Dies
After passing through the breaker plate molten plastic enters the die. The die is what gives the final product its profile and must be designed so that the molten plastic evenly flows from a cylindrical profile, to the product's profile shape. Uneven flow at this stage would produce a product with unwanted stresses at certain points in the profile. These stresses can cause warping upon cooling. Almost any shape imaginable can be created so long as it is a continuous profile.” (Wikipedia, Extrusion, 8/13/2009)
Recent US Patents
1/4/2011
7,862,755
Constant shear rate extrusion die
Elgindi, Wisconsin, developed an extrusion die for extruding thermoplastic materials to produce a sheet of substantially uniform thickness with a manifold width that increases from the centerline toward the die exit or lip. The increasing width manifold arms, with the preland portion, provide a constant shear rate at all areas of the die and a constant residence time, so that every fluid particle path through the die has the same residence time. By having the increasing width manifold arms, the preland area of the extrusion die is decreased, usually by about 30%, often about 40-60%, compared to a Winter die, thus decreasing clam-shelling effect and allowing design and extrusion of wider sheets. (RDC 7/18/2011)
Recent Journal Articles
Design feature sensitivity analysis in a numerical model of an extrusion spider die
(3537–3543) Journal of Applied Polymer Science 122 #6 (2011)
Mamalis, Kouzilos and Vortsela of the National Center of Scientific Research and the National Technical University of Athens, Greece developed an optimum design for a spider die used for the extrusion of high-density polyethylene tubes. For this purpose, a computational-fluid-dynamics-based model using the generalized Newtonian approach was employed to investigate the pressure drop, flow, and temperature uniformity in the die. (RDC 9/7/2011)
In situ fibrillation of polyamide 6 in isotactic polypropylene occurring in the laminating-multiplying die
(237–245)Polymers for Advanced Technologies 22 #2 (2011)
Shen et al of Sichuan University, China prepared polyamide 6 (PA6)/isotactic polypropylene (iPP) in situ fibrillation composites using an extrusion die with an assembly of laminating-multiplying elements (LMEs). These elements elongate, break, and stabilize the dispersed PA6 phase in the iPP matrix along the flowing direction (FD). The morphology development of PA6 with different LME numbers greatly affects the rheological properties, crystalline behaviors, and mechanical properties. The dynamic rheological test performed at 195°C shows that the increased spatial restriction of the high-aspect-ratio PA6 particles increases the viscoelastic moduli, complex viscosity, and relaxation time. The crystalline analysis reveals that the heterogeneous nucleation becomes predominant and the transcrystalline morphology is observed in those samples produced by more LMEs. The tensile tests indicate that both, breaking strength and elongation, enhanced simultaneously because of the fibrillation of dispersed phase and the improvement in interfacial adhesion between the fibers and the matrix. (RDC 2/4/2011)