gives them kinetic energy sufficient to lock onto the target. The use of heavier gases, including air, was believed to be doomed.

The work of experimental spray equipment gave a good result: particles of most industrially used metals, dispersed in a stream of helium, adhered well to the substrate and formed dense coatings.

However, the engineers were not completely satisfied. It was clear that light gas systems would inevitably be expensive and could only be used in companies that manufacture high-tech products (only there are high-pressure helium lines). And compressed air freeways are available in almost every workshop, auto repair company, and repair shop.

Numerous experiments with compressed air seem to confirm the worst expectations of the developers. However, an intensive search made it possible to find a solution. Coatings of satisfactory quality were obtained when the compressed air in the chamber in front of the nozzle was heated and finely dispersed ceramic or solid metal powder was added to the metal powder.

The fact is that when heated, the air pressure in the chamber increases according to Charles' law and, consequently, the flow velocity from the nozzle also increases. Metal particles that have reached an enormous speed in a gas flow are softened and welded on when they hit a substrate. Ceramic particles play the role of microscopic sledgehammers - they transfer their kinetic energy to the layers below, compacting them and reducing the porosity of the coating.

Some ceramic particles get stuck in the coating, others bounce off it. In this way, coatings are only obtained from relatively ductile metals - copper, aluminum, zinc, nickel, etc. The part can then be subjected to all known methods of mechanical processing: drilling, milling, sharpening, grinding, polishing.

MAIN CONDITION - SIMPLICITY AND RELIABILITY

Technologists' efforts are in vain if designers cannot develop simple, reliable, and economical devices in which to implement the process invented by technologists. The basis of the device for spraying metal powders is a supersonic nozzle and a small electric compressed air heater that can bring the flow temperature to 500-600ºC.

The use of ordinary air as the working gas made it possible at the same time to solve another problem that the developers of light gas systems were faced with. The point is to introduce a sprayed powder into a gas stream. In order to maintain the tightness, the inlets had to be installed up to the critical section of the nozzle, i. H. The powder had to be fed into the high pressure area. Purely technical difficulties were exacerbated by the fact that metal particles, passing through the critical section, caused wear on the nozzle, deteriorated its aerodynamic properties and prevented the stabilization of the coating conditions. When designing the device with air flow, the engineers applied the principle of a spray gun, which everyone else was familiar with from experiments in physics at school. When a gas flows through a channel of variable cross-section, its velocity increases in a narrow place and the static pressure drops and can even be lower than atmospheric pressure. The channel through which the powder came out of the feeder was exactly at such a point, and the powder moved into the nozzle due to air suction.

As a result, a portable device for applying metal coatings was born. It has a number of advantages that make it very useful in different industries:

all that is needed for the device to work is just a power supply and an air line or a compressor that delivers a compressed air pressure of 5 to 6 atm and a flow of 0.5 m 3 / min.

when coating, the temperature of the substrate does not exceed about 150;

coatings have high adhesion (40-100 N / mm 2) and low porosity (1-3%);

the device does not emit any harmful substances or radiation.

the dimensions of the device allow it to be used not only in the workshop, but also in the field.

coatings of almost any thickness can be sprayed.

The structure of the system includes the actual spraying device with a weight of 1.3 kg, which the operator holds in his hand or secures in the manipulator, an air heater, powder feeders, a control unit for operating the sprayer and the feeder. All of this is rack mounted.

I had to work hard creating consumables. Industrially produced powders have particle sizes that are too large (on the order of 100 micrometers). Technology has been developed that makes it possible to obtain powders with grains of 20-50 micrometers in size.

FROM SPACE TO SEED

A new method of spraying metal coatings can be used in a variety of industries. It is particularly effective in repair work when product sections need to be restored, e.g. B. to repair a crack or a sink. The low process temperatures make it easy to restore thin-walled products that cannot be repaired in any other way, such as surface treatment.

Since the spray zone has clear boundaries, the sprayed metal does not fall on defect-free areas. This is very important when repairing parts of complex shape such as gear cases, engine cylinder blocks, etc.

Sprayers are already used in the aerospace industry, in the electrical industry, in nuclear systems and in agriculture, in car repair shops and in foundries.

The method can be very useful in many cases. Here are just a few of them.

