EXPERIMENTAL-OBSERVATION ON ENTRANCE FLOW INSIDE EXTRUSION DIES

A flow visualization technique was employed to observe the flow fields at the entrance region inside extrusion dies. Four types of solutions , i.e., Newtonian, shear-thinning, Boger, and viscoelastic fluids, wer e used as test fluids. Entrance flows inside center-fed and end-fed di es of different configurations were examined. It was found that, even though the swirling motions appear in the entrance region of center-fe d dies, no vortex develops. Shear-thinning behavior tends to enhance s wirling, but fluid elasticity suppresses the swirling. On the other ha nd, vortices exist at certain end-fed die geometries, and vortices wil l grow if the fluid exhibits shear-thinning, yet fluid elasticity redu ces the size of vortices. Several inlet designs effective for eliminat ing vortices were studied.