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1.
A mathematical model was proposed for the characteristics of solid transportation in the feeding zone of an intermeshing co-rotating
twin screw extruder. The model was based on the observations made from a “transparent” extruder. The analysis considered optimal
solid conveyed with maximum throughput rate, i.e., when the upper and lower intermeshing zones, and the two sides of the screws
were all partially filled with solid resin to an extent that a slight increase in the solid filling would immediately cause
blocking of the solid transportation. Because of these starve-fed characteristics, the conventional approach for analysing
solid feeding used in single-screw extruders was inadequate for twin-screw extruders. This paper also suggests a solution
for the mathematical expressions describing the stress and velocity fields in the solid feeding zone of a twin-screw extruder.
Finally, the predicted values are compared with our experimental findings. 相似文献
2.
Chris J. Rauwendaal 《Polymer Engineering and Science》1981,21(16):1092-1100
Twin screw extruders can he classified according to their geometrical configuration. The main distinction is made between intermeshing and nonintermeshing extruders. Another distinguishing characteristic is the sense of rotation. The most important characteristics of the various twin screw extruders are examined, with particular emphasis on the effect of screw geometry on the conveying characteristics. A brief review is given of the state of the art in theoretical analysis of twin screw extruders. Experiments with two lab scale, intermeshing twin screw extruders are described, one co- and one counterrotating. Results are presented on power consumption, residence time distribution, and mixing characteristics of the two extruders. The counterrotating extruder exhibits a narrower residence time distribution and better dispersive mixing capability. The corotating extruder showed a better distributive mixing capability. These results can be explained in terms of the conveying and mixing mechanisms in both extruders. The overall extruder performance seems to be dominated by the effect of the intenneshing region. Any realistic, theoretical analysis of twin screw extruders should be centered around the flow behavior and mixing characteristics of the intermeshing region. The corotating extruder appears to be best suited for melt blending operations, while the counterrotating extruder seems to be preferred in operations where solid fillers have to be dispersed in a polymer matrix. 相似文献
3.
A novel melting model for single screw extruders with a grooved melting zone was established. The whole solid plug, which came from the grooved feed zone, was ruptured and melted mainly by continuously changing the volume of the barrel grooves and the screw channel in the grooved melting zone. A new single screw extruder platform with hydraulic clamshell barrels was constructed to investigate the melting of solid polymer with different combinations of barrels and screws. The melting model was verified by experiments. The results showed that the melting started earlier and finished in a shorter length for single screw extruders with a grooved melting zone than that for conventional single screw extruders and the melting efficiency was improved by introducing a grooved melting zone to a single screw extruder. The theoretical values are consistent with experimental results. The novel single screw extruder with grooved melting zone can dramatically increase the plasticizing efficiency and the throughput. 相似文献
4.
Trihono Sastrohartono Yogesh Jaluria Mukund V. Karwe 《Polymer Engineering and Science》1995,35(15):1213-1221
A new simplified approach has been proposed for the numerical simulation of the thermal transport in corotating, tangential, and self-wiping twin-screw extruders. It is assumed that the flow domain in a twin-screw extruder can be divided into (i) the translation region (T-region), which represents a flow similar to that in a single-screw channel and (ii) the intermeshing region (I-region), which is located between the two screws. The two regions are simulated separately and then coupled for each screw section to model the overall transport in tangential and self-wiping twin-screw extruders. A finite difference method is employed for the developing flow and temperature fields in the T-region, in order to minimize the computing effort, while a finite element method is employed for determining the interchannel flow mixing and the thermal transport in the I-region. Results are obtained in terms of temperature, velocity, and pressure variations along the screw channels and mixing between the two screws. 相似文献
5.
Krzysztof Wilczyński 《Polymer-Plastics Technology and Engineering》2013,52(3):449-477
A fully predictive computer model has been developed for a single-screw plasticating extrusion (with conventional screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, melt conveying) and the die, and describes an operation of the extruder-die system, making it possible to predict a mass flow rate of the polymer, pressure and temperature profiles along the screw channel and in the die, solid bed profile, and power consumption. Moreover, mixing degree, temperature fluctuation and viscoelastic properties of the polymer are estimated. The simulation parameters are the material and rheological properties of the polymer, the screw, hopper and die geometry, and the operating conditions (screw speed and barrel temperature profile). Such a comprehensive approach to the modeling of extrusion creates the possibility of optimizing the process, for example, from the point of view of the quality of extrusion. The model has been verified experimentally for a low-density polyethylene on a 45 mm diameter single-screw extruder. 相似文献
6.
Theoretical model for intermeshing twin screw extruders: Axial velocity profile for shallow channels
Charles E. Wyman 《Polymer Engineering and Science》1975,15(8):606-611
Positive displacement intermeshing twin screw extruders have been analyzed by a simple model for flow in the channel formed by the screw root and screw flights. The model considers the down channel flow to be a combination of drage flow resulting from the relative motion of the barrel and screw and pressure flow resulting from the positive displacement action of the device. The pressure flow in this situation is distinguished from pressure flow in a single screw extruder in that the pressure forces induce flow toward the die for the twin screw model rather than away from the die as in a single screw extruder. Comparison of the down channel shear rate profile of apositive displacement twin screw extruder with that of a single screw extruder with no net flow reveals that they are identical but inverted with respect to channel depth. The model presented does not consider leakage between the twin screws or the rotational motion of the second screw. 相似文献
7.
利用EDEM软件对一种普通锥形和两种双锥型螺杆挤出机固体输送段进行模拟.分析了高密度聚乙烯(PE-HD)颗粒在锥形双螺杆挤出机内的运动状态和分布规律.对比分析了3种锥形螺杆挤出的质量流速率、填充率、平均速度、平均压力、平均剪切应力和力矩等参数,给出了普通型和双锥型螺杆挤出机固体输送机理以及主要影响因素.结果表明,相比于... 相似文献
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9.
In many operations in polymer processing, such as polymer blending, devolatilization, or incorporation of fillers in a polymeric matrix, continuous mixers are used; e.g., corotating twin-screw extruders (ZSK), Buss Cokneaders and Farrel Continuous Mixers. Theoretical analysis of these machines tends to emphasize the flow in complex geometries rather than generate results that can be directly used (1–5). In this paper, a simple model is developed for the hot melt closely intermeshing corotating twin-screw extruder, analogous to the analysis of the single-screw extruder carried out in 1922 and 1928 (6, 7). With this model, and more specifically with its extension to the complete nonisothermal, non-Newtonian situation, it is possible to understand the extrusion process and to calculate the energy, specific energy, and temperature rise during the process with respect not only to the viscosity of the melt, but also to the screw geometry (location and number of transport elements, kneading sections and blisters, pitch, positive or negative, screw clearance, and flight width) and screw speed. To support the theoretical analysis, model experiments with a Plexiglas-walled twin-screw extruder were performed, in addition to practical experiments with melts on small- and large-scale extruders, with very reasonable results, In Part 2, the Buss Cokneader will be analyzed analogously. 相似文献
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12.
The flow of chemically reactive non‐Newtonian materials, such as bio‐polymers and acrylates, in a fully intermeshing, co‐rotating twin‐screw extruder is numerically investigated. A detailed study of the system transient behavior is carried out. The main transient aspects, including response time, variation of system variables, and instability of operation, are studied for both single‐ and twin‐screw extruders, since single‐screw extruder modeling closely approximates the region away from the intermeshing zone in a twin‐screw extruder. The effect of a time‐dependent variation in the boundary conditions is studied. The coupling due to conduction heat transfer in the screw barrel is found to be very important and is taken into account for single‐screw extruders. In the absence of this conjugate coupling, the response time is much shorter. Several other interesting trends are obtained with respect to the dependence of the transient response on the materials and operating conditions. Steady state results are obtained at large time. The calculated velocity distributions in the screw channel are compared with experimental results in the literature for steady state flow and good agreement has been obtained. The calculated results for transient transport agree with the few experimental observations available on this system. Chemical reaction, leading to chemical conversion of the material, is also considered and the resulting effects on the flow and transport determined. These results will be useful in the design, control and optimization of polymer extrusion processes. 相似文献
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14.
Ning He Wang 《Polymer Engineering and Science》2007,47(11):1920-1926
The concept of surface renewal for polymer devolatilization (DV) in screw extruder was defined based on the traditional penetration theory, and a measuring criterion and comparing methods for comparing surface renewal devolatilizing performance (SRDP) between different extruders and between different types of extruders were proposed based on this concept and the extrusion–devolatilization theory previously developed by the authors. Their proprieties were further verified by using the literature data obtained in a single screw extruder (SSE) and an intermeshing co‐rotating twin‐screw extruder (ICoTSE). Moreover, the effects of some important screw geometry factors on the SRDPs of both the extruders were discussed, and the comparisons of the SRDPs between them and between types of SSE and ICoTSE were given and discussed. POLYM. ENG. SCI., 47:1920–1926, 2007. © 2007 Society of Plastics Engineers 相似文献
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16.
