The technological process of painting includes the following operations: preparation of the surface for painting, application of coatings and their curing (drying)
Surface preparation for painting
Performance characteristics and service life coatings largely depend on the method and cleanliness of surface preparation. The purpose of the preparation is ■ to remove from the surface any contaminants and deposits that prevent direct contact of the coating with the metal. These include oxides (scale, rust), oil, grease and mechanical impurities, old polymer coatings.
Surface preparation methods can be divided into three main groups: mechanical, thermal and chemical.
Mechanical cleaning methods
From mechanical methods surface preparation is especially common jet abrasive and hydroabrasive treatment: sandblasting, hydrosandblasting, shot blasting, shot blasting. Cleaning by this method consists in exposing the metal surface to abrasive particles that come at a high speed and have significant kinetic energy at the moment of impact with the metal. In this case, the metal surface becomes rough (depressions reach 0.04-0.1 mm), which improves the adhesion of the coatings. However, abrasive blasting is applicable only when painting thick-walled products (more than 3 mm thick); products with thinner walls can be deformed during such processing.
Sandblasting and hydrosandblasting usually use clay-free quartz sand with a particle size of 0.5-2.5 mm, silicon carbide, fused aluminum oxide. The abrasive for shot-blasting and pre-blasting methods of processing is cast or split cast iron, as well as steel shot with a particle size of not more than 0.8 mm or shot chopped from steel wire with a diameter of 0.3-1.2 mm. To clean the surface of ferrous metals, it is most advisable to use crushed shot with a particle size of not more than 0.8 mm. In this case, the cleaning efficiency increases by 1.5-2 times compared to cleaning with cast shot. Deggie metals and alloys (aluminum, magnesium alloys, etc.) are treated with soft abrasives - powders from aluminum alloys (sometimes with the addition of 5-6% cast iron sand). The cheapest abrasive is quartz sand. However, it quickly wears out (crushes); in this case, fine dust is formed, which is harmful to the health of workers, therefore it is used to a limited extent - only in automatic installations with good sealing and ventilation, preventing the spread of dust into the premises.
Metal sand, unlike quartz sand, almost does not form dust, its consumption is much less, and the efficiency mechanical impact is also quite high. Cleaning with metal sand (shot) is carried out in closed chambers or cabins equipped with supply and exhaust ventilation.
Various types of equipment are used for shot blasting. The most widely used are one- and two-chamber devices of periodic and continuous action, in which the shot is sprayed under a pressure of 0.5-0.7 MPa. Productivity of devices on the cleared surface - from 1 to 8 m 3 /h.
Shot blasting differs from shot blasting in that the shot flow is created not by compressed air, but under the influence of centrifugal force from a rotor rotating at a high frequency (2500-3000 rpm) - a turbine wheel with blades. The shot blasting method is 5-10 times more productive than the shot blasting method and several times more economical; when using it, the dust content of the premises is minimal. The disadvantages of the shot blasting method include the rapid wear of the blades (the service life of cast iron blades does not exceed 80 hours) and unsuitability for processing products of complex shape.
In hydroabrasive cleaning, a suspension or suspension of abrasive in a liquid medium is used. In this case, the abrasives are quartz sand, granite, electrocorundum, glass, ground slag and other solid powder materials with a fineness of 0.15-0.50 mm, and the liquid medium is water with the addition of surfactants and corrosion inhibitors. In particular, a suspension consisting of quartz sand or electrocorundum, sodium nitrite and soda ash. For hydrosandblast cleaning, apparatuses of the GPA-3, TO-266, GK-2, TV-210 brands of discharge and suction type are used, in which the pulp is supplied under a pressure of 0.5-0.6 MPa.
Thermal cleaning methods
Removal of scale, rust, old paint, oils and other contaminants from the surface can be carried out thermally, for example, by heating the products of the flue of an oxy-gas burner (fire cleaning), electrical
electric arc (air-electric arc cleaning) or annealing in furnaces in the presence of an oxidizing or reducing environment.
During fire and air-electric arc cleaning, metal (steel ingots, slabs) is quickly heated to 1300-1400 °C. In this case, the contaminated surface layer burns out and partially melts, after which it is mechanically removed, and the metal is cooled.
Annealing in a reducing (protective) atmosphere is used to prepare the surface of rolled metal. Rolled steel is heated in an atmosphere of nitrogen-hydrogen mixture (93% N 2 and 7% H 2) to 650-700 °C. Traces of grease present on the surface are sublimated, and iron oxides are reduced to metallic iron.
Thermal removal of organic contaminants (old coatings, grease and oil deposits) is conveniently carried out in an oxidizing environment. When heated to 450-500 ° C, most organic substances sublime, decompose or burn. However, in order to avoid the formation of coke, products are annealed at higher temperatures (600-800 ° C) in fire convective or thermoradiation (open or muffle) furnaces equipped with ventilation. You can also use gas or kerosene-oxygen burners.
Thermal cleaning methods are economical and productive, but they can only be used for products with a wall thickness of at least 5 mm in order to avoid warping and deformation of the metal.
Chemical cleaning methods
Degreasing. The metal surface of products to be painted usually contains grease and other contaminants, since many metal parts and semi-finished products (in particular, from aluminum alloys) are protected during storage with various lubricants. In addition, products can become contaminated during the machining process.
Metal surfaces must be degreased before painting. The degreasing process can be carried out various methods, the choice of which is determined mainly by the type of pollution, the required degree of purification and cost. The methods of degreasing with alkaline solutions, organic solvents and emulsion compositions have received the greatest application.
