Which technology does not require paint heating. Powder coating of metal products, application rules

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". Using the control unit, you can control the temperature of the oven, the time of staining and set a timer to automatically turn off the oven 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 in our more correspond to ovens with air recirculation. Application chambers made of dielectrics with an electrically conductive coating provide uniform distribution powder paint on the surface of the part, however, when misuse 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 (temperature variation of at least 5°C is allowed in different parts of the furnace) 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.

The time of obtaining the required temperature on 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.

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

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.

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.

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 the mechanical methods, there is blasting and abrasive processing using 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 with detergents 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 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 high voltage corona electrode. 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 thermal insulation panel is made of 100mm thick basalt slabs 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 (

Powder paints were developed in the 60s of the XX century due to the need to protect the painted surfaces, give them an attractive appearance, reduce painting costs, and also in order to reduce environmental damage. At the same time, an electrostatic coating method and an anodizing system arose. Coatings with a metallic effect and paints resistant to adverse external factors began to appear.

Polymer powder coating is first sprayed onto the product, and then polymerized in a special oven and at a certain temperature. Powder coating technology involves the following steps:

Surface preparation
Application of powder paint
Polymerization

Surface pretreatment

Pre-treatment of the product is the longest and most labor-intensive process, which is sometimes not given the necessary attention, while the durability, quality and elasticity of the coating depend on it. Preparation of the surface for the painting process includes the removal of any contaminants, degreasing and phosphating in order to increase adhesion, as well as protect the metal from corrosion.

Cleaning of the treated surface can be carried out mechanically or by chemical means. In the case of mechanical cleaning, steel brushes or grinding discs are used, lapping with a clean cloth soaked in solvent is possible. As for chemical treatment, it is carried out using acidic, alkaline or neutral substances and solvents, which are selected depending on the degree of contamination, material, size and type of surface to be treated and other factors.

The application of a conversion sublayer helps prevent various kinds of contaminants and moisture from getting under the coating, which cause peeling and subsequent destruction of the coating. Phosphating the surface with the application of a layer of inorganic paint makes it possible to increase adhesion, that is, the adhesion of the surface to the paint by 2-3 times, and protect it from rust. When removing oxides (scale, rust and oxide films), abrasive (mechanical, shot blasting, shot blasting) and chemical cleaning, that is, pickling, are very effective.

Abrasive cleaning is carried out with the help of small particles (shot, sand), iron or steel granules, walnut shells, which are fed to the surface at high speed by means of compressed air or centrifugal force. These particles break off pieces of metal with scale, rust or other contaminants, which significantly increases the adhesion of the coating.
Etching is the removal of oxides, rust and other contaminants using solutions based on hydrochloric, sulfuric, nitrogen, phosphoric acid or caustic soda. They contain inhibitors that slow down the dissolution of the cleaned surface. The advantages of chemical cleaning over abrasive cleaning are greater productivity and ease of use. But after it, it is necessary to rinse the cleaned surface from solutions, and this, in turn, necessitates additional use cleaning agents.
The final stage of surface preparation is passivation. In other words, body treatment with sodium and chromium nitrate compounds. Passivation is carried out in order to prevent the occurrence of secondary corrosion at any stage of surface preparation - after degreasing, phosphating or chromating.

