Theory Study And Development On The Nested Screw Novel Extruder

The research object was only screw in the traditional extrusion theory and few studies were focused on the system of screw and barrel which was researched as the whole system in present paper.Based on the development and theory of the nested screw novel extruder,the design principle,feeding system,extrusion system,drive system,solids conveying model and solids temperature model,and melt conveying model and melt temperature model were studied herein.Based on the systematic design and theory analysis,the nested screw novel extruder with the diameters of 30mm and 90mm corresponding to inner screw and outer screw respectively was firstly developed in China with own independent intellectual property.Two-layer co-extrusion was made successfully using the single novel extruder.The research fills the national blank of coextrusion technology using single extruder.The key of the nested screw novel extruder was that one outer screw and one inner screw were nested.Outer screw and inner screw were drived by independent drive unit.Outer screw kept rotating and inner screw kept stationary or rotating opposite to outer screw.Rotating outer screw also worked as the barrel of the inner screw.The structures and functions of the nested screw novel extruder were analyzed using the systematic design principle,especially included the structures of feeding system,extrusion system,drive system,and double-layer bar die.The new solids conveying model and two-dimension non-isothermal model in solids conveying of the nested screw novel extruder were built.The effects of centrifugal force and material compressibility were firstly considered in the present solids conveying model and traction angle,pressure distribution and velocity distribution were discussed.The experimental result was in accord with the theoretical analysis.Interfaces temperatures in the locations of barrel inner surface,outer screw bottom and inner surface of the outer screw were solved using finite difference method.The effects of barrel temperature,screw speed,friction coefficients and pressure on the solids temperature were also discussed.The theoretical analysis and calculated results can provide the scientific basis for the correct design the geometric parameters and process parameters of the nested screw novel extruder. Considering the effects of positive drag flow due to barrel,positive displacement flow due to screw flight and opposite drag flow due to screw core together,the new melt conveying model and melt temperature model in melt conveying of the novel extruder were built.By comparison with the results of the literatures,the feasibility of this method was checked. Volumetric flow rate,velocity and equal velocity lines distributions and cross flow of inner screw were discussed.Theoretical analysis was in accord with the experimental result.The analytic solution of the melt temperature distributions was made by employing Laplace transformation method.The melt temperature distributions of inner screw and outer screw along axial and channel depth directions were simulated specially for power-law fluid.The work can provide the theoretical basis for the scientific design screw geometric parameters and setting process parameters of the nested screw novel extruder.Generally speaking,all the preliminary investigations can provide not only the theoretical basis for the development and application of the equipment,but also a new scientific research stage for the improvement of the polymer materials science and technology of China.