Methods and technology of metal powder coating. Powder coating technology Application of powder materials

Differences in the composition and technology of use, distinguish this species coverage in a "special class" relative to the rest paintwork materials. At present, powder coating of metal products has become widespread in industry, ranging from aircraft construction to the production of household goods and accessories.

Powder coating of metal products: process technology and main stages

Technological process powder coating are divided into the following stages:

• preparation of the painted surface;
• applying paint in powder form;
• formation of a liquid film at high temperature;
• chemical curing of the film-forming material (when using thermosetting paints);
• final formation of the coating.

Surface preparation

When preparing the surface to be painted, it should be taken into account that it is necessary to ensure not only wettability with the liquid phase of the film former, but also a uniform distribution of powder materials during spraying. Attention is paid to both removing all kinds of surface contaminants and providing the surface with the necessary roughness. In addition to mechanical methods of surface preparation, chemical methods, such as etching or phosphating, can also be used.

Application of powder materials

Powder coating of metal is carried out:

• electrostatic spraying;
• immersion in a suspended layer of electrified powder;
• gas flame method.

Due to its simplicity and versatility, the application of paint has received the greatest application. electrostatic spraying. For flat surfaces, special magnetic brush rollers can be used according to the technologies used in copying technology. Dipping into the "fluidized bed" used on automatic lines in the conveyor production of the same type of products. flame method due to the excessive unevenness of the layer and the properties of the resulting coating, it has not received distribution. The existing plasma spraying is distinguished by the use low temperature plasma for heating particles and using an inert gas; limited to the use of heat-resistant powders when applying thin coatings to heat-resistant materials.

Retention and uniformity of distribution of powder materials on the surface of metal products are provided due to the electrostatic forces of interaction between charged particles of paint and an “electrically neutral” surface. Before spraying, the paint particles in the gun are electrically charged:

• in the field of the coronary charge created by the electrode;
• due to friction on the surface of the equipment.

The particle charge is usually negative, the charge value must correspond to the optimal range that allows particles to be kept on the surface until a liquid film is formed and does not violate the deposition technology. It is regulated by the characteristics of the electrode or the speed of movement of particles during friction against the surface of the equipment, by the area and material of the surface.

With electrostatic spraying, coatings are formed with the same quality on horizontal and vertical surfaces. Zero charge metal product provided with grounding.

Liquid film formation

Film formation occurs when powder materials are heated to a viscous-fluid state, and the following occurs:

• deformation and viscous flow of the material;
• air removal;
• wetting liquid material substrate surface.

in the production of pipes and metal profile the application of powder in a "fluidized bed" is used on preheated workpieces, the process of forming a liquid film occurs due to the accumulated heat or additional heating.

In the case of using thermosetting paints at high-temperature exposure, the chemical curing of the liquid film additionally occurs due to polymerization or polycondensation of film formers. This lengthens the high-temperature holding time, increases costs and reduces productivity. There are compositions based on thermosetting resins, the accelerated curing of the films of which occurs under ultraviolet irradiation.

Final coating formation

The final formation of the film occurs when the product is cooled. The conditions may differ both in the cooling rate and in the medium. The strength characteristics of the coating and the adhesion force, depending on the conditions of formation, can vary by tens of percent. At the same time, for different types polymers, accelerated and delayed cooling is practiced. Cooling the coating in plasticizing polymeric environments can reduce the internal stresses of the coating to zero.

Unlike thermoset paints, thermoplastic paints make it easy to repair coating defects using re-sintering.

Powder coating is widely used in the construction industry in the production of profiles from steel and aluminum, the manufacture of doors, gates and other metal structures. In the automotive industry, it is used in the production of wheel rims and other parts.

Despite the complexity of tinting, some manufacturers provide powder paints up to 250 colors according to RAL tables.

Preparation process metal parts for painting

When painting metal products with powder paint, both on industrial lines and with your own hands at home, you must follow these recommendations:

1. Use powder materials from trusted manufacturers.
2. Without proper grounding of a metal product, the electrostatic mechanism for holding and distributing powder materials on the surface is disrupted. Therefore, it is necessary to monitor the condition of the hanging hooks that provide grounding of the parts. should provide technological operation cleaning hooks and monitoring the ground circuit.
3. Spraying of powder materials must be carried out to a minimum necessary quantity air. Excessive air supply leads to:

• overspending paint;
• increased wear of equipment;
• violation of the technology of electrization of powder particles;
• change in the granulometric composition of the paint;
• poor visibility in the spray booth.

1. A high-quality coating is obtained by using air of the required condition. In this case, attention should be paid not only to the absence of dust, but also to the content of moisture and oil in the air. Appropriate filters must be used prior to supplying the air mixture to the equipment. In quality air:

• the size of solid particles does not exceed 0.3 microns;
• the dew point does not exceed 4 °C (i.e. at 20 °C humidity is not more than 35%);
• oil content is not more than 0.1 ppm.

1. At reuse powder materials take into account the change original composition, primarily granulometric. The amount of allowed additions of regenerated materials to the original powders should not be exceeded. Thoroughly homogenize the powder mixture before use.
2. Avoid mixing paint various colors and types. When changing to another paint, it is necessary to thoroughly clean all equipment. It is advisable to have separate supply hoppers and hoses for each paint used.
3. Without surface preparation you will not receive quality coverage. In this case, the purpose and operating conditions of the product should be taken into account. The bicycle frame must be prepared somewhat differently than the elements office desk. Careless preparation leads to:

• surface defects of the coating;
• peeling paint;
• premature destruction of the coating in an aggressive environment.

1. The cost of the initial powder does not determine the real economy of the coating. Should be considered:

• material consumption per unit surface area;
• coating durability;
• resistance to harmful conditions;
• appearance.

1. Consider storage conditions for powder materials. Elevated temperature can reduce both the processing characteristics of the powder and operational properties coatings. The containers used must be waterproof due to the high hygroscopicity of the materials. Typically, the recommended temperature in the warehouse should not exceed 25 ... 28 ° C, humidity should not exceed 50%.
2. Strictly follow the recommended technology of "sintering" the powder. It should be noted that the air temperature in working area kiln is indirect characteristic technical process. The operation of the installation should ensure uniform heating of the metal of the product to optimal temperatures. Depending on the type of material and weight of the product optimum temperature air and exposure time may vary and are reflected in the instructions.
3. Timely follow the technical regulations to maintain the operability of the site equipment. Preventive maintenance, including regular cleaning, inspection, repair and replacement of components, is the basis for flawless operation and quality products. Use spare parts original manufacturers. TESLA equipment has proven itself well.

Safety

The main types of threats in the powder coating of products are.

The great demand in mechanical engineering, construction and other industries has led to the fact that polymer powder paint has begun to be used for finishing metal parts, as the most effective method and durable material. The application is mainly carried out by manual or automatic sprayers by tribostatic or electrostatic charging in chambers of a continuous or dead-end type.

We will not be able to tell you thoroughly the entire production technology. But here you get a basic understanding of how it's done. In addition, you can watch the thematic video in this article as additional material.

Features of application in conditions of serial and small-scale production

Application technology

1. The production process is environmentally friendly and harmless to others. At the same time, excellent decorative and protective-decorative coatings are obtained. The composition is distributed over the surface of the part, which is then placed in a powder paint polymerization oven. There is a heat treatment process at a certain temperature.

1. The principle of coating in general terms is as follows: the workpiece is grounded and charged particles of paint are attracted to it.

In general, the whole process is divided into three stages, these are:

• Part preparation (surface treatment);
• Spraying powder from a sprayer;
• Melting of the applied powder or polymerization.

1. The quality of the finishing of parts, first of all, will depend on the careful observance of the technology at each stage. In addition, the instructions require that burrs, protruding welds, splashes and burns, as well as oil and other stains, be completely absent.

Training

Note. To remove old coatings, scale and rust from the surface, chemical and mechanical methods are used to a greater extent.

Among mechanical methods there is blasting and abrasive processing with the help of sandblasting, shot-blasting and shot-blasting machines. And as degreasers, aqueous alkaline and acidic cleaning solutions, as well as organic solvents are used.

Considering that organic solvents such as white spirit, 646 are harmful to health, the production instructions limit rubbing during degreasing manually cotton rags and this applies only to small batches.

