A STUDY OF THE ENTRY-REGION LENGTH OF CIRCULAR-EXTRUSION DIES

The flow properties of a visco-elastic fluid in the entry region of a circular die in the extrusion process have been investigated. Using th e proposed approach, the time required for the fully developed flow of a visco-elastic fluid can be predicted. It has been found that the fl uid flow will become fully developed when the residence time t(R) is s even times the relaxation time tau. On the basis of the results, an eq uation for calculating the entry-region length of circular dies has be en derived, and the entry-region length of two rubber compounds in cap illary extrusion has been determined, the results showing that the ent ry-region length is about 1 similar to 2 times the die diameter. (C) 1 998 Elsevier Science S.A.