The production of plastic-coated composite pipes is a complex and precise process that combines the strength of metallic materials with the corrosion and wear resistance of plastic materials. Below are the main steps in the production of plastic-coated composite pipes:
Preparation of Raw Materials
Metal Pipe Preparation: Steel pipes are typically chosen as the substrate and must meet specific dimensional and quality standards.
Plastic Raw Materials: Thermoplastic or thermoset plastics such as polyethylene (PE) and epoxy resin (EP) are used for the plastic layer, offering excellent corrosion and wear resistance.
Surface Treatment of Steel Pipes
Cleaning: The steel pipe surface is thoroughly cleaned to remove oil, dust, and other impurities.
Rust Removal: Rust and oxide scale on the steel pipe surface are removed by sandblasting, shot blasting, or other methods to ensure a smooth and flawless surface.
Phosphating or Passivation: Further treatment of the steel pipe surface to improve adhesion between the coating and the pipe.
Preparation and Application of Coating
Coating Preparation: Plastic raw materials are heated to a molten state for coating application. For thermoset plastics like epoxy resin, additives such as curing agents may be required.
Coating Methods: Various coating methods include internal and external spray coating, curtain coating, fusion winding, and hot-dip coating.
Internal and External Spray Coating: Using the theory of electrostatic adsorption, a spray gun is used to apply molten plastic powder to the inner and outer walls of the steel pipe.
Curtain Coating: The plastic powder is applied to the heated outer wall of the steel pipe through a sieve using a curtain method.
Fusion Winding: Materials such as hot-melt adhesive and polyethylene are wound around the heated steel pipe through an extruder to form a three-layer structure.
Hot-Dip Coating: The steel pipe is dipped into molten plastic to form a film 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 unit.
Quality Inspection and Packaging
Quality Inspection: Plastic-coated composite pipes undergo quality inspections including appearance inspection, thickness inspection, adhesion test, corrosion resistance test, etc., to ensure compliance with relevant standards and requirements.
Packaging: Qualified plastic-coated composite pipes are packaged for transportation and use.
Other Considerations
During production, strict control of process parameters such as temperature, time, and pressure is required at each stage to ensure product quality.
Plastic-coated composite pipes for different applications may require different production processes and raw material ratios to meet specific usage requirements.