Large batches are degreased not with their own hands, but detergent compositions at a temperature of 40⁰C-60⁰C. The process itself occurs by dipping the part in a liquid for 5-15 minutes or spraying for 1-5 minutes, followed by washing and drying.

Powder application

The application process, as seen in top photo, is carried out in powder spraying chambers, where air exhaust and aspiration systems operate to prevent particles from entering the workshop room ().

In dead-end chambers, the product is suspended and through a special window or on the side of KN-2, KN-5, painting is carried out, and the part is transported past the painter through the passage chamber, through the working area of ​​​​spraying KN-3, KN-6. For long parts, there are two-station walk-through cameras KN-3-2, KN-6-2 (two single-station cameras are turned opposite each other by 180⁰).

Since the dye for polymers is the powder itself and no mixing is necessary, a manual spraying unit (URN-2) was developed for small-scale production. It has the advantage that the powder is supplied there from the original box in which it was packed at the factory, that is, it does not need to be poured into any container.

The suction nozzle is equipped with a fluidization device, which, together with an injector and a vibrating table, allows processing powders with high moisture content.

URN-2 can be equipped with an electrostatic and/or tribostatic spray gun. In it, the combined unit was designed for different types of paints and surfaces of varying complexity. The combination allows you to almost instantly switch from electrostatic mode to tribo mode. This increases the efficiency of production and at the same time, naturally, the price of manufactured products falls.

Note. The electrostatic method involves the forced charging of particles using a corona electrode, which is under high voltage. The tribostatic method involves the charging of particles as they pass through the tribo-electrifying unit of the tribo-barrel (tribo effect).

reflow

After the powder has been applied to the product (this is not a polymer floor paint at all), it is sent to a PP-16 type oven to form a coating by melting the layer.

Furnaces can also be dead-end or walk-through and consist of heat-insulating panels, one (dead-end) or two (walk-through) door blocks, as well as from one to eight heating blocks with an air recirculation system. The heat shield is made from basalt slabs 100 mm thick, which are sandwiched between galvanized profiled panels.

In most cases, the curing temperature of powder paint is 150⁰C-180⁰C with an accuracy of +-5⁰C and a holding time of 10 to 20 minutes, although this depends on the instructions of the powder manufacturer. Such requirements are best met by air recirculation ovens.

Conclusion

It should be noted that Zinga electrically conductive paint, as well as Polystil fire-retardant paints for metal, have nothing to do with polymerization in an oven. The reflow process is carried out exclusively by powder dyes (

There are four main powder coating processes: electrostatic spray, fluidized bed, electrostatic fluidized bed, and flame spray.

Electrostatic spraying is the most popular powder coating method today. For all application methods, surface preparation (i.e., cleaning and conversion coating) must create good foundation for coating. The surface must be prepared accordingly.

Features of four different powder coating methods:

1. In the process electrostatic spray dry powder particles acquire an electrical charge, while the surface to be painted is electrically neutral. The charged powder and neutral work area create an electrostatic field that attracts dry paint particles to the surface. Once on the surface to be painted, the powder coating retains its charge, which keeps the powder on the surface. The surface painted in this way is placed in a special oven, where the paint particles melt and are absorbed by the surface, gradually losing their charge.
2. Second method application involves the powder paint particles being held in suspension by air flow. Coming into contact with a preheated surface to be painted, these particles melt and are firmly held on its surface. The thickness of the powder coating depends on the temperature, the degree of heating of the surface, and also on the duration of contact with the powder particles. When applying thermoplastic coatings, post-heating is generally not required. However, in some cases, additional heating is necessary to completely cure the powder coating.
3. Electrostatic powder coating with air flow in many ways similar to the previous one, however, in this case, the air flow holding the paint particles is electrically charged. Ionized air molecules charge the paint particles as they move up in a special oven, where the surface to be painted is placed, and form a cloud of charged particles. The surface to be painted, which has a neutral charge, is covered with a layer of charged particles. In this case, pre-heating of the surface to be painted is not required. This technology is suitable for painting small and simple objects.
4. Flame dyeing method appeared relatively recently and was mainly used for thermoplastic powder coatings. The thermoplastic powder is melted under the influence of compressed air and enters a special gun, where it passes through burning propane. Melted paint particles are applied to the surface to be painted, forming a durable layer. Since this method does not require direct heating, it is suitable for most materials. With this technology it is possible to paint surfaces made of metal, wood, rubber and stone. Flame application is also suitable for large or fixed objects.

