Studies On The Novle Extrusion Theory For Helically Grooved Single Screw Extruders

Grooved barrel single screw extruders were widely used to processplastics for molding because higher throughput and better pressure invariancewere revealed than before during extrusion. Based on the study of the novelextrusion theory in helically grooved single screw extruders, the solidsconveying mechanism, throughput model and energy consumption was deeplyresearched and detailed in this paper. By the systematic research andtheoretical analysis, the novel helically grooved single screw extruder withpositive conveying was first designed and manufactured. In the novel extruder,not the friction-drag conveying mechanism but the positive conveyingmechanism similar to that in the counter-rotating twin-screw extruder wasachieved, which made up for the technology blank of the single screwextrusion. The main research efforts are summarized as follows:1. In the theory, screw channel rotated against static grooves, whichbehaved as the cooperative twin-screws. They turned as two parallel arc plates,between which an arc-plate solid-plug composed of the solids embedded in thegroove and screw channel was assumed. By analyzing the forces and torque on the solid-plug, the boundary condition equations for positive conveyingwere built and used to guide the reasonable designs of the groove and screwgeometry to positively convey the solid-plug in the helically grooved feedzone, which achieved the effective control for solids conveying characteristics.2. After analyzing the forces on the solid-plug, the continuity equationand kinematic equation was resolved to obtain the pressure equation in thesolids conveying zone and the conveying velocity equation of the solid-plug inthe positive conveying mechanism. In addition, the effects of the groove andscrew geometry and the friction coefficients on the characteristics of thepressure distribution in the solids conveying zone were theoreticallyresearched and well verified with the experimental data. Based on these, thepressure-building mechanism with positive conveying was accurately revealedto achieve steady extrusion.3. A novel particle-size conveying model was proposed by the differentdimension relationships of the groove depth, screw channel depth and particlesize in the helically grooved feed section. In the model, shear interfaces insidethe solid-plug were determined and the effects of the different differentdimension relationships on the solids conveying mechanism on the shearinterfaces were discussed by the boundary condition equations for positiveconveying. After the theoretical analysis being examined by the measured data,the calculating models for the throughput and energy consumption of thesolids conveying zone were established with different solids conveying mechanisms.4. By the systematic analysis and theoretical research, the novel helicallygrooved single screw extruder with positive conveying was invented. On thebasis of the novel extruder, a specially designed instrument, called onlinetesting instrument of solids conveying zone for single screw extrusion, wassuccessfully developed to online measure the pressure, throughput and energyconsumption of the solids conveying zone.Generally speaking, all the preliminary research achievements canprovide not only the theoretical guideline for industrial application but also ascientific research stage for the improvement of the polymer materials scienceand technology of China.