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

With the rapid development of the Chinese economy and the continuous upgrading of the industrial structure,the demand for plastic films continues to grow,and at the same time,higher requirements are placed on the quality of plastic films.Traditional plastic films are mostly single-layer films composed of one material.The performance of this single-layer film is relatively single and cannot meet the needs of today's industrial development.Therefore,composite films composed of multiple materials have gradually become the mainstream of coated products in current market.Multi-layer co-extruded blown film is a kind of multi-layer composite film,widely used in aerospace,agriculture,food,medical,optics and other fields.The core of determining the quality of multi-layer co-extrusion blown film is the design of multi-layer co-extrusion blown film die.At present,the main domestic multi-layer co-extrusion blown film die processing companies mainly rely on surveying and experience when designing the die method,but this method has a long design cycle and consumes a lot of manpower and material resources,while computer-aided technology can solve these problems.Therefore,it is significant to use computer-aided technology to systematically study the three-layer co-extrusion film blowing die.Taking a practical three-layer co-extrusion film blowing die as the research object,the three-dimensional isothermal model of the flow channel was established by Polyflow software 1:1,and the flow field was simulated and analyzed.The influences of geometric parameters,process and the material parameters on the pressure field of the die channel,the uniformity of the velocity distribution at the outlet end,the degree of deviation of the interface from the theoretical interface,and the uniformity of the melt layer thickness distribution were systematically studied.Regarding the flow field of the die channel,the research shows that the pressure drop decreases continuously along the extrusion direction as a whole,and the pressure drop curve in the laminar distribution channel is distributed stepwise;the center of the spiral groove on the laminar distribution channel has the highest velocity,along the spiral the velocity in the radial direction of the groove gradually decreases,the velocity fluctuation of the confluence of the melt layers of the co-extrusion flow channel is large,and the secondary flow occurs.The flow rate of the melt in the compression section increases fastest and reaches the maximum at the end of the compression section.The value of the melt has shifted at the interface at the exit end of the die,the main manifestation is that both interface 1 and interface 2 are offset to the middle layer of the melt,that is,the thickness of the LDPE melt layer on both sides increases,and the middle HDPE melt layer thickness is reduced.In terms of the geometric parameters of the die,the effects of the inlet angle,the length of the shaped section,and the compression angle on the flow field of the three-layer co-extrusion film blowing die channel were systematically studied.The research shows that the length of the shaping section and the compression angle have no obvious effect on the position of the interface;the smaller the inlet angle,the longer the length of the shaping section and the smaller the compression angle,the better the uniformity of the outlet velocity distribution and the melt layer thickness distribution.uniformity.In terms of process and material parameters,the effects of inlet mass flow rate ratio,flow channel wall slip degree,and non-Newton index ratio of materials on the flow field of the three-layer co-extrusion film blowing die were systematically studied.Studies have shown that increasing the inlet mass flow rate ratio and non-Newtonian index ratio is not conducive to the uniformity of the velocity distribution at the outlet end,but is conducive to the uniformity of the melt layer thickness distribution;the smaller the wall slip coefficient,the more favorable the outlet velocity distribution Uniformity,stability of interface position and uniformity of melt layer thickness distribution.