The choice of powder paint depends on the desired surface characteristics. The properties of the powders must meet the individual requirements of the client in relation to surfaces. Powder coatings are divided into different categories, depending on the specific application. Thermoplastic coatings are used to paint denser surfaces and provide durability to the coatings, while thermostatic powder coating is used to paint more thin materials mainly for decorative purposes. Powder coatings use polyethylene, polyvinyl, nylon, fluoropolymers, epoxy resin, polyester and acrylic resins.

Material Compatibility

• Electrostatic airflow technology is best suited for painting small metal objects.
• As with all types of painting, powder coatings are applied to a clean, smooth and well-prepared surface. The surface to be painted does not require pretreatment however, additional surface preparation (e.g. iron phosphate for steel, zinc phosphate for electrochemical cells, or steel and chromium phosphate for aluminum surfaces) markedly improves the quality of the powder coating.
• Only materials that can be heated to high temperatures can be powder coated using electrostatic spray, airflow or electrostatic air application. Therefore, these technologies are most suitable for small metal objects.

Health and safety

• Powder paints can ignite easily near open flames. The concentration of powder in the air must be reliably controlled to ensure a safe working environment. Despite the absence of flammable solvents, any organic material such as dust or powder can form an explosive substance in the air.
• When coloring, inhalation of paint powder should be avoided, as this can damage the lungs and protective membranes of the body.

A typical powder coating process is the following sequence of operations:

1. Preparing the surface of the product for painting.
2. The application of a powder coating to the surface to be painted in the spray chamber using a sprayer in which the particles of the polymer powder are electrically charged, and which, using compressed air, transports the powder to the part. Under the action of electrostatic forces, powder particles are attracted to the surface of the part to be painted and are arranged in uniform layers on it.
3. Heating of the product in a reflow and polymerization oven at a temperature of 140-220°C (depending on the type of paint). As a result of heating, the powder melts, polymerizes and the coating acquires the necessary protective and decorative properties.

After applying powder paint, the product is sent to the stage of coating formation. It involves the melting of the paint layer, the subsequent production of the coating film, its curing and cooling. Melting and polymerization take place in a special furnace. There are many varieties of polymerization chambers, their design may vary depending on the conditions and characteristics of production at a particular enterprise. In appearance, the oven is a drying cabinet with electronic "stuffing". The control unit can be used to control temperature regime oven, staining time and set the timer for automatic shutdown furnace at the end of the process. The energy sources for polymerization ovens can be electricity, natural gas and even oil.

Furnaces are divided into continuous and dead-end, horizontal and vertical, single and multi-pass. For dead end furnaces important point is the rate of temperature rise. This requirement is best met by furnaces with air recirculation. Coating chambers made from electrically conductive dielectric coatings ensure uniform distribution of powder paint on the surface of the part, however, if used incorrectly, they can accumulate electrical charges and be dangerous.

Melting and polymerization occurs at a temperature of 150-220 ° C for 15-30 minutes, after which the powder paint forms a film (polymerizes). The main requirement for polymerization chambers is to maintain a constant set temperature (in different parts oven, a temperature variation of at least 5 ° C is allowed) for uniform heating of the product.

When heated in an oven, a product with a layer of powder paint applied, the paint particles melt, go into a viscous state and merge into a continuous film, while displacing the air that was in the powder paint layer. Part of the air may still remain in the film, forming pores that degrade the quality of the coating. To avoid the appearance of pores, painting should be carried out at a temperature above the melting point of the paint, and the coating should be applied in a thin layer.

With further heating of the product, the paint penetrates deeply into the surface and then cures. At this stage, a coating is formed with the specified characteristics of the structure, appearance, strength, protective properties etc.

When painting large metal parts, their surface temperature rises much more slowly than for thin-walled products, so the coating does not have time to fully harden, resulting in a decrease in its strength and adhesion. In this case, the part is preheated or its curing time is increased.

