1. Powder coating curing temperature and time
The curing process of the plastic powder is a process of chemical cross-linking to form a film. The ideal curing prerequisite for epoxy-polyester hybrid powder coatings is: 180℃, 20min (there are also plastic powders with other curing prerequisites, please refer to its imitation list).
If the curing temperature is too high and the plastic powder is too long, it will show signs of coating aging, and the white coating will turn yellow after aging. If the curing furnace plan is properly divergent and the temperature difference is too large, there will be a phenomenon of partial yellowing; at this time, the hot air circulation system should be increased, and the furnace temperature should be adjusted to a suitable scale. Generally, the coating becomes brittle after aging. Some manufacturers take too long to heat up. It takes 2-3 hours to rise from room temperature to 180°C. After reaching 180°C, the temperature is kept constant for 20 minutes. This is also easy and moderate curing. The oven should be sealed and kept warm. The temperature rise time is 20-40 minutes. . And make the external hot air convection each other, the temperature is even.
When using the far-infrared heating tube to heat up, pay attention to the distance between the workpiece and the heating tube (not less than 200mm). If the limited space of the garden is too close, the white coating will bake moderately and turn yellow, which can be between the workpiece and the heating tube. Add a piece of iron plate (thickness 1.5-2mm), perforate the steel plate, if allowed to reduce the "bake yellow" ability.
For coatings whose curing temperature is too low or the time is too short, the cross-linking film formation is not complete and the coating adhesion is poor. For matt and matte powders, the gloss is too high and the adhesion is poor. If this kind of problem is present, only need to be cured again reasonably to obtain a qualified product.
2. The impact of manipulation proficiency
The proficiency of the operators is also an important factor that affects the appearance quality of the coating and the spray area.
Manual manipulation is generally easy to control the coating thickness at 80-90μm under the premise of not leaking the bottom. When spraying, it should always be perpendicular to the workpiece. The left and right translation rate is average, and the upper and lower spacing is moderate, but the spray does not miss the spray. After the gun is shot, it is not aimed at the spraying part, and the powder is averaged before spraying (a small amount of spray guns have signs of powder spitting when they are just fired).
For iron wire, thin strip and tube-shaped workpieces, the powder output should be smaller, and the moving speed of the gun should be slower, generally the translation speed is 80-120mm/sec. For iron-like workpieces, because the powdering rate is high, the powder output can be adjusted larger, and the gun can be moved faster. These measures are effective means to ensure a high powdering rate and less powder recovery.
3. Supporting application with pre-treatment
For the coating of metal workpieces, the effect of pre-treatment is extremely critical. Pre-treatment refers to the complete removal of oil and rust (oxidized scale) on the outside of the metal before coating, and a natural phosphate film with superior bonding force to the coating is created. Comprehensive process.
For the finished iron sheet, it must be coated with a layer of anti-rust oil and attached to a lot of dust (cold plate), and the scale must be heavy. If it is not cleaned and painted, it will be like a high-rise building on a sandy bank. The effect can be imagined. !
Failure to clean it will not only greatly affect the adhesion, but also reduce the amount of plastic powder adsorbed on the outside, and the leveling of the outside is very poor, so pre-treatment must be done. For the part with pits on the outside, it is also necessary to apply conductive putty and dry naturally or at a medium temperature (100-120℃), and then sand paper until the outside is flat for coating treatment.
After shot blasting, the dust attached to the outside should be wiped (not clean with damp cloth). For the pits, the outside should be coated with conductive putty and dried naturally or at medium temperature (100-120℃ 30 minutes), and then polished with emery cloth until the outside is flat. Paint and dispose of the condition.
Fourth, the rare drawbacks in the painting process and countermeasures
Powder coating is a new technology and a new process in the modern coating industry, and it is also one of the new technologies that our country focuses on. It is applied to home appliances and other fields, and has great advantages. Powder coating is a high-protection, high-decoration coating method. To obtain a satisfactory coating effect, it is necessary to control the factors that affect the coating effect. As the operator of powder coatings, if they do not have sufficient knowledge of the disadvantages that are likely to occur in the coating process, they will be helpless to produce a qualified product or will be at a loss when there is a problem.
In the powder coating process, the divergence rate incurred due to the influence of circumstances, painting equipment, operator status, and pre-processing effects reached 80-90%, while the powder coating’s own account only accounted for 10-20%. Failure to accurately identify the source of the malpractice can make production helplessly proceed and cause major losses to the enterprise.