ã€China Aluminum Industry Network】 Powder coatings, like other coatings, inevitably cause some problems during the construction process. First, analyze the cause of coating defects to effectively handle the failure. 2, factors affecting the quality of the coating 2.1 Poor quality of powder coating Unqualified raw materials: Quality problems with powder coatings can easily cause defects in the coating. Must start from the paint quality, choose a good quality paint, and improve the paint into the factory's various technical inspections. Poor formula design: formula design must not only meet the high quality requirements of products, but also have market competitiveness, but also to make the formula have stability and continuity. The imperfect formula design will reduce the performance of the powder coating and affect the coating performance. The production process is not standardized: The production process of the powder coating is a physical mixing process, and the production equipment must be operating normally, and there must be standardized operating procedures. Bad recovery powder: There are impurities in the recycled powder. The ratio of new powder and recycled powder is unreasonable, etc., which will affect the quality of the coating. The recovery powder should be controlled: the ratio of new powder is 1:1 or 2:3. Mixed powders: If the leveling agent in the two powders is different or the powder contains silicone oil additives, the two powders are incompatible. Mixing the two powders will reduce the gloss of the coating or cause shrinkage. Poor storage of materials: Powder coatings cannot absorb moisture, squeezing, etc., so as to avoid caking and reduce quality. At the same time can not be stored for a long time in the powder bucket, or fluidization is not good. The quality inspection system is not perfect: powder coatings must be carefully sampled before leaving the factory. 2.2 Spraying process is not strict Poor pretreatment: Degreasing, rust removal, poor phosphating, residual surface, resulting in coating orange peel, shrinkage, particles and other defects and reduce coating adhesion. The workpiece is not completely dry, causing the coating to foam. Process conditions out of control: compressed air is not clean, lack of gas pressure, easy to produce poor powder leveling, spit powder defects, to control the pressure of 9.8 - 20.6kPa is better. The voltage is too high or too low, and the voltage is not stable, so that the depressed part of the workpiece can not be powdered or the powder rate is reduced, and the coating thickness is not uniform. The voltage should be controlled to 60 - 90 kV. The curing temperature is too low or too high, the coating has low impact strength and hardness, and the appearance and gloss are poor. There are orange peels and so on. Improper operation: The position or direction of the gun mouth is incorrect, and the powder rate is low. Adjust the orientation of the gun nozzle so that the powder cloud is directed toward the recessed area of ​​the workpiece. Too close distance will produce strong anti-ionization phenomenon, resulting in electrostatic breakdown, causing the powder to burn and ignite, or the formation of lines or metal flash effect is not good; jetting too far too far will reduce the amount of powder. The spray distance should be maintained at 10-20 cm. The spray gun comes into contact with the powder coating cabinet or metal objects, causing the workpiece to be grounded poorly, causing the powder to burn and ignite. The local residence time of the spray gun on the workpiece is too long, resulting in electrostatic breakdown, which is one of the reasons that the coating generates pinholes and bubbles. A poor grounding of the workpiece: the grounding wire and the joint of the workpiece are sprayed with paint to reduce the conductivity of the wire, so that the powder rate is reduced, the coating thickness is uneven, orange peel, pinholes, wrinkles, sag, adhesion is poor Wait. The movable shielding tube can be put on the joint. When the material is loaded, only the shielding tube needs to be moved to expose the joint of the wire, then the tied wire of the workpiece is connected, and then the shielding tube is covered to ensure the grounding of the workpiece is good. 2.3 The equipment and accessories are not good Microplate plugged: caused by ultra-fine powder or compressed oil in the air, impurities, resulting in poor fluidization of the powder. Powder Fouling of Powder Fouling: Due to the high spray velocity, the powder collides with the melt and builds up in the wall of the pipe, plus regular cleaning and replacement is not enough. This will eventually lead to powder blockage. At this time, the air pressure should be reduced. Powder spraying process does not meet the requirements: the internal resistance is low, resulting in excessive current, the voltage is too high; Second, powder atomization and dispersion is not good, resulting in spit powder, affecting the appearance of the coating quality. The ventilation ducts were blocked causing the powder to fly. The powder feeder is powdered or clogged so that the amount of powder is not uniform. The venturi wears heavily to reduce or irregular powder, and the coating develops. The nozzle should be replaced at this time. Inappropriate use of the powder feed tube: The use of reinforced plastic tubes makes it easy to form coating stains (species other than coating color). The solution is to replace the powder conveying pipe; the powder injection pipe is too long to cause uneven spraying, and the corresponding solution is to shorten the powder conveying pipe and minimize the distance between the powder supply device and the spray gun. The powder recovery unit did not operate normally and caused the powder to fly. At this point check the recovery device. 