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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Effects of Molecular Structure of Polyethylenes on Their Processabilities in Film Blowing Extrusion Process
In this work, bubble instabilities of metallocene and Ziegler-Natta catalyzed polyethylenes (PEs) were studied by using an in-line scanning camera. Levels of long chain branching (LCB) and breadth of molecular weight distribution (MWD) of PEs were systematically varied to study their effects on bubble instabilities. Gel permeation chromatograph traces and small amplitude oscillatory shear data were used to verify the molecular structure of PEs. In addition, tensile stress growth coefficients and apparent uniaxial extensional viscosities were also determined by using Meissner type rheometer and converging die techniques. It was found that LDPE shows the most stable working windows confirming the previous arguments that the polymer showing strong strain hardening has the broader working window. It was also found that two branched metallocene catalyzed PEs show better bubble stability than PEs with broad MWDs implying that the presence of LCB plays a much more important role than the broadening of the MWD. The order of bubble instabilities can be properly evaluated based on a plot of normalized tensile stress growth coefficient vs Hencky strain or normalized extensional viscosities vs extensional stress.
Cluster Computing in Numerical Simulation of Extrusion Flow
In this research, a parallel finite volume method was developed to simulate non-isothermal non-Newtonian steady flow in a coat-hanger extrusion die on PC clusters. We implemented the algorithm by domain decomposition methods that distribute the computational parts equally among the PCs and balance the loading of each PC to the utmost. Each PC exchanged data and information according to MPI (message passing interface) standard, and the governing equations were solved by using the three-dimensional collocated cell-centered finite volume method. In this approach, the extrusion flow can be predicted efficiently and accurately. Moreover, the effects of interconnect network were also discussed in this paper. The present numerical approach proved to be a promising solution for complicated extrusion problems.
Evaluation of Variability in Injection Molding (IM) Molds
The use of injection molding (IM) in high precision manufacturing relies upon the capability of the process to deliver parts consistently conforming to specifications. Characterizing such capability is a matter of understanding the most important sources of variation in IM and to find ways to provide robustness to the process. In this study, a statistical analysis of several sources of variability in IM is presented to precede a future optimization task in which the aim will be to find variable settings that provide the balance between high performance in selected measures as well as low variability around these indicators. The results presented here are meant to be an evaluation of IM molds for use in high precision manufacturing. A method that capitalizes on the strengths of statistical analysis is demonstrated here through two case studies where the variability in parts produced by different molds is assessed. The adequacy of these molds for high-precision manufacturing is determined.
Identifying the Best Compromises between Multiple Performance Measures in Injection Molding (IM) Using Data Envelopment Analysis (DEA): Preliminary Results
Injection molding (IM) is considered to be the most important mass production process for plastic products. A substantial amount of research has been directed towards finding settings for the IM process variables as well as the optimal location of the injection gates. These objectives have been mostly approached through the optimization of performance measures (PMs) as functions of the process’ variables. The use of computer-aided engineering (CAE) has played a pivotal role in trying to achieve these objectives. The aim of this work is to demonstrate a method based on CAE, artificial neural networks (ANNs), and data envelopment analysis (DEA) to find the optimal compromises between multiple PMs to prescribe the settings of IM process variables and the location of the injection gate. Two case studies are presented for this purpose. The first case refers to the production of a cylindrical canister where part shrinkage plays an important role for an effective mold release. The second case analyzes the production of a generic part with cut-outs such as a window frame where the location of weld-lines is critical. Also in this second case flatness is considered an important measure.
Novel Impact Modification in Olefin Systems
Unique additives enable increases in the Gardner impact strength of polyolefins by a factor of 10 while maintaining up to 90% of the material flexural modulus. The effects of resin and additive loading level are addressed in a statistically designed experiment. Physical performance, rheological effects, thermal characterization, and morphological characterization are reported.
Dynamic Rheological Properties of Polypropylene Containing Thermoplastic Elastomer Compounds
The dynamic rheological properties of two types of thermoplastic elastomer (TPE) compounds were studied at ambient and processing temperatures. The linear viscoelastic properties of Thermoplastic Vulcanisates (TPV) and PP/SEBS compounds can be described using models based on mechanical mixing rules. The results were evaluated as a function of composition.
