Study On Fluid Flow Characteristics In Melt Spinning

Spinning pack is one of the core elements of the spinning apparatus, its role is to filter out impurities from the melt and to establish a certain pressure of components, in order to mix the melt fully and spin stable fiber from the spinneret orifice eventually. The flow of melt in the components and the outlet nozzle hole uniform or not will directly impact the performance of the fiber, the uniformity of a single filament and the stability of fiber spinning. Because spinning needs high temperature and pressure, it’s difficult to observe the flow state inside of the components and to get visualizational data. In the paper, an visualizational experiment platform of flow filed in the spinning pack was established. We studied the motion of fluid in the spinning pack and the uniformity of spinneret extrusion systematically. The influence of porous media on the performance of PA6 melt flow also be studied by hot model experiments. It provides a reliable basis for designing the new fiber module with optimized structure.In the paper,syrup solution was used as analog medium,and through controlling the temperature, PAM solution concentration to control its viscoelasticity. At low shear rates, Rheological properties of syrups solution is Newtonian fluid;shear viscosity show shear thinning behavior with the increase of shear rate, showing pseudoplastic fluid properties,it’s similar to PA6 melt.With the increase of the added amount of PAM, the storage model "G’" and loss modulus "G"" have increased;and die swell ratio(B) increased With the increasing of the amount of PAM or the extrusion rate.Comparing melt rheological properties with syrup solution,they have similar rheological curve,The shear viscosity and number of Wi can be close in a certain range of shear rate,indicating that the syrup solution adding a certain amount of PAM is feasible as an analog medium.Throughing visualization methods,we have directly observated flow condition in component.Results showed that:the fluid residence time is difference in the sand cavity;material flow out in a shorter time in the cavity surrounding than the center; In addition,porous media (sand filtration, the filter) is present, it can be made more uniform flow.We Used PIV testing methods to study the velocity of fluid flow in cavity.The results showed that:when there is no filter, the fluid flow from the over-flow distribution plate cover to have a process converge toward the center, however when this flow trend weakened after adding the filter;the velocity of the fluid flow does’t have significantly affect to the trajectory;From Observing velocity in different regions, the we have found that flow velocity around the inflow chamber is fastest than the center of the cavity or wall,the fluid speed in overcurrent and sand cover around just below the cavity wall is very slow.Observing the state of fluid flow before the nozzle plate,the results showes that:material start to diffuse from the diversion hole in spinneret deflector,and velocity is reducing with increasing of radial;The arrangement of the inner hole of the nozzle plate have a significant impact on the flow of fluid.Fluid radially outwardly from the guide hole diffusion,when there is no filters,will give priority to direct outflow nozzle hole of the inner ring,and on the outside of the hole will produce retention area; When there is a plate filter, it will make the material easier to flow out along the gap between the baffles and screens,helping to improve the uniformity of the extrusion nozzle plate.Automatic metering system was used to study each nozzle orifice spinneret extrusion uniformity.The results showed that:Viscoelastic fluids are not equal in each circle hole,When there’s no filter plate in front of Spinneret,the nozzle plate flow law is:inner circle is more than middle circle,and middle circle is more than outer circle;Spinneret unevenness of total flow rate is decreasing with the increase of the viscoelasticity of the syrup solution;as the same to the fluid flow rate increases, beneficial for the uniformity of fiber; Spinneret pore size is smaller, more conducive to improving the spinneret uniformity;if spinneret holes arranged in a more uniform, the smaller the overall spinneret uneven rate;when there’s a filters in spinneret,increasing the uniformity of the spinneret pressure,so that eventually the overall eccentricity is reduced.As the PA6 melt flowed through porous media,the pressure difference increased with velocity and has reduced along with melt temperature growth.With the increase of flow rates,the pressure difference dependents of temperature become more sensitive.The relationship of pressure difference and flow velocity of PA6 melt in porous media could be described by the Forchheimer equation. The inertial resistance factor was lager two orders of magnitude than the viscous drag factor at 265℃,and both of them has reduced along with melt temperature growth.The pressure difference was mainly from viscous losses as PA6 melt flowed porous medium.The inertia of the loss caused by the elasticity was proportional to the flow rate.The filtration precision is higher, the increase is more obvious.