hole
The main reasons are: ① Rust on the board; ② Galvanized substrate contains hydrogen ions; ③ Yellowing after phosphating pretreatment; (4) After the workpiece is phosphatized, it can't be washed clean with water, especially round pinholes appear around the workpiece; ⑤ The softened water of anion exchange resin is acidic; ⑥ Silty.
Solution: ① Drying in time after phosphating and spraying immediately; ② Dehydrogenation at about 200℃ for 2h; ③ Adjust the parameters of phosphating solution, and pay attention to that the concentration of free acid should not be too high; ④ Replace the nozzle with fresh water, and clean the nozzle to make the water pressure >1.5 bar; ⑤ Temporarily stop using tap water, and detect that the pH value reaches 6 ~ 7; ⑥ Take fresh sample powder, age it according to standard conditions, and check the powder quality.
shrinkage cavity
The main reasons are: ① Water or oil enters the milling process. Its shrinkage cavities are evenly distributed, showing small round pits or large pinholes; (2) Other powders are mixed in the spraying process, resulting in shrinkage cavity due to incompatibility; (3) The spraying system is polluted by external interfering substances, including workpieces, especially the silicon-containing release agent and water release agent in the workshop; ④ There are large and deep holes on the casting surface; ⑤ The coating has a big round pit, commonly known as "fisheye"; ⑥ Compressed air has high oil content.
Solution: ① Contact the manufacturer to change the powder; ② The powder changing and cleaning room must be thorough, and it is best to arrange the cleaning and inspection procedures; (3) Carefully check the powder spraying site, eliminate these interfering substances, and strictly implement rules and regulations to prevent these interfering substances from being brought in; ④ Sand blasting should be thorough, and the castings can be preheated, and the preheating temperature and time depend on the material and thickness; ⑤ Adjust the parameters of degreasing section, clean up the pollution of drying and curing drying channels, and check whether the elevator and adhesive tape pollute the powder; ⑥ Check the filter of the compressor, install an oil-water separator, and discharge regularly in each shift.
The coating falls off locally or in a large area.
The main reasons are: ① there is a layer of rust on the surface of the substrate, which has not been completely removed; (2) water washing, especially after phosphating; (3) incomplete removal of oil on the surface of the substrate; (4) The lubricating oil on the lifting chain drips onto the workpiece; ⑤ The galvanized sheet bubbles and the coating falls off.
Solution: ① Rust removal should be thorough; (2) Check the flushing flow, water quality and nozzle, and check the flushing flow and pressure; (3) Chemical degreasing is more suitable for animal and vegetable oils. If it is not suitable for mineral oil, degrease it with alkali, strengthen water washing after degreasing, and pay attention to water quality; (4) Check the quality index of lubricating oil, replace the lubricating oil with high temperature resistance when necessary, or put the oil receiving tank below the oil dripping place;
The coating turns yellow and discolors.
The main reasons are: ① the set temperature of drying tunnel or oven is too high; ② Direct fuel gas enters the oven or drying tunnel; ③ The workpiece stays in the drying tunnel or oven for too long, or the conveyor chain stops running; ④ Powder quality; ⑤ The workpiece is baked repeatedly for more than 2 times; ⑥ The paint is seriously discolored.
Solution: ① Understand the normal curing conditions and make adjustments; (2) installing a heat exchanger; ③ Understand the baking situation, pay close attention to whether the conveyor chain operates normally during production, and if it is necessary to stop production, all workpieces should be baked and discharged; ④ The powder supply factory provides samples under different baking conditions for reference when spraying; (5) Try to finish baking at one time, and concentrate the workpieces that need to be baked twice, and first determine the conditions for repeated baking; ⑥ Check whether the baking temperature is too high, such as > 230℃ or higher. Check the temperature resistance of the powder. five
Gloss instability
The main reasons are: ① low gloss; 2 high gloss; ③ Gloss fluctuates up and down; (4) The gloss drops suddenly.
Solution: ① Check whether the baking temperature is too high or the baking time is too long, consult the powder factory for baking conditions, and also check the water content of the powder and the temperature of the spraying room; ② Check the baking temperature and time, and check the glossiness, workpiece thickness and baking conditions according to ①; (3) Whether the gas stove is directly used or not, and check whether there is any change in the ambient temperature of powder mixing and spraying. Check whether the temperature of drying tunnel and oven is stable; (4) Check whether the temperature is out of control, check whether the air compression system and oil-water separator work normally, and check whether other powders are mixed.
Local unevenness and instability of smoothness
The main reasons are: ① uneven film thickness; ② The particle size of powder changes greatly before and after; ③ High voltage breakdown; (4) The venturi tube is worn and the powder is uneven; ⑤ The powder conveying pipe used does not match the equipment; ⑥ The conveyor chain is crowded and the speed is uneven; ⑦ The perforated plate in the fluidization cylinder is damaged or partially blocked.
Solution: ① Strengthen the film thickness control, and check whether the powder supply, recovery and spray gun voltage of the powder injection system are normal; (2) notify the powder factory for inspection; (3) Reduce the powder feeding voltage, but ensure the normal film thickness, which can increase the powder discharging pressure or expand the distance between the spray gun and the workpiece; ④ Check and replace; ⑤ Contact the equipment supplier for inspection and replacement; ⑥ Overhaul the suspension chain to make it uniform; ⑦ Check the fluidization and repair the perforated plate.
sand
The main reasons are: ① uniform and compact appearance; (2) It is a protruding circle with few numbers; (3) a small amount of sand, two different sizes; (4) There are impurities on the surface of the workpiece, sometimes radial or slender; ⑤ A small amount of black particles.
Solution: ① Determine whether the film thickness meets the process requirements; (2) Check whether there are colloidal particles in the powder, and check whether the surface of the phosphating workpiece is clean and free of impurities; ③ It is mostly caused by unclean environment, so the environment must be kept clean at all times; (4) Check the powder quality, and the operator should try not to wear clothes and gloves that are easy to lose fine fibers; (5) colloid and other impurities fall on the clean floor in the drying tunnel. Clean and dry the tunnel regularly.
The spray gun does not produce powder or the amount of powder is getting less and less.
The main reasons are as follows: ① the material of powder spraying pipe is poor, and powder is easy to adhere to the inner wall of the pipe; ② Insufficient air pressure or air volume; (3) heating the powder conveying pipe, and the powder is agglomerated in the pipe; ④ The powder conveying pipe is bent and twisted; ⑤ The powder caked and could not be fluidized normally.
Solution: ① Replace the high-quality powder spraying pipe; (2) Check the air source and air pressure and adjust them; (3) A spray booth with air conditioning. Check the particle size of powder, if it is too coarse, notify the powder factory to correct it; (4) Check the powder conveying pipeline and adjust the placement position of the pipeline; ⑤ Sieve first, and change the powder if it cannot be improved.
Powder flow powder rod
The main reasons are as follows: ① uneven powder discharge when the spray gun starts to work; ② Powder spraying is too thick and the powder layer falls off; (3) Insufficient phosphating and vermicelli phenomenon; ④ The output of electrostatic gun is unstable.
Solution: ① Before formal spraying, let the spray gun spray for 3 ~ 5 minutes, and then enter the formal spraying after the powder is stable; (2) control the conditions of the spray gun, so as not to make the powder layer too thick, and control the conveyor chain to move smoothly without shaking; ③ Clean the phosphating nozzle to make it smooth; ④ Ask the equipment manufacturer to adjust the test.
Spray snowflakes twice.
The main reasons are: ① the voltage is too high; ② Excessive powder output; ③ The distance between the spray gun and the workpiece is too close; (4) phosphating the workpiece to be sprayed again.
Solution: ① reduce the voltage; (2) reduce the powder output, reduce the powder supply pressure and improve the atomization pressure; ③ appropriately increase the spraying distance; ④ The returned workpiece does not need phosphating, but only needs polishing and blowing.
Fly powder, low powder loading rate
The main reasons are: ① there is no high voltage or insufficient voltage in the electrostatic generator; ② The workpiece is poorly grounded; ③ The air pressure is too high; (4) The hanger has poor conductivity; ⑤ The powder quality is poor; ⑥ The air duct of the recovery device is blocked or the recovery system cannot work normally.
Solution: ① Check whether there is high voltage output; (2) check whether the transmission chain grounding is good; (3) reducing the powder outlet pressure; ④ Regular cleaning, paint removal or replacement; ⑤ Check the powder quality, such as particle size and resin content; ⑥ Check the air duct and fan.
The edge of the workpiece is exposed.
The main reasons are: ① the corners of the workpiece are too sharp; (2) Low curing temperature and long powder fluidization time; (3) The powder has poor electrification and less edge powder; ④ The melting viscosity of powder is too low; ⑤ The gelatinization time of powder is too long.
Solution: ① Repair the corner of the workpiece before spraying to make it arc-shaped; (2) If the curing temperature is properly raised, it is necessary to pay attention to whether the temperature resistance of the powder is good; (3) increasing the voltage, shortening the distance between the spray gun and the workpiece or appropriately extending the spraying time of the edge; (4) The powder factory must modify the formula; ⑤ The powder factory must modify the formula.
The yellow spots, wrinkles and local hammer marks disappeared.
The main reasons are: (1) square hangers are mostly used, and liquid accumulates in the hangers, which volatilizes or oozes when solidified; (2) The clothes rack is tilted in the opposite direction, so the accumulated water cannot be dried; (3) There is liquid on the workpiece, which cannot be completely dried.
Solution: ① Change the clothes hanger into a thin round stick shape; (2) The hanger inclines forward, which can discharge accumulated water in time; (3) improve the hanging mode of the workpiece, or modify the edge structure of the workpiece, so that there is no water when baking.
Coating acetone test failed.
The main reasons are: ① insufficient baking time or low temperature; ② The powder quality is not good; (3) The powder is out of date. Solution: ① Adjust the baking temperature and time, and then check; ② Powder factory improves powder quality; (3) Check the production date of the powder, and the expired powder can be used only if it is qualified.
The coating has poor impact performance and low adhesion.
The main reasons are: ① the phosphating film is too thick; (2) The baking temperature is low, and the powder is not completely solidified; ③ poor powder quality; (4) the powder is out of date; ⑤ The coating is too thick; ⑥ Incomplete oil and rust removal; ⑦ Mix two powders with different properties.
Solution: ① Coating phosphating parameters such as concentration, temperature and time; (2) adjusting curing conditions; ③ Powder factory improves powder quality; (4) Check the production date of the powder, and the expired powder can be used only if it is qualified; ⑤ Measure the film thickness and adjust the spraying parameters; ⑥ Strengthen pretreatment; ⑦ Strengthen site management.