Plastic journeyman
Methods for assembling plates, tubes and membranes
Thermoplastic can be welded because the material softens when heated and melts together when two surfaces are brought into contact under pressure and then cooled. This distinguishes thermoplastic from thermoset which cannot be welded. Common materials are PE (polyethylene), PP (polypropylene), and PVC used for pipes, sheets, containers, and membranes.
§Material knowledge is a prerequisite
You can only weld plastic types that fit together — PE is welded to PE, PP to PP. If the materials are confused, the joint becomes weak or without bonding. Therefore, the material is identified before work, and the welding parameters are adjusted to the specific plastic, because melting temperature and behavior vary from type to type.
§Hot air welding
With hot air welding heated air is blown at the seam and a filler wire of the same material is pressed into the softened seam. The method is widely used for sealing membranes foil joints and minor sheet work and requires a stable interaction between temperature air velocity feed rate and pressure.
§Mirror-reversed square signals
With mirror welding the pipe ends are heated against a hot mirror (a flat heating plate) after which the mirror is removed and the ends are pressed together and held under pressure while the joint cools. The method is used for PE and PP pipes and gives a strong homogeneous joint when the ends are clean flat and aligned correctly.
§Extrusion and electrofusion welding.
Extrusion welding supplies melted filler material from an extruder and is used for stronger plate joints and containers. Electrofusion uses fittings with built-in resistance wires: when power is applied, the wires heat the plastic so fitting and pipe melt together. Electrofusion is common with PE pipes because the method is relatively robust against contamination and gives uniform joints.
§Clean surfaces and control
Regardless of method, the same basic principle applies: understand how colour is transferred to the material and you understand how to troubleshoot and improve the result.