Rejection is recommended for more than low temperatures and over a longer period of time. This mode reduces the likelihood of defects and improves the mechanical properties of the coating.

At the time of receipt required temperature the surface of the product is affected by the mass of the product and the properties of the material from which the part is made.

After curing, the surface is subjected to cooling, which is ensured by lengthening the conveyor chain. Also for this purpose, special cooling chambers are used, which can be part of the curing oven.

The appropriate mode for coating formation must be selected taking into account the type of powder paint, the characteristics of the product to be painted, the type of oven, etc. It must be remembered that temperature plays a decisive role in powder coating, especially when coating heat-resistant plastics or wood products.

Powder coating is becoming more and more popular today. What is it? it modern technology designed for decorative and protective coatings High Quality. Polymer powders are used in the work (hence the name - "powder"). They turn into a coating due to the impact high temperatures. Because of this feature of the procedure, powder coating of metal and glass is most common.

Advantages

This process has a number positive aspects. These include:

Profitability. The fact is that such paint can be reused if it does not settle when sprayed.
on the treated surface. Thus, the loss of material is no more than 5%. By the way, this indicator for ordinary paints will be 8 times higher - about 40%. also in this case no need for solvents.

Ease of use. Materials for this type of work are produced completely ready. This guarantees stable high quality coatings. In addition, it is very easy to clean the equipment after work, because the powder is easily removed from the parts.

Speed. Powder coating does not require drying products before placing them in the oven. If the surfaces covered regular paint, it is necessary to dry for quite a long time, then in this case the process is reduced significantly.

Durability. The technology of these works involves the polymerization of a layer of elastic plastic, which has a fairly high adhesion, directly on the surface that is being painted. The result is durable coating, which boasts excellent electrical insulating and anti-corrosion properties, as well as resistance to various substances.

Environmental friendliness. As already mentioned, solvents are not used in this case, which has a positive effect on the environment. The wastelessness of production also plays a role.

Decorative. Powder paints make it possible to obtain a surface of any shade. The palette of presented materials today includes more than 5 thousand colors and shades with various textures. If desired, you can get a glossy or matte surface, as well as under granite, moire, etc.

Powder coating as a business idea

Given all the advantages of this type of work, it becomes obvious that such a business will be quite profitable. If you do not have the opportunity to immediately invest a large amount in your business, it is advisable to at least just learn how do-it-yourself powder coating is done.

But it is worth considering that you still have to spend money. First of all, you will need to take care of the availability of special equipment and a separate room. As the latter, a simple garage is quite suitable, but on the condition that it has enough space to accommodate all the tools and direct work. What equipment is needed for powder coating?

Camera

Work will be impossible without a special camera. It is in it that most of the whole process is performed. The powder coating chamber is needed for air purification (recovery process), in addition, it is due to it that it remains possible to reuse the material. Here, the paint that does not fall on the surface to be treated is sent to the filters, and then dumped.

Such equipment may be various sizes. Which one to choose - you need to decide in each case individually, having previously determined which products you plan to work with.

Furnace and gun

You will also need a reflow oven. This is a prefabricated structure consisting of panels (their thickness is 100 mm). Thermal insulation material – basalt fiber. If you are just trying yourself in this type of work, it is not necessary to immediately buy a special oven. For this purpose, it is quite possible to use a conventional oven. However, to build a business, it is still recommended to purchase professional equipment.

Powder coating technology also requires a spray gun that allows the use of compressed air. It can also be used as a compressor. If you have made a choice in favor of the latter, then please note that a filter for high pressure must be installed on it.

Recuperator and transport system

Powder paint residues are collected using a recuperator. Instead, at first, you can use a cyclone type vacuum cleaner. In this case, you must first check the power supply in the room and make sure that grounding is present.

If you plan to work with large-sized products, then you should also consider purchasing transport system. In it, the workpieces are moved on special trolleys that move along rails. Thus, a powder coating line is built. Such equipment improves the productivity of the process, ensuring its continuity.

