Manufacture Technique

Pretreatment of the steel pipe surface

The oxide skin, oil pollution and impurities on the surface of the steel pipe are removed by shot blasting and rust removal process to achieve the cleanliness of Sa 2.5 level (ISO 8501-1 standard), and the surface roughness of 50-90 μ m is formed to enhance the adhesion of the coating. Then use compressed air to dust to ensure that the substrate is clean and dry.

Coating

Preheat with the FBE bottom coating

The steel tube is heated to 180-220℃ by intermediate frequency induction, and the molten epoxy powder (FBE) is evenly covered on the surface by electrostatic spraying technology. At high temperature, FBE melts and solidifies to form a dense bottom layer of 80-150 μ m, which has excellent cathode peel resistance and chemical corrosion resistance, and strong adhesion of acid and alkali resistance.

Coating of adhesive in middle layer

When the FBE layer is still in a molten state, coat the vinyl-acrylic acid copolymer (EAA) or vinyl-vinyl acetate copolymer (EVA) adhesive with a thickness of approximately 170-250 μ m. The adhesive is chemically bonded with the FBE and the subsequent HDPE layer at high temperature to effectively prevent the interlayer peeling.

HDPE outer layer molding

After heating and melting the high density polyethylene (HDPE) particles, the extruder spiral is wound around the adhesive layer and coated by extrusion winding process to form a 1.8-3.7mm thick outer protective layer. The HDPE layer is quickly finalized by water cooling, and has strong mechanical impact resistance, ultraviolet resistance and waterproof permeability, and adapts to the complex geological and climate environment.

Cooling setting

Through the rapid cooling of the water cooling system, the HDPE layer is crystalline and solidified, forming a protective shell with mechanical damage resistance and strong weather resistance.

Quality inspection and repair

1. Electric spark detection: use 15-30kV high voltage detector to scan the coating and check the pinhole, crack and other defects.

2. Thickness test: Magnetic thickness tester verifies that the thickness of each layer meets the ISO 21809 or DIN 30670 standards.

3. Adhesion test: peel test is used to ensure that the bonding strength of the adhesive layer is greater than or equal to 70N/cm.

When defects are found, they should be partially polished and remelted to ensure the integrity of the protective layer.