Sharkskin instabilities and the effect of slip from gas-assisted extrusion

The effect of die exit curvature, die surface roughness and a fluoropolymer additive on sharkskin extrusion instabilities in polyethylene processing

“…A reduction in sharkskin would, therefore be expected for certain levels of partial slip. Further details and results of partial slip simulations are given in [45]. …”

“…It was a parallel slit die with 90 • entry and exit angles and a larger gap width of 3.8 mm. The geometry is different to those described previously as this set of simulations were carried out for a related program, further details of which can be found in [45]. The parameters used were for Dowlex at 190 • C. In order to simulate partial slip the simplest law available in polyflow was used, defined as: where f s is the friction at the wall, v s the velocity tangential to the wall and f slip is the slip coefficient.…”

Effects of the Process Conditions on the formation of the Gas Layer in the Plastic Profile Gas-assisted Co-extrusion Processes

“…Since then, Huang Li and Qian Bainian [2,3] also successfully applied the gas-assisted molding technology in rubber production. In 2001, Liang RF et al [4] applied the gas-assisted molding technology in the polymer extrusion process for the first time and found that the technology could effectively relieve the swell phenomenon of extruded products and improve the quality of the extrusion and co-extruded products [5][6][7][8][9][10]. Current studies of the gas-assisted molding extrusion were mostly focused on numerical simulation and related experimental data were seldom reported.…”

An experimental evaluation of the formation of an instability in monodisperse and polydisperse polystyrenes

“…There are a number of reviews on viscoelastic instabilities [1][2][3][4][5][6] and a recent review [6] highlighted three forms of polymer instability observed in extrusion which occur at increasing levels of flow deformation. These are the "Sharkskin" instability [7][8][9][10][11], the "stick-spurt instability" [12][13][14], and "upstream extrusion instabilities", also termed "gross melt fracture" or "volume instabilities" [15][16][17][18][19][20][21][22][23][24].…”