Extrusion Operations Research Articles

Predication of critical distance of wall‐slip phenomenon during extrusion of carbon black‐filled natural rubber/cis‐polybutadiene rubber compound

AbstractThe wall‐slip phenomenon during extrusion of polymer fluids is an important characteristic of viscoelasticity. The wall‐slip behavior and the factors affecting it for natural rubber (NR)/cis‐polybutadiene rubber (BR) filled with carbon black compound were investigated by using a Monsanto processability tester in a temperature range of 90–130°C and at shear rates that varied from 50 to 103 s−1. Under simplified supposition conditions, a mathematical model for description of the relationship between pressure variation, polymeric properties, and extrusion operation parameters when wall‐slip phenomenon occurs was established by using a tensor analysis method. On the basis of this model, an equation for estimation of critical slip distance (or position) was derived. The results showed that the measured critical pressure drop, when wall‐slip begins to occur, was consistent with the theoretical predictions. The wall‐slip phenomenon of the sample happened near the exit of the die. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3239–3243, 2004

Effect of hydroperoxide decomposer and slipping agent on recycling of polypropylene

Polypropylene (PP) recycling has always been challenging because the polymer is highly susceptible to thermooxidative degradation during extrusion. Recycled (degraded) PP is normally blended with virgin PP to achieve reasonable mechanical properties after reprocessing operations. However, impurities present in recycled PP tend to degrade even the virgin PP in this process. In this study, standard recycled PP was produced in a laboratory by repeated extrusion and pelletization operations of virgin PP. This material was blended with virgin PP in a ratio from 3 : 7 to 7 : 3. An attempt was made to stabilize the recycled blend by adding a peroxide decomposer (triphenylphosphite, TPP) and a slipping agent (zinc stearate) in contrast to radical scavengers normally used in reprocessing. It was found that by using 0.3–0.5 wt % of TPP and 2 wt % of zinc stearate, this degradation could be effectively attested. Compared to the tensile strength retention of 68% (based on strength of pure virgin PP) of a 60 : 40 (recycled : virgin) PP blend without any stabilizer, a value of 77% was obtained for the same blend with the above-mentioned stabilizers. This stabilization effect was attributed to decomposition of unstable hydroperoxides to stable compounds in the recycled materials by TPP, and lower generation of new radicals in the presence of zinc stearate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3247–3251, 2004

Preparation of Granular Systems by Extrusion/Spheronization: A Twin Product/Process Approach

The extrusion/ spheronization technique makes a notable contribution to the existing range of pharmaceutical forms, especially in the area of oral controlled-release product. Analysis of this technique leads the authors to make a parallel study of the influences of the aspects linked to formulation (water content) and to processing used (extruder screw speed) with the aim of optimizing the product quality. Textural variables, porosity, saturation degree and water content were monitored throughout the elaboration process. The kneading operation brings the material to a state in which porosity is linked to water content. The extrusion operation densities the material to saturation point, while spheronization is simply a shaping process which maintains the hygrotextural state. Also emphasized is the presence of solid/liquid ratios optimizing pellet quality independently of the operating variables. In parallel to this, a range of water content for which the influence of the process parameter is relevant is identified.

Extrusion, contraction: their discretization via Whitney forms

The v×B term in eddy current equations for conducting fluids is an instance of contraction of a differential form by a vector field. We search for a natural way to discretize such contractions. Looking at the operation of extrusion of a manifold, which is dual to contraction, provides the main clue. Two example applications, Carpenter's gauge and Eulerian computations in MHD problems, are suggested.

Analysis of temperature and component form-error variation with the manufacturing cycle during the forward extrusion of components

The definition of the form-errors of component in nett-forging required the analysis of error generation by considering both thermal and mechanical factors in the forging. To-date, however, most of the analyses have only referred to a single manufacturing cycle. Since forging productions are largely multi-cycle operations, component form-errors can vary with the manufacturing cycle. Using a developed procedure, the temperature change in the die during multi-cycle forward extrusion operations was computed. The computed temperature distributions in the die were then used for initiating the analysis of component form-errors for given manufacturing cycles. The analysis refers to forward extrusion for both single solid die- and compound die-set-configurations.

