SPE Library
The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Conference Proceedings
Coextrusion of LDPEs in the Cast Film Process
This work shows results of experiments on a coextrusion cast film line and is focused mainly on studying conditions for the onset of zig-zag interfacial instabilities. The measurements were performed for a wide range of LDPEs polymerized by different polymerization methods. It is shown that for a group the materials prepared by a similar polymerization method there exists a critical shear stress value at the interface that determines the onset of the instability. The values determined for different material groups are different and it seems that there is a correlation between the molecular weight distribution width and the critical shear stress value. The broader is the MWD the lower is the critical shear stress value.
Investigation of Interfacial Instabilities in Nanolayer Extrusion
Multilayer structures have been prepared by coextrusion technology using a feedblock with layer multiplying elements (LME) to split the melt stream and then layer the two streams together. Polycarbonate (PC), polypropylene (PP), and a cyclic olefin polymer were extruded to form alternating structures by repeated layer multiplications using the layer multiplying elements. The materials were characterized by microscopy to study the effect of polymer properties and process conditions on layer instabilities. Instabilities were found at the layer interfaces, predominantly in the center of the samples, resulting from high interfacial shear stresses. This could be reduced by increasing the temperature of the LMEs and decreasing the total flow rate of both materials.
The Effect of Using Preheated Pellets in Co-Rotating Twin-Screw Extruders
Experiments with a co-rotating twin-screw extruder show that a considerable throughput increase can be achieved by feeding the extruder with preheated pellets. The use of preheated pellets is also advantageous in that, for a given throughput, the extrusion of preheated pellets requires a lower torque. Thus, when shifting from cold to preheated pellets, the screw speed can be lowered until the original torque is again reached. As a result, the temperature of the exiting melt is lower too. The use of preheated pellets thus gives an extra degree of freedom in terms of the maximum throughput of a given extruder, and control of degradation-sensitive polymers.
Realtime Process and Quality Control in Polymer Extrusion - Detection and Sizing of Particulate Inhomogeneities in Flowing Polymer Melts
By application of different unique microphotometric sensors it is possible to detect and quantify disturbing particles (gels, unmolten resins, black spots, additive agglomerates, bubbles) within a flowing polymer melt in realtime during extrusion processing. These particles result in disadvantageous optical and mechanical properties of a final polymer product. Sensors can be adapted inline and online to different extruders at various positions. This seems to give technical and economic benefit to quality control and process optimisation in polymer processing.
Residence Time Distribution in Twin-Screw Extruder Measured by Non-Destructive Ultrasonic Device
In this study, we performed RTD measurement at the die exit of co-rotating twin screw extruder using a non-destructive ultrasonic device. The ultrasonic device was composed of a steel buffer rod and 10 MHz longitudinal piezoelectric ultrasonic transducer. Steel buffer rod is a safety implement for the protection transducer against hot operating temperature. This in-line method is based on the ultrasonic response of a filled polymer, where the solid particles act as a tracer. To determine RTD, calcium carbonate (CaCO3) was used as a tracer. The RTD measurements involved the use of ultrasonic tracer and the measurement of the variation of ultrasonic signal strength with time caused by the tracer concentration change. The ultrasonic tracer, pellet types of compounded CaCO3 in polymer were used in this study. The effects of CaCO3 concentration on RTD and flow patterns were studied in the extrusion of a thermoplastic resin. Experiments on the residence functions of different screw speed, feeding rate and screw configurations were also carried out.
Study of Processing Behavior of Extrudate PTFE Paste
Polytetrafluoroethylene (PTFE) is a remarkable material having high melting temperature, high chemical resistance, low frictional and dielectric coefficients, etc. Due to its high melting point, PTFE cannot be processed using the conventional methods such as the injection molding, extrusion and blow molding, etc. In this research, PTFE is processed by a number of techniques including paste extrusion, rolling and calendering. It is necessary to preform the PTFE powder-lubricant mixture before extrusion to ensure paste densification. The processing behavior of extruded PTFE pastes was first studied. The length of extension zone was changed to investigate the variation of extrusion pressure profile. Two-colored preform paste packed sequentially was used to observe the flow behavior in extrusion process. It was found that the extrusion pressure increases in the reduction zone and decreases after the paste passed the extension zone. Increasing the packing time in the performing will result in a more steady extrusion pressure. Higher extension length would raise the required pressure for paste extrusion. Furthermore, it was also found that an increase in the lubricant content increases the extent of density uniformity. The paste flow exhibits laminar behavior of viscous fluid. However, highly non-Newtonian characteristics and slip boundary also occur.
Comparison of the Flow in Co-Rotating and Counter-Rotating Twin-Screw Extruders
Polymeric flow in intermeshing co-rotating and counter-rotating twin-screw extruders is simulated. Effect of the elongational viscosity of the polymer on the flow in the two extruders is included by using independent Carreau models for the shear and elongational viscosities of the polymer. It is found that for similar screw cross-sections and rotational speed, axial velocity as well as degree of mixing is higher in the co-rotating extruder, whereas pressure build up is higher in the counter-rotating extruder. In contrast to the flow in the co-rotating extruder, where the velocity was always maximum at the screw tips, in the counter rotating extruder the velocity was higher in the intermeshing zone.
Extrusion of HDPE-Wood Blends
In previous studies1-3, both rheological and extrusion characteristics of a 50% wood-HDPE composite as well as its virgin HDPE resin were investigated. In this paper, the extrusion characteristics of the blends made up of these two materials were studied. It was found that for a screw which has the higher compression ratio, for all the blends, the pressures increased with increasing RPM with the exception of 50% HDPE-wood composite at 50RPM; whereas for a screw with lower compression ratio, for the 36% and 50% wood-HDPE blend, there was no pressure generation at any RPM even though the output increased in a nearly linear fashion. The effect of temperature on pressure generation was also looked at and will be presented here. Similar to the previous studies, the experimental results were compared to those simulated using a commercially available computer program, Flow 2000™.
Evaluation of Pulsed Cooling in Injection Mould Tools
Pulse cooling technology, intermittent flow of the cooling medium in the mould tool and accurate control of the tool temperature during injection moulding has been shown to reduce cycle time and energy consumption. Several papers in previous ANTEC meetings have reported on this technology and since those meetings further experimental work and modelling has been carried out to compare direct cooling (conventional cooling) with pulsed cooling. Results will be presented for polycarbonate and polypropylene filled with additives, talc and LNP Engineering’s Konduit on injection moulding cycle time.Also to be discussed will be initial results from computational fluid dynamics study to model the functions of pulsed cooling and direct cooling during injection moulding.
Simulation and Verification on the Drop Test of Mobile Phone Housing
Drop test performance has become one of the most crucial evaluations for Computer, Communication, and Consumer (3C) products. Both simulation tool and practical platform for drop test must be established for detailed study. A patented drop test platform is designed for the purpose of impact angle repeatability and instantaneous drop image capture at impact instance. These parameters are two crucial computer-aid-engineering (CAE) inputs used for drop impact simulations. Post data processing procedures such as sampling rate, and signal filtering specifications was also studied and found to be important for the accurate interpretation of drop simulations as well. It was found from simulations that a small angle variation (±5°) may result in up to 36% difference in predicted internal stress. Accurate identification on the impact angle, therefore, is recommended as an important parameter on internal component stress calculation. Good consistency between measured acceleration data and simulated results verifies the practicality of the developed data processing procedure and numerical methodology.
Isolating and Quantifying the Development of Shear vs. Pressure Generated Heat in the Plastic Melt during Injection Molding
Whether pressure or shearing of a material has a larger effect on its temperature rise through a typical injection molding cycle is a debated subject. Both of these factors may have a theoretical effect, but they have not been quantified. This experiment utilizes temperature and pressure sensing equipment with conventional injection molding to respond to this issue. From the data collected, both shear and pressure heating affects on the melt can be quantified and will be contrasted to that predicted by injection molding simulations.
Comparison of Drive Concepts on Injection Molding Machines under Production Conditions
The aim of our studies was to figure out the differences concerning energy consumption of several drive concepts for injection molding machines. During the comparison of the collectively 10 machines at 5 manufactures we focused on the energy needs of the drives as well as on the energy consumed by the complete production cell, including ancillary units. A correct evaluation is warranted by parallel accumulation of process- and product-parameters to characterize reproducibility.Respectively to the drives, our results show energy saving potential using electro mechanical concepts.
Integrated Numerical Simulation of Injection Molding Using True 3D Approach
The application of true 3D simulation in the injection molding is becoming popular in the recent years. However, a unified CAE analysis based on solid model for the predictions of molding and warpage of the injection-molded part is seldom reported in the literature due to the numerical and hardware limitations. In this paper, an integrated true 3D approach is developed to simulate the filling, packing and cooling stages in injection molding, as well as the part warpage after ejection. All the simulations can be carried out on the same solid model, in which both cavity and mold base are meshed with solid elements of different topologies. Thanks to the highly efficiency of the proposed methodology, a typical integrated 3D analysis of part with hundred thousand elements can usually be finished on a regular PC within one day. Several numerical examples are reported to indicate the success of the present model
Three-Dimensional Warpage Simulation for Injection Molding
Simulation of polymer injection molding processing traditionally employs a 2.5D shell finite element/finite difference solution. This form of analysis has served well for the analysis of thin walled components. However, these approximations are not suitable when the geometry has complex three-dimensional features which cannot be well approximated by 2.5D shells.True 3D flow and cooling simulation was developed several years ago. In this paper, we describe the extension of the true 3D simulation technique to warpage analysis for both unfilled and fiber filled materials. The warpage results from the simulation are presented and compared with the actual molding cases.
Three-Dimensional Insert Molding Simulation in Injection Molding
For the recent years, the insert molding in injection molding has been very popular. Insert molding is a more efficient technology to the assembly of discrete parts. It reduces the assembly and labor costs and increases the design flexibility. Its benefits are over the traditional method, such as soldering, connectors...etc. The different insert parts will cause different effect for injection molding process. The metal inserts are used to increase the performance of drawing heat from the cavity. However, the plastic insert reduce the cooling effects. This paper develops a numerical approach to simulating the mold insert molding in injection-molded part of complex geometry. This developed approach is proved from numerical experiments to be a cost-effective method for true 3D simulation in mold insert molding analysis.
Analysis of the Three Dimensional Mold-Filling Process in Injection Molding
For the three decades, the mold-filling of injection molding process was modeled as Hele-Shaw model. However, this model can not consider the 3D effect. In this paper, numerical simulations of three dimensional mold-filling during the filling phase were performed. The governing equations were discretized by segregated finite element method, which used equal order interpolation for pressure and velocity fields. The iterative linear equation solver (JCG) was employed for the solution of the momentum and pressure equations. Flow Analysis Network (FAN) was employed for the melt front advancement. To check the validity of the numerical results, the results were compared with the experimental ones. The agreements between the experiment and the numerical results were found to be satisfactory.
Two-Material Injection Molding Filling Simulation
Two-material injection molding is gaining popularity due to its potential to produce multifunctional plastic parts at reduced cost. It is postulated that the influence of the interface boundary on the flow pattern of the overmold is insignificant due to high filling rates normally encountered in two-material injection molding. In this paper, a simulation program is developed to study the effect of the interface boundary for the overmold filling process. The simulation uses the bulk temperature of the substrate at the end of packing as the overmold's boundary temperature on the contact surface. Comparison of results with conventional injection molding revealed that flow pattern and injection pressure are both affected by the different temperature boundary condition.
A Coupled Filling-Structural Simulation on a Water Manifold Injection Mold
An injection mold for a water manifold was experiencing deflection on an extremely long core, causing a high defect rate on the finished product. In addition, inserted small plastic capillaries were being crushed if the mold parameters were outside a narrow window. By taking the pressure output from a filling simulation and using it as the boundary condition for a stress analysis on the mold itself, excellent correlation was achieved with the existing molding problems. This led to insight into the true cause of the core deflection along with a successful redesign of the tool to produce consistent, quality parts.
Simulating the Melting Behavior and Melt Temperature Inhomogeneity in the Injection Molding Processes
In the injection molding process, one of the most important process conditions is the temperature and/or temperature distribution of the polymer melt. Since the melt temperature can be the guideline to predict the quality of the molded parts. The ability to better predict and control the polymer melt temperature will help to obtain better products. However, the problem is that the true polymer melt temperature is very difficult to determine and so an estimate is used for the mold filling and packing simulation, which can provide misleading results. Hence, to better predict the melting temperature, the simulation of the injection screw in the injection molding system has been added. This paper shows how the ability to simulate the melting behavior will provide improved simulation accuracy to the entire injection molding process and a better prediction of product quality.
Validation of Shrinkage Predictions for Injection Molded Parts
Shrinkage predictions from a commercial simulation package were compared with shrinkage of parts molded from neat and glass-filled grades of polycarbonate, poly(butylene terephthalate) (PBT), polyamide-6, and polyamide-6,6 various over a range of processing conditions. For both the neat and filled materials, the simulations overpredicted in-flow shrinkage and cross-flow shrinkage near the gate. Cross-flow shrinkage at the end of fill was underpredicted for glass-filled materials, did not correlate with values predicted for neat materials. The validation of shrinkage prediction for thin walled parts was also done using PC+PET blends.
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