Simulation Analysis Of Head Flow In The Three-layer Blow Film Extrusion Process

Application of plastic film is wide, mainly used in packaging industry, textile industry and aerospace. In the forming methods of plastic film, the most widely used method is extrusion blow molding, the three elements of extrusion blow molding which are summed up by the practice, reasonable extrusion process, advanced extrusion equipment, and efficient extrusion head and setting devices. In the extrusion equipment, the extrusion head is an integral part, the structure of head in the production of film products plays a decisive role. Analyzing flow field of head is the most critical part, various parameters were not only the efficiency of production, but also the life of head mold,the precision of products,the cost of mold tooling and the improvement of process methods. Extrusion die is import in machining process of blown film, researching the flow field of head is greatly significance.Using PRO/E to establish the solid model of head mandrel, importing it into GAMBIT, and using Boolean operation to establish the 3d model of spiral flow, the fracture surface is less in meshing by this kind of method to establish model, it can compartmentalize grid directly, without repairing the model additionally. Compartmentalize grid of the geometric model directly by GAMBIT,because head flow is complex, dividing it into tetrahedron grid will be good.According to the structure characteristics and the material properties of head flow, making assumption,and using the basic knowledge of fluid mechanics to establish mathematical model.Finite element method is applied to analyze flow, importing grid file into FLUENT, setting physical parameter, exerting boundary conditions, using software to compute fluid equation, analyzing the residual diagram, and then analyzing the pressure distribution diagram and the velocity distribution diagram of head flow, analyzing and explaining distribution diagram,finally summarizing the pressure distribution rule and velocity distribution rule, analyzing the uniformity of the exit speed. Researching the uniformity of flow distribution by qualitative approach. Using two ways to research the uniformity of flow qualitatively, analyzing the velocity distribution of the section and the velocity circumferential distribution diagram of the ring section. According to the first kind of diagram it can see the uniformity of speed distribution on section,it can observe the speed changing along the circumferential direction directly from the second kind of diagram.Analyzing the changes of entrance velocity, buffer tank length, case-hardened length and the non-newtonian index bring some influence to flow field, summarizing the flow field changing rule of the different parameters changing,analyzing the parameters changing bring some influence to the uniformity of exit speed, inlet pressure and pressure drop. Results show that changing entrance velocity and non-newtonian index bring greate influence to the uniformity of exit velocity distribution, inlet pressure and pressure drop, but changing buffer tank length and case-hardened length has not any influence to the uniformity of the exit velocity distribution nearly.And it also has very big effect to the inlet pressure and pressure drop.The study provides the basis of optimization flow structure to people.