Powder paint has been used for a long time. But if you do not own the technology of its application to the required extent, if you do not have the necessary experience, you will have to thoroughly study all the information in order to avoid mistakes. It is to their prevention that we dedicate this material.
Peculiarities
Powder paint is made from polymers that are powdered and then applied to certain surface spraying method. To give the coating the desired properties, it is thermally processed, the molten powder turns into a film that is uniform in thickness. The key advantages of this material are corrosion resistance, significant adhesion. Under the influence of high temperatures, including when they alternate with low ones, powder paint retains its positive qualities for a long time. Mechanical and chemical effects are also well tolerated by it, and contact with moisture does not disturb the surface.
All these advantages powder paint retains for a long time along with visual appeal. You can paint the surface, achieving a variety of tones and textures, varying the additives introduced. Matte and glossy sheen are just the most obvious examples; this decor is created quickly and easily with powder paint. But more original painting is also possible: with a three-dimensional effect, with the reproduction of the appearance of wood, with imitation of gold, marble and silver.
The undoubted advantage of powder coating is the ability to complete all the work with the application of one layer; when working with liquid compositions, this is unattainable. In addition, you will not need to use solvents and monitor the viscosity of the paint composition. Any unused powder that has not adhered to the desired surface can be collected (when working in a special chamber) and sprayed again. As a result, at constant use or with large one-time volumes of work, powder paint is more profitable than others. And the good thing is that there is no need to wait for the ink layer to dry.
All these advantages, as well as optimal environmental friendliness, no need for powerful ventilation, the ability to almost completely automate the work, it is worth considering.
Don't forget about negative aspects such a technique:
- If some defect appears, if the coating is damaged during operation or subsequent use, the entire object or at least one of its faces will have to be repainted from scratch.
- At home, powder painting is not carried out, it requires very complex equipment, and the size of the chambers limits the size of the objects to be painted.
- It is impossible to tint the paint, nor can it be used for parts, structures that are to be welded, since the burnt parts of the paint layer are not restored.
What surfaces can be used?
Strong adhesion makes the powder coating process ideal for stainless steels. In general, when processing metal products for household, industrial and transport purposes, powder is used much more often than liquid formulations. This is how the components of warehouse and vending machines, machine tools, metal pipelines and wells. In addition to the ease of application, the attention of engineers to this method of processing is attracted by the safety of paint in fire and sanitary terms, the zero level of its toxicity.
Forged structures, aluminum and stainless steel products may well be powder coated. This method of coating is also practiced in the production of laboratory, medical equipment, sports equipment.
Products made of ferrous metals, including those with an external zinc layer, ceramics, MDF, plastic can also be a good substrate for powder coating.
Dyes based on polyvinyl butyral are distinguished by increased decorative properties, are resistant to gasoline, do not conduct electricity, and tolerate contact with abrasive substances well. The ability to survive the ingress of water, even salty, is very useful when creating pipelines, heating radiators, and other communications in contact with liquid.
When applying a special powder to the surface of an aluminum profile, the priority is not so much corrosion protection as giving a beautiful appearance. Be sure to select the mode of operation, depending on the composition of the dye and the characteristics of the substrate, take into account the specifics of the equipment. Aluminum profile with a thermal insert, they process at most 20 minutes when heated not higher than 200 degrees. The electrostatic method is worse than the tribostatic method when painting metal products with blind holes.
The use of powder fluorescent paint is practiced when working on road signs and other informational structures when glow in the dark is more important. For the most part, aerosol formulations are used, as the most practical and creating the most even layer.
How to breed?
The question of how to dilute powder paint, in what proportion it should be diluted before coating, is not in front of professionals in principle. As you already know, staining with this type of paint is done in a completely dry form, and no matter how experimenters try to dilute, dissolve this mixture, they will not succeed.
Consumption
There are decorative, protective and combined coatings, depending on belonging to a particular group, a layer of various thicknesses is formed. You also need to take into account geometric shape surface and the difficulties of working with it.
Coloring
As you already know, it is impossible to paint anything with powder paints at home. The main difficulties in using them on an industrial scale arise in the process of preparatory work. The technology provides that the slightest contamination should be removed from the surface, degreased. Be sure to phosphate the surface so that the powder adheres better.
Failure to follow the preparation method will lead to a deterioration in the elasticity, strength and external attractiveness of the coating. Dirt can be removed during mechanical or chemical cleaning, the choice of approach is determined by the decision of the technologists.