2.4 The production environment is not clean There are scattered materials in the spraying workshop. The application site: At this time, the hard attachments of the workpiece racks, recycling equipment, catenary and drying tunnels, etc. shall be removed, and the air circulation and supplementary air of the spraying workshop shall be filtered and maintained. There is a positive pressure inside and outside the workshop. In addition, it is not necessary to walk around the air inlet and polish the workpiece. A screen (60-70 mesh stainless steel screen) is installed at the air outlet of the air duct to filter the circulating hot air in the oven. Use towels instead of cotton yarn when servicing equipment. The oven is contaminated: Some substances in the powder volatilize as gas at the curing temperature and become loose solids when the curing oven mouth is cold. When accumulated to a certain thickness, it loosens and falls off to the dusting workpiece, causing sand collection. Therefore, regular removal or flushing of volatiles from the oven mouth is required. The powder room is contaminated: the coating shrinks. The contaminants should be removed from the site, and it is better to seal off the powder house or stop using the contaminated powder. 3, common troubleshooting 3.1 Poor fluidization Insufficient air pressure: The air filter must be cleaned and the pressure increased as appropriate. Powder agglomeration: Artificial powders need to be loosely filtered. Too much fluidized bed load will also affect the powder fluidization. At this time, the fluidized bed should be reduced in powder loading. The general powder dosage is 2/3 of the fluidized bed volume. 3.2 powder blocking gun Poor fluidization of the powder: The amount of powder in the fluidized bed should be reduced. The amount of powder added is controlled to be 2/3 of the volume of the fluidized bed. The content of ultrafine powder in the powder is high: It is necessary to reduce the proportion of recycled powder added to the original powder and check the particle size distribution of the original powder. 3.3 Powder sprayed on the workpiece Compressed air contains water or oil: it is necessary to check the purification of the air source and improve the compressed air purification equipment. The content of ultrafine powder in powder is high: it is necessary to reduce the proportion of recycled powder added to the original powder and check the particle size distribution of the original powder. Too much powder: It is necessary to properly reduce the pressure of the powder and control the amount of powder to be 150-200g/min. Poor fluidization of the powder: reduce the amount of powder in the fluidized bed, generally the amount of powder added is 2/3 of the volume of the fluidized bed. 3.4 The powder rate is not high The static voltage of the spray gun is insufficient: static voltage should be checked and properly adjusted; additionally, the gun head electrode can be cleaned. The rate of powder ejection is too fast: the pressure of the powder to be fed must be properly reduced. The content of ultrafine powder in the powder is too high: the proportion of the recycled powder added to the original powder should be reduced, and the particle size distribution of the original powder should be checked. The amount of air drawn by the spray booth is too large: the amount of air drawn should be reduced. The particle size of the powder is too thick or the density is too high: The powder size distribution and the specific gravity of the coating should be controlled when milling. 3.5 powder burning fire Excessive powder concentration: The output pressure should be reduced and the recovery device checked. Dusty room humidity is too high: The humidity should be kept ≤ 80%. 3.6 coating adhesion is not good In case of poor pretreatment, incomplete rust removal of the workpiece or residues in the pressure gap, the material will bleed out when the workpiece is baked at a high temperature and flow to the lower end of the workpiece. At this point, the spray angle should be adjusted to reduce the drying temperature of the phosphating film and coating. Process hole design is unreasonable (circular): The process hole needs to be changed to a waist shape and opened at the bottom of the workpiece. Insufficient curing of the coating: The baking temperature should be increased and the curing time extended to achieve the curing specification. Insufficient output voltage: The output voltage should be increased. The powder resistivity is too high or too low: the resistivity of the powder should be adjusted. 3.7 coating hardness is low or poor wear resistance Insufficient curing of the coating: The baking temperature should be increased and the curing time extended to achieve the curing specification. Over-coating of the coating causes the embrittlement of the cross-linked coating structure to decrease in hardness. The baking temperature should be appropriately reduced and the curing time should be shortened. The cure temperature ramp rate is too slow. During the slow melt flow, some leveling aids migrate up to the surface of the coating. Should increase the heating rate. 3.8 Orange peel The coating is too thick or too thin: The coating thickness can be controlled by adjusting the spray equipment and adjusting the spray parameters. The curing temperature of the coating is too low: the baking temperature is adjusted to the process requirements. The heating rate of the oven is too fast: The heating rate should be appropriately slowed down. Generally, the time required for the workpiece to rise from the normal temperature to the curing temperature should be controlled within 4 to 5 minutes. Strong deionization: Reduce the voltage and increase the spray gun-to-work distance. The phosphating film is too rough to impede powder flow. In this case, the denseness and fineness of the phosphating film should be improved. Powder atomization is not good: voltage and air pressure can be adjusted. Powder agglomerates: The powder should be protected from moisture. 