Restore worn or damaged surfaces. Spraying uses parts of gears, pumps, compressors, investment casting molds and molds to make plastic packaging that are damaged during operation to repair parts. The new method has become of great help to employees of auto repair companies. Now you literally close cracks in cylinder blocks, silencers, etc. "on your knees". Eliminate defects (caverns, fistulas) in cast aluminum without any problems.

Elimination of leaks.The low gas permeability of coatings allows you to eliminate leaks in pipelines and containers if sealants cannot be used. The technology is suitable for repairing containers that operate under pressure or at high and low temperatures: heat exchangers, car coolers, air conditioning systems.

The application of electrically conductive coatings.By spraying it is possible to apply copper and aluminum films to a metal or ceramic surface. In particular, the method is economically more effective than conventional methods for copper-plating current-carrying tires, galvanizing contact surfaces on grounding elements, etc.

Corrosion protection. Aluminum and zinc foils protect surfaces against corrosion better than paints and many other metal coatings. The low productivity of the installation does not allow the processing of large surfaces, but it is very useful for protecting vulnerable elements such as welds. Spraying zinc or aluminum can expose corrosion in places where insects appear on the painted surfaces of car bodies.

Restoration of plain bearings. Babbitt liners are usually used in plain bearings. Over time, they wear out, the gap between the shaft and the sleeve increases and the lubricant layer is broken up. Traditional repair technology requires either liner replacement or weld defects. You can restore the liners by spraying. In this case, ceramic cannot be used to seal the spray metal layer. Solid inclusions within minutes of starting operation will deactivate the bearing and damage the surfaces of both the bushings and the shaft. I had to use a nozzle with a special design. You can use it to apply a coating of pure babbit in the so-called thermokinetic mode. Powder particles immediately after the critical section of the nozzle are accelerated by a supersonic air flow, then the flow velocity drops sharply to transonic. As a result, the temperature rises sharply and the particles heat up almost to the melting point. Upon contact with the surface, they deform, partially melt and adhere well to the layer below.

TO THE SPECIALIST - NOTE

literature

Kashirin A. I., Klyuev O. F., Buzdygar T. V. Device for the gas dynamic coating of powder materials. RF Patent for Invention No. 2100474. 1996, MKI6 C 23 C 4/00, publ. 12/27/97. Bull. No. 36.

Kashirin A.I., Klyuev O.F., Shkodkin A.V. The process of making coatings. RF Patent for Invention No. 2183695. 2000, MKI7 C 23 C 24/04, publ. 06/20/02. Bull. Number 17.

The coordinates of the developers and the conditions for purchasing their technologies or products can be found in the publisher.

In fact, it is a more advanced version of the long-established gas-thermal method of restoring various metal parts and surfaces. Cold spray or simply CGN greatly expands the possibilities of the "hot" method of processing products.

At the moment, this is undoubtedly the most advanced technology for restoring and protecting materials, widely used in both the industrial and civil sectors.

The principle of action, the advantages and disadvantages of CGN

It has two main differences from the gas thermal recovery method. Firstly, a protective or restorative coating is sprayed at a reduced temperature of no more than 150 ° C, which in turn does not cause any stress on the workpieces and their deformation. Second, “cold” technology allows you to create a layer of adjustable thickness and on well-defined boundaries. We'll talk about other pros and cons a little later, but for now about the authors of the method and how it works.

Its developer is "Obninsky Center of Powder Spraying" (Russia). The equipment they produce is called DIMET ®. It is certified according to the GOST R system and protected by patents of Russia, the USA, Canada and other countries. The technology is based on the principle of supersonic exposure of the smallest particles of fusible and other materials on the treated surface. These are mainly polymers or alloys of carbides with metals with a particle size of 0.01-0.5 micrometers. When mixing with gas, they are fed to the product at a speed of 500-1000 m / s.

Depending on the composition of the consumable (powder) and changes in the regimes of use, it is possible to obtain a homogeneous or composite coating with a solid or porous structure and its functional task. This can be: restoring the product geometry, hardening and protecting the metal from corrosion, increasing the heat and electrical conductivity of the material, as well as forming a wear-resistant coating that can withstand chemically active environments, high thermal loads, etc.