To remove oxides, corroded areas and scale, shot blasting machines spraying sand or special granules made of cast iron or steel are often used. Abrasive particles are thrown in the right direction by compressed air or centrifugal force. This process occurs at high speeds, due to which foreign particles are mechanically beaten off the surface.
Hydrochloric, nitric, phosphoric or sulfuric acid is used for chemical preparation of the surface to be painted (so-called etching). This method is somewhat simpler, since there is no need for complex equipment, and the overall performance is increased. But immediately after etching, you need to wash off the remaining acids and neutralize them. Then a special layer of phosphates is created, its formation plays the same role as the application of a primer in other cases.
Next, the part must be placed in a special chamber: it not only reduces the consumption of the working mixture, trapping it, but also prevents paint pollution of the surrounding room. Modern technology is invariably equipped with hoppers, vibrating sieves, and suction devices. If you need to paint a large thing, they use a through-type camera, and relatively small parts can be processed in dead-end machines.
In large industries, automated painting chambers are used, in which a manipulator of the “pistol” format is built in. The cost of such devices is quite high, but getting fully finished products in seconds justifies all the costs. Normally, the atomizer uses an electrostatic effect, that is, the powder first receives a certain charge, and the surface receives the same charge with opposite sign. The “gun” “shoots” not with powder gases, of course, but compressed air.
Powder coating is becoming more and more popular today. What is it? it modern technology, designed to obtain decorative and protective coatings of high quality. Polymer powders are used in the work (hence the name - "powder"). They turn into a coating due to exposure to high temperatures. Because of this feature of the procedure, powder coating of metal and glass is most common.
Advantages
This process has a number of positive aspects. These include:
Profitability. The fact is that such paint can be reused if it does not settle when sprayed. 
on the treated surface. Thus, the loss of material is no more than 5%. By the way, this indicator for ordinary paints will be 8 times higher - about 40%. also in this case no need for solvents.
Ease of use. Materials for this type of work are produced completely ready. This guarantees stable high quality coatings. In addition, it is very easy to clean the equipment after work, because the powder is easily removed from the parts.
Speed. Powder coating does not require drying products before placing them in the oven. If the surfaces covered regular paint, it is necessary to dry for quite a long time, then in this case the process is reduced significantly.
Durability. The technology of these works involves the polymerization of a layer of elastic plastic, which has a fairly high adhesion, directly on the surface that is being painted. The result is durable coating, which boasts excellent electrical insulating and anti-corrosion properties, as well as resistance to various substances.
Environmental friendliness. As already mentioned, solvents are not used in this case, which has a positive effect on the environment. The wastelessness of production also plays a role.
Decorative. Powder paints make it possible to obtain a surface of any shade. The palette of presented materials today has more than 5 thousand colors and shades with various textures. If desired, you can get a glossy or matte surface, as well as under granite, moire, etc.
Powder coating as a business idea
Given all the advantages of this type of work, it becomes obvious that such a business will be quite profitable. If you do not have the opportunity to immediately invest a large amount in your business, it is advisable to at least just learn how do-it-yourself powder coating is done.
But it is worth considering that you still have to spend money. First of all, you will need to take care of the availability of special equipment and a separate room. As the latter, a simple garage is quite suitable, but on the condition that it has enough space to accommodate all the tools and direct work. What equipment is needed for powder coating?
Camera
Work will be impossible without a special camera. It is in it that most of the whole process is performed. The powder coating chamber is needed for air purification (recovery process), in addition, it is due to it that it remains possible to reuse the material. Here, the paint that does not fall on the surface to be treated is sent to the filters, and then dumped.
Such equipment may be various sizes. Which one to choose - you need to decide in each case individually, having previously determined which products you plan to work with.
Furnace and gun
You will also need a reflow oven. This is a prefabricated structure consisting of panels (their thickness is 100 mm). Thermal insulation material- basalt fibre. If you are just trying yourself in this type of work, it is not necessary to immediately buy a special oven. For this purpose, it is quite possible to use a conventional oven. However, to build a business, it is still recommended to purchase professional equipment.
Powder coating technology also requires a spray gun that allows the use of compressed air. It can also be used as a compressor. If you have made a choice in favor of the latter, then please note that a filter for high pressure must be installed on it.
