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Screw Elements (screw + element)

Distribution by Scientific Domains
Chemistry42%

Selected Abstracts

A study of residence time distribution in co-rotating twin-screw extruders.

POLYMER ENGINEERING & SCIENCE, Issue 12 2003
Part I: Theoretical modeling
A theoretical model to determine the residence time distribution (RTD) in a co-rotating twin-screw extruder is proposed. The method consists of coupling a continuum mechanics approach with a chemical engineering one and allows us to obtain the RTD without any adjustable parameter. The process parameters are obtained using Ludovic® twin-screw modeling software, and ideal reactors are chosen to depict the screw profile. The influence of screw speed, feed rate and viscosity on RTD are described on a fictive screw profile. The predictions of the model are in qualitative agreement with literature data. The key point of this procedure is obviously the correct association between an ideal reactor and a screw element. [source]

Poly­[di­aqua-,4 -oxalato-di-,6 -phos­phato-tetrazinc]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2004
You-Ju Zhong
The structure of the title compound, [Zn4(C2O4)(PO4)2(H2O)2]n, which was synthesized under hydro­thermal conditions, consists of zinc phosphate layers joined by bridging oxalate ligands to generate a three-dimensional framework. An extended zinc phosphate layer lies parallel to the ab plane and within this layer there are helical chains, composed of ZnO6 octahedra and ZnO5 square pyramids, that run parallel to the b axis and coincide with the 21 screw element. The oxalate groups sit on crystallographic inversion centers. [source]

Evaluation of numerical simulation methods in reactive extrusion

ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2005
Linjie Zhu
Abstract Reactive extrusion is a complex process, and numerical simulation is an important method in optimizing operational parameters. In the current work, two different simulation methods, one-dimensional (1D) model and three-dimensional (3D) model, were introduced to predict the polymerization of ,-caprolactone in fully filled screw elements. The predicted results of polymerization progression under different simulation conditions based on these two methods were compared. The simulation results show that the simplifications and assumptions in 1D model make it difficult to capture the complex mixing mechanism, heat generation, and heat loss in reactive extrusion. 1D model is feasible only under particular conditions, such as low screw rotating speed, small heat from reaction, and small screw diameter, whereas 3D model is a more powerful simulation tool for much wider processing conditions. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 183,193, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20041 [source]

Wet granulation in a twin-screw extruder: Implications of screw design

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2010
M.R. Thompson
Abstract Wet granulation in twin-screw extrusion machinery is an attractive technology for the continuous processing of pharmaceuticals. The performance of this machinery is integrally tied to its screw design yet little fundamental knowledge exists in this emerging field for granulation to intelligently create, troubleshoot, and scale-up such processes. This study endeavored to systematically examine the influence of different commercially available screw elements on the flow behavior and granulation mechanics of lactose monohydrate saturated at low concentration (5,12%, w/w) with an aqueous polyvinyl-pyrrolidone binder. The results of the work showed that current screw elements could be successfully incorporated into designs for wet granulation, to tailor the particle size as well as particle shape of an agglomerate product. Conveying elements for cohesive granular flows were shown to perform similar to their use in polymer processing, as effective transport units with low specific mechanical energy input. The conveying zones provided little significant change to the particle size or shape, though the degree of channel fill in these sections had a significant influence on the more energy-intensive mixing elements studied. The standard mixing elements for this machine, kneading blocks and comb mixers, were found to be effective for generating coarser particles, though their mechanisms of granulation differed significantly. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2090,2103, 2010 [source]

Local mixing effects of screw elements during extrusion

POLYMER ENGINEERING & SCIENCE, Issue 3 2005
R.M. van den Einde
An in-line method was applied to determine local residence time distribution (RTD) at two places in a completely filled corotating twin screw extruder. Axial mixing effects of different types of elements were evaluated. Paddles +90° induced flow patterns that appear to be circular, both upstream and downstream, whereas paddles ,30° induced flow patterns that appear to be circular and mainly upstream. Transport and single-lead elements induced backflow. The results could be explained from pressure differences and direction of drag flow in the elements. All elements were characterized using an equivalent additional mixing length ,, dependent on the type of element and its position in the extruder, which may be practically useful for extrusion design. POLYM. ENG. SCI. 45:271,278, 2005. © 2005 Society of Plastics Engineers. [source]

3-D non-isothermal flow field analysis and mixing performance evaluation of kneading blocks in a co-rotating twin srew extruder

POLYMER ENGINEERING & SCIENCE, Issue 5 2001
Takeshi Ishikawa
We have developed a three-dimensional non-Newtonian and non-isothermal flow analysis of the twin screw extruder (TSE) using the finite element method. This code can simulate the fully filled parts of several kinds of screw elements, such as full flight screws, kneading blocks, rotors and their combinations. A marker particle tracking analysis has also been developed to evaluate the mixing performance of the screw elements. In this paper, simulations for the kneading blocks in a co-rotating TSE were carried out. The screw configurations are combinations of 2-lobe kneading blocks with several stagger angles and disk widths. The effects of screw configurations on pressure and temperature distributions are examined. We also evaluate the dispersive and distributive mixing via stress magnitude and area stretch obtained by marker particle tracking analysis. Additionally, we discuss the desirable stagger, disk width and their combinations that promote the mixing performance. [source]

Experimental investigation of the energy balance for the metering zone of a twin screw extruder

POLYMER ENGINEERING & SCIENCE, Issue 2 2000
Stephan Tenge
The object of this study is to investigate experimentally the mechanical power transported from the screws to the polymer melt, the heat dissipated in the polymer melt, and the heat transferred to the barrel of the metering zone of a co-rotating twin screw extruder. For the experimental investigations, different screw elements, mixing elements, and kneading discs are used. The experimental results for the dissipation show good agreement with known calculation models. For the calculation of the heat transfer, a new equation is used to calculate the mean temperature difference under consideration of the dissipation. The Nusselt-number can be calculated in good agreement with the experimental results as a function of the Brinkmann-number. [source]