Degreasing in aqueous alkaline solutions is based on the chemical destruction of saponifiable fats and oils and the solubilization and emulsification of unsaponifiable contaminants. As electrolytes, sodium hydroxide and carbonate, sodium silicate (liquid glass), trisodium phosphate and sodium pyrophosphate are used. To increase the degreasing ability of these compounds, they are injected with
surfactants - emulsifiers OP-4, OP-7,
sintanol DS-10, DNS, etc.).
The choice of degreasing composition depends on the degree of contamination, type of production (single or serial); the processing mode is determined by the processing method (in baths, spraying). Ready-made detergents: KM-1, KME-1, ML-52.
In the presence of emulsifiers in aqueous solutions (liquid glass, OP-7 or OP-Yu), animal fats are saponified, forming soluble soaps, and mineral oil residues are emulsified. Liquid glass also helps to reduce the aggressive effect of the solution on aluminum. The formation of an emulsion and mixing of solutions accelerates the separation of fat particles from the metal surface.
Degreasing of parts in a freshly prepared solution lasts no more than 3 minutes, and as sodium hydroxide is consumed, no more than 5 minutes. Overexposure in the degreasing bath leads to cracking of the surface of the parts and the formation of sparingly soluble phosphates.
Grease contaminants that collect on the surface of the solution must be periodically removed through the drain pocket of the bath. After degreasing, the parts are washed first in warm running water at a temperature of at least 20 ° C, and then in cold water.
The quality of degreasing can be controlled by the appearance of the flowing film of cold water. From a well-skimmed surface, water flows in a continuous stream; if water lingers on the surface in the form of droplets, degreasing should be repeated. Details with various welded joints are not subjected to degreasing in alkaline solutions, since they are hardly removed from the inter-seam space.
Degreasing in organic solvents is based on the dissolution of oil and grease contaminants. For these purposes, solvents are used that have high activity with respect to contaminants, stability, low surface tension, and moderate volatility. The most widespread are aliphatic and chlorinated hydrocarbons. The latter are non-flammable, but more toxic than aliphatic ones, which necessitates the degreasing process in special closed-type installations.
Degreasing of parts in chlorinated hydrocarbons is carried out sequentially in two phases: vapor and liquid. A two-phase system is also used. The essence of the process is that water and an organic solvent that does not mix with it are poured into the installation. As a solvent for a two-phase system, methylene chloride and trichlorethylene are used. When processing parts in a two-phase system, not only fat, but also water-soluble compounds are removed.
The cleaned parts are kept in a layer of water for some time. After unloading from the installation, the parts are washed with water to remove solvent drops and dirt particles, and then dried with hot air.
Solvent degreasing can be applied to almost all metals. However, for degreasing aluminum, magnesium and their alloys, trichlorethylene can be used only with the addition of an inhibitor to avoid interaction of the solvent with the metal surface.
Emulsion degreasing is a combined method that allows you to use the advantages of cleaning with organic solvents and aqueous alkaline solutions. The most common are emulsions based on chlorinated hydrocarbons and aqueous alkaline solutions stabilized by surfactants. These emulsions are explosion and fireproof. In the presence of solvents such as trichlorethylene and methylene chloride in emulsions, they can be used not only for degreasing, but also for removing old paints.
Degreasing with ultrasound. Degreasing with solvents, alkaline and emulsion detergents is accelerated when the process is carried out in an ultrasonic field. This cleaning method has been used to remove oil, carbon deposits, residues of polishing pastes and other contaminants from small items with deep or blind holes. The ultrasonic cleaning method is based on the creation of high-frequency vibrations in liquids used as cleaning solutions. The vibrations communicated to the liquids have a high mechanical energy, which ensures the destruction and detachment of particles of contaminants with a continuous supply of the solution to the surface of the products. Depending on the composition and properties of contaminants, the process can last from several seconds to several minutes. Ultrasonic cleaning is carried out in special baths equipped with magnetostrictive, piezoceramic or ferrite transducers. The most common ultrasonic baths are UZV-15m, UZV-16m and UZV-18m.
Etching. Scale, rust and other oxides are most often removed from the surface of metals by etching in acid solutions. For ferrous metals, sulfuric, hydrochloric, and orthophosphoric acids with various additives are most widely used as pickling solutions. On carbon steels, scale consists of several layers of iron oxides - FeO, Fe 3 0 4 and Fe 2 0 3.
Iron oxides are soluble in mineral acids; especially well soluble oxide FeO, which is etched off in the first place and contributes to the exfoliation of the layers lying above.
Scale dissolution proceeds by chemical and electrochemical mechanisms. The dissolution process can be divided into four periods. In the first period, the scale is impregnated with acid, oxides and metal are slightly dissolved at the bottom of the pores and cracks in the scale; the metal practically does not dissolve. In the second period, the impregnation of scale with an acid solution continues and the chemical and electrochemical dissolution of oxides begins. At the end of the period, a new process is possible - the deposition of salts of corrosion products in pores and cracks. The third period, during which about 70% of the scale is removed, is characterized by high rates of scale dissolution. In the middle of the period, hydrogen begins to be released, loosening and tearing off scale. The dissolution of steel occurs mainly as a result of the work of galvanic pairs of metal - scale; in addition, metal corrosion proceeds with hydrogen depolarization. In the fourth period, the electrochemical dissolution of scale residues and exfoliation of the sparingly soluble component of scale Fe 3 0 4 by hydrogen occurs. During this period, 25-30% of the scale is removed and an intensive dissolution of the metal occurs.
It should be noted that the solubility of metal oxides and the rate of scale dissolution in hydrochloric acid is higher than in sulfuric acid, at an equal concentration. In addition, it reacts less actively with iron, so the loss of metal during etching in hydrochloric acid is somewhat less. In hydrochloric acid, scale is removed mainly due to its dissolution, while in sulfuric acid it is mainly due to its detachment from the surface as a result of metal pickling and loosening of the scale by evolving hydrogen.
To reduce the dissolution of the metal and its hydrogenation, corrosion inhibitors are introduced into the pickling solutions: katapin, ChM, BA-6, PKU, I-1-A, etc.
Etching of metals in phosphoric acid is carried out much less frequently than in sulfuric and hydrochloric, because of its lower activity and higher cost. Phosphoric acid is used to remove rust with small degrees of metal contamination. In this case, dilute (1-2%) solutions of H 3 P0 4 are suitable, which, along with the dissolution of oxides, cause passivation of the metal - the formation of insoluble iron phosphates on the surface. The advantage of using phosphoric acid is also that after treatment with this acid, such a thorough washing of the metal is not required, as when using sulfuric and hydrochloric acids.
Metal etching is carried out in baths and jet chambers. In the latter case, pickling solutions of lower concentration are used, and the process is carried out at higher temperatures. At the same time, productivity increases significantly.
To remove corrosion products from the surface of large-sized products, special liquid or viscous compositions (pastes) are used. They are prepared by introducing fillers (diatomaceous earth, asbestos, kaolin) and polymers into liquid pickling solutions. The pastes are applied to the surface with a spatula and kept for 1-6 hours. After that, the surface is washed with water, a passivating paste is applied, and after 0.5 hours it is again washed and dried.
Removal of old coatings. Chemical method removal of old coatings from the surface of the product is based on the dissolution, swelling or chemical destruction of the film, i.e., the transformation of the film into a state in which it can be easily removed from the surface mechanically.
To remove coatings, washes are used, as well as some emulsions. As a rule, washes consist of organic solvents, thickeners, evaporation retarders and emulsifiers. To prevent the washes applied to the surface from running off, thickeners are introduced into them, for example, cellulose nitrate, ethyl and methyl cellulose, and to slow down the volatilization, small amounts of waxy substances, most often paraffin, are introduced into the washes. In this case, additional washing of the surface with organic solvents is required to remove paraffin residues.
As solvents, methylene chloride is mainly used together with alcohols, ketones and esters. Acids are added to some washes to accelerate penetration into old coatings.
The domestic industry produces washes of the following brands: SD (SP), AFT-1, SP-6 and SP-7, SPS-1. Organic washes are applied to the surface with a spatula. After 5-30 minutes after application, the swollen coating is removed mechanically or washed off with a stream of water.
Surface phosphating is a method of surface preparation, which consists in creating a film on the metal, consisting of insoluble phosphates, which, in combination with a paint film, provide increased durability of the coating. The fine-grained structure of the phosphate film contributes to the good absorption of paints and varnishes and thereby improves their adhesion. In addition, with local damage to the paint film and the phosphate layer, the spread of rust is localized, while on non-phosphated metal, rust quickly spreads under the paint film. Basically, steel, zinc and galvanized steel are subjected to phosphating.
Phosphating is carried out by dipping the product into a bath with a phosphating solution or by spraying the solution in a jet chamber. The latter method is preferable, since when using it, the uniformity of the phosphate layer in thickness increases, and the mass of the coating decreases; this results in a denser layer.
The greatest application in industry received zinc
cophosphate solutions containing zinc monophosphate, nitric and phosphoric acids. Ready-to-use liquid phosphating concentrates are also produced: KF-1, KF-3, KFA-4A, etc.
After phosphating, the products are washed with water, and then the surface is passivated.
anodic oxidation. Paints and varnishes have poor adhesion to aluminum alloys, especially under conditions high humidity. To improve adhesion and increase the protective properties of paint coatings, aluminum alloys are subjected to anodic oxidation. Anodic oxidation, or anodizing, is the process of electrochemical processing of aluminum and its alloys in an electrolyte to obtain an oxide film on the surface. As electrolytes, sulfuric acid is used, less often - chromic and oxalic acids.
The main method of anodic oxidation of parts made of aluminum alloys is sulfuric acid. The advantages of this method compared to others include the highest oxidation rate, lower cost of the electrolyte, and lower power consumption. Anodized in sulfuric acid sheet material, wrought alloys of all grades and machined parts. This method is not suitable for oxidizing parts with riveted joints, assemblies consisting of different metals, as well as cast parts with pores.
In addition to anodizing in sulfuric acid, the method of anodic oxidation in chromic acid is used. It is used to prepare parts from cast alloys. In a solution of chromic acid, it is not recommended to anodize alloys in which the copper content exceeds 6%. Copper dissolves in chromic acid faster than in sulfuric acid, so the resulting oxide film has insufficient protective properties.
Anodizing parts in chromic acid is carried out in the same way as in sulfuric acid. Since the electrical conductivity of chromic acid solutions is lower than the electrical conductivity of sulfuric acid solutions, it is necessary to apply a higher voltage and electrolyte heating. The colorless or gray anode films formed during oxidation have a small thickness (3 μm), but they are denser than films obtained in sulfuric acid. The adhesion of paint coatings to surfaces anodized in sulfuric or chromic acid is approximately the same.
Chemical oxidation, or chromating, finds wide application. The purpose of oxidation is to improve the decorative and protective properties of metals. The coatings formed on the metal surface contribute to a significant increase in the adhesion of paints and varnishes. The advantages of this method compared to anodizing are
simplicity, efficiency and short duration of the process. Coatings obtained by chemical oxidation are used not only as a sublayer for paint coatings, but also for temporary protection of parts during storage in heated warehouses. Both ferrous and non-ferrous metals are subjected to oxidation. Oxide coatings are used in combination with paint coatings and independently. In terms of protective ability, they are significantly inferior to phosphate ones, so oxidation is more often used in preparing the surface of non-ferrous metals for painting; ferrous metals are predominantly phosphated.
Of non-ferrous metals, aluminum, magnesium, copper, zinc and their alloys are most often subjected to chemical oxidation. Chromic acid and its salts, nitrites and alkali metal persulfates are used as oxidizing agents. Oxidation is carried out in an acidic or alkaline environment; the duration of oxidation at 15-20 °C is 10-20 minutes. After oxidation, the parts are washed in cold, then in warm water, after which they are dried at a temperature not exceeding 60 ° C or blown with warm air.
Methods for applying paints and varnishes
Manual methods of applying paints and varnishes - with a brush, hand rollers, swabs, as well as using aerosol cans - are used for small amounts of painting work, mainly in everyday life. In a number of branches of mechanical engineering, they also use manual ways staining - when using materials containing highly toxic components, such as red lead, copper compounds, etc.
Manual staining methods are economical. Their disadvantages include low productivity and high labor intensity.
Dipping and pouring are mainly used to obtain primer and single-layer coatings on products of varying complexity.
The principle of application by dipping and pouring is based on wetting the surface to be painted with a liquid paint and varnish material and keeping it on it in a thin layer due to the viscosity of the material and adhesion. The advantages of this method are the simplicity of the equipment used and good quality the resulting coatings. The disadvantages of these methods include relatively large losses of materials and some non-uniformity of the thickness of the coatings along the height. This can be avoided by keeping freshly painted products in solvent vapors. This method, called jet pouring, has found wide application in agricultural, tractor and transport engineering enterprises. It is one of the most productive ways of applying paints and varnishes, providing good sanitary and hygienic working conditions.
The essence of the method of jet pouring followed by exposure of products in solvent vapors is as follows. Products on an overhead conveyor move inside the plant. When products pass through the painting zone, they are poured with paints and varnishes from the nozzle system. In the steam zone of the tunnel, the concentration of solvent vapors is maintained within the range of 15-20 mg/l. Under these conditions, the evaporation of solvents from freshly painted products slows down, which contributes to the spreading of the paintwork material over the surface to be painted and the formation of a coating more uniform in thickness than when immersed.
Pneumatic spraying is one of the most common painting methods. Approximately 70% of the produced paints and varnishes are applied in this way. With pneumatic spraying, the paint material is crushed by a jet compressed air. The resulting aerosol coagulates upon collision with the product, and a layer of the applied material settles on the surface of the product. Using this method, uniform layers of primer, varnish, enamel (including quick-drying ones) can be applied to the surface, painting over underdried primers or a paint layer that has a “tack” can be applied.
The disadvantages of the pneumatic spraying method include fogging, which worsens the sanitary and hygienic working conditions and leads to significant losses of paints and varnishes (up to 25-55%). In addition, when using it, the consumption of solvents for bringing the paintwork material to the required viscosity increases.
During pneumatic spraying, the temperature of paints and varnishes drops sharply when leaving the nozzle of the nozzle. This is due to the adiabatic expansion of air and the evaporation of solvents. A decrease in temperature in the spray zone and partial volatilization of solvents leads to a significant increase in the viscosity of the sprayed material, which prevents it from spreading. Therefore, it is often necessary to apply varnishes and paints with a known lower viscosity (diluted large quantity solvent). Viscosity can be reduced by heating paints or the surface to which they are applied.
Heating of paints and varnishes can significantly increase the efficiency and economy of the process of painting products. Due to the decrease in viscosity when heated, it becomes possible to use more viscous materials without resorting to their additional dilution with solvents.
To apply heated paints and varnishes, stationary installations of the UGO type and paint sprayers equipped with portable heaters are used.
For applying paints and varnishes, manual paint sprayers of various brands are used: KR-Yu, KRU-1M, 0-45, ZIL, GAZ, KRM, S-592, etc. Method for applying paints and varnishes manual paint sprayers has many disadvantages, since the performance and quality of painting are largely determined by the work of the apparatchik. Therefore, in the in-line production of products that have the same dimensions and relatively regular shape, it is recommended to use automatic paint sprayers equipped with actuators for automatic switching on and off. In mechanical engineering, the KA-1 automatic paint sprayer is most widely used.
Airless spray. According to this method, the paint material is sprayed under the influence of high hydraulic pressure created by a pump in the internal cavity of the spraying device and displacing the paint material through the nozzle opening. In this case, the potential energy of the paintwork material under pressure, when it enters the atmosphere, passes into kinetic energy, and the dispersed paintwork material moves towards the product to be painted. When the paint material exits the spray nozzle at a rate exceeding the critical one for a given viscosity, the volatile part of the solvent that is part of the paint material evaporates intensively, which is accompanied by a significant increase in the volume of the material and its additional dispersion.
Application of the method airless spray under high pressure paints and varnishes due to the reduction of fogging losses allows to reduce the consumption of paints and varnishes (by 20%) and solvents due to the higher viscosity of the materials. The disadvantages of the method include the difficulty of using it for painting products of complex configuration.
Airless spray can be applied paints and varnishes paint sprayers both with heating (UBR-3) and without heating (Fakel-3; Raduga-0.63P; VISA-1; VISA-2; KIT-1654). The KIT-1654 installation is also used for applying high-viscosity compounds, mastics and thixotropic materials.
electrostatic spray. The principle of the staining method in electric field high voltage is as follows. An electric field is created between two electrodes that are energized and located at some distance from each other. One of the electrodes is the product to be painted (positive ground electrode), and the other is the corona (negative) electrode. A sprayed paint and varnish material is introduced into the high-voltage constant electric field created between them, the particles of which, being charged from ionized
air or the edge of the electrode, move along the lines of force of the electric field and are deposited on a grounded product, forming a uniform coating on its surface.
In an electric field, only paints and varnishes with certain electrical properties can be sprayed (for example, volume resistivity - 1 ■ 10 6 -1 10 7 Ohm-cm; dielectric constant 6-10).
For painting products in an electric field, hand-held electrostatic sprayers or spraying devices mounted permanently on separate racks are used.
Electrodeposition is one of the most promising methods for applying paints and varnishes, which consists in the deposition of a paintwork material in the form of a concentrated precipitate on the surface of products under the influence of constant electric current. Deposition is carried out as a result of imparting to the particles of the paintwork material, which are in an electrically conductive liquid medium, an electric charge opposite in sign to the charge of the coated product. If the paintwork material is able to pass into the ionic state in this medium, then its transfer is carried out due to the charge of ions - cations, or anions. Depending on what the product to be painted is - an anode or a cathode - there are anodic deposition (anaphoresis) or cathode deposition (cataphoresis). A necessary condition for electrodeposition is the presence of an electrically conductive medium. In this way water and organic dispersions of polymers and oligomers are applied.
In industry, the most widely used method is anodic electrodeposition, in which the product in the bath is the anode, and the body of the bath is the cathode. Increasingly, the method of cathodic electrodeposition is beginning to receive. With this method, the product to be painted is the cathode, and special plates are used as the anode; the bath is grounded. Applying the method of cathodic deposition, it is possible to obtain coatings with high corrosion resistance and uniform in thickness. This is explained by the fact that during cathode deposition, the oxidative reaction of binders with oxygen does not occur, since hydrogen is released at the cathode.
Autophoretic precipitation— new way application of dispersion paints and varnishes without the use of electric current. The method is based on "wall" coagulation of aqueous dispersions (latexes) of pleicogenic substances stabilized by ionic surfactants by creating an electrolyte concentration gradient at the surface-medium interface. To obtain coatings by this method, latexes of various film formers are used. Inorganic and organic acids such as hydrofluoric, phosphoric, tartaric, etc. serve as electrolytes. The rate of dissolution of the metal and the stability of dispersions are controlled by the introduction of oxidizing agents, surfactants, as well as by using various methods of preparing the metal surface.
The main advantages of this method are the high continuity of the coatings, the absence of power consumption and the possibility of obtaining coatings on products of any complexity.
Application of powder coatings
All the above methods of application are applicable to liquid paints and varnishes. The application of powder paints and varnishes is based on their ability to easily turn into aerosols, which are deposited on a solid surface as a result of electrification of aerosol particles; contacting the aerosol with a heated surface; contacting the aerosol with the sticky surface of the substrate; aerosol condensation on a cold surface.
Powder paints and varnishes are applied by the gas-flame method, in a fluidized bed, in an electric field and by the plasma method.
The method of flame spraying consists in the fact that a jet of compressed air with particles of polymers suspended in it is passed through the flame of an oxy-acetylene torch. In this case, the polymer particles are heated, melted and directed by a jet of air to the heated surface. Sticking to the surface, the particles fuse and form a continuous coating having good adhesion to metal. For gas-flame spraying, an installation of the UPN type is used.
The advantage of flame spraying is that it eliminates the need for solvents and drying of coatings.
Application in a fluidized bed. Parts heated above the melting point of polymers are immersed in a porous bottom apparatus, where a fluidized layer of powder is created with the help of air. In this case, a uniform coating is formed on the surface of the parts.
Deposition in an electric field. The polymer in the form of a powder enters the zone of a high voltage electric field, acquires a charge of the corresponding polarity and is deposited on a metal surface, which has the opposite charge. The polymer can be applied with automatic and manual electrostatic sprayers; in an ionized fluidized bed; in a cloud of charged particles.
The plasma application method consists in the fact that the powder material is heated in a plasma stream having a temperature of up to 8000 ° C, and, melting, is applied at high speed to the surface to be treated. Plasma is obtained by passing an inert gas (argon, helium, nitrogen) through a voltaic arc. Rapid heating (within a few seconds)' in an inert gas environment prevents degradation of the polymer. With this method, plasma sprayers are used to apply the paintwork material.
Coating Curing Methods
The process of curing coatings from paint and varnish systems can be carried out in natural conditions at ambient temperature and in artificially created conditions - with thermal and radiation effects on the material.
When choosing a method and mode of curing (drying) coatings, many factors are taken into account: the type of paintwork material, the nature of the substrate, the dimensions and degree of complexity of the coated product, the flow of production, etc. quality.
Curing in natural conditions is used mainly for quick-drying coatings. It can also be used for some "irreversible" coatings (alkyd, epoxy, polyurethane), especially when coatings are applied to large products that do not fit in drying chambers, as well as products that contain non-metallic parts (rubber, plastic) that do not allow drying at elevated temperatures.
