Volume 13, Issue 4

Recently, several investigators have challenged the simplifying assumption of using a stationary screw with a rotating barrel when analyzing the flow in single screw extruders. The investigators claim that there are significant differences between the realistic and simplified cases, such as a 12 percent difference in throughput [1]. This paper presents an analytical derivation for the flow in a laid out system and one which includes the curvature of the screw. An experimental set-up was built which allows the rotation of the barrel with a stationary screw and the rotation of the screw with a stationary barrel, and a three dimensional flow simulation program was used to model the flow in the extruder using the two conditions. The analytical, experimental and numerical analyses show that it is justified to use the stationary screw assumption when modeling the flow in single screw extruders.

The axial discharge continuous mixer-LCMAX 40, which combines the features of a continuous mixer and the co-rotating twin screw extruder, was analyzed in this work for its distributive mixing efficiency. We analyzed the distributive mixing performance for various rotor configurations. Four designs with either alternating or block arrangements of pushing and counter-pushing units were investigated. A fluid dynamics analysis package-FIDAP, based on the finite element method was used to model the flow behavior of a power law model fluid. Distributive mixing was quantified using particle distributions along the axial distance. Residence time distribution (RTD) functions were calculated and found to reveal interesting information related to design features. The influence of design on the evolution of the particle path length and shear strain distribution was also discussed. The counter-pushing units and their arrangements were found to play an important role in distributive mixing.

A simulation is presented of the flow and pumping behavior of an intermeshing counter-rotating twin screw extruder. The problem of incorporating the positive displacement characteristics of moving machine parts in a cylindrical coordinate Flow Analysis Network (FAN) analysis is presented. Screw pumping characteristic curves were determined for various elements of the Leistritz GG modular counter-rotating twin screw extruder for a Newtonian fluid. We discuss the analysis of composite modular counter-rotating twin screw extruders using these screw pumping characteristics.

A series of experiments were performed on an assembly of four commercially available polymer pellets at room temperature. An automated deformation controlled triaxial testing system was used for the entire testing program. Lubricated end platens were used to assure uniform strain conditions during the application of compressive loading on the confined cylindrical specimen of a given polymer pellet type at a target bulk density. The test results in terms of the deviator stress-strain and volume change characteristics of polymer pellets were obtained for use in the modeling and analysis of solids conveying in plasticating screw extruders. Testing procedures are described that can be used routinely to obtain the strength and deformation behavior of an assemblage polymer pellets. The deviator stress-axial strain and volumetric strain-axial strain curves are presented for four confining stress levels (l00, 200, 300 and 400 k Pa) for these materials using both dry and saturated specimens. The water saturated specimens were used in parallel for obtaining reliable measurements of the volumetric strain variation during the application of deviator stress. The effect of using water as the pore fluid on the mechanical behavior was also discussed. The angles of internal friction of these four polymeric materials were determined and the use of Mohr-Coulomb failure criteria was evaluated. These confining pressure dependent friction angles are compared with the angle of repose measurements. The stress transfer coefficients as a function of wall friction for the potential states of confinement of these polymer pellets in the solids conveying portion of an extruder are also summarized.

The disposal of used automobile tires has become a major environmental problem, and although there are obvious environmental reasons for recycling waste tires, to date it has not taken place because it is not cost-effective. The aim of this study was to find a more effective method of recycling used automobile tires. This was done by comparing the methods of using vulcanized crumb rubber as a filler, and investigation of the effect of surface treatment with microscopic examination of the fracture morphology of the filled crumb rubber elastomers. The experimental results indicate that crumb rubber filler end-product properties were enhanced by the chlorination of crumb rubber, and by developing a crumb rubber incorporation method. We found that much improvement of the mechanical performance of the crumb rubber filled elastomer compounds could be achieved by developing a better crumb rubber incorporation technique.

The die in the melt spinning process distributes the whole melt stream into individual small melt streams that pass the die parallel to each other. The number of holes in the die determines the number of filaments in the spun fiber bundle. As the whole melt stream (i. e. the total throughput) is enforced by a precise gear pump (the spinning pump) the sharing out into the single hole throughputs is dependent on the pressure and the flow resistances of the single holes. Only for constant pressure and equal resistances the single hole throughputs are equal, too. The present paper deals with the influence of geometrical inaccuracies of the holes in the spinning die on the fineness and structural variations across the spun fiber bundle.

Biomedical segmented polyurethanes (SPU) are frequently processed by solution-casting techniques in order to obtain multilayerfilms. For processing parameters setup empirical criteria is currently applied. However, the selected conditions can strongly affect the physico-chemical properties of the finished articles and they must be accurately established. In order to describe the SPU coating formation, balances of heat, mass and momentum transfer must be considered. To study the drying process, two new medical-grade SPU solutions commercially available, Biospan TM and Chronoflex AR TM , were dried at different temperatures. Desorption curves and drying rate, both as a function of temperature, were obtained from experimental data. The mathematical model to describe this process take into account the heat and mass transfer and film shrinkage along the whole drying step. The diffusion coefficients and the control mechanism were determined from the best experimental data fitting. To obtain the solvent concentration profile, residual solvent and film, thickness at any time, heat and mass transfer balances were numerically solved using an explicit finite-difference method. The formulations showed different behavior. For Biospan drying, performed in the range from 5°C to 8°C, a two-stage process was observed. The first one controlled by mass transfer in the gas phase and the second one with mix control. When 4°C drying temperature was applied, a mix control was found along the whole process. This change could be attributed to the acrylic additive present in the SPU matrix, which has a glass transition temperature value in the range of the process temperature. Chronoflex samples showed a two-stage process in all cases and lower diffusion coefficients than Biospan samples.