Powder Coating Technology

The process of doing the work itself is divided, as it was already possible to understand, into several stages:

1. Let's talk about each stage separately. Preparation of the product, or rather its surface, for processing.
2. Apply paint in powder form.
3. Polymerization, i.e. heating the product in an oven.

Preparatory stage: cleaning, degreasing

We can say that this stage is the most time-consuming. And it depends on him how high-quality and resistant the coating will turn out. In the process of preparing the surface, it is necessary to remove all contaminants from it, degrease it.

Cleaning is carried out either mechanically or chemically. The first option involves the use of steel brushes or grinding disc. You can also perform lapping with a clean cloth, after wetting it in a solvent.

The second cleaning option involves the use of an alkaline, neutral or acidic composition, as well as solvents. Their choice depends on how dirty the surface is, what material the product is made of, what type it is and what dimensions it has.

Phosphating and chromating

Next, a conversion underlayer can be applied to the product, which will prevent moisture and dirt from getting under the coating. Phosphating and chromating procedures provide better adhesion and protect the surface from rust. For this purpose, iron phosphate (for steel), zinc (when working with galvanic cells), chromium (for aluminum) or manganese and chromic anhydride are most often used.

Then it will be necessary to remove the oxides, which is carried out using abrasive and dry cleaning. The first is produced by means of abrasive particles (shot, sand), walnut shells. These substances are supplied compressed air at a fairly high speed. As a result, particles "crash" into the surface of the product and bounce off it along with pollution.

Etching (chemical cleaning) is the removal various pollution using special pickling solutions, the main components of which are sulfuric, hydrochloric, nitric, phosphoric acid or caustic soda. This method is considered more productive, however, after such processing, the product must be washed from solutions.

Passivation

This is the final step in the surface preparation phase. It is necessary to process the part with sodium and chromium nitrate compounds. This is done in order to prevent the recurrence of corrosion.

After all have been produced preparatory work, the product is rinsed and dried in an oven. Now powder coating of the surface can be performed directly.

Paint application

What is powder coating technology itself? The prepared product must be placed in the chamber. Here powder (paint) will be applied to it. If you have a dead end box, then only small details can be painted in it. Large items can only be processed in long chambers.

Most often, the method of electrostatic spraying is used to apply paint. In this case, powder coating guns are used. Such instruments are also called spray guns or applicators. This device is a pneumatic spray gun that applies an electrostatically charged substance to a pre-grounded part.

Coating formation

Let's move on to the next stage of work. The paint has been applied, now you need to form a coating. First of all, the product is sent to the polymerization oven. Such cameras can be different: vertical, horizontal, again, dead-end or walk-through, single- and multi-pass.

The mentioned equipment for powder coating provides heating of the surface up to certain temperature- 150-220 o C. Processing lasts about half an hour, resulting in the formation of a film. At this stage, it is important that the part is heated evenly, which is possible only if the temperature in the chamber is stable.

Which mode to choose for processing a particular part depends on it itself, on the type of paint and equipment. After polymerization is completed, the product must be cooled in air. All work done.

Applications

As you can see, powder coating is a rather time-consuming job that requires certain investments. What products are subject to it? The painting method in question is ideal for processing aluminum or forged products, as well as galvanized surfaces.

Powder paints in our time are finding more and more "fans". Now they are used in instrument making, and in construction, and in the automotive industry, as well as in other areas. With their help, paint medical equipment, roofing materials, household appliances, items made of ceramics, plaster and glass, furniture. Among car enthusiasts, powder coating of disks is gaining more and more popularity.

Business organization

These works in specialized centers today are quite expensive. If you want to try yourself in this business, then if you have financial resources you may well get started. Of course, powder coating line ( automated system) is far from affordable for everyone, but thanks to our recommendations, you can replace some elements with other tools at first.

Start with small items. It can be plaster figurines, ceramic tableware And much more. Try painting something in your house first (start with something you don't mind ruining). Gradually, you will have the necessary skills and dexterity, then you will be able to take orders from friends. However, you should not expect a large income if you interrupt only with one-time orders from individuals.

The best scenario for the development of events involves the presence of a large start-up capital. In this case, you can immediately purchase necessary equipment and hire workers. Customers should be sought among enterprises engaged in the production of metal products. Only the presence of such customers will allow your business to exist and develop.