The drying process is significantly accelerated by continuous air circulation, which carries away solvent vapors from the surface of the product to be painted. However, the rate of evaporation of solvents should not be excessively high, since internal stresses may arise in the coating that adversely affect its properties. In addition, if too fast removal solvents from the upper layer of the coating, the viscosity of this layer increases sharply, and a surface film is formed, which makes it difficult to remove the solvent from the lower layers. With further drying, the vapor of the remaining solvent, tending to evaporate, inflates the formed film, and small bubbles, pores, and other defects appear in it. The drying mode of the coating is selected in such a way that the volatilization of solvents occurs gradually: at the beginning of drying, rapidly volatile solvents should evaporate, and then high-boiling solvents.
Curing in artificially created conditions. Heating is used to accelerate the formation of coatings. According to the method of heat supply to the coating, the following curing methods are distinguished: convective, thermoradiation, induction.
The convective curing method is carried out by transferring heat from the surrounding air or flue gases. The heat transferred to the surface gradually spreads into the film, so the coating hardens from the film-gas medium interface.
Due to the low thermal conductivity of gases, only the layer in direct contact with the product takes part in the convective heat transfer to the coating. To improve heat transfer, mixing of heated gases is recommended, which causes additional cost energy. Therefore, the convective curing method is inefficient and energy intensive. However, the widespread use of this method is due to its versatility (suitable for curing any paint and varnish materials), uniformity of heating, simple design and ease of operation of drying plants.
For convective curing, batch dryers (dead end or chamber) and continuous dryers (through passage or in-line) are used, equipped with heat-ventilation units. According to the type of heat carrier, dryers are divided into steam, electric, steam-electric, gas.
The thermoradiation curing method is based on the use of radiant energy emitted by heated bodies (incandescent lamps, metal and ceramic plates, spirals, gas-burners and etc.). ‘
The degree of perception by paints and varnishes of radiant energy with different wavelengths is not the same, respectively, and the effect of its action during curing is also different. Unpigmented liquid paints and varnishes, as well as solid coatings in layers up to 50 µm, are sufficiently permeable to IR rays; in this case, the permeability decreases with increasing wavelength. This pattern holds true for powder materials. As the coatings are formed, the permeability of powder film formers for IR rays increases sharply.
The thermoradiation curing of coatings is also affected by such factors as the mass and thermophysical properties of the substrate material, the power of the emitter, and its distance from the surface to be painted. Coatings are formed more slowly on thick-walled substrates with high thermal conductivity than on thin-walled substrates with low thermal conductivity.
During thermoradiation curing, the supply of heat to the product is significantly accelerated, as a result of which the stage of raising the temperature of the painted product is sharply reduced. The coating layer is heated not from the outside, but from the inside, from the substrate, which ensures the unhindered release of volatile products from the film. Due to this, the process of coating formation is significantly accelerated: with thermoradiation heating, the curing time
compared with the convective method is reduced by 2__ 10 times.
For curing coatings under the influence of IR radiation, drying chambers of continuous and periodic action are used. As radiation sources, special incandescent lamps, panel-tile heaters, tubular electric heaters with aluminum reflectors, etc.
The induction curing method is based on the fact that the painted product is placed in an alternating electromagnetic field of currents of various frequencies. Heating occurs due to eddy currents induced in the substrate of ferromagnetic materials. Coatings are cured using drying installations in the form of metal shields or chambers in which cassettes with a set of heating elements- inductors. When an alternating current passes through the turns of the inductor, a powerful pulsating magnetic field is created. If a painted product is placed in the immediate vicinity of the inductors, it will heat up, transferring heat to the coating. Heating can be done at any speed and up to any temperature. Usually curing of coatings is carried out at 100-300 °C. The drying time of coatings (for example, alkyd) is 5-30 minutes.
Installations with induction heating are used in industry for curing coatings on wagons, containers, steel strip, wire and other products.
Painting Metal necessary to protect the metal from adverse environmental factors. Together with a primer, such painting creates a strong anti-corrosion bond.
Our company uses the following types of painting: aluminum, liquid plastic, for galvanized metal and for non-ferrous metals and alloys.
Metal Painting Technology
Depending on the type of metal, the stages of painting and surface treatment may differ, but in any case, there are three main stages in the metal painting technology:
- Surface cleaning and degreasing.
- Primer and surface putty.
- Direct coating application.
When choosing a material for painting, we focus on the specifics of the metal and further conditions its operation. One material may be ideal for painting a given metal, but completely incompatible with another. We do all painting work. metal products in the workshop, but if necessary, we can go to the site.
Metal Painting Price
The price of metal painting will directly depend on the type of metal product, the complexity of painting it, and the materials used. We carefully calculate all possible nuances when working with a particular metal.
Metal structures are widely used in many areas of human activity. Metal products are inexpensive, they are practical, easy to install and transport. However, metal structures need constant care, as they are highly responsive to impact. environment.
Metal painting is not only one of the ways to protect the product from corrosion, but also a great opportunity improve appearance designs.
Painting of metal products is necessary to give them additional protective and decorative properties. Coloring is widely used as a method of protection because of its simplicity and relative cheapness. In addition, unlike other protective coatings, paint color can be chosen.
How is metal painted?
Applying an anti-corrosion coating is possible absolutely for any metal surfaces. For this, apply various paints, but best method Powder coated metal is considered. The main advantages of such a coating can be called high strength, durability and economy. 
Powder coating can be applied to most existing metal products.
The dimensions and type of construction do not matter: the paint is equally successfully used for both external and internal work.
The whole process of spraying polymer powder paint is safe and fully complies with high environmental standards.
Advantages
The durability, cost-effectiveness and environmental friendliness of powder coatings are pushing traditional paint out of the metalworking industry, particularly in the automotive industry. In this way, you can paint not only the body, but also the engine and other parts. Protection of large structures is also achieved by applying a layer of paint.
By and large, we are all indifferent to the color of the power transmission line mast, but its service life is important, and the easiest way to protect the mast from corrosion is painting. Painting of metal products with a decorative and protective purpose is important in architecture, where many metal structures are used. These are fences and gates, bars on the windows, fences and fences, metal doors and railing.
An additional advantage is the possibility of painting metal products of complex configurations.
Do not stand aside and furniture, mainly office and industrial. Are stained metal tables, workbenches, racks, cabinets and safes.
Types of paints for metal
A wide range allows you to choose the right paint that is optimal for each surface and its purpose. In particular, for painting metal in the city of Moscow, the following options for coloring mixtures are presented:
1. Paints applied with an airbrush. Allows painting hard-to-reach places of the product.
2. Paints used to protect non-ferrous metals.
3. Paints for quick application to metal, which do not require prior removal of rust.
4. Polymers for powder coating.
On the one hand, the painting of metal products follows the path of simplifying the process, and on the other hand, it is becoming increasingly difficult to choose the right one in the kaleidoscope of assortment.
Oil paint is better suited for interior surfaces, it quickly loses color and cracks on the outside, and it also does not tolerate temperatures above 80 degrees.
Alkyd paints are used for galvanizing, they fit well, but are also sensitive to high temperatures and combustible.
Many now prefer acrylic paints- they are durable and do not fade, protect against corrosion. Withstand temperatures up to 120 degrees - they can cover heating batteries. These paints are environmentally friendly and do not burn.
The choice of paint for metal should be made, first of all, based on the purpose of the product prepared for painting.
Paint that was applied to the structure without violating the norms technological process, provides quality protective layer and also performs an aesthetic function.
Powder coating of metal products
Powder coating technology can be used to paint ceramics, glass, heat-resistant plastic, wood, but the most common material is metal. Metal can be anything: steel, cast iron, stainless steel, aluminum and its alloys, galvanized steel, non-ferrous metals, etc. 
We paint everything: rivets, fences, canopies, doors, self-tapping screws, clamps for fastening facades, instrument cases, lamps, terminals, containers, bins, radiators, racks, supports, frames, ebbs, parapets, facade cassettes and much more.
How to order metal painting in Moscow?
In order to learn more about the options for applying an anti-corrosion coating to metal, please contact our consultants at any of the telephone numbers provided.
We will select a painting method that will best meet your requirements. Metal painting in Moscow is carried out only by qualified specialists in rooms equipped with modern technology.
If your product meets the parameters of our equipment in terms of dimensions and weight, then we will paint it with high quality and in a short time.
Metal structures have a number of advantages: less weight (when compared with reinforced concrete products); convenience and speed of construction; ease of installation and dismantling; simplicity and serial production; transportability; strength and durability; reliability in operation.
At the same time, the susceptibility of metal structures to corrosion makes it necessary to protect them from aggressive environmental influences.
There is a great many metal structures used in construction. The most common metal structures include beams, columns, trusses, reinforcing meshes, frames, panels, profiles, stained-glass windows, gates, fences and other building envelopes.
Also, these are supporting metal structures (power transmission line masts) and service structures - stairs, gratings, fences, platforms. Tanks can also be added here. various types, containers, tanks, etc.
Protection of metal structures against corrosion is carried out by galvanizing metal structures and painting metal.
Anti-corrosion protection of structures
Before you start painting a metal structure, you need to choose a protective anti-corrosion coating. Before doing so, the following factors should be assessed:
- surface preparation: blasting, mechanical cleaning, manual cleaning;
- the place where the coating is supposed to be applied;
- environmental conditions and application methods used.
There are many different surface conditions of metal structures that require cleaning before painting. This is especially true for the repair of previously painted metal structures.
The age of the structure, its location, surface quality, the number of defects and rust, the type of previous and future aggressive conditions, the properties of the old coating - all these factors affect the surface preparation and the choice of a corrosion protection system for metal structures.
It must always be remembered that the preparation of the metal surface for painting is one of the main conditions for successful anti-corrosion protection.
For various schemes painting of metal structures KrasCo company offers several types of anti-corrosion primers for metal at once:
- Phosphosoil- Phosphating primer for ferrous and non-ferrous metals, cold metal phosphating.
- Zinconol- zinc-filled primer-protector for metal protection, cold galvanizing of metal.
- Phosphomet- rust converter, phosphating rust modifier.
Painting of metal structures
For painting metal structures, the most various materials. For long-term protection of metal structures in atmospheric conditions, it is recommended to use an integrated protection system, which includes an anti-corrosion primer and top coat.
For reliable protection and painting of metal structures KrasCo company offers several types of coating anti-corrosion enamels:
- stainless steel- paint on rust, anti-corrosion alkyd enamel for metal. The paint is a 3 in 1 product (three in one). Combines a rust converter, anti-corrosion primer and wear-resistant enamel.
- Rapid Thrower- quick-drying paint, anticorrosive primer-enamel for metal. It features high drying speed, good hiding power, excellent adhesion, possibility of application at low temperatures.
- Polymeron- special enamel for metal, anti-corrosion wear-resistant coating. Enamel is specially developed for protection of metal surfaces in the conditions of the heavy industrial atmosphere.
- Silver- aluminum paint, silver-white anti-corrosion enamel for ferrous metal and galvanization. It is used for painting any metal structures operated in a humid atmosphere, in sea and fresh water conditions.