Incidentally, the engineers from Obninsk have already developed several modifications of DIMET ® units. Given the widespread demand for these devices, both manual and automated cold gas dynamic spray devices are now being mass produced, making them suitable for use in small parts processing industries, the oil and gas industries, and small businesses. In addition, the technology itself is not particularly complicated. In order for the complex to work (in addition to the spray material), only compressed air (supplied under a pressure of 0.6-1.0 MPa and a flow rate of 0.3-0.4 m3 / min) and an electrical network with a voltage of 220 V.

Now for the advantages and disadvantages of the method. Firstly, in contrast to the gas-thermal method, CGN can be effectively applied at normal pressure in any temperature range and humidity level. Second, it is completely environmentally safe. Thirdly, due to its high speed, it can also be used for abrasive cleaning of the surface. The only downside to the technology is the ability to only coat from relatively ductile metals like copper, aluminum, zinc, nickel, etc.

Scope of CGN

I would like to elaborate on the areas where the technology of cold gas dynamic spraying with powder materials is used to visually show how in demand it is today.

Repair, surface repair and sealing

All of this is work that even small businesses can do. In small workshops, for example, parts made of light metals (e.g. parts of an automobile structure), especially aluminum and aluminum-magnesium, can be repaired. In addition, defects that have arisen both during the production process and during operation can be easily eliminated. And the lack of strong heating and the low energy of the process make it possible to repair even thin-walled products.

CGN is also great for restoring worn surfaces. For example, a time-consuming process like “building” metal in the bearing seats can now be done by small businesses, not to mention re-sealing (when the use of liquid sealants is not possible) in pipelines, heat exchangers or tanks for Working gases, liquids.

It is very effective in repairing complex products that require accurate restoration of geometric parameters in order to eliminate hidden defects, while maintaining all operational characteristics, as well as presentation. For this reason, this method is actively used in the military-industrial complex, in the railway and aerospace industries, in agriculture, in gas pumping, etc.

This technology cannot be dispensed with when creating contact surfaces. Due to the possibility of simply coating metal, ceramic and glass surfaces, CGN is also used in the manufacture of electrical products. For example, in the processes of copper plating, the creation of current-carrying power networks, the laying of power lines, the manufacture of underlayers for soldering, etc.

Corrosion protection treatment and removal of deep defects

Spraying the so-called friction coating is a highly effective way of removing local damage (deep chips, grooves, scratches). This avoids full replenishment or even replacement of the product, which of course is not economically viable.

And when it comes to anti-corrosion treatment and protection against high-temperature corrosion of various means of communication, this method is not at all comparable. By the way, various modifications of the equipment DIMET ® provide high quality machining of the inner surface of pipes with a diameter of 100 mm and a length of up to 12 m.

Kawasaki robots are used when spraying complexes with DIMET technology. This technology allows you to apply a metal layer on different surfaces: metal, glass, ceramic, stone. A feature of the technology is the ability to apply a metal powder to metals that are not suitable for welding and soldering. For example, it is possible to deposit copper efficiently on aluminum, which is of great value for electrical engineering.

About technology

The technology of gas-dynamic spraying of metal powder and its conversion into a monolithic coating is implemented on DIMET equipment manufactured by the Obninsk Powder Spraying Center. Coatings are formed on any hard surface such as metal, glass, ceramic, or stone. The coating material is selected when solving a specific production or creative task, since a solution can be obtained using various types of powder materials.

Compressed air (5-8 atm) is heated (300-600 ° C) and fed into the nozzle, where a supersonic flow is formed:

  • powders containing metal and ceramic particles are introduced into this stream
  • Particles are accelerated by a gas flow to a speed of several hundred meters per second and sent to the substrate in an unmelted state
  • upon impact with the substrate, the kinetic energy of the particles is converted into heat and then into the binding energy of the particles with the substrate
  • as a result of such high-speed impacts, particles are fixed on the substrate and form a dense coating.

The main processes that determine the adhesion of particles to the substrate and to each other:

  1. Close contact between the crystal lattices of the particles and the substrate (or various particles) until metal bonds are formed in at least some parts of the contact point. In this case, melting of a particle or substrate does not occur anywhere. This coupling mechanism is similar to the coupling mechanism used in explosion welding.
  2. In the case of individual protrusions and irregularities of the falling particles, their melting can occur and spot micro-welding can occur.
  3. When young surfaces of different materials come into close contact, an intermolecular interaction of these materials can occur. A typical example of such a mechanism is the deposition of a mirror aluminum coating on glass.
  4. A mechanical role may play a role under the condition of deep penetration of particles into the substrate. The specific ratio of the relative role of different adhesion mechanisms in different cases can differ significantly from one another and is the subject of a separate study.