3.9 Low gloss after high gloss powder curing During the curing process of the coating, bubbles escaping form a large number of micro-pinholes. First, it is necessary to check whether the substrate has pores or moisture, and the moisture of the workpiece should be dried before painting. The excessive volatilization of the original powder and the recovered powder and the humidity of the compressed air are too high. At this time, the powder coating must be sampled at the factory to reduce the humidity of the compressed air. Over-curing: It is necessary to control the curing conditions of the powder. 3.10 After the low-light powder curing high gloss Incomplete curing: The heating system needs to be checked to ensure the baking curing temperature and the residence time of the workpiece in the oven. The heating rate of the oven is too slow: it is necessary to increase the heating rate of the oven. 3.11 Pinholes and Bubbles The surface of the workpiece has pores: using a preheating method, baking at a temperature higher than the solidifying temperature of 20% for 20 min to eliminate microbubbles. Defoamers can also be added to the paint to help eliminate air bubbles. If the rust removal of the workpiece is not complete or the rinsing is not clean after phosphating, the quality of the pretreatment must be improved. If the moisture does not completely dry after surface treatment, it is necessary to appropriately increase the preheating temperature. Compressed air is not clean: check the air purification and improve the compressed air purification equipment. The coating is too thick: reduce the number of spraying. Voltage too high: Adjust the voltage. Too close a spray distance (electrostatic breakdown): Increase the spray distance, and note that the spray gun should not stay too long on the workpiece during operation. 3.12 shrink hole Compressed air contains a small amount of oil: check the air purification and improve the compressed air purification equipment. Uneven powder: Remove the clogging problem from the powder supply system. The surface quality of the workpiece is poor: the surface of the workpiece is not deoiled and it is necessary to strictly control the pre-treatment process. If the surface of the workpiece has significant uneven holes, the flatness of the workpiece surface needs to be increased. Mix in other types of powders and impurities: Strengthen cleaning work. 3.13 film is snow-like The coating is too thick: reduce the thickness. Voltage too high: Reduce the voltage. Spraying too close: Increase the spray distance. Spraying too many times: Decrease times. 3.14 Color change High curing temperature and long time: control curing conditions. Uneven curing temperature, local overheating and poor convection conditions: Adjust the layout of heating elements and equipment structures. 3.15 particles The coating is too thin: increase the coating thickness (50 - 60um). Spraying and baking environment are not clean: remove hard attachments such as coating hangers, recycling equipment, hanging curtains and drying tunnels; air circulation and replenishment of emptying and filtering of the spray shop, and maintain a positive pressure inside and outside the workshop; Should use high temperature, not easy to rust material for the oven wall; regularly remove or flush the volatiles in the oven mouth. Inadequate pre-treatment of the workpiece, rough phosphating film, hanging ash, etc.: improve the quality of the phosphate film; cleaning the workpiece after rework is not clean: removing wear debris from the grinding surface. The powder itself contains impurities exceeding the standard or insolubles: Replace the qualified powder material (including the recovered powder). 3.16 line or metal flash effect is not good The coating is too thick or too thin: control the thickness. Curing temperature increase rate is too slow or too fast: adjust the rate. Insufficient charge of powder: check the static voltage and increase it properly; otherwise, clean the tip electrode. Powder separation in the hopper: when the air pressure is too high, the pressure should be reduced; the content of the ultra-fine powder in the powder control and the fluidized bed loading powder should be controlled; the powdery buds should be loosened and sifted for the agglomerated powder; check whether the micro-holes are normal The powder pressure should be adjusted when the powder jet speed is too high or too low. The spray distance is too close or too far: adjust the spray big. Most art-type powder coatings have poor spraying performance after recycling: less recycled powder is used. 3.17 uneven coating Spraying too close: Adjust the spray distance. High-voltage electrostatic generator voltage instability: detection of output voltage. Aluminum Casement Windows,Aluminum Insulated Casement Window,Aluminum Fly Screen Window,Aluminum Casement Window With Fly Screen Guangdong Jihua Aluminium Co., LTD , https://www.gdaaluminiumprofile.com