Hot Melt Extrusion Welding Method for Steel Belt Reinforced Pipes
2021-06-021. Structure Principle of Hot Melt Extrusion Welding
This welding method adopts special hot air extrusion welding equipment. Firstly, heat the two pipe ends to be connected, then extrude molten polyethylene material via welding torch, so as to fuse and integrate polyethylene materials on both sides of the joint. It is a rigid connection way that forms an integral polyethylene structure.
Based on the principle of molecular thermal motion, the extrusion welding gun heats PE welding rods to turn them into viscous fluid and extrude them out. Meanwhile, the built-in hot air blower preheats the welding surfaces of steel belt pipes. Under external force, PE materials at the joint bond tightly, realizing sufficient molecular diffusion and interweaving, so as to firmly connect the pipes as a whole and achieve stable welding effect.
2. Key Construction Points of Hot Melt Extrusion Welding
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Before welding, check whether the pipe end faces are cut flat and trim uneven surfaces if needed. Align the welding position at the center of pipe corrugation troughs, and keep two pipes on the same central axis with ends closely matched. Reserve a joint gap of 1-3 mm for convenient welding, and the maximum gap shall not exceed 5 mm. Trim the joint locally from inside or outside of the pipe (inner trimming applicable for pipes above DN800) if the standard is not met. Keep the welding area clean and dry without dust or impurities, and polish inner and outer surfaces to remove oxide layers.
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Special welding rods matched with steel belt pipes shall be provided by pipe manufacturers. The rods shall be made of the same polyethylene material as the pipes or materials with excellent fusion compatibility, with uniform round cross-section and proper specification matching the welding torch. All welding rods must be kept clean, dry and free of stains.
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Qualified extrusion welding machines equipped with hot air devices are mandatory. The hot air system shall fully preheat polyethylene at pipe joints to ensure extruded molten material can fuse closely with pipe bodies. All welding seams shall be full and compact without missing welding or fracture defects.
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Double-sided welding (inner and outer sides) is required for pipes with diameter larger than DN800.
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Set proper melting material temperature and hot air temperature according to on-site ambient conditions, maintain stable welding pressure and reserve sufficient slow cooling time after welding.
In short, all welding procedures and operating specifications shall be strictly implemented in accordance with the official operation guidelines issued by the pipe manufacturer.
