A little about the history of powder coating

It does not use fire-hazardous or harmful liquid solvents, so this painting is practically safe for both humans and fauna. The absence of such solvents reduces the cost of painting. In addition, the choice of tones, textures and colors is practically unlimited by the wishes and needs of the customer.

Powder painting can provide any colors, shades and textures: from golden or silver metallic to bronze, wood or granite surfaces. By painting with powder paint, surfaces with different glosses are obtained, as well as with a relief texture, such as antique or anthracite. Powder paint is already tinted, which does not require such expensive procedures as viscosity control and tone selection. This gives them the greatest efficiency and strength, durability and longevity, and with all this, excellent quality, evenness and uniformity of the painted surface are achieved. Powder painting provides an impact-resistant anti-corrosion coating that operates at temperatures from 150 to -60 C and provides reliable electrical insulation. And does not react to sudden temperature changes.

Powder paint and its economic advantages:

Low percentage of waste;

On work surface up to 96% of paint is applied;

In case of overspraying, the paint is collected in the dyeing chamber and is ready for the next application;

Highly automated technology makes it easy to maintain the coating, there is no need to clean it and it is easy to train workers (mainly in large factories); Also available for small businesses with manual powder coating.

Lack of cleaners and solvents, which does not require time for their evaporation, nor the cost of removing vapors.

Powder paint and ecology:

There are no harmful organic compounds;

Environmentally friendly production technology;

Low fire hazard;

Reduced emissions of chemical odors;

Sanitary and hygienic working conditions are much higher than with conventional painting methods;

During the polymerization process, extremely acceptable standards concentrations of volatile substances are not achieved.

Advantages of powder paints compared to solvent paints:

At traditional ways painting it is impossible to achieve excellent physical-chemical and decorative properties coatings;

Best performance properties, high quality coatings;

There is no need to prime surfaces;

One coat is enough to apply powder paint. This is achieved due to the 100 percent dry matter content; expensive multi-layer paints do not have this property;

Compared to conventional paints, powder paints have better impact resistance and anti-corrosion properties. Less porosity in powder coating;

Since powder paint is supplied ready-made, it does not require special preparation or viscosity control;

Losses during powder painting are about 2-5%; when painting with liquid paints, losses will be up to 45%

Hardening of powder paints is 30 minutes;

Powder paint does not take up much space, so it does not require large storage facilities;

The high strength of powder paints during transportation ensures minimal damage to painted surfaces, which reduces packaging costs.

Possible disadvantages:

When changing colors, a clean container is required;

To prevent an explosion, strict control of the painting process is required;

Difficulties in painting very thin layers arise;

At low temperatures, painting difficulties also arise;

For prefabricated structures or non-standard forms There are some restrictions in painting.

Powder painting technology

There are three main stages of powder coating technology:

1. Degreasing and removing dirt from the surface of painted products;

2. Powder paint is applied in the spray chamber.

3. Melting and polymerization occurs in the polarization oven. Then a coating film is formed and the painted surface is cooled and cured.

It is best to prepare and paint products on the transport system. Using the transport system, painted products easily travel from the spraying chamber to the polymerization oven and vice versa. It is also easier to prepare painted surfaces for painting using the transport system. The carriages in the transport system move easily along the rails. Work productivity is increased due to the continuous painting process on the transport system.

At the beginning of the powder coating process, the parts are suspended on a transport system. Workers must understand what surfaces need to be painted, in what places technological holes can be drilled for hanging parts, and how to minimize the cost of painting time, labor and the paint itself. For example, when painting a decorative façade cover, it can be hung with its back sides facing each other, which ensures a smaller volume occupied in the oven and a smaller amount of paint, because paint sprayed on one side will fall on the other side and, accordingly, better paint the product.

The painted products are then fired. To do this, they are driven into a special oven for drying in order to prevent moisture from entering them, after which they are cooled.

The next stage is placing the structures in the spraying chamber, where powder paint is applied to the surface to be painted under the action of compressed air and an electric sprayer. The paint particles acquire an electrical charge in the spray guns. Due to this, paint particles are attracted to the surface being painted and are evenly distributed over it.

Then the parts to be painted with a coat of paint are placed in a polymerization oven for 20 minutes. The temperature in the oven ranges from 180 to 220 degrees, it all depends on the paint manufacturer. The formation of the surface occurs due to melting and fixation on the surface to be painted. After the coating film has formed, the parts are cooled and removed from the carriages.

The longest and most labor-intensive process is surface pre-treatment. Often little attention is paid to it, but it is at this stage that the necessary conditions to obtain high-quality coverage. Pre-treatment ensures durability, elasticity, durability of the coating, optimal adhesion of the powder paint to the surface and improved anti-corrosion properties. First, the parts need to be cleaned and degreased. This is achieved mechanically or chemicals. At mechanical cleaning sandblasting machines, sandpaper or sandblasting pumps are used; also, for small surfaces or already painted surfaces, they can be wiped with a clean cloth soaked in solvent or white spirit. Another method is chemical cleaning, using alkaline, acidic or neutral substances, as well as solvents. Chemical cleaning Mainly used in factories in special baths. During chemical processing, parts are immersed in special baths with a solution or processed using a jet method (the solution is fed under pressure through technological holes). IN in this case the processing efficiency is much higher, since the part is subjected to mechanical stress and the flow of clean solution to the surface is continuous. After firing, the parts cool naturally. Then, using a transport system, they are fed into the painting chamber, where powder paint is applied. In the chamber, non-settled paint is collected for further disposal or reuse. The chamber is equipped with a filter system, as well as cyclone systems. Cells can be either pass-through or dead-end. Dead-end chambers are used for painting small-sized products, walk-through chambers are good for use for painting long products. Factories widely use automatic spraying chambers, in which paint is applied very quickly using manipulator guns.

Electrostatic spraying is the most common method of applying powder paint. Electrostatically charged powder is applied to the grounded product using a spray gun. Sprayers combine different modes:

The tension extends both down and up. The strength of the torch (flow) of paint and the speed of its release are regulated. The distance from the torch to the surfaces to be painted changes. Powder paint is poured into the barrel. Air is supplied under pressure through the partition of the barrel, causing the paint to “boil.” Then the air suspension from the container is supplied using an air pump (ejector), diluted with air to a low concentration and fed into a sprayer, where this mixture acquires an electrostatic charge due to friction. Using compressed air, charged powder paint hits a neutrally charged surface, settles and is held on it due to electrostatic attraction. There are two types of electrostatic spraying: electrostatic with charging particles in a coronal charge field and tribostatic spraying. With the electrostatic spraying method, the particles receive a charge from an external source of electricity (for example, a corona electrode), and with the tribostatic spraying method, as a result of their friction against the walls of the spray turbine. The final stage of dyeing occurs in a melting and polymerization oven. The paint is melted and polymerized at a temperature of 180-220 ° C for 20-30 minutes, after which the powder paint forms a film (polymerizes). The main requirement for the oven is to maintain a constant temperature (the temperature spread in the oven should not exceed 5 degrees) for uniform heating of the product. When heated in an oven, products with a coat of paint melt, go into a viscous state and form a continuous film, while displacing the air contained in the layer of powder paint. Some air still remains in the film, forming pores, which deteriorates the quality of the coating. To prevent the appearance of pores, painting should be carried out at more high temperature than the melting temperature of the paint is about 10-20 degrees higher, and the paint layer should be thinner. To paint large metal products with thick-walled partitions, it is necessary to increase the heating time in the oven for better polymerization and adhesion.

Powder coating methods

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

Electrostatic Spray - the most popular powder painting 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. Best quality paint application is achieved by painting with the so-called “Faraday grid”. This is when the product is first painted vertically over the surface, then horizontally and leveled with a slight distance from the gun in the horizontal direction. The recommended distance of the gun from the surface to be painted is 20-30cm. It all depends on the profile, type of paint and settings of the gun itself. Determining the paint release pressure, the distance of the gun flame from the surface to be painted, and the amount of paint mixed with air can be determined by an experienced and skilled worker (usually this is achieved through trial and error).

Scope of application of powder paints

Powder painting is an environmentally friendly, waste-free technology for producing high-quality protective and protective-decorative coatings. Coatings are formed from polymer powders, which are applied to the surface of the product using electrostatic spraying. Such coatings are very strong and durable. This method is ideal for painting forged products, aluminum profiles and galvanized surfaces.

The scope of application of powder paints is constantly expanding. They are widely used in construction, agricultural engineering and instrument making, automotive and other areas of industry for painting:

Metal structures and aluminum profiles(doors, facades and aluminum windows);

Sports equipment (bicycles, motorcycles and snowmobiles);

Medical equipment (beds, chairs, tables);

Roofing materials (metal roofs, gutters);

Household appliances (refrigerator cases, washing machines, computers)

Furniture items;

Non-metallic products (items made of plaster, ceramics, glass), etc.

Differences in composition and technology of use highlight this type coatings in a “special class” relative to the rest paint and varnish materials. Currently, powder coating of metal products has become widespread in industry, from aircraft manufacturing to production household goods and accessories.

Powder coating of metal products: process technology and main stages

The technological process of powder painting is divided into the following stages:

• preparation of the surface to be painted;
• applying paint in powder form;
• formation of a liquid film at high temperatures;
• 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 uniform distribution of powder materials during spraying. Attention is paid to both removing all kinds of surface contaminants and ensuring the surface has the required roughness. In addition to mechanical methods Surface preparation can also be chemical, such as etching or phosphating.

Application of powder materials

Powder coating of metal is carried out:

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

Thanks to its simplicity and versatility, greatest application received paint application electrostatic spraying. For flat surfaces, special magnetic brushes and rollers can be used using technologies used in copying equipment. Dipping into a "fluidized bed" used on automatic lines for conveyor production of similar products. Gas flame method due to the excessive unevenness of the layer and the properties of the resulting coating, it did not spread. Existing plasma spraying is characterized by the use of low-temperature plasma to heat the particles and the use of an inert gas; limited to the use of heat-resistant powders when applying thin coatings to heat-resistant materials.

The retention and uniform distribution of powder materials on the surface of metal products is ensured by the electrostatic forces of interaction between charged paint particles and the “electronically neutral” surface. Before spraying, the paint particles in the gun receive an electrical charge:

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

The charge of the particles is, as a rule, negative; the charge value must correspond to the optimal range that allows the particles to be retained on the surface until a liquid film is formed and does not interfere with the application 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, the area and material of the surface.

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

Formation of liquid film

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 powder is applied in a “fluidized bed” to preheated workpieces; the process of forming a liquid film occurs due to accumulated heat or additional heating.

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

Final coating formation

The final formation of the film occurs when the product cools. Conditions may differ in both cooling rate and environment. The strength characteristics of the coating and adhesion force, depending on the formation conditions, can vary by tens of percent. At the same time for different types Accelerated and slow cooling is practiced in polymers. Cooling the coating in plasticizing polymer media can reduce the internal stresses of the coating to zero.

Unlike thermoset paints, thermoplastic paints can easily eliminate coating defects using repeated “sintering”.

Powder coating is widely used in the construction industry in the production of steel and aluminum profiles, 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 in up to 250 colors according to RAL tables.

The process of preparing 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 the 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 ensure grounding of the parts. The technological operation of cleaning the hooks and monitoring the grounding circuit should be provided.
3. Spraying of powder materials must be done with the minimum required amount of air. Excessive air supply leads to:

• excess paint;
• increased wear of equipment;
• violation of the technology of electrification of powder particles;
• changes in the granulometric composition of the paint;
• reduced visibility in the spray booth.

1. 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 before introducing the air mixture into 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 the humidity is no more than 35%);
• oil content no more than 0.1 ppm.

1. When reusing powder materials, changes in the original composition, primarily granulometric, are taken into account. The amount of permitted additions of regenerated materials to the original powders should not be exceeded. Homogenize the powder mixture thoroughly before use.
2. Do not mix paint of different colors and types. When changing to a different paint, all equipment must be thoroughly cleaned. It is advisable to have separate supply hoppers and hoses for each paint used.
3. Without surface preparation you will not get a high-quality coating. In this case, the purpose and operating conditions of the product should be taken into account. The bicycle frame must be prepared slightly differently than the elements office desk. Sloppy preparation leads to:

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

1. The cost of the initial powder does not determine the actual cost-effectiveness of the coating. Should be considered:

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

1. Consider the storage conditions for powder materials. Fever can reduce both the technological characteristics of the powder and the performance properties of the coating. The container used must be waterproof due to the high hygroscopicity of the materials. Typically, the recommended temperature in a warehouse should not exceed 25...28 ° C, humidity no more than 50%.
2. Strictly follow the recommended powder sintering technology. It should be taken into account that the air temperature in work area furnace is an indirect characteristic of the technical process. The operation of the installation must ensure uniform heating of the metal of the product to optimal temperatures. Depending on the type of material and weight of the product optimal temperature air and exposure time may vary and are reflected in the instructions.
3. Timely comply with technical regulations to maintain the operation of site equipment. Preventative maintenance, including regular cleaning, inspection, repair and replacement of components, is the basis for smooth operation and quality products. Use spare parts original manufacturers. TESLA equipment has proven itself well.

Safety precautions

The main types of hazards when powder coating products are:

• dust entering the painter’s lungs and onto the surface of the painter’s skin;
• formation of an explosive dust-air mixture.

Video: powder painting of metal doors

These threats are eliminated by the use of personal protective equipment and quality system ventilation, both the paint booth and the sintering oven. It is mandatory to carry out high-quality grounding of the equipment used.

Popular articles: