New building materials and technologies have radically changed attitudes towards finishing works, including application paint coatings. A new level of approach is ensured, first of all, by a significant improvement in operational and decorative properties, as well as an expansion of the types of surfaces suitable for applying paint and varnish coatings.
Statistics show that the majority of defects appear due to improper preparation of the base to be mowed. It is important to choose the right painting system and follow the technology. The most unlikely defect is poor quality paint.
To understand the nuances of the above, we will understand the features of each type of possible defect and note the actions that need to be taken to avoid these consequences.
Preparing the substrate to be painted
Before carrying out work, you need to assess the quality of the base visually, and also pay attention to damage. The base can be made of inorganic and organic materials, and also have a dense or porous structure. On concrete foundations There should be no form release agent. The base surface must be clean and dry. If you plan to apply paintwork to an old base, then its reliability can be checked in the following way. Masking tape is applied to the old coating and then abruptly torn off. If the paint material does not come off as a result, then its strength will be sufficient.
The absorbency of the surface is also assessed. If water is quickly absorbed, then the applied compounds (diluted with water) will not gain sufficient strength. In this case, the surface is pre-treated with special primers. If shedding or uneven absorption is detected, special primers are also used.
Selecting a paint system
The service life of the coating will depend on the choice of painting system. Besides, right choice will avoid additional costs.
When choosing a particular system, pay attention to the operational requirements for the surface, physical properties systems and possible color solutions.
The most popular systems are:
- Acrylic (suitable for almost any surface; have rich color options);
- Silicate (best permeability of water vapor and carbon dioxide; color range is very limited);
- Silicone (high permeability of water vapor and carbon dioxide; high water repellency; suitable for almost any mineral surface; best performance and decorative properties; the only negative is high cost).
Application
In order for the coating to provide the specified properties, it is necessary that the thickness of the dried film be equal to 100-120 microns (for an area of 1 m 2 about 200 ml of paint). If you use liquid paint on a vertical surface, it will be necessary to apply about 4-5 layers. The result can be achieved in one pass using high-quality thixotropic paints. The paint liquefies under mechanical influence and thickens at rest; moreover, when using such paint it becomes possible to use technology airless spray Airless, allowing you to create the perfect surface.
To summarize, it should be said that applying paint and varnish coatings is a fairly simple process, but this process has many nuances, which were discussed in the article. And the more correctly all stages are completed, the longer the service life will be. This will also allow you to avoid high costs later when carrying out repair work in the future.
The main methods of their application are: pneumatic spraying (unheated or heated), airless spraying, high voltage electrostatic field spraying and electrodeposition. The temperature of the surfaces to be painted before applying coatings should be equal to the air temperature in the room. The most common is pneumatic spraying.
Pneumatic spray without heating(Fig. 3.12) are used for applying almost all paintwork materials on various surfaces(except internal). Material, diluted
Rice. 3.12.
materials:
1,3,4 - hoses; 2 - paint sprayer; 5 - oil and water separator; 6 - tank
to a viscosity of 17-30 s (according to a VZ-246 viscometer with a nozzle with a diameter of 4 mm), when sprayed, it is crushed into particles 10-60 microns in size. When applying the coating, the spray gun is moved at a speed of 300^400 mm/s parallel to the surface to be painted at a distance of 250-300 mm from it. The shape of the paint “torch” is oval in cross-section, the major axis of the oval is about 300 mm. However, the process is accompanied by the formation of fog harmful to the health of workers with a loss of 20^40% of paintwork materials and requires the use of special painting booths with complex devices for air extraction and purification. Manual paint sprayers ZIL with paint supply through a hose, KRU-1 with an upper tank and S-512 with a lower tank are common.
Pneumatic Heated Spray Paintwork proceeds without the additional use of solvents. Heating reduces the viscosity and surface tension of the paintwork. The method reduces the consumption of solvents by 30-40%, allows the use of materials with high initial viscosity, increases the hiding power of the material, reduces losses due to its fogging due to a decrease in the solvent content in the paintwork material, and increases the gloss of the coating. The method provides spraying of bituminous varnishes, glyphthalic, nitrocellulose and perchlorovinyl varnishes and enamels. For heating coatings, for example, an explosion-proof UGO-5M installation is used, the heater power of which is 0.8 kW, the material temperature with a hose length of 4 m is 70 ° C and the pressure is 0.1-0.4 MPa, the air temperature is 50 ° C and its pressure is 0.2-0.4 MPa.
The use of superheated steam with a temperature of about 130 °C under a pressure of 0.3-0.4 MPa instead of compressed air ensures savings of 10-20% in materials and the use of thick synthetic enamels.
Airless spray The paintwork material consists of heating the paintwork material to a temperature of 40-100 °C and applying it to a spray device under a pressure of 4-10 MPa. The spray “torch” is formed due to the pressure drop as the paintwork material exits the spray nozzle and the subsequent rapid evaporation of part of the heated solvent, which is accompanied by its significant expansion. The productivity of airless spraying is almost 2 times higher than air spraying.
The installation diagram for airless spraying is shown in Fig. 3.13. In this installation, paint from a container 1 pump 2 served through a heater 6 and filter 7 for the spray gun 9. Paint temperature is measured with a thermometer 8, and pressure - with a pressure gauge 3. The unused part of the paint is directed through the valve 4 back to container 1. After finishing work, the paint is drained from the system through tap 5.
The “torch” of applied materials during airless spraying has clear boundaries and is protected from environment shell of solvent vapor. Compared to pneumatic spraying, the method reduces fogging losses by 20-35% and solvent consumption by 15-25% with a reduction in painting time. For airless spraying, URB-2, URB-3 and URB-150P installations with spray devices 1B, 2B, ZB, 4G and 5A are used
Rice. 3.13.
materials:
1 - tank; 2 - pump; 3 - pressure gauge; 4 - valve; 5 - tap; 6 - heater; 7 - filter; 8 - thermometer; 9 - paint sprayer with a spray pattern width from 100 to 410 mm. Paint consumption 320-1000 g/min. Spraying without heating is carried out at a paintwork temperature of 18-23 ° C and a pressure of 10-25 MPa. The method is recommended when painting large-sized products.
The performance of paint spraying is increased by using painting robots.
Essence spraying in a high voltage electrostatic field(Fig. 3.14) consists in the transfer of charged paint particles in the air due to the potential difference between the electrodes. Primers, nitro enamels, pentaphthalic, glyphthalic, melamine-alkyd and perchlorovinyl enamels are applied in an electrostatic field. The anode is the corona spray device, and the cathode is the product to be painted. Spray heads 7, which are driven by an electric motor 3 and gearbox 4, spray paint in a plane perpendicular to the axis of rotation. Crushed paint particles enter an electrostatic field, having a positive charge, move and are deposited on the surface of the product. When the voltage between the electrodes is 60-140 kV, created by the transformer and the kenotron, a voltage of 2.4-6.5 kV/cm and an operating current of 20-70 mA per atomizer are maintained. The distance from the sprayer to the surface to be painted is 250-300 mm. The method makes it possible to precipitate 95-98% of the material, increase labor productivity up to 2.5 times and improve its sanitary and hygienic conditions. Painting in an electrostatic field is carried out in stationary chambers or using mobile installations such as UERTs-1 or UERTs-4.
Rice. 3.14.
1 - overhead conveyor; 2 - camera; 3 - electric motor; 4 - gearbox; 5 - rectifier; 6 - transformer; 7 - spray heads; 8 - painted products; 9 - gear pump
Essence electrodeposition water-based coatings are based on the phenomenon of electrophoresis in liquid and consist in the transfer of charged particles of the material to one of the electrodes (product) as a result of the applied voltage. Particles of paintwork materials are suspended in demineralized water. The method is used for applying primers. Unlike previous methods, electrodeposition coating is less toxic and fire-safe.
On an uneven primed surface, in order to level it, apply a layer of putty manually with a spatula or by spraying. This layer is first leveled with a spatula and then treated with abrasive sandpaper manually or mechanically.
It is recommended to paint engines with aluminum nitrocellulose enamel NTs-273 without primer. The rear and front axles, gearboxes and steering are painted with water-borne primer VLM-0143 and black enamel MCh-123, NTs-184 or MS-17. The cardan shafts are painted with GF-089 primer and MCh-123 or MS-17 enamel, and the front suspension springs and shock absorber rods are painted with KCh-190 or MS-17 enamel. Wheel rims passenger cars painted with powder paint P-EP-134. Hot-drying melamine-alkyd enamels are widely used, among them ML-152 for painting car bodies and for repair painting of equipment, ML-1196 for painting chassis and radiators. Urea enamel MCh-124 is used for painting radiators and gas tanks.
The last decade in Russian construction market marked by the active emergence of a large number of new building materials and technology. 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, elementary technological rules, and builders expect that high-quality finishing material will cover all the flaws preparatory stages works 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; there should be no form lubricant on the concrete bases. 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.Very important for correct execution work checking 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 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 may occur when used in foundation various materials. 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 finishing coat will peel 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 an optimal combination of 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 as opposed to 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 it is optimal solution when painting buildings ancient building 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 are provided faster 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. Applying more thin 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, at least 4-5 layers will be required. 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 subjected to mechanical action, they liquefy, and after such action is removed, 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 high-quality coating with 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 for subsequent repair and restoration work.
Several different methods have been developed: jet pouring, spraying electric field, pneumatic spraying, electrodeposition, pouring, aerosol spraying, drum spraying, under-pressure spraying high pressure, 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. Often, for certain paints and varnishes, an optimal initial viscosity is recommended. 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 receive compressed air, use mobile compressors SO-62M, SO-45A, SO-7A, etc.
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), differ quite high performance(30 m 3 / h). Their safety valve is adjusted to an excess pressure of 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. An indisputable advantage The diaphragm compressor SO-45A 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 the 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 of different 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;
Number of revolutions idle move– 290 per minute;
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. High pressure external mixing paint sprayers include 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 having 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 large quantity holes for air (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 supplied to the paint sprayer (on the corona edge), where it is negatively charged, and under the influence electrical forces sprayed. 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 a fairly simple shape are painted: housings washing machines, car bodies, housings of various devices, electric motors, refrigerators, etc.
18-9. METHODS OF APPLYING PAINT COATINGS
Paints and varnishes are applied to the surface of products various methods: pneumatic spraying, high pressure spraying, electric field spraying, aerosol spraying. electrodeposition, jet deposition, dipping, pouring, rollers, drums, brush and spatula.
Most effective method application of paint and varnish material for a specific electrical apparatus is selected from the requirements for coating, dimensions and configuration of the electrical apparatus, assembly unit or part, production conditions, economic feasibility, production volume.
Pneumatic spray painting. About 70% of manufactured paints and varnishes are applied using this method. Pneumatic spraying is used mainly without heating.
High pressure spray painting (airless spray). For spray painting with heating, paint and varnish materials are heated to 40 - 100 ° C and supplied to the spray device under a pressure of 4 - 10 MPa with a special pump. The spray torch is formed due to the pressure drop when the paint and varnish material exits the spray nozzle and the subsequent instantaneous evaporation of part of the heated solvent. Losses of paint and varnish material range from 5 to 12%. Advantages of this method" -compared with air spray painting are as follows:
1) losses on paints and varnishes are reduced by 20 - 35%;
2) the consumption of solvents is reduced;
3) the painting cycle is shortened.
This method is recommended for painting medium, large and especially large devices in serial and individual production.
When painting by spraying under high pressure without heating, the paint material is supplied to the spray device under pressure at 18 - 23 ° C.
Heatless spray painting has a number of advantages over heated spraying:
installations are simpler in design and have lower energy consumption.
Spray painting in a high voltage electric field. This method is based on the transfer of charged paint particles in a high-voltage electric field created between a system of electrodes, one of which is a corona spraying device, the other is the electrical apparatus or part being painted. The paint and varnish material enters the corona edge of the sprayer, where it acquires a negative charge and is sprayed under the influence of electrical forces, after which it is directed to the grounded product, deposited on it
surfaces.
(Fig. 18-11). This method involves placing a product, painted with paint material from the nozzles of a dousing device, into an atmosphere containing a controlled amount of organic solvent vapors. Keeping the applied layer of paint and varnish material in an atmosphere of solvent vapor allows you to slow down the process of solvent volatilization from it at the initial moment of coating formation. This allows the excess amount of paint and varnish material to drain from the product, and the remaining one to be evenly distributed over the surface. Compared to painting in an electric field, it provides best quality covering parts of any configuration.
The jetting method is used for priming and painting products in serial and mass production(Fig. 18-11).
Aerosol spray painting. The method is effective when repair work, as well as when applying stencils and inscriptions and other small-scale painting operations. Paintwork aerosol cans produced with a capacity of 0.15; 0.3; 0.5; 0.6l.