Pressure losses during the annular conical die flow of a rubber compound

The flow behavior of polymer melts in an annular conical extrusion die is discussed in the present paper. Annular die extrusion is a common way of producing tube-like products in polymer processing but the rheological behavior of polymer fluids during extrusion is relatively complex. On the basis of simplified suppositions, a mathematical model for estimation of the pressure drop during the die flow of polymer melts was established by a using tensor analysis method. The flow properties during extrusion of rubber compound were investigated by using a capillary rheometer in a temperature range of 85–110°C and apparent shear rates varied from 50 to 10 3 s −1. It was found that the sample shear flow obeyed roughly the power law. The pressure drop of the sample flowing in an annular conical die installed in an industrial screw-extruder was measured at the same extrusion operation conditions. The results showed that calculations from the mathematical model were approximately consistent with the measured pressure drop data from the experiments.

A study on the automated process planning system for cold forging of non-axisymmetric parts using FVM simulation

A process planning system for cold forging of non-axisymmetric parts of comparatively simple shape was developed in this study. Programs for the system have been written with Visual LISP in AutoCAD. When a product is drawn on AutoCAD, it needs that the shape of the product is drawn with the solid line and the hidden line, and with the plane and front view, as well. At the plane, the system recognizes the external shape of non-axisymmetric portions—the number of the sides of the regular polygons and the radii of circles inscribing and circumscribing the polygon of n sides. At the front view, the system cognizes the diameter of axisymmetric portions and the height of the primitive geometries such as polygon, cylinder, cone, concave, convex, etc. And the system perceives that the list developed from the solid line must be formed by the operation of forward extrusion or upsetting, and that the list developed from the hidden line must be formed by the operation of backward extrusion. Suitability of the process planning was analyzed using SuperForge of FVM simulation package. The results of analysis showed good formability.

비축대칭 제품의 냉간단조 공정설계시스템의 개발

A process planning system for cold forging of non-axisymmetric parts of comparatively simple shape was developed in this study. Programs for the system have been written with Visual LISP in AutoCAD. Shape of the product must be drawn with the solid line and the hidden line, and with the plane and front view, as well. At the plane, the system recognizes the external shape of non-axisymmetric portions - the number of the sides of the regular polygons and the radii of circles inscribing and circumscribing the polygon. At the front view, the system cognizes the diameter of axisymmetric portions and the height of the primitive geometries such as polygon, cylinder, cone, concave, convex, etc. The system perceives that the list developed from the solid line must be formed by the operation of forward extrusion or upsetting, and that the list developed from the hidden line must be formed by the operation of backward extrusion. The system designs the intermediate geometries again by considering clearance between workpiece and die, and then finally the billet diameter, in reverse order from the finished product, on the basis of volume constancy and using the operations, the forming sequence, the number of operations and the intermediate geometries which were already designed. The design rules and knowledges for the system were extracted from the plasticity theories, handbook, relevant reference and empirical knowledge of field experts. Suitability of the process planning was analyzed using SuperForge of FVM simulation package. The results of analysis showed good formability.

Effects of extrusion conditions on rheological behavior of acrylonitrile–butadiene–styrene terpolymer melt

AbstractThe influence of temperatures and flow rates on the rheological behavior during extrusion of acrylonitrile–butadiene–styrene (ABS) terpolymer melt was investigated by using a Rosand capillary rheometer. It was found that the wall shear stress (τw) increased nonlinearly with increasing apparent shear rates and the slope of the curves changed suddenly at a shear rate of about 103 s−1, whereas the melt‐shear viscosity decreased quickly at a τw of about 200 kPa. When the temperature was fixed, the entry‐pressure drop and extensional stress increased nonlinearly with increasing τw, whereas it decreased with a rise of temperature at a constant level of τw. The relationship between the melt‐shear viscosity and temperature was consistent with an Arrhenius expression. The results showed that the effects of extrusion operation conditions on the rheological behavior of the ABS resin melt were significant and were attributable to the change of morphology of the rubber phase over a wide range of shear rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 606–611, 2002

Recycling of a starch-based biodegradable polymer

A new starch-based polymeric system, ZIIOU from Novamont, mainly composed of starch and polycaprolactone, was reprocessed several times in an extruder to investigate the recyclability of this biodegradable polymer. A previous investigation of the thermomechanical degradation in a mixer has been also done. The degradation is mostly due to the thermal stress but the presence of the mechanical stress strongly increases the degradation kinetic. During melt processing two concurrent processes take place: the first is the degradation, i.e. the breaking and shortening of polymeric chains, mostly occurring in the PCL phase; the second is the formation of some crosslinked structure in the starch phase. The rheological and mechanical properties, measured on samples subjected to repetitive extrusion operations carried out in a single screw extruder, clearly indicate that, in the adopted processing conditions, no significant modifications are observed. Only after five extrusions some decrease of these properties was measured.

Kinematic waves and draw resonance in film casting process

Draw resonance, one of major instabilities frequently occurring in fiber spinning, film casting and film blowing processes, arises as the drawdown ratio is increased beyond its critical value and is manifested by sustained periodic variations in spinline variables such as cross-sectional area and tension. The approach which was introduced by Hyun and coworkers [1–6] based on kinematic waves traveling on the spinline to explain the physics behind this draw resonance in spinning and to derive its criterion, has been applied to film casting in the present simulation study. It has then been revealed that the same mechanism and criterion govern the draw resonance in film casting as in spinning, but at the same time, some differences also have emerged. Particularly, the nonlinear dynamics of the film width whose counterpart does not exist in spinning has been found quite complex and also very sensitive to process parameters like fluid viscoelasticity and the aspect ratio of the casting equipment. This contrasts dramatically with that of the film thickness which shows rather simple dynamic patterns, almost insensitive to the changing parameters values. The good control of film width is of as much importance as that of film thickness in many industrial processes including paper coating. An ingenious coating method [7] exemplifies how critical the film width control is for the successful operation of extrusion coating of polymer films on paper substrates.

Steady-state modeling of slurry and bulk propylene polymerizations

A mathematical model for steady-state slurry and bulk propylene polymerizations is developed and implemented. The model is based on the detailed formulation of mass balances for all chemical species present in the reaction environment, of energy balances for the reactor mixture and cooling water and of momentum balances. The model allows the computation of mass and energy inventories and the prediction of polymer molecular structure and morphology, including the molecular weight distribution, the chain composition distribution, the particle size distribution and the stereo-block distribution. Besides, end-use properties, such as the melting-flow index, the impact strength and the flexural modulus, are described through empirical models that depend on the molecular and morphological properties of the polymer resins, as described by Latado et al. (Polymer Testing 20(4) (2001) 419–439). The model also allows the simulation of the extrusion operation and is validated with actual operation data for two different polymerization plants, using different Ziegler–Natta catalysts.

Development of Emission Factors for Polyamide Processing

ABSTRACT Emission factors for selected volatile organic compounds (VOCs) and particulate material were developed during processing of commercial grades of polyamide 6, polyamide 66, and polyamide 66/6 resins. A small commercial-type extruder was used, and melt temperatures ranged from 475 to 550 °F. An emission factor was calculated for each substance measured and is reported as pounds released to the atmosphere per million pounds of polymer resin processed. Scaled to production volumes, these emission factors can be used by processors to estimate emission quantities from similar polyamide extrusion operations.

Thickening: an operation for animation

In this paper, we present a modelling operation dedicated to animation. This operation, called thickening, is a generalization of the extrusion operation. It allows to build from a graph 3-D objects with circular section and 4-D objects with spherical or toric section. Moreover, the date and the number of mergings and splittings in the associated animation are perfectly controlled, and the trajectory of each of the animated objects is completely established. Several types of thickening are presented in this paper, to build a surface or a volume, starting from a graph drawn in a surface or in a volume. Copyright © 2000 John Wiley & Sons, Ltd.

Dynamic slip and nonlinear viscoelasticity

AbstractSeveral significant problems arise when film is fabricated on a large scale. One of these is the appearance of irregularities on the extrudate surfaces when the polymer melt is extruded at high rates. These irregularities vary in intensity and form and are generally known as sharkskin melt fracture. This phenomenon, which occurs when the wall shear stress exceeds a critical value, is a limiting factor for production rates in many industrial extrusion operations such as film blowing of polyethylene. We used a sliding plate rheometer incorporating a shear stress transducer to study slip in both steady and unsteady flows. By combining a dynamic slip model with a nonlinear viscoelastic constitutive model, we determined the slip model parameters for LLDPE film resin with and without a fluoropolymer sharkskin suppressant. The models give good prediction of our slip data in steady shear but show insufficient gap dependence in exponential shear. Our own film blowing studies demonstrated the efficiency of the sharkskin suppressant; it has more than doubled the throughput in our laboratory setup. The fluoropolymer additive was found to profoundly affect both the steady and dynamic slip parameters. Hence, the sharkskin suppressant alters how the LLDPE remembers its past slipping motions.

