One、How to dissolve powder coating
Powder coating involves spraying without dissolution. Powder electrostatic spraying utilizes the principle of high-voltage electrostatic corona fields. A high-voltage negative electrode is connected to the metal guide plate at the spray gun head, while the workpiece is grounded to form a positive electrode, creating a strong electrostatic field between the spray gun and the workpiece. When compressed air is used as the carrier gas, the powder coating is sprayed from the powder hopper through the nozzle to the guide rod of the spray gun, where the electrostatic discharge generated by the high-voltage negative electrode on the guide rod creates a dense negative charge in its vicinity, causing the powder to acquire a negative charge and enter a high-intensity electrostatic field. Under the combined action of electrostatic force and carrier gas, the powder is uniformly sprayed onto the grounded workpiece surface to form a uniform coating, which is then heated and solidified to form a durable coating. The construction process includes: pre-treatment, drying, spraying, inspection, baking, inspection, and finished product.
Two. How to use powder coatings
1、Pre-treatment
The quality of the pre-treatment process directly affects the quality of the powder coating film. Poor pre-treatment leads to issues such as film detachment and blistering. Therefore, pre-treatment work must be given due importance.
For sheet metal stamped parts, chemical pre-treatment methods can be used. This includes: degreasing → rust removal → cleaning → phosphating (or passivation), etc. For most parts with significant rust or thick surface corrosion, mechanical methods such as sandblasting and shot blasting can be used to remove rust. However, after mechanical rust removal, it is essential to ensure that the surface of the parts is clean and free of residue.
Apply putty powder according to the extent of defects on the workpiece. After drying, smooth the surface with sandpaper, and proceed to the next step.
Protection (also known as covering). If certain areas of the work piece do not require a coating, they can be covered with protective tape or other materials before preheating to prevent the application of the coating.
Preheat. Preheating is generally not required. If a thicker coating is desired, the workpiece can be preheated to 100～160℃, which will increase the coating thickness.
2、Spraying
The workpiece is conveyed to the spraying gun position within the spray booth, ready for application. The electrostatic generator releases high-voltage static electricity (negative polarity) from the electrodes in the gun nozzle towards the workpiece.
The powder and compressed air mixture exiting the spray gun, along with the ionized air around the electrode, creates an electric field. The workpiece, secured by a fixture and connected to the grounding pole, is then subjected to double forces: the electrostatic force and the pressure of the compressed air. This allows the powder to reach the surface of the workpiece, forming a uniform coating due to electrostatic attraction.
3、Curing by baking
After powder coating, the coated articles are conveyed onto a conveyor belt and then transferred to a curing oven with a temperature of 180～200℃. They are heated and kept at this temperature for the required time (15-20 minutes), which allows the coating to melt, level, and solidify, resulting in the desired surface finish. (Different powders require different curing temperatures and times.) This is an important step in the curing process.
4、Cleaning
After the coating has cured, remove the protective covering and smooth out any rough edges.
5、Inspection
The finished products should be primarily inspected for appearance (smoothness, gloss, and absence of defects such as particles, shrinkage, and etc.) and thickness (controlled within 55～90μm). For products with defects such as overspray, pinholes, scratches, and bubbles, repair or re-application should be performed.