The rheological properties of rubber unvulcanized compounds have been investigated by using a Monsanto processability tester(MPT) and a set of capillary dies. It was found that the die-swell ratio(B) increased with increasing shear rate and the diameter ratio of the reservoir to the die( Dp/D) at the test temperatures. A mathematical model for describing the polymer melt die-swell in short die extrusion is presented in this paper,
B = (1 + 2KSr + 2/3K2S2r)1/4 where ? is the entry convergence flow parameter and Sr is the recoverable shear strain. Better agreement is show between prediction and measurement for experiments on the sample and data reported in references.