Academic literature on the topic 'Intermeshing counter-rotating twin screw extruders'

Polymeric fused filament fabrication technology (FFF), a subfield within additive manufacturing (AM), is becoming a contender for the reintroduction of the small-scale manufacturing of customized consumer products to a mass-production dominated world market. However, before this technology can be widely implemented, there remain significant technological hurdles to overcome. One issue that has been addressed at great length in other traditional polymer manufacturing fields is the inclusion of fillers in the component for physical property enhancement or the introduction of entirely new properties to the matrix material. Experiments conducted in this study examined the inclusion of carbon microfibers (CMFs) into the matrix material prior to the printing process, and the effect of different processing parameters on the final filler structure of the composite parts post printing. Prior work on microstructural evolution during extrusion in a 3D printer has been conducted computationally to study the effects of extrusion rate, matrix rheology, and nozzle geometry on fiber orientation [1]. It was found that varying the nozzle geometry generated significantly different microstructures, and that the remainder of the parameters could be varied to fine-tune microstructural characteristics. Findings indicated that, by varying the nozzle geometry from a converging to a diverging conical section, microstructures ranging from axially oriented (with respect to the extrusion direction) to radially oriented are theoretically possible. Current work performed on extruders and FFF platforms indicates that during the extrusion process, fibers tend to align very closely to the axis of extrusion in shear flow (i.e. converging or straight dies). However, in some applications, this may not be the most effective filler structure for property enhancement, so there remains interest in exploring methodologies for fiber rotation during extrusion. For this study, CMFs and acrylonitrile butadiene styrene (ABS) were compounded using a 28mm fully-intermeshing co-rotating twin-screw (CoTSE) extruder. 3D printer feedstock was manufactured in-house. A range of concentrations from 0%wt to 15%wt fabricated and tested. Analysis of the feedstock indicated nearly axial fiber alignment post-manufacture. This feedstock was then used in a Lulzbot TAZ4 printer to manufacture composite tensile testing specimens. Printed composite properties were then identified and compared to neat ABS and bulk composite properties. It was found that using a purely converging die, highly aligned filler structures were produced (with respect to the bead laid by the printer). Using a diverging nozzle, more random filler structures were produced. Improvements in both intra-layer properties were observed using the diverging nozzle geometries to reorient fibers during extrusion. Property improvements were not found to be as high as longitudinal properties for highly aligned filler structures. Using insights gained through these experiments, we are currently working on exploring added functionality for the composites using different types of fillers as well as multi-scale filler combinations.

In this study, the viscosity of high-density polyethylene (HDPE)-wood flour composites compounded in different processing condition was measured using the Hakke online rheometer (Hakke Proflow). Composites were prepared in an intermeshing co-rotating twin-screw extruder. Influence of HDPE melt index on the melt shear viscosities of the composites was studied. To investigate the viscosity in different processing condition, two screw configurations and three screw speeds were considered. The results showed that the effect of wood on increasing the viscosity was more pronounced in higher melt index HDPE composites. The viscosity decreased with increasing screw speed from 100rpm to 300rpm. In terms of screw configuration, both small-pitch conveying screw element and kneading elements with wide disks and large staggering angle were benefit to the flow of HDPE-wood composites. Medium shear should be selected to optimize the flow. Higher HDPE melt index wood composites processed in shear and longitudinal mixing flow field presented more shear-thinning behavior.

Polypropylene (PP)/nano-calcium carbonate (nano-CaCO3) composite was prepared using a co-rotating, intermeshing twin-screw extruder. The effect of flow fields on the morphology of the nanocomposite was investigated. Transmission electron microscopy (TEM) was used for the determination of the morphology in the nanocomposite. The crystallization behavior of the nanocomposite was studied by using differential scanning calorimetry (DSC) and the melt shear viscosity was investigated by a melt flow index tester. The study showed that the flow field, through appropriately combining the type of the screw elements in this work, plays an important role in developing morphology of the nanocomposite. In addition, it was shown that the melt viscosity for the nanocomposite at the filler content less than 10 wt% is lower than that of neat PP.

The addition of nano-scale and micro-scale fillers has been proven to increase tensile and thermal properties in polymer composites. Orientation of high aspect fillers, however, has not been studied before despite being crucial to altering physical properties. When fibers are included during extrusion, they tend to align in the direction of the flow. This phenomena leads to longitudinal improvements in mechanical properties, and thus provides great benefits in some applications; however, it is beneficial to have improved properties in the transverse direction as well. Therefore, it is crucial to study reorientation phenomena in composites. The purpose of this experiment is to study property enhancement resulting from fiber structure. The material properties are compared for the range of weight percentages of fillers. This is done for the purpose of finding an ideal fill concentration. Two dies are used to study different orientation distributions: straight and divergent. Thermal and tensile properties and optical micrographs are analyzed and compared. Composites were processed on a Coperion ZDSK-28mm co-rotating, fully-intermeshing, twin-screw extruder. Polybutylene terephthalate (PBT) was used as the polymer matrix. 0 W% to 2 W% multi-walled carbon nanotubes (CNTs) and 0 W% to 30 W% carbon microfibers (CMFs) were used as fillers. Preliminary results showed a clear trend in increased tensile strength of the composite with the increase of concentration of CMFs and CNTs in the slit die up to 25 W% CMF. After 25 W% CMF, however, there was a depreciation in properties. Similarly, thermal conductivity results have shown a clear peak at 25 W% CMF with 30 W% showing a decrease in thermal properties. Preliminary results for the divergent die showed that, with addition of carbon microfibers to the polymer matrix, thermal properties of the composite increased up to 15 W%, then dropped and increased again as more CMFs were added. In addition, on average, material extruded through the divergent die showed better results of thermal conductivity than that extruded through the slit die. This indicates that when using a diverging die, fiber become oriented perpendicular in relation to the direction of the flow, thus improving heat flow in the transverse direction.