Recuperator and transport system
Powder paint residues are collected using a recuperator. Instead, at first, you can use a cyclone type vacuum cleaner. In this case, you must first check the power supply in the room and make sure that grounding is present.
If you plan to work with large-sized products, then you should also consider purchasing transport system. In it, the workpieces are moved on special trolleys that move along rails. Thus, a powder coating line is built. Such equipment improves the productivity of the process, ensuring its continuity.
Powder Coating Technology
The process of doing the work itself is divided, as it was already possible to understand, into several stages:
- Let's talk about each stage separately. Preparation of the product, or rather its surface, for processing.
- Apply paint in powder form.
- Polymerization, i.e. heating the product in an oven.
Preparatory stage: cleaning, degreasing
We can say that this stage is the most time-consuming. And it depends on him how high-quality and resistant the coating will turn out. In the process of preparing the surface, it is necessary to remove all contaminants from it, degrease it.
Cleaning is carried out either mechanically or chemically. The first option involves the use of steel brushes or grinding disc. You can also perform lapping with a clean cloth, after wetting it in a solvent.
The second cleaning option involves the use of an alkaline, neutral or acidic composition, as well as solvents. Their choice depends on how dirty the surface is, what material the product is made of, what type it is and what dimensions it has.
Phosphating and chromating
Next, a conversion underlayer can be applied to the product, which will prevent moisture and dirt from getting under the coating. Phosphating and chromating procedures provide better adhesion and protect the surface from rust. For this purpose, iron phosphate (for steel), zinc (when working with galvanic cells), chromium (for aluminum) or manganese and chromic anhydride are most often used.
Then it will be necessary to remove the oxides, which is carried out using abrasive and dry cleaning. The first is produced by means of abrasive particles (shot, sand), walnut shells. These substances are supplied with compressed air at a fairly high speed. As a result, particles "crash" into the surface of the product and bounce off it along with pollution.
Pickling (chemical cleaning) is the removal of various contaminants using special pickling solutions, the main components of which are sulfuric, hydrochloric, nitric, phosphoric acid or caustic soda. This method is considered more productive, however, after such processing, the product must be washed from solutions.
Passivation
This is the final step in the surface preparation phase. It is necessary to process the part with sodium and chromium nitrate compounds. This is done in order to prevent the recurrence of corrosion.
After all the preparatory work has been done, the product is rinsed and dried in an oven. Now powder coating of the surface can be performed directly.
Paint application
What is powder coating technology itself? The prepared product must be placed in the chamber. Here powder (paint) will be applied to it. If you have a dead end box, then only small details can be painted in it. Large items can only be processed in long chambers.
Most often, the method of electrostatic spraying is used to apply paint. In this case, powder coating guns are used. Such instruments are also called spray guns or applicators. This device is a pneumatic spray gun that applies an electrostatically charged substance to a pre-grounded part.
Coating formation
Let's move on to the next stage of work. The paint has been applied, now you need to form a coating. First of all, the product is sent to the polymerization oven. Such chambers can be different: vertical, horizontal, again, dead-end or walk-through, single- and multi-pass.
The aforementioned equipment for powder coating provides heating of the surface to a certain temperature - 150-220 ° C. The treatment lasts about half an hour, resulting in the formation of a film. At this stage, it is important that the part is heated evenly, which is possible only if the temperature in the chamber is stable.
Which mode to choose for processing a particular part depends on it itself, on the type of paint and equipment. After polymerization is completed, the product must be cooled in air. All work done.
Applications
As you can see, powder coating is a rather time-consuming job that requires certain investments. What products are subject to it? The painting method in question is ideal for processing aluminum or forged products, as well as galvanized surfaces.
Powder paints in our time are finding more and more "fans". Now they are used in instrument making, and in construction, and in the automotive industry, as well as in other areas. With their help, paint medical equipment, roofing materials, household appliances, items made of ceramics, plaster and glass, furniture. Among car enthusiasts, powder coating of disks is gaining more and more popularity.
Business organization
These works in specialized centers today are quite expensive. If you want to try yourself in this business, then if you have financial resources you may well get started. Of course, not everyone can afford a powder coating line (automated system), but thanks to our recommendations, you can replace some elements with other tools at first.
Start with small items. It can be plaster figurines, ceramic tableware And much more. Try painting something in your house first (start with something you don't mind ruining). Gradually, you will have the necessary skills and dexterity, then you will be able to take orders from friends. However, you should not expect a large income if you interrupt only with one-time orders from individuals.