Rotating rolls are used to distribute liquids onto papers or other materials in order to coat their surfaces with thin films for further technical applications of the composed materials. In this contribution a numerical method is applied which solves the momentum balance in the liquid phase with the support of the Finite Element Method (FEM), taking free surfaces into consideration. The coupled equations of momentum and energy are solved on the basis of the Boundary Element Method (BEM). The process parameters are summarized in the friction number, the capillary number, the Reynolds number, the Stokes number and several ratios of the linear dimensions. Their influence on the fields of pressure, velocity, tension, and temperature is investigated and displayed graphically. A temperature gradient superimposed to the flow through the gap between the roll surfaces results in an additional influence on the velocity field and the coating thickness. The results of the numerical calculations are approximated by rather simple empirical equations.

The control-volume finite element method (CVFEM) has been used widely to simulate the mold filling process in polymer processing because it is more user friendly and more robust than the conventional finite element or finite difference methods. However, using lower order interpolation functions in CVFEM may result in significant numerical errors. This is especially true for convection–diffusion problems with a changeable source term as in reactive liquid composite molding (LCM). In this study, an Eulerian–Lagrangian approach is proposed where an Eulerian coordinate system is used to solve the velocity field, while the chemical species balance and the energy balance are based on a Lagrangian coordinate system. This approach is used to simulate the non-isothermal LCM process.

The quality of injection moulded products is determined by a complex coupling between polymer properties, mould geometry, and process dynamics. To increase the flexibility and consistency of the injection moulding process, a method was devised to simultaneously control cavity pressure at multiple locations in a mould. This control was achieved by installing multiple dynamic valve stems into the feed system of a hot runner manifold, each of which can control polymer flow. This system was used in a commercial application with four gates to deliver consistent product quality and provide manufacturing-stage flexibility. Across all eleven measured dimensions, the process capability index Cp increased between 50 and 400%. Also, multiple dimensions could be independently and simultaneously adjusted by locally controlling material shrinkage.

In this paper, we aim at a synergism of improvements of impact strength of polypropylene by the addition of β-crystal nucleator and of its rigidity by the addition of α-crystal nucleator. Co-addition of both the nucleators has been studied. 30 ppm of γ-quinacridone which is a β-crystal nucleator and 0 to 10000 ppm of talc (FC), aluminum salt of benzoic acid (BA), or dibenzylidene sorbitol (GA) which are α-crystal nucleators were added to a homo isotactic polypropylene (PP). Flexural and lzod impact test specimens were injection-molded from the PPs under constant molding conditions and the structure and properties have been investigated. Although the α-crystal nucleators scarcely affect the β-crystal content (K value) at nucleator contents below 100 ppm, the K value decreases with increasing nucleator content at contents above 100 ppm. The decrease is in the order of BA > GA > TC Although the lzod impact strength scarcely changes at α-crystal nucleator contents below 100 ppm, it decreases with increasing nucleator content at contents above 100 ppm. The decrease is the larger as the decrease of K value is the larger. The flexural modulus shows a reverse tendency of the lzod impact strength. From above, it may be said that the properties of injection molding of β- and α-crystal nucleator-added PP are unitarily determined by the β-crystal content and thus the expected synergism could not be obtained.

Aiming at a synergism of improvements of impact strength of polypropylene by the addition of β-crystal nucleator and of its rigidity by the filling of particulate, the addition of the nucleator to particulate-filled polypropylenes has been studied. 0 to 3000 ppm of γ-quinacridone (GQ) which is a β-crystal nucleator was added to homo isotactic polypropylenes (PP) filled with 0 to 30 wt-% of talc (TC) which shows an α-crystal nucleating effect, of mica (MC), or of glass flake (GF), last two of which show β-crystal nucleating effects. Flexural and Izod impact test specimens were injection-molded from the PPs under constant molding conditions and the structure and properties have been investigated. The β-crystal content is reduced by the filling of particulates. The degree of the reduction is in the order of TC >MC >GF, which agrees with that of the crystallization temperature. The flexural modulus decreases slightly with increasing GQ content and increases with increases in particulate contents. The increase is in the order of MC > TC > GF, which agrees with that of the aspect ratio. The enhancing effect of the Izod impact strength by the addition of GQ decreases with increasing particulate contents and diminishes at contents above 10 wt-%. Particulates deteriorate the enhanced impact strength of β-PP. Thus the expected synergism could not be obtained enough.

This paper contains a systematic study on warpage of injection moulded plates and corner products as a function of mould temperature difference and holding pressure. The study is restricted to unfilled amorphous materials. As expected, experiments showed that warpage increased linearly with the applied temperature difference between mould halves. Not expected was that at low holding pressures the plates curved towards the hot side, whereas at high holding pressures they warped towards the cold side. A simple thermoelastic theory is proposed which could explain all observations qualitatively and quantitatively. Standard simulation software, on the other hand, was seen to predict warpage behaviour at the higher holding pressures which was completely opposite to the experimental observations.