After rinsing and drying the part in the oven (curing section), the surface can be considered ready for powder coating.
Applying powder paint to the surface of the product
When pre-treatment is completed, the object to be painted is placed in the spray chamber, where powder paint is directly applied to it.
The main purpose of this box is to trap powder particles that have not settled on the product to be painted, to dispose of the paint, and to prevent it from entering the room. Such a chamber is equipped with a filter system, cleaning means (vibrating screen, hoppers, etc.) and suction systems.
There are dead-end and walk-through types of boxes. In dead-end chambers, products are usually painted small size, while large items are in long ones. There are also automatic models, where in a matter of seconds the powder coating is applied using pistol manipulators.
The most common way to apply powder paint is electrostatic spraying, that is, applying an electrostatically charged powder to a grounded product using a pneumatic spray gun, also called a gun, applicator or spray gun.
Coating formation
When the paint has already been applied to the product, it is sent to the next stage - coating formation, which includes melting the paint layer, obtaining a coating film, curing it and cooling.
The reflow process is carried out in a special furnace or chamber. There are many types of polymerization chambers, depending on the specifics of production, their design may vary. In simple terms, such an oven is a kind of drying cabinet with electronic “stuffing”. With the help of the control unit, it is possible to control the temperature regime of the chamber and the staining time, adjust automatic shutdown at the end of the process. The energy source for the polymerization oven can be electricity, natural gas, or even oil.
Separate horizontal and vertical, continuous and dead-end, single and multi-pass furnaces. Melting and polymerization occur at a temperature of 150-220 ° C for 15-30 minutes, resulting in a film, that is, powder paint polymerizes.
The main requirement for polymerization chambers is to constantly maintain the set temperature for uniform heating of the product to be painted. The required mode for the formation of the coating is selected taking into account the features this product, type of powder coating, type of oven, etc.
At the end of polymerization, the part to be painted is cooled in air, and after it has cooled down, we can assume that the coating is ready.

When processing large-sized parts or large volumes of production, a transport system is used. Thanks to it, the painted products are easily moved from one stage of painting to another. The principle of operation is that the painted objects are fed on a special suspension or trolleys moving along rails. Such a transport system makes it possible to continuously carry out the painting process, which, in turn, can significantly increase work productivity.
Benefits of Powder Coatings
Metal powder coating technology has many advantages:
Excellent physico-chemical and decorative properties of coatings, which cannot be achieved by other methods of painting, including a rich palette of possible colors.
Good performance properties of coatings
Durability of products painted with powder paints
Single layer coating due to 100% dry matter content, which means economical use of powder coatings
Small porosity
Improved impact and corrosion resistance compared to other paints
No need to control viscosity, as powder paints are delivered to the direct consumer in a ready-to-use form
Losses when painting with powder paints are 1-4%, and, for example, when using liquid paints– about 40%
Hardening of the coating within 30 minutes
No need for large rooms for storage of powder paints
Minimize damage to painted parts during transportation and reduce the cost of their packaging
Ecological safety of painting with powder paints

In view of all the above advantages this method metal coloring, most industrialists today give their preference to it.

Powder paint has been around for a long time. But if you do not own the technology of its application to the required extent, if you do not have the necessary experience, you will have to thoroughly study all the information in order to avoid mistakes. It is to their prevention that we dedicate this material.

Peculiarities

Powder paint is made from polymers that are powdered and then applied to a specific surface by spraying. To give the coating the desired properties, it is thermally processed, the molten powder turns into a film that is uniform in thickness. The key advantages of this material are corrosion resistance, significant adhesion. Under the action of high temperatures, including when they alternate with low ones, powder paint retains its properties for a long time. positive traits. Mechanical and chemical effects are also well tolerated by it, and contact with moisture does not disturb the surface.

All these advantages powder paint retains for a long time along with visual appeal. You can paint the surface, achieving a variety of tones and textures, varying the additives introduced. Matte and glossy sheen are just the most obvious examples; this decor is created quickly and easily with powder paint. But more original painting is also possible: with a three-dimensional effect, with the reproduction of the appearance of wood, with imitation of gold, marble and silver.

Undoubted advantage powder coating is the ability to complete the entire work with the application of one layer, when working with liquid compositions this is unattainable. In addition, you will not need to use solvents and monitor the viscosity of the paint composition. Any unused powder that has not adhered to the desired surface can be collected (when working in a special chamber) and sprayed again. As a result, with constant use or with large one-time volumes of work, powder paint is more profitable than others. And the good thing is that there is no need to wait for the ink layer to dry.

All these advantages, as well as optimal environmental friendliness, no need for powerful ventilation, the ability to almost completely automate work, are worth considering.

