Process Flow of Steel Plate Coating Line

1. Pretreatment

• Surface Cleaning: The steel plate is first subjected to a cleaning process to remove impurities such as rust, scale, and dirt. This is typically achieved through shot blasting. High-speed shot media are projected onto the steel plate surface, which effectively strips away the contaminants and also roughens the surface slightly to enhance the adhesion of the subsequent coating. The shot blasting equipment is carefully calibrated to control parameters like the intensity and coverage of the shot, ensuring thorough and uniform cleaning.

• Dust Removal: After shot blasting, any residual dust and debris are removed from the steel plate surface. This is usually done using suction or blowing devices to ensure a clean surface for the coating application.

2. Coating Application

• Primer Coating: A primer is then applied to the steel plate. The primer is selected based on the specific requirements of the steel plate's end use and the characteristics of the environment it will be exposed to. It is sprayed onto the surface using automated spray guns. The spray guns are adjusted to achieve a uniform and consistent layer of primer, with a typical thickness ranging from 15 to 25 micrometers. The spraying process is carried out in a controlled environment, such as a spray booth, to minimize overspray and ensure proper drying and curing of the primer.

• Intermediate Coating (if required): In some cases, an intermediate coating may be applied. This additional layer provides enhanced protection and can improve the overall appearance and durability of the final coating. The application process is similar to that of the primer, with careful attention paid to achieving the correct thickness and smoothness.

• Topcoat Application: The final topcoat is then applied. The topcoat determines the color and finish of the steel plate. It can be a variety of types, such as acrylic, polyurethane, or epoxy-based coatings, depending on the desired aesthetic and performance properties. The topcoat is sprayed evenly over the primed and/or intermediate coated surface, with a thickness usually between 30 and 50 micrometers. The spraying parameters are optimized to ensure a flawless and durable finish.

3. Curing

• Drying and Curing: After each coating application, the steel plate is moved to a curing area. The curing process involves allowing the coating to dry and harden. This can be achieved through natural drying at room temperature or, more commonly, by using heat curing. In heat curing, the steel plate is exposed to a specific temperature and humidity environment for a set period of time. The temperature and time are carefully controlled to ensure proper polymerization and cross-linking of the coating resins, resulting in a hard and durable finish. For example, a typical heat curing temperature for some coatings might be around 60 to 80 degrees Celsius, with a curing time of 30 to 60 minutes.

4. Quality Inspection

• Visual Inspection: The coated steel plates undergo a visual inspection to check for any surface defects such as pinholes, runs, or unevenness in the coating. Trained inspectors carefully examine each plate to ensure it meets the required quality standards.

• Thickness Measurement: The thickness of the coating layers is measured using specialized instruments such as thickness gauges. This ensures that the primer, intermediate coat (if present), and topcoat are within the specified thickness ranges, which is crucial for the performance and durability of the coating.

• Adhesion Testing: Samples of the coated steel plates may also be subjected to adhesion tests to verify that the coating is firmly adhered to the steel surface. This can involve methods such as cross-cut testing or pull-off testing.

5. Finishing and Packaging

• Trimming and Edging: Any excess coating or rough edges on the steel plate are trimmed and smoothed to give a clean and finished appearance.

• Packaging: The final coated and inspected steel plates are then packaged for shipment or storage. They are usually wrapped in protective materials such as plastic film or paper to prevent damage during handling and transportation.