Research On Flow Field Of Three-layer Coextrusion Blown Film Die

Extrusion products with barrier property, transparency, printability,heat sealability and significantly decreased cost can be obtained by coextrusion technology, therefore coextrusion technology is being applied more and more broadly. With the massive consumer market, multilayer coextrusion blown film as one of the coextrusion products has vast potential for future development, in whose production process a coextrusion die is the core component. Stacked flat blown film die is attracting more and more attention with the properties of unlimited stacked layers and thermal insulation between adjacent layers. With features of the stacked flat die and a actually used flat spiral die taken into consideration, the flow channel geometry of three-layer coextrusion blown film die was built and then meshed by ICEM CFD with all-hexahedral elements, whose flow field numerical simulation was solved by POLYFLOW to analyse the pressure field, velocity field,interface shape and position. Influence of geometry parameters, material physical parameters and processing parameters on the flow channel was studied.It was shown that pressure drop of the layer distribution channel was relatively high and coextrusion channel low. Retention regions were found in layer distribution channel. Each layer tended to change the velocity distribution type of adjacent layers to its own when they met the coextrusion channel. Interface position change was found where each layer met the coextrusion channel.For the geometry parameters, the influence of incipient slit height was studied, it indicated that decreasing the value of incipient slit height can avail velocity distribution uniformity of each layer on outlet surface and thickness distribution uniformity of the first and third layers, also decrease the interface position fluctuation; the influence of outlet axial position was studied, it indicated that increasing the value of outlet axial position affect thickness distribution uniformity and interface position fluctuation very slightly.For the processing and material physical parameters, the influence of inlet volumetric flow rate and non-newtonian index was studied. Study of the former indicated that increasing inlet volumetric flow rate of the second layer can avail general thickness distribution uniformity of all the three layers on the outlets and decrease the interface position fluctuation,while be negative for general velocity distribution uniformity of all the three layers. Study of the latter indicated that increasing non-newtonian index of the second layer can avail velocity distribution uniformity of the first, the third layers and thickness distribution uniformity of the first layer, also decrease position fluctuation of interface 1.