Areas of application

IndustryapplicationCovers

foundry

Repair of defects on injection parts

Vacuum

In the cooling form

Lost wax models

Coatings for restoring the shape and size of parts.

Sealing coatings

(low gas permeability)

Metallurgical production

Reduction of the electrical resistance of the contacts of the cells

High temperature corrosion protection

Conductive coatings

Heat-resistant coatings

automobile

Repair of castings

Sealing coatings

Anti-corrosion coatings

Coatings used to repair mechanical damage to cylinder head, BC, units

Gasket cracks from cylinder head, BC, radiators, pipes, air conditioning systems

Corrosion protection of local hot spots

Restoring the shape of body parts made of aluminum without putty

Sealing coatings

Anti-corrosion coatings

Aircraft industry, aircraft repair

Repair of casting and manufacturing defects in aluminum parts

Coatings for restoring the shape and size of parts.

Sealing coatings

Rocket and space technology

Special

Coatings for sealing products made from heat-hardened aluminum

Heat radiating coatings

Shipbuilding, ship repair

Profile protection of weld seams

Restore bearing seats

Coatings for restoring the shape and size of parts

Anti-corrosion coatings

Sealing coatings

Oil and gas industry

Restoration of the geometry of parts of gas pump units

Prevents joints with strong threads from seizing up

Plain bearing restoration

Coatings for restoring the shape and size of parts

Anti-grip coatings

Antifriction

Electrical engineering

Metallization of electrical contact surfaces

Application of the electrically conductive coating

Heat transfer metallization

Aluminum sub-layers and solder glass

Conductive coatings

Tool making

Overhaul molds for plastic and glass packaging

Reclaim molds for rubber products

Recovery of equipment for pressing parts from press materials (AG4, DSV, Carbolite)

Make an intrinsically safe tool

Coatings for restoring the shape and size of parts

Intrinsically safe coatings

Restoration of monuments and sculptures

Restoration of the lost elements of monuments. Corrosion protection

Coatings for restoring the shape and size of parts

Anti-corrosion coatings

Project completed

Robot complex for coating the contact surfaces of conductive tires used in the ITER project tokamak reactor. The developer of the complex is Acton LLC (Robowizard partner and system integrator).

Scheme of the complex:

The problem solved:

Spraying a two-layer copper coating onto a flat electrical contact surface of conductive aluminum bars. The spray area is up to 0.5 m 2, the tires themselves reach a length of 12 meters and a mass of 4 tons.

The composition of the complex:

  1. PLC Aries;
  2. Kawasaki Robot RS006L;
  3. Spray chamber;
  4. Controller E01;

The implemented complex enables the following tasks to be performed:

  • process execution with the function of program control and parameter management;
  • spray movement along a predetermined path, synchronized with the operation of technological devices, by transmitting information messages;
  • visualization of process parameters on the operator's touchscreen as well as means for changing operating modes, organized using dialog box elements.

If you need such a solution, leave your contact details in the application form. Our experts will advise you and discuss the details of the cooperation.

Project gallery

Cooperation program

The essence of the process is the formation of coatings due to the high kinetic energy of unmolten metal particles. This method is currently known as Cold spray -cold spray.

It should be noted that in the most common gas thermal coating processes for their formation from the particle stream it is necessary that the particles falling on the base have a high temperature, usually above the melting point of the material. In the case of gas dynamic spraying, this state is not absolutely necessary, which determines its uniqueness. In this case, particles that are in an unmelted state but at a very high speed interact with a solid base.

In contrast to the plasma hot spray process, a gas-dynamic cold coating process was developed, the essence of which was to set a certain threshold speed at which cold plastic particles formed a dense coating. With different granulations (large and small particles in a single stream), smaller particles deposited on the substrate at a higher rate and larger particles at a lower rate bounced off the surface and were not involved in the formation of the coating.