- Stainless steel- thick-layer primer-enamel 3 in 1 (three in one) for ferrous metals. It is used for painting ferrous metal in cold and moderate climatic conditions.
- Cyclol- paint for galvanized metal, weather-resistant anti-corrosion paint for roofs. The paint has excellent characteristics in terms of water resistance and weather resistance.
- Nerzhaplast- enamel "liquid plastic". Represents anticorrosive enamel for metal with plastic effect.
- Molotex- hammer enamel, decorative paint with a patterned hammer effect.
Painting metal with anti-corrosion paint provides reliable protection metal from corrosion and significantly extends the service life of metal structures.
Anti-corrosion painting of metal is carried out in accordance with the selected protection system. At this stage of work, it is required to strictly follow the requirements of the regulations and the technical instructions of the material manufacturers.
If the preparation of the metal surface is correctly performed and the instructions of the manufacturer of the coating material are not violated, then you can not worry about the quality of the finish coating.
On the site website.
The site presents full information on the protection of structures and painting of metal (painting of metal, protection of metal structures, painting of metal structures). We hope that the sections of the site will help you to implement right choice metal protection systems and choice of anti-corrosion coating.
Specialists Companies KrasCo we are always ready to listen carefully to all your requirements and choose the best option for the protective painting of metal structures for your facility.
In most cases, it becomes necessary to paint certain metal products with your own hands. In order to properly perform such an event, it is necessary to take into account some of the nuances of this process.
Consider how to paint a metal surface and what to look for when self-fulfillment this procedure.
Is it possible to paint metal with your own hands?
Only at first glance it may seem that this work can be done easily and quickly. I smeared more or less suitable paints and varnishes on the surface of the metal element and everything is ready, but in fact it is not so simple. Paints for metal surfaces are very different. It should also be noted that one metal alloy is different from another alloy - this circumstance determines the choice of a suitable paint and varnish material.
Note: Painting metal surfaces according to SNiP provides for a clearly defined technology.
Compliance with all aspects of the technological process, in turn, guarantees the quality of such work.
Types of metal surfaces
Different types of paints can react completely differently to a particular metal, so it is advisable to study a little the specifics of metal surfaces intended for subsequent painting:
- So, for example, ferrous metals are best treated with alkyd or oil formulations and do it better as quickly as possible until the surface reacts with a humid environment, begins to oxidize and rust, and as a result may lose its original margin of safety, especially in open weather-prone areas;
- As for the processing of elements made of galvanized steel, it is a little simpler here, since a zinc alloy applied in a thin layer to the ferrous metal base protects it well from various aggressive influences. But, nevertheless, it will not be superfluous to cover the surface of the element with alkyd-based enamel to increase the service life;
- Non-ferrous metals are best treated not with paints, but with varnishes based on polyurethane and epoxy.
Note: Oil-based paint formulations are not very suitable for treating galvanized surfaces, since their molecular structure does not adhere strongly enough to the zinc alloy base, in turn, this threatens to quickly crack and peel off the paint layer from the treated base.
Stages and technology of painting metal surfaces
The service life of the paintwork directly depends on the quality of the prepared base. As a rule, an unprepared or poorly prepared surface has a lower degree of adhesion due to high content metal oxides and other undesirable chemical compounds, which leads to a significant reduction in the service life of the protective or decorative coating.
cleaning
In order for the coating to last for a sufficiently long period, the surface to be treated must be carefully prepared. Having spent quite a bit of time and effort on this, you can save a lot on subsequent (repeated) repairs in the future.
Cleaning the surface from metal oxides (rust), grease residues and possible old paintwork is done using special solvents and metal brushes or electric grinders with appropriate nozzles.
Important to know: In some special cases, when the old paint layer is difficult to partially or completely remove, use suitable types of paints and apply them directly on top of the old layer.
The price of such materials is much higher than the usual ones, but it fully justifies itself.
In any case, when there is no way to completely remove old layer paints, it is advisable to purchase suitable compositions, albeit a little more expensive, but with a guarantee that the work will be done efficiently and the funds will not be wasted.
After thorough cleaning of the base, it must be primed with special surfaces. Primer compositions adhere strongly to the metal surface, ensuring subsequent, uniform application of paint or varnish.
The primer is applied to the base in a variety of ways with brushes, manual and electric sprayers, rollers, and in some cases even the part is dipped into the composition. Depending on the composition of the primer-solution, it is applied, as a rule, in one or two layers. After application, the treated base must be thoroughly dried.
Tip: Preparatory and subsequent painting work is best done in well ventilated but not dusty areas.
Metal coloring
As soon as the surface dries, you can safely proceed directly to the application of the paint itself.
Instructions for applying varnish or paint to metal are practically no different from applying to any other base. It is worth noting only one advantage of the metal - it does not absorb the solution, unlike, for example, and it is quite enough to cover the part with one thin layer of paint.
But in some cases, when a perfectly high-quality surface is required, it is necessary to cover the part in two or three layers, thereby hiding even significant irregularities.
To prevent smudges and streaks that are visually perceptible, it is necessary to apply the layer as thin as possible. It is still better to cover the part with two thin layers, after drying the first one, thus you will not allow inevitable smudges during the work.
The paint is applied with a spray gun. At the same time, it is desirable to choose high-quality tools that do not leave villi from the roller and hairs from the brush on the painted surface.
Conclusion
High-quality painting of metal surfaces today, given the rich assortment of materials to choose from, is quite feasible. Observing technological standards and using only paints and varnishes suitable for specific purposes, you can easily do all the work on painting metal surfaces with high quality and independently. For better understanding technologies for performing these works, be sure to watch the video in this article.
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