An innovational vane extruder made polymeric materials endure an elongation stress that was much larger than the shearing stress in the extrusion process. The operating principle of the vane extruder was completely different than that of conventional screw extruders. As the first stage of polymer processing in the vane extruder, the process of solids conveying was composed of feeding, compacting, and discharging. Most of the energy was consumed in the compacting process of polymer particulate solids in this stage. A mathematical model was developed to analyze the power consumption in the process. The model showed that the power consumption was mainly influenced by the structural parameters of the vane extruder, including the rotor diameter, eccentricity, and axial width of the vane unit. The analysis indicated that more energy was used to generate pressure in the vane extruder than in a screw extruder. The theoretical model was verified by the experimental results. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
17.
Huiwen Yu Baiping Xu Biao Liu Yaoxue Du Jian Song Yanhong Feng 《Polymer Engineering and Science》2020,60(1):151-160
Fill degree is a key parameter impacting twin screw extruders' (TSEs) mixing performance and melting behavior. The conventional conveying model of partially filled fluid relies mainly on empirical methods. A nontwin screw geometry introduces a speed difference between the two intermeshing screws to change the conveying means, and this speed difference offers a challenge for establishing a new conveying model. A visualization prototype with a global transparent barrel was developed in this article with carboxymethylcellulose sodium solution used as working fluid. Fill length was measured under different outputs and screw rotation speeds in a nontwin screw channel versus a corresponding twin screw channel; thus, fill degree was obtained using the observed fill lengths and nontwin screw geometries. A new conveying model of partially filled fluid was proposed which isolated positive displacement flow as an independent factor, and visualization observations revealed that due to differences in screw flight width, the positive displacement flow in a nontwin screw channel is larger than that in a traditional twin-screw channel. Results showed that dimensionless positive displacement conveying increased linearly with fill degree for a non-TSE geometry while it was independent of fill degree for a TSE geometry. POLYM. ENG. SCI., 60:151–160, 2020. © 2019 Society of Plastics Engineers 相似文献
18.
A knowledge of flow behavior is important in the study of laminar flow in twin-screw extrusion processes to predict the velocity distribution and to understand the mixing process. The flow of a power law fluid in self-wiping twin-screw extruders is examined using a two-dimensional finite element analysis of a mid-channel section of intermeshing screws. Theory is compared with experiment using food biopolymer and plastic materials. Comparisons showing overprediction of throughputs, but similarities in behavior, suggest that this model could provide an upper limit for melt conveying. For most of the throughput range examined, pumping of intermeshing self-wiping screws appears to be almost independent of the power law flow index of the melt extruded, but the value of the flow index determines the degree of influence intermeshing has on the overall pressure gradient generated in the extruder. 相似文献
19.
R. C. Donovan 《Polymer Engineering and Science》1971,11(3):247-257
A theoretical model for melting in plasticating extruders is described. Compared to previous models, this model introduces more accurate and less restrictive assumptions, adds a mass balance on the entire channel, and replaces certain approximate solutions by exact solutions. Flow of the solid bed is represented by a solid bed acceleration parameter, SBAP, which permits solid bed acceleration in a screw compression section. New experimental melting data for a variety of screw designs, polymers, and extruder sizes are presented and compared to the theoretical predictions. With the optimum SBAP, reasonably accurate model prediction of the melting profiles is observed for a wide variety of cases. 相似文献
20.
Laminar mixing in a single screw extruder between two miscible liquids is considered. Studies are presented which examine the mixing performance in single screw extruders with mixing sections, variable geometry screws, and multi-viscosity mixtures. Model extruders, set up on engine lathes, were used to mix colored silicone rubber which eventually cured in the screw channel. The cured silicone was then removed and sliced to measure the mixing. Results show mixing as a function of both down channel location and total average strain. For the mixing section study, results support the theory of interfacial area reorientation as the key mechanism in mixing section performance. Increasing viscosity ratio for the multi-viscosity study showed a decrease in mixing rate. 相似文献