The best scenario for the development of events involves the presence of a large start-up capital. In this case, you can immediately purchase necessary equipment and hire workers. Customers should be sought among enterprises engaged in the production of metal products. Only the presence of such customers will allow your business to exist and develop.
After applying powder paint, the product is sent to the stage of coating formation. It involves the melting of the paint layer, the subsequent production of the coating film, its curing and cooling. Melting and polymerization take place in a special furnace. There are many varieties of polymerization chambers, their design may vary depending on the conditions and characteristics of production at a particular enterprise. In appearance, the oven is a drying cabinet with electronic "stuffing". Using the control unit, you can control the temperature of the oven, the time of staining and set a timer to automatically turn off the oven at the end of the process. Energy sources for polymerization ovens can be electricity, natural gas and even fuel oil.
Furnaces are divided into continuous and dead-end, horizontal and vertical, single and multi-pass. For dead end furnaces important point is the rate of temperature rise. This requirement is best met by furnaces with air recirculation. Coating chambers made from electrically conductive dielectric coatings ensure uniform distribution of powder paint on the surface of the part, however, if used incorrectly, they can accumulate electrical charges and be dangerous.
Melting and polymerization occurs at a temperature of 150-220 ° C for 15-30 minutes, after which the powder paint forms a film (polymerizes). The main requirement for polymerization chambers is to maintain a constant set temperature (in different parts oven, a temperature variation of at least 5 ° C is allowed) for uniform heating of the product.
When heated in an oven, a product with a layer of powder paint applied, the paint particles melt, go into a viscous state and merge into a continuous film, while displacing the air that was in the powder paint layer. Part of the air may still remain in the film, forming pores that degrade the quality of the coating. To avoid the appearance of pores, painting should be carried out at a temperature above the melting point of the paint, and the coating should be applied in a thin layer.
With further heating of the product, the paint penetrates deeply into the surface and then cures. At this stage, a coating is formed with the specified characteristics of the structure, appearance, strength, protective properties etc.
When painting large metal parts the temperature of their surface rises much more slowly than that of thin-walled products, so the coating does not have time to fully harden, resulting in a decrease in its strength and adhesion. In this case, the part is preheated or its curing time is increased.
Rejection is recommended for more than low temperatures and over a longer period of time. This mode reduces the likelihood of defects and improves the mechanical properties of the coating.
The time of obtaining the required temperature on the surface of the product is affected by the mass of the product and the properties of the material from which the part is made.
After curing, the surface is subjected to cooling, which is provided by lengthening the conveyor chain. Also for this purpose, special cooling chambers are used, which can be part of the curing oven.
The appropriate mode for coating formation must be selected taking into account the type of powder paint, the characteristics of the product to be painted, the type of oven, etc. It must be remembered that temperature plays a decisive role in powder coating, especially when coating heat-resistant plastics or wood products.
Curing (polymerization) of powder polymer coatings should be carried out as rationally as possible and at the same time not violate the quality of the resulting coating (PC), which is still sensitive to external influences.
Powder polymer coating proceeds depending on the composition of the composition, according to the laws of kinetics, at certain temperature and time in the polymerization oven. When stoving, the entire layer of powder paint must be heated as quickly as possible to the required temperature with its uniform distribution in the cured layer. Only under such conditions can the powder paint melt reach a minimum viscosity without impairing flowability as a result of the ongoing polymerization reaction. With slow heating in the thickness of the layer of powder paint, the polymerization process begins even before it has sufficiently spread over the surface of the product, as a result of which the cured surface is uneven. Typically, the stoving temperature for powder coatings is 110 - 250°C, and the holding time is 5 - 30 minutes. The shape and thickness of the painted products have a certain influence on the curing-polymerization process. The residence time in the oven usually refers to the time during which the product is in the active zone of the polymerization oven. It is divided into heating and holding time. The stoving temperature and the required holding time are determined by the type of powder coating, and the heating time is determined by the thickness of the substrate material and constructive form heating zones. Consistent stoving temperature and temperature control during the heating process ensures a uniform gloss coating and prevents overheating of the polymer powder coating.
Structural varieties of drying chambers
Depending on the type of loading, dryers are divided into chamber and continuous action. The bodies of the dryers usually consist of double-walled cassettes made of sheet metal between which there is an insulating material. The individual cassettes must fit snugly against each other at the joints, so careful assembly using a suitable sealing compound is essential. At the same time, the use of silicone-containing sealants should be avoided in the powder coating area, since their residues lead to the formation of defects (craters).
