The production of plastic-coated composite pipes is a complex and intricate process that combines the strength of metallic materials with the corrosion and abrasion resistance of plastic materials. Below are the main steps involved in the production of plastic-coated composite pipes:
Raw Material Preparation
Metal Pipe Preparation: Steel pipes, usually selected as the substrate, must meet certain dimensional and quality standards.
Plastic Raw Materials: Thermoplastic or thermoset plastics such as polyethylene (PE) and epoxy resin (EP) are commonly used for the plastic layer due to their excellent corrosion and abrasion resistance.
Steel Pipe Surface Treatment
Cleaning: Thoroughly clean the steel pipe surface to remove oil, dust, and other impurities.
Rust Removal: Use methods such as sandblasting or shot blasting to remove rust and oxide scale from the steel pipe surface, ensuring a smooth and flawless finish.
Phosphating or Passivation: Further treat the steel pipe surface to enhance adhesion between the coating and the steel pipe.
Coating Preparation and Application
Coating Preparation: Heat the plastic raw materials to a molten state for application. For thermoset plastics like epoxy resin, additives such as curing agents may be required.
Application Methods: Various methods include internal and external spray coating, curtain coating, fusion winding, and hot dip coating.
Internal and External Spray Coating: Use electrostatic adsorption to spray molten plastic powder onto the inner and outer walls of the steel pipe.
Curtain Coating: Apply plastic powder to the heated outer wall of the steel pipe using a curtain method through a sieve containing the powder.
Fusion Winding: Wrap materials such as hot-melt adhesive and polyethylene around the heated steel pipe using an extruder, forming a three-layer structure.
Hot Dip Coating: Immerse the steel pipe in molten plastic to form a coating in a single step.
Curing Process
Heat Treatment: After coating application, the steel pipe enters a high-temperature oven for curing. This step is crucial for ensuring a strong bond between the coating and the steel pipe. Typically, temperatures can reach around 200°C, causing the coating and steel pipe surface to undergo thermal fusion and curing, forming a complete integral structure.
Quality Inspection and Packaging
Quality Inspection: Conduct quality inspections on the plastic-coated composite pipes, including visual inspection, thickness measurement, adhesion testing, corrosion resistance testing, etc., to ensure compliance with relevant standards and requirements.
Packaging: Package the inspected and qualified plastic-coated composite pipes for transportation and use.
Other Considerations
Strictly control the process parameters of each step, such as temperature, time, and pressure, to ensure product quality.
Different plastic-coated composite pipes for various applications may require different production processes and raw material ratios to meet specific usage requirements.
