Powder Coatings

Electrostatic spray coating technology is a surface treatment technology that has been rapidly developed in recent years. Its characteristics are solvent-free, environmentally friendly, powder can be recycled, easy to automate production, easy to use, and various coating colors can meet different requirements. Weather resistance performance requirements. However, there are often some defects in the electrostatic assembly line that affect the appearance quality and performance of the product. The following is a brief introduction to the common causes of coating defects and control measures. Possible reasons for disgorge powder during Coating Genetic analysis: The fluid is poorly fluidized by the agglomeration of the powder, and the powder concentration in the powder feeding tube is not uniform; the fluidized plate is blocked by the powder, and the fluidization effect of the powder feeding device is poor; the powder tube, the powder pump, the venturi tube, the electrostatic needle, Dust or wear is attached to the accessories such as the nozzle and the nozzle, resulting in uneven powder output and powdery phenomenon. The diameter of the powder tube is reduced; the air flow in the powder tube is too low; the short-time high consumption causes the fluctuation of the compressed air; the problem of the powder pump. Solution: Improve the powder storage environment, seal the powder in time to avoid the moisture of the powder; do the maintenance of the powder supply equipment; timely clean the dust on the spray equipment accessories and replace the wear parts. High-quality powder tubes should be used to maintain the same inner diameter; powdered and concentrated gas should be added; water in the air reservoir or air tank should be installed before the high-consumption point. The powder is easily contaminated by external air suspension. After spraying, the surface of the profile is prone to flocculation or shrinkage. After baking, it affects the smoothness of the surface of the profile. Therefore, the spray booth should adopt sealing measures to prevent the intrusion of pollutants. The residual powder in the trachea should be cleaned and cleaned in time. If it is not used for a long time, it will easily agglomerate, and the powder will easily produce powder spit, which will affect the spraying effect.In the actual powder coating production, each process must be carefully managed, and the coating defects should be treated as appropriate to avoid repeated occurrence of similar coating defects, so as to reduce the production cost and improve the powder coating quality.

Gerenlly we find the problems from follows aspect.1.Curing furnace impuritiesThe solution is use a damp cloth and vacuum cleaner to thoroughly clean the inner wall of oven .The focus is on the gap between the hanging chain and the duct. If it is a black large particle impurity, it is necessary to check whether the air supply pipe is damaged or not, and change it if bad.2.Dusting Room ImpuritiesMainly are the dust, clothing fibers, equipment abrastive particles and dusting system fouling. The solution is to use compressed air to sweep it before painting every day. Thoroughly clean the dusting equipment and the dusting chamber with a damp cloth and vacuum cleaner.3.Hanging Chain ImpuritiesMainly include the corrosion of the acid and alkali vapours before the treatment of hanging Chain and water tray of the first spreader.(The material is the hot galvanized sheet). Clean up these facilities.4.Powder ImpuritiesThe main problems are excessive powder additives, uneven dispersion of pigments. And powder spots caused by powder extrusion. Improve the quality of the powder and improve the powder storage and transportation methods. 5.Before processing impuritiesMainly caused by large particle of phosphorus slag impurities and yellow rust caused by the film of small impurites. Clean up the slag in phosphating bath and spray pipe and control the concentration.6.Water Quality ImpuritesCaused by excessive sand content and salt content in the water used for the pretratement. The solution is to increase the water filter and use pure water as the last two levels of cleaning water.

Electrostatic spray operation process(1) Check and clear each powder supply line and spray gun before painting. (When cleaning the spray gun, make sure that line is in good contact with the nozzle and the powder supply line is clear of the nozzle). And clean the powder spray booth and powder tank.(2) Close the power switch, turn on the electrostatic power, and turn on the powder and fan. Turn on compressed air. (The ground wire is normal).(3) Turn on the Electrostatic generator switch and check if the parts are working properly. Adjust the voltage to the specified process value, and then the gun is opened for powdering and spraying. During the painting,adjust the spray gun and powder output according to the workpiece. (The distance between the spray gun head and the workpiece is less than 150mm) to ensure the quality of the coating film. Safe operation.(4) Dusting operators must hold the gun in the bare hand (if necessary, gloves must be cut in the palm of the hand.) This ensures direct skin and metal contact.(5) After the operation, check the equipment, turn off the electricity and air supply, hang the spray gun, and clean the powder Spray room. 

