Study On Solid Conveying Theory Of Tri-screw Extruder

Solid conveying is an important part of extrusion process, researching on it has veryimportant significance for improving solid conveying efficiency and productivity. Tri-screwextruder has excellent plasticizing, mixing and self-cleaning ability, however, so far there hasbeen little research on solid conveying theory of tri-screw extruder, therefore, studying onsolid conveying theory of tri-screw extruder is particularly important and meaningful.In this paper, solid conveying mechanism in tri-screw extruder was observed, describedand analyzed, the results showed that: in the upper and lower intermeshing region is positivedisplacement conveying, in the non-intermeshing region is solid friction conveying. In thispaper, physical model and mathematical model in the intermeshing region were established,throughput was also obtained. Meanwhile, this paper established physical model of non-plugsolid conveying in the non-intermeshing region, and then mathematical model was obtainedby the use of virtual work principle.We solved three-layer model of non-plug solid conveying,got average velocity of material, and then solid conveying efficiency in the non-intermeshingregion was obtained. By introducing transformation coefficient, the intermeshing region wasturned into non-intermeshing region, thus solid conveying in the intermeshing region andnon-intermeshing region was integrated into non-plug solid conveying, equivalent screwchannel fill ratio and solid conveying efficiency were obtained. This can provide theoreticaldirection for solid conveying of tri-screw extruder.In order to verify solid conveying theory established in this paper, some experimentswere done with particulate material (LDPE) and powder material (PP). The results indicatedthat theoretical throughput agree well with experimental throughput, this showed that solidconveying theory established in this paper was reasonable and correct. Results from theoryanalysis and experiment showed that: if screw channel fill ratio was certain, throughput willincrease as screw speed increases, there was a linear relationship between throughput andscrew speed; if screw speed was certain, throughput will increase as screw channel fill ratioand feeding speed increase; screw channel fill ratio will increase with the increase of feedingspeed; the increase of screw speed will result in the decrease of screw channel fill ratio; withthe increase of friction coefficient between screw and plastic, friction coefficient between plastic and plastic, throughput index increased at first and then decreased; the increase offriction coefficient between plastic and barrel will lead to the decrease of throughput index.The research will lay a foundation of further studies on tri-screw extrusion theory and providea theoretical guidance for designing tri-screw extruder.