A Mixed Lubrication Model for Computer Simulation of Extrusion Processes

A mixed lubrication/friction model for extrusion process is developed in the present research. The model combines a rigid-plasticity finite element code to simulate the interface condition between the tooling and workpiece in the extrusion operation. The influence of surface roughness on lubricant flow is treated by using the average Reynolds equation. The active lubrication regime and appropriate friction factor were determined from the current local values of interface variables such as mean lubricant film thickness and workpiece and tooling roughness, in addition to the more traditional external variables such as interface pressure, node sliding velocity and strain rate of the workpiece. Numerical results using the coupled code include friction stress and normal pressure under different lubrication conditions are compared with experimental investigation. The discrepancy is very small and the proposed model proved to be very efficient in predicting interface friction condition in the extrusion processes.

One‐line measurement of the residence time distribution in screw extruders

AbstractA fluorescence monitoring device was constructed to measure in real time the residence time distribution (RTD) function in screw extruders. Its centerpiece was an optical fiber probe capable of transmitting optical excitation energy to the processed flow stream and detecting the subsequent fluorescence emission. The source of fluorescence emission was an anthracene‐bearing substance that was injected to the flow stream as a pulse (tracer) in very small amounts. This device was validated against an off‐line ultraviolet spectrophotometer and self‐checked as well. In addition to its great sensitivity to fluorescence emission and ease of implementation on an extrusion line, this device could be used to monitor in real time subtle variations of an extrusion operation. The influence of the nature of anthracene‐bearing compounds on the measured distribution and the effects of processing parameters on the RTD function were also investigated.

PVC‐Based TPEs for year 2000 and beyond

AbstractSoft, low‐compression‐set and chemically resistant TPEs have been developed from advanced PVC blend technology. These blends have low‐temperature flexibility comparable to that of commonly used TPEs and can be made flame‐retardant. These new TPEs are suitable for applications in consumer products, automotive, wire and cable insulation, and jacketing. This new class of TPEs, suitable for injection and extrusion operations, represents a significant advance in PVC compounding technology.

Development of Emission Factors for Polypropylene Processing

ABSTRACT Emission factors for selected volatile organic compounds and particulate emissions were developed during extrusion of commercial grades of propylene homopolymers and copolymers with ethylene. A small commercial extruder was used. Polymer melt temperatures ranged from 400 to 605 °F. However, temperatures in excess of 510 °F for polypropylene are considered extreme. Temperatures as high as 605 °F are only used for very specialized applications, for example, melt-blown fibers. Therefore, use of this data should be matched with the resin manufacturers' recommendations. An emission factor was calculated for each substance measured and reported as pounds released to the atmosphere per million pounds of polymer processed [ppm (wt/wt)]. Based on production volumes, these emission factors can be used by processors to estimate emission quantities from polypropylene extrusion operations that are similar to the resins and the conditions used in this study.

Effect of martensitic phase transformation and deformation twinning on mechanical properties of Fe–Mn–Si–AI steels

Deformation twinning, martensitic phase transformation and mechanical properties of austenitic Fe–(15–30) wt-%Mn alloys with additions of Al and Si have been investigated. Tensile tests were carried out at different strain rates and temperatures. The formation of twins, α′ (bcc)- and ε (hcp)-martensite in the γ (fcc) matrix during plastic deformation was analysed by optical microscopy, X-ray diffraction, and scanning electron microscopy. Depending on the content of the alloying elements different phase transformations γ → ε, γ → α′ (TRIP effect), or the formation of deformation twins (TWIP effect) occurred. Additions of Al increased the stacking fault energy (γfcc) and suppressed the γ → ε transformation while Si decreased γfcc and sustained the γ → ε transformation. These steels with reduced densities of about 7.3 Mg m−3 exhibit high tensile ductility up to 95% with true tensile strength of about 1100 MPa. The excellent plasticity induced by twinning or phase transformation up to extremely high strain rates of about <disp-formula><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="splitsection2-m1.tif"/></disp-formula> results in an extraordinary shock resistance and allows for deep drawing and backward extrusion operations of parts with complex shapes.