Several Tips for Eliminating Surface Particles in Aluminum Powder Spraying (1) Painting work environmentThe production environment surrounding the dusting room will directly affect the surface quality of the coating. For the coating of the corona electrostatic spray gun , some of the dust and particles in the environment will be brought into the powder coating booth, and charged by the electrostatic effect. Impurities are adsorbed on the surface of the coating and become particles on the surface of the coating when the powder is melted and leveled. The clean production environment has a good effect on product quality. Persons entering the workshop shall wear on the work clothes and change shoes; do a good job of sanitary work in the workshop; often wipe the production equipment with a semi-moist cloth or use a vacuum cleaner to remove the dust from all parts of the workshop. (2) Workpiece surface treatmentGenerally powder-sprayed aluminum workpieces need go through the following process: shelf-degreasing-water-washing-chromatization-curing-discharging; impurities such as chromium residue in the surface treatment process may adhere to the workpiece. This results in the presence of particles after film formation. (3) Control of Film thikcnessFor spraying technicians, it is understand that if the film too thin, in addition to particles, it will produce poor leveling, severe orange peel, and poor hiding power of the light colors, while the acid and alkali resistance, Salt tolerance,water-tolerant and other performance of coating will be worse. Appropriate increase the thickness of coating can effectively reduce the formation of particles, and not be too thick. Generally, if too thick will affect the size of workpiece, and the properties such as impact resistance, flexibility and adhesion will be reduced. Layer thickness control between 40~120um. We can control the film thickness in the following ways:a. The number and arrangement of the spray guns in the powder spray booth. b. The powder output and air pressure of the spray gun (powder out, atomization, fluidization parameters)c. Running speed. Chain speed.d. Suspending method and arrangement of coated workpieces.

Relationship between particle size and powder quality:The particle size distribution of plastic powder is closely related to the texture, smoothness, glossiness, particle size,  electrification effect, powder fluidization effect, storage stability, and powder recovery rate.1, appearance, leveling and quality.  In general, the smaller the particle size of the powder, the better the planarity of the coating when cured;  at the same spray thickness, particles with a smaller particle size are less prone to particles; and appearance is smoother.2, charged effect and powder rate:Increasing the charging ability of the powder particles will increase the powdering rate of the powder coating. The main adsorption force of  spraying is electrostatic force, and the powder on powder rate mainly depends on how much the powder particles are charged. The charge of the powder is proportional to the square of  the particle size of the powder. Increasing the particle size increases the amount of powder charge and increases the rate of dusting. However, the particle size of the powder particles can not be too large,otherwise, the gravity of the large particle powder exceeds the aerodynamic force and electrostatic force. In the flying process, the powder coating has fallen to the surface of the workpiece due to the effect of gravity, cause the rate is reduced. The powder is too thin and the chargeability is reduced, and the coating efficiency will be reduced. The ultra-fine powder (particle size 3, Fluidization effect of powder:When the powder is too fine, the fine powder will bind into the powder mass and will not spread when fluidized. When sprayed on the workpiece, it forms a sleek packet that affects the appearance of the coating. When the powder is too thick, the powder is not easily fluidized in the powder bucket.4, The stability of StorageStability refers to the ability of the powder coating keep the size of powder particle, shape and hardness under the certain conditions, that is to say whether the powder absorbs moisture and clumps, and the stability is decreased. 

Powder paint itself is only a semi-finished product. It is only after spraying and curing that it becomes the final product. Consumers only pay attention to the effect and quality of the coating, that is to say, the use of powder paint is as important as the production of powder paint. If the powder is of low quality, the spraying equipment is better, the pretreatment  is more meticulous, and the coating process is strict, the high-quality products will not be produced; however the powder is good quality, the spraying equipment, the process and the pretreatment has problems, there will no high-quality products. The reality is that most of the attention of coating users is focused on the powder coating product itself, with quality problems only looking for problems on the powder, but if pay not enough attention and research on the coating construction technology. As a result, a large number of coating products can not achieve the desired results. Each kind of powder coating has its own curing characteristic curve, which can be cured completely within a certain temperature  and time range. In order to improve efficiency, reduce cost and violate rules, it is not advisable to shorten curing time. If the curing temperature or time is not enough, the curing will be incomplete, the due properties will not be able to play out,  its physical properties will be greatly reduced, and the chemical resistance will not be good, decorative, anticorrosive, Weather resistance is not as good as expected. Some coatings cured at low temperature, even if they are completely cured, there is no better performance than those after high temperature solidification. In particular, some workpieces formed after curing will form small cracks in stamping and bending. The water will penetrate along the cracks and corrode the substrate quickly, and we can see the outdoor traffic barriers, and soon after they are put into use, there will be rust marks at the corner of the intersection. This is directly related to baking temperature and time and bending after spraying.