Don't forget about negative aspects such a technique:

If some defect appears, if the coating is damaged during operation or subsequent use, the entire object or at least one of its faces will have to be repainted from scratch.
At home, powder painting is not carried out, it requires very complex equipment, and the size of the chambers limits the size of the objects to be painted.
It is impossible to tint the paint, nor can it be used for parts, structures that are to be welded, since the burnt parts of the paint layer are not restored.

What surfaces can be used?

Strong adhesion makes the powder coating process ideal for stainless steels. In general, processing metal products household, industrial and transport purposes, the powder is used much more often than liquid formulations. This is how the components of warehouse and trading devices, machine tools, metal of pipelines and wells are painted. In addition to ease of application, the attention of engineers to this method of processing is attracted by the safety of paint in fire and sanitary, zero level its toxicity.

Forged structures, aluminum and stainless steel products may well be powder coated. This method of applying coatings is also practiced in the production of laboratory, medical equipment, and sports equipment.

Products made of ferrous metals, including those with an external zinc layer, ceramics, MDF, plastic can also be a good substrate for powder coating.

Dyes based on polyvinyl butyral are distinguished by increased decorative properties, are resistant to gasoline, do not conduct electricity, and tolerate contact with abrasive substances well. The ability to survive the ingress of water, even salty, is very useful when creating pipelines, heating radiators, and other communications in contact with liquid.

When applying a special powder to the surface of an aluminum profile, the priority is not so much corrosion protection as giving a beautiful appearance. Be sure to select the mode of operation, depending on the composition of the dye and the characteristics of the substrate, take into account the specifics of the equipment. An aluminum profile with a thermal insert is processed for a maximum of 20 minutes when heated to no higher than 200 degrees. The electrostatic method is worse than the tribostatic method when painting metal products with blind holes.

The use of powder fluorescent paint is practiced when working on road signs and other information structures, when glow in the dark is more important. For the most part, aerosol formulations are used, as the most practical and creating the most even layer.

How to breed?

The question of how to dilute powder paint, in what proportion it should be diluted before coating, is not in front of professionals in principle. As you already know, staining with this type of paint is done in a completely dry form, and no matter how experimenters try to dilute, dissolve this mixture, they will not succeed.

Consumption

There are decorative, protective and combined coatings, depending on belonging to a particular group, a layer of various thicknesses is formed. You also need to take into account geometric shape surface and the difficulties of working with it.

Coloring

As you already know, it is impossible to paint anything with powder paints at home. The main difficulties in using them on an industrial scale arise in the process of preparatory work. The technology provides that the slightest contamination should be removed from the surface, degreased. Be sure to phosphate the surface so that the powder adheres better.

Failure to follow the preparation method will lead to a deterioration in the elasticity, strength and external attractiveness of the coating. Dirt can be removed during mechanical or chemical cleaning, the choice of approach is determined by the decision of the technologists.

To remove oxides, corroded areas and scale, shot blasting machines spraying sand or special granules made of cast iron or steel are often used. Abrasive particles are thrown in the right direction by compressed air or centrifugal force. This process occurs at high speeds, due to which foreign particles are mechanically beaten off the surface.

Hydrochloric, nitric, phosphoric or sulfuric acid is used for chemical preparation of the surface to be painted (so-called etching). This method is somewhat simpler, since there is no need for complex equipment, and the overall performance is increased. But immediately after etching, you need to wash off the remaining acids and neutralize them. Then a special layer of phosphates is created, its formation plays the same role as the application of a primer in other cases.

Next, the part must be placed in a special chamber: it not only reduces consumption working mixture, capturing it, but also prevents paint contamination of the surrounding room. Modern technology invariably equipped with hoppers, vibrating screens, suction devices. If you need to paint a big thing, use the through-type cameras, and relatively small parts can be processed in dead-end machines.

In large industries, automated painting chambers are used, in which a manipulator of the “pistol” format is built in. The cost of such devices is quite high, but getting completely finished products justifies all costs in seconds. Usually the atomizer uses an electrostatic effect, that is, the powder first receives a certain charge, and the surface receives the same charge with the opposite sign. The “gun” “shoots” not with powder gases, of course, but with compressed air.