Experimental studies on radial extrudate swell and velocity profiles of flowing PS melt in an electro‐magnetized die of an extrusion rheometer

Abstract

This article investigates the radial extrudate swell and velocity profiles of polystyrene melt in a capillary die of a constant shear‐rate extrusion rheometer, using a parallel coextrusion technique. An electro‐magnetized capillary die was used to monitor the changes in the radial extrudate swell profiles of the melt, which is relatively novel in polymer processing. The magnetic flux density applied to the capillary die was varied in a parallel direction to the melt flow, and all tests were performed under the critical condition at which sharkskin and melt fracture did not occur in the normal die. The experimental results suggest that the overall extrudate swell for all shear rates increased with increasing magnetic flux density to a maximum value and then decreased at higher densities. The maximum swelling peak of the melt appeared to shift to higher magnetic flux density, and the value of the maximum swell decreased with increasing wall shear rate and die temperature. The effect of magnetic torque on the extrudate swell ratio of PS melt was more pronounced when extruding the melt at low shear rates and low die temperatures. For radial extrudate swell and velocity profiles, the radial swell ratio for a given shear rate decreased with increasing r/R position. There were two regions where the changes in the extrudate swell ratio across the die diameter were obvious with changing magnetic torque and shear rate, one around the duct center and the other around r/R of 0.65–0.85. The changes in the extrudate swell profiles across the die diameter were associated with, and can be explained using, the melt velocity profiles generated during the flow. In summary, the changes in the overall extrudate swell ratio of PS melt in a capillary die were influenced more by the swelling of the melt around the center of the die. Polym. Eng. Sci. 44:2298–2307, 2004. © 2004 Society of Plastics Engineers.

Effects of Roller Speed, Die Temperature, Volumetric Flow Rate, and Multiple Extrusions on Mechanical Strength of Molten and Solidified LDPE under Tensile Deformation

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Hardness, adhesion index and microstructure of PEEK coating on Al or Fe substrate by LVOF flame spray

“…The mechanism for the magnetic field effect on the degree of crystallinity was associated with a large diamagnetic anisotropy of the benzene molecules within the PEEK molecules, which resulted in the magnetic torque acting on the polymer molecules. The magnetic torque, occurring as a result of the motion of the existing electrons and distortions of the electron clouds within the benzene rings within the PEEK molecules, can be sufficiently large to induce appreciable orientation and alignment of the molecules [28,29]. If so, the molecular configuration and alignment changes of the melt while coated on the substrate, to some extent, would change, and this led to the changes in molecular crystallization during the cooling.…”

Flow visualization & extrudate swell behavior of natural rubber compound in annular die capillary rheometer

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