The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform

T Jager - One of the best experts on this subject based on the ideXlab platform.

  • mixing effects of constituting elements of mixing Screws in Single and twin Screw Extruders
    Powder Technology, 1999
    Co-Authors: D.j. Van Zuilichem, E Kuiper, W Stolp, T Jager
    Abstract:

    Abstract In extrusion, mixing of solids and melts has always been problematic, leading to diverse models describing the melting process. It is found that for foods based on cereals, only a few are valid, due to the simultaneous presence of water and high viscous non-Newtonian material. Mixing trials are summarised for Single and twin Screw Extruders, with particulate solids of different particle sizes like, maize grits, wheat flour, sucrose crystals and glucose syrup. Special mixing-heads for Single Screw Extruders like, pineapple-heads, and slotted flight sections for counter-rotating twin Screw Extruders are investigated. The effects of Screw geometry on mixing has been measured using co-rotating twin Screw extruder modular elements like: Single lead elements, mixing paddles and reversed pitch elements in a translucent model extruder by means of a study of flow phenomena and residence time distribution (RTD) measurements. Mixing effects are reported and their influences on viscous dissipation, residence time, curve spread and stagnancy are explained.

Hezhi He - One of the best experts on this subject based on the ideXlab platform.

  • effect of the axial vibration of Screw on total shear strain distribution of melt in Single Screw Extruders
    Journal of Applied Polymer Science, 2008
    Co-Authors: Yanhong Feng, Jinping Qu, Hezhi He
    Abstract:

    Single Screw Extruders are known as good melt pumps with the high, stable pressure needed for part extrusion. However they have a particular disadvantage in achieving good mixing. In a vibration-induced polymer extruder (VIPE), a vibration force field (VFF) is introduced into the whole extrusion process by the axial vibration of Screw, which affects the mixing process. It is well-known that the total shear strain (TSS) has been widely used to measure the effect of melt mixing in a laminar system. In this study, an analytic model for pulsating TSS was developed and the TSS distribution of the melt in the Screw channel of the melt conveying section in a VIPE was calculated to further understand the time-dependent dynamic laminar mixing process. A comparison of the TSS distribution of melt in Screw channel with and without vibration shows that the TSS of melt increases with the application of vibration and the larger the vibration frequency and amplitude are, the larger the TSS that the melt may experience while melt traveling through the melt conveying section, which is favorable for melt mixing. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

  • effect of Screw axial vibration on polymer melting process in Single Screw Extruders
    Journal of Applied Polymer Science, 2006
    Co-Authors: Jinping Qu, Yanhong Feng, Guansheng Zeng, Hezhi He
    Abstract:

    A model for investigating the melting process of polymer in a vibration-induced Single-Screw (VISS) extruder is presented. The key feature of this model is as follows: vibration force field is introduced into the overall course of extrusion by the axial vibration of the Screw, and the velocity distribution in the polymer melt behaves strongly nonlinear and time-dependent. To analyze this model, half-open barrel visible experimental method and low-density polyethylene material are adopted to investigate the effect of the vibration parameters on the melting process, which goes into further details of study and research on the melting mechanism, and thus, a novel physical melting model is derived. Combining the conservation equations of mass, movement, energy, and constitutive, analytical expressions of the melting rate, the energy consumption, the length of melting section, and the distribution of solid bed are obtained. This model enables the prediction of the processing and design parameters in the VISS Extruders from which the optimum conditions for designing VISS extruder and polymer processing are obtained. The theory is supplemented by a calculation sample and experiment, which shows that the introduction of vibration force field can improve the melting capacity and decrease the power consumption of extruder greatly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3860–3876, 2006

  • effect of the axial vibration of Screw on residence time distribution in Single Screw Extruders
    Polymer Engineering and Science, 2006
    Co-Authors: Jinping Qu, Yanhong Feng, Hezhi He
    Abstract:

    An analytic model has been developed to analyze the residence time distribution of melt in the Screw channel of the melt conveying section in a novel extruder of which the Screw can vibrate axially. A comparison of the residence time distribution of melt in Screw channel with and without vibration shows that the residence time of melt increases with the apply of vibration and the larger the vibration frequency and amplitude are, the longer time it will take the melt to travel through the melt conveying section, which is in favor of the improvement of the effect of melt mixing. POLYM. ENG. SCI. 46:198–204, 2006. © 2005 Society of Plastics Engineers

José A. Covas - One of the best experts on this subject based on the ideXlab platform.

  • a quantitative approach to assess the mixing ability of Single Screw Extruders for polymer extrusion
    Journal of Polymer Engineering, 2012
    Co-Authors: N. Domingues, A Gasparcunha, José A. Covas
    Abstract:

    The financial support of the Portuguese Science Foundation (FCT - Fundacao para a Ciencia e Tecnologia) under grants POCTI CTM/48448/2002 and SFRH/BD/19605/2004 is gratefully acknowledged.

  • morphology development of immiscible polymer blends during melting in Single Screw Extruders effect of composition and compatibilization
    PPS 27 - Proceedings of the Polymer Processing Society Annual Meeting, 2011
    Co-Authors: S M Cunha, A Gasparcunha, José A. Covas
    Abstract:

    Melting in Single Screw Extruders began to be studied in the fifties, based on the pioneering work of Maddock. Most theoretical and experimental studies used homopolymers as model systems. However, in practice, there has been a considerable evolution in terms of the complexity of the materials being extruded. In the case of polymer blends, the morphology developed during melting should determine the final blend properties. Therefore, this work aims at investigating the morphology evolution during the melting stage of immiscible physical and chemically compatibilized PA6/PP blends. In general, the sequence of steps of morphology evolution reported for twin Screw Extruders and batch mixers was observed, though adapted to the flow kinematics along a helical Single Screw channel. The global morphological development is not affected by blend composition, but distinct domains seem to be formed when in situ reactive compatibilization takes place.

  • modeling of agglomerate dispersion in Single Screw Extruders
    International Polymer Processing, 2010
    Co-Authors: N. Domingues, Marco Camesasca, Miron Kaufman, Ica Manaszloczower, A Gasparcunha, José A. Covas
    Abstract:

    Abstract A model for solid agglomerate dispersion in Single Screw Extruders is proposed. The model combines numerical simulations of flow patterns in the metering section of a Single Screw extruder with a Monte Carlo method of clusters rupture and erosion mediated by a local fragmentation number. Particle size distributions and Shannon entropy are used for mixing characterization. The model is quite general and can be adapted for different polymer-additive systems as well as for different processing equipment.

  • melting of polymer blends and concomitant morphology development in Single Screw Extruders
    Proceedings of the Polymer Processing Society Annual Meeting (PPS 26), 2010
    Co-Authors: S M Cunha, A Gasparcunha, José A. Covas
    Abstract:

    The current understanding of the melting stage in Single Screw Extruders results from pioneering research efforts that were initiated in the fifties and continued for more than thirty years. Most of these theoretical and experimental studies used homopolymers as model systems, whereas in industrial practice there has been a considerable evolution in terms of the complexity of the materials being extruded. This work reports an attempt to monitor the melting sequence and the morphology development of immiscible physical and chemically compatibilized PA6/PP blends. A hybrid melting mechanism, incorporating elements of the Tadmor and of the Dispersive melting mechanisms seems to develop; the early stages of morphology development seem to be similar to those observed in the Haake mixer and Twin-Screw extruder.

  • melting of immiscible physical and compatibilized polymer blends in Single Screw Extruders
    Polymer Processing Society Annual Meeting (PPS 25), 2009
    Co-Authors: S M Cunha, A Gasparcunha, José A. Covas
    Abstract:

    Melting is a major step in plasticating Single Screw extrusion, but most of the existing phenomenological know how was gathered by performing Maddock-type experiments with homopolymers. Given the current widespread industrial use of polymer blends, it is worth determining whether the same mechanisms and mathematical models apply, or whether different sequences develop. This work reports the results of Maddock-type experiments using a PA6/PP blend, both in its immiscible and compatibilized varieties. A melting mechanism combining the features of the classical Tadmor mechanism and of the dispersed melting mechanism, also previously reported in the literature, was observed.

Helmut Potente - One of the best experts on this subject based on the ideXlab platform.

  • flexible use of Single Screw Extruders through multiple process optimization
    Macromolecular Materials and Engineering, 2002
    Co-Authors: Helmut Potente, Jens Pape
    Abstract:

    Using general-purpose Screws to process different types of material offers considerable cost advantages over special-purpose Screws. Designing Screws of this type is generally a difficult task, since modifications to different aspects of the geometry can run counter to each other in some cases. Optimization software is thus of particular benefit here. For this reason, a program was developed for the optimization of general-purpose Screws. A central feature of this program is an appraisal system for the computer-aided evaluation of Single-Screw simulations. The performance of the software was verified on the basis of actual extrusion experiments.

  • Bulk Density of Plastic Pellets in a Screw Channel
    International Polymer Processing, 1995
    Co-Authors: Helmut Potente, Volker Schöppner
    Abstract:

    Abstract For a correct calculation of the material throughput of Single Screw Extruders in the by solids dominated feed area, the accurate knowledge of the effective bulk density is important. In the Screw channel the bulk density measured in a quasi infinite vessel cannot be achieved during processing. The effective density is reduced according to the wall influences. If a two component system exists in the feed area, for example, when processing moulding compounds or regrind, then the bulk density changes likewise. In the following a procedure is described, by which the effect of the Screw core measurement and the percentage composition of two material mixtures on the effective bulk density can be calculated.

  • design of tightly intermeshing co rotating twin Screw Extruders
    International Polymer Processing, 1994
    Co-Authors: Helmut Potente, J Ansahl, B Klarholz
    Abstract:

    Abstract Composite models for the calculation of the filling level profiles, the pressure profiles, the melting profiles, the residence time distributions, the temperature profiles, the shear stress profiles, and the power consumption in modular tightly intermeshing co-rotating twin Screw Extruders (ZSK) are developed. A complex systematic design procedure was compiled, which is explained in part in this paper. The simulation of the intermeshing co-rotating machine involves both Screw and kneading disc elements, including left- and right-handed sections. Kneading blocks were approximated by a Screw of “equivalent pitch” with making allowance for the leakage flow across the flights from one channel to the adjacent channel. The mathematical treatment of co-rotating twin Screw Extruders has been based up according to the theory of Single Screw Extruders. There was seen to be a good correlation between calculated and experimental results.

K J Wang - One of the best experts on this subject based on the ideXlab platform.

  • studies on the effect of pellet size on positive conveying in helically grooved Single Screw Extruders
    International Polymer Processing, 2013
    Co-Authors: K J Wang
    Abstract:

    The helical grooved barrel feed section permits, when the barrel channel aspect ratio and the barrel channel helical angle are properly designed, an operating mode where the positive conveying is prevailing. While the pellet size of materials is varied, different dimension relationships of the barrel channel depth and pellet size could induce different equivalent barrel channel aspect ratios with the transformation of solids conveying mechanisms from the positive conveying to the friction-drag conveying. Considering the effect of dimension relationships on the solids conveying mechanism, a novel pellet-size physical model was established to guide the available design of the barrel channel geometry for positive conveying. In the pellet-size model, one or two shear interfaces were identified inside the solid-plug resulting in different equivalent barrel channel aspect ratios, based on which the solids conveying mechanism on the shear interfaces was detailed by the boundary condition equations for positive c...

  • studies on positive conveying in helically channeled Single Screw Extruders
    Express Polymer Letters, 2012
    Co-Authors: K J Wang
    Abstract:

    A solids conveying theory called double-flight driving theory was proposed for helically channeled Single Screw Extruders. In the extruder, Screw channel rotates against static barrel channel, which behaves as cooperative embedded twin-Screws for the positive conveying. They turn as two parallel arc plates, between which an arc-plate solid-plug was assumed. By analyzing the forces on the solid-plug in the barrel channel and Screw channel, the boundary conditions when the solid-plug is waived of being cut off on barrel wall, were found to have the capacity of the positive conveying. Experi- mental data were obtained using a specially designed extruder with a helically channeled barrel in the feeding zone and a pressure-adjustable die. The effects of the barrel channel geometry and friction coefficients on the conveying mechanism were presented and compared with the experimental results. The simulations showed that the positive conveying could be achieved after optimizing extruder designs. Compared with the traditional design with the friction-drag conveying, the throughput is higher while Screw torque and energy consumption are decreased. Besides, the design criteria of the barrel channel were also discussed.