The operation of individual extrusion welder is different, but below are some general tips for extrusion welding:
Avoid large temperature differences between components as it can cause considerable strain - for example, with a rise in temperature of 10°C a steel tube 10m in length will experience an expansion of 1.2 mm whereas a PE tube 10 m in length will experience an expansion of 34.0 mm.
Welding speed depends on the output capacity of the extruder and the seam volume, some important things to remember are:
All hot air and extrusion joints need to have a root bead on the opposite side to avoid cracking and give more strength to the weld. It is necessary to weld into the welding root.
Starting the weld: Before beginning the welding operation, the welding shoe must be warmed up, since a rough and uneven surface of the welded seam is obtained if welding is carried out with a cold welding shoe. The warm air available or the warm extrudate are suitable for warming up.
Continuing the weld: Keep extruder perpendicular to weld surface. The welding shoe must be aligned centrally with the weld and must not come into contact with the weld edges around it’s nose.
Weld cooling: The thermal contraction and the shrinking during cooling may cause residual stresses and even blowholes. Especially big extrusion welds of polypropylene tend to show shrink-induced blowholes in the center of the extrudate. In order to avoid this, the weld seam is covered with a special fabric after welding. The fabric must be sufficiently heat resistant. e.g. aramid (Kevlar).
Welding Seam Preparation
Welding area & weld rod must be:
General Welding Parameters
Common Welding Problems
Building of blowholes and vacuoles: