Powder spraying process

1, electrostatic spraying process principle

Powder coating is sprayed on the surface of workpiece by electrostatic powder spraying equipment, and under the action of static electricity, powder will be uniformly adsorbed on the surface of workpiece to form powder coating; Powder coatings are baked at high temperature, leveled and cured to become final coatings with different effects. The spraying effect is superior to the coating process in mechanical strength, adhesion, corrosion resistance and aging resistance.

Step 2: Pretreatment

The pretreatment process directly affects the quality of powder coating, and poor pretreatment can easily cause the coating to fall off and blister. Therefore, we must attach importance to pretreatment.

Chemical pretreatment can be used for metal plate stamping parts. Namely: degreasing → derusting → cleaning → phosphating (or purification), etc. Most rusty or thick surface workpieces should be derusted by mechanical methods such as sandblasting and shot blasting, but after mechanical derusting, the surface of the workpiece should be clean and free of scale.

Blow putty. According to the defect degree of the workpiece, apply conductive putty, dry and smooth with sandpaper, and then proceed to the next process.

Protection (also known as coverage). If some parts of the workpiece do not need painting, they can be covered with protective glue before preheating to avoid painting.

Preheat. Generally, preheating is not required. If the coating is required to be thick, the workpiece can be preheated to 100 ~ 160℃, which can increase the coating thickness.

3, spraying

The workpiece enters the spray gun position of the powder spraying room through the conveyor chain to prepare for the spraying operation. The electrostatic generator releases high-voltage static electricity (negative electrode) to the space in the direction of the workpiece through the electrode needle at the muzzle of the spray gun, so that the workpiece can be removed from the workpiece.

The mixture of powder and compressed air ejected from the spray gun nozzle and the air around the electrode are ionized (negatively charged). The workpiece is grounded (grounded) through the hanger and the conveying chain, so that electric field powder is formed between the spray gun and the workpiece, which reaches the surface of the workpiece under the double push of electric field force and compressed air pressure, and a uniform coating is formed on the surface of the workpiece through electrostatic attraction.

4, baking and curing

The sprayed workpiece is sent to the drying room at 180 ~ 200℃ by the conveyor chain for heating, and the corresponding time (15-20 minutes) is kept for melting, leveling and curing, so as to obtain the required surface effect of the workpiece. Different powders have different baking temperatures and time. This should be paid attention to in the curing process.

Step 5: Clean up.

After the coating is cured, remove the protective layer and smooth the burr.

6, check

After curing, mainly check the appearance (whether it is smooth and bright, whether there are defects such as particles and shrinkage cavities) and thickness (controlled at 55 ~ 90μ m). Repair or repaint the detected defective workpieces such as missed spray, pinholes, bulges and bubbles.

7. packaging

After passing the inspection, the finished products will be classified and placed in transport vehicles and turnover boxes, and separated from each other by soft packaging cushioning materials such as foamed paper and bubble film to prevent scratches and wear (packaging can be made according to customer requirements).

Extended data

Outstanding advantages of powder spraying technology

1, a very thick coating can be obtained by one coating, such as coating100 ~ 300μ m. It takes about 4 ~ 6 times to coat with ordinary solvent, but this thickness can be achieved by powder coating at one time. The coating has good corrosion resistance.

2, the powder coating contains no solvent, no three wastes pollution, and improves the labor hygiene conditions.

3. The new technology such as powder electrostatic spraying is adopted, which has high efficiency and is suitable for auto production line painting; The powder has high utilization rate and can be recycled.

4. Besides thermosetting epoxy, polyester and acrylic acid, there are a large number of thermoplastic fat-resistant powder coatings, such as polyethylene, polypropylene, polystyrene, fluorinated polyether, nylon, polycarbonate and various fluorine-containing resins.

Powder coatings began to be used for protection and electrical protection. With the development of science and technology, it is widely used in automobile industry, electrical insulation, corrosion-resistant chemical pumps, valves, cylinders, pipelines, outdoor steel components, steel furniture, castings and other surfaces.

In China, experimental research on powder coatings has been carried out since 1960s, and it has been widely used in production.

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