The Comparasion of a Short-Term and Long-Term Capital Market Investment Tools
The article discuss the evaluation of ways of investment occasions on a capital market, taking under consideration the availability and cost of investment money. It is considering the time-factor related to the actual market environment an describing the specific possibilities of the trading tools as the technological conciliator of the investment in the chemical and plastic industry.
The Genealogy of Polymers
The supply chain for polymeric materials is a drastically changing environment. This paper will focus on the types of trade names used. Changes of ownership along with historic trade names will be discussed. Predictions of future uses and types of trade names will be made.
Thermal Control of Melt Flow in Cylindrical Geometries
The control of plastic freeze-off and melt flow through a cylindrical nozzle is studied. Analysis of the temperature distribution of a nozzle contacting the mold shows a significant temperature distribution as a function of the axial and radial position in the metal and plastic. The temperature of the plastic melt determines the viscosity and subsequent flow through the nozzle. Experimental investigation validates the analysis by characterizing the pressure needed to induce flow as a function of nozzle and mold temperature. Control of the polymer freeze-off and melt flow is necessary for fully automatic production, as well as development of advanced molding processes.
Concept and Preliminary Result of a Nozzle Pressure Virtual Sensor of Injection Molding Process
This paper proposes a new virtual sensing approach for on-line monitoring process variables of injection molding process. In particular, a nozzle pressure virtual sensor has been developed. Exploiting the dynamic interaction between the machine and process variables, the virtual sensor utilizes the screw velocity data (a machine variable) to predict behavior of the nozzle pressure (a process variable). The virtual sensor was designed based on nonlinear observer theory. Experiment evaluation on a commercial injection molding machine was carried out, confirming the effectiveness of the virtual sensor.
Water-Assist Injection Molding – An Innovative Process Technology for Productivity Improvement - Developments in Processing, Equipment and Materials
Although water-assist injection molding is still in its infancy, this enabling technology promises productivity improvements for applications that may otherwise be cost prohibitive with gas-assist injection molding. Cycle times are reduced through cooling time reductions and the utilization of water as a cost-effective cooling medium when compared to nitrogen. For example, automotive suppliers have the potential for a broad range of cost savings with the production of conduits like cooling pipes or oil pipes. Other parts with large cross sections may also be produced in a cost-effective manner with water-assist injection molding. In fact, production parts in Europe are now beginning.Compared to the gas-assist injection molding details of the process, equipment, and the special material developments will be examined in this paper.
Effect of Injection Speed on Gas Penetration Length, Residual Wall Thickness and the Melt Front Position during Gas-Assisted Injection Molding
Extensive experiments were conducted to study the effect of injection speed on gas penetration length, residual wall thickness, the melt front position and short-shot weight of gas-assisted injection molded part. Experiments were performed on polystyrene melts filling a spiral tube cavity at three different melt temperatures. Simultaneous measurements of the screw position and the evolution of gas pressure and melt pressure in the cavity were performed. At a constant shot size, the length of melt propagation and the weight of moldings were found to increase with an increase of injection speed. An implication of these finding for gas penetration in gas-assisted injection molding was discussed.
Transient Gas/Melt Interface and Gas Penetration during Gas-Assisted Injection Molding: Simulation and Experiment
Theoretical and experimental studies have been carried out on the transient gas-liquid interface development and gas penetration behavior during the cavity filling and gas packing stage in the gas-assisted injection molding of a spiral tube cavity. The evolution of the gas/melt interface and as well as the distribution of the residual wall thickness of skin melt along with the advancement of gas/melt front have been investigated. The physical model for both the primary and secondary gas penetrations was developed based on the Hele-Shaw approximation combined with interface kinematics and dynamics. Numerical simulations were implemented on a fixed mesh covering the entire cavity. The residual thickness of a polymer layer and the length of gas penetration in moldings were calculated using a commercial software (C-Mold) and both the simulation and model developed in this study. Extensive molding experiments were performed on polystyrene at different processing conditions. The obtained results on the gas bubble dynamics and penetration behavior were compared with those predicted by the present simulation and C-Mold.