The design of dryers should always be such that there are as few "thermal bridges" as possible between their outer and inner skins. Starting from a certain length and temperature ranges, special joints should be provided that take into account the expansion of the material and are sufficient to compensate for fluctuations in the length of the internal and outer skins corps. In addition, it is necessary to ensure the complete tightness of all air ducts and air channels. The fans must be connected to the housing in such a way that no vibrations are transmitted that interfere with operation.
Chamber dryers are the most simple designs polymerization ovens and loaded in batch mode. These dryers are used for low bandwidth and/or under significantly changing stoving conditions, e.g. different time drying or when different drying temperatures are used when using different powder coatings.
The big disadvantage of these ovens is the loading of products in separate batches. When the dryer doors are opened for loading or unloading, the temperature in the oven drops noticeably and it takes a certain amount of time to reach the required temperature. However, for optimal polymerization and good spreadability of paintwork materials on the surface required temperature product must be reached in the shortest possible time.
Continuous dryers in serial production are loaded in line mode - continuously or periodically, in most cases using transport installations. In this type of dryer, the inlet and outlet are located on opposite sides. A reverse layout is possible, in which the transportation system is designed in such a way that the products change the direction of their movement one or more times.
Continuous dryers and reversible dryers are currently equipped with so-called A-locks, which are zones designed to prevent heat loss at the inlet and outlet of the dryer by means of ascending or descending inclined sections of the transport system inside the dryer. In this case, the inlet and outlet are located at the same level, below the bottom of the dryer. If the plant is operated intermittently, the dryer can be equipped with sliding or lifting doors to prevent heat loss. This design is used mainly for large sizes of painted products and lower throughput. In this case, the area on which the oven is located increases by the amount occupied by the lifting section of the conveyor system, which is the shorter, the steeper the conveyor can rise, taking into account the method of suspension of the painted products. A sufficient distance between two workpieces is 100 mm, the minimum is 80 mm.
With a lack of production space, it is often not possible to implement a design that includes an A-lock with a section of the conveyor system that fully corresponds to it. A compromise in this case is achieved due to the fact that a cutout is made in the end wall for the conveyor and suspension, and only the wider products to be painted enter the oven from below. Losses in the area of the narrower cut can be reduced by installing protective elements made of elastic material.
Trough dryers are devices, the design of which provides for loading vertically from above in a periodic mode. Excessive heat loss is prevented by folding doors. Trough dryers are often used in submersible installations with baths equipped with mobile lifting and transport systems. They are also used when transporting large-sized products to be painted along the submersible installation using automatic loading machines (mobile lifting and transport systems). The temperature in the furnace is maintained by placing a lid with hangers on top, on which the workpiece is hung, and in the absence of hangers, with the help of hinged or movable covers.
Combined dryer or block type dryer. Since, before applying powder coatings, products, as a rule, are subjected to preliminary chemical treatment In addition to the curing oven, most application plants also require a drying chamber to remove water. The combination of these units allows some savings due to the presence of a common dividing wall for each furnace and the absence of transmission losses through the outer wall. In addition, the exhaust air of the polymerization oven can be mixed with air drying chamber and from there to bring it out as a spent one. Thus, it is not necessary to have an exhaust air removal pipe, and it is possible to recover energy according to the temperature difference between the polymerization oven and the water removal dryer. that the length of the body is most often approximately the same as a block-type dryer.
Drying methods
Depending on the nature of the heat transfer, drying is distinguished due to convection or various types of irradiation. Convection or circulation drying is carried out due to the movement of the flow of heated air on the products, and intensive heat exchange occurs on their surface. The heated air is cooled by thermal energy dyed product. At the same time, the temperature of the product rises and the paintwork is heated.
All known sources of energy can be used to heat the air in circulation type dryers. In practice, the most commonly used diesel fuel, natural gas, electricity, oils, hot water and steam. The source of energy is chosen based on economic or plant-specific considerations, as well as the temperature required for drying.
Distinguish between direct and indirect heating. In indirectly heated dryers, the transfer of energy to the circulating air is carried out by means of heat exchangers. In direct fired units, the drying medium is heated by introducing heated gases resulting from the combustion of natural gas or boiler fuel.