This behavior of the particles enabled the introduction of larger abrasive particles into the flow of the coating material. It was sandblasted and coated at the same time. From a surface preparation point of view, such a coating scheme is optimal when the youthful surface of the substrate loses its activity due to the adsorption of gases on the delayed deposition surface. At the same time, a system was developed in which gas (air, nitrogen) with a pressure of 2.5 to 3.5 MPa in a metal coil is heated to 350 to 600 ° C by an electric current flowing through it from a welding transformer. The sprayer is equipped with a Laval nozzle that enables a supersonic flow of a two-phase jet.

In Fig. 2.48 is a flow diagram of a process. With gas dynamic cold spraying, you can apply coatings made of ductile metals with the addition of other materials.

Figure 2.49 shows the dependencies of the velocity and temperature of gas and particles through a Laval nozzle for a two-phase jet (nitrogen + solid copper particles with a size of 5 and 25 μm) at one pressure R. \ u003d 2.5 MPa and temperature T 0 \ u003d 950 ° C. In this case, the ratio of the initial diameter /) in to the critical /) to /) in / G \ u003e k \ u003d 9.

Cowardly. 2.48.


Cowardly. 2.49.Air temperature T d Air velocity as well as the temperature and velocity of copper particles with a diameter of 5 and 25 micrometers in a profiled supersonic nozzle

The house installation "DIMET" is produced by the Powder Spray Center Obninsk in two versions - manual output 2 kW and stationary output 7 kW. Recommendations for the use of powder materials are given in the table. 2.10.

The main application of GDN is the application of anti-corrosion coatings of the profile type based on aluminum and zinc. Wear-resistant coatings are applied on the basis of plastics - Babbitt, copper, nickel, etc. Compared to GN and EDM processes, HDNs do not have these disadvantages when a metal melts and is saturated with gases, including hydrogen, which reduces the protective properties of the coating. Hydrogen does not dissolve in solid particles. The coating effectively protects the steel from corrosion. The process is widely used to protect car bodies from corrosion in the area of ​​weld seams.

The main

components

covers

work

Aluminum, zinc

Sealing leaks in metal pipes, radiators, condensers, heat exchangers, etc., including sealing leaks in welds, repairing corrosion and mechanical damage. Seal cracks, chafe marks and other defects on aluminum, steel and cast iron parts

Aluminum, zinc

Restoring the shape of metal parts. Filling voids, pores, cracks and other defects in products made from aluminum and its alloys (including engine parts, molds, etc.). Restoration of bearing seats in aluminum, steel and cast iron parts

Aluminum, silicon carbide

Filling cavities, cracks and other defects in engine parts made of aluminum, steel and cast iron

Aluminum oxide

Cleaning and abrasive preparation of the surface of steel and cast iron for the application of metal coatings

Conductive coating (on steel, aluminum, ceramic). Tin solder layer for aluminum, steel and cast iron parts

Copper, zinc

Filling cavities, cracks and other defects on engine parts made of steel and cast iron

The main

components

covers

work

Purpose of coatings, repair and restoration items

Corrosion protection. Sealing of defects, micro-cracks, threaded connections

Heat-resistant coating to protect against high-temperature corrosion. Conductive coating for electrical pads

Nickel, zinc

Filling of voids, burnouts and other defects in steel products.

For products that work at high temperatures

Conductive coating for electrical pads

Corrosion protection of steel parts and weld seams on steel structures

The company's installation scheme is presented in Fig. 2.50 Linden tree (UNITED STATES). The latest achievements in the implementation of the procedure are the manufacture of manual spray guns, the characteristics of which are given in the table. 2.11.

Table 2.11

Properties of spray guns

properties

Model 412

Model 403

Productivity A1, g / min

The number of temperature conditions

Dimensions (mm) and weight (kg):

spray unit

450 x 64 x 85 mm; 1.3 kg

450 x 64 x 85 mm; 1.3 kg

340 x 260 x 320 mm; 8 kg

560 x 260 x 490 mm; 16 kg

properties

coverings:

adhesive strength, MPa

porosity,%

surface roughness, micrometers

R, \ u003d 20-40


Cowardly. 2.50.The scheme of installation of the cold spraying company Linden:

1 - tankers with liquefied petroleum gas (Ag); 2 - Evaporator; 3 - compressor; 4 - fan heater; 5 - powder feeder; 6 - spray

Low gas acceleration requirements and low power consumption enable the creation of portable systems with DIMET technology.