On the Breakup of a Non-Newtonian Drop in an Extensional Flow
The condition for the breakup, of a power-law non-Newtonian slender drop in a Newtonian liquid in an axisymmetric extensional flow, has been theoretically studied. The problem is governed by four dimensionless numbers: The capillary number, the Reynolds number, the viscosity ratio and the power-law index. The results suggest that the critical capillary number for drop breakup increases as the Reynolds number, the viscosity ratio and the power-law index decrease.
Molecular Dynamics Simulation of Nano-Scale Polymeric Rheological Properties and Extrusion Flows
In this work the rheological properties of polymer have been studied by molecular dynamics simulation. Couette flow with various shear rates are used to investigate the degree of slip, shear viscosity and normal stress difference. The fluid consists of chains of n-hexadecane and is confined between two structured gold atomic walls. Isothermal simulations (350K) of 4 to 1 unsteady extrusion flow with various extrusion rates are conducted.
Optimization of a Flat Die Geometry
Geometry of a flat die for polymer sheet extrusion is optimized to obtain a uniform velocity distribution across the exit of the die. While optimizing the exit velocity distribution, the constraint optimization algorithm used in this work enforced a limit on the maximum allowable pressure drop in the die. Effect of the shear as well as elongational viscosity of the polymer on the flow in the flat die is taken into account.
The Effect of Stabiliser Type and TiO2 Concentration on the Rheology of uPVC Profile Formulations
A range of unplasticised polyvinylchloride (uPVC) profile extrusion grade formulations, containing calcium/zinc, organotin and lead based stabiliser systems were blended with different concentrations of TiO2. Rheological analysis showed that the concentration of TiO2 (2phr - 8phr) had little effect on viscosity over the shear rate (200-1000s-1) and temperature range (170 – 190°C) studied. Mechanical analysis showed higher tensile and flexural modulii for the organotin stabilised formulations.
Setup and Optimisation of the Gas Assisted Injection Moulding Process Using an Expert System
An expert system has been developed here to assist the machine setter eliminate common defects from a gas assisted injection moulded product. The system breaks down the range of possible mould tool configurations into four main modes of operation. A process starting point is determined by an initialisation routine. The process is changed according to specified product defects to provide acceptable products. A further routine optimises the process by ensuring the process envelope, defined by natural random variation, does not move outside the moulding window. A multicavity mould tool has been used to validate the routines.
Three-Dimensional Simulation of Gas-Assisted Injection Molding Process
In this study, the application of a finite volume discretization and volume-of-fluid method has been demonstrated to simulate three-dimensional gas-assisted injection molding processes. An effective fluid concept is employed to compute segregated multi-fluid flows. The modified Cross model and Arrhenius temperature equation are implemented in the numerical scheme in order to calculate the rheological properties of polymer flows. The numerical results successfully depict some important three-dimensional phenomena, such as the jetting effect, race-tracking effect, corner effect, and the flow asymmetry after the gas is injected, which could not be described by any two-and-half dimensional model commonly used in the current commercial CAE applications.
Comparative Performance of a H13 and Beryllium-Copper Core Caps in a Thin-Wall Injection Molding Application
As a result of heat transfer properties superior to that of standard tool steel, copper-beryllium alloy inserts are expected to provide cycle time improvements in some injection molds. However, issues such as manufacturing cost can limit the benefits of using such inserts. A thin-wall single cavity container mold with inter-changeable H13 and Copper Beryllium core caps was used to quantify the possible differences between these materials. Under optimized single cavity process conditions (cycle time below 3 seconds), the cycle time could be significantly reduced by using the copper beryllium core cap. However, the impact properties of the resulting cups were reduced for some of the materials under investigation. No such disparity either in the process or in the mechanical properties could be observed when a stack mold process (cycle time around 5 seconds) was simulated. There is evidence that the container’ impact behavior is mostly determined by the local internal stresses near the injection gate.
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