Process Flow of Valve Coating Line

The valve coating line is a crucial process to enhance the appearance, durability, and corrosion resistance of valves. The following is a detailed description of its typical process flow:

1. Incoming Inspection

Before valves enter the coating line, a comprehensive incoming inspection is carried out. This includes checking the valve's dimensions, surface condition (for any scratches, dents, or casting defects), and material quality. Only valves that meet the specified quality standards are allowed to proceed to the next stage.

2. Pretreatment

2.1 Degreasing

The valves are first subjected to a degreasing process. They are placed in a degreasing tank or passed through a degreasing spray system. Alkaline or solvent-based degreasers are used to remove any oils, greases, or other contaminants from the valve surface. The degreasing time and temperature are carefully controlled to ensure effective cleaning. After degreasing, the valves are rinsed thoroughly with clean water to eliminate any remaining degreaser residues.

2.2 Shot Blasting (Optional)

For valves that require a rougher surface profile to improve coating adhesion, shot blasting may be employed. Small metal pellets or beads are propelled at high speed onto the valve surface, creating a uniform and clean textured surface. This process also helps to remove any loose oxides or scale from the valve body.

2.3 Phosphating (Optional)

In some cases, a phosphating treatment is carried out. The valves are immersed in a phosphating solution, which reacts with the metal surface to form a thin phosphate layer. This layer acts as a good base for the subsequent coating, enhancing adhesion and providing additional corrosion protection. The phosphating parameters such as concentration, temperature, and immersion time are precisely adjusted according to the valve material and coating requirements.

3. Coating Application

3.1 Spray Coating

• The valves are transferred to a coating booth equipped with spray guns. For painting lines, the paint is atomized and sprayed onto the valve surface. The spray guns can be adjusted in terms of spray pattern, paint flow rate, and air pressure to achieve a uniform and smooth paint coating. Electrostatic spray guns may also be used, where the paint particles are charged and attracted to the grounded valve, resulting in higher transfer efficiency and better coverage.

• For powder coating lines, the powder coating material is charged electrostatically and sprayed onto the valve. The charged powder adheres to the valve surface, and any overspray is collected and recycled through a recovery system.

3.2 Dipping Coating (for Valve Dipping Molding Line)

In the valve dipping molding line, the valves are immersed in a tank of liquid plastic or coating material. The valves are slowly dipped into the tank and then withdrawn at a controlled speed, allowing a layer of the coating material to adhere to the surface. The thickness of the coating can be adjusted by controlling the viscosity of the dipping material and the speed of dipping and withdrawal.

4. Curing

• After coating application, the valves are sent to a curing oven. For paint coatings, the oven heats the painted valves to a specific temperature range, usually between 60°C and 150°C, for a certain period, typically 30 minutes to 2 hours, depending on the paint type and thickness. This process allows the paint to dry, harden, and develop its final properties.

• For powder coatings, the curing temperature is usually higher, ranging from 150°C to 200°C, and the curing time is around 10 to 30 minutes. The heat causes the powder particles to melt, flow, and cross-link, forming a hard and durable coating.

5. Cooling and Quality Inspection

5.1 Cooling

Once the curing process is completed, the valves are allowed to cool. They can be cooled naturally in a cooling area or by using forced-air cooling systems. Cooling is necessary to handle the valves safely and to prevent any damage to the coating due to rapid temperature changes.

5.2 Quality Inspection

After cooling, the valves undergo a quality inspection. This includes visual inspection for any coating defects such as runs, sags, bubbles, or uneven coating. The coating thickness is measured using non-destructive testing methods such as magnetic induction or eddy current gauges to ensure it meets the specified standards. The valves are also checked for proper sealing and functionality. Any valves that do not pass the quality inspection are either reworked or rejected. The valves that pass the inspection are then ready for packaging and shipment.