Properties paint coatings depend not only on the quality of the paints and varnishes used, but also on such facts as the method of preparing the surface for painting, right choice and compliance technological mode painting and drying. The main stages of the paint application process are given below.
PSURFACE PREPARATION
Surface preparation before painting is great importance to obtain a high-quality coating and ensure a long service life. Surface preparation involves removing corrosion products, old paint, grease and other contaminants. Surface preparation methods are divided into three main groups: mechanical, thermal and chemical.
TO mechanical methods include: cleaning with tools (brushes, grinders), cleaning with sand, shot, a mixture of sand and water. Using these methods, you can obtain a well-cleaned surface with uniform roughness, which promotes the best adhesion of the paint film.
TO chemical surface methods, first of all, include degreasing the surface, which is carried out using alkaline detergents or using active solvents (washes), depending on the type of contamination.
Thermal The method is used to clean metal from rust and scale using the flame of an oxygen-acetylene torch.
Thus, when renewing the paintwork, it is necessary to first inspect the surface. If the old paintwork adheres firmly to the surface in the form of a continuous layer, it should be washed with warm water and dried. If the coating does not adhere firmly, it must be completely removed.
PADDING
The first operation after surface preparation is priming. This is one of the most important and responsible operations. Since the first primer layer serves as the basis for the entire coating. The main purpose of the primer is to create a strong bond between the surface to be painted and subsequent paint layers, as well as to ensure the high protective ability of the coating.
Priming should be done immediately after completing surface preparation work. The primer can be applied by brush, spray gun or other method. When painting surfaces exposed to high humidity or used in atmospheric conditions, it is recommended to apply priming with a brush. Drying of the soil should be carried out in accordance with the regime provided for by the technology. When a glossy surface of the soil forms, it should be lightly sanded with fine sandpaper.
The thickness of the primer film when painting with traditional paints and varnishes (primers such as GF, KhV, KhS) should not be excessively large, usually 20-30 microns. For anti-corrosion protection with modern paintwork materials based on epoxy and polyurethane, the thickness of the primer, on the contrary, should be greater than the thickness of the top enamel layer. This is due to the fact that in this case the main protective load and anti-corrosion properties are carried by the primer layer.
PUTTY
This operation is intended to level surfaces. Both excessively thick and insufficient layers of putty can crack during operation, as a result the protective properties of the coating will be reduced. Therefore, the putty should be applied in a specified layer. First, local putty is applied to the primed surface, and then continuous putty. Each layer of putty must be thoroughly dried. The number of layers should not be more than three. If it is necessary to use a large amount of putty, a layer of primer is applied between them.
GRINDING
The putty surface after drying has unevenness and roughness. Irregularities and specks are also observed on dried surfaces of primers, varnishes and enamels. Grinding is used to remove irregularities, debris and smooth out roughness. During the grinding process, the surface being processed is exposed to many tiny abrasive grains, as a result of which scratches are formed and it becomes dull. This significantly improves adhesion between coating layers. For grinding, abrasive sandpaper on a paper or fabric basis is used. The grain size (numbers) of the sandpaper for sanding is selected depending on the type of coating being processed.
APPLICATION OF PAINT COATINGS
The putty surface after drying has unevenness and roughness. Irregularities and specks are also observed on dried surfaces of primers, varnishes and enamels. Grinding is used to remove irregularities, debris and smooth out roughness. During the grinding process, the surface being processed is exposed to many tiny abrasive grains, as a result of which scratches are formed and it becomes dull. This significantly improves adhesion between coating layers. For grinding, abrasive sandpaper on a paper or fabric basis is used. The grain size (numbers) of the sandpaper for sanding is selected depending on the type of coating being processed.
As a rule, when painting, not one paint is used, but a whole system of coatings; in this case, the question of compatibility of the applied paint coatings always arises. When choosing a coating scheme, the optimal compatibility will be a system that satisfies simple rule paint compatibility:
Chemically curing paints and varnishes are never applied to physically drying coatings.
The method of applying paintwork materials must correspond to the rheological, physicochemical and other properties of these materials, as noted in the manufacturer’s recommendations. Everyone knows the methods of applying paints and varnishes. Commonly used airless spray, air spray, brush, roller, etc.
Painting with a brush.
This staining method is relatively slow and inefficient. Typically a brush is used to paint small areas with decorative paints. However, the method is indispensable for coating complex structures where the use of spray will result in significant losses due to dispersion, and also for stripe painting prior to the application of anti-corrosion spray coatings.
Most thick build coatings (greater than 150 microns) are designed to be painted by airless spray, so the required film thickness will not be achieved when applied by brush. To achieve a brush thickness comparable to airless spray, double the number of coats must be applied.
Painting with a brush requires caution when applying multi-layer coatings of paints such as CV, CS, NC, which contain active solvents. Solvents in a wet coating will easily re-dissolve the previous dry layer. In this case, the movements of the brush will cause “picking up” of the previous coating, which will lead to a negative result. To avoid this, movements with the brush should be smooth and light, and the number of passes with the brush in one place should be minimal.
Painting with a roller
The productivity of painting using a roller on large, flat surfaces is higher than using a brush and is used for applying most decorative paints. However, when using a roller it is difficult to obtain the required film thickness. As with a brush, it is usually not possible to apply a thick coat. It is necessary to carefully select the type of roller and the length of the pile, depending on the type of paint and the degree of surface roughness. The roller should be well-fitted, with a soft pile coating; the paint should not dissolve the roller coating. Before use, the roller should be pre-rinsed to remove any loose fibers.
Pneumatic (air) spraying.
It is widely accepted quick method coating application in which the paint enters a low-pressure air stream and is atomized. Traditional air spray equipment is relatively simple and inexpensive, but to achieve good atomization and a defect-free paint film, the correct combination of volume, air pressure and fluid flow must be used. The process of air spraying is accompanied by fairly high losses associated with the dispersion of paint in the atmosphere: “undershooting” or ricochet of paint from the surface, paint carryover by air flow. This method is also limited by the viscosity of the paintwork material - highly filled, thick-layer coatings cannot be applied by this method, since for satisfactory atomization most paints must be diluted to the appropriate viscosity, which precludes obtaining a layer of sufficient thickness.
Airless spray.
Unlike air spraying methods, airless spraying does not mix air with the paint, hence the name. Atomization is achieved by passing the paint through specially designed nozzles under high pressure. The required paint pressure is created by the air in the pump, giving a high ratio of fluid outlet pressure to initial air pressure. There are pumps with ratios ranging from 20:1 to 60:1, with 45:1 being the most common. The main advantages of airless spraying:
1. Highly filled, thick-layer coatings can be applied without thinning.
2. Very high productivity is possible, giving a significant economic effect.
3. Compared to air spraying, which has an increased paint consumption, the use of airless spraying leads to reduced material loss and less hazardous dust and fumes.
Paint spray nozzles are subject to high abrasive wear, so it is more effective to use nozzles made of hard alloys, such as tungsten carbide. The sprayed “fan” is produced by a crevice nozzle mounted on the front part of the hole. Available different sizes holes along with different angles of inclination of the slot. The choice of nozzle is made based on the required liquid pressure, the viscosity of the supplied coating material (nozzle diameter), and the type of structure to be painted (nozzle angle). At the same time, to minimize losses and increase productivity when painting small-sized or lattice structures, it is recommended to use narrow-angle nozzles, and wide-angle nozzles for continuous large-sized surfaces. The thickness of the paint coating is controlled by the fluid flow rate.
PAINTING CONDITIONS.
When applying protective and decorative coatings, one of the most important factors that affect the quality of the coating are the following:
- surface temperature;
- paint temperature;
- atmospheric conditions during painting.
Paint application should be carried out in good atmospheric conditions with mild weather prevailing. Painting should not be done:
- when the air temperature falls below the drying temperature or the limit allowed by the specification;
- during fog or high humidity, as well as when rain or snow is inevitable;
- when moisture condenses on the surface to be painted or when condensed moisture may appear during initial period drying.
It must be taken into account that at night the temperature of the surface being painted drops. During the day it rises again, but due to the delay in heating/cooling compared to the ambient temperature, condensation may occur on the non-absorbent surface (metal). Atmospheric air condensation. To avoid condensation, paint should not be applied if the metal temperature is more than 3°C below the dew point.
The paint should not be applied to wet or icy surfaces after rain.
Extreme conditions.
TO extreme conditions refers to ambient temperatures below +5°C and above +40°C.
Below +5°C, drying and curing of coatings slows down sharply, and for some of them it simply stops. This is especially true for chemically cured coatings (such as EP, PU) and coatings cured with air oxygen (such as PF, GF). Therefore, the use of such paintwork materials at low temperatures is not allowed, except in cases stipulated by the specifications for paintwork materials (modern modified epoxy and polyurethane paintwork materials). To others protective coatings extreme low temperatures They don’t work that hard; Chlorinated rubbers and vinyls are suitable for use at temperatures below 0°C provided the surface is clean and free of ice or frost. More details about the conditions for the formation of paint coatings of various types are described in the article “Modern trends in anti-corrosion protection”.
At other extreme temperatures (+40°C and above), paints dry and cure quite quickly, which can result in dry spraying due to too rapid loss of solvent along the path from the spray nozzle to the surface. This can be avoided if:
1. Hold the gun at a minimum distance from the area to be painted and at an angle of 90° to the surface.
2. Add solvents if necessary.
In conditions high temperatures The formation of defects such as voids, inclusions, bubbles, and shagreen is also possible due to the rapid evaporation of the solvent.
The implementation of all stages of painting technology allows you to obtain a coating with the most complete protective properties and maximum durability.
Depending on the scale and type of production, painting work is concentrated in one or several places. This is caused by the need to protect finished parts from the occurrence of corrosion damage during their movement and storage. With this organization of production, painting work is carried out in areas (or in painting departments).
The adopted dyeing technology is reflected in the route maps of technological processes that are developed for individual species products. The cards indicate all stages of the dyeing process, the materials used, the consumption rates of these materials, the drying mode and some other indicators.
The choice of painting method depends on a number of conditions, for example, on the requirements for the coating (coating class), on the type of paint and varnish materials used, the configuration and size of the products, the scale and type of production. When painting products, several methods can be used. In each specific case, the issue of choosing a dyeing method is decided by production possibilities and economic feasibility.
The technological process of painting consists of the following basic operations: surface preparation, priming, puttying, application coating materials(paint, enamels, varnish) and drying of coatings.
Preparation of painting materials. Before use, painting materials are thoroughly mixed electromechanically or by vibration, filtered and diluted with appropriate solvents to the required working viscosity.
Preparing the surface of a part for painting is carried out to remove various types of contaminants, moisture, corrosion damage, old paint, etc. Approximately 90% of labor costs are spent on preparatory work and only 10% - for coloring and drying. The durability of the paint and varnish coating largely depends on the quality of surface preparation.
The surface to be painted, depending on the cleaning method used, may have varying degrees of roughness, differing in the size of the protrusions and the depth of the depressions. To ensure protection of the metal from corrosion, the thickness of the paint layer should exceed the ridges protruding on the metal by 2... 3 times. Preparing surfaces for painting includes cleaning parts, degreasing, washing and drying. Parts are cleaned of contaminants by mechanical treatment (mechanical tools, dry abrasive, water jet cleaning, etc.) or chemically (degreasing, simultaneous degreasing and etching, phosphating, etc.). Non-greasy dirt can be removed with water or brushes. Wet surfaces are wiped with a dry cloth.
In repair practice, three methods are used to remove old paint - fire, mechanical and chemical.
With the fire method, old paint is burned off the surface of the part with a flame. gas burner or blowtorch(this method is not recommended for removing old paint from body parts and tail parts), and for mechanical removal - using mechanically driven brushes, shot, etc. The chemical method of removing old paint is the most effective method in terms of both quality and performance. Old paint is most often removed with organic removers (SD, AFT-1, AFT-8, SP-6, SP-7, SPS-1) and alkaline solutions (solutions of caustic soda (caustic) with a concentration of 8... 10 g/l , mixtures of caustic soda with soda ash, etc.). The sequence of removing old paint with washes is: cleaning from dirt, grease, washing parts or the body; drying after washing; applying the wash to the surface of the body part with a brush; hold for 15...30 minutes (depending on the brand of remover and type of coating material) until the old paint swells completely; removal of old swollen paint mechanically (brushes, scrapers, etc.); washing, degreasing the surface with white spirit or other organic solvents; drying after washing, degreasing.
Alkaline solutions are used to remove old paint in bathtubs. The sequence of removing old paint is: cleaning from dirt, degreasing, washing; drying after washing; immersion and exposure in a bath with an alkaline solution (at a solution temperature of 50...60°C); neutralization in a bath with a solution of phosphoric acid with a concentration of 8.5...9.0 g/l phosphoric acid (at a concentration of 10 g/l caustic in an alkaline bath) or 5...6 g/l phosphoric acid in an acid bath ( at a concentration of 10 g/l soda ash in an alkaline bath); washing in a bath with running water at a temperature of 50...70°C; drying after washing.
After removing old paint and corrosion products, degreasing, etching, phosphating and passivation operations are carried out.
Parts made of ferrous metals, nickel, and copper are degreased in alkaline solutions. Products made of tin, lead, aluminum, zinc and their alloys are degreased in solutions of salts with lower free alkalinity (sodium carbonate or phosphorus, potassium carbonate, liquid glass).
Pickling is the cleaning of metal parts from corrosion in solutions of acids, acid salts or alkalis. In practice, etching and degreasing operations are combined.
Phosphating is a process of chemical treatment of steel parts to obtain on their surface a layer of phosphoric acid compounds that is insoluble in water. This layer increases the lifespan of the paint and varnish coating, improves its adhesion to the metal and slows down the development of corrosion in places where the paint and varnish film is damaged. Body and cabin parts must be phosphated.
Passivation is necessary to increase the corrosion resistance of the paint coating applied to the phosphate film. It is carried out in baths, jet chambers or by applying a solution of potassium dichromate or sodium dichromate (3...5 g/l) with hair brushes at a temperature of 70...80°C for a treatment duration of 1...3 minutes.
Before applying paint and varnish, the surface of the product must be dry. The presence of moisture under the paint film prevents its good adhesion and causes corrosion of the metal. Drying is usually carried out with air heated to a temperature of 115...125°C for 1...3 minutes until visible traces of moisture are removed.
The painting process should be organized so that after preparing the surface it is immediately primed, since with long breaks between the end of preparation and priming, especially for ferrous metals, the surface becomes oxidized and contaminated.
Padding. The use of a particular primer is determined mainly by the type of material being protected, operating conditions, as well as the brand of coating enamels and paints applied and the possibility of using hot drying. The adhesion (adhesion) of the primer layer to the surface is determined by the quality of its preparation. The primer should not be applied in a thick layer. It is applied in a uniform layer with a thickness of 12...20 microns, and phosphating primers - with a thickness of 5...8 microns. Primers are applied using all the previously described methods. To obtain a primer layer with good protective properties that is not destroyed when applying putty or enamel, it must be dried, but not overdried. The primer drying mode is specified in the regulatory and technical documentation according to which these products are painted. When irreversible primers (phenol-oil, alkyd, epoxy, etc.) overdry, the adhesion of topcoat enamels to them, especially those that dry quickly, sharply deteriorates.
Puttying. The surfaces of parts may have dents, small depressions, cavities, discontinuities at joints, scratches and other defects that are repaired by applying putty to the surface. Putty helps to significantly improve the appearance of coatings, but since it contains a large amount of fillers and pigments, it worsens the mechanical properties, elasticity and vibration resistance of coatings.
Puttying is used in cases where other methods (preparation, priming, etc.) cannot remove surface defects.
Surfaces are leveled in several thin layers. Each subsequent layer is applied only after the previous one has completely dried. The total thickness of quick-drying putties should not be more than 0.5...0.6 mm. Solvent-free epoxy putties can be applied up to a thickness of 3 mm. When applying putty in thick layers, it dries unevenly, which leads to cracking of the putty and peeling of the paint layer.
The putty is applied to a previously primed and well-dried surface. To improve adhesion to the primer, treat the primed surface with sandpaper and then remove the stripping products. First, the most significant depressions and irregularities are puttyed, then the putty is dried and sanded, after which the entire surface is puttyed.
The putty is applied to the surface using pneumatic spraying, a mechanical or hand spatula. After the putty has dried, the putty surface is carefully sanded.
Grinding. To remove roughness, unevenness, as well as debris, dust particles and other defects from the putty surface, grinding is performed. For grinding, various abrasive materials are used in powder form or in the form of abrasive skins and tapes on a paper and fabric basis. Only completely dry coating layers can be sanded. Such a layer should be hard, not torn off during grinding, and the abrasive should not immediately become “greasy” from the coating. The grinding operation is carried out manually or using a mechanized tool.
“Dry” and “wet” grinding is used. In the latter case, the surface is moistened with water or some inert solvent, the sanding paper is also moistened from time to time with water or solvent, washing it from contamination with sanding dust. As a result, the amount of dust is reduced, the service life of the abrasive increases and the quality of sanding improves.
Applying outer layers of coatings. After applying the primer and putty (if necessary), the outer layers of coating are applied. Number of layers and selection paint and varnish material determined by the requirements for appearance and the conditions in which the product will be used.
The first layer of enamel over putty is “revealing”; it is applied more thinly than subsequent ones. The detection layer is used to detect defects on the putty surface. Identified defects are eliminated with quick-drying putties. The dried putty areas are sanded and the stripping products are removed. After eliminating the defects, several thin layers of enamel are applied. Enamels are applied using a spray gun.
To obtain coatings good quality with a beautiful appearance, the area (department) should be clean, spacious, and have a lot of light; The room temperature should be maintained within 15...25°C with a humidity not exceeding 75...80%. Exhaust ventilation should provide suction of solvent vapors, prevent the settling of paint dust, which heavily contaminates the surface and deteriorates appearance coverings.
Each subsequent layer of enamel is applied on a well-dried previous layer and after eliminating defects.
The last layer of coating is polished with polishing paste to give a more beautiful appearance.
Polishing. To give the entire painted surface a uniform mirror shine, polishing is performed. For this purpose, special polishing pastes are used (No. 291, etc.). Polishing is carried out in small areas. This operation can be performed manually (with a flannel swab) or using mechanical devices.
Drying. After applying each layer of paint and varnish materials, drying is carried out. It can be natural and artificial. Natural drying processes are accelerated by intense solar radiation and sufficient wind speed. Most often, natural drying is used for quick-drying paints and varnishes. The main methods of artificial drying: convection, thermoradiation, combined.
Convection drying. It is performed in drying chambers a stream of hot air. Heat flows from the top layer of paint to the metal of the product, forming a top crust that prevents the removal of volatile components, thereby slowing down the drying process. The drying temperature, depending on the type of paintwork, ranges from 70... 140°C. Drying duration is from 0.3...8 hours.
Thermoradiation drying. The painted part is irradiated with infrared rays, and drying begins from the surface of the metal, spreading to the surface of the coating.
Combined drying (thermoradiation-convection). Its essence is that in addition to irradiating products with infrared rays, additional heating is performed with hot air.
Promising methods for drying paint coatings are ultraviolet irradiation and electron beam drying.
Quality control of product painting. Control is carried out by external inspection, measurements of the thickness of the applied film layer and the adhesive properties of the prepared surface.
External inspection reveals the presence of gloss of the coating, dirt, scratches, drips and other defects of the painted surface. On the surface, no more than 4 pieces are allowed per 1 dm2 area. specks no larger than 0.5x0.5 mm, slight shagreen, individual marks and strokes. The paintwork should not have smudges, waviness or different shades.
Determining the degree of drying of paints and varnishes by the deposition of dust on the surface is the most common method in practice and consists of testing the condition of the drying surface by touching a finger. A finger test is carried out every 15 minutes, then every 30 minutes, subjectively determining the degree of drying of the film. The film is considered to be free of dust if, when lightly swiping with a finger, no traces remain on it. On a film that has dried out from dust, strong sticking is still possible.
The degree of practical drying can most simply and reliably be determined with a fingerprint. The film is considered almost dry if, when pressed with a finger (without special effort) it does not come off and there is no imprint left on it.
The thickness of the paint film without compromising its integrity is determined by the ITP-1 magnetic thickness gauge, which has a measurement range of 10...500 microns. The operation of the device is based on measuring the force of attraction of a magnet to a ferromagnetic substrate depending on the thickness of the non-magnetic film.
Control of adhesion (stickiness) of the coating to the metal is carried out using the lattice cut method. On the inner surface of the product, 5...7 parallel cuts are made to the base metal with a scalpel along a ruler at a distance of 1...2 mm, depending on the thickness of the coating, and the same number of cuts perpendicularly. The result is a lattice of squares. The surface is then cleaned with a brush and graded using a four-point system. Complete or partial (more than 35% of the area) peeling of the coating corresponds to the fourth point. The first score is assigned to the coating when no peeling of its pieces is observed.
The last decade in the Russian construction market has been marked by the active emergence of a large number of new building materials and technologies. Their appearance changed both the approach to performing work and the general trends in the decoration of interiors and facades. For example, painting walls and ceilings has become relevant again, but at a higher technological level. This is ensured, first of all, by a qualitative improvement in the decorative and performance properties of paint and varnish coatings and by expanding the types of bases for painting.
Domestic builders have to master new ones on the go, Hi-tech, often learning from my own mistakes. Unfortunately, there are practically no specialized training centers, competent sales support and technical support. As a result, when performing work, basic technological rules are violated, and builders expect that high-quality finishing material will cover all the shortcomings of the preparatory stages of work. However, statistics on complaints about paint coatings show that:
Preparing the base
When starting work, the painter must evaluate the quality of the base. For this purpose, primarily visual control is used. At the same time, the type and condition of the base material, visible damage are determined, and technological errors in its implementation are identified. The type and composition of the base allows you to evaluate its effect on the coating and choose the right painting system. The base can be made of organic or inorganic materials and have a porous or dense structure. In addition, it is necessary to evaluate how clean and dry it is, on concrete bases There should be no form release agent. By tapping the plaster, possible voids or peelings are determined. If old paintwork is used as a base, its strength can be determined by testing using masking tape: you need to stick it to the surface and then sharply tear it off. If the coating is not damaged, then its strength is sufficient.It is very important for the correct execution of work to check the absorbency of the base. This is done by moistening the surface. Depending on the rate of moisture absorption, they are distinguished: highly absorbent, normally absorbent and weakly absorbent bases. If water quickly sinks into the base, then when applying compounds diluted with water, the process of film formation is disrupted and the coating will not gain sufficient strength. Therefore, in this case it is necessary to use special primers.
A serious problem is the unequal absorption capacity of different areas of the base. This can happen when different materials are used in the base. If this difference is not eliminated, then the transition boundaries will be noticeable on the finished paintwork. And if, as a result of the inspection, chalking or crumbling of the base is revealed, then the presence of such a defect can lead to the fact that the finishing coating peels off along with top layer grounds. When identifying such properties of the base, it is necessary to use special primers for them. They must be non-pigmented and finely dispersed, sufficiently liquid and penetrate capillaries well, not dry very quickly, provide adhesion for subsequent coatings, and not form a thick film. When applied, such primers should not form a glossy film. It is not necessary to treat surfaces with normal and uniform absorbency with special primers; It is enough to apply the paint with a small addition of water (the dilution percentage is usually indicated in the description). The final coat can then be applied without thinning. Substrates that poorly absorb moisture are treated with pigmented primers, which have particularly high adhesion or form chemical compounds with the base. They are applied in a fairly thick layer and serve as a connecting bridge between the base and the next coating.
For decorative and gypsum plasters use primers with the addition of fine quartz sand. Then there is no need for outdated methods of improving the adhesion of the decorative layer to the base - applying notches or attaching a special mesh.
System selection
The correct choice of paint system will ensure optimal timing service and at the same time will avoid extra costs. Most often the choice is between acrylic, silicate and silicone systems. When choosing a particular system, it is necessary to take into account the operational requirements for the coating, their physical properties, as well as color design features.Acrylic dispersion paints contain polymers or copolymers of acrylic as a binder. Systems based on them are suitable for almost all substrates used in construction. Coatings with acrylic paints have good vapor permeability, i.e. allow the base to “breathe”. At normal conditions operation they provide optimal combination price quality. In addition, such coatings offer the greatest opportunities for color design surfaces.
In silicate-based materials, liquid potassium glass is used as a film-forming agent, which is obtained by jointly melting potash and quartz, followed by dissolving the resulting product in water. This binder is a mineral binder. Film formation, unlike acrylic paints, occurs as a result of a two-stage chemical reaction. Silicate paints are mainly used for painting mineral substrates, such as concrete, sand-lime brick etc., as well as surfaces previously painted with mineral paints. They have the highest permeability to water vapor and carbon dioxide, so this is the optimal solution for painting ancient buildings and architectural monuments.
An important property of silicate coatings is that they do not support the development of microorganisms and therefore do not require special biocidal additives. However, the high alkalinity of the paint makes it necessary to protect glass, aluminum, a natural stone from splashes that can leave permanent stains. For tinting it is necessary to use only pigments that are alkali-resistant and resistant to liquid potassium glass, so the color range of silicate materials is very limited.
Silicone paints are among the most modern paints. They combine almost everything best properties acrylic and silicate paints. First of all, this is high permeability to water vapor and carbon dioxide (for silicone paints these indicators are close to silicate paints), but with a high water-repellent ability of the surface. They are suitable for almost all types of mineral surfaces and are well compatible with both mineral and synthetic paints. Silicone coatings, like silicate ones, do not support the development of microorganisms. Therefore, they do not require the use of special fungicidal and algicidal additives.
Silicone paints currently have the best decorative and performance properties of coatings. The only drawback limiting their use is their high cost.
Application of paint and varnish coatings
As you know, the main functions of paint and varnish coatings are decorative and protective. Good hiding power and whiteness provide rather decorative functions. But in order for the coating to meet the requirements for moisture resistance, abrasion resistance, and resistance to climatic influences, it is necessary to achieve a certain thickness of the dried film. For facade coatings this is usually 100 - 120 microns, i.e. approximately 200 ml of paint per 1 m2. Application of thinner layers leads to defects in the paintwork and subsequently to damage to the enclosing structures.If applied liquid paints to obtain a thick film on vertical surfaces, you will need to apply at least 4-5 layers. If you use high-quality, thixotropic paints, then such a coating can be obtained in one pass. (Thixotropic paints have a thick consistency when at rest, when mechanical influences they liquefy, and after removing this effect they again acquire a jelly-like consistency). In addition, thixotropic paints allow you to use the most progressive and productive method of airless spraying - Airless.
Paint tinting
Paint tinting is one of the important and very pressing issues. For tinting, you can use both manual and computer tinting. Computer tinting is most convenient for builders and requires minimal labor, especially when performing large volumes of work. For high-quality tinting, the material must have a very precise dosage both in volume and in individual components. Well-designed bases allow you to accurately match the color, regardless of the amount of paint being tinted, and guarantee the fulfillment of the declared properties of the coating.For small volumes, manual tinting is still relevant. Here you can choose tinting with full-color paints or universal pigment pastes that do not contain a binder. Universal pastes allow you to tint both water-based paints and solvent-based enamel. However, if pigment pastes are used incorrectly, you can easily upset the balance between the amount of binder and filler and, for example, instead of an abrasion-resistant coating, you can get a surface that gets dirty when wiped dry, or a coating that easily fades. The use of full-color paints containing a binder is only possible for materials with the same binder. But the reliability and quality of this method are higher, so they are preferable for manual tinting.
Exploitation
During operation, it is necessary to take into account that eternal paint and varnish coatings do not exist. Protecting the base from harmful effects, it wears out. However, a properly executed coating will provide a high-quality coating with a long service life. The service life of coatings depends on many reasons: the application technology and the impact on the coating during operation. For example, façade coatings based on II acrylic last 8-10 years, and under gentle conditions - much longer (for example, the façade is in the shade or is covered by a canopy). But if all technological aspects were observed during the work, then the coating can be updated without large financial costs. As a result, painted structures will last a long time and will not create additional problems for their owners.Therefore, when starting new construction, it is wiser to immediately complete all stages of work efficiently, without falling into excessive savings. This will avoid significant costs subsequently for repair and restoration work.
The technological process of painting CONSISTS OF the following three main operations: priming, puttying, final painting.
Priming on prepared metal - applying the first layer of paint and varnish material to a cleaned, degreased, washed, and phosphated metal surface. The primer layer is the basis of the coating. It provides reliable adhesion to the metal prepared for painting and the subsequent layer of paint, has high anti-corrosion properties and mechanical strength.
For better leveling, one or two layers of a second primer are often applied to a previously primed and putty surface, which differs from the first in composition, properties, color, application and drying methods. For preliminary priming, water-borne primers are most often used, applied by electrodeposition. To apply the second layer, epoxy, epoxyester and other types of primers are used, using various spraying methods.
Each layer of applied primer is dried in accordance with technical requirements. Then the surface is sanded with abrasive waterproof sandpapers with abundant wetting of the surface with water. Grinding is done manually or using special grinding machines. In mass and large-scale production, in order to reduce labor intensity and improve the quality of surface finishing, the grinding operation is mechanized.
Then the areas sanded down to metal are primed. Typically, primers are used for this, which dry quickly when room temperature.
Water-based primers used for preliminary priming are dried at a temperature of 180-190°C, primers for the second and subsequent layers are dried at a temperature of about 160°C.
Puttying is the process of leveling identified minor defects on previously primed body surfaces. Rubber, plastic, wooden and metal spatulas are used as the main tool for this operation. Sprayers are used to apply liquid putties. The thickness of the putty layer applied to the primed surface should not exceed
0.5 mm. The exception is epoxy putties, which can be applied to both primed and metal surfaces with layer thickness up to 15 mm.
The final painting is carried out on the primed, putty and sanded surface of the body (cabin). Due to their high durability during operation and less labor-intensive application, synthetic enamels of the ML grades are most widely used. Synthetic enamels can be applied in a variety of ways, but to obtain a high-quality enamel surface, it is recommended to apply it by pneumatic spraying or spraying in a high-voltage electric field. An important indicator that determines the quality and service life of a paint coating is the total film thickness. A thin coating is not resistant to abrasion, does not provide the required protection against corrosion, and does not provide the necessary shine. An excessively thick coating becomes brittle and loses its properties with sudden changes in temperature. The optimal total coating thickness is from 80 to 120 microns.
There are various methods of applying paint and varnish coatings.
Hand painting with brushes is used for final finishing when touch-up of small defects on the non-facial surface of the body is required, assembly unit or details.
Dip painting has become widespread in industry. The part is immersed in a bath of paint and varnish material, then removed from it, held for some time over the bath to drain excess paint from the surface and dried. In mass production, dip painting is carried out using overhead conveyors equipped with hangers of various shapes in the form of hooks, fir trees, rakes, etc.
Several various methods: jet spraying, electric field spraying, pneumatic spraying, electrodeposition, pouring, aerosol spraying, drum spraying, high pressure spraying, application using rollers, spatulas, brushes, etc.
The method of applying paint and varnish material is selected taking into account the type of part, its dimensions, purpose, requirements for the finished coating, economic feasibility, production conditions, etc.
Pneumatic spray
Pneumatic spraying is the most common method of applying paints and varnishes. Pneumatic spraying can be carried out with or without heating the paint material (used more often).
Pneumatic spraying with heating of paint and varnish material
Heating allows you to spray paint material with increased viscosity without the use of solvents (additional dilution of paints), because When heated, the surface tension and viscosity of the coating material decreases. It is often recommended for certain paint materials optimal indicator initial viscosity. The extent to which the viscosity will decrease depends to a large extent on the film-forming component of the paint system.
The coating obtained using this method is of higher quality. This is due to the fact that when the paint is heated, its fluidity increases, its gloss increases and the surface does not “whiten” from moisture condensation.
Pneumatic spraying with heating of paint and varnish material has some advantages over spraying without heating:
Due to fewer layers applied, productivity increases;
Thanks to heating, less solvents are consumed (about 40% for pentaphthalic, oil, glyphthalic, melamine, urea alkyd materials, and up to 30% for nitrocellulose materials);
Can apply materials with high dry matter content and high viscosity;
Due to the speed of application and the reduced content of solvents in paintwork materials, losses due to fogging are reduced;
When heated, the hiding power of the paint and varnish material increases and the thickness of the applied protective layer increases, thereby reducing the number of applied layers.
Not all paints and varnishes can be applied using heated air spray. Only those whose structure does not change when heated are suitable, and the coating is formed with high protective properties. Nitroglyphthalic, nitrocellulose, bitumen, glyphthalic enamels and varnishes, urea, melamine alkyd, perchlorovinyl, nitroepoxy enamels of the XB-113 brand are widely used.
Paint coatings applied by pneumatic spraying with preheating are not inferior in mechanical and physical properties and corrosion resistance to layers of the same materials diluted to the required viscosity with a solvent and applied by spraying without heating (with the same thickness).
In mechanical engineering, heated paints and varnishes are most often applied using a UGO-5M(hot painting installation). This device is explosion-proof.
Technical characteristics of UGO-5M:
Consumption of coatings at a temperature of 70 °C – 0.25 – 0.35 m 3 /hour;
The temperature of the paint and varnish material leaving the paint heater is 50 - 70 °C;
Temperature of compressed air (at the outlet of the air heater) – 30 - 50 °C;
The productivity of the apparatus (by air) at a temperature of 50 °C is 20 m 3 / hour;
The operating pressure of paintwork materials when supplied to the paint sprayer is 1 – 4 kgf/cm 2 ;
The pressure of compressed air supplied to the sprayer is 2 – 4 kgf/cm 2;
The maximum duration of preheating of paintwork materials is 45 minutes;
The maximum duration of compressed air preheating is 30 minutes;
The required mains voltage is 220 V;
Air heater power – 0.5 kW;
Paint heater power – 0.8 kW;
Dimensions of the UGO-5M installation – 580×380×1775 mm;
The weight of the UGO-5M installation is 130 kg.
Defects that occur during pneumatic spraying and methods for eliminating them
| Defect | Cause of occurrence | How to fix |
| The paint is sprayed unevenly (to the side) |
The nozzle is not centered relative to the head, the gap between the nozzle and the head is clogged | Screw the body and nozzle tightly together, remove the head from the spray gun and rinse the nozzle thoroughly |
| Increased fogging, the jet sprays very strongly | High air pressure | Air pressure needs to be adjusted |
| The paint is supplied to the nozzle intermittently, the torch is intermittent | Contaminated paint, very little paint in the tank, clogged nozzle | Filter the paint, add paint to the paint tank, disassemble and rinse the nozzle well |
| The spray is not spraying strongly enough | Air leak or low air pressure | Inspect the air supply hose and air valve, increase air pressure |
| When the nozzle is not working, paint oozes out. | The needle is poorly adjusted (does not close the nozzle tightly), the nozzle is clogged | Adjust the needle position, disassemble and wash the nozzle |
| Air comes out of the spray head when not working. | Air valve gasket worn |
Replace gasket |
| The covering has shagreen | High air temperature in the painting room, cold air, high paint viscosity | Change the composition of the solvent and change the heating temperature, add high-boiling solvents or heat the air to room temperature, adjust the optimal viscosity of the paintwork material |
| Swelling and peeling of the coating occurs | The air is poorly purified from oil and moisture | Clean and blow out the oil/water separator |
| Coating with specks | Paint does not filter well | Filter paint according to specifications |
Pneumatic spraying without heating the paint material
Paints, enamels and other coatings made from almost all types of film formers are applied by pneumatic spraying without heating.
Disadvantages of the method:
Quite a high cost of solvents;
Significant consumption of paints and varnishes for fogging (from 20 to 40%, and sometimes more);
It is necessary to carry out painting in special chambers with good ventilation and an air purification system;
Expensive operation of painting booths.
Components of a pneumatic spray installation: oil and moisture separator, centralized compressed air line (or a mobile, portable compressor), spray gun (paint sprayer), hoses for supplying paint and compressed air, paint injection tank with mixing device and gearbox.
In order to obtain compressed air, mobile compressors SO-62M, SO-45A, SO-7A, etc. are used.
For large volumes of painting work, SO-7A and SO-62M compressors are often used, because they are mobile vertical, operate at high pressure (6 kgf/cm2), and are characterized by fairly high productivity (30 m3/h). Their safety valve is adjusted to overpressure 8 kgf/cm2. The receiver capacity is 22 and 24 liters, and the engine power is 3.0 and 4.0 kW, respectively. The weight of the SO-7A mobile unit is 140 kg, and the SO-62M is 165 kg.
Compressor SO-45A is portable, therefore more mobile. The maximum pressure is two times less than that of its vertical relatives, and the productivity is 10 times. The electric motor power of the SO-45A compressor is 0.15 kW. There is no receiver. The safety valve is adjusted to an excess pressure of 3.1 kgf/cm 2. And the weight is only 21 kg. The indisputable advantage of the SO-45A diaphragm compressor is that it can act as a vacuum pump to create a vacuum (about 25 mm Hg).
Double cylinder single stage piston compressors simple action with cylinder cooling using air can create operating pressure air about 4 – 7 kgf/cm2.
The single-stage portable diaphragm compressor SO-45A is used for paint sprayers that operate at low air pressure (up to 3 kgf/cm2). In most cases these are airbrushes.
High-quality compressor devices are produced by VZSOM (Vilnius Construction and Finishing Machinery Plant).
Oil and moisture purifiers can be suspended (SO-15A or S-418A) or floor-mounted (S-732) designed at VZSOM.
IN industrial conditions paint injection tanks of types SO-13, SO-12 and SO-42 (VZSOM) are often used.
Installation SO-13 (paint injection tank)- This is a completely sealed container with a lid. It is on the lid that the tank fittings are mounted. In order to reduce the air pressure on the paint, a reducer is used. From the gearbox, one part of the air flows to the paint sprayer, and the other (in which the pressure is reduced) is directed to the paint injection tank and displaces paint to the paint sprayer. If excess pressure builds up in the tank, it can be relieved manually by turning the pressure release valve screw. If for some reason the person working at the installation does not relieve the excess pressure, then it is released independently when the pressure reaches 4.5 kgf/cm 2 . Self-relief of pressure is carried out using a safety valve. This ensures additional work safety and product safety.
VZSOM produces a large number various installations and devices. One of them is pneumatic turbine S-417A. It is necessary to transmit rotational motion to the stirrer.
Technical characteristics of the S-417A turbine:
Power – 0.2 hp;
Maximum pressure – 5 kgf/cm2;
Idle speed – 290 rpm;
Hose diameter – 13 mm;
Air consumption – 0.45 m3/h;
Weight – 4.1 kg.
Hoses go from the paint injection tank to the sprayer, through which the paint and varnish material is supplied. The hoses are made from pressure-suction rubber-fabric hoses for oils and liquid fuels. This hose is produced in accordance with GOST 2318-43, type B - resistance to gasoline. Hydraulic pressure during testing is not less than 20 kgf/cm 2 , and during operation – up to 7 kgf/cm 2 . The inside diameter of the sleeve can be 9, 12 or 16 mm.
Spray guns
Depending on the type of spray head and operating principle, paint sprayers are divided into:
High pressure (working pressure from 3 to 6 kgf/cm2);
Low pressure (2.5 - 3 kgf/cm2).
Also, paint sprayers can be internal or external mixing. High-pressure internal mixing paint sprayers (spray guns) include S-512, which is almost never used in mechanical engineering. To paint sprayers high blood pressure external mixing includes the following brands: KRU-1, O-37A, ZIL, KR-10, KA-1.
The most widely used spray gun KRU-1. It is used to spray paints and varnishes that have a working viscosity at room temperature (18 – 23 °C) up to 40 s according to VZ-4.
The supply of paint and varnish material to the spray gun can be carried out from a glass (small tank), which is attached to the lower or upper part of the spray gun, or from the paint injection tank through the lower fitting.
Almost all spray guns are similar in structure to the KRU type spray gun. But still, they can be equipped with an improved spray head and have a larger number of air holes (with their help you can change the shape of the torch).
To adjust the sprayer, valves are used to regulate the supply of air and paint material. Paint sprayers with increased productivity include devices of the ZIL brand.
The KA-1 paint sprayer (the needle opens automatically with air) is widely used when painting parts with heated or cold paintwork materials on automatic production lines.
Electropainting (spraying in a high voltage electric field)
The essence of electropainting is the transfer of charged paint particles in a high-voltage electric field. An electric field is created between two electrodes, one of which is the product being painted, and the other is the spray corona device. The product is grounded, and a high voltage (often negative) is connected to the spray gun. The paint and varnish material is fed to the spray gun (on the corona edge), where it is negatively charged and sprayed under the influence of electrical forces. The flow of sprayed paint and varnish material is directed to the product to be painted and deposited on its surface. Electropainting is used to apply protective layers to both metal and non-metallic surfaces (rubber, wood, etc.).
Painting is often carried out on conveyor lines using stationary installations or manual paint sprayers. The productivity of the painting process depends on what types of paint sprayers are used and how many of them there are. Manual paint sprayers are characterized by a rather low productivity, although they have a number of advantages: low consumption of paint and varnish material (no loss), the ability to paint products with a lattice structure, etc.
In stationary installations, parts of fairly simple shapes are painted: washing machine bodies, car bodies, housings of various devices, electric motors, refrigerators, etc.
