Affect the powder electrostatic spraying quality of many factors
Because powder electrostatic spraying adopts powder coating, the recovery efficiency is high, the coating performance is superior, the production process is shortened, the cost is reduced, the process is simple and so on, so the powder electrostatic spraying is becoming more and more widely used.
The quality and effect of powder electrostatic spraying (finished product) are closely related to its equipment, process and coating. Therefore, in the application, according to the size of the workpiece, shape, coating requirements and other specific circumstances, select the appropriate spray Powder equipment, the use of a reasonable spraying process and the selection of appropriate powder coating and curing equipment, so as to obtain a good spraying effect, the following impact on the electrostatic spraying powder coating quality and effect of electrostatic spraying equipment, spraying process, etc. to the gate Described.
1. Powder electrostatic spraying equipment
Powder electrostatic spraying equipment mainly includes: 1) high voltage electrostatic generator; 2) gun; 3) powder feeder; 4) spray and recovery system; 5) compressed air; 6) curing furnace;
1) high-voltage electrostatic generator: it is the key to powder electrostatic spraying equipment; its high pressure for the powder on the workpiece adsorption capacity has a greater impact. In general, the voltage increases, the amount of adhesion increases, when the voltage exceeds a certain value, the amount of powder attached to reduce; voltage up to the powder dielectric breakdown, so that spray coating surface shrinkage, eye and other symptoms.
2) gun: the role of the gun is to fly the powder particles charged, and effectively atomized and sprayed to the workpiece; gun tip of the tip of the discharge part of the powder particles should have a strong charge effect, and as much as possible Atomization and diffusion, in order to obtain a higher powder rate. To meet the different
Spray the workpiece, should be equipped with a different deflector to change the spray pattern, to achieve better spraying effect, the nozzle should also be adapted to a different amount of powder, and not blocked.
3) Feeder: (Venturi pump, powder barrels, powder tube, etc.), it is also an important part of the spraying system, such as the feeder can not meet the requirements of the gun, even if the gun performance no matter how good, spraying work can not be carried out, The powder is required to make the amount of powder uniform and stable, in order to ensure the uniformity of the thickness of the coating, the other powder to the powder must also be able to adjust to meet the requirements of different coating thickness.
4) spray room and recovery system: spray room is the workpiece into the static dust powder work area, in order to effectively carry out electrostatic spraying, spray airflow disturbance can not be too large, generally controlled at 0.3-0.6m / s,
To prevent powder spray overflow, pollution of the environment. Powder recovery system, in the entire spraying equipment for reducing production costs, play a vital role, it should have a good ventilation system to ensure that no powder spill, and the amount of ventilation can be adjusted, the workpiece and the nozzle should be There is a distance, so as to avoid the impact of the coating on the coating.
5) Compressed air: The compressed air supplied to the spraying equipment should be clean and should never contain oil and water; and the pressure should be stable and should not fluctuate. The air pressure should not be too low, usually at 7 bar.
Powder electrostatic spraying process
Electrostatic spraying process should be based on the workpiece state, the size of the workpiece and the coating requirements to determine. Here are some of the main aspects of the process:
1) surface treatment: the workpiece surface treatment, must be oil to rust, to ensure that the surface of the workpiece is not fat, corrosion and moisture, so as to improve the adhesion of coated metal, phosphate film should not be too thick, otherwise it will affect the powder Coating adhesion and mechanical strength.
2) Spraying process: Spraying voltage should not be too high, for the workpiece cavity, corner parts and surface traps, spraying voltage should be reduced, while the gun powder is slightly higher; spray gun and workpiece spray distance to maintain appropriate According to the size of the workpiece, the shape to choose; spray powder to keep the powder uniform; the number of workpiece spraying should not be too much.
3) curing process: curing process must be strictly in accordance with the requirements of powder technical conditions and different parts of the temperature and time, the temperature is too high and too long, the coating will change yellow color, local aging, resulting in poor gloss and poor coating, if The curing temperature is too low and the time is too short to reach full cure, so that the mechanical strength and adhesion of the coating decreased significantly. Curing should try to make the furnace temperature uniformity, to avoid part of the regional temperature is too high or too low, and affect the performance of the coating; another baking of the workpiece should be far infrared satin heating components, hot air circulation to maintain a certain distance to To ensure uniformity of the curing temperature and to avoid being coated with the coating of the wind blown away.
4) coating process: the powder material is not the same, for the required spray voltage, spray distance is not the same, so according to the spray material to determine the choice of spray voltage and spray gun distance. The size of the powder particles affect the thickness of the coating, the powder is large particles, with strong power, but the leveling is not good, easy to have space caused by air needle. Small powder, with the power difference, but also easy to spray thicker parts, therefore, the powder coating should have a reasonable distribution of powder; the other powder coating should be placed dry, ventilated, ambient temperature does not masonry more than 40 ℃ conditions, So as to avoid powder damp caking.
