Production Process Flow of Pretreatment and Powder Coating Line

1. Loading Process

Operators neatly place workpieces to be processed (mostly metal materials, such as hardware parts, auto parts, etc.) on the automated conveyor belt. The conveyor belt sends the workpieces to the subsequent processing links at a preset speed. During this step, it is necessary to ensure that the workpieces are placed stably to prevent displacement or falling during transportation.

2. Pretreatment Process

This process is the core of ensuring coating quality and mainly consists of four key steps:

Degreasing and Derusting

Workpieces first enter the degreasing tank and derusting tank. With the help of chemical agents (such as degreasers, derust agents), oil stains, dust, oxide scales and rust on the workpiece surface are removed, laying a foundation for subsequent coating adhesion. The concentration of chemicals and processing time need to be accurately adjusted according to the degree of oil stains and rust on the workpieces.

Water Washing and Cleaning

After degreasing and derusting, the workpieces enter the water washing tank. Flowing clean water is used to rinse off residual chemical agents on the surface, preventing the residual agents from affecting subsequent processes. Usually, 2-3 water washing procedures are set up to ensure the workpiece surface is clean.

Phosphating Treatment

The cleaned workpieces enter the phosphating tank, where a uniform and dense phosphating film (mostly gray or colored) is formed on the surface. This film can significantly improve the corrosion resistance of the workpieces and at the same time enhance the adhesion between the subsequent powder coating and the workpiece surface. The phosphating temperature is generally controlled at 30-50°C, and the treatment time is about 5-10 minutes.

Drying

The workpieces that have completed phosphating enter the drying oven. Hot air circulation (with a temperature usually of 80-120°C) is used to completely dry the moisture on the surface, avoiding defects such as bubbles and pinholes in the powder coating caused by moisture. The dried workpieces must remain in a dry state before entering the spraying process.

3. Powder Spraying Process

Workpieces are transported by the conveyor belt into a closed spraying booth, which is equipped with electrostatic spray guns. Under the action of high-voltage static electricity, the spray guns atomize the powder coating (such as epoxy resin powder, polyester powder, etc.) into charged particles. These charged particles are adsorbed onto the surface of the grounded workpieces, forming a uniform-thickness powder coating (the coating thickness can usually be adjusted between 50-150μm according to requirements). During the spraying process, it is necessary to control the dust concentration in the spraying booth to ensure the safety of the working environment.

4. Curing Process

The sprayed workpieces enter the curing oven. The curing oven heats the workpieces according to a preset temperature curve (usually at a temperature of 160-220°C with a heat preservation time of 15-30 minutes). This causes the powder coating on the workpiece surface to gradually melt, level, and finally solidify into a hard and smooth protective film. The curing temperature and time must be strictly controlled: if the temperature is too low or the time is insufficient, the coating will not cure completely, which affects its wear resistance and corrosion resistance; if the temperature is too high or the time is too long, the coating may discolor or age.

5. Cooling and Unloading Process

After being sent out of the curing oven, the cured workpieces are first cooled down by natural cooling or an air-cooling system (cooled to near room temperature to prevent scalding from high-temperature workpieces or damage to the coating during subsequent handling). When the temperature drops to a safe range, operators remove the workpieces from the conveyor belt and inspect the coating appearance (checking for defects such as sagging, missing spray, pinholes, etc.). Qualified workpieces move to the next link (such as assembly, packaging), while unqualified workpieces undergo rework (such as paint stripping before re-entering the production line)