Direct heating is more advantageous in terms of energy savings, but can only be used in cases where the purity of the flue gases excludes the possibility of contamination of the surface to be painted, otherwise yellowing of the coating or the introduction of soot particles resulting from incomplete combustion. With particularly high requirements for the quality of the coatings obtained, it is possible to filter both circulation and fresh air dryers to reliably protect the uncured coating from contamination. Fans, usually of radial type, are used to circulate hot air. Convection dryers usually operate with an air circulation speed of 1-2 m/s. In some cases, despite the high energy consumption, it makes sense to significantly increase the power of the fans that provide air circulation. In practice, speeds up to 25 m/s are usually chosen.
The most important advantage of the circulating dryer lies in the possibility of its universal use in a wide range production programs. This explains their high prevalence. Various by geometric parameters parts having the same mass-to-surface ratio reach same speed heating. Therefore, products of various sizes and shapes, but of the same thickness, can be dried at the same temperature regime, i.e. simultaneously. Temperature equalization occurs even when processing batches of large products by the various shapes. Moreover, thanks to the same temperature regime the risk of “burning out” of the coating is reduced to a minimum, i.e. damage due to overheating on some products. Due to the small difference between temperature environment and the processed product, even violations of work with a stop of the conveyor, as a rule, do not lead to manufacturing defects. However, care must be taken to ensure that the temperature and exposure time comply with the manufacturer's instructions, as exceeding these parameters may lead to discoloration. In the event of a malfunction and temporary stoppage of production, appropriate measures must be taken to reduce the temperature of the furnace and / or remove the coated products from it.
Infra-red drying uses another way of transferring energy to cure paintwork. The intensity of IR radiation depends on the wavelength range and the temperature of the emitter. There are long-, medium-, short- and ultrashort-wave radiation. The relationship between wavelength and IR temperature is given in table.
Sometimes, instead of the wavelength, the temperature of the thermoradiation wall is estimated. In this case, dark and light emitters are distinguished. The so-called "dark emitters" correspond approximately to the lower wavelength range. These radiators are channels made of black sheet in which flue gases circulate at a temperature of 300 - 400°C and are generally used in applications where waste heat of the appropriate temperature is available, such as dryers for car bodies with thermal treatment outgoing air. Due to the large mass, these emitters are very inertial when regulated. In addition, due to the large surface of the heat exchangers, heat loss due to convection is very large, which leads to significant heating of the air.
In the medium, short and ultrashort wave ranges, electrical emitters are usually used. They provide more precise control of the surface temperature of the coated products.
IR rays, depending on the properties of the irradiated surface, can be absorbed or reflected. Light-colored smooth surfaces, as when exposed to light rays, reflect most of the radiation compared to rough and dark surfaces. The unreflected part of the irradiation is converted into heat, which leads to an increase in the temperature of the products and heating of the paintwork layer from the inside as well. The advantage of drying with IR irradiation is also the possibility of transferring a large number energy in a very short period of time. This allows you to quickly prepare the dryer for work, heat up the products to be painted faster, and also significantly save working space due to the shorter path of the products during the drying process.
These advantages can be fully utilized when drying products with even thin walls. Products over complex shape and different thicknesses differ in different heating rates. Since heating at more high temperature emitter is faster, in certain places the PC can overheat very quickly. This can be avoided by using expensive technical solutions, providing additional regulation or a significant increase in air circulation, which negates all the advantages of thermoradiation drying. Medium-wave infrared (IRM) emitters are the most common type. They are distinguished by their robust construction and long service life. Their disadvantage is relatively slow heating: it takes about 2 minutes to reach full power. Short-wave electric IR emitters are superior to IRM emitters when regulated, but have much more short term services. Gas infrared emitters combine the advantages of thermoradiation heating with a cheap coolant.
Air ducts are an important element in convection heating, since air is necessarily heated in thermoradiation drying ovens. In order to avoid overheating and achieve uniform heat distribution, thermoradiation ovens circulate the air inside the oven and remove the exhaust air. When using infrared and gas emitters, water cooling can be additionally applied to avoid overheating. In addition, gas emitters must be equipped with exhaust gases by means of fans or in combination with a nearby air circulation dryer.
Special curing methods. In other accelerated curing methods, such as UV or electron radiant drying, the radiation serves not for heating, but as a catalyst for the polymerization of the film former. High frequency drying (heating products using an inductive or capacitive reactance in a high frequency field) is also a special curing method in which only inductive drying can be used to coat metals. It is used in some cases for coating pipes, wire and packing tape.
Inductive heating involves placing the product in a magnetic field and heating it with the help of eddy currents that occur inside. As a result, heat is generated directly inside the product. Thus, the drying of the coating always takes place in the direction from the inside to the outside, and not from the outside to the inside, as with other methods.
Inductive heating is suitable for all drying methods, including paints containing solvents. Inductive drying significantly improves the adhesion of the coating. In addition, according to one of the manufacturers, relatively fast heating is possible: in some cases within seconds. Can also be dried large sizes, since the energy conversion occurs depending on the choice of frequency only on the surface, i.e. exactly where heating is needed. The induction coil used for heating is in most cases a ring or linear inductor selected according to the workpiece. Thanks to the appropriate design of the induction coils, it is also possible to heat only separate zones processed product.
The condition for the use of induction drying is a certain geometry of the products, which contributes to a uniform distribution of the incoming current, which ensures the same temperature. Pipes, rods or bolts are ideal for this kind of drying. In the automotive industry, this method is also used for drying when painting drive shafts, brake discs, clutch pedals or wheel bearings. Inductive heating can be combined with traditional drying methods. For example, preheating can be done by inductive method and further curing by convection or irradiation. In this way, temperatures can be reached very quickly, only slightly below the maximum level, with the result that the entire drying process is significantly reduced.
Microwave drying is a completely new method that heats the coating from the inside out. high frequency electromagnetic waves penetrate the paint film and heat the substrate. Thus, in this case, the initial curing of the film on the surface, as is the case with convection drying, is prevented. The wavelengths used in microwave drying range from 1 mm to 15 cm. They are created in a tube with a magnetic field (magnetron) with a frequency range of 2.45 GHz. Due to the fact that microwave drying provides an intensive effect and gives a very fast result, it is possible to create shorter installations compared to the traditional process and thereby reduce total costs to dry. It should also be borne in mind that such installations require a special permit for use. Thermoset drying involves the use of thermoreactors. This method is suitable for both powder and liquid coatings. Thermoreactors are catalytic IR emitters that produce thermal radiation with IR wavelengths. Since the emission spectrum is in the region of 2-8 µm, the power can be adjusted very flexibly. With these systems, it is also possible to achieve a significant reduction in the drying time and thus the processing time of the products in the dryers. According to reports, energy savings can be up to 50%.
Powder coating is a modern technology that allows you to achieve a reliable and durable coating on almost any surface. Application is not difficult if you have skills, but requires the use of special equipment. A feature of this method is that the painting takes place in a dry way, and protective layer formed on subsequent heating.
Although the powder staining method has been known for quite a long time, its technical development began relatively recently. During this time, several ways of carrying out the process have appeared.
The demand for the first method of painting is explained by the fact that this option has a greater technological development. With other methods, everything is more complicated: the second method needs careful selection of temperature, and the third one appeared relatively recently.
Necessary equipment
Although the number of tools and fixtures needed depends on the scope of the work, the following are required:
Naturally, large productions have special suspension and delivery systems, which facilitates work and speeds up the pace.
Whatever method of applying the composition is used at the finishing stage, the part must be heated in the oven On a note! Heating, which is necessary in the last stage of dyeing, does not allow the process to be carried out with materials subject to thermal deformation. Therefore, the most popular is the processing of metal parts and elements.
Pros and cons
Powder coating has many positive properties among which stand out in particular:
But with all the advantages, the method is not without its drawbacks:
On a note! Usage powder method very rational indeed, but design plan inferior to other options. Although at present there are special mixtures with different visual and tactile effects.
It is impossible to achieve high-quality results without high-quality equipment. Work order
The technology of powder coating of various metal products is a set of measures. A detailed list of works includes an important stage - the preparation of the subject, the quality of which determines the result.
Training
You need to do the following:
The surface is thoroughly cleaned. For this, a number of procedures are carried out:
A conversion sublayer is formed. It is necessary to protect the surface from the ingress of various contaminants. The compositions for this are selected based on the type of material being processed. So, for aluminum parts, chromic anhydride is used, and for steel, iron phosphate is used.
If required, passivation is performed. This process is aimed at fixing the anti-corrosion coating.
Should know! The stages of preparation may vary depending on which products are processed and their scope of application. Sometimes a thorough cleaning and degreasing is enough.
Dye application
Powder coating of metal is carried out as follows.