Symptom, analysis, solution
Through the above spray equipment and process analysis, we can see that the choice of good spraying equipment and master the spray process parameters is very important, but also easy to analyze and solve problems,
But also can see the emergence of each symptom, is not a unilateral reason, but need to consider many aspects: "symptoms", "analysis of reasons", "solution" list is as follows: (common)
| symptom | Analyze the reasons | Solution |
1.The powder is not attached to the workpiece | 1.High pressure is not enough or no high pressure; 2. workpiece grounding is not good; 3. workpiece pre-treatment degreasing, rust, drying is not complete; 4. pressure is too high; 5. powder damp
| 1.Increase the voltage or check the high-voltage electrostatic generator; 2. Check the workpiece is grounded; 3. Check the pre-treatment is complete; 4. Adjust the air pressure; 5. Check the powder; |
| 2. No gun powder: | 1. Fluid powder without powder; 2. powder tube twist, blocking; 3. whether the powder fluidization; 4. suction tube and venturi pump is blocked; 5. powder at the nozzle at the hardening; 6. | 1.Increase the "fluidization gas"; 4. Check whether the block; 5 clean up; 6. Adjust the supply of air; the same time, |
| 3. Powder powder powder is not uniform: | 1.-6. Ibid; 7. Compressed air shortage and pressure fluctuations; 8. Whether the powder is damp; | 1.-6. Same as above; 7. Increase and stabilize the air pressure; 8. Check the powder; |
4. powder and workpiece ignition: | 1. Poor ground; 2. Spray gun and workpiece distance is too close; 3. Spray powder room powder concentration is too large; 4. Sprayer humidity is too high; 5. Spray gun, high pressure generator problem | 1. Check the ground; 2. Workpieces and gun to maintain a certain distance; 3. Reduce the pressure and check the recovery device; 4. Try to keep the humidity below 80 ℃; 5. Replace the advanced equipment; |
5. powder overflow flying: | 1. Recycling device is not normal; 2. Recycling pipeline may be blocked; 3. Improper adjustment, air pressure is too large, too much powder; | 1. Check the recovery device; 2. Check the pipeline; 3. Recalibrate, reduce the "supply of gas" and so on; |
| 6. After curing the coating with the workpiece adhesion is not strong, easy to fall off the bubble; | 1. Pretreatment is poor, oil, rust is not clean, cold is not ideal, the water is not drying; 2. The workpiece surface mechanical damage, so that the coating heating and cooling shrink or bubble to make the film easy to fall off; For the powder flow of oil and water; 4. powder has volatile ingredients; 5. curing, the holding time is insufficient; 6. high pressure; 7. grounding is not good; | 1. To improve the quality of compressed air; 4. Replace the powder; 5. Keep the temperature increase; 6. Improve the high pressure; 7 check the quality of the compressed air; Grounded’ |
| 7. Coating color uneven: | 1. powder problem; 2. curing temperature is inconsistent; 3. oven temperature is not the same point; | 1. Check the powder; 2. According to technical requirements; 3. Improve the temperature uniformity of the oven; |
| 8. Coating impact strength, poor adhesion, lack of hardness: | 1. Coating curing temperature and time is not appropriate; 2. Base metal untreated clean; | 1. According to the technical conditions of curing, and check the baking temperature and time; 2. Strengthen the surface treatment; |
| 9. pinhole |
| 1Adjust the voltage; 2. Increase the spray distance; 3. Reduce the amount of powder or spray time; |
| 10.Shrinkage | 1. The surface of the workpiece to the oil, rust is not clean; 2. The workpiece surface is not flat; 3. Mixed with other different types of powder; 4. The supply of impurities, oil, water; | 1. Strengthen the oil to rust; 2. Surface polished smooth; 3. After spraying to strengthen the clean-up; 4. Check the gas; |
| 11. orange peel | 1. Coating is too thick; 2. Check the type and quality of powder used; 3. Curing time, temperature improper; | 1. Master the spray process; 2. Choose good meet the requirements of the paint; 3. Adjust to the technical requirements; |
| 12. Uneven coating | 1. Workpiece and gun too close; 2. Spray gun and exhaust outlet too close; 3. High-voltage electrostatic generator high pressure instability; 4. Gun powder uneven; 5. Improper adjustment; 6. Workpiece pretreatment is not good ; 7. Before curing by the outside air, vibration, get collision, etc .; 8. Operator improper operation; | 1. Adjust the spacing; 2. Adjust the spacing; 3. Check the output voltage; 4. Adjust the powder evenly; 5. Re-adjust; 6. Reprocess; 7. Reduce the impact of the external environment; |
| 13. powder damp | 1. powder damp; 2. storage temperature of more than 40 ℃; 3. compressed air with water and oil pollution; 4 placed too long; | 1. Store in a dry place; 2. Temperature should be controlled below 40 ℃; 3. Check the oil and water separator; 4. Should not be placed too long, the construction is completed, to clean up the powder supply system equipment, used powder to be sealed To prevent moisture into; 5. Storage, there must be no heavy extrusion; 6. Packaging containers should be sealed; |