RADIAL WALL-THICKNESS PROFILING FOR SMALL PARISON DIAMETERS IN EXTRUSION BLOW MOLDING

Many complex blow molded parts demand wall-thickness influencing systems to achieve a homogenous wall-thickness distribution in the part. This way the converter can save material as well as cooling time and the productivity can be improved. For small parison diameters the standard systems cannot be used because of the high stiffness of the usually used deformable metal rings. A new die concept with rotating elliptical rings and an elliptical mandrel makes it possible to influence the flow channel height over the circumference. By different flow channel geometries the swell behavior at the die outlet can be influenced and the radial wall thickness distribution in the parison can be varied during extrusion. To separate the rotation of the rings and the polymer melt a fiber reinforced silicone diaphragm has been developed. Without a separation the parison would twist at the outlet and the position of the wall-thickness could not be controlled.