Application range of Sandblasting1, Sandblasting before the coating and bonding of workpiece can remove all the rust and other dirt on the surface of the workpiece, and to establish a very important basic pattern (that is usually called the rough surface), further more via change the abrasives with different particle sizes. for example, the abrasive of fly-swept abrasives to reache different degrees of roughness, which greatly improves the binding force between workpieces and coatings and plating materials. Then make the adhesive bond more firm and better quality.2,  Cleaning and polishing sandblasting can clean the casting surface, heat treatment after the workpiece castings and forgings, all of the dirt (such as oxide skin, oil and other residues), and the workpiece surface polishing to improve the workpiece finish, Can make the workpiece exposed uniform metal color, so that the appearance of the workpiece is more beautiful,goodlooking.3, Cleaning and surface beautification the machined parts burrSandblasting can clean the tiny burrs on the surface of the workpiece and make the surface more smoother, eliminating the danger of burrs and improving the grade of the workpiece. And can make a small round at the interface of the workpiece surface, making it more beautiful and  precise. 4, Improve the mechanical properties of the partsAfter sandblasting mechanical parts, it can produce even and fine uneven surface on the parts, so that the lubricating oil can be stored, thus improving the lubrication conditions, reducing the noise and improving the service life of the machinery.5, Decorative effect for some special purpose workpiecesSandblasting can be used to achieve different reflective or matte finishes. Such as stainless steel workpieces, plastic grinding, polishing jade, wooden furniture surface matt, frosted glass surface patterns, as well as the fabric surface of the wool processing.

The powder coating for electrostatic spraying needs to pay attention to the following several parameters in order to ensure the smooth implementation of the electrostatic spraying process and obtain a high-performance coating film.The significant difference between powder coatings and solvent-based coatings is the dispersion medium. In solvent-based coatings, organic solvents are used as the dispersion medium; but in powder coatings, use the purified compressed air . The powder coating is in a dispersed state during spraying and cannot adjust the particle size of the coating. 1, powder coating particle finenessFor the powder electrostatic spraying process, the key point to consider is that the powder coating particles receive electric charge, maintain the charge and the charge distribution of charge, which directly affects the power of the powder on the workpiece adsorption and deposition efficiency, in addition, it is important that the uncured powder coating The layer must withstand the mechanical vibration of the conveying mechanism without falling powder. In fact, the main factor affecting the charge and charge retention of the powder particles is the dielectric constant of the powder coating. The lower the dielectric constant of the powder, the easier it is to charge the particles, also easier to lose the charge. This reflects the absorption of the powder on the workpiece. The adhesive force is not strong, and the powder is powdered by vibration. For electrostatic spraying powder coatings, high dielectric constant should be used as much as possible, which will greatly increase the power of powder adsorption.2.The resistivity and dielectric constant of powder coatingsThe hygroscopicity (moisture content) of the powder coating itself directly affects the self-resistance dielectric constant of the powder. If the powder is heavily hygroscopic, it will be clumped. This cannot be electrostatically sprayed. The general moisture absorption, in addition to affecting its charging performance, will also reduce the powder's fluidity and film formation, so that the coating film is not smooth or even difficult to adsorb on the workpiece and the coating film will produce bubbles and pinholes.The moisture absorption of powder coating is not related to the preservation and storage, but also related to the degree of compressed air purification during spraying.3, The water content of powder coatingThe stability of powder coating refers to whether the powder will agglomerate during storage or use, the leveling characteristics and the charging effect will be worse, the orange pattern of coating film will be obvious, the gloss will be weakened, and the pinhole bubbles will occur.

  1.  At present, the powder coatings sold on the market are mainly two kinds of thermal plastic and thermosetting, of which the use of thermosetting powder coatings is very much. The thermosetting powder coating is a kind of coating which is made of thermosetting resin as the membrane material, and then added the curing agent of cross-linking reaction. After heating, it is insoluble and hard. When using this kind of paint, pay special attention to the details in the process of use, so as not to cause harm to your health.  2. Generally, there is a special construction workshop when spraying the workpiece to the thermosetting powder coating. If it is not properly operated, it may cause some danger. Therefore, it is necessary to be careful in the spraying process of thermosetting powder coatings. If the powder coating appears in the spraying process of leakage, the power should be cut off immediately, and should be cleaned, if accidentally inhaled powder or into the eyes, must be timely with large amounts of water for cleaning, if serious need to immediately go to the hospital for treatment。   3. Ventilation: the purpose of ventilation is to reduce the concentration of solvent vapor or dust in the construction site, so as to reduce the possibility of burning and explosion and reduce the content of toxic substances, so as to ensure the health of builders. When ventilating, it is necessary to have at least one intake, one out of the tuyere, in order to help air convection and improve the effect of ventilation. The steam of flammable organic solvents is generally heavier than air, and tends to accumulate on the ground or at low level, especially in the lower part of the cabin. The outlet must be placed near the ground. The work of ventilation is in charge of the special person, from the beginning of the painting operation。 

What products suitable the power coating?A process called electrostatic spray deposition (ESD) is typically used to achieve the application of the powder coating to a metal substrate. This application method uses a spray gun, which applies an electrostatic charge to the powder particles, which are then attracted to the grounded part.That is to say powder coating can worked on the any metal surfaces products. such as fencing, motorcycle wheel and frame, car rims, furnitures and construction material and so on. The more and more products which you seen in the daily life is finishing by powder coating applications technology.It is smoother, longer lasting, cleaner, less expensive, and more ecologically friendly than any other finishing technique. No toxins or aerosols are used.

Good penetration performance, can smooth all kinds of diffcult to fight the corner. Powder in all corners of the uniform can be evenly attached. combined with a strong. reaching the thickness of the user's need. the coating is beautiful.On one time, the powder was high, the powder was less, and the powder was saved.Spray gun, anti fall. long-term use is not reliable ignition. long service life.

Process flow of powder coating.Part preparation or the pre-treatmentremove the oil,dusty,rust from the surface of workpiece, and creat the layer of resistant to corrosion increase the adhesion force "phosphate coating"Chemical pre-treatments involve the use of phoshpates or chromates in submersion or spray application. The pre-treatment process both cleans and improves bonding of the powder to the metal. The powder applicationThe most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun, or corona gun. The imparts a positive electric charge to the powder, which is then sprayed towards the grounded object by mechanical or compressed air spraying and then accelerated toward the workpece by the powerful electrostatic charge.Powder CuringWhen a thermoset powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher molecular weight polymer in a network-like structure. This cure process, called crosslinking, requires a certain temperature for a certain length of time in order to reach full cure and establish the full film properties for which the material was designed. Normally the powders cure at 180-200 for 15 minutes. The application of energy to the product to be cured can be accomplished by convection cure ovens, infrared cure ovens, gas fired ovens, electric oven.

What is rate of powder coating spraying?Rate of spray coat the powder coating that is to say how many powder coating adsorb to the workpieces by electrostatic painting of the all of the powder coating, that is to say efficiency of deposition. The efficiency of deposition is higher, recycle of powder is lower.Rate of powder coating spraying relations with the type of spray gun, tecnological parameter, shape of workpieces and method of painting. Whey we say the powder coating, we can not ignore  the one time rate of coating, the good spray gun one time coating rate up to 80%, then we only consider recycle of the 20% powder coating.Many company and customer only noticed the maximo coating powder , in fact the enlarge the compress air and pressure, then increase the coating powder . But the question is if the high voltage can supply the electric to so many powder or not?. The powder spray gun from different factory , with different quality.

Powder coating is a dry finishing process that has become extremely popular . Representing over 15% of the total industrial finishing market, powder is used on a wide array of products. More and more companies specify powder coatings for a high-quality, durable finish, allowing for maximized production, improved efficiencies, and simplified environmental compliance.  Used as functional (protective) and decorative finishes, powder coatings are available in an almost limitless range of colors and textures, and technological advancements have resulted in excellent performance properties.AutomotiveArchitecturalFurnitureMedical  and safetyFencing