In extrusion, weld lines are formed in the production of hollow profiles shaped by dies encompassing torpedoes supported by spider legs, or when flow separators are used with a view to improve the flow distribution, solution commonly employed in inherently high unbalanced dies. Weld lines are known to have a detrimental effect on the mechanical performance of the extruded profiles and may also affect their aesthetics. However, the subject is rarely reported in technical literature. Consequently, there are no guide-lines to assist decisions concerning the location/geometry of the spider legs or information on the extruded profile loss of mechanical performance promoted by the use of flow separators.
In order to study in detail the consequences of the formation of weld lines in extruded profiles, a prototype extrusion die system was conceived aiming to produce tapes with a weld line formed in varied and controlled conditions and also without weld line. In this work, the referred prototype system was used to assess the effect of the following variables on the weld lines quality: axial location where the independent flow fronts merge (three locations along the flow channel), extrusion flow rate and temperature, and polymer system (an amorphous polymer, polystyrene, and a semi-crystalline one, polypropylene). For comparison purposes the tapes produced with and without weld line